A presentation about nanoelectronics-what it is and why it is used widely nowadays, its advantages and industrial applications and the future use. Also describes some problems faced by nanoelectronics.
1) Photocatalysis involves using light energy to facilitate chemical reactions. Photocatalysts like chlorophyll and titanium dioxide are able to breakdown organic matter into carbon dioxide and water when exposed to light.
2) Nanoparticles are necessary for high activity photocatalysts due to quantum size effects. Smaller nanoparticles have a larger surface area and better adsorption potential.
3) Photocatalysts have various applications including air purification by decomposing volatile organic compounds, self-cleaning surfaces, water purification by oxidizing pollutants, and dye degradation.
This document discusses top-down and bottom-up approaches for designing and preparing nanoparticles. The top-down approach involves breaking down bulk materials into nano-sized particles using methods like ball milling. The bottom-up approach involves building nanoparticles from individual atoms or molecules using nucleation and growth methods. Both approaches have advantages like control over particle size but also disadvantages such as potential contamination from milling or difficulty producing at large scale.
In this presentation a brief introduction is given on parts of wind turbine, classification of wind turbines, importance of wind turbines, current status like installed capacity (annual and cumulative) . Then there is a explanation on theory behind the design of wind turbine blades i.e, AERODYNAMICS OF WIND TURBINES which includes explanation about shape of an aerofoil, its different parameters, lift force, drag force, different equations about lift drag force, NACA profiles, Blade Element Momentum Theory, etc.
A presentation about nanoelectronics-what it is and why it is used widely nowadays, its advantages and industrial applications and the future use. Also describes some problems faced by nanoelectronics.
1) Photocatalysis involves using light energy to facilitate chemical reactions. Photocatalysts like chlorophyll and titanium dioxide are able to breakdown organic matter into carbon dioxide and water when exposed to light.
2) Nanoparticles are necessary for high activity photocatalysts due to quantum size effects. Smaller nanoparticles have a larger surface area and better adsorption potential.
3) Photocatalysts have various applications including air purification by decomposing volatile organic compounds, self-cleaning surfaces, water purification by oxidizing pollutants, and dye degradation.
This document discusses top-down and bottom-up approaches for designing and preparing nanoparticles. The top-down approach involves breaking down bulk materials into nano-sized particles using methods like ball milling. The bottom-up approach involves building nanoparticles from individual atoms or molecules using nucleation and growth methods. Both approaches have advantages like control over particle size but also disadvantages such as potential contamination from milling or difficulty producing at large scale.
In this presentation a brief introduction is given on parts of wind turbine, classification of wind turbines, importance of wind turbines, current status like installed capacity (annual and cumulative) . Then there is a explanation on theory behind the design of wind turbine blades i.e, AERODYNAMICS OF WIND TURBINES which includes explanation about shape of an aerofoil, its different parameters, lift force, drag force, different equations about lift drag force, NACA profiles, Blade Element Momentum Theory, etc.
Ultrasonic motors use piezoelectric materials to generate ultrasonic vibrations that produce motion. They were first introduced in 1965 and have advantages over traditional electromagnetic motors like higher torque at lower speeds, greater precision, and no magnetic interference. Common piezoelectric materials used include quartz, barium titanate, and lead zirconate titanate. Ultrasonic motors find applications in areas like cameras, watches, printers, and medical devices due to their small size and precision.
APPLICATION OF NANO-TECHNOLOGY IN MEDICAL FIELDKanchan Ramteke
Nanotechnology involves manipulating matter at the atomic and molecular scale. It has many potential applications in medicine. Nanoparticles can be used for more precise drug delivery and targeted cancer treatment. Surgical instruments and robots at the nanoscale could enable minimally invasive microsurgeries. Future applications may include nanorobots injected into the body to repair cells or detect infections and diseases. Nanotechnology promises to revolutionize healthcare by enabling new diagnostic and therapeutic capabilities at the smallest of scales.
Atomic force microscopy (AFM) uses a sharp tip attached to a flexible cantilever to scan the surface of a sample and map its topography with nanoscale resolution. As the tip is scanned across the surface, interactions between the tip and sample cause the cantilever to deflect, and these deflections are used to construct a 3D image of the surface. AFM can operate in contact, non-contact, or tapping mode and is capable of measuring properties like roughness, elasticity, and adhesion in addition to topography. It provides magnification from 100X to over 100 million X with nanometer scale resolution and does not require complex sample preparation, making AFM a versatile high-resolution imaging tool.
The document discusses the principles, instrumentation, and applications of atomic force microscopy (AFM). It was invented in the 1980s to overcome limitations of scanning tunneling microscopy. AFM uses a sharp tip to scan over a sample surface, detecting interatomic forces to generate topological images with atomic resolution without needing lenses or light. The key components are a cantilever with a tip, piezoelectric scanners, and a laser and photodetector that together detect tip deflection. AFM can operate in contact, non-contact, or tapping modes and is used in fields like materials science, biology, and nanotechnology due to its ability to image a wide range of surfaces.
This document discusses piezoelectricity and its use in energy harvesting. It begins with a brief history of piezoelectricity's discovery. It then explains the basic components and working principle of a piezoelectric energy harvesting circuit using diodes, a capacitor, switch, and LED. Applications discussed include using piezoelectric sensors in floors, gym equipment, vehicles, keyboards to harvest vibration energy. Both advantages like being pollution-free and disadvantages like low output are summarized. The document concludes that piezoelectric energy harvesting is a promising green energy source.
This document discusses carbon nanotubes, including their discovery in 1952, types (single-walled and multi-walled), structure, properties, synthesis methods, and potential applications. Carbon nanotubes have extraordinary strength and stiffness, along with high thermal and electrical conductivity. However, they can also be toxic and have crystallographic defects. The three main synthesis methods are arc discharge, laser ablation, and chemical vapor deposition. Carbon nanotubes show promise for applications in materials science, electronics, medicine, and other fields due to their unique properties at the nanoscale.
This document discusses electrodeposition of nickel-based nanocomposites. Electrodeposition is a process that uses electrical current to coat a thin film of material onto a conductive surface. It can be used to improve properties like corrosion protection, wear resistance, and aesthetics. The document focuses on electrodepositing nickel-silicon carbide nanocomposites. Key parameters that affect the silicon carbide content in the coatings include current density, temperature, particle concentration, and bath composition. Optimizing these parameters can produce nanocomposite coatings with improved properties for applications like engine and mold protection.
Nanomaterials in biomedical applicationsumeet sharma
This document discusses nanomaterials and their biomedical applications. It begins by defining nanomaterials as objects with at least one dimension between 1-100 nanometers. It then classifies nanomaterials and discusses some common terms like nanoshells and quantum dots. The document focuses on the biomedical applications of nanomaterials, including biological imaging using quantum dots, targeted drug delivery using nanoparticles, and cancer treatment using magnetic nanoparticles. In summary, the document outlines different types of nanomaterials, their properties, and various ways they can be used for biomedical purposes such as imaging and targeted drug delivery.
Nanotechnology has applications in agriculture to address challenges like declining soil quality and nutrient deficiencies. It can be used to precisely deliver nutrients and pesticides to promote productivity while ensuring environmental safety. Examples include nano-fertilizers, nano-herbicides, and nano-sensors. Nanotechnology is also being used in food packaging to increase shelf life, such as bottles that prevent carbon dioxide leakage and films packed with nanoparticles to reduce oxygen flow and moisture leakage. Nanosensors can also detect bacteria, contaminants, and food spoilage.
Scanning Probe microscopy (AFM and STM) head point
AFM: Configuration of AFM
Parts of AFM system and Principle of AFM
Three Modes of AFM
AFM Instrument
Advantage and disadvantage
STM
Schematic Diagram
AFM and STM
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The document provides an overview of scanning electron microscopes (SEM). It discusses that SEMs produce high-resolution images by scanning a sample surface with a focused beam of electrons. The electrons interact with atoms in the sample to provide information about topography and composition. Key components of SEMs are described, including the electron gun, lenses, detectors, and vacuum chamber. SEMs can achieve higher magnification than light microscopes and provide information about surface features, morphology, composition and crystal structure at high magnifications. Sample preparation such as drying, mounting and coating are outlined to prepare non-conductive specimens for imaging.
The document provides information about scanning tunneling microscopy (STM). It begins by explaining the quantum mechanical principles behind STM, specifically electron tunneling. It then describes the key components of an STM, including the scanning tip, piezoelectric scanner, distance control system, data processing unit, and vibration isolation system. The document discusses the two main imaging modes of STM - constant height mode and constant current mode. It also outlines how STM works by applying a voltage bias between the tip and sample and measuring the tunneling current. The document concludes by discussing advantages and disadvantages of STM as well as sources of artifacts in STM images.
1. The stress-freezing method locks in deformations caused by applied loads in a diphase polymeric material by using its property of secondary bonds breaking down at the critical temperature.
2. Scattered light polariscopes use the phenomenon that light scattered within a photoelastic model is plane-polarized perpendicular to the incident beam direction, allowing visualization of stress information without slicing the model.
3. Scattered light can act as an interior polarizer or analyzer by resolving the polarized scattered light into components along principal stress directions, allowing measurement of stress differences over interior planes using fringe patterns.
Quantum dots are semiconductor nanoparticles that confine electrons and holes in all three dimensions. They are made using different methods like lithography, colloidal synthesis, or epitaxy. Quantum dots have discrete energy levels that depend on their size and shape. They have potential applications in solar cells, LEDs, bioimaging, drug delivery, and anti-counterfeiting due to their tunable light emission properties.
The document provides an overview of various lithography techniques including photolithography, electron beam lithography, nanolithography, X-ray lithography, AFM nanolithography, soft lithography, nanoimprint lithography, and dip-pen nanolithography. It discusses the basic principles, steps involved, advantages, and applications of each technique for fabricating nanostructures.
This document summarizes a student project to measure local density of states using scanning tunneling spectroscopy (STS) techniques. The student demonstrated STS on three samples - gold, highly ordered pyrolytic graphite, and bismuth telluride. Several images of each sample's surface topology and conductance maps were obtained. Spectroscopy data was also collected by averaging 30 sweeps to reduce thermal drift effects. Further work is needed to convert the data to standard units and characterize tip quality to obtain fully quantitative results.
Resonant-tunneling-diode effect in Si-based double-barrier structure sputtere...IJRES Journal
This paper presents the resonant-tunneling-diode (RTD) effect in a SiO2/n-Si/SiO2/p-Si double-barrier structural thin films fabricated using radio frequency (RF) magnetron sputtering at room temperature (300 K). The implementation of a circuit prototype is first accomplished by modulating a Si-based RTD with a solar-cell bias voltage. The important electrical properties of the peak current density and peak-to-valley current ratio (PVCR) are 184 nA/cm2 and 1.67, respectively. The connection between the two RTDs in series is biased by a solar cell. The value of the switching transition time is 24.37 μs; oscillation occurs with an operating frequency of 41.6 KHz. In semiconductor applications, the developed RTD is characterized by stability, enduring environmentally elevated temperature and relative humidity.
Ultrasonic motors use piezoelectric materials to generate ultrasonic vibrations that produce motion. They were first introduced in 1965 and have advantages over traditional electromagnetic motors like higher torque at lower speeds, greater precision, and no magnetic interference. Common piezoelectric materials used include quartz, barium titanate, and lead zirconate titanate. Ultrasonic motors find applications in areas like cameras, watches, printers, and medical devices due to their small size and precision.
APPLICATION OF NANO-TECHNOLOGY IN MEDICAL FIELDKanchan Ramteke
Nanotechnology involves manipulating matter at the atomic and molecular scale. It has many potential applications in medicine. Nanoparticles can be used for more precise drug delivery and targeted cancer treatment. Surgical instruments and robots at the nanoscale could enable minimally invasive microsurgeries. Future applications may include nanorobots injected into the body to repair cells or detect infections and diseases. Nanotechnology promises to revolutionize healthcare by enabling new diagnostic and therapeutic capabilities at the smallest of scales.
Atomic force microscopy (AFM) uses a sharp tip attached to a flexible cantilever to scan the surface of a sample and map its topography with nanoscale resolution. As the tip is scanned across the surface, interactions between the tip and sample cause the cantilever to deflect, and these deflections are used to construct a 3D image of the surface. AFM can operate in contact, non-contact, or tapping mode and is capable of measuring properties like roughness, elasticity, and adhesion in addition to topography. It provides magnification from 100X to over 100 million X with nanometer scale resolution and does not require complex sample preparation, making AFM a versatile high-resolution imaging tool.
The document discusses the principles, instrumentation, and applications of atomic force microscopy (AFM). It was invented in the 1980s to overcome limitations of scanning tunneling microscopy. AFM uses a sharp tip to scan over a sample surface, detecting interatomic forces to generate topological images with atomic resolution without needing lenses or light. The key components are a cantilever with a tip, piezoelectric scanners, and a laser and photodetector that together detect tip deflection. AFM can operate in contact, non-contact, or tapping modes and is used in fields like materials science, biology, and nanotechnology due to its ability to image a wide range of surfaces.
This document discusses piezoelectricity and its use in energy harvesting. It begins with a brief history of piezoelectricity's discovery. It then explains the basic components and working principle of a piezoelectric energy harvesting circuit using diodes, a capacitor, switch, and LED. Applications discussed include using piezoelectric sensors in floors, gym equipment, vehicles, keyboards to harvest vibration energy. Both advantages like being pollution-free and disadvantages like low output are summarized. The document concludes that piezoelectric energy harvesting is a promising green energy source.
This document discusses carbon nanotubes, including their discovery in 1952, types (single-walled and multi-walled), structure, properties, synthesis methods, and potential applications. Carbon nanotubes have extraordinary strength and stiffness, along with high thermal and electrical conductivity. However, they can also be toxic and have crystallographic defects. The three main synthesis methods are arc discharge, laser ablation, and chemical vapor deposition. Carbon nanotubes show promise for applications in materials science, electronics, medicine, and other fields due to their unique properties at the nanoscale.
This document discusses electrodeposition of nickel-based nanocomposites. Electrodeposition is a process that uses electrical current to coat a thin film of material onto a conductive surface. It can be used to improve properties like corrosion protection, wear resistance, and aesthetics. The document focuses on electrodepositing nickel-silicon carbide nanocomposites. Key parameters that affect the silicon carbide content in the coatings include current density, temperature, particle concentration, and bath composition. Optimizing these parameters can produce nanocomposite coatings with improved properties for applications like engine and mold protection.
Nanomaterials in biomedical applicationsumeet sharma
This document discusses nanomaterials and their biomedical applications. It begins by defining nanomaterials as objects with at least one dimension between 1-100 nanometers. It then classifies nanomaterials and discusses some common terms like nanoshells and quantum dots. The document focuses on the biomedical applications of nanomaterials, including biological imaging using quantum dots, targeted drug delivery using nanoparticles, and cancer treatment using magnetic nanoparticles. In summary, the document outlines different types of nanomaterials, their properties, and various ways they can be used for biomedical purposes such as imaging and targeted drug delivery.
Nanotechnology has applications in agriculture to address challenges like declining soil quality and nutrient deficiencies. It can be used to precisely deliver nutrients and pesticides to promote productivity while ensuring environmental safety. Examples include nano-fertilizers, nano-herbicides, and nano-sensors. Nanotechnology is also being used in food packaging to increase shelf life, such as bottles that prevent carbon dioxide leakage and films packed with nanoparticles to reduce oxygen flow and moisture leakage. Nanosensors can also detect bacteria, contaminants, and food spoilage.
Scanning Probe microscopy (AFM and STM) head point
AFM: Configuration of AFM
Parts of AFM system and Principle of AFM
Three Modes of AFM
AFM Instrument
Advantage and disadvantage
STM
Schematic Diagram
AFM and STM
https://www.linkedin.com/in/preeti-choudhary-266414182/
https://www.instagram.com/chaudharypreeti1997/
https://www.facebook.com/profile.php?id=100013419194533
https://twitter.com/preetic27018281
Please like, share, comment and follow.
stay connected
If any query then contact:
chaudharypreeti1997@gmail.com
Thanking-You
Preeti Choudhary
The document provides an overview of scanning electron microscopes (SEM). It discusses that SEMs produce high-resolution images by scanning a sample surface with a focused beam of electrons. The electrons interact with atoms in the sample to provide information about topography and composition. Key components of SEMs are described, including the electron gun, lenses, detectors, and vacuum chamber. SEMs can achieve higher magnification than light microscopes and provide information about surface features, morphology, composition and crystal structure at high magnifications. Sample preparation such as drying, mounting and coating are outlined to prepare non-conductive specimens for imaging.
The document provides information about scanning tunneling microscopy (STM). It begins by explaining the quantum mechanical principles behind STM, specifically electron tunneling. It then describes the key components of an STM, including the scanning tip, piezoelectric scanner, distance control system, data processing unit, and vibration isolation system. The document discusses the two main imaging modes of STM - constant height mode and constant current mode. It also outlines how STM works by applying a voltage bias between the tip and sample and measuring the tunneling current. The document concludes by discussing advantages and disadvantages of STM as well as sources of artifacts in STM images.
1. The stress-freezing method locks in deformations caused by applied loads in a diphase polymeric material by using its property of secondary bonds breaking down at the critical temperature.
2. Scattered light polariscopes use the phenomenon that light scattered within a photoelastic model is plane-polarized perpendicular to the incident beam direction, allowing visualization of stress information without slicing the model.
3. Scattered light can act as an interior polarizer or analyzer by resolving the polarized scattered light into components along principal stress directions, allowing measurement of stress differences over interior planes using fringe patterns.
Quantum dots are semiconductor nanoparticles that confine electrons and holes in all three dimensions. They are made using different methods like lithography, colloidal synthesis, or epitaxy. Quantum dots have discrete energy levels that depend on their size and shape. They have potential applications in solar cells, LEDs, bioimaging, drug delivery, and anti-counterfeiting due to their tunable light emission properties.
The document provides an overview of various lithography techniques including photolithography, electron beam lithography, nanolithography, X-ray lithography, AFM nanolithography, soft lithography, nanoimprint lithography, and dip-pen nanolithography. It discusses the basic principles, steps involved, advantages, and applications of each technique for fabricating nanostructures.
This document summarizes a student project to measure local density of states using scanning tunneling spectroscopy (STS) techniques. The student demonstrated STS on three samples - gold, highly ordered pyrolytic graphite, and bismuth telluride. Several images of each sample's surface topology and conductance maps were obtained. Spectroscopy data was also collected by averaging 30 sweeps to reduce thermal drift effects. Further work is needed to convert the data to standard units and characterize tip quality to obtain fully quantitative results.
Resonant-tunneling-diode effect in Si-based double-barrier structure sputtere...IJRES Journal
This paper presents the resonant-tunneling-diode (RTD) effect in a SiO2/n-Si/SiO2/p-Si double-barrier structural thin films fabricated using radio frequency (RF) magnetron sputtering at room temperature (300 K). The implementation of a circuit prototype is first accomplished by modulating a Si-based RTD with a solar-cell bias voltage. The important electrical properties of the peak current density and peak-to-valley current ratio (PVCR) are 184 nA/cm2 and 1.67, respectively. The connection between the two RTDs in series is biased by a solar cell. The value of the switching transition time is 24.37 μs; oscillation occurs with an operating frequency of 41.6 KHz. In semiconductor applications, the developed RTD is characterized by stability, enduring environmentally elevated temperature and relative humidity.
The document describes experiments on digital communication lab including:
1. Pulse amplitude modulation and time division multiplexing where amplitude of pulses is varied according to modulating signal and samples from different signals are combined in time domain and transmitted over a common channel.
2. Pulse time modulation and demodulation (PWM and PPM) where pulse width or repetitive frequency is varied according to information signal to save transmitter power.
3. Analog to digital and digital to analog conversion where analog signals are sampled, quantized into discrete levels represented by binary codes, and reconverted to analog for transmission and reception.
This document presents the design of a high performance folded cascade OTA and sample and hold circuit. The OTA is designed to achieve 10-bit resolution while operating at a 28 MHz sampling frequency. Simulation results show the OTA achieves a high open loop gain of 72 dB and bandwidth of 112 MHz, with a phase margin of 73 degrees. A low resistance transmission gate switch is designed to reduce charge injection and clock feedthrough effects during sampling. The circuit is implemented in a 130 nm CMOS technology.
Simulation and Partial Discharge Measurement in 400kv Typical GIS SubstationIOSR Journals
1) The document simulates partial discharge (PD) in a typical 400kV gas-insulated substation using very fast transients (VFT) modeling.
2) PD models are applied to different points in the substation, including bus bars 91 and 92. Voltage measurements at points in the substation show disturbances from PD.
3) Changing the location of PD between bus bars 91 and 92 alters the voltage waveforms, demonstrating how PD location could potentially be identified through voltage analysis.
An Gt101 A Microwave Power Amplifier Fundamentals 08 10 27cf_home
This document provides a summary of microwave power amplifier fundamentals. It discusses the need for amplification at microwave frequencies and describes spatially combined distributed amplifier topologies that can provide broadband, high power amplification over a decade of frequency range. Key amplifier specifications such as gain, power output, and return loss are defined. Measurement techniques for verifying amplifier performance are also reviewed.
Area Efficient Pulsed Clocks & Pulsed Latches on Shift Register TannerIJMTST Journal
This paper introduced a design and implementation of shift register using pulsed latches and flip-flops. As
flip-flop based shift registers requires a clock signal to operate. Multistage flip-flop processes with high clock
switching activity and then increases time latency. Flip-flops also engages fifty percent power out of total
circuit power in clocking. To reduce such power consumptions and to achieve area optimization flip-flops are
replaced by pulsed latches. The design is implemented with 250nm technology in Tanner EDA Tool. With
Vdd=1.8V, Freq=100MHz. Average power of total circuit is 0.465uW and delay of 0.312 us.
Transient Monitoring Function based Fault Classifier for Relaying Applications IJECEIAES
This paper proposes Transient monitoring function (TMF) based fault classification approach for transmission line protection. The classifier provides accurate results under various system conditions involving fault resistance, inception angle, location and load angle. The transient component during fault is measured by TMF and appropriate logics applied for fault classification. Simulation studies using MATLAB ® /SIMULINK ™ are carried out for a 400 kV, 50 Hz power system with variable system conditions. Results show that the proposed classifier has high classification accuracy. The method developed has been compared with a fault classification technique based on Discrete Wavelet Transform (DWT). The proposed technique can be implemented for real time protection schemes employing distance relaying.
Control Radiation Pattern for Half Width Microstrip Leaky Wave Antenna by Usi...IJECEIAES
In this paper, a novel design for single-layer half width microstrip leakywave antenna (HW-MLWA) is demonstrated. This model can be digitally control its radiation pattern at operation frequency and uses only two values of the bias voltage, with better impedance matching and insignificant gain variation. The scanning and controlling the radiation pattern of leaky-wave antennas (LWA) in steps at an operation frequency, by using switches PIN diodes, is investigated and a novel HW-MLWA is introduced. A control cell reconfigurable, that can be switched between two states, is the basic element of the antenna. The periodic LWA is molded by identical control cells where as a control radiation pattern is developed by combining numerous reconfigurable control cells. A gap capacitor is independently connected or disconnected in every unit cell by using a PIN diode switch to achieve fixedfrequency control radiation pattern scanning. The profile reactance at the free edge of (HWMLWA) and thus the main lobe direction is altered by changing the states of the control cell. The antenna presented in this paper, can scan main beam between 18o to 44o at fixed frequency of 4.2 GHz with measured peak gain of 12.29 dBi.
This document presents a new method for locating ungrounded faults in underground distribution systems using wavelet analysis and artificial neural networks (ANNs). Voltage and current signals are simulated for different fault types, locations, and conditions using EMTP software. Wavelet analysis is used to extract features from the signals related to fault classification and location. ANNs are then applied to classify fault types based on the extracted features and to determine the fault location for each fault type based on additional extracted features. The results indicate the technique can accurately locate faults under a variety of system conditions.
ConorWilman_Manchester_Investigation of an effective low-cost THz TDS systemConor Wilman
The document summarizes an experiment to design a low-cost THz time-domain spectroscopy system using multimode laser diodes instead of expensive femtosecond lasers. Bowtie antennas were fabricated on low-temperature gallium arsenide and tested with laser diodes, but no THz signal was detected. Possible reasons for failure include low laser power, poor antenna quality, and lack of optimal equipment. The experiment provides a starting point for improving the system by using higher power lasers, better antenna design, and additional equipment in future attempts.
Optimal Body Biasing Technique for CMOS Tapered Buffer IJEEE
This paper represents Fixed Body Biased CMOS Tapered Buffer which is designed to minimize the average power dissipation across large capacitive load. The implementation of Reverse Body Bias (RBB) in the proposed Buffer chain is to vary Vth value of NMOS in the first stage. And with the increase in Vth /sub-threshold leakage current and power has been reduced. The technology constraints on the threshold voltage does not allow designer to set high threshold voltage for MOS devices. Hence, this was found that in proposed circuit that when optimal Reverse Body Bias value is set within (0.2 VDD to 0.4 VDD) range, the average power dissipation across capacitive load reduces to 82.2 % at very less penalty in delay. Thus CMOS buffer designers can use the proposed method to vary Vth while keeping VDD constant, which could improve the performance parameters of Tapered Buffer. The proposed analysis is verified by simulating the 3-stage tapered buffer schematics using standard 180nm CMOS technology in Cadence environment.
Monitoring and Control of Power System Oscillations using FACTS/HVDC and Wide...Power System Operation
Power oscillations are a growing concern among power system operators worldwide. Traditionally, the
main countermeasure against dangerous power oscillations has been the installation of power system
stabilizers (PSS). Essentially, the potential for inter-area power oscillations depends on the strength of
the tie lines between different areas and the load on the ties. From a European perspective, with the
anticipated integration of remote renewable energy sources such as offshore wind power from the
North-sea region and solar power from southern Europe or Africa, we can expect the average
transmission distances to grow and consequently also tie line flows. Unless tie lines are also reinforced
we expect more oscillation events in the European grid in the future.
From an operational point of view, it is of high priority to be able to estimate the damping of
oscillatory modes reliably in real-time in order to take appropriate and timely measures in case
damping becomes poor. Recent developments in wide-area phasor monitoring have resulted in a new
power oscillation monitoring algorithm that uses multiple measurements from different locations in
the grid. An equivalent system model of the power grid is estimated in real-time and based on this
model, the damping and frequency as well the activity of oscillatory modes can be determined from
ambient process variations. As basis for this, a wide-area measurement system (WAMS) can provide
time synchronized signals from phasor measurement units (PMUs) that can measure voltage, current
and frequency with adequate accuracy and resolution in time. This paper shows results from pilot
operation of the new application at swissgrid, including recordings from an actual and representative
event in the continental ENTSO-E interconnected power system. This example demonstrates the
performance of the new application as well as provides information about the oscillatory modes
present in the continental ENTSO-E system today.
This document summarizes some key challenges for digital circuits related to process, voltage, and temperature variations. It discusses techniques to prevent latchup and electrostatic discharge issues in integrated circuits. It also describes simultaneous switching noise that can occur when large numbers of circuits switch simultaneously. The document proposes using adaptive body biasing techniques to compensate for PVT variations and control output slope under different conditions. Simulation results show this approach can adjust rising and falling times of an output buffer for different substrate bias voltage conditions.
Conducted EMI Reduction Accomplished via IEEE 1588 PTP for Grid Connected Par...idescitation
This paper introduces a distributed approach for
interleaving paralleled power converter to reduce EMI and
voltage ripple, accomplished via IEEE 1588 Precision time
protocol. An open source software stack of IEEE 1588v2 named
PTPd-2.2.0 is used to implement software stack over stellaris
series microcontroller from Texas Instruments (TI). A general
methodology for achieving distributed interleaving is proposed,
along with a specific software based implementation approach
using the PTPdv2. The effectiveness of such methods in terms
of EMI reduction is experimentally validated in grid connected
Paralleled Solar Power Inverters.
The document discusses using IEEE 1588 Precision Time Protocol (PTP) to achieve distributed interleaving of paralleled solar power inverters. PTP allows networked devices to synchronize clocks with microsecond accuracy over Ethernet networks. The paper proposes using PTP to introduce phase shifts between inverter switching signals, which reduces electromagnetic interference and voltage ripple. Experimental results validated the EMI reduction achieved through this software-based distributed interleaving approach using PTP.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
ESDEMC_PB2009.08 A Measurement Technique for ESD Current Spreading on A PCB u...ESDEMC Technology LLC
Abstract—Electrostatic discharge (ESD) can cause interference or damage in circuits in many ways e.g., by E- or Hfield coupling or via conduction paths. Although we can roughly estimate the voltage and current at the injection point during an ESD event, the real offending parameter is mostly the ESD current spreading throughout the system. Those currents can be simulated if great simplifications of the system are accepted.
However, even in moderately complex systems the ability to simulate is limited by lack of models and computational resources. Independent of the complexity, but obviously not free of its own limitations is a measurement technique that captures the current as a function of time and location through the system.
This article describes the proof on concept of ESD such a measurement technique that allows reconstructing the spreading current as a movie from magnetic field measurements. It details the technique, question of probe selection and how to process the data to present the current spread as a movie.
This document describes the design and implementation of an integrated ultrawideband (UWB)/reconfigurable-slot antenna for cognitive radio applications. A slot resonator is embedded in a disc monopole radiator to achieve a narrowband antenna, and a varactor diode is inserted across the slot to provide frequency reconfiguration between 5-6 GHz. Simulation and measurement results show the antenna achieves UWB performance from 3-11 GHz as well as tunable narrowband operation across the targeted range. Isolation between the UWB and narrowband functions is better than 16 dB across most of the operating bands.
A fully integrated temperature compensation technique for piezoresistive pres...mayibit
This document describes a technique for fully integrating temperature compensation into piezoresistive pressure sensors. It presents a sensor model used to evaluate temperature and pressure characteristics with variations from the fabrication process. The technique aims to compensate for errors from a sensor's inherent cross-sensitivity to temperature and processing variations between sensors, allowing operation from -40°C to 130°C over a pressure range of 0-310 kPa. Hardware is specified to implement the technique, and an analysis discusses its effectiveness over the desired operating conditions.
The document summarizes the structure and function of the mechanosensitive channel of small conductance (MscS) in bacterial cells. MscS acts as a floodgate, allowing bacteria to release water from their cells in response to osmotic shock. The structure of MscS was elucidated in 2008, revealing its heptameric structure and iris-like opening mechanism using the movement of transmembrane helices. This structural insight helped explain how MscS is able to rapidly release water and ions from cells under osmotic pressure, as well as its ability to adapt when pressure returns to normal levels. While the structure provided significant understanding, many questions remain regarding the detailed mechanisms of gating, adaptation, and M
Intramembrane proteases are a family of proteases that function within cell membranes. They were discovered in 1997 and represent a new class of proteases that use different mechanisms than the traditional water-soluble protease classes. Structural studies have provided insights into their catalytic mechanisms and gating movements that allow substrate access despite operating in the low-water environment of membranes. Further research is still needed to understand aspects of intramembrane protease structure, function, and regulation.
Quazar Technologies develops indigenously data acquisition systems and other scientific instrumentation. It aims to support research in India through high-quality, customized products. Its data acquisition systems (QDA) are tailored solutions for applications like structural vibration monitoring, temperature measurement, and strain gauge testing. The QDA systems integrate modular hardware and software and can be adapted over time based on customer needs and feedback. Quazar has installed QDA systems at several research institutions in India.
This document discusses programming on Linux. It covers the Linux command line, text editors like vim and nano, compiling code using tools like gcc and g++, and running programs. It also mentions integrated development environments (IDEs) and compiling/running languages like C/C++, Java, Python, Perl, Lisp, HTML/PHP/CSS, and Fortran.
This document summarizes a lecture about connecting with the Linux community. It discusses finding answers to Linux questions by reading documentation, searching online, and asking on forums and mailing lists. It also encourages contributing back to the community by submitting bug reports, testing software, and helping other users on IRC channels. The lecture emphasizes respecting others and avoiding elitism when interacting with the community.
A basic introduction to the philosophy behind and internals of linux based operating system distributions, meant to be presented by someone who knows this stuff rather that as a DIY thing.
Sadly, I seem to have lost the sources for this after my hard drive crashed.
This document discusses electronic interconnect protocols for communication between devices. It begins by explaining the need for interconnect protocols due to the diverse nature of technical systems and their components. The document then outlines the speaker's agenda to introduce basic communication protocol elements and focuses on nearby small-scale systems rather than large networks. Key topics to be covered include common communication protocols, synchronizing communication through clocks and timing, differences between serial and parallel protocols, and establishing order through use of bus masters.
The document discusses Pelizaeus-Merzbacher Disease (PMD), a rare degenerative neurological disorder caused by mutations in the proteolipid protein 1 (PLP1) gene. PMD affects the growth of the myelin sheath and causes deterioration of motor and intellectual abilities. There are different types of PMD classified by severity, from the most severe connatal PMD to pure spastic paraplegia 2. Animal studies showed that PLP deficiency relates to myelin deficiencies in mutants like the jimpy mouse. The disease mechanism involves PLP1's role in myelin structure and how various mutations affect its function.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The technology uses reclaimed CO₂ as the dyeing medium in a closed loop process. When pressurized, CO₂ becomes supercritical (SC-CO₂). In this state CO₂ has a very high solvent power, allowing the dye to dissolve easily.
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
Travis Hills' Endeavors in Minnesota: Fostering Environmental and Economic Pr...Travis Hills MN
Travis Hills of Minnesota developed a method to convert waste into high-value dry fertilizer, significantly enriching soil quality. By providing farmers with a valuable resource derived from waste, Travis Hills helps enhance farm profitability while promoting environmental stewardship. Travis Hills' sustainable practices lead to cost savings and increased revenue for farmers by improving resource efficiency and reducing waste.
Describing and Interpreting an Immersive Learning Case with the Immersion Cub...Leonel Morgado
Current descriptions of immersive learning cases are often difficult or impossible to compare. This is due to a myriad of different options on what details to include, which aspects are relevant, and on the descriptive approaches employed. Also, these aspects often combine very specific details with more general guidelines or indicate intents and rationales without clarifying their implementation. In this paper we provide a method to describe immersive learning cases that is structured to enable comparisons, yet flexible enough to allow researchers and practitioners to decide which aspects to include. This method leverages a taxonomy that classifies educational aspects at three levels (uses, practices, and strategies) and then utilizes two frameworks, the Immersive Learning Brain and the Immersion Cube, to enable a structured description and interpretation of immersive learning cases. The method is then demonstrated on a published immersive learning case on training for wind turbine maintenance using virtual reality. Applying the method results in a structured artifact, the Immersive Learning Case Sheet, that tags the case with its proximal uses, practices, and strategies, and refines the free text case description to ensure that matching details are included. This contribution is thus a case description method in support of future comparative research of immersive learning cases. We then discuss how the resulting description and interpretation can be leveraged to change immersion learning cases, by enriching them (considering low-effort changes or additions) or innovating (exploring more challenging avenues of transformation). The method holds significant promise to support better-grounded research in immersive learning.
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
Unlocking the mysteries of reproduction: Exploring fecundity and gonadosomati...AbdullaAlAsif1
The pygmy halfbeak Dermogenys colletei, is known for its viviparous nature, this presents an intriguing case of relatively low fecundity, raising questions about potential compensatory reproductive strategies employed by this species. Our study delves into the examination of fecundity and the Gonadosomatic Index (GSI) in the Pygmy Halfbeak, D. colletei (Meisner, 2001), an intriguing viviparous fish indigenous to Sarawak, Borneo. We hypothesize that the Pygmy halfbeak, D. colletei, may exhibit unique reproductive adaptations to offset its low fecundity, thus enhancing its survival and fitness. To address this, we conducted a comprehensive study utilizing 28 mature female specimens of D. colletei, carefully measuring fecundity and GSI to shed light on the reproductive adaptations of this species. Our findings reveal that D. colletei indeed exhibits low fecundity, with a mean of 16.76 ± 2.01, and a mean GSI of 12.83 ± 1.27, providing crucial insights into the reproductive mechanisms at play in this species. These results underscore the existence of unique reproductive strategies in D. colletei, enabling its adaptation and persistence in Borneo's diverse aquatic ecosystems, and call for further ecological research to elucidate these mechanisms. This study lends to a better understanding of viviparous fish in Borneo and contributes to the broader field of aquatic ecology, enhancing our knowledge of species adaptations to unique ecological challenges.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
1. Local density of states measurements using STM/STS techniques
Chintalagiri Shashank∗
Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016
(Supervisor : Prof. Deshdeep Sahdev)†
(Dated: April 20, 2012)
The goal of the project is to develop the infrastructure and expertise necessary for Scanning Tun-
neling Spectroscopy (STS). Taking a two pronged approach, we have moved closer to this goal and
qualitatively demonstrated the ability to perform STS on various samples. The principle infrastruc-
ture necessary for this activity, specifically a lock-in amplifier, and its integration with an STM not
designed for STS is described. Various sets of data acquired, indicators of the fidelity of the data,
and the rationale for the designs chosen are also presented.
PACS numbers: 07.79.Cz, 68.37.Ef
I. INTRODUCTION
The Scanning Tunneling Microscope (STM) was in-
vented in 1981 by Gerd Binnig and Heinrich Rohre at
IBM Zurich. An STM is a non-optical microscope which
typically has atomic resolution. The STM is based on the
concept of quantum tunneling. When a conducting tip
is brought within a few Angstroms of the surface to be
examined, a bias voltage applied between the tip and the
sample can allow electrons to tunnel through the vacuum
or air barrier between them. The resulting tunneling cur-
rent is a function of tip position, applied voltage, and the
local density of states (LDOS) of the sample. Informa-
tion is acquired by monitoring the current as the tip’s
position scans across the surface. The use of an STM is
generally limited to electrically conducting samples, and
requires extremely clean and stable surfaces, sharp tips,
excellent vibration isolation, and sophisticated electron-
ics.
Since its invention, a number of applications have been
found for the STM and many variants developed to per-
form measurements of different kinds. The application
targeted in this project is that of Scanning Tunneling
Spectroscopy (STS). In order to achieve this goal, an ad-
ditional step of the development of a lock-in amplifier
was identified. Section III deals with this effort. Simul-
taneously, the rest of the steps necessary for STS were
performed using a commercial lock in amplifier, the de-
tails of which are included in section II.
II. SCANNING TUNNELING SPECTROSCOPY
Scanning Tunneling Spectroscopy (STS) is a technique
used to characterize electronic distribution as a func-
tion of energy at the surface of conducting and semi-
conducting samples with the help of an STM1–3
. It can
be used to measure the local density of states at various
points on the surface and generate conductance maps of
the surface. Band gaps can also be measured using this
technique. It can be shown that the local density of states
is well represented by the differential tunneling conduc-
tance dI/dV, where I is the tunneling current and V the
bias voltage.
The focus in this project is to demonstrate STS by
measuring the local density of states of three samples,
namely Gold (Au), Highly ordered pyrolytic graphite
(HOPG), and Bismuth Telluride(Bi2Te3). These sam-
ples are well documented in literature, such as in4,5
.
A. Experimental Setup
The experimental setup is centered on the nanoREV
Air STM. A lock-in amplifier (LIA) is used to measure
tunneling conductance directly. The data presented here
was taken using a commercially available EG&G Prince-
ton Applied Research Model 5209 lock-in amplifier. In
addition, a Tektronix TDS210 digital oscilloscope was
used for testing the setup and monitoring various phases
of the acquisition, most commonly the amplified tunnel-
ing current and the output of the lock-in amplifier. Fig-
ure 1 shows a simplified block-diagram of the experimen-
tal setup.
The nanoREV Air STM consists of two distinct sec-
tions. The first is the scan head, which contains the
sample holder, tip, piezos, and the Tunneling Current
Amplifier (TCA). The scan head is enclosed inside a
shroud and is placed on a vibration isolation platform.
A spring-mass system is used to damp external vibra-
tions and isolate the scan head from them. Additionally,
a cover provides shielding from ambient air flows. The
second part of the nanoREV STM is the electronics box,
which contains the bulk of the electronics of the STM.
The electronics box contains the circuitry necessary to
generate a DC bias voltage, which can be applied to the
sample holder, drives the piezoelectric actuators. The
feedback and acquisition circuitry is also located inside
the electronics box.
The various constraints marked in the figure are those
of bandwidth and frequency limitations of the smaller
blocks. These are discussed below, with their effective
values in the unmodified STM and the implications in
terms of the experimental design.
2. 2
FIG. 1. Simplified block diagram of STS experimental setup,
showing only the relevant blocks. Blocks in blue are additions
to the regular STM setup. The relevant constraints in band-
width and timing are marked in the diagram and discussed
in the text. The details of the lock-in amplifier are dealt with
separately.
BWTCA: Bandwidth of the TCA. The TCA, operating
at a gain of 109
, has a bandwidth specified by the
RC constant of the circuit at its input, along with
the pin, of about 800 Hz. This bandwidth was also
observed experimentally in the form of attenuation
in the AC modulation of the signal beyond 1 KHz.
The high gain in the TCA is necessary to amplify
the tunneling current from the picoampere range
to a voltage level which is easier to handle.
BWIA: Bandwidth of the Instrumentation Amplifier that
follows the TCA. The instrumentation amplifier is
operated at a gain of 1, and its purpose is to convert
the differential output signal of the TCA into a sin-
gle ended signal referred to the circuit ground. This
signal is then used in the feedback circuit as well as
can be digitized. This amplifier has a bandwidth of
1 MHz at a gain of 1. The combined bandwidth of
the TCA and the IA, well represented by the lower
of the two values, presents the effective limitation
on the AC modulation of the bias voltage that may
be applied for STS measurements.
fFB: The feedback circuit of the STM is used in the con-
stant current mode, where the Z-direction piezo is
used to maintain the tip at a height where the tun-
neling current is kept constant. When scanning,
this makes the tip roughly follow the topology of
the surface. When an AC modulation is applied
over the bias, it is necessary to ensure that fre-
quency of the modulation is higher than the fre-
quency response of the feedback, so that the feed-
back does not cause additional movement of the tip
at that frequency. The frequency response of the
feedback was estimated to be around 600 Hz.
fREF: The frequency reference signal generated by the
lock-in, and therefore that of the AC modulation
of the bias. This frequency is to be chosen so as to
remain within the bandwidth of the amplifiers, and
above the response frequency of the feedback.
fSample: The effective sampling rate is dependent on the
mode the STM is used in. For constant height
imaging and spectroscopy, where the feedback is
turned off during the actual acquisition of data, the
effective sampling rate needs to be high to suppress
the effects of thermal drift in the piezos, as well as
creep that may arise. The upper limit on this fre-
quency is determined by the time it takes for the
repositioning of the tip in the case of scanning, and
the time it takes to acquire the data from the lock-
in, in the case of spectroscopy.
tWait: There are a few cases in which a wait time be-
tween samples is required. In the case of imaging,
it is the time for the tip to relocate and the feed-
back to correct the Z-position of the tip. In the
case of spectroscopy, two wait times are necessary.
The first is a wait time between sweeps of the bias
voltage, during which the feedback may be allowed
to correct any drift that may have occurred dur-
ing the sweep. Additionally, a wait time between
samples is necessary to allow the lock-in output to
stabilize.
The lock-in amplifier adds a few constraints in terms of
the time it takes for its output to be valid. This is a con-
sequence of way in which the lock-in amplifier functions,
and the final stage of the lock-in amplifier being a low-
pass filter. For the STS measurements taken, we assume
that the lock-in output is valid after approximately ten
time periods of the reference signal. The time constant
of the low pass filter is selected to be around three time
periods of the reference signal.
B. STM Modifications
A few changes were necessary to allow the STM to per-
form STS measurements. The changes and the problems
they were designed to overcome are described below.
1. Addition of AC modulation
The modulation of the bias voltage is necessary to be
able to use the lock-in amplifier. The intended conse-
quence of using an AC modulated bias instead of a DC
bias or a simple sweeping of the bias across the range
of interest is to suppress 1/f noise in the measurement
and to accurately measure the differential conductance
(dI/dV), instead of attempting to calculate it numeri-
cally from noisy data. An adder circuit was added in the
bias generation path, so as to be able to inject the AC
reference signal into the bias.
Further, It was found that when the AC modulation
was applied, it was being picked up by the TCA. Since
the goal is to measure the effect of the change of bias on
the tunneling current, this pickup is detrimental to the
measurement. Various experiments performed on this
3. 3
(a) Au Large Area Scan (b) Bi2Te3 Large Area Scan (c) HOPG Large Area Scan
(d) Au Small Area Scan (e) Bi2Te3 Small Area Scan (f) HOPG Small Area Scan
(g) Au Conductance Map (h) Bi2Te3 Conductance Map (i) HOPG Conductance Map
FIG. 2. Images taken with the modified nanoREV 4.0 Air STM
pickup by varying the amplitude resulted in the following
observations :
1. The pick-up existed even in the absence of a tunnel-
ing current. Increased modulation amplitude led to
increased pick-up amplitude.
2. The frequency of the pick-up matched the fre-
quency of the modulation. The two signals were,
however, not in phase. The phase relationship was
found to be frequency dependent. At a 1 KHz mod-
ulation frequency, the phase difference was about
20 degrees.
3. The amplitude of the pick-up increased with in-
creasing modulation frequency up to about 1 KHz.
It then stabilized up to around 3 KHz, after which
it started reducing slowly. The pickup survived up
to a modulation frequency of 50 KHz.
This suggested that the pick-up may have been partially
capacitive, and that the TCA bandwidth limitation was
appearing in these experiments as well. In order to mini-
mize the pick-up, a metallic shield was added between the
tip and the sample, with a small slot provided through
which the tip could reach the sample for tunneling. This
shield reduced the pick-up level by an factor of three.
2. Changes for digitization of differential conductance
The output of the lock-in amplifier, being the differ-
ential conductance (dI/dV), needed to be digitized and
stored. Even though the lock-in amplifier used allowed
for computer access via GPIB, it was decided not to use it
so as to minimize the changes necessary when the home-
made lock-in amplifier was swapped in. An analog mul-
tiplexer at the input of the ADC was added, so as to
digitize the lock-in output instead of the tunneling cur-
rent when making STS measurements. For better LDOS
measurements, though, both will have to be measured
simultaneously so that (dI/dV / I/V) can be calculated,
which is closer to the local density of states.
In addition, the necessary changes in the software to
adjust the acquisition rate when obtaining spectra or con-
ductance maps such that the temporal spacing between
adjacent readings was longer than 10 times the time pe-
riod of the reference signal were made.
Further, it was noticed that the slower acquisition of
the spectra, and the increase in the number of sweeps
taken to 30, introduced significant errors in the spectra.
It was determined that the cause of these errors in the
spectra were due to thermal drifts and creep in the piezos,
which cause a slow change in the tip-sample separation.
In order to compensate for this, an additional wait state
was added between two adjacent sweeps, with the feed-
back turned on. This allowed the feedback to correct for
any drift that may have taken place during the sweep.
4. 4
3. TCA bandwidth enhancement
The bandwidth limitation of the TCA was discussed
along with the other timing constraints mentioned pre-
viously. It was desirable to have a higher modulation
frequency, so as to decrease the acquisition time and
the associated drift during a single sweep. Addition-
ally, the frequency response of the feedback was close to
the allowed modulation frequency and would have inter-
fered with conductance map imaging. To suppress these
sources of error, the bandwidth of the TCA was increased
from 800 Hz to approximately 8 KHz by redistributing
the gain between the TCA and the following instrumen-
tation amplifier. By reducing the amplification at the
TCA state to 108
from the original 109
, and adding a
gain of 10 at the instrumentation amplifier, the effective
bandwidth (which was dictated solely by the TCA) was
increased by a factor of 10.
4. Validation of changes
In order to validate the STM itself after these changes,
a number of images of the three samples were taken, some
of which are shown in figure 2. The top row of images
are large area scans showing the surface topology. The
middle row shows the topology of a smaller area, and the
bottom most row shows the conductance map obtained
for that area. Of these small area scans, the ones of
HOPG are of atomic resolution.The conductance maps
shown in the bottom row of images were obtained using
the commercial lock-in amplifier by reducing the acquisi-
tion time during imaging to its lowest setting of 1.5 usec.
Slower acquisition will likely be required to get cleaner
conductance maps.
In addition, a few images from an attempt to obtain
atomic resolution images with Bi2Te3 with AC modula-
tion of the bias turned on are shown in figure 3. This was
done using the modified STM. While hints of the atoms
were visible, clear images at atomic resolution were not
obtained. Further refinement of the process, including
preparation of the tip and the surface just before imag-
ing, may be necessary before success can be declared in
this direction.
C. Methods
1. Topographical Imaging
The process of topographical imaging using an STM
is well established in literature and in practice. There
are two distinct modes of imaging - constant height and
constant current. Constant height imaging involves open
loop control of the STM tip, moving it over the surface
at a fixed z position. This form of imaging is susceptible
to thermal drift and comes with the possibility of the tip
colliding with features in a rough surface, but provides
(a) Bi2Te3 large area topology
(b) Bi2Te3 scan with discernible atoms
FIG. 3. Topographical Scans of Bi2Te3
for a greater resolution. The image of the surface itself is
generated using the tunneling current measured at each
point. None of the images presented here are constant
height images. Typically, constant height imaging is pre-
ferred when attempting atomic resolution scans. It is
possible that performing these scans using the constant
height mode will produce cleaner images.
The second mode, constant current imaging, is used
when imaging a large area or using rough surfaces. In
this case, the tip’s z position is maintained via closed
loop control, where the tip is moved to maintain a fixed
tunneling current. The image is generated from the tip’s
z-position at each point which produced the specified tun-
neling current. The images presented here have all been
taken in the constant current mode. This allowed us
the advantage of being able to acquire these scans at a
slightly lower rate, thereby producing topographical im-
ages with closer parity to the conductance maps.
The process of topographical imaging starts with at-
tempting to correct for any local slope that may exist in
the sample in the region of interest. The X-slope and Y-
slope can be modified separately to allow the electronics
to compensate for such features. And other long range
slope that is observed in the image, as it often is, is due
to to the thermal drift of the piezo during the course of
the imaging. The correction for this drift is incorrectly
marked as a slope in the surface. It is compensated for
finally during the course of processing the image.
For each scan, the image is acquired row-by-row or
column-by-column. Each row (or column) is acquired
twice, once in the scan direction and again in the retrace
direction, where the tip moves back along the path it
traced. Positive correlation between the scan and retrace
image confirm that the data acquired corresponds to real
features in the surface and is not the effect of a transient
disturbances. All the scans presented here are shown
5. 5
along with the retrace images acquired.
The scans shown in figures 2a, 2b, 2c, 2d, 2e, 2f, 3, and
5a are all topographical images.
2. Acquisition of Spectra
The acquisition of conductance spectra as well as I-V
curves are done at a specified point. The steps involved
in topological imaging are noted below :
1. A topographical image of the surface is first ac-
quired, and a point of interest is marked.
2. The tip is moved to that location, and is set to
constant current mode at a nominal bias voltage
for an initial settling time. This brings the tip to
a reasonably well defined point with respect to the
sample.
3. The feedback loop is stopped and spectroscopy be-
gins. The bias is set at the lowest point in the range
of interest, and the tunneling current in the case of
I-V spectroscopy or the lock-in output in the case of
differential conductance spectroscopy are digitized
after a duration specified by the sample wait time.
This wait time is determined by the frequency of
the modulation and other parameters, as discussed
previously.
4. The bias is moved up by the defined step size, and
the process is repeated until the maximum bias
voltage of interest is reached.
5. The bias is set to the nominal point and feedback
is turned on. A 5 second wait time allows the tip
to return to the point it started at, if there was any
drift during the intervening time.
6. The process is repeated for as many sweeps as re-
quired.
The conductance spectra shown here were obtained by
taking 30 sweeps one after the other using the process
defined above and the results averaged. The other pa-
rameters involved are :
Modulation Frequency: 2.5 KHz
Modulation Amplitude: 30 mV
Lock-in Time Constant: 3 msec
Acquisition Time: 5 msec
Nominal Bias: 200 mV
The spread of data obtained in a single set of sweeps is
believed to be caused by an as yet uncorrected thermal
drift in the piezo. Methods to further enhance acquisition
rate, given the various bandwidth constraints, are being
explored.
3. Conductance Imaging
The conductance maps presented here, in figures 2g,
2h, 2i, and 5b have been obtained using the same process
used to acquire the topological images. And additional
digitization mode was added to the software, which would
use the process used for constant current imaging to ac-
quire the data. A longer acquisition time was used to
acquire the images due to the low modulation frequency,
as discussed above. Figure 5 shows a conductance image
acquired of Bi2Te3 and the corresponding topological im-
age of the same region.
III. LOCK-IN AMPLIFIER
The measurement of small signals is a subject of great
interest in very many fields of experimental science, in-
cluding physics, chemistry, biology, and the many inter-
disciplinary fields that have arisen. The need for such
measurement stems from the fact that a number of phe-
nomena are characterized by small but ultimately de-
tectable changes in a measurable parameter. Conven-
tional measurement techniques, however, fail to measure
the small changes accurately due to a number of reasons.
The use of a lock-in amplifier enables the measurement
of signals with amplitude much lower than the noise of
the measurement itself.
A. Motivation
Lock-ins are used in a wide variety of applications. The
basic requirement for a measurement to be compatible
with a lock-in is that the physical phenomenon to be de-
tected should be such that it can be turned on and off,
or modulated, according to an external signal called the
’reference signal’. The frequency of this reference signal
is constrained by the capabilities of the lock-in ampli-
fier, other instruments in the experimental setup, and
the characteristics of the physical phenomena involved.
In the context of this project, the lock-in amplifier was
looked at to attempt performing, among other things,
measurements of the local density of states (LDOS) using
the STM. The LDOS measurement using STM requires
detecting and quantifying voltage changes well below the
noise floor. The amplitude of the bias voltage changes
itself is close to the typical noise level in garden vari-
ety digital electronics. The theoretical limit to the en-
ergy resolution of the measurement, assuming an ’ideal’
lock in amplifier, is given by KbT, which at 4.2K corre-
sponds to 0.36meV and at room temperature corresponds
to 25meV. Practical measurement at the levels of the ex-
pected changes in tunneling current tend to be difficult,
since they lie below the noise floor of the system. The
’ideal’ goal of the lock-in amplifier, then, is to come as
close to this theoretical limit as possible, and if possible
6. 6
(a) Au I-V (b) Bi2Te3 I-V (c) HOPG I-V
(d) Au dI/dV vs V (e) Bi2Te3 dI/dV vs V (f) HOPG dI/dV vs V
FIG. 4. STS Results
(a) Bi2Te3 topology map
(b) Bi2Te3 conductance map
FIG. 5. Scans of Bi2Te3 in constant current mode, with cor-
responding conductance map obtained through the lock-in.
to cross it, so that the resolution is limited by the physics
of the system being measured itself. .
B. Review of lock-in techniques
The basic principle in phase sensitive detection is that
the phase and frequency information contained in the ref-
erence signal can be used to separate the signal from the
noise, which is a superimposition of sinusoids of all pos-
sible frequencies and phases at random amplitudes. The
lock-in process is easily seen mathematically as a multi-
plication of all the time domain Fourier components of
the input signal with the reference signal. The only terms
that survive subsequent time averaging are those which
contain only the components of the reference signal.
The fundamental lock-in process itself is fairly
straightforward and is a direct consequence of simple
mathematics.6
presents a frequency domain description
of the lock-in amplifier. The implementation of the lock-
in itself varies as per the design used, and the details of
process may vary slightly, but the approach in all lock in
amplifiers is fundamentally the same.
It may be noted that as long as the input signal is in
phase with the reference, the process described above
is mathematically sufficient to perform measurements.
However, the reference and signal are often out of phase
with each other. One of the major reasons for this is that
the underlying physical system takes a finite amount of
time to respond to changes in the reference frequency.
This produces a phase lag between the driving signal (the
reference) and the measurable quantity (the input to the
7. 7
lock-in).
In order to handle signals of this sort, and to accu-
rately measure the phase lag between the two signals, it
is possible to simply perform the lock-in process with the
quadrature of the reference signal. The two DC outputs
thus obtained can be used to calculate the amplitude
and phase lag of the input signal with respect to the ref-
erence. In this case also, however, the phase relationship
between the input and reference must be time invariant
for the signal to survive the final low-pass stage.
C. Lock-in amplifier design
The actual implementation of the lock-in amplifier is
generally not as straightforward as the mathematics. The
process of ’multiplying’ two signals is non-trivial. In real-
ity, the lock-in process is done using a variety of different
processes, each with its set of advantages and disadvan-
tages. Broadly, there are three different ways in which it
is implemented in literature :
1. Analog Multiplication of sines.
2. Analog Demodulation against a reference signal.
3. Manipulation of the digitized signal.
The first, the analog multiplication of sines, is the clos-
est to the mathematical formulation of the lock-in de-
scribed earlier. Multiplication of analog signals, how-
ever, is not easily achieved with discrete components.7
describes the development of a lock-in amplifier using
the AD734 multiplier from Analog Devices.
The second, analog demodulation against a reference
signal, is used more often in low-cost approaches. In
this case, the reference signal is essentially treated as a
square wave rather than as a sinusoidal wave. When the
reference signal is in its positive half cycle, the signal is
allowed through. When it is in its negative half cycle, ei-
ther the output is grounded or the signal is inverted and
allowed through. This, along with subsequent low-pass
filtering, causes the demodulation of the input signal, re-
moving the AC components added in by the reference
signal.8
describes the development of a lock in amplifier
based on Analog Devices’ AD6309
, a balanced modula-
tor/demodulator. A number of other sources have essen-
tially built on this work, including10
. This is the basis
for the design made during the course of this project.11,12
describe designs which perform essentially the same func-
tion.
The third involves digitization of the input signal, gen-
erally after some preamplification, and the digitized sig-
nal is manipulated in software. Both the above two tech-
niques are used for the calculation in software, as well
as a number of other approaches, including random sam-
pling. There has been a fair amount of contention about
whether analog or digital lock-ins are superior.13
men-
tions the disagreement. Over the years, digital lock-in
FIG. 6. Block diagram of the lock-in amplifier designed.
amplifiers have generally surpassed analog ones due to
their ability to achieve higher dynamic ranges. The in-
creasing speed and performance of digital electronics and
analog to digital converters have generally aided in their
improvement. Various approaches to digital lock-in am-
plifiers are described in literature14–16
.
A block diagram of the lock-in being developed is show
in Figure 6. The various blocks shown are functionally
distinct, and are developed individually before putting
them together as a lock in amplifier.
AC Coupling: Both the input signal as well as the ref-
erence signal are AC coupled to the circuit. This
removes any DC bias that may exist in the signal,
which would otherwise cause saturation of the in-
put amplifiers. The AC coupling is also necessary
for the lock-in ’logic’ to function as desired. In this
design, AC coupling is achieved by using a high pass
filter with a virtual ground. The design proposed
in17
may be used for greater noise immunity.
Broadband Preamplification: The second section in
the input signal’s path is the broadband pre-
amplification. INA114, a Precision Instrumenta-
tion Amplifiers is used to do this so as to protect
signal integrity while it is vulnerable to noise. In
the process, the noise contained in the input signal
is also amplified by the same amount. Multi-stage
amplification is used to overcome gain limitations
of op-amps. This allows further manipulation of
the signal easily.
Extraction of Signal from Noise: The preamplified
signal is then handled using one of the techniques
for Lock-In Amplification. The AD630 demodu-
lator is used to perform this task. The signal is
allowed to pass through only when the reference
signal is in its positive half wave. When the signal
is in its negative half wave, the output is grounded.
Components of the signal which are not related
to the reference signal die out in the time average
caused by a subsequent low pass filter, as described
previously.
8. 8
Low Pass Filter: A low pass filter is used finally to per-
form the time averaging of the AD630 output. Ad-
ditionally, a DC amplifier is used to allow ampli-
fication of the output voltage to comfortably mea-
surable levels as needed. A simple RC filter is used
to achieve this.
Reference Signal: A simple sine wave generator circuit
based on the XR2207 IC is constructed to generate
the sine wave necessary for the AC modulation. In
this design, a simple RC integrator circuit is used to
simulate the 90 degree phase shift necessary. This
approxmation is sufficient for the AD630, since all
reference signals are treated as if they are square
waves.
1. Lock-In Output
The following are the characteristics of the output of
a lock-in amplifier.
• The DC component of the input signal is discarded
completely.
• The amplitude of the signal at the reference fre-
quency, in phase with the reference shows up as
the DC output.
• The reference signal is phase shifted by 90 degrees
and the process repeated to extract the out of phase
(quardature) component.
• The amplitude and phase relationship can be ex-
tracted from the two DC outputs.
IV. CONCLUSIONS
During the course of the project, the infrastructure
necessary to perform STS using the nanoREV Air STM
was developed. Data obtained from three samples corre-
spond well to the curves expected for the three samples.
Imaging performed on the samples has been used to val-
idate the changes made to the STM during the course of
the project.
While it was initially proposed that the STS data will
be reacquired using the home-made lock-in amplifier,
that has not been possible as of yet. The lock-in am-
plifier designed has reached closer to a stage of maturity,
and testing of the device is underway. In the meanwhile,
a printed circuit board of the design has been sent for
fabrication, which should eliminate some of the uncer-
tainty regarding the sources of noise. It is expected that
the lock-in amplifier would be ready for obtaining reliable
data within the next two months.
ACKNOWLEDGMENTS
I am grateful to Prof. Deshdeep Sahdev for his guid-
ance and the opportunity to work with him on this
project. I would also like to thank Prof. Anjan Kumar
Gupta for sharing his experience with STS. I also thank
Quazar Technologies Pvt. Ltd., particularly Mr. Joshua
Mathew, for their support in making the necessary mod-
ifications to their nanoREV Air STM.
∗
chintal@iitk.ac.in; shashank.chintalagiri@gmail.com
†
ds@iitk.ac.in
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