1. The document summarizes an experiment measuring photocurrent on the edges of graphene. The initial goal was to detect charge accumulation on graphene edges but instead photocurrent was detected when shining a laser on graphene edges under an applied potential.
2. Further experiments showed that the maximum photocurrent occurred when the laser was focused on the graphene edge. The results also indicated that resistances or contaminants on the graphene could be removed by applying a sufficiently high current.
3. Additional analysis found the photocurrent peaked at the beginning of the graphene edge rather than the middle, though more experiments are needed to explain this phenomenon. In conclusion, while charge accumulation was not observed, photocurrent was detected and its properties were analyzed.
This document summarizes research on the effects of strain on the lattice thermal conductivity in silicon thin films using first-principles calculations and solving the phonon Boltzmann transport equation. The key findings are:
1) Thermal conductivity in the in-plane [100] direction has a weaker dependence on strain than the cross-plane [001] direction.
2) Thermal conductivity increases with compressive strain and decreases with tensile strain in the [001] direction due to changes in phonon velocities.
3) For a 20nm thin film, boundary scattering does not dominate thermal transport in the in-plane [100] direction, and strain has a small effect on thermal conductivity in this direction.
This research, presented at the 2014 APS March Meeting in Denver, Colorado, characterizes magnetic phase transitions in the manganese-doped dichalcogenide TaS2.
1) The document studies using electric fields of 40 GVm-1 created by ionic liquid electric double layers to control the magnetic properties of thin films.
2) Experiments showed applying a voltage decreased the coercivity of 5nm permalloy thin films by 54% and reduced the magnetic moment by 54%.
3) Analysis found the voltage exposure increased oxidation of the permalloy, as shown by reductions in metal peaks and increases in oxide peaks in X-ray photoelectron spectroscopy, which explains the changes in magnetic properties.
National Policy Direction for Pest Management 2015Gina Chamberlain
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive functioning. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
This document is a literature review on the driving forces behind enterprise risk management (ERM) and the value it provides organizations. The review examines how firm size, complexity, industries and other factors influence adoption of ERM. Larger, more diversified and complex firms tend to implement ERM more due to greater needs and resources. While ERM provides benefits, some studies note its challenges for internationally diversified companies. Overall the review aims to understand what drives ERM adoption and identify the value it creates within different organizational structures.
This document summarizes research on the effects of strain on the lattice thermal conductivity in silicon thin films using first-principles calculations and solving the phonon Boltzmann transport equation. The key findings are:
1) Thermal conductivity in the in-plane [100] direction has a weaker dependence on strain than the cross-plane [001] direction.
2) Thermal conductivity increases with compressive strain and decreases with tensile strain in the [001] direction due to changes in phonon velocities.
3) For a 20nm thin film, boundary scattering does not dominate thermal transport in the in-plane [100] direction, and strain has a small effect on thermal conductivity in this direction.
This research, presented at the 2014 APS March Meeting in Denver, Colorado, characterizes magnetic phase transitions in the manganese-doped dichalcogenide TaS2.
1) The document studies using electric fields of 40 GVm-1 created by ionic liquid electric double layers to control the magnetic properties of thin films.
2) Experiments showed applying a voltage decreased the coercivity of 5nm permalloy thin films by 54% and reduced the magnetic moment by 54%.
3) Analysis found the voltage exposure increased oxidation of the permalloy, as shown by reductions in metal peaks and increases in oxide peaks in X-ray photoelectron spectroscopy, which explains the changes in magnetic properties.
National Policy Direction for Pest Management 2015Gina Chamberlain
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive functioning. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
This document is a literature review on the driving forces behind enterprise risk management (ERM) and the value it provides organizations. The review examines how firm size, complexity, industries and other factors influence adoption of ERM. Larger, more diversified and complex firms tend to implement ERM more due to greater needs and resources. While ERM provides benefits, some studies note its challenges for internationally diversified companies. Overall the review aims to understand what drives ERM adoption and identify the value it creates within different organizational structures.
This document recounts the events of Pentecost from the Bible where the Holy Spirit descended upon the disciples in the form of a mighty wind and tongues of fire. It describes how the disciples were filled with power and began speaking in other languages, praising God. The document encourages believers to receive this "salutary water" through faith, humility, prayer and perseverance so they too may be filled with power in their hearts.
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive function. Exercise causes chemical changes in the brain that may help alleviate symptoms of mental illness and boost overall mental well-being.
Gregory Thomas has worked as a special educator, English teacher, and Pride Lead for over 22 years in Baltimore City Public Schools. He comes from a humble background but believes education is important for becoming a productive member of society. His goal is to advance his own education so he can better effect change in the lives of young people.
Автоматизированная передача уведомлений о залоге движимого имущества от банка или финансовой организации к нотариусу, и обратная передача свидетельств о регистрации залогов из нотариальной конторы залогодержателю.
Craig Dietz is a botanist who has rescued over 5,471 plant species in Chiapas, Mexico since 1994. He graduated from UCLA Film School in 1974 and worked as a commercial photographer before moving to Chiapas. In 1994 he began rescuing plants and in 2009 he opened the Orquideas Moxviquil Botanical Garden to showcase the rescued plants and educate visitors. The document discusses Dietz's rescues over the years, the construction and development of the botanical garden, techniques for pollinating and transplanting orchids and bromeliads, and projects currently taking place at the garden.
The hatch window is the time between the first and last chick hatching. A wide hatch window can cause health issues for early and late hatching chicks. Multiple factors influence hatch time, including physiological, physical, and genetic variables as well as management techniques. Proper management of egg size, age, pre-warming time, incubator type, production stage, fertility, and basket filling can help control hatch time and shorten the hatch window. Conducting hatch time surveys provides information to effectively manage factors and optimize hatching.
The document discusses the structure of proteins at various levels of organization:
- Proteins are composed of amino acids linked together by peptide bonds to form polypeptide chains. The sequence and interactions of these chains determine the protein's structure.
- There are four levels of protein structure - primary, secondary, tertiary, and quaternary. Secondary structure includes alpha helices and beta sheets formed by hydrogen bonding between amino acids in the chain. Tertiary structure describes the overall 3D shape formed by interactions between amino acid side chains. Quaternary structure involves the interaction of multiple polypeptide chains.
- Protein structure enables proteins to perform their diverse functions through processes like enzyme catalysis, oxygen transport, and providing structure
Project Follow Through was a large federally-funded experiment in education from 1967-1995 that aimed to provide educational services to disadvantaged elementary students. Due to limited funding, it shifted focus from services to research and development. Direct Instruction was one approach developed through this project that emphasized explicit instruction, ability grouping, and frequent assessment to accelerate learning. Research found Direct Instruction had substantial positive effects on student achievement.
1) The document discusses how the angle of the high voltage probe used in electrospinning affects the direction of the bending instability of the polymer jet and the deposition location of the nanofibers.
2) Experiments showed that when the probe was placed at different angles, the nanofibers deposited in different locations, oriented opposite to the probe angle and furthest from it.
3) Placing the probe outside the electrospinning box eliminated its effect, and nanofiber deposition location did not change with probe angle. This confirms the probe exerts a repellent force that influences bending instability and deposition location.
Students used a charpy impact tester to collect data on testing brass and marble specimens. They analyzed the data to calculate the absorbed impact energy, work done during impact, and elastic and plastic portions of energy absorption. Brass absorbed more energy and required more work to fracture, showing it is the stronger material. The rate at which a force is applied affects material properties, and dynamic loading is different than static loading since the applied force is not constant during impact.
1) The author worked on several projects to prepare the ISOLTRAP facility at CERN for new beams and upgrades, including wiring plugs for valve actuators, testing vacuum chambers, characterizing the electrical contact of the laser ion source, and measuring the leakage resistance of capacitors for the MR-ToF mass separator.
2) He tested individual vacuum chambers and identified leaks using helium spraying.
3) Using a multimeter and LabVIEW, he characterized the electrical contact between the rotating plate and electrode in the laser ion source.
4) He developed a method using a high voltage supply, resistor, capacitor, and picoammeter to measure capacitor leakage resistance, which is important for noise
This report discusses an experiment on flow visualization of electro-kinetic force chemical mechanical planarization (EKF-CMP). Straight and radial electrode specimens were created in glass chambers to observe flow patterns under various voltages and solution conditions using video and simulations. Results showed that lower gap lengths and radial electrode orientation produced faster fluid flow. While solution pH had little effect, EKF-CMP was found to significantly improve material removal rate over conventional CMP, making it suitable for creating refined 3D stacked wafers needed to satisfy Moore's Law. In conclusion, the experiment validated that external voltage application enhances CMP performance.
This document reports on a lab experiment using a scanning electron microscope (SEM) to examine how different SEM parameters affect image quality. Groups of students tested acceleration voltage, beam current, sample tilt, and working distance. For acceleration voltage, higher voltages produced brighter but less clear images due to charging effects. Medium voltages of 5-10kV provided the best balance of brightness and contrast. Higher beam currents created smoother but lower resolution images. Tilting the sample resulted in non-uniform illumination. Variations in working distance revealed trade-offs between resolution and depth of field. The lab helped students learn SEM operation and parameter optimization to obtain high-quality images.
This document describes a method for fabricating both negative and positive patterns on a single layer of positive photoresist. The method involves locally crosslinking the photoresist using laser exposure, followed by a flood UV exposure and development. The crosslinked areas form a negative pattern, while the non-exposed areas form a positive pattern. Experimental results showed that the height of the negative pattern can be controlled by varying the laser exposure energy and other processing parameters.
- The document describes an atomic force microscopy (AFM) lab experiment using a Veeco Digital Instruments CP-II AFM to image gold nanoparticles and a cicada wing in contact (C-AFM) and intermittent contact (IC-AFM) modes.
- Scans were taken of both samples in each mode and measurements were made of particle diameters and center-to-center distances.
- The IC-AFM mode did not function properly, only allowing imaging in C-AFM mode which produced higher resolution images as expected.
This document summarizes an internship project involving characterization of atomic force microscopy (AFM) tip radius using two different methods. The internship involved learning AFM operation and scanning sample images. For the project, tip radius was quantified before and after imaging using both the capacitance method from electrostatic force microscopy measurements and relating the critical oscillation amplitude to tip radius. Comparing the results found the capacitance method was less accurate for small tips while the tips did not significantly change after imaging. The internship provided valuable experience learning AFM fundamentals and practical techniques.
This lab report summarizes a heat transfer experiment with the following key points:
1) The experiment tested the inverse square law and radiation properties of different surfaces using a thermal radiation cube and Stefan-Boltzmann lamp.
2) Results found that radiation intensity followed the inverse square law, decreasing exponentially with distance.
3) Different surfaces had different radiative properties, with black having highest absorptivity and polished aluminum having the lowest.
SIMULATION OF THE SOLAR CELLS WITH PC1D, APPLICATION TO CELLS BASED ON SILICONAEIJjournal2
A way of exploiting the solar energy is to use cells photovoltaic which convert the energy conveyed by the
incidental radiation in a continuous electric current. This conversation is based on the photovoltaic effect
engendered by the absorption of photons. A part of the absorbed photons generates pairs electron-hole in
which an electric field created in the zone of load of space of a junction p–n.
Thus, the junction p-n, its characteristics, its components and its dimensions are the parameters
responsible of the efficiency and the performances of a solar cell. To study this, we are going to use a very
known software in the mode of the simulation of solar cells, the PC1D, and we are going, at the end, to
draw a conclusion around the ideal parameters that a good solar cell has to have.
This document recounts the events of Pentecost from the Bible where the Holy Spirit descended upon the disciples in the form of a mighty wind and tongues of fire. It describes how the disciples were filled with power and began speaking in other languages, praising God. The document encourages believers to receive this "salutary water" through faith, humility, prayer and perseverance so they too may be filled with power in their hearts.
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive function. Exercise causes chemical changes in the brain that may help alleviate symptoms of mental illness and boost overall mental well-being.
Gregory Thomas has worked as a special educator, English teacher, and Pride Lead for over 22 years in Baltimore City Public Schools. He comes from a humble background but believes education is important for becoming a productive member of society. His goal is to advance his own education so he can better effect change in the lives of young people.
Автоматизированная передача уведомлений о залоге движимого имущества от банка или финансовой организации к нотариусу, и обратная передача свидетельств о регистрации залогов из нотариальной конторы залогодержателю.
Craig Dietz is a botanist who has rescued over 5,471 plant species in Chiapas, Mexico since 1994. He graduated from UCLA Film School in 1974 and worked as a commercial photographer before moving to Chiapas. In 1994 he began rescuing plants and in 2009 he opened the Orquideas Moxviquil Botanical Garden to showcase the rescued plants and educate visitors. The document discusses Dietz's rescues over the years, the construction and development of the botanical garden, techniques for pollinating and transplanting orchids and bromeliads, and projects currently taking place at the garden.
The hatch window is the time between the first and last chick hatching. A wide hatch window can cause health issues for early and late hatching chicks. Multiple factors influence hatch time, including physiological, physical, and genetic variables as well as management techniques. Proper management of egg size, age, pre-warming time, incubator type, production stage, fertility, and basket filling can help control hatch time and shorten the hatch window. Conducting hatch time surveys provides information to effectively manage factors and optimize hatching.
The document discusses the structure of proteins at various levels of organization:
- Proteins are composed of amino acids linked together by peptide bonds to form polypeptide chains. The sequence and interactions of these chains determine the protein's structure.
- There are four levels of protein structure - primary, secondary, tertiary, and quaternary. Secondary structure includes alpha helices and beta sheets formed by hydrogen bonding between amino acids in the chain. Tertiary structure describes the overall 3D shape formed by interactions between amino acid side chains. Quaternary structure involves the interaction of multiple polypeptide chains.
- Protein structure enables proteins to perform their diverse functions through processes like enzyme catalysis, oxygen transport, and providing structure
Project Follow Through was a large federally-funded experiment in education from 1967-1995 that aimed to provide educational services to disadvantaged elementary students. Due to limited funding, it shifted focus from services to research and development. Direct Instruction was one approach developed through this project that emphasized explicit instruction, ability grouping, and frequent assessment to accelerate learning. Research found Direct Instruction had substantial positive effects on student achievement.
1) The document discusses how the angle of the high voltage probe used in electrospinning affects the direction of the bending instability of the polymer jet and the deposition location of the nanofibers.
2) Experiments showed that when the probe was placed at different angles, the nanofibers deposited in different locations, oriented opposite to the probe angle and furthest from it.
3) Placing the probe outside the electrospinning box eliminated its effect, and nanofiber deposition location did not change with probe angle. This confirms the probe exerts a repellent force that influences bending instability and deposition location.
Students used a charpy impact tester to collect data on testing brass and marble specimens. They analyzed the data to calculate the absorbed impact energy, work done during impact, and elastic and plastic portions of energy absorption. Brass absorbed more energy and required more work to fracture, showing it is the stronger material. The rate at which a force is applied affects material properties, and dynamic loading is different than static loading since the applied force is not constant during impact.
1) The author worked on several projects to prepare the ISOLTRAP facility at CERN for new beams and upgrades, including wiring plugs for valve actuators, testing vacuum chambers, characterizing the electrical contact of the laser ion source, and measuring the leakage resistance of capacitors for the MR-ToF mass separator.
2) He tested individual vacuum chambers and identified leaks using helium spraying.
3) Using a multimeter and LabVIEW, he characterized the electrical contact between the rotating plate and electrode in the laser ion source.
4) He developed a method using a high voltage supply, resistor, capacitor, and picoammeter to measure capacitor leakage resistance, which is important for noise
This report discusses an experiment on flow visualization of electro-kinetic force chemical mechanical planarization (EKF-CMP). Straight and radial electrode specimens were created in glass chambers to observe flow patterns under various voltages and solution conditions using video and simulations. Results showed that lower gap lengths and radial electrode orientation produced faster fluid flow. While solution pH had little effect, EKF-CMP was found to significantly improve material removal rate over conventional CMP, making it suitable for creating refined 3D stacked wafers needed to satisfy Moore's Law. In conclusion, the experiment validated that external voltage application enhances CMP performance.
This document reports on a lab experiment using a scanning electron microscope (SEM) to examine how different SEM parameters affect image quality. Groups of students tested acceleration voltage, beam current, sample tilt, and working distance. For acceleration voltage, higher voltages produced brighter but less clear images due to charging effects. Medium voltages of 5-10kV provided the best balance of brightness and contrast. Higher beam currents created smoother but lower resolution images. Tilting the sample resulted in non-uniform illumination. Variations in working distance revealed trade-offs between resolution and depth of field. The lab helped students learn SEM operation and parameter optimization to obtain high-quality images.
This document describes a method for fabricating both negative and positive patterns on a single layer of positive photoresist. The method involves locally crosslinking the photoresist using laser exposure, followed by a flood UV exposure and development. The crosslinked areas form a negative pattern, while the non-exposed areas form a positive pattern. Experimental results showed that the height of the negative pattern can be controlled by varying the laser exposure energy and other processing parameters.
- The document describes an atomic force microscopy (AFM) lab experiment using a Veeco Digital Instruments CP-II AFM to image gold nanoparticles and a cicada wing in contact (C-AFM) and intermittent contact (IC-AFM) modes.
- Scans were taken of both samples in each mode and measurements were made of particle diameters and center-to-center distances.
- The IC-AFM mode did not function properly, only allowing imaging in C-AFM mode which produced higher resolution images as expected.
This document summarizes an internship project involving characterization of atomic force microscopy (AFM) tip radius using two different methods. The internship involved learning AFM operation and scanning sample images. For the project, tip radius was quantified before and after imaging using both the capacitance method from electrostatic force microscopy measurements and relating the critical oscillation amplitude to tip radius. Comparing the results found the capacitance method was less accurate for small tips while the tips did not significantly change after imaging. The internship provided valuable experience learning AFM fundamentals and practical techniques.
This lab report summarizes a heat transfer experiment with the following key points:
1) The experiment tested the inverse square law and radiation properties of different surfaces using a thermal radiation cube and Stefan-Boltzmann lamp.
2) Results found that radiation intensity followed the inverse square law, decreasing exponentially with distance.
3) Different surfaces had different radiative properties, with black having highest absorptivity and polished aluminum having the lowest.
SIMULATION OF THE SOLAR CELLS WITH PC1D, APPLICATION TO CELLS BASED ON SILICONAEIJjournal2
A way of exploiting the solar energy is to use cells photovoltaic which convert the energy conveyed by the
incidental radiation in a continuous electric current. This conversation is based on the photovoltaic effect
engendered by the absorption of photons. A part of the absorbed photons generates pairs electron-hole in
which an electric field created in the zone of load of space of a junction p–n.
Thus, the junction p-n, its characteristics, its components and its dimensions are the parameters
responsible of the efficiency and the performances of a solar cell. To study this, we are going to use a very
known software in the mode of the simulation of solar cells, the PC1D, and we are going, at the end, to
draw a conclusion around the ideal parameters that a good solar cell has to have.
The document discusses several key operational variables and techniques for scanning electron microscopy (SEM). It describes how working distance and aperture size affect depth of field and resolution, with smaller apertures and longer working distances providing greater depth of field but reducing resolution. Magnification is defined based on the ratio of scan line lengths on the specimen versus image. Acceleration voltage and probe current impact resolution, with higher voltages providing better resolution but also increasing interaction volume. Specimen preparation techniques like sputter coating and freeze drying are discussed to address charging and dehydration issues.
1. The document describes the design and testing of an electrostatic adhesion device (EAD) for potential use in orbital debris removal. Key aspects of the EAD design include high voltage circuit pads to generate adhesive force and the use of macro-fiber composites as actuators.
2. Laboratory testing was conducted to determine optimal circuit designs for adhesion and observe the EAD's behavior on different material surfaces. Additional tests measured the EAD's strain and deflection capabilities when integrated with actuators.
3. A zero-gravity simulation environment was used to model the EAD's potential behavior in space. Models analyzed collision effects and the use of static friction to represent adhesive manipulation. The simulation sought to validate the practical
SIMULATION OF THE SOLAR CELLS WITH PC1D, APPLICATION TO CELLS BASED ON SILICONAEIJjournal2
A way of exploiting the solar energy is to use cells photovoltaic which convert the energy conveyed by the incidental radiation in a continuous electric current. This conversation is based on the photovoltaic effect engendered by the absorption of photons. A part of the absorbed photons generates pairs electron-hole in which an electric field created in the zone of load of space of a junction p–n. Thus, the junction p-n, its characteristics, its components and its dimensions are the parameters responsible of the efficiency and the performances of a solar cell. To study this, we are going to use a very known software in the mode of the simulation of solar cells, the PC1D, and we are going, at the end, to draw a conclusion around the ideal parameters that a good solar cell has to have.
SIMULATION OF THE SOLAR CELLS WITH PC1D, APPLICATION TO CELLS BASED ON SILICONAEIJjournal2
A way of exploiting the solar energy is to use cells photovoltaic which convert the energy conveyed by the incidental radiation in a continuous electric current. This conversation is based on the photovoltaic effect engendered by the absorption of photons. A part of the absorbed photons generates pairs electron-hole in which an electric field created in the zone of load of space of a junction p–n. Thus, the junction p-n, its characteristics, its components and its dimensions are the parameters responsible of the efficiency and the performances of a solar cell. To study this, we are going to use a very known software in the mode of the simulation of solar cells, the PC1D, and we are going, at the end, to draw a conclusion around the ideal parameters that a good solar cell has to have.
MEMS relays provide reliable and inexpensive solutions to operate a circuit that requires a large current. We provide the design and fabrication of a magnetic relay that uses a space-saving coil capable of producing an actuation force of 1 µN and a stroke of 1 mm. The method of action is a cantilever beam that deflects in-plane with the wafer. The device should require less than 1.5 mA to bring the beam into contact with the opposing part, effectively turning the switch on. The coil is made of copper and the cantilever beam is made of a Ni/Fe permalloy. The relay is fabricated with a sacrificial layer underneath the beam, so that when it is removed, the beam can actuate. A layer of SU-8 between the magnetic core and conductive coil is used to provide electrical isolation. Our fabrication process is CMOS compatible.
Microscopy microanalysis microstructures_the european physical journal_applie...Andrea Sentimenti
This document describes a method for fabricating nano-sized carbon tips in a scanning electron microscope (SEM) using controlled carbon contamination. Key steps include: using a 30kV beam for highest contamination rate; smallest spot size (~5nm); stable, well-focused beam; and a carbon block nearby to increase carbon concentration. Tips with 10° aperture and ~5nm tip are produced in under 60 seconds. Successive focusing during growth produces tips shaped like stacked cones rather than a single paraboloid. The tips are used as probes in atomic force microscopy, achieving higher resolution than conventional probes due to their small size and shape. They are also used as field emitters for electron guns due to their nanoscale size and
The study of semiconductor layer effect on underground cables with Time Domai...IOSR Journals
This document presents a study on how the semiconductor layers in underground cables can affect Time Domain Reflectometry (TDR) measurements. The researchers developed a circuit model that includes the electrical resistance of the semiconductor layers to better simulate TDR signals. Simulations using the proposed model showed good agreement with measurements from a new cable but not an aged cable. The model was updated to represent resistance in the aged cable's semiconductor layers caused by degradation over time. Simulations with this updated model matched experimental TDR results from the aged cable better than the original model. The study demonstrates that changes in semiconductor layer resistance due to aging can impact TDR pulse propagation in cables.
The main stake is to detect a defective component or likely to become it during manufacture or inservice inspections, while improving control productivity. In this context, we develop a simulation tool of EC fastened structures testing, integrated to the ANSYS platform, aimed at conceiving testing methods, optimizing and qualifying it. The finite element method has been chosen, it is suitable for this type of problem. Various configurations have been considered for the inspection of a target with a defect in different thicknesses. Due to the impossibility to detect a defect located at a distance much greater than the skin depth δ. Indeed, the eddy currents amplitude are less than 95% of the maximum amplitude beyond a depth greater than 3 δ. We are interested in the detection of defects located at depths higher to three times the skin depth.
Transition metal dichalcogenide heterostructures were synthesized through three methods: Series A, B, and C. Series C involved transferring separate transition metal dichalcogenide monolayers onto a substrate to form a heterostructure and showed no evidence of alloying through Raman spectroscopy. Optical characterization found the band gaps of the heterostructures, which approximately matched theoretical predictions. Future work will investigate properties of these materials and incorporate them into devices to demonstrate applications in optoelectronics.
1. 1
Photocurrent on the edges of grapheme
Jakub Ondracek, Georgia Institute of Technology
Abstract
My project was focused on measuring an accumulation of charge on edges of grapheme. After building
all crucial parts to conduct the experiment, we did not get a positive result. On the other hand the project
shifted towards measuring photocurrent on the edges of grapheme. This phenomenon was detected and
additional experiments were conducted to analyze the photocurrent more accurately. The results showed
when a potential difference is applied while shining a laser on different parts of graphene, the maximum
current occurs while shining laser upon the edge. In addition, resist or air absorbents can be removed by
sufficiently high current flowing through a graphene sheet.
Preparation
Initially the focus of my project was to detect an
accumulation of charge on the edge of graphene.
To do this, we first had to grow a sample with
plates of graphene and gaps between them. The
samples have been grown on Si-face of semi-
insulating SiC substrate from AB wafer (II-VI
Inc). Two samples ABKB and ABKD were
grown for use in this experiment. The samples
were grown such that there is a gap between
1µm and 5µm between the plates. Once the
samples were grown we needed to make a
proper sample holder such that we can apply a
potential difference between the graphene plates
while shining laser on the sample. Figure 1
shows the sample holder from the profile and
figures 2 and 3 show the Chip from the inside.
Figure 1: Sample holder from the side
Since the chip’s depth prevents a microscope to
focus on the sample, we had to find a way how
to elevate the sample such that the sample is
raised above the edges of the chip. We found
two possible ways how to raise the sample. First
one is shown from a profile in figure 2 and
second one is shown from the top in figure 3.
Figure 2: Inside of chip viewed from
side (1. possible way)
Figure 3: Inside of chip viewed from top
(2. Possible way)
Double
Sided Tape
Goldcontact
Sample
Gold contact
Glass
Wire
Chip
Wire
Tape
Chip Glass
Substrate
Sample
Glass
Black TapeWood
2. 2
First way of elevating the sample was to stack
small pieces of wood and glass and glue the
sample on top. However, while making the chip
this way, we found background noise of Raman
spectroscopy being increased by glue used to
attach the sample to the chip. In addition
background was increased by the piece of wood
used to elevate the sample. As the result the
black tape was used to eliminate the background
noise due to the wood. This way the chip was
usable and since we could access all contacts on
the chip, it was a viable option. However, we
have decided to use the second chip depicted in
figure 2 mainly for its simplicity and its
decreased possibility of background noise. In
this case the edges of the sample were glued to
the glass and the glass was glued to the edges of
the chip. The width of the glass was chosen to be
about the width of the sample and length a little
bit smaller than the length of the chip for
multiple reasons. The width of the glass should
be the width of the sample such that there is
enough space to wirebound the wires but the
glass has to be wide enough so the gluing of the
sample is as easy as possible. To cut the glass
the piece of glass we want to use is pressed
between two pieces of sharp metal with double
sided tape on them. Glass should be scratched by
a diamond and the scratch should align with the
two metal pieces. Force is then applied on the
rest of glass from the scratched side. The
technique to cut the glass is depictured in figure
4.
In the next stage of preparation, we had to
determine the state of all the devices on our
samples to see which ones can be used (see
figure 5). Once we found the working devices
we had to determine the voltage at which the
current starts to flow through the gap between
them so we know what voltage we should apply
to see the desired effect
Figure 4: Glass in a wise
Figure 5: One out of 4 structures on a
sample
Measurements
Once the sample holder was made and the
devices were analyzed, we have pursued to
measure the accumulation of charge on the
edges of graphene by detecting a shift in G peak
while applying potential difference to the
graphene plates. We did not detect any shift in
the peaks, but we noticed an IV curve change
while shining a laser on the edge of the
graphene. The change can be seen in figure 6.
Force applied
Double
Sided
Tape
Glass
Diamond
cut
Sharp
edge
metal
Gold
Contact Graphene
Device
3. 3
This shifted the focus of the project from
detection of accumulation of charge into
detection of photocurrent.
Figure 6: IV curve with laser on and off
Figure 7: IV curve of different positions
First we measured the current with voltage
ranging from -120V to 120V and the laser
turned on at selected positions on the sample.
All of the positions were spaced 0.2 µm or 0.5
µm on a single line covering two plates of
grapheme and a gap between them. The
resulting graph is shown in the figure 7. From
the figure you can see the current dependence on
the position of the laser which clearly shows the
appearance of the photocurrent.
After each measurement with laser on, we
measured the current at the same position and
conditions but with the laser turned off and the
results are shown in figure 8. This graph shows a
decrease of maximum current produced after
application of potential difference which might
suggest degradation of grapheme under the
relatively high voltage combined with the light
from the laser. However, this hypothesis was
later rejected when additional experiments were
done on the sample.
Figure 8: IV curve with laser off at
initial position (red) and position half
way though the scan (blue)
This degradation was also visible on the actual
sample. The gap has widened and it looked like
the graphene was damaged between the
electrodes. Figure 9a shows the initial state of
the device before an experiment and Figure 9b
shows the final state of the same device.
4. 4
Figure 9a: Device before a scan
Figure 9b: Device after a line scan with
a circle indicating the degradation of
graphene
To determine a state of the graphene after the
experiment, we mapped the device and looked at
the G peak and 2D peak. The map is shown in
figure 10. From the map we concluded that the
graphene itself was not damaged as previously
implied, but rather a resist or air absorbents on
the sample was affected.
Figure 10: Raman Spectroscopy map
after a scan. Figure a) showing G peak,
figure b) showing 2D peak.
To decrease the effects of current and light on
quality of the sample, we scanned focused laser
(1 μm in diameter) between the two contacts
while measuring Raman spectra to detect
position of graphene sheets. The photocurrent
was measured simultaneously while constant
bias was applied between the two contacts. We
again measured the intensity of G peak, but this
time we measured current as function of position
of the laser as well. Figure 11 shows the
intensity of G peak in upper figure and current
as a function of position of the laser in the lower
figure. Both graphs were normalized such that a
vertical line can show a relationship between the
intensity of G peak and current at given point.
a)
b)
5. 5
Figure 11: Upper figure shows the G
peak intensity and the bottom figure
shows the current at given position
Figure 11 shows another interesting
phenomenon as the peak of the current is at a
beginning of the edge. It is hard to say why the
peak of the current is at the bottom of the edge
rather than in the middle. It might be due to the
laser shining on the most outer edge and therefor
creating free charges the closest to the other
graphene, but more experiments need to be done
to determine the cause of this phenomenon.
Conclusion
Even though we did not get to measure an
accumulation of charge on the edge of graphene,
we found that there is a photocurrent produced
at the edge of the graphene when a laser is
shined on it. Further analysis has shown that
resist or air absorbents on graphene can be
eliminated by high enough current flowing
through a sample which decreases graphene’s
electric capabilities.