Time of Flight (ToF) Secondary Ion Mass Spectroscopy (SIMS) is an extremely sensitive surface analysis technique where the mass to charge ratio of an ion or molecular fragment is determined by its velocity in the time domain. The commercially available ToF SIMS instruments available today have their roots in close to a century’s worth of academic research, and their ability to gather elemental and molecular information with excellent depth resolution and high sensitivity is incomparable.
This document discusses the use of photoluminescence to analyze optimal growth factors in quantum nanowires for solar energy applications. It describes how nanowire semiconductors present a more economical alternative to planar semiconductors for solar cells. The study aims to observe the photoluminescence of different gallium arsenide quantum wire samples grown using molecular beam epitaxy under various conditions to determine the most efficient samples. Molecular beam epitaxy is described as the bottom-up technique used to grow the nanowire semiconductor samples by depositing elemental beams of gallium and arsenide onto a silicon wafer substrate.
This document discusses backscattering spectrometry, which uses elastic scattering of ions to determine the elemental composition of materials. It describes how Rutherford scattering can be used for low energy particles, while higher energies require solving the Schrodinger equation. Examples are given of using kinematic factors to identify elements in a spectrum and calculating stopping power and cross sections. The document outlines approaches for thin film analysis using peak integration and mean energy calculations to determine areal densities and stoichiometry.
Secondary ion mass spectrometry (SIMS) is an analytical technique that bombards a sample surface with a primary ion beam, causing charged secondary ions to emit. These secondary ions are then analyzed using mass spectrometry to determine their mass-to-charge ratios. SIMS has high sensitivity and can detect elements down to parts-per-million or parts-per-billion levels. It provides both elemental and molecular composition of solid surfaces with good depth resolution and lateral resolution in the 2-5 nm and 20 nm to 1 μm range, respectively. SIMS finds applications in composition analysis, depth profiling, trace detection in semiconductors, and imaging of surfaces.
The document discusses magnetic properties and different types of magnetic materials. It defines key terms like magnetic field strength, induction, permeability, susceptibility, and saturation magnetization. It describes the origins of magnetic moments from orbital and spin motions. It classifies materials as diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, or ferrimagnetic based on their relative magnetic permeabilities and behaviors in an external magnetic field. It explains the temperature dependence of magnetization and how thermal vibrations reduce the saturation magnetization above critical temperatures like the Curie or Neel points.
Physical vapor deposition (PVD) involves depositing thin films onto surfaces through the condensation of vaporized material in vacuum conditions. There are various PVD techniques that vaporize material through processes like evaporation, sputtering, and pulsed laser deposition. Common applications of PVD coatings include improving hardness, wear resistance, and oxidation resistance for tools, medical devices, aerospace and automotive components. Magnetron sputtering is a widely used PVD technique that ejects material from a target using energetic ions from a plasma to deposit films for applications like semiconductor manufacturing.
- A crystal structure is formed by arranging basis groups of atoms in a periodic three-dimensional lattice. The smallest repeating unit of a crystal structure is the unit cell.
- Key parameters that define a crystal structure include the lattice type, basis, unit cell dimensions and angles, crystal system, and Miller indices of lattice planes.
- Common crystal structures include simple cubic, body-centered cubic, face-centered cubic, and hexagonal close-packed. Polymorphism and allotropy refer to a material having more than one possible crystal structure.
محاضرة تمهيدية للدكتور حازم فلاح سكيك قسم الفيزياء جامعة الازهر - عزة عن فكرة عمل الليزر موجهة لطلبة المرحلة الثانوية، القيت المحاضرة ضمن فعاليات المعرض العلمي الرابع لقسم الفيزياء في العام 2009
This document discusses the use of photoluminescence to analyze optimal growth factors in quantum nanowires for solar energy applications. It describes how nanowire semiconductors present a more economical alternative to planar semiconductors for solar cells. The study aims to observe the photoluminescence of different gallium arsenide quantum wire samples grown using molecular beam epitaxy under various conditions to determine the most efficient samples. Molecular beam epitaxy is described as the bottom-up technique used to grow the nanowire semiconductor samples by depositing elemental beams of gallium and arsenide onto a silicon wafer substrate.
This document discusses backscattering spectrometry, which uses elastic scattering of ions to determine the elemental composition of materials. It describes how Rutherford scattering can be used for low energy particles, while higher energies require solving the Schrodinger equation. Examples are given of using kinematic factors to identify elements in a spectrum and calculating stopping power and cross sections. The document outlines approaches for thin film analysis using peak integration and mean energy calculations to determine areal densities and stoichiometry.
Secondary ion mass spectrometry (SIMS) is an analytical technique that bombards a sample surface with a primary ion beam, causing charged secondary ions to emit. These secondary ions are then analyzed using mass spectrometry to determine their mass-to-charge ratios. SIMS has high sensitivity and can detect elements down to parts-per-million or parts-per-billion levels. It provides both elemental and molecular composition of solid surfaces with good depth resolution and lateral resolution in the 2-5 nm and 20 nm to 1 μm range, respectively. SIMS finds applications in composition analysis, depth profiling, trace detection in semiconductors, and imaging of surfaces.
The document discusses magnetic properties and different types of magnetic materials. It defines key terms like magnetic field strength, induction, permeability, susceptibility, and saturation magnetization. It describes the origins of magnetic moments from orbital and spin motions. It classifies materials as diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, or ferrimagnetic based on their relative magnetic permeabilities and behaviors in an external magnetic field. It explains the temperature dependence of magnetization and how thermal vibrations reduce the saturation magnetization above critical temperatures like the Curie or Neel points.
Physical vapor deposition (PVD) involves depositing thin films onto surfaces through the condensation of vaporized material in vacuum conditions. There are various PVD techniques that vaporize material through processes like evaporation, sputtering, and pulsed laser deposition. Common applications of PVD coatings include improving hardness, wear resistance, and oxidation resistance for tools, medical devices, aerospace and automotive components. Magnetron sputtering is a widely used PVD technique that ejects material from a target using energetic ions from a plasma to deposit films for applications like semiconductor manufacturing.
- A crystal structure is formed by arranging basis groups of atoms in a periodic three-dimensional lattice. The smallest repeating unit of a crystal structure is the unit cell.
- Key parameters that define a crystal structure include the lattice type, basis, unit cell dimensions and angles, crystal system, and Miller indices of lattice planes.
- Common crystal structures include simple cubic, body-centered cubic, face-centered cubic, and hexagonal close-packed. Polymorphism and allotropy refer to a material having more than one possible crystal structure.
محاضرة تمهيدية للدكتور حازم فلاح سكيك قسم الفيزياء جامعة الازهر - عزة عن فكرة عمل الليزر موجهة لطلبة المرحلة الثانوية، القيت المحاضرة ضمن فعاليات المعرض العلمي الرابع لقسم الفيزياء في العام 2009
This document provides an overview of thin film deposition methods and thin film characterization techniques. It discusses the objectives of the course, which are to provide an understanding of thin film deposition methods, their capabilities and limitations. Hands-on demonstrations and experiments will help participants understand each deposition method and stimulate discussion. The document then summarizes various thin film deposition techniques like evaporation, sputtering, chemical vapor deposition, their principles and examples of applications. It also summarizes various characterization techniques used to analyze thin films and determine properties like composition, structure, thickness and defects.
Crystals are solids with atoms arranged in regular repeating patterns in all directions. There are several key concepts in crystallography:
1) Crystals have a crystal lattice structure defined by lattice vectors and a unit cell that repeats to form the crystal.
2) Unit cells have lattice constants and contain one or more atoms. Primitive, body-centered, and face-centered unit cells have different atomic packing factors.
3) Crystal structures demonstrate symmetry operations like translation and rotation that leave the structure unchanged. Miller indices represent crystallographic planes and directions.
Maxwell's Equations describe how electric and magnetic fields propagate and interact with each other and objects. The equations show that electromagnetic waves, including visible light, radio waves, and more consist of oscillating electric and magnetic fields. Maxwell's Equations include Gauss' Law, Gauss' Law for Magnetism, Faraday's Law of Induction, and Ampere's Law with Maxwell's addition. They relate electric and magnetic fields to their sources and explain the generation and propagation of electromagnetic waves.
Effects of ionizing radiation on the layered semiconductor tungsten diselenideRoger Walker
This document summarizes research on the effects of ionizing radiation on tungsten diselenide (WSe2), a two-dimensional material with potential applications in space electronics. The research examined how WSe2 is impacted by exposure to x-rays, electrons, protons at different energies, and heavy metal ions like iron and silver. It was found that thin films of WSe2 grown via MOCVD were stable against soft x-rays, but exfoliated WSe2 ionized in response to protons and was destabilized by heavy metal ions. The band alignment of WSe2 on silicon carbide substrates was also modified by ionization. Exposure to air led to oxidation of WSe2 damaged by
This document discusses various types of defects that can occur in crystal structures, categorizing them based on dimensionality. Point defects are irregularities around a single atom and include vacancies, interstitials, Frenkel defects, and Schottky defects. Line defects distort atomic bonds around a dislocation line and include edge and screw dislocations. Surface defects occur at grain boundaries where crystal orientations change. Bulk defects in the volume of the material include precipitates, dispersants, inclusions, and voids. Defects can impact material properties and are sometimes deliberately introduced to improve characteristics.
The document discusses different types of crystal structures including simple cubic (SC), body centered cubic (BCC), and face centered cubic (FCC). It defines key terms like unit cell, lattice points, coordination number, and atomic packing factor. SC has a coordination number of 6 and atomic packing factor of 52%. BCC has a coordination number of 8 and packing factor of 68%. FCC has a coordination number of 12 and packing factor of 74%.
Rutherford scattering & the scattering cross-sectionBisma Princezz
1) Rutherford performed an experiment where he bombarded a thin gold foil with alpha particles and observed that most passed through without deflection, some were deflected by small angles, and a few were deflected back.
2) This led Rutherford to propose an atomic model where the atom has a small, dense nucleus containing its mass and positive charge, surrounded by electrons in orbits.
3) This was a major departure from the previous "plum pudding" model where charge and mass were thought to be uniformly distributed. However, Rutherford's model failed to explain the stability of electron orbits.
X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that uses X-rays to eject electrons from a material's surface and measure their kinetic energy to determine the elemental composition and chemical states. Kai Siegbahn developed XPS in the 1950s and won the Nobel Prize for his work. A study used XPS to analyze the surface chemistry of langasite crystals before and after vacuum annealing, finding that higher-temperature annealing reduced the surface concentration of gallium. XPS provides quantitative and chemical state information from the top 10-100 Angstroms of a surface.
X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that uses X-rays to eject electrons from the surface of a material. An XPS instrument measures the kinetic energy of the ejected electrons to identify the elements present and analyze the chemical and electronic states of the surface. XPS can analyze the top 10-100 angstroms of a material in an ultra-high vacuum environment. The technique works by measuring the binding energy of electrons ejected from a material by X-ray photons, each element has characteristic binding energies that can be used for identification and analysis of oxidation states or impurities in the surface.
This document provides an overview of crystallography and crystal structures. It discusses how crystals form periodic arrangements that can be described by unit cells defined by lattice parameters. The most common crystal structures for metals are face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP) since metals form dense, ordered packings with low energies. These crystal structures differ in their unit cell contents and atomic packing factors (FCC has the highest at 0.74). Directions in crystals are described by Miller indices written as [uvw].
The document discusses magnetic particle inspection (MPI), a non-destructive testing method used to detect surface and near-surface flaws in ferromagnetic materials. MPI works by magnetizing the test specimen and applying iron particles coated with dye. Any discontinuities will cause magnetic leakage fields that attract and cluster the particles, revealing indications of flaws. The document covers the basic MPI procedure, types of magnetic particles, interpretation of indications, and examples of flaws found using MPI. It also provides background information on magnetism and ferromagnetic materials.
- Crystallography is the study of crystalline solids using techniques like X-rays, electron beams, and neutron beams.
- In 1912, Max von Laue proved X-rays were diffracted by crystals, demonstrating diffraction patterns. He received the 1914 Nobel Prize in Physics for this discovery.
- In 1913, father and son team William and Lawrence Bragg developed Bragg's Law to explain X-ray diffraction by crystals and their invention of the X-ray spectroscope earned them the 1914 Nobel Prize in Physics.
The ideal, perfectly regular crystal structures in which atoms are arranged in a regular way does not exist in actual situations. In actual cases, the regular arrangements of atoms disrupted . These disruptions are known as Crystal imperfections or crystal defects
The document summarizes the key components and operating principles of a scanning electron microscope (SEM). The SEM uses an electron beam to scan the surface of a sample to produce images. It can achieve high magnification from 10-300,000x. The electron beam interacts with the sample, producing various signals containing information about the sample's surface topography and composition. Secondary electrons are used to view morphology while backscattered electrons provide material contrast and composition data. X-rays emitted are used for elemental analysis.
This document discusses electron diffraction and neutron diffraction techniques. Electron diffraction works by firing electrons at a crystal sample and observing the interference pattern of diffracted electrons. This allows determining atomic structure. Neutron diffraction also determines atomic structure by firing neutrons at samples and observing diffraction patterns. Key advantages of neutron diffraction are its ability to locate light atoms and detect isotopes via nuclear scattering, and reveal magnetic structure via magnetic scattering. Both techniques provide structural information at the atomic scale but neutron diffraction can analyze bulk properties and magnetic structures.
The document discusses ferromagnetism and magnetic domains. It defines ferromagnetic materials as those that exhibit spontaneous magnetization from aligned atomic magnetic moments, even without an external magnetic field. It describes how ferromagnetic materials contain many small regions called magnetic domains, where atomic dipoles are aligned within each domain. In an unmagnetized material, the domains are randomly oriented, resulting in no net magnetization. An external magnetic field causes domains aligned with the field to grow at the expense of others, through the movement of domain walls, increasing the material's overall magnetization.
This document provides an overview of crystal structures and bonding in materials. It discusses topics such as the differences between crystalline and amorphous solids, unit cells, lattice structures, metallic crystal structures like body centered cubic and face centered cubic, atomic packing factors, and anisotropic vs isotropic materials. The key concepts covered include how crystal structures are composed of a periodic arrangement of points in a lattice, with atoms attached at each lattice point, and how properties can differ based on crystal structure and orientation.
Molecular beam epitaxy (MBE) is a method for growing thin films one layer at a time under ultra-high vacuum conditions. It involves heating solid sources of material in effusion cells to create molecular beams that are deposited on a heated substrate. The absence of carrier gases and ultra-high vacuum environment result in films of the highest purity. MBE is widely used to manufacture semiconductor devices and is considered a fundamental tool for nanotechnology development due to its precise control over layer thickness down to a single atomic layer.
Mass spectrometry is an analytical technique used to identify unknown compounds and quantify known compounds by measuring the mass-to-charge ratio of ions. It works by ionizing sample molecules and separating the resulting ions based on their mass-to-charge ratios using electric or magnetic fields. There are four main components: a sample inlet, ionization source, mass analyzer, and detector. Ionization methods include protonation, deprotonation, cationization, electron ejection, and electron capture. Common ionization sources are electrospray ionization, atmospheric pressure chemical ionization, and matrix-assisted laser desorption/ionization. Mass spectrometry has been developed over the past century since its discovery by J.J. Thomson
Mass spectrometry is an analytical technique used to identify unknown compounds and quantify known compounds by measuring the mass-to-charge ratio of ions. It was pioneered in the late 19th century by J.J. Thomson and has since been significantly advanced. A mass spectrometer introduces a sample, ionizes it, separates the ions by their mass-to-charge ratio using electric or magnetic fields, and detects the ions. It has become a powerful tool for elucidating molecular structure and properties across many fields due to developments like soft ionization methods.
This document provides an overview of thin film deposition methods and thin film characterization techniques. It discusses the objectives of the course, which are to provide an understanding of thin film deposition methods, their capabilities and limitations. Hands-on demonstrations and experiments will help participants understand each deposition method and stimulate discussion. The document then summarizes various thin film deposition techniques like evaporation, sputtering, chemical vapor deposition, their principles and examples of applications. It also summarizes various characterization techniques used to analyze thin films and determine properties like composition, structure, thickness and defects.
Crystals are solids with atoms arranged in regular repeating patterns in all directions. There are several key concepts in crystallography:
1) Crystals have a crystal lattice structure defined by lattice vectors and a unit cell that repeats to form the crystal.
2) Unit cells have lattice constants and contain one or more atoms. Primitive, body-centered, and face-centered unit cells have different atomic packing factors.
3) Crystal structures demonstrate symmetry operations like translation and rotation that leave the structure unchanged. Miller indices represent crystallographic planes and directions.
Maxwell's Equations describe how electric and magnetic fields propagate and interact with each other and objects. The equations show that electromagnetic waves, including visible light, radio waves, and more consist of oscillating electric and magnetic fields. Maxwell's Equations include Gauss' Law, Gauss' Law for Magnetism, Faraday's Law of Induction, and Ampere's Law with Maxwell's addition. They relate electric and magnetic fields to their sources and explain the generation and propagation of electromagnetic waves.
Effects of ionizing radiation on the layered semiconductor tungsten diselenideRoger Walker
This document summarizes research on the effects of ionizing radiation on tungsten diselenide (WSe2), a two-dimensional material with potential applications in space electronics. The research examined how WSe2 is impacted by exposure to x-rays, electrons, protons at different energies, and heavy metal ions like iron and silver. It was found that thin films of WSe2 grown via MOCVD were stable against soft x-rays, but exfoliated WSe2 ionized in response to protons and was destabilized by heavy metal ions. The band alignment of WSe2 on silicon carbide substrates was also modified by ionization. Exposure to air led to oxidation of WSe2 damaged by
This document discusses various types of defects that can occur in crystal structures, categorizing them based on dimensionality. Point defects are irregularities around a single atom and include vacancies, interstitials, Frenkel defects, and Schottky defects. Line defects distort atomic bonds around a dislocation line and include edge and screw dislocations. Surface defects occur at grain boundaries where crystal orientations change. Bulk defects in the volume of the material include precipitates, dispersants, inclusions, and voids. Defects can impact material properties and are sometimes deliberately introduced to improve characteristics.
The document discusses different types of crystal structures including simple cubic (SC), body centered cubic (BCC), and face centered cubic (FCC). It defines key terms like unit cell, lattice points, coordination number, and atomic packing factor. SC has a coordination number of 6 and atomic packing factor of 52%. BCC has a coordination number of 8 and packing factor of 68%. FCC has a coordination number of 12 and packing factor of 74%.
Rutherford scattering & the scattering cross-sectionBisma Princezz
1) Rutherford performed an experiment where he bombarded a thin gold foil with alpha particles and observed that most passed through without deflection, some were deflected by small angles, and a few were deflected back.
2) This led Rutherford to propose an atomic model where the atom has a small, dense nucleus containing its mass and positive charge, surrounded by electrons in orbits.
3) This was a major departure from the previous "plum pudding" model where charge and mass were thought to be uniformly distributed. However, Rutherford's model failed to explain the stability of electron orbits.
X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that uses X-rays to eject electrons from a material's surface and measure their kinetic energy to determine the elemental composition and chemical states. Kai Siegbahn developed XPS in the 1950s and won the Nobel Prize for his work. A study used XPS to analyze the surface chemistry of langasite crystals before and after vacuum annealing, finding that higher-temperature annealing reduced the surface concentration of gallium. XPS provides quantitative and chemical state information from the top 10-100 Angstroms of a surface.
X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that uses X-rays to eject electrons from the surface of a material. An XPS instrument measures the kinetic energy of the ejected electrons to identify the elements present and analyze the chemical and electronic states of the surface. XPS can analyze the top 10-100 angstroms of a material in an ultra-high vacuum environment. The technique works by measuring the binding energy of electrons ejected from a material by X-ray photons, each element has characteristic binding energies that can be used for identification and analysis of oxidation states or impurities in the surface.
This document provides an overview of crystallography and crystal structures. It discusses how crystals form periodic arrangements that can be described by unit cells defined by lattice parameters. The most common crystal structures for metals are face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP) since metals form dense, ordered packings with low energies. These crystal structures differ in their unit cell contents and atomic packing factors (FCC has the highest at 0.74). Directions in crystals are described by Miller indices written as [uvw].
The document discusses magnetic particle inspection (MPI), a non-destructive testing method used to detect surface and near-surface flaws in ferromagnetic materials. MPI works by magnetizing the test specimen and applying iron particles coated with dye. Any discontinuities will cause magnetic leakage fields that attract and cluster the particles, revealing indications of flaws. The document covers the basic MPI procedure, types of magnetic particles, interpretation of indications, and examples of flaws found using MPI. It also provides background information on magnetism and ferromagnetic materials.
- Crystallography is the study of crystalline solids using techniques like X-rays, electron beams, and neutron beams.
- In 1912, Max von Laue proved X-rays were diffracted by crystals, demonstrating diffraction patterns. He received the 1914 Nobel Prize in Physics for this discovery.
- In 1913, father and son team William and Lawrence Bragg developed Bragg's Law to explain X-ray diffraction by crystals and their invention of the X-ray spectroscope earned them the 1914 Nobel Prize in Physics.
The ideal, perfectly regular crystal structures in which atoms are arranged in a regular way does not exist in actual situations. In actual cases, the regular arrangements of atoms disrupted . These disruptions are known as Crystal imperfections or crystal defects
The document summarizes the key components and operating principles of a scanning electron microscope (SEM). The SEM uses an electron beam to scan the surface of a sample to produce images. It can achieve high magnification from 10-300,000x. The electron beam interacts with the sample, producing various signals containing information about the sample's surface topography and composition. Secondary electrons are used to view morphology while backscattered electrons provide material contrast and composition data. X-rays emitted are used for elemental analysis.
This document discusses electron diffraction and neutron diffraction techniques. Electron diffraction works by firing electrons at a crystal sample and observing the interference pattern of diffracted electrons. This allows determining atomic structure. Neutron diffraction also determines atomic structure by firing neutrons at samples and observing diffraction patterns. Key advantages of neutron diffraction are its ability to locate light atoms and detect isotopes via nuclear scattering, and reveal magnetic structure via magnetic scattering. Both techniques provide structural information at the atomic scale but neutron diffraction can analyze bulk properties and magnetic structures.
The document discusses ferromagnetism and magnetic domains. It defines ferromagnetic materials as those that exhibit spontaneous magnetization from aligned atomic magnetic moments, even without an external magnetic field. It describes how ferromagnetic materials contain many small regions called magnetic domains, where atomic dipoles are aligned within each domain. In an unmagnetized material, the domains are randomly oriented, resulting in no net magnetization. An external magnetic field causes domains aligned with the field to grow at the expense of others, through the movement of domain walls, increasing the material's overall magnetization.
This document provides an overview of crystal structures and bonding in materials. It discusses topics such as the differences between crystalline and amorphous solids, unit cells, lattice structures, metallic crystal structures like body centered cubic and face centered cubic, atomic packing factors, and anisotropic vs isotropic materials. The key concepts covered include how crystal structures are composed of a periodic arrangement of points in a lattice, with atoms attached at each lattice point, and how properties can differ based on crystal structure and orientation.
Molecular beam epitaxy (MBE) is a method for growing thin films one layer at a time under ultra-high vacuum conditions. It involves heating solid sources of material in effusion cells to create molecular beams that are deposited on a heated substrate. The absence of carrier gases and ultra-high vacuum environment result in films of the highest purity. MBE is widely used to manufacture semiconductor devices and is considered a fundamental tool for nanotechnology development due to its precise control over layer thickness down to a single atomic layer.
Mass spectrometry is an analytical technique used to identify unknown compounds and quantify known compounds by measuring the mass-to-charge ratio of ions. It works by ionizing sample molecules and separating the resulting ions based on their mass-to-charge ratios using electric or magnetic fields. There are four main components: a sample inlet, ionization source, mass analyzer, and detector. Ionization methods include protonation, deprotonation, cationization, electron ejection, and electron capture. Common ionization sources are electrospray ionization, atmospheric pressure chemical ionization, and matrix-assisted laser desorption/ionization. Mass spectrometry has been developed over the past century since its discovery by J.J. Thomson
Mass spectrometry is an analytical technique used to identify unknown compounds and quantify known compounds by measuring the mass-to-charge ratio of ions. It was pioneered in the late 19th century by J.J. Thomson and has since been significantly advanced. A mass spectrometer introduces a sample, ionizes it, separates the ions by their mass-to-charge ratio using electric or magnetic fields, and detects the ions. It has become a powerful tool for elucidating molecular structure and properties across many fields due to developments like soft ionization methods.
This document provides an overview of ion mobility spectrometry (IMS). IMS works by separating ions based on their mobility through a gas under an applied electric field. Ions travel through a drift tube, being subjected to an electric field. Their drift time depends on factors like size, shape and charge, allowing differentiation. Key applications discussed are explosives and drug detection by analyzing samples for characteristic ion spectra. Other uses mentioned are biological analysis, environmental monitoring and clinical/medical applications.
This document provides an overview of mass spectrometry. It discusses the brief history of mass spectrometry from 1913 to 2002. It then summarizes the basic principles and components of mass spectrometers, including sample inlet systems, ion sources like electron impact and electrospray ionization, mass analyzers like quadrupole and time-of-flight, detectors, and applications in fields like pharmaceuticals, clinical work, environment and biotechnology. The document aims to introduce readers to mass spectrometry through examining its origins, instrumentation, and uses.
This document summarizes the state of atom probe tomography (APT) as applied to electronic materials. APT allows for 3D atomic-scale imaging and analysis of materials composition with subnanometer spatial resolution and high sensitivity. Specimen preparation, especially using focused ion beam techniques, has enabled APT analysis of a wide range of electronic materials including semiconductor devices. APT provides unique capabilities for characterizing nanoscale structures in electronic materials such as buried interfaces and dopant profiles. The applications of APT to electronic materials are growing rapidly as the technique becomes more widely used.
This document provides information about mass spectrometry including definitions, principles, components, and methods of ionization. It defines mass spectrometry as a technique that ionizes chemical species and sorts them by mass-to-charge ratio. The key components of a mass spectrometer are described as the inlet system, ion source, mass analyzer, and detector. Common ionization methods like MALDI and electrospray ionization are explained in terms of how they work to ionize samples for analysis.
1) SOFIA is a joint US-German airborne observatory consisting of a 2.5-meter telescope mounted in a modified Boeing 747. It will observe in the infrared and submillimeter wavelengths between 0.3-1600 microns.
2) Nine instruments are under development to cover this wavelength range with both imaging and spectroscopic capabilities at resolutions from narrow bands to high resolution spectroscopy.
3) Key early science goals include studying the interstellar medium of galaxies using fine structure lines, measuring the interstellar deuterium abundance using HD lines, and conducting spectral surveys to identify new spectral lines.
Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is guided through an ultra thin specimen, interacting with the specimen as it passes through.An image is formed from the fundamental interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be observed by a sensor such as a CCD camera.
This document summarizes the forensic applications of nanotechnology. It discusses how nanotechnology allows for the analysis of smaller samples and evidence than was previously possible. Some common nanoscale analysis techniques used in forensics are transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and Raman microspectroscopy. These techniques can be used to analyze trace evidence like gunshot residues, explosives, and DNA. The document also discusses some of the novel properties of nanomaterials and how they may assist in evidence collection and detection.
During the last decades a large effort has been invested in the development of a new
discipline devoted to benefit from optical excitations in materials where metals are
key element (Plasmonics). We will make an introduction on this topic below, but let’s
anticipate that two application areas are sensing and information technologies.
The following height extended abstracts, presented during the one-day NANOMAGMA
Symposium (Bilbao, Spain – April 13, 2011 reflects some of the latest developments on magneto-plasmonics.
In 2010 and 2011, the nanoICT project (EU/ICT/FET Coordination Action) launched
two calls for exchange visits for PhD students with the following main objectives: 1.
To perform joint work or to be trained in the leading European industrial and academic research institutions; 2. To enhance long-term collaborations within the ERA; 3. To
generate high-skilled personnel and to facilitate technology transfer;
The first outcome report was published in the issue 22 (August 2011) and this edition
contains four new articles providing insights in relevant fi elds for nanoICT.
We would like to thank all the authors who contributed to this issue as well as the European Commission for the financial support (projects nanoICT No. 216165 and NANOMAGMA No. FP7-214107-2).
Dr. Antonio Correia Editor - Phantoms Foundation
The document summarizes key aspects of nano measurement techniques, specifically scanning probe microscopy. It introduces scanning tunneling microscopy (STM) and atomic force microscopy (AFM) as two prominent types. STM works by measuring tunneling current between a tip and sample, allowing atomic-scale imaging. The document derives equations to describe quantum tunneling and factors that influence current. It also provides examples of STM images and discusses how STM advanced nanocharacterization and manipulation at the atomic scale.
1. The document discusses amateur radio astronomy, proposing areas of work accessible to amateur experimenters, such as receiving very low frequency electromagnetic phenomena induced by the ionosphere or solar/astronomical events.
2. It describes feasible amateur radio astronomy projects and the necessary equipment, such as antennas, receivers, and data acquisition systems, to conduct successful observations across different frequency bands.
3. The document provides examples of electronic modules with software that allow amateurs to build instruments for radio astronomy applications and contribute to the diffusion of this discipline.
Samuel Haste - Building a Cosmic Ray Detector.Samuel Haste
This document describes the design and construction of a cosmic ray detector in the form of a spark chamber. Key details include:
- The spark chamber consists of 15 stainless steel plates placed within a glass bell jar filled with a helium-neon gas mixture. Two scintillators with attached avalanche photodiodes are used to detect cosmic ray muons passing through.
- The design was inspired by previous spark chamber designs at Birmingham and Cambridge universities. It aims to be a self-contained, free-standing detector that does not require permanent gassing.
- When a muon passes through, it leaves an ion trail in the gas. A high voltage applied across the plates causes a spark to jump along the ion
International Journal of Computational Engineering Research (IJCER) is dedicated to protecting personal information and will make every reasonable effort to handle collected information appropriately. All information collected, as well as related requests, will be handled as carefully and efficiently as possible in accordance with IJCER standards for integrity and objectivity.
This document discusses nanoscience and nanotechnology concepts. It begins with an introduction to nanoscience topics like quantum effects at the nanoscale. It then discusses various nanostructures such as nanoparticles, nanotubes, thin films and their potential applications. The document also covers magnetic nanostructures such as ferromagnetism and magnetic domains. Measurement techniques like scanning tunneling microscopy are described. Finally, the document discusses thin film fabrication and the giant magnetoresistance effect in multilayer thin films.
This document provides an overview of a science education module focusing on the analysis of samples collected by the Genesis solar wind mission. The module includes teacher guides, student texts, and an interactive simulation activity on secondary ion mass spectrometry (SIMS). The activity simulates using SIMS to remove and analyze solar wind particles from collectors at different depths. It allows students to interpret mass spectrometry data and identify elements. The module addresses various science standards and provides background on the challenges of analyzing the tiny Genesis samples, which total only 0.4 milligrams in mass.
instrumentation of Mass spectroscopy by LaiqIMRANLAIQ1
This document summarizes the key components and working of a mass spectrometer. It discusses the inlet system that introduces samples, commonly used ion sources like fast atom bombardment, and mass analyzers like the quadrupole and time-of-flight analyzers. It also covers the different types of detectors used like photomultiplier, faraday cup, and photographic detectors. The document provides an overview of the instrumentation and process of mass spectroscopy.
Alfa, beta and gamma ray detection research has been done with Geiger Muller
detector which is aimed to know the influence of distance to the radiation intensity and
the influence of barrier thickness to the radiation intensity of radioactive rays. In this
study three radioactive sources of alpha, beta and gamma rays were used. While the type
of barrier used were aluminum, copper and plastic. Based on the results of the research,
it was found that the radiation intensity of radioactive rays was inversely proportional to
the square of the radioactive source distance to the Geiger Muller detector. In addition,
the thicker the barrier through which the radioactive rays are, the smaller the radiation
intensity shown in the digital counter. In this case based on the thickness of the buffer, the
barrier which has the greatest radiation intensity to the smallest are the plastics,
aluminum, and copper. When comparing the intensities of the three radioactive sources,
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Paul Ahern - Time of Flight Secondary Ion Mass Spectroscopy [ToF-SIMS] theory & practice
1. Paul Ahern - http://www.linkedin.com/in/paulahern1
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
Abstract—Time of Flight (ToF) Secondary Ion Mass
Spectroscopy (SIMS) is an extremely sensitive surface analysis
technique where the mass to charge ratio of an ion or molecular
fragment is determined by its velocity in the time domain. The
commercially available ToF SIMS instruments available today
have their roots in close to a century’s worth of academic
research, and their ability to gather elemental and molecular
information with excellent depth resolution and high sensitivity is
incomparable.
Keywords — Nanomaterials, thin films, surface analysis, Time
of Flight, Secondary Ion Mass Spectroscopy, SIMS.
I. INTRODUCTION
The ever-shrinking geometries of new materials and novel
devices built at the nanoscale with ever thinner layers has
driven the requirement for ever more sensitive and insightful
analytical techniques capable of viewing and understanding
matter at closer to the atomic level. Surface science
techniques are now more than ever a pre-requisite to
characterize and understand the complex interaction between
chemical composition and surface morphology of materials.
One such surface analysis instrument which has found
increasing application in the mainstream in the past decade is
Secondary Ion Mass Spectroscopy (SIMS), an experimental
technique which allows the analysis of a material in terms of
its molecular, chemical and elemental structure.
Figure 1 – Photograph of the ToF-SIMS instrument located
at the Environmental Molecular Sciences Laboratory
(EMSL) in Washington, USA (Image courtesy of
www.flickr.com/EMSL under Creative Commons license).
A sub-set of this technique is the so-called “Time-of-Flight”
or “ToF” method, which uses a more sophisticated time-
sensitive detection system to separate ions based upon their
mass, and has the advantage of increased sensitivity compared
to the more traditional magnetic sector or quadrupole
detectors. Detection limits of better than 1 part per million
(ppm) are achievable with excellent isotropic sensitivity and
three dimensional imaging1
.
II. HISTORY OF TECHNIQUE DEVELOPMENT
The origins of the Time of Flight technique can be found in
the early experiments of J. J. Thomson in 1909. Thomson
observed that the discharge of a positive secondary ion could
be encouraged by bombardment of a metal surface with a
source of primary ions2
. Further refinement of his apparatus
allowed Thomson to separate differently charged isotopes of
Neon with divergent atomic masses of 20 and 223
.
K. S. Woodcock built upon the foundations laid by
Thomson, and in 1931 published his studies into the creation
of negative ion spectra from surfaces under positive ion
bombardment4
. Woodcock carried out his measurements by
reflecting lithium ions off of a metal surface, with the
innovative step of using an applied electric field to slow down
the positive ions so that the negative ion spectra could be
recorded, a principle that is still used to this day to decelerate
secondary ions for SIMS analysis5
.
In 1946 William Stephens of the University of Pennsylvania
had proposed the first concept of a linear “Time-of-Flight
Mass Spectrometer”6
at a meeting of the American Physical
Society. Stephens’s mass spectrometer separated ions based
on their relative speed as they travelled in a straight trajectory
towards a detector. Many would regard the work of Herzog
and Viehboeck of the University of Vienna published in 1949
as being similarly ground-breaking, as they were the first to
develop an instrument which used an electron impact ion
source7
to generate their primary beam, a progression that was
directly enabled by advances in vacuum pump technology in
the previous years.
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) -
Theory and Practice (April 2013)
Paul Ahern, School of Electronic Engineering, Dublin City University, Glasnevin, Dublin 9, Ireland.
paul.ahern3@mail.dcu.ie
2. Paul Ahern - ie.linkedin.com/in/paulahern1 1
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
Figure 2 – Schematic from William E. Stephens original
1952 patent for a “Time of Flight” spectrometer8
.
Meanwhile, Wiley and McLaren9
built upon Stephens’s
study and via their Bendix Corporation released the first Time-
of-Flight mass spectrometer with a similar “EI” or “electron
ionisation” source in 1955, capable of sensitivities of less than
100 amu for the first time. Another notable development was
the work of Richard Honig of RCA Laboratories in New
Jersey, who through the search for new hot cathode materials
for vacuum tubes led him to assemble first a two-stage mass
spectrometer, and then in 1958 a full secondary ion mass
spectrometry instrument10
.
Further advances came in the 1960’s under the stewardship
of NASA who funded Liebel and Herzog of Geophysics
Corporation of America (GCA) Corp to create an analytical
instrument11
to examine moon rock samples brought back to
earth from the Apollo space flights. In 1967 Liebel, now of
Applied Research Laboratories, created an instrument with an
improved design12
which now used a duoplasmatron as the ion
source and mass separation to improve the purity of the
primary ion beam; the mass spectrometer design used a new
arrangement with no entrance slit and an Einzel lens.
In the early 1970’s Wittmaack13
demonstrated that the
secondary ion yield could be increased to a high value using
O2
+
ions as the primary ion beam medium, and that there was
a self-induction effect due to the mechanism of recoil
implantation on the sample surface. The subsequent work by
Magee14
working again with Honig at RCA Labs showed
success with the first quadrupole mass analyser complemented
by a high current density 40
Ar+
primary beam, and presented
an instrument that was capable of speedy depth profiling
where an ultra-high vacuum environment helped to maximize
detection sensitivity. This was also the first time that the issue
of the large amount of output data from SIMS as an analytical
technique was addressed, as Magee’s system had computer
automated control and acquisition modules.
In the 1970’s Prof. Benninghoven15
and co-workers at the
University of Münster developed the first “static” SIMS
instrument, which was deemed to be much less harsh on the
surface under analysis than its dynamic SIMS counterpart.
The reason for the reduction in surface damage was the much
lower dose density of the primary ion beam on the sample
surface, with primary ion beam current densities of less than
1nA per cm2
being typical. This allowed slower rates of
material removal but maintained the high sensitivity which
ToF-SIMS would become noted for, as a sufficient amount of
spectral information could be captured quickly before the
sample surface was modified significantly16
, typically at levels
of less than 1%.
In common usage, though sometime the terms “static” and
“Time of Flight” are used interchangeably to describe this
subset of SIMS analysis techniques, they are actually very
different. The main difference being that in Time of Flight
SIMS, the atomic mass peaks are monitored and recorded
more or less simultaneously, whereas in static SIMS only one
peak can be measured at any one time. Benninghoven showed
the static technique was very useful to analyse organic
molecules which had been deposited onto conducting
substrates.
Subsequent improvements and refinements in the technique
have been directly due to the advances that have been made in
constructing high performance Time of Flight detectors, which
has seen it become a key technique in the study of surfaces,
especially those made up of organic materials.
III. OVERVIEW OF TECHNIQUE
To understand the operating principles of the ToF-SIMS
technique it is useful if we summarise the basic steps of the
process first, before we then break down the instrument into
it's constituent parts and describe the phenomenon happening
in each section in more detail.
Figure 3 – Atomic scale representation of the ion sputtering
process which takes place in SIMS when a primary ion
beam impinges up a sample surface17
.
Overview: In basic terms, the SIMS technique is one where a
vacuum is created and within this vacuum region a beam of
primary ions at an energy of hundreds to thousands of electron
volts (eV) is accelerated onto a focussed spot on the surface of
a sample to be analysed. Various elastic and inelastic
processes occur at the surface (and subsurface) atomic layers,
4. Paul Ahern - ie.linkedin.com/in/paulahern1 3
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
Figure 6 – Diagram of the parts of a liquid metal ion source
(LMIS)21
with the parts as labelled (a) emerging metal ions
(b) extractor plate (c) liquid metal film (d) capillary feed
tube (e) liquid metal reservoir (f) crucible needle.
In electron impact sources, oxygen or another noble gas
flows into an ionisation region where a filament resides.
Electrons from this filament are then accelerated by anodic
grid while an extraction cathode (such as a Weinhalt aperture)
accelerates the ions to the lens array where they are focussed
and rastered if in imaging mode. In the case of a
duoplasmatron, which is common in dynamic SIMS
instruments also, plasma is formed in the extraction region and
a pair of off-setted magnetic lenses is used to form the primary
beam and tune it to a usable outline before it is extracted by
the anode.
Figure 7 – Block diagram of the primary ion column in a
typical SIMS instrument22
.
In instruments which have only one ion source, it is
common to use an element in the middle of the
electronegativity table which can successfully liberate both
negative and positive ions at sufficient amounts. Recent
advance have shown that the use of primary cluster ion
sources such as those derived from Bismuth (Bi1+
, Bi3+
) and
polyatomic Carbon (C60+
) have benefits when used to analyse
biological samples, with Bi3+
showing the best surface
sensitivity for lower atomic-mass molecular fragments23
.
Other recent peptide analysis work with Argon (Arn+
) primary
ion beam sources24
has shown its usefulness in terms of
minimising surface damage and allowing the user to maintain
a constant sputter rate with an associated reduction in
secondary ionization mechanisms.
Once the ions have been formed, they must then be
extracted and focussed into the primary beam before they are
accelerated to the required energy25
.
B. Beam / Sample Interaction: Once the primary ion beam
has been formed, it is focussed and pulsed in short (typically
between a 2ns and 20ns interval) onto the sample surface,
giving rise to sputtering. One consequence of this pulsed ion
beam regime is that a sufficient interval must be allowed so
that the heaviest, and thus slowest-moving, secondary ions can
vacate the detection region before the next bundle of
secondary ion data can be accepted.
Figure 8 – Diagram of some of the myriad and complex
phenomena at play during the interaction between the
primary ion beam and the sample in SIMS26
. The
progression of the ion cascade started by a sole primary ion
can be seen.
Ideally the primary ion beam pulse is kept as short as
possible, by using a device known as an electrodynamic pulse
“buncher” in the primary ion column as shown in figure 9, to
time focus the sputter pulse to a Gaussian profile of typically
less than 1 nanosecond (1ns)27
. This primary beam pulse
width value is termed tbeam, and one other consequence of
this arrangement is that the AC current is only a smaller
fraction of the DC current which further preserves the static
conditions on the sample surface allowing for better chemical
mapping.
5. Paul Ahern - ie.linkedin.com/in/paulahern1 4
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
Figure 9 – Simplified schematic diagram of the construction
of a linear buncher for Time of Flight analysis.
Ions with a small first ionisation potential will be readily
ionised by the primary beam, while those with a greater
potential will form positive ions much less readily; ions with
high electron affinity will preferentially give rise to negative
ions more readily. The timespan for the creation of these
secondary ions is typically in the picosecond (ps) regime.
Figure 10 – representation of total ion yield during
sputtering, {S}, and a function of the incident ion energy
{E}28
.
Ion images are produced in a slightly different way,
whereby the primary ion beam is rastered over the area of
interest and the number of ions as a function of the {x,y} co-
ordinates is presented. Secondary electrons generated as a by-
product of his process can also be collected in a resident
Everhardt-Thornley photomultiplier and used to generate a
standard secondary electron image.
The total sputter yield of secondary ions for a particular
element depends on the incident ion energy as shown in figure
10 and also the angle of incidence when the primary beam
strikes the sample surface as shown in figure 12; the vast bulk
of the species evolved from the sputtered surface will actually
be neutrals but it is only the very small positively or
negatively charge portion of the secondary particle flux that is
detected.
A complete understanding of the formation of secondary
ion species in ToF-SIMS has not yet been accepted, although
many competing thesis have been proposed in the literature
and have had limited success in predicting experimental
results for a narrow subset of defined materials.
i. Local Thermal Equilibrium (LTE) model: This (now
defunct) historical model, sometimes also categorised as the
“surface excitation model” proposed that underneath the
bombardment area, surface plasma was created wherein the
sputtered atoms became ionised.
Under equilibrium conditions, the ionisation potential could
be calculated by the use of the Saha-Eggert ionisation
equation29
in the bombardment region. The only important
factor was deemed to be the plasma temperature30
and this
could be estimated by taking into account the amounts of each
element present.
The results from this model are strictly semi-quantitative as
the exponential term in the S-E equation is compatible with
quantum mechanical terms31
. As V. E. Krohn32
of the US
Dept. of Energy laboratory in Argonne, Illinois summarised
succinctly “Unfortunately, surface ionization is an
equilibrium process, whereas secondary-ion emission is not.”
ii. Electron Tunnelling model: This model of secondary ion
formation (sometimes called the Schroeer model33
) is based on
quantum mechanical principles, and describes how the
electron which sits in the conduction band (CB) has the ability
to tunnel into the valence band (VB) of the ejected atom34
.
The ionisation potential of the sputtered element governs
the probability statistics that govern this phenomenon, as well
as the adiabatic surface ionisation function and the velocity of
the sputtered atom.
However, in line with this model, the work function is
autonomous of how the work function change, , is being
induced - as long as the external ions in the primary beam
used to induce does not change the chemical state of the
target atoms35
, as shown in figure 11 below.
Figure 11 – Simplified energy diagram of a charged particle
separating from a metal surface36
. At the distance ZC, the
atomic level intersects the Fermi level of the metal and
charge exchange can occur by tunnelling.
6. Paul Ahern - ie.linkedin.com/in/paulahern1 5
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
iii. Broken Bond model: In this model, proposed initially by
Šroubek37
the electronic temperature, Te, within the region of
the collision cascade was calculated for different materials
from a starting point of electron transport theory, and these
values were compared to calculated values formulated in
conjunction with empirical SIMS data.
The resultant model tackles the process from the standpoint
of the creation of ionic compounds in an idealised electronic
lattice under bombardment from a primary ion beam of
oxygen, and a prerequisite is that there be present an oxide
layer on the surface of the sample to be analysed. In this
model, the binding electrons stay with the oxygen atom and
there is only emission of positively ionised species.
Figure 12 – Secondary ion sputter yield plotted versus the
angle of incidence, , of the primary ion beam (as measured
referenced to the normal plane)38
.
In the theoretical case whereby all the available secondary
ions could be ionised by the incoming beam, and detected by
the spectrometer, then the signal could be related to the
specimen composition by the equation39
below:
iS = iPS
where iS is the sputtered ion current, is the atomic fraction of
the element of interest, iP is the primary ion beam current, S
the total effective sputter yield, and the specific sensitivity
of the detector (which includes the previously explained effect
of the incident angle of detection). Each spectrometer
configuration will also have an inherent angular acceptance
range and a reduction in mass resolution can be observed
when angular divergence becomes too large.
C. Secondary Ion Acceleration: Typically less than 1% of the
sputtered ions from the primary beam are ionised, with the
resultant cloud of ejected atomic and molecular secondary
ions accelerated by a potential into the Time-of-Flight region.
Since the lighter ions travel faster, they thus arrive at the ion
detection module first and can be counted. The Time-of-
Flight relationship can be understood simply as the travel time
of a secondary ion being proportional to the square root of its
mass, and by this mechanism all secondary ions can be
isolated and detected discretely once they impinge upon the
detector.
The drawing out and collimating of the secondary ion signal
emitted from the sample surface is by means of a combination
of transfer and immersion lenses which control the image
amplification and, by way of apertures, serve to limit the
angular acceptance angle of the mass spectrometer detector.
Secondary particles are accelerated by an applied constant
voltage, Vacc such that they now have a fixed kinetic energy
{E} which overrides their initial kinetic energy at source. In
this case their accelerated velocity in the drift region dpends
solely upon their mass, by the equation40
qVacc = E = ½ mv2
The overall secondary ion transmission can thus be greater
than 40%. To further increase the detector effectiveness for
dense ions (m>1,000 Da) a post –acceleration area (10-20
keV) can be sited between the end of the drift region and the
entrance cone of the detector.
D. Charge Neutralisation: Since many of the common
samples analysed by ToF-SIMS are organic molecules or
polymers and are non-conductive, a separate source of
electrons is needed to provide a tuneable charge compensation
function; this is achieved by producing low energy electrons
and introducing them around the analysis area on the sample
surface.
A recurring issue in achieving good spectral quality with
SIMS is adequate monitoring and control of the sample’s
surface potential41
to ensure that as uniform an ion emission
profile as possible is generated, as even a very slight increase
in the electric field on the sample surface can significantly
shift the energy level accepted by the energy filter into an
undesirable region, whereupon the ion yield being generated is
negligible and a impractical spectra with large intensity losses
will be recorded.
Typically a LaB6 or Tungsten filament electron source is
used, and in some cases the removal of surface charge can be
further facilitated by placing an earthed metal grid (such as a
TEM grid) over or close to the area of interest on the sample
surface. This method is useful as the pulsed low energy
electrons automatically steady themselves further over time, as
a positive surface potential serves to minimise the losses of
7. Paul Ahern - ie.linkedin.com/in/paulahern1 6
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
secondary ions which would serve to decrease the overall
potential of the surface42
. Another complication with
instruments that operate in the time domain such as ToF-SIMS
is that charge neutralisation must typically done in a pulsed,
cyclical manner in between the repeated sequences of
secondary ion generation and acceleration.
E. Mass Analysis Detection: Early SIMS instruments relied
upon the quadrupole mass spectrometer for detection,
consisting of four elements at equal distances whereby
alternating pairs of DC and RF voltages were applied to act as
a filter allowing only ions with a specific charge to mass ratio
to traverse into the detector. However, the disadvantages of
poor transmission (typically <1%, which decreases further
with increasing mass number) and a” lossy” data collection
method as it can only operate in scanning mode, meant that
better detection methods were needed for ToF-SIMS to
advance further.
i. Reflectron Analyser
Today the most common in commercial ToF-SIMS
instrumentation, mass-reflectron analysers were first proposed
by Russian physicists Mamyrin & Karataev43
in 1972. A
modern reflectron detector offers a good balance of much
enhanced mass resolution in a smaller equipment footprint44
.
Figure 13 – Schematic representation of the nascent Time of
Flight instrument (complete with reflectron) used by
Benninghoven and co-workers at the University of
Münster45
. The parts are labelled as shown – (a) Electron
ion source (in this case, Ar+
). (b) Ga+
liquid metal ion
source (LMIS). (c) Sample holder (temperature
controllable). (d) Secondary ion acceleration lens. (e)
Reflectron of the gridless type design. (f) Mass
spectrometer detector.
The method of operation is that the secondary ions are
accelerated towards an ion “mirror” which functions as an
electrostatic reflector that then turns the ions and reflects them
back towards the direction of the detector in a “folding”
arrangement, preserving the time-focussed nature of the ions
and enhancing the mass resolution by an order or magnitude.
The travel time is governed by the equation -
√
√
This setup offers mass resolution of the order of 10,000 amu
when a deceleration & re-acceleration grid is used, but by
moving to a gridless design superior mass resolution of up to
50,000 amu is reliably achievable46
. As measuring the usable
secondary ion yield can be problematic, transmission is
instead estimated using a Thomson distribution47
based on the
incoming kinetic energy of the primary beam; however ,this
approximation neglects any influence from detector efficiency.
The detector itself is normally a combination of a Faraday
cup and microchannel plate48
which contains an array of
electron multipliers, similar in design to the historic
channeltron. The signal amplification is by means of an
electron cascade from the inner lining of leaded glass when it
is struck by an incoming secondary ion with secondary
excitation being provided by a phosphor screen.
Figure 14 - Diagram of secondary ion detection in a ToF-
SIMS instrument with a combination of a Faraday Cup and
an Electron Multiplier49
; the bias voltage is equally divided
across the cathodes & anodes.
To boost the detection of slow-moving, heavy ions a pre-
acceleration region is often incorporated immediately before
the detection plate. Between these two complimentary
detectors the full dynamic range of the mass window can be
sufficiently covered – the Faraday cup being useful at high
count rates of >5x104
c/s and the electron multiplier at lower
intensities of <5x106
c/s.
9. Paul Ahern - ie.linkedin.com/in/paulahern1 8
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
IV. SELECTED NOTABLE APPLICATIONS
As previously described, the complex nature of Time of Flight
spectral data means that often the technique is used in a
comparative rather than an absolute sense, with samples
analysed to show the differences between them as a method of
side-stepping the arduous task of trying to understand all the
uncertainties in the analytical results.
ToF-SIMS excels rather at being a very sensitive technique
with high surface specificity and resolution and it is in this
niche that it has found use in fields such as nanoelectronics,
composites, catalyst formulation, biomedical, and general
failure analysis. A select few of these applications are detailed
in the following sections.
Semiconductor Analysis: ToF-SIMS has found a natural home
in the labs of many semiconductor manufacturers where they
leverage the tools analytical capability very successfully,
especially in the arena of thin film analysis and defect
metrology. The ability of SIMS to perform analysis using
depth profiling has meant that three dimensional analyses of
defects and structures has become commonplace, if a little
time consuming. Several ToF-SIMS manufacturers provide
instruments with large, fast entry load locks with differential
pumping and five axes motorised stages which can hold and
navigate a 12 inch silicon wafers.
Figure 16 – Parallel ToF imaging used for defect identification
and analysis56
. Ion maps of C-
, Si3-
, InO-
and others used to
show the presence and composition of a defect on a thin film
transistor (TFT) array ( Imaged using a 25 keV Ga+
primary
ion source over 128µm2
area).
Indeed ToF-SIMS allows the analyst to understand
delicate properties, for instance how far an implant has
progressed into the silicon lattice or what exact layer of the
fabrication process that a particle has been introduced. When
used in conjunction with defect isolation information from in-
fab metrology tools, ToF-SIMS can be an excellent method to
understand subtle defects which arise in the manufacturing
process and accurately pinpoint where they come from as
depth profiling allows you to etch back to the layer where the
defect was originally detected in-line even if the wafer has
progressed all the way to end of line electrical test & sort.
Figure 17 – A typical high mass resolution positive ion
ToF-SIMS spectra of a contaminated silicon wafer57
. A
plethora of different contaminants are shown, especially
hydrocarbons which ToF-SIMS is especially sensitive to.
More general analysis of molecular contamination of
incoming virgin silicon and of thin films deposited during the
fabrication process can also be done, and increasingly the
results are used as part of routine process monitoring in certain
sensitive parts of the process; for instance, when selective
epitaxial growth is being carried out, to ensure the starting
substrate is free from contamination; or to monitor surface
oxidation levels on electroplated copper backend layers which
have a narrow time window in which they can be allowed to
progress to the next process step.
Molecular Analysis: ToF-SIMS makes it possible to amply
detect ppb levels of low-volatility molecules such as
hydrocarbons, which is one of the reasons why it is so useful
for molecular and polymer analysis at the nano scale.
Everything from the composition of self-assembled
monolayers, plant herbicides, interplanetary meteorites and
photocopier paper have been analysed by ToF-SIMS.
Polymer chemists have relied upon ToF-SIMS techniques
for many years to understand how they can adjust a polymer’s
composition through process alterations and variations in
formulation. ToF-SIMS ion imaging allows them to visualise
the molecular structure of the surface polymer while depth
profiling brings an understanding of chemical distribution
with submicrometer resolution, for instance when blend and
copolymer thin films undergo understated modification to
their molecular structure during annealing processes.
10. Paul Ahern - ie.linkedin.com/in/paulahern1 9
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
Figure 18 – Ion images obtained by ToF-SIMS from the
“Nakhla” Martian meteorite58
.
Pharmacological & Biomedical Analysis: ToF-SIMS is a
common analytical technique in the field of pharmaceuticals
as it is well suited to the parallel analysis of tablets and
formulations which have numerous organic and inorganic
ingredients.
In the biomedical field, advances in charge neutralisation
and data interpretation have seen ToF-SIMS become more
widely utilised, especially in the analysis of biocompatible
surfaces and coatings. Typically cluster ion sources such as
bismuth are used to generate the secondary ions while caesium
or oxygen are employed as a sputtering medium for rapid
depth profiling.
Figure 19 below shows a typical application, where ToF-
SIMS is used to understand the coating homogeneity and drug
loading of a stent with the aid of reducing inflammatory stent
thrombosis. By calibrating the {x} axis from sputter time to
depth, the film thicknesses can be readily measured.
Figure 19 – Negative ion ToF-SIMS depth profile of a stent
coated with Paclitaxel on a Parylene substrate59
.
Biological samples can also be tackled through the use of
appropriate pre-treatments of the sample. The major
roadblock with adoption of ToF-SIMS in this field is the
requirement for an ultra-high vacuum environment, and the
still improving sensitivity for high mass ions which are typical
in bio-molecular analysis specimens. Figure 20 shows high
resolution parallel ion imaging by ToF-SIMS of human cancer
cells.
Figure 20 – Positive ion images by ToF-SIMS60
of human
breast cancer cells pre-treated with 2-amino-1-methyl-6-
phenylimidazo[4,5-b]pyridine and a fluorescent
carbocyanine dye.
Aside from ion imaging for qualitative analysis, depth
profiling has also be used for the study of single or groups of
cells where the high lateral resolution of the technique has
been very beneficial. Breitenstein61
and co-workers used ToF-
SIMS to profile the levels and types of amino acids present in
11. Paul Ahern - ie.linkedin.com/in/paulahern1 10
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
cells from a rat kidney, while Fletcher62
showed in 3D a
similar result but constrained within a single freeze-dried cell
using a primary beam of clustered C60
.
Figure 21 – Fletcher’s 3D ToF-SIMS depth profile using
C60
clusters of a single freeze-dried lipid cell, showing the
amino acid fragments attributable to different proteins.
V. CONCLUSION & FUTURE DIRECTION
ToF-SIMS as an analytical technique can very successfully be
used for the characterisation of nano-materials and films.
Using it’s combination of depth profiling, ion imaging and
static mode analysis it can give huge amounts of information
relating to chemical, molecular and elemental composition of
the sample under investigation.
This has arisen due to decades of development of all the
constituent parts which together make up the instrument; from
the vacuum system to the ion source, an understanding of the
interaction between the primary beam and the generation of
secondary ions, charge neutralisation, signal detection and
data analysis.
The recent adoption of new techniques, such as the use of
exotic cluster sources with highly sensitive mass
fragmentation patterns for negative ion analysis of ultra thin
layers at low impact energies, should pay dividends and
ensure that ToF-SIMS remains a workhorse for nano-
characterisation for the foreseeable future.
In the longer term, the continuing efforts to refine new
techniques related to ToF SIMS, such as the EU FP7
supported 3D NanoChemiscope tool housed in Switzerland
which blends a Time of Flight detector with an AFM tip
scanning approach to manipulate and analyse matter atom by
atom for the creation of in-situ spatial 3D depth analysis,
should see the skillsets of ToF mass spectrometry scientists
remain useful and in demand for some time to come.
In the rapidly advancing biological space, the advent of
tandem mass spectroscopy has been applied to ToF
instruments where ions have multiple disassociative steps
taking place over time in a hybrid instrument with both a
quadrupole and a Time of Flight detector. This approach has
proven to be very useful in analysing molecular peptide chain
arrays rapidly63
, and may one day be able to easily sequence a
strand of DNA to check for genetic diseases. New
instrumental designs are on the horizon that will allow a
purely DC primary ion beam64
that has many advantages for
use with clustered polyatomic sources.
Across all disciplines the challenge remains of forging a
deeper understanding of the shortcomings presented by low
ionisation efficiency, and the data deconvolution processes
necessitated by sputtering matrix effects in the sample.
VI. ACKNOWLEDGMENT
The author would like to thank Dr. Rajani K. Vijayaraghavan
of the School of Electronic Engineering in Dublin City
University for her proposal of this review topic, as well as her
patience in explaining many of the important theoretical
principles and concepts that underlie the ToF-SIMS analytical
technique as a tool for nanomaterial characterisation.
12. Paul Ahern - ie.linkedin.com/in/paulahern1 11
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) – Theory & Practice
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