Auger Scanning Electron Microscopy Research Articles

Layer etching of mica nanosheets using a focused electron beam

Mica, a cleavable layered material, is a single-crystalline phyllosilicate having unique electronic and mechanical properties such as a wide bandgap and tolerance to strong electric fields and high temperatures, and is applicable to flexible electronics. This paper describes the nanometer-level layer etching of mica nanosheets exfoliated from artificially synthesized phlogopite and affixed on substrates, using a focused electron beam for fine-pattern fabrication of the nanosheets. The dependence of the etching on the irradiation time, beam current, and beam energy is examined. The etching process was analyzed by in situ scanning Auger electron spectroscopy and microscopy. The layer etching of mica nanosheets leads to the micro- and nano-fabrication of mica-based two-dimensional heterodevices.

Graphene Nucleation Preferentially at Oxygen-Rich Cu Sites Rather Than on Pure Cu Surface.

Graphene nucleation at oxygen-rich Cu sites instead of on the commonly assumed pure Cu surface is discovered using high-spatial-resolution scanning Auger electron microscopy, which reveals a strong O signal existing underneath the graphene seeds, along with density functional theory calculations.

Nanoscale analysis of the influence of pre-oxidation on oxide formation and wetting behavior of hot-dip galvanized high strength steel

Hot-dip galvanized (HDG) 2nd generation advanced high strength steel (AHSS), nano-TWIP (twinning induced plasticity) with 15.8wt.% Mn, 0.79wt.% C, was analyzed at the interface between steel and zinc by scanning Auger electron microscopy (AES) in order to confirm and improve an existing model of additional pre-oxidation treatment before annealing and immersion into the hot zinc bath. Furthermore these steel samples were fractured in the analysis chamber of the AES and analyzed without breaking vacuum. In these measurements the results of an aluminothermic reduction of the manganese and iron surface oxides on the steel could be confirmed by AES.

Interface‐Induced Plasmon Nonhomogeneity in Nanostructured Metal‐Dielectric Planar Metamaterial

Transformations of the electronic structure in thin silver layers in metal‐dielectric (TiAlN/Ag) multilayer nanocomposite were investigated by a set of electron spectroscopy techniques. Localization of the electronic states in the valence band and reduction of electron concentration in the conduction band was observed. This led to decreasing metallic properties of silver in the thin films. A critical layer thickness of 23.5 nm associated with the development of quantum effects was determined by X‐ray photoelectron spectroscopy. Scanning Auger electron microscopy of characteristic energy losses provided images of plasmon localization in the Ag layers. The nonuniformity of plasmon intensities distribution near the metal‐nitride interfaces was assessed experimentally.

Direct mapping of Li distribution in electrochemically lithiated graphite anodes using scanning Auger electron microscopy

The spatial distribution of Li ions in electrochemically lithiated graphite anodes for Li-ion battery is characterized by scanning Auger electron microscopy. We show that direct mapping of Li KVV peak intensity reveal the spatial distribution of intercalated Li and its chemical state in a quantitative manner. Furthermore, we demonstrate that mapping using a C KVV peak also reflects the spatial distribution of Li due to the change in the electronic properties of C atoms induced by the electrode reaction (Li intercalation). Mapping measurements on three samples with different charging states (20%, 50%, and 100%) show that at the early stage of charging Li ions do not intercalate homogenously into all the graphite particles but selectively into some specific ones with higher rates. Our method provides the criteria to evaluate structure-correlated Li intercalation from nanometer- to micrometer-scale, such as conductivity network in the electrodes due to a non-uniform morphology of binder and conductive additives.

The effect of Ce3+ on structure, morphology and optical properties of flower-like ZnO synthesized using the chemical bath method

Ce3+ doped ZnO flower-like structures were synthesized by the chemical bath deposition method (CBD). The influence of Ce3+ as a dopant on the crystallization, surface morphology, optical and luminescent properties of ZnO flowers-like structures were investigated. The X-ray diffraction (XRD) spectra of the ZnO:Ce3+nanostructures correspond to the various planes of a single hexagonal ZnO phase for the lower Ce concentration samples. The estimated grain sizes calculated using the XRD spectra were found to be in order of 42±2nm. The grain size was found to be not dependent on the concentration of the Ce3+ ions used up to 3mol% of Ce. Scanning Auger electron microscopy and scanning electron micrographs indicate that the addition of Ce3+ influence the morphology of the samples. The flower-like structures obtained for the undoped and low concentration Ce doped ZnO changed into a mixed structure with the emergence of pyramid shapes for higher concentration Ce doped samples. The solid undoped and low concentration Ce doped powder showed good optical properties with a high reflectance in the visible regions. The properties, however, diminished at higher Ce concentration. The band gap energies decreased linearly with concentration from 3.0±0.1 to 2.4±0.3eV for ZnO:0mol% Ce3+ up to ZnO:10mol% Ce3+. Under 248nm excitation, the undoped and low concentration Ce doped ZnO flower-like rods exhibited a green emission, peaking at about 559nm. The higher Ce concentration (0.3mol% and above) was emitted at 436 and 503nm due to the Ce transitions. The intensity of these emission spectra of the ZnO:Ce3+ decreased with the addition of more Ce3+ ions.

Void and Nanostructure Formations during Thermal Decomposition of 20-nm-Thick Silicon Oxide Layer on Si(100)

We investigate the thermal decomposition of 20-nm-thick silicon oxide layers on Si(100) at a temperature of 1050 °C in vacuum by X-ray photoelectron spectroscopy, scanning Auger electron microscopy, and atomic force microscopy. Time evolutions of chemical-shift components in Si 2p core-level spectra are analyzed with the SiO2-decomposition model based on void formation. The experimental data can be reproduced well if the void area is proportional to the square of the annealing time, being consistent with the model in which the reaction at the void periphery is the rate-limiting step for void growth. Microscopic images show that the void periphery is square with rounded corners, and many silicon nanostructures are formed inside the void. These observations reflect reaction processes of the thermal decomposition of the silicon oxide layer.

Chemical-state imaging of Li using scanning Auger electron microscopy

The demand for measurement tools to detect Li with high spatial resolution and precise chemical sensitivity is increasing with the spread of lithium-ion batteries (LIBs) for use in a wide range of applications. In this work, scanning Auger electron microscopy (SAM) is used to image chemical states of a partially oxidized Li surface on the basis of the Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) data obtained during an oxidation process of a metal Li. We show that distribution of metallic and oxidized states of Li is clearly imaged by mapping the intensity of the corresponding AES and EELS peaks. Furthermore, a tiny difference in the extent of oxidation can be distinguished by comparing the elemental map of an AES peak with that of an EELS peak owing to the different behaviors of those signals to the chemical states of Li.

Spin-polarized scanning electron microscopy

Spin-polarized scanning electron microscopy (spin-SEM) is a magnetic domain observation method. In spin-SEM, polarization of secondary electrons emitted from a sample in a scanning electron microscope is detected by a spin detector and used as a signal for forming an image. The characteristics of spin-SEM are detection of all three magnetization vector components, which leads to the detection of the magnetization vector direction, high spatial resolution of around 3 nm and applicability to samples with rough or even 3D surfaces. Spin-SEM combined with other imaging methods using an electron probe beam such as scanning Auger electron microscopy for imaging element distribution and electron backscattering diffraction microscopy for imaging crystal direction distribution provides additional information that is important to study the magnetism. Spin-SEM with these excellent characteristics has a broad range of applications from basic research to applied research and developments in various industries.

Studies of YBa2Cu3O6+x degradation and surface conductivity properties by Scanning Spreading Resistance Microscopy

Local surface conductivity properties and surface degradation of c-axis oriented YBa2Cu3O6+x (YBCO) thin films were studied by Scanning Spreading Resistance Microscopy (SSRM). For the surface degradation studies, the YBCO surface was cleaned by ion beam etching and the SSRM surface conductivity map has been subsequently repeatedly measured over several hours in air and pure nitrogen. Average surface conductivity of the scanned area was gradually decreasing over time in both cases, faster in air. This was explained by oxygen out-diffusion in both cases and chemical reactions with water vapor in air. The obtained surface conductivity images also revealed its high inhomogenity on micrometer and nanometer scale with numerous regions of highly enhanced conductivity compared to the surroundings. Furthermore, it has been shown that the size of these conductive regions considerably depends on the applied voltage. We propose that such inhomogeneous surface conductivity is most likely caused by varying thickness of degraded YBCO surface layer as well as varying oxygen concentration (x parameter) within this layer, what was confirmed by scanning Auger electron microscopy (SAM). In our opinion the presented findings might be important for analysis of current–voltage and differential characteristics measured on classical planar junctions on YBCO as well as other perovskites.

Simultaneous growth of diamond and nanostructured graphite thin films by hot-filament chemical vapor deposition

Diamond and graphite films on silicon wafer were simultaneously synthesized at 850 °C without any additional catalyst. The synthesis was achieved in hot-filament chemical vapor deposition reactor by changing distance among filaments in traditional gas mixture. The inter-wire distance for diamond and graphite deposition was kept 5 and 15 mm, whereas kept constant from the substrate. The Raman spectroscopic analyses show that film deposited at 5 mm is good quality diamond and at 15 mm is nanostructured graphite and respective growths confirm by scanning auger electron microscopy. The scanning electron microscope results exhibit that black soot graphite is composed of needle-like nanostructures, whereas diamond with pyramidal featured structure. Transformation of diamond into graphite mainly attributes lacking in atomic hydrogen. The present study develops new trend in the field of carbon based coatings, where single substrate incorporate dual application can be utilized.

Initiation and Inhibition of Dealloying of Single Crystalline Cu3Au (111) Surfaces

Dealloying is widely utilized but is a dangerous corrosion process as well. Here we report an atomistic picture of the initial stages of electrochemical dealloying of the model system Cu(3)Au (111). We illuminate the structural and chemical changes during the early stages of dissolution up to the critical potential, using a unique combination of advanced surface-analytical tools. Scanning tunneling microscopy images indicate an interlayer exchange of topmost surface atoms during initial dealloying, while scanning Auger-electron microscopy data clearly reveal that the surface is fully covered by a continuous Au-rich layer at an early stage. Initiating below this first layer a transformation from stacking-reversed toward substrate-oriented Au surface structures is observed close to the critical potential. We further use the observed structural transitions as a reference process to evaluate the mechanistic changes induced by a thiol-based model-inhibition layer applied to suppress surface diffusion. The initial ultrathin Au layer is stabilized with the intermediate island morphology completely suppressed, along an anodic shift of the breakdown potential. Thiol-modification induces a peculiar surface microstructure in the form of microcracks exhibiting a nanoporous core. On the basis of the presented atomic-scale observations, an interlayer exchange mechanism next to pure surface diffusion becomes obvious which may be controlling the layer thickness and its later change in orientation.

Comprehensive Comparison of Various Techniques for the Analysis of Elemental Distributions in Thin Films

The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 μm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limits.

Preparation of a visible light-reactive low molecular-O-carboxymethyl chitosan (LM-O-CMCS) derivative and applicability as an anti-adhesion agent

Photo-reactive low molecular-O-carboxymethyl chitosan (LM-O-CMCS) was synthesized by introducing a furfuryl group to the amine groups of LM-O-CMCS. The prepared photo-reactive LM-O-CMCS was characterized by FTIR, 1H NMR, and a cross-linking test, whereas scanning Auger electron microscopy (SAM) and a MTT assay were used to confirm the cell viability. The water contact angle measurement and cell attachment test were carried out to determine the applicability of LM-O-CMCS as an anti-adhesion agent.

Simultaneous Formation of NiSi Contact and Cu Plug/Ti Barrier

As an alternative to the W plug used in MOSFETs, a Cu plug with a NiSi contact using Ta / TaN as a diffusion barrier is currently being considered. Conventionally, Ni was first deposited and then NiSi was formed, followed by the barrier and Cu deposition. In this study, Ti was employed as a barrier material and simultaneous formation of the NiSi contact and Cu plug / Ti barrier was attempted. Cu(100 nm) / Ti / Ni(20 nm) with varying Ti thicknesses were deposited on a Si substrate and annealed at <TEX>$4000^{\circ}C$</TEX> for 30 min. For comparison, Cu/Ti/NiSi thin films were also formed by the conventional method. Optical Microscopy (OM), Scanning Probe Microscopy (SPM), X-Ray Diffractometry (XRD), and Auger Electron Microscopy (AES) analysis were performed to characterize the inter-diffusion properties. For a Ti interlayer thicker than 50 nm, the NiSi formation was incomplete, although Cu diffusion was inhibited by the Ti barrier. For a Ti thickness of 20 nm and less, an almost stoichiometric NiSi contact along with the Cu plug and Ti barrier layers was formed. The results were comparable to that formed by the conventional method and showed that this alternative process has potential as a formation process for the Cu plug/Ti barrier/NiSi contact system.

Probing the heat affected zone by chemical modifications in femtosecond pulse laser ablation of titanium nitride films in air

A new approach is presented to quantify the so-called “heat affected zone” (HAZ) during femtosecond laser pulse processing. Ablation of titanium nitride (TiN) thin films (∼3 μm thickness) by multiple femtosecond laser pulses (τ=130 fs, λ=800 nm) in air environment was studied by means of two different surface analytical methods both being sensitive to chemical alterations at the surface. Scanning Auger electron microscopy was applied for a visualization of the spatial distribution of specific elements (Ti, O) within the laser-modified areas. The chemical state of the irradiated surface was revealed by complementary x-ray photoelectron spectroscopy. Both methods were used for a depth-profiling chemical analysis (tracking the elements Ti, N, O, and C) using an Ar-ion beam for surface sputtering. In a narrow laser fluence range slightly below the ablation threshold of TiN significant superficial oxidation can be observed leading to the formation of substoichiometric TiO2−x. At fluences above the ablation threshold, an increased titanium concentration is observed within the entire ablation craters. Following upon sputter removal the elemental distribution into the depth of the nonablated material, the results allow an estimation of the heat-affected zone for femtosecond laser ablation in air environment. According to our analyses, the HAZ extends up to a few hundreds of nanometers into the nonablated material.

Structural characterisation of gold nanowire arrays

This study is devoted to a thorough crystallographic and microstructural characterisation of gold nanowire arrays. The nanostructures were produced by directional solid-state decomposition of the Fe–Au eutectoid. The system structure and microstructure were investigated using differential thermal analysis (DTA), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM) and scanning Auger electron microscopy (SAEM). The most relevant sample features, with particular attention to the microstructure evolution, morphology and crystallography of the gold nanoarrays, are critically discussed. Gold nanofibres exhibit a faceted morphology with an average width of 20 nm, length of 100 nm and inter-wire distance of 250 nm. HRTEM analysis revealed that the obtained nanostructures are single crystalline and that the fibre-matrix crystallographic orientation relationship is of the Nishiyama–Wassermann type.

Improvement of display-type spherical mirror analyzer for real space mapping of electronic and atomic structures

We have improved a display-type spherical mirror analyzer (DIANA) at Ritsumeikan University SR Center BL-7 for in situ real space mapping of electronic and atomic structures that uses a focused electron beam and a linearly polarized synchrotron radiation (SR). The outer sphere was fully optimized. Compared to the previous analyzer, the energy resolution ( Δ E / E ) has been improved from 1% to 0.09 ± 0.02 %. A newly designed electron gun for measurement of atomic structures was installed inside the analyzer. Thus the measurement of electronic and atomic structures at the same sample position became possible. Here we report on the improvements of the new DIANA and the results of the first in situ measurement of real space mapping of the valence band and scanning Auger electron microscopy (SAM) of a multiple domain Kish graphite. The crystal orientations of each domain were determined from the electronic structures.

Ion etching methods for depth profiling of complex three-dimensional samples in combination with scanning Auger electron microscopy

Ion etching of surfaces combined with detection of secondary events (particles or radiation emitted) are used for depth profiling of samples with interesting features at-, near-, or somewhat below the surface. These methods are destructive and relatively slow, and compete with non-destructive methods like Rutherford backscattering spectroscopy, energy-dispersive X-ray spectroscopy in the scanning electron microscope or angle-resolved photoemission spectroscopy, which are non-destructive and relatively faster methods. In this work we have concentrated on the use of noble gas ion sputtering with low-energy beams in combination with electron excited Auger electron spectroscopy and imaging for analysis of nanostructured and microstructured samples. No attempt will be made here to justify this method over the other methods, as their relative merits depend on the nature of the sample and the problem at hand. We have thus chosen to study samples and problems for which this technique would be obvious to use. This work is also aimed at providing practical standards and guidelines (“metrology”) for the use of the technique in the context of industrial nanotechnology. The use of Auger electron spectroscopy instead of photoemission spectroscopy is preferred for laterally non-uniform samples due to the presently better resolution capabilities of electron beams and narrower information depths of typical Auger electron transitions. The use of Auger electrons for concentration sampling, and low-energy beams of noble gas ions for sputtering, reduces the adverse influence of atomic mixing. In this report two systems are intensively studied with sputter profiling in combination with Auger electron spectroscopy and scanning electron imaging: a hard disk and a surface of a stainless-steel sample.

Local Oxidation Induced by Inhomogeneous Stress on Blistered Si Surface

By utilizing surface stress to modify surface reaction potential and increase surface reactivity, a technique for the two-dimensional patterning of surface chemical reactions may be realized by surface stress modulation. Blister is local protrusion on a solid surface induced by gas ion irradiation, and is considered to create local stress on surface layers. Si(100) substrate was irradiated with H+ (incident energy: 10 keV, fluence: 1 ×1022 m-2) at an angle of 30° to the surface normal. Blisters of 1–5 µm in diameter at the base were formed. After the ion irradiation, the substrate was oxidized. Scanning Auger electron microscopy revealed that, compared with the flat surface, the perimeters of the blisters had a higher oxygen intensity whereas the blister tops had a lower oxygen intensity. The stress distribution of the blister was calculated using the finite element method. It was found that the surface layers were stretched laterally at the blisters tops and compressed at the perimeters, relative to the flat surface. There was a clear correspondence between the O distribution and the stress distribution on the surface. Our results indicate that the patterned oxidation of the Si surface can be governed by the application of surface stress.