Auger Scanning Electron Microscopy Research Articles

Modification of surface and bandgap on Sb-incorporated CuInSe2 thin films by (NH4)2Sx sulfurization

In this work, we study the effect of the addition of antimony, and chemical sulfurization of CuInSe2 thin films with (NH4)2Sx solution. CuInSe2 thin films were deposited by the molecular beam deposition method and trace amounts of antimony have been added. The antimony, detected by scanning Auger electron microscopy, reacts with the bi- or tri-coordinated In to saturate the dangling bonds on the growing surface as surfactants. During (NH4)2Sx sulfurization, the sulfur atoms enter the thin films through a pathway which is created by the replacement of antimony atoms segregated on the thin film surface. A portion of the selenide film is transformed into an alloy of CuInSe2 and CuInS2 on the grain surface. Significant amounts of sulfur (35%) distributed throughout the thin film of CuInSe2 under an antimony source temperature of 510°C in the film growth was shown from the Auger electron depth profile, and an increase of energy bandgap up to 1.3 eV as determined from optical absorption measurements. The chemical reactions are justified from thermodynamic considerations.

A study of the cleavage fracture behavior of PST TiAl alloys

Abstract Samples of two polysynthetically twinned (PST) TiAl alloys (Ti–49at.%Al and Ti–49at.%Al-0.6at.%Cr) were fractured in different environments at room temperature and the fracture surfaces were analyzed using scanning Auger and scanning electron microscopy. These techniques were employed to determine the fracture mode and the chemical composition of the fracture surfaces of the TiAl alloys. Our study clearly indicates that all of the fracture surfaces exposed by bend testing were α2, except when fracture occurred across the lamellae. No chromium enrichment was observed on any of the surfaces exposed during the fracture. From these observations, it was concluded that the fracture mode for these materials is cleavage through the α2-phase.

Cell attachment on silicon nanostructures

Advances in neural probe technology are currently hindered by a lack of understanding of the cues and mechanisms responsible for rejection and isolation of probes implanted in the central nervous system. To gain additional insight into this topic, the attachment of astrocytes on nanoscale textured silicon surfaces was investigated. Silicon surfaces were textured using a reactive ion etch process designed to produce nanometer-scale columnar structures in silicon (“silicon grass”). Standard photolithographic techniques were used to pattern the surface thereby allowing selective modification of the surface texture by a wet chemical etch for silicon. The resulting surface allowed a side-by-side presentation of different surface textures to cells grown in culture. The silicon surfaces were characterized by scanning electron microscopy (SEM) and scanning Auger electron microscopy. The cell attachment and morphology were observed with laser scanning confocal microscopy and SEM. Transformed astrocytes from a continuous cell line showed a preference for wet-etched regions over grassy regions. In contrast, primary cortical astrocytes from neonatal rats showed a preference for silicon grass over the wet-etched surface. For the transformed astrocytes cells, the degree of response was continuous with the degree of wet-etch modification.

Scanning Auger Electron Microscopy Evaluation and Composition Control of Cantilevers for Ultrahigh Vacuum Atomic Force Microscopy

Atomic force microscopy (AFM) tips have been evaluated on a submicrometer scale using a scanning Auger electron microscope (SAM) with a field emission electron gun. The commercially available AFM tips on the cantilever as supplied were usually covered with carbon and oxide layers as identified by the Auger spectra. A piezoresistive cantilever can be easily heated by passing a small current into the resistive film on the lever. The carbon and oxide layers can be reduced by heating the cantilever at temperatures higher than 700°C and simultaneously irradiating with an electron beam. However, the layer in which carbon is strongly combined with the Si substrate cannot be completely removed by the above method. The tip then was cleaned by Ar ion sputtering and thermally oxidized to form a clean Si oxide layer. The oxide layer was removed only by heating at 700°C. Thus a clean Si tip can be obtained in an ultrahigh vacuum (UHV) AFM chamber by heating the tip, which is then covered with clean Si oxide as a protective layer.

Titanium distribution on the surface of Ziegler-Natta catalysts observed by scanning Auger electron microscopy

Scanning Auger electron microscopy (SAM) with a field emission electron gun was used to analyze the surface of two different types of Ziegler-Natta catalysts. The SAM revealed the chemical composition, morphology, and distribution of the specific elements on the surface of the catalysts. The analysis also showed the difference between the surface distribution of titanium on MgCl 2-supported catalyst and that on TiCl 3. The results obtained in this study demonstrate that the SAM has great potential as an effective tool for the characterization of Ziegler-Natta catalyst.

Thermal stability of uniform silver clusters prepared on oxidized silicon and aluminum surfaces by electron beam lithography in oxidizing and reducing ambients

100 and 750 nm silver nanoclusters are fabricated on oxidized silicon and aluminum surfaces by electron beam lithography. Silver nanoclusters are characterized by atomic force microscopy, scanning electron microscopy, scanning Auger electron microscopy and high-resolution optical microscopy. The ordered structure of silver nanoclusters facilitates a thermal stability study in both reducing and oxidizing conditions. In reducing conditions, silver clusters are stable on the surfaces up to ~700°C before evaporation. The thermal stability of silver clusters is significantly lower in oxidizing conditions. In the presence of oxygen, the silver cluster surface is oxidized and roughened <300°C. Heating above 350-400°C in oxidizing conditions induces a migration of silver clusters. Micron-size and submicron-size amorphous silver clusters are formed, which spread over the oxide support. On oxidized silicon substrate, annealing treatment at 300°C induces silver silicate formation or spreading of oxidized silicon support onto the silver clusters, causing a buildup of silicon on the silver cluster surface. On the oxidized aluminum surface, by contrast, no spreading or reaction of the oxide substrate with the silver clusters was detected.

An Auger investigation of the fracture behavior of PST TiAl alloys

Abstract Samples of two polysynthetically twinned (PST) TiAl alloys (Ti-49 at% Al and Ti-49 at%Al-0.6 at%Cr) were fractured under different environmental conditions at room temperature, and the fracture surfaces were analyzed using scanning Auger and scanning electron microscopy. These techniques were employed to determine the fracture mode and the chemical composition of the fracture surfaces of the TiAl alloys. Our study clearly indicates that all of the fracture surfaces exposed by bend testing were α2, except when fractures occurred across the lamellae. No chromium enrichment was observed on any of the exposed surfaces. From these observations, it was concluded that the fracture mode for these materials is cleavage through the α2-phase.

Aluminum nitride buffer layer for diamond film growth

The role of aluminum nitride (AlN) as a buffer layer on the nucleation and growth of diamond on silicon and steel substrates during hot filament chemical vapor deposition (HF-CVD) has been investigated systematically. The scanning Auger electron microscopy (AES) is employed to study chemistry and content of carbon on the surface and in subsurface regions of AlN as a function of HF-CVD parameters. It is found that AlN offers an excellent diffusion barrier for carbon over a wide range of temperature and hydrocarbon content of CVD gas environment, with simultaneous inhibition of graphitization. It also facilitates nucleation of diamond phase. The surface reactions between AlN and carbon are discussed in terms of hydrogen-assisted phase transformations. We have developed a two-step procedure to obtain a continuous diamond film on steel substrates. The characteristic features of AlN have been exploited to obtain adherent and graphite-free diamond deposits on various types of steels, including low carbon steel, tool steel, high speed steel, and bearing steel.

Thermal Agglomeration of Thin Single Crystal Si on SiO2 in Vacuum

Changes in the surface structure of the single-crystal Si/SiO2/Si system during vacuum heating (950-1200° C) have been investigated using atomic force microscopy and scanning Auger electron microscopy. When the top Si layer is sufficiently thin, e.g., below ∼30 nm for heating at 1100° C, holes are formed due to Si agglomeration. The buried SiO2 surface emerges at the bottom of the holes and Si atoms accumulate around them. These holes expand and coalesce with increasing temperature, and Si islands are finally formed at 1200° C. This Si agglomeration starts at the points where the Si layer is locally extremely thin due to SiO2 protrusions and proceeds anisotropically; the shape of the holes is hexagonal for the (111) surface and square for the (001) one. In both cases, their sides are in the <110> directions. The driving force of agglomeration in a single-crystal film is discussed.

Diamond nucleation and growth at the early stages on Si(100) monitored by electron spectroscopies

Diamond growth on Si(100) is studied by scanning Auger microscopy (SAM), Auger electron spectroscopy (AES), electron loss spectroscopy (ELS) and X-ray photoelectron spectroscopy (XPS) focussing on the early stages of nucleation and growth. The low nucleation density allows us to monitor the evolution of both the substrate and the deposit intensities during the deposition process. Using the structural and chemical imaging probe provided by scanning Auger electron microscopy, we localize areas formed by carbon, only of diamond-type, and featureless areas with C, Si and O. The carbon nature on these last domains is initially a complex mixture of amorphous carbon, carbide and diamond. The amorphous deposit rapidly disappears (30 min), but the occurrence of surface carbide is still detected even after 120 min of growth. The surface carbon content, recorded both by AES focussed on the featureless domains and by XPS, initially drops. This is interpreted by the formation of silicon carbide embedding or removing the amorphous carbon layer. We identify three different sites of nucleation, which are (i) diamond seeds left by the substrate pretreatment; (ii) amorphous carbon at the very beginning of the nucleation process and (iii) silicon carbide. Then the diamond growth and the carbide formation are competitive processes, limited by (i) the reactive content in the gas phase and (ii) diffusion and etching of the silicon.

Contrast and resolution in REM, SEM and SAM

Reflection electron microscopy (REM) in fixed beam and scanning modes, secondary electron microscopy (SEM) and scanning Auger electron microscopy (SAM) are related in that they provide nanometer-scale resolution of surfaces in moderate or ultra-high vacuum using incident electron beams having energies of the order of 100 keV. They may, in many cases, be used in conjunction or in parallel to provide complementary information on crystal structure, morphology and compositional variations with sensitivity to single surface-layers of atoms. Experiments have shown in each case that the achievable resolution is considerably better than had previously been thought possible. Recent theoretical developments and exploratory investigations have provided at least a partial explanation of why sub-nanometer resolutions can be achieved. In the case of REM, the main limitations to resolution and contrast of the images arise from the inelastic scattering processes. Experiments with a new energy-filtering electron microscope have confirmed that images are considerably improved if formed by using only elastically scattered electrons.

Conformal chemical beam deposition of thin metal film for fabricating high density trench capacitor cells

The difficult aspect of conformal metal film deposition in narrow, high aspect ratio trenches such as those used in the fabrication of high density metal-oxide-semiconductor trench capacitor cells for computer memory technology is addressed. This work demonstrates the proof of principle of highly conformal deposition of a 40 nm Pt film on the surfaces of a 0.5-μm-wide, 1.5-μm-deep, and 2-mm-long array of oxidized silicon trenches, using the thermal decomposition of a molecular precursor under chemical beam conditions. In addition, scanning electron, x-ray photoelectron, and scanning Auger electron microscopy analyses reveal highly uniform and complete coverage on all surfaces, small metal grain size, and the absence of detectable impurities.

Scanning Auger Microscopy Study of Heterogeneous Growth of SiC Film on Si(100) by Reaction with a C2H2 Beam

A Si(100) surface which was reacted with a well-collimated C2H2 beam was studied using scanning Auger electron microscopy (SAM) after storage in air for a long period of time. Formation of a SiC film was confirmed by the chemical shifts of the C KLL, Si LVV, and Si KLL peaks in the AES integral mode. Chemical maps of the surface were obtained using SAM. A sharp boundary of the region of SiC formed by the C2H2 beam irradiation was observed. The grains with bright tones in the SEM image observed at high magnification were identified as SiC crystals using SAM. The dark areas among the grains were the elemental Si regions. It is clear that the SiC film on the Si surface was not uniformly formed on a µm scale. This suggests that the SiC film grows via nuclear growth.

Nanometer-resolution scanning Auger electron microscopy

New instrumental developments are described, based on STEM optics and through-the-lens electron detection, which allow scanning Auger electron microscopy (SAM) to be performed at the nanometer level. Example Auger images with 3 nm resolution are shown of silver islands deposited on Si(100). A consistent definition of SAM edge resolution is given with emphasis placed on the distinction between image and analytical resolution. The structure of ideal samples for testing resolution, at the level where localization effects may become important, is discussed.

TEM Moiré Pattern and Scanning Auger Electron Microscope Analysis of Anomalous Si Incorporation into MBE-grown Ge on Si(111)

Ge islands are grown by molecular beam epitaxy (MBE) on Si(111) surfaces with an SPE-grown buffer layer, which was expected to prevent intermixing between the epitaxial Ge layer and the Si substrate. The epilayer composition analyzed from the spacing of the Moiré fringe indicates that the Ge islands should be a Si-Ge alloy rather than pure Ge and that the alloying of Ge with Si is greater near the edges of the island. The alloying phenomenon was verified by the compositional depth profile analysis using the scanning Auger electron microscope (SAM) technique. The Si incorporation into the Ge islands observed here cannot be explained by a bulk diffusion mechanism and is a seriously anomalous phenomenon since Si diffusion into Ge would be negligible at the growth temperature and time used ill this experiment.

Proton-induced grain boundary segregation in stainless steel

Abstract A technique is developed which addresses the problem of irradiation assisted stress corrosion cracking of stainless steels in light water reactors using high energy protons to induce grain boundary segregation. These results represent the first grain boundary segregation measurements in bulk produced by proton irradiation of stainless steel. The technique allows the study of grain boundary composition with negligible sample activation, short irradiation time, rapid sample turnaround and at minimal cost. Scanning Auger electron microscopy is used to obtain grain boundary composition measurements of irradiated and unirradiated samples of ultra high purity (UHP) type 304L stainless steel and UHP type 304L steels with the additions of phosphorus (UHP + P) and sulphur (UHP + S). Results show that irradiation of all three alloys causes significant Ni segregation to the grain boundary and Cr and Fe away from it. Irradiation of the UHP + P alloy also results in segregation of P at the grain boundary from...

Characterization of pure YBa 2Cu 3O 7− x and its silver added ceramic composites by Auger electron spectroscopy

Microstructural properties of pure YBa 2Cu 3O 7− x ceramics and the silver-added YBa 2Cu 3O 7− x / (10 and 30 wt.%) Ag ceramic composites have been investigated by high-resolution scanning Auger electron microscopy (AES). The studies include the measurements of the grain size distribution as well as the elemental composition, both as a function of the silver addition. Moreover, effects of interfacial diffusion of silver into the YBa 2Cu 3O 7− x phase have been investigated by AES mapping and depth profiling measurements. Silver has been found (ref. [1]) to enhance significantly the YBa 2Cu 3O 7− x grain growth with mean grain sizes up to 17 μm for a 30 wt.% silver addition level, (2) to have no strong influence on the structural composition of single grains, and (3) to show no detectable effects of interdiffusion into the YBa 2Cu 3O 7− x phases. It is suggested that these common features of the microstructure should reduce the contact resistances between grains and thus explain the enhanced transport-current carrying capacity of such silver-added YBa 2Cu 3O 7− x /Ag ceramic composite superconductors.

Problems of scanning Auger electron microscopy

Some problems of scanning Auger electron microscopy (SAEM) concerning instrumentation and experimental techniques are described and briefly discussed in the light of the fundamental limitations of the method set by the nature of the phenomena themselves.

Multispectral Surface Analytical Microscopy: A Third-Generation Scanning Auger Electron Microscope

The quantitative interpretation of scanning Auger electron microscope (SAM) images has been shown to require the use of multi-spectral imaging of the surface under study. In a multi-spectral analytical microscope (MULSAM) a set of maps (bands) is acquired from the same area of a sample using scattered electrons with different kinetic energies as well as other signals from the sample such as current flowing to ground, the conventional SEM signal and characteristic x-rays. The resulting set of bands is a multi-spectral image which can be processed using models of the electron scattering in the sample and statistical transforms well known in LANDSAT imaging technology. The processed images can separate the mixed effects of topography, surface chemical inhomogeneity and bulk chemical composition fluctuations occurring in the bands of raw data.A computer controlled, UHV, energy analysing, scanning electron SEM will be described in this paper. The microscope contains facilities for collecting up to 23 256 by 256 pixel image bands from the same area of the sample.

ChemInform Abstract: Auger Spectroscopy of Pit Initiation at the Site of Inclusions in Stainless Steel.

AbstractA high resolution scanning Auger electron microscope with an X‐ray analysis system is used to study the surface chemistry of inclusion groups in stainless steel 316 relative to the bulk composition.