Vincent S. Smentkowski

Trends in sputtering

Abstract During the past century, there have been hundreds of manuscripts published reporting different aspects of sputtering. The purpose of this article is to summarize the trends observed when elemental and multicomponent materials are exposed to energetic ion beams. Attention is focused on low-energy (

Atom Probe Tomography of Compound Semiconductors for Photovoltaic and Light-Emitting Device Applications

Compound semiconductors belong to the most important materials for optoelectronic applications. Many of them exhibit favorable optical properties, such as a direct energy band gap (in contrast to silicon) and high-absorption coefficients over a wide spectral range. Moreover, varying the composition of the compound or substituting some of its elements often allows for controlled band gap engineering and optimization for specific applications. Because many compound semiconductors enable efficient conversion of light into electricity and vice versa, they are commonly used materials for optoelectronic devices.

Characterization of dilute species within CVD‐grown silicon nanowires doped using trimethylboron: protected lift‐out specimen preparation for atom probe tomography

Three‐dimensional quantitative compositional analysis of nanowires is a challenge for standard techniques such as secondary ion mass spectrometry because of specimen size and geometry considerations; however, it is precisely the size and geometry of nanowires that makes them attractive candidates for analysis via atom probe tomography. The resulting boron composition of various trimethylboron vapour–liquid–solid grown silicon nanowires were measured both with time‐of‐flight secondary ion mass spectrometry and pulsed‐laser atom probe tomography. Both characterization techniques yielded similar results for relative composition. Specialized specimen preparation for pulsed‐laser atom probe tomography was utilized and is described in detail whereby individual silicon nanowires are first protected, then lifted out, trimmed, and finally wet etched to remove the protective layer for subsequent three‐dimensional analysis.

Atomic-scale phase composition through multivariate statistical analysis of atom probe tomography data.

We demonstrate for the first time that multivariate statistical analysis techniques can be applied to atom probe tomography data to estimate the chemical composition of a sample at the full spatial resolution of the atom probe in three dimensions. Whereas the raw atom probe data provide the specific identity of an atom at a precise location, the multivariate results can be interpreted in terms of the probabilities that an atom representing a particular chemical phase is situated there. When aggregated to the size scale of a single atom (∼0.2 nm), atom probe spectral-image datasets are huge and extremely sparse. In fact, the average spectrum will have somewhat less than one total count per spectrum due to imperfect detection efficiency. These conditions, under which the variance in the data is completely dominated by counting noise, test the limits of multivariate analysis, and an extensive discussion of how to extract the chemical information is presented. Efficient numerical approaches to performing principal component analysis (PCA) on these datasets, which may number hundreds of millions of individual spectra, are put forward, and it is shown that PCA can be computed in a few seconds on a typical laptop computer.

Time of flight secondary ion mass spectrometry: A powerful high throughput screening tool

Combinatorial materials libraries are becoming more complicated; successful screening of these libraries requires the development of new high throughput screening methodologies. Time of flight secondary ion mass spectrometry (ToF-SIMS) is a surface analytical technique that is able to detect and image all elements (including hydrogen which is problematic for many other analysis instruments) and molecular fragments, with high mass resolution, during a single measurement. Commercial ToF-SIMS instruments can image 500 microm areas by rastering the primary ion beam over the region of interest. In this work, we will show that large area analysis can be performed, in one single measurement, by rastering the sample under the ion beam. We show that an entire 70 mm diameter wafer can be imaged in less than 90 min using ToF-SIMS stage (macro)rastering techniques. ToF-SIMS data sets contain a wealth of information since an entire high mass resolution mass spectrum is saved at each pixel in an ion image. Multivariate statistical analysis (MVSA) tools are being used in the ToF-SIMS community to assist with data interpretation; we will demonstrate that MVSA tools provide details that were not obtained using manual (univariate) analysis.

Metal-dielectric interface toughening by molecular nanolayer decomposition

Recent work has shown that copper–silica interfaces can be toughened several fold by combining interface functionalization with an organosilane molecular nanolayer (MNL) and thermal annealing. In order to understand the role of annealing-induced MNL instabilities on interface toughness, we studied the effects of interface chemical changes on the fracture toughness of copper–silica interfaces tailored with organosilane or organogermane MNLs. Our results indicate that MNL decomposition into its inorganic constituents and consequent intermixing can provide an interface toughening mechanism. Organogermane–tailored interfaces exhibit higher toughness values due to Ge-diffusion induced copper silicate formation, not observed at organosilane tailored interfaces. These findings show that organic nanolayer decomposition at a buried interface could be exploited to tailor interfacial properties through appropriate choice of MNL chemistry and processing treatments.

Exploration of a Butterfly Wing Using a Diverse Suite of Characterization Techniques

Much effort is currently being expended in nanotechnology and other fields to build biometric, or nature-inspired, materials. The first step in this process is often to develop a more complete understanding of the structure and chemistry of biological systems. In this presentation, we will compare and contrast data collected on a simple biological sample, a butterfly wing, using a variety of analytical techniques. Transmission Electron Microscopy (TEM) was used in order to perform high lateral resolution imaging of the sample cross section [1]; Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to provide structural information of the outer wing surface at various magnifications [1]; Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was used in order to image the chemical composition of the outer most surface layer; and Focused Ion Beam (FIB) techniques were used to cut (micro machine) features into the wing [1]. Each of these analytical techniques have sample preparation and data collection challenges which will be summarized and compared [1]. We will demonstrate that these analytical techniques provide complimentary information which helps the researcher understand the sample.

Introduction to a Special Issue on Surface Analysis

The surface, or topmost layers of a material, is the region that is in contact with the environment. The composition and chemistry of the surface often can be drastically different from that of the bulk. For many materials systems (catalysts, coatings, biomedical devices, etc.), the surface chemistry and/or properties determine the device performance. Adhesion, delamination, staining, and corrosion are among the important surface phenomena that need to be understood in industrial settings. Over the past forty years, a number of surface analysis techniques have been commercialized to characterize the composition and microstructure of the surface. The most commonly used techniques are summarized in this issue of Microscopy Today .

Silicon carbide oxidation in the presence of cesium: Modeling and analysis

In this work we have focused on investigating the interaction of cesium (Cs) atom/ion with the oxidant and carbon cluster defects at the SiC/SiO2 interface using atomistic scale computational techniques and experimental characterization methods. We observe that Cs behaves significantly different from sodium (Na) at the SiC/SiO2 interface. Our analyses indicate that Cs tends to form a strong bond with the incoming oxygen molecule, leading to the formation of Cs oxide and suboxides. Results suggest that Cs does not reduce the penetration barrier of the impinging oxidant (O2 molecule). Also, unlike Na, Cs is unable to increase the Fermi energy of SiC/SiO2 interface. Finally, lateral metal–oxide–semiconductor field-effect transistors (MOSFETs) were fabricated (using Cs) yielding mobilities less than 1 cm2/V s versus ∼100 cm2/V s fabricated using Na.

Analysis of Thin Phase-Shifter Films using Surface Analysis Techniques

Many types of phase-shifters have been developed for use in place of the TEM objective aperture [1]. The phase shifters act to increase phase contrast by providing high transfer of information over a very wide spatial-frequency range. Unfortunately, many of these devices fail shortly after being installed into the instrument due to charging in the electron beam, so we have been experimenting with surface deposition of novel thin-film metals. In some cases, it is essential that the electronscattering cross-section of the metal film be as small as possible, so the films must often be quite thin (less than 10 nm thick). Accurate analysis of such thin films is required to understand the composition of the layers, unexpected impurities both in the films and at the interfaces, the oxidation state of the layers, and the lateral uniformity of the layers.