John A. Small

Growth of SnO2 films on micromachined hotplates

Arrays of micromachined hotplates have been used for materials processing on a microscopic scale. The temperature of individual elements ‘‘micro‐hotplates’’ of an array is controlled by addressing a given element with a specified current and measuring the temperature from a resistance change. This unique temperature control capability has been exploited to deposit SnO2 overlayers onto micro‐hotplates with individually controlled temperatures using reactive sputter deposition and organometallic chemical vapor deposition. Post‐deposition heating in vacuum was used to alter the stoichiometry of films. The result is an array of separately, but simultaneously, processed films. The micro‐hotplates have excellent thermal isolation from other devices (transistors, logic elements) on the chip. Electrical contact pads allow for in situ electrical characterization of the films. The use of micro‐hotplates allows high‐temperature growth to occur on portions of a silicon substrate, while other portions remain at room t...

Modeling of the bremsstrahlung radiation produced in pure-element targets by 10-40 keV electrons

A new global relationship has been developed for predicting electron‐excited bremsstrahlung intensities over a wide range of accelerating voltages 10–40 keV, atomic numbers 4–92, and x‐ray energies 1.5–20 keV. The new relationship was determined empirically from the mathematical modeling of extensive data and is designed for calculating bremsstrahlung intensities in analytical procedures, such as those requiring peak‐to‐background measurements, where the direct measurement of the bremsstrahlung intensities is impracticable. The distribution of errors between the data and the model is symmetrical, centered around zero error with 63% of the values falling between ±10% relative error.

Improving the quality of electron backscatter diffraction (EBSD) patterns from nanoparticles

In this study, we investigated the relative contributions of atomic number (Z) and density (ρ) to the degradation of the electron backscatter diffraction (EBSD) pattern quality for nanoparticles < 500 nm in diameter. This was accomplished by minimizing the diffuse scattering from the conventional thick mounting substrate through the design of a sample holder that can accommodate particles mounted on thin‐film TEM substrates. With this design, the contributions of incoherently scattered electrons that result in the diffuse background are minimized. Qualitative and quantitative comparisons were made of the EBSD pattern quality obtained from Al2O3 particles approximately 200 nm in diameter mounted on both thick‐ and thin‐film C substrates. For the quantitative comparison we developed a ‘quality’ factor for EBSD patterns that is based on the ratio of two Hough transforms derived from a given EBSD pattern image. The calculated quality factor is directly proportional to the signal‐to‐noise ratio for the EBSD pattern. In addition to the comparison of the thick and thin mounting substrates, we also estimated the effects of Z and ρ by comparing the EBSD pattern quality from the Al2O3 particles mounted on thin‐film substrates with the quality of patterns obtained from Fe–Co nanoparticles approximately 120 nm in diameter.

In situ conductivity characterization of oxide thin film growth phenomena on microhotplates

Through the use of silicon micromachining, we have developed a microhotplate structure capable of reaching temperatures in excess of 500 °C, onto which thin films have been selectively grown via metalorganic chemical vapor deposition. The microhotplate structure contains surface electrical contacts which permit conductance measurements to be made on films during and after deposition, and therefore presents some unique opportunities for the in situ characterization of growing films as well as for novel gas sensing approaches. We have investigated the deposition of conducting oxides such as SnO2 and ZnO on these microhotplate platforms for gas sensing applications. The conductance of the deposited films has been measured in situ as a function of time, and used in combination with postdeposition thickness measurements to provide insights into the growth rate of the oxide films. Results indicate that our conductance measurements are sensitive, in certain cases, to changes in the film thickness on the order of...

Characterization of SiGe films for use as a National Institute of Standards and Technology Microanalysis Reference Material (RM 8905).

Bulk silicon-germanium (SiGe) alloys and two SiGe thick films (4 and 5 microm) on Si wafers were tested with the electron probe microanalyzer (EPMA) using wavelength dispersive spectrometers (WDS) for heterogeneity and composition for use as reference materials needed by the microelectronics industry. One alloy with a nominal composition of Si0.86Ge0.14 and the two thick films with nominal compositions of Si0.90Ge0.10 and Si0.75Ge0.25 on Si, evaluated for micro- and macroheterogeneity, will make good microanalysis reference materials with an overall expanded heterogeneity uncertainty of 1.1% relative or less for Ge. The bulk Ge composition in the Si0.86Ge0.14 alloy was determined to be 30.228% mass fraction Ge with an expanded uncertainty of the mean of 0.195% mass fraction. The thick films were quantified with WDS-EPMA using both the Si0.86Ge0.14 alloy and element wafers as reference materials. The Ge concentration was determined to be 22.80% mass fraction with an expanded uncertainty of the mean of 0.12% mass fraction for the Si0.90Ge0.10 wafer and 43.66% mass fraction for the Si0.75Ge0.25 wafer with an expanded uncertainty of the mean of 0.25% mass fraction. The two thick SiGe films will be issued as National Institute of Standards and Technology Reference Materials (RM 8905).

Comparison of high- and low-voltage x-ray mapping of an electronic device

In recent years, field-emission gun scanning electron microscopes, FEG-SEMs, with high-brightness electron guns and excellent performance at low electron beam energies (E0⩽5 keV) have become readily available. Concurrently the performance of solid-state x-ray detectors such as the Si-Li detector has improved significantly and with the addition of ultra-thin window materials these devices are easily capable of detecting characteristic x-rays with energies as low as 150 eV. In conventional x-ray mapping the energy of the electron beam is usually 15 keV–25 keV and the maps are acquired with the K, L, and M shell x-ray lines with energies from 1 keV to 15 keV. At these electron beam energies, the lateral resolution of the x-ray maps is on the order of 1 μm–3 μm. Reducing the electron beam energy to 5 keV or below and utilizing the K, L, and M lines with energies from 400 eV to 4 keV should significantly improve the lateral resolution of the x-ray maps. In this study, x-ray maps were acquired for Si-K x-rays a...

Low Energy X-Ray Detection with a Silicon Multi-Cathode Detector for Microanalysis

This paper presents several aspects of our design efforts toward the development of a large-area, high energy resolution analytical x-ray spectrometry system for x-ray microanalysis and x-ray spectrum imaging [1]. The spectrometer achieves excellent energy resolution and is capable of operating at very high counting rates (up to 600,000 cps throughput). The Vortex-EM spectrometer is based on a thermoelectrically-cooled silicon multi-cathode detector (SMCD), which is a type of “drift” detector [2-3]. The detector is specifically designed for optimal performance in the 0.2 40 keV range. Recent advancements in the detector design enhance the low energy x-ray performance. The spectrometer utilizes a non-cryogenic design, operating with thermoelectric cooling and passive heat transfer to the ambient without using any moving parts; a photograph of the spectrometer is shown in Figure 1.

High Spatial Resolution Quantitative Electron Beam Microanalysis for Nanoscale Materials

Transmission and scanning electron microscopes provide platforms for a powerful arsenal of electron and x-ray spectrometries that yield chemical characterization of nanoscale particles and nanostructured bulk materials. Combined with the imaging and crystallographic measurement functions of TEMs and SEMs, comprehensive characterization of morphology, crystal structure, and composition becomes possible. The advent of more efficient electron optical systems, spectrometers, and digital imaging devices promises to increase the throughput of these instruments, many of which are already capable of automatic, unattended operation, at least in some operational modes, to vastly increase the accumulation of data. Thus, techniques that are capable of isolating a single nanoparticle or nanostructure feature are also becoming capable of accumulating a great deal of information about a particle array or complex bulk nanostructure. Such large scale databases of information themselves pose a challenge to extract relevant information. Parallel developments in “data mining” techniques will increasingly come into play to solve the challenges raised by nanoscale materials.

A Silicon Multi-Cathode Detector For Microanalysis Applications

Microanalysis Applications Shaul Barkan and Liangyuan Feng Radiant Detector Technologies, LLC Jan S. Iwanczyk, Bradley E. Patt and Caroiyn R, Tull Photon Imaging, Inc. Dale E. Newburyand John A. Small National Institute of Standards & Technology Introduction Anew class of silicon multi-cathode detector (SMCD) has been developed for microanaiysis spectrometry applications. The detector has excellent energy resolution (< 150 eV FWHM) and high count rate capability (>1 Mcps). An energy resolution of 143 eV FWHM at 5.9 keV was measured with the SMCD at 6 us peaking time. At a

Heated Inlet Sampling System for Removing Carbonaceous Aerosol

ABSTRACT A method for separating airborne particles made of refractory materials from ambient aerosol particles has been developed. A heated inlet device was fabricated from a tube furnace and tested using aerosol produced in the laboratory and found in the ambient outdoor environment. By removing interfering particulate matter, this heated inlet increases the efficiency for microanalysis of small refractory particles. Areas of application include the analysis of mineral particles (ambient crustal dusts, asbestos, etc.) and particles from nuclear accidents.