X-ray Spectrum Imaging Research Articles

Rapid X-ray Spectrum Imaging with the Silicon Drift Detector (SDD): Multivariate Statistical Analysis

Rapid X-ray Spectrum Imaging with the Silicon Drift Detector (SDD): Multivariate Statistical Analysis

X-ray spectrometry and spectrum image mapping at output count rates above 100 kHz with a silicon drift detector on a scanning electron microscope

A third-generation silicon drift detector (SDD) in the form of a silicon multicathode detector (SMCD) was tested as an analytical x-ray spectrometer on a scanning electron microscope. Resolution, output count rate, and spectral quality were examined as a function of the detector peaking time from 8 micros to 250 ns and over a range of input count rate (dead time). The SDD-SMCD (50 mm2 active area) produced a resolution of 134 eV with a peaking time of 8 micros. The peak width and peak channel were nearly independent of the input count rate (at 8 micros peaking time, the peak width degradation was 0.003 eV/percent dead time and peak position change was -0.7 eV over the dead time range tested). Maximum output count rates as high as 280 kHz were obtained with a 500 ns peaking time (188 eV resolution) and 500 kHz with a 250 ns peaking time (217 eV resolution). X-ray spectrum imaging was achieved with a pixel dwell time as short as 10 ms (with 1.3 ms overhead) in which a 2048 channel (10 eV/channel) spectrum with 2-byte intensity range was recorded at each pixel (scanned at 128 x 128). With a 220 kHz output count rate, a minor constituent of iron (present at a concentration of 0.04 mass fraction or 4 weight %) in an aluminum-nickel alloy could be readily detected in the x-ray maps derived from the x-ray spectrum image database accumulated in 185 s.

Sensitivity and Accuracy in Processing X-ray Spectrum Images

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

Quantitative characterization of nanoprecipitates in irradiated low-alloy steels: advances in the application of FEG-STEM quantitative microanalysis to real materials

The characterization of the solute-enriched features (clusters or nanoprecipitates in irradiated low-alloy steels) requires extremely high spatial and elemental resolution, previously necessitating analysis using atom probe field-ion microscopy. In this investigation, field-emission gun-scanning transmission electron microscope (FEG-STEM) quantitative energy dispersive X-ray (EDX) microanalysis (spectrum imaging) has been applied to the characterization of the irradiation-induced nanoprecipitates in a low-alloy forging steel. Refinements in the EDX data have been possible via the application of multivariate statistical analysis (MSA) to the spectrum images, resulting in significantly reduced noise in the images. Most importantly, MSA permitted the clear identification of other elements in these Ni-enriched nanoprecipitates—including Mn and Cu. The processed X-ray spectrum images also provided direct evidence of the preferential formation of these irradiation-induced features along pre-existing dislocations within the steel, as well as the formation of intragranular nanoprecipitates. This research has provided the first direct X-ray spectrum images of irradiation-induced nanoprecipitates in high Ni A508 Gr4N forging steel, and has demonstrated the significant improvements attainable though the application of MSA techniques to the spectrum images. These results independently confirmed the analyses of the Ni-enriched nanoprecipitates previously conducted by 3D-APFIM, with the performance of the FEG-STEM/EDX technique shown to be comparable to that of the 3D-APFIM technique.

The New X-ray Mapping: X-ray Spectrum Imaging above 100 kHz Output Count Rate with the Silicon Drift Detector

Electron-excited X-ray mapping is a key operational mode of the scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometry (EDS). The popularity of X-ray mapping persists despite the significant time penalty due to the relatively low output count rates, typically less than 25 kHz, that can be processed with the conventional EDS. The silicon drift detector (SDD) uses the same measurement physics, but modifications to the detector structure permit operation at a factor of 5-10 times higher than conventional EDS for the same resolution. Output count rates as high as 500 kHz can be achieved with 217 eV energy resolution (at MnKalpha). Such extraordinarily high count rates make possible X-ray mapping through the method of X-ray spectrum imaging, in which a complete spectrum is captured at each pixel of the scan. Useful compositional data can be captured in less than 200 s with a pixel density of 160 x 120. Applications to alloy and rock microstructures, ultrapure materials with rare inclusions, and aggregate particles with complex chemistry illustrate new approaches to characterization made practical by high-speed X-ray mapping with the SDD.Note: The Siegbahn notation for characteristic X-rays is commonly used in the field of electron beam X-ray spectrometry and will be used in this article. The equivalent IUPAC notation is indicated in parentheses at the first use. In this article, the following arbitrary definitions will be used when referring to concentration (C) ranges: major: C > 0.1 (10 wt%), minor: 0.01 </= C </= 0.1 (1-10 wt%), and trace: C < 0.01 (1 wt%).

The New X-ray Mapping: Applying the Silicon Drift Detector (SDD) for X-ray Spectrometry and Spectrum Imaging with Output Count Rates above 100 kHz

The New X-ray Mapping: Applying the Silicon Drift Detector (SDD) for X-ray Spectrometry and Spectrum Imaging with Output Count Rates above 100 kHz

Quantitative X-ray Spectrum Imaging of Extraterrestrial Materials with a Field-Emission STEM

Quantitative X-ray Spectrum Imaging of Extraterrestrial Materials with a Field-Emission STEM

Determining the Local Bulk Chemistry of Martian Aqueous Alteration via X-ray Spectrum Imaging: A Link to Global Dust on Mars?

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Quantitative X-ray Mapping and Spectrum Imaging

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Improvements of Elemental Mapping via X-ray Spectrum Imaging Combined with Principal Component Analysis and Zero-Peak Deconvolution

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Microstructure and Oxidation of a Cast Nickel Aluminide Alloy

ABSTRACTSpecimens of the cast Ni3Al alloy IC221M were annealed in air at 900°C to examine the effects of oxidation and thermal aging on the microstructure. The alloy is comprised of a dendritically solidified γ-γ′ matrix containing γ+Ni5Zr eutectic colonies in the interdendritic regions. Microstructures of aged specimens were examined by optical microscopy and energy dispersive X-ray (EDX) spectrum imaging in the scanning electron microscope (SEM). Two primary changes in the microstructures were observed: (1) there is considerable homogenization of the cast microstructures with aging, and (2) the volume fraction of the γ+Ni5Zr eutectic decreases. Oxidation products were identified using x-ray diffraction and EDX spectrum imaging with multivariate statistical analysis (MSA). During the initial stages of oxidation, the first surface oxide to form is mostly NiO with small amounts of Cr2O3, ZrO2, NiCr2O4, and θ-Al2O3. Initially, oxidation occurs primarily in the interdendritic regions due to microsegregation of alloying elements during casting. With further aging, a continuous film of α-Al2O3forms immediately beneath the surface that eventually evolves into a double layer of α-Al2O3and NiAl2O4. Although these oxides are constrained to the near surface region, others penetrate to greater depths facilitated by oxidation of the γ+Ni5Zr eutectic colonies. These oxides appear in the microstructure as long, thin spikes of ZrO2surrounded by a thin sheath of Al2O3.

Edx Spectrum Imaging of Bulk Specimens: Its Role in Quantitative X-Ray Microanalysis

Energy-dispersive X-ray (EDX) spectrum imaging, where a full spectrum is acquired at each pixel in a rastered image, combines the advantages of imaging and analysis for quantitative compositional mapping. This method has great advantages for the analysis of compositional variations, because the contrast inherent in EDX spectrum images arises from the distinctiveness of the characteristic X-ray spectra in various regions of the surveyed microstructure. EDX spectrum imaging provides for simultaneous spatial, spectral and temporal resolution of the X-rays emitted from the specimen. Many EDX manufacturers have incorporated a spectrum imaging capability within their acquisition and analysis software, and ongoing improvements in computing power will enhance the practicality of spectrum imaging methods, in particular the acquisition, manipulation and analysis of the large raw data files that are generated with this method. This paper surveys the potential role of spectrum imaging in tasks that support true quantitative X-ray microanalysis of bulk specimens: robust qualitative analysis, the construction of representative spectra that describe the specimen, and the extraction of elemental concentrations from the representative spectra.

Automated Analysis of X-Ray Spectrum Images from the SEM: A Practical New Tool for Microanalysis

It is a conundrum that faces microanalysts every day: how do you comprehensively survey the chemistry of a microstructure in a reasonable time? Traditional solutions in the SEM would include taking an image and then collecting x-ray spectra from a series of points. This method relies heavily on the operator’s ability to identify chemically distinct regions. in addition, for a complex microstructure, this could take a considerable amount of time to do correctly. On the positive side, if care is taken, these ‘point spectra’ can be readily quantified. An alternative method that has been used widely is x-ray mapping, where a window of intensity in the spectra is integrated and displayed as an image. This has the advantage that qualitative elemental distributions from an area of a microstructure can be visualized. The disadvantages are that maps are generally not quantitative, can be susceptible to artifacts, and rely on fore knowledge of the elements to map.

Automated Analysis of X-Ray Spectrum Images from the STEM

For failure analysis and process control it is critical to perform comprehensive microanalysis. The desire to perform this analysis thoroughly but quickly is the ultimate goal. Typical analyses of this sort have been performed by collecting x-ray spectra at points, along lines, by mapping, and more recently by spectrum imaging where a complete x-ray spectrum is collected over a 2D array of points. Spectrum imaging is perhaps of greatest interest for its potential to thoroughly and comprehensively sample a given area of a microstructure. The problem is that the techniques available for analyzing large (&gt; 1000 spectra) spectrum image (SI) data sets have been limited to mapping after the fact and perhaps thresholding the maps and summing the resultant spectra from those pixels. As a result, there is a need for more sophisticated SI analysis tools, capable of reducing the SI to its essence-the chemical components. Software is currently commercially available for the automated analysis of x-ray spectrum images (SIs) from the SEM

Correlation of contact resistance with microstructure for Au/Ni/Al/Ti/AlGaN/GaN ohmic contacts using transmission electron microscopy

Ohmic contacts to AlGaN/GaN heterostructures which have low contact resistance and good surface morphology are required for the development of commercial high power, high frequency transistors in the GaN system. The development of such contacts would be helped by a better understanding of the effect of microstructure on electrical behavior, which is studied here. Au/Ni/Al/Ti/AlGaN/GaN ohmic contact structures were rapid thermal annealed in argon for 60 s at temperatures in the range 550–900 °C. The variation of contact resistance with anneal temperature was correlated with the phase distribution observed by transmission electron microscopy (TEM). A combination of TEM techniques was required to determine the resulting microstructure, including energy filtered TEM, high resolution electron microscopy and energy dispersive x-ray spectrum imaging. Contacts with the lowest resistance were formed after 700 °C annealing. Very little consumption of the 30 nm AlGaN layer was observed. An unidentified phase containing Al, Ti and Au is present at the interface in the samples with low specific contact resistance. The identification of the observed thin interfacial phases (including TiN and AlN) is discussed, along with the effects of oxidation and possible mechanisms of ohmic contact formation.

PC/MAC* Image Processing Freeware for Examining Spectral Images

Abstract MacLispix, a public domain image processing system for the Macintosh*, has been applied to a variety of image processing problems, such as using Principal Component Analysis to explore correlated images. The tools provided by MacLispix are now available in Lispix, the updated version that runs on both the PC and the Macintosh. I will illustrate the utility of Lispix by way of an example ‘data cube', a low voltage energy dispersive x-ray spectrum image provided by Ian Anderson. The ‘cube'is 200x150 pixels, each pixel having a spectrum of 512 two-byte channels The spectra were smoothed and reduced by adding adjacent channels to reduce them to 256 channels each. Since Lispix is image oriented rather than spectrum oriented, the reduced cube is stored, and represented internally as 256 images (one image for each channel in the spectrum), rather than as 200x150 spectra (one spectrum for each pixel in the image).

Statistical Analysis Of SEM-EDX Spectrum Images Of A Metal-Ceramic Braze

Abstract Spectrum imaging, where a complete spectrum is acquired at each pixel in an image, is potentially a very powerful technique for the characterization of materials. The primary challenge to overcome is to extract all of the relevant information from what are typically large data sets that cannot be readily visualized in their entirety. For energy-dispersive X-ray (EDX) spectrum images, simple mapping has typically been done. In this work, the application of multivariate statistical analysis (MSA) to the characterization of a metal/alumina braze by SEM-EDX spectrum images is described. The braze characterized in this work joins polycrystalline alumina and a copper-silver eutectic alloy containing some titanium (an ‘active’ metal). The specimen geometry consisted of a sandwich of two pieces of alumina, two braze layers and a Kovar (primarily Fe, Ni and Co) filler layer in the middle. The entire assembly was heat-treated to bond the interfaces and then a polished cross-section was prepared.

SEM/EDX Spectrum Imaging and Statistical Analysis of a Metal/Ceramic Braze

AbstractEnergy dispersive x-ray (EDX) spectrum imaging has been performed in a scanning electron microscope (SEM) on a metal/ceramic braze to characterize the elemental distribution near the interface. Statistical methods were utilized to extract the relevant information (i.e., chemical phases and their distributions) from the spectrum image data set in a robust and unbiased way. The raw spectrum image was over 15 Mbytes (7500 spectra) while the statistical analysis resulted in five spectra and five images which describe the phases resolved above the noise level and their distribution in the microstructure

Compression of Polymer-Coated Laser-Fusion Targets to Ten Times Liquid DT Density

Polymer-coated glass microspheres filled with DT fuel and argon seed gas were irradiated on the SHIVA 1.06-..mu..m laser using 4-kJ 200 ps (full width at half maximum), Gaussian pulses. Measured light absorption, x-ray spectrum, neutron yields, and x-ray continuum images compare favorably with detailed computer simulations. Pusher neutron activation and argon line imaging diagnostics were utilized to measure fuel density. Fuel densities of 1-3 g/cm/sup 3/ or 5-15 times liquid DT density were inferred.