Grazing-exit Electron Probe Microanalysis Research Articles

Improvement of reproducibility in grazing‐exit EPMA (GE‐EPMA)

AbstractIn grazing exit electron probe microanalysis (GE‐EPMA), characteristic x‐rays emitted from only near surface regions of a specimen are detected at extremely low exit angles near 0°. Therefore, GE‐EPMA is useful for localized surface analysis. However, there is a practical problem with GE‐EPMA, namely, reproducibility of angle adjustment. Therefore, we developed a new instrument, a ‘laser beam and four‐separated photodetector system’, to adjust the sample inclination. It was found that the reproducibility of angle adjustment was improved by about one‐tenth by applying this system. Copyright © 2005 John Wiley & Sons, Ltd.

Grazing exit electron probe microanalysis of submicrometer precipitates in a copper base alloy

We applied the grazing exit electron probe microanalysis (GE-EPMA) to analyses of a submicrometer precipitate, which consisted of Si and Ni, in a copper base alloy. We measured X-rays emitted from the precipitate projected onto the etched sample surface with a conventional EPMA method (exit angle: 30°) and grazing exit conditions (exit angle: near 0°). We also measured X-rays emitted from precipitates extracted from the matrix by the EPMA method and compared the results. Characteristic X-rays of Cu emitted from the interior of the matrix as well as the background X-rays drastically decreased in the GE-EPMA spectrum, as compared to that of the conventional EPMA method. We, then, could observe the X-ray peaks of Si and Ni emitted solely from the analyzed precipitate with extremely low background in the GE-EPMA spectrum. The Si Kα/Ni Kα net intensity ratio in the GE-EPMA spectrum was, however, much different from that of the conventional EPMA method or those of the extracted precipitates. These results indicated that the X-ray intensities in the GE-EPMA analysis were affected by the X-ray absorption by other precipitate projected onto the surface or projection parts of the matrix in extremely low exit angles.

Grazing exit electron probe microanalysis of submicrometer inclusions in metallic materials.

Grazing exit electron probe microanalysis (GE-EPMA) is a new method of EPMA in which characteristic X-rays emitted from only near-surface regions of a specimen are detected at extremely low exit angles near 0 degrees (the grazing exit condition). This technique requires the analytical objects exist on a flat surface. Therefore, the GE-EPMA analysis has been used only for the analysis of particles or a thin film on a flat substrate so that there were only few applications for practical analysis. As a new application, we have carried out GE-EPMA analysis of approximately 0.2-microm inclusions on stainless steel, which appeared to be a projection on the specimen surface with chemical etching. The GE-EPMA quantitative results were in excellent agreement with those of inclusions that were extracted from the stainless steel and analyzed by EPMA with conventional exit condition (30 degrees). This method could be, therefore, applied to the analysis of the submicrometer inclusion in a wide variety of metallic materials if the inclusion appears to be a projection with chemical etching treatment.

Localized thin-film analysis by grazing-exit electron probe microanalysis

We have studied the application of grazing-exit electron probe microanalysis (GE-EPMA) for surface and thin-film analysis. In this method, characteristic X-rays are measured at small take-off angles of less than 1°. Under grazing-exit conditions, the X-rays emitted from deep inside the sample are not detected because they are stopped by a slit mounted in front of the energy-dispersive X-ray detector. Hereby, it becomes possible to perform localized surface analysis with GE-EPMA. We applied this method to thin-film analysis of a small surface area. The exit-angle dependence of the characteristic X-ray intensities was measured for thin films of Cr and Ti. Thickness and density of thin films were determined by fitting the experimental plots with theoretically calculated curves. Differences were found in the densities of two Cr thin films deposited by magnetron sputtering and vacuum evaporation. The advantage of GE-EPMA is that non-destructive thin-film analysis of small surface areas can be incorporated in simple scanning electron microscope (SEM) analysis.

Grazing Exit Electron Probe Microanalysis of Inclusions in a Stainless Steel

凹凸が生じた金属材料表面上に存在する介在物の分析に斜出射EPMA法を応用し、その有効性を検討した.斜出射EPMA法は,平坦な表面上に分析対象物が存在することを必要とする.この条件のために,応用範囲が狭く,応用例が少なかった.本研究では,一般の走査型電子顕微鏡(SEM+EDS)で斜出射EPMA法を行う方法として,試料のZ軸上の位置を変化させてX線の取り出し角度を調整する方法を開発した。そして、この方法を腐食を施したステンレスの凹凸面上に観察された微小な介在物(約0.3ミクロン)の分析に応用した.その結果,斜出射EPMA法によって介在物の構成元素を正確に同定できることが分かった。介在物はMg,Al,Si,Ca,Ti,CrおよびMnを含む複合酸化物であり,Fe,Niは含まれていなかった.

New experimental equipment for grazing-exit electron-probe microanalysis

New grazing-exit electron-probe microanalysis (GE-EPMA) equipment is developed. In GE-EPMA, characteristic x rays are measured at the grazing-exit angle. X rays emitted from deep positions in the substrate are reduced under grazing-exit conditions; therefore, surface-sensitive analysis is possible with low background. In previous equipments, the sample holder was tilted to change the exit angle. In this new equipment, the energy-dispersive x-ray detector is moved to change the exit angle, and the analyzed position is stable even if the exit angle is changed. Therefore, this equipment is useful especially for particle analysis. The new GE-EPMA equipment is applied to Pd–Se–Te single-particle analysis. Although it was difficult to measure the Se Kα line at an exit angle of 45° due to the large Au Lβ radiation emitted from the Au substrate, Se Kα was measured without any Au signals at the grazing-exit angle near zero.

Surface studies by grazing‐exit electron probe microanalysis (GE‐EPMA)

AbstractSurface analysis was performed by a new analytical method, grazing‐exit electron probe microanalysis (GE‐EPMA). At grazing‐exit (small x‐ray take‐off) angles, only characteristic x‐rays emitted from the near‐surface regions are measured because of strong absorption and refraction effects at the surface. The exit angle was carefully determined using a stepping motor (with a minimum step angle of 0.018°), and the emergent x‐rays were measured by an energy‐dispersive x‐ray detector and analyzed with a multi‐channel analyzer (MCA). A computer controlled both the stepping motor and the MCA so that the exit‐angle dependence of the characteristic x‐ray intensities was measured automatically. The angle‐dependent curve for a thin cobalt film (5 nm thick) deposited on a silicon wafer indicated that the cobalt x‐rays predominated at grazing exit angles, demonstrating that high surface sensitivity was obtainable under these conditions. The results from a polished stainless‐steel sample revealed chromium enrichment at grazing exit angles, which corresponds to a thin passivation layer of chromium oxide at the surface. Both sets of data suggest that GE‐EPMA is a promising technique for localized surface analysis. Copyright © 2001 John Wiley & Sons, Ltd.

Comparison of grazing-exit particle-induced X-ray emission with other related methods

Particle-induced X-ray emission (PIXE) is recognized as a trace analysis method; the Bremsstrahlung background, however, still limits the detection power in the low-energy region of spectrum. The grazing-incidence or grazing-exit arrangements are considered to be useful in order to reduce the background intensity. We measure grazing-incidence PIXE (GI-PIXE) and grazing-exit PIXE (GE-PIXE) using an identical sample vacuum chamber to evaluate the performance of both methods. The sample used is a standard sample (Ca, Fe, Ni and Zn) prepared on Si wafer by the spin-coating method. In GI-PIXE mode, a collimated 2.5 MeV proton beam irradiates the surface of the sample at grazing incident angles. However, it was difficult to reduce sufficiently the background intensity in the GI-PIXE spectra because of the Bremsstrahlung background induced by secondary electrons. In the GE-PIXE mode, proton-induced X-rays are measured at grazing-exit angles. The background intensity is reduced, because only the X-rays emitted from the near-surface layer can be detected in the grazing-exit arrangement. Furthermore, the result obtained for an Au–Cu thin film sample by GE-PIXE method was compared with the result obtained by other related methods: grazing-exit X-ray fluorescence and grazing-exit electron probe microanalysis. Similar results were obtained by different methods, indicating that the same phenomena occur in all grazing-exit X-rays measurements. One of the merits of the grazing-exit microprobe analysis method is in microanalysis using a small diameter electron probe; however, the damage by electron irradiation is more severe than that in GE-PIXE.

Detection Limits of Grazing-Exit EPMA for Particle Analysis

In conventional electron probe microanalysis (EPMA), the electron-induced X-rays are measured at large take-off angles of about 45°. In the grazing exit EPMA (GE-EPMA) method, they are measured at small angles (< 1°). X-rays emitted from deep positions can not be detected at grazing exit angles due to refraction effects at sample-vacuum interface; therefore, it is possible to measure X-rays emitted only from near the surface with a low background. GE-EPMA is especially suitable for the analysis of particles deposited on a flat sample carrier. The detection limits of GE-EPMA were investigated for artificial particles (Al2O3, Fe2O3 and PbO2 , particle sizes: 1 ∼ 18 μm) deposited on flat sample carriers of Au thin films–Si wafers. The detection limits improved with decreasing exit angle. The detection limits for characteristic X-rays at an exit angle of approximately 1.1° were 2–4 times lower than at 45°. A minimum detection limit of ca. 0.1% was obtained for Al in small particles.

Enhancement of electron-induced X-ray intensity for single particles under grazing-exit conditions

Grazing-exit electron probe microanalysis (GE-EPMA) was performed for single Al2O3 and atmospheric particles, deposited on a flat Si substrate coated by gold, by using an aperture (1 mm in diameter) in front of an energy-dispersive X-ray detector. Silicon Kα X-rays from the Si substrate were strongly observed at an exit angle of ∼45°. However, they disappeared at grazing-exit angles about 0° and only the X-rays from particles were detected. Furthermore, Al Kα and O Kα intensities from single Al2O3 particle were enhanced approximately three- and sixfold at the grazing-exit angles (∼1°), respectively, in comparison with those at large angle (∼7°). The background intensities at the energy of Al Kα and O Kα almost monotonously decreased with decreasing exit angle. As a result, the intensity ratios of Al Kα and O Kα X-rays to the background intensities were enhanced five- and sixfold, respectively. This enhancement is considered to be caused by the interference effect of both directly detected X-rays and reflected X-rays on the flat substrate. The similar results are also obtained for Al Kα, Si Kα, K Kα and Ca Kα emitted from single atmospheric particle. The significance of the matrix effect in the particle is also pointed out.

Grazing Exit Electron Probe Microanalysis for Surface and Particle Analysis

We developed a new method of grazing exit electron probe microanalysis (GE-EPMA) and applied it to analyze both Si surfaces and Mg-salt particles. In conventional EPMA, X-rays are detected at an exit (takeoff) angle of approximately 45°. Therefore, when particles collected on a sample carrier are analyzed by EPMA, the X-rays from both the particles and the carrier are detected, although we need only the X-rays emitted from the particle itself. In contrast to this, the X-rays are detected at grazing exit angles in GE-EPMA. The X-rays emitted from deep inside of the sample are not detected under grazing exit conditions, and only X-rays emitted from the surface and the particle are measured. It was found that surface-sensitive analysis of a Si wafer was possible with low background at grazing exit angles. The intensity ratio of O Kα to Si Kα increased near zero degrees, indicating that the Si wafer is covered with a native Si oxide. Moreover, Mg Kα X-rays from a Mg-salt particle, which was deposited on the Si wafer, were detected with a small Si Kα intensity at grazing exit angles of less than 0.5°. By decreasing the exit angle to less than zero, only the top of the particle was observed; therefore, GE-EPMA measurement would make it possible to investigate the surface layer of one particle.

Elemental X-ray images obtained by grazing-exit electron probe microanalysis (GE-EPMA)

A new method, grazing-exit electron probe microanalysis (GE-EPMA), was studied. Only X-rays emitted from the near-surface layer are measured at grazing-exit angles (e.g. <0.5°), whereas, with conventional EPMA, X-rays emitted from deep positions are also measured. Therefore, X-ray spectra with low background are obtained by GE-EPMA. Here, elemental mapping by GE-EPMA is shown for the first time. It was found that surface-sensitive elemental X-ray images were obtained for a thin Au film deposited on a Si wafer. The problems that occur at boundaries of different heights are discussed. Furthermore, it was difficult to recognize elemental distributions of Si, S, Ca, Na and Fe for aerosols deposited on a Si wafer in noisy X-ray images when using conventional EPMA; however, clear X-ray images were obtained under grazing-exit conditions.