Secondary X-rays Research Articles

The inclusion of secondary electrons and Bremsstrahlung X-rays in an electron beam resist model

A theoretical analysis and an experimental verification have been carried out to investigate the need for the inclusion of secondary electron emission and Bremsstrahlung absorption into e-beam lithography simulations for the correct prediction of the proximity effect at high beam voltages and sub-100-nm dimensions. The experimental verification has been performed at 100 kV for a variety of exposure and development conditions for sub-250-nm features. In all cases, good agreement between simulation and experimental data has been obtained using a simplified chemically amplified resist model with the inclusion of secondary electron emission in the Monte Carlo calculations. The role of the Bremsstrahlung X-ray absorption in the resist has been estimated to be negligible. The deficiency of the model when using only primary electrons in the Monte Carlo calculations is also discussed.

Application of the Electron Probe Microanalyzer to the Analysis of Planetary and Geological Materials: a Historical Perspective.

Castaing first presented his idea to use secondary X-rays excited by a focused electron beam from a polished solid sample for microanalysis in 1949 at the First European Regional Conference on Electron Microscopy in Delft, Netherlands. As part of his dissertation, he then not only built the first electron probe microanalyzer (EPM), but also established many of the theoretical and analytical principles of the technique. This technique offered enormous analytical advantages to earth scientists over other analytical methods available at the time. For example, it allows qualitative and quantitative analysis of individual mineral grains a few microns in diameter; mineral grains can be viewed during analysis, thus ensuring accurate correlation between composition and grain morphology; for most purposes, the method is non-destructive; in situ analysis of minerals in polished thin sections results in retention of textural relationships among coexisting minerals; because of the small excitation volume, the technique is ideally suited for the study of zoned minerals, minute inclusions, exsolution lamellae, etc.; and once suitable standards are prepared and correction procedures are established, a large number of quantitative analyses can be obtained in a comparatively short time.

X-Ray Pole Figure Measurement and Texture Mapping of Selected Areas Using an X-Ray Scanning Apparatus

An x-ray scanning apparatus (XSA) for imaging the spatial distributions of crystal texture and elements in bulk samples has been further improved and extended to pole figure measurements on selected areas. A beam collimator is used to stop down the white primary beam to a narrow spot on the specimen surface. A broad spectrum of secondary x-rays is emitted which is composed of diffraction peaks, characteristic fluorescence lines and a low background. Peak separation and intensity measurement is performed by energy-dispersive x-ray spectroscopy. The spatial distributions of selected crystallographic directions or elements in the sample surface are acquired by translating the sample step by step on a user defined grid. Local resolution is presently limited to 50 μm by the low intensity of a collimated primary beam. The completion of the XSA by a Philips X'Pert goniometer stage enables pole figure measurement to be performed at a high spatial resolution as a supplement to crystal texture mapping. Texture components significant for mapping can thus readily be selected.

Study of secondary X-rays from radiographic intensifying screens

To reduce the radiation dose in radiology, fluorescent intensifying screens for X-ray films are used. They produce visible light which increases the efficiency of the film. In addition, there are two other effects that will degrade the image resolution. First, the gadolinium present in the screens produces X-rays isotropically. Second, the primary radiation can be scattered elastically (Rayleigh scattering) and inelastically (Compton scattering). The intensity and angular distribution of these secondary radiation were measured, showing that the ratio of secondary-to-primary radiation incident on the X-ray film is about 16%.

Secondary fluorescence correction formulae for X-ray microanalysis — I Parallel-sided thin foil, wedge, and bulk specimens

Secondary fluorescence correction formulae have been derived for specimen geometries that are commonly employed in the analytical electron microscope. Formulae have been derived for parallel-sided thin foil and bulk (electron probe microanalysis) specimens, for which established correction formulae currently exist, and for wedge-shaped specimens, for which no formulae have been available to date. All derivations explicitly account for the absorption of fluoresced X-rays leaving the specimen en route to the spectrometer, which the existing correction formulae neglected wholly or in part. It is shown that the existing secondary fluorescence correction formula of Nockolds et al. for parallel-sided thin foils, which entirely neglects the absorption of secondary X-rays, is sufficiently accurate as long as the “sec α” factor is omitted. An additional factor ( y (x + y) in Reed's notation) should be appended to the existing secondary fluorescence correction formula for bulk specimens in the electron probe microanalyzer to account for near-surface absorption of fluoresced X-rays, which was neglected by Castaing. The difference in the secondary fluorescence corrections calculated with the Φ( ϱz) dependencies of Lenard (exponential) and Packwood and Brown (modified Gaussian) is shown to be negligible.

Secondary x-ray fluorescence for in vivo transdermal absorption measurements

A modification of an X-ray fluorescence (XRF) technique that could be applied to the noninvasive measurement of transdermal absorption in human subjects with a low absorbed radiation dose was investigated. Secondary X-rays that were produced in a samarium foil by an isotopic 241Am source were used to induce iodine Kα X-rays in an iodine-containing compound. The disappearance of this compound was measured following topical administration to a human volunteer. The use of the secondary X-ray fluorescence technique resulted in an 11-fold reduction in the absorbed radiation dose to the skin compared to conventional XRF bringing the technique within acceptable dosimetry limits for human studies.

Nuclear microprobe analysis of chlorine distribution in the blue-light-exposed rat retina

Blue-light exposure is a possible environment factor which causes senile macular degeneration, a prominent cause of visual impairment in elderly. Blue-light exposure causes inner segment edema and photoreceptor degeneration, probably by inhibiting the sodium-potassium pump on the inner segment membrane. Disturbance of the pump function may cause chlorine and sodium redistribution in the inner and outer segments, and edema in the inner segment. In the present study, 11 eyes from 11 Sprague-Dawley rats were used. Six rats were exposed to blue light (404 nm) at a retinal dose of 380 kJ/m 2, five were control. Chlorine and sulphur distribution were measured with the Lund Nuclear Microprobe (beam size: 12 × 12 μm, proton energy: 2.55 MeV, beam density at the target: 10–20 pA/μm 2). The chlorine concentration was calculated using sulphur as reference. The secondary characteristic X-rays were measured with a Kevex Si(Li) detector. The mean chlorine concentration was 0.82 mg/mg sulphur in the control inner segment layer. It was 1.83 and 2.00 mg/mg sulphur, 1 and 12 h after exposure, respectively. The mean chlorine concentration was 2.55 mg/mg sulphur in the control outer segment layer. It was 1.17 and 1.21 mg/mg sulphur, 1 and 12 h after exposure, respectively. The sodium signal is severely attenuated by the detector window, and the sodium distribution is assumed to be indicated by the chlorine distribution since these two elements follow each other closely in the cellular edema caused by metabolic inhibition. An accumulation of chlorine and sodium could be one of the reasons of the inner segment edema after blue-light exposure.

X-ray examination of liquid metal ion sources

Secondary electron-excited X-rays were used for investigation of a liquid metal ion source (LMIS). Ga LMISs were studied using camera obscura with a 25 μm diameter pin-hole. The results are in agreement with computer calculations of secondary electron trajectories. In some cases at high ion currents (> 50 μA) an X-ray halo around the emitter was noticed. This was probably due to Ga atoms excited by secondary electrons and/or X-rays. No trace of droplets was visible. This could be due to a droplet velocity much higher than the thermal velocity of neutral atoms. Disintegration of the majority of the droplet population immediately after their emission may be equally the reason for the absence of droplet traces.

The Synchrotron Self-Compton Model for X-Ray and gamma -Ray Emission from Pulsars

view Abstract Citations (18) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Synchrotron Self-Compton Model for X-Ray and gamma -Ray Emission from Pulsars Cheng, K. S. ; Wei, D. M. Abstract We compare the observed X-ray luminosity emitted from pulsars with that calculated from various theoretical models and find that the X-ray emission from six pulsars is much stronger than that predicted by theoretical models. We suggest that these pulsars with unusually intense X-ray emission could also be γ-ray emitters. Electrons/positrons are accelerated in the outer magnetospheric gap and lose most of their energy via curvature radiation (primary photons), which will be converted to secondary e± pairs outside the gap in collision with the secondary X-rays. A simple synchrotron self-Compton model is then used to calculate the X-ray and γ-ray emission from the secondary e± pairs. This model only contains a single free parameter, which characterizes the size of the acceleration region and can be estimated by comparison with that of the Crab pulsar. Our model results are consistent with the observed data and upper limits of γ-ray emission and phase separation between pulses. Other implications for future observations are also discussed in the text. Publication: The Astrophysical Journal Pub Date: July 1995 DOI: 10.1086/175959 Bibcode: 1995ApJ...448..281C Keywords: ELEMENTARY PARTICLES; GAMMA RAYS: THEORY; RADIATION MECHANISMS: NONTHERMAL; STARS: NEUTRON; STARS: PULSARS: GENERAL; X-RAYS: STARS full text sources ADS | data products SIMBAD (15)

Physical mechanisms of mutation induced by low energy ion implantation

Physical mechanisms of mutation induced by low energy ion implantation are discussed from the point of view of direct and indirect action. In direct action the average range of 110 keV 56Fe + ions implanted into wheat embryo was experimentally measured to be 210 ± 30 nm. Further, the energy deposition distribution with implantation depth was calculated with the TRIM 88 code from the measured ion concentration implanted at different depths. In indirect action, energetic secondary electrons, characteristic X-rays and thermal spikes are discussed.

An X-ray observation in the atmosphere during the August 7, 1972 solar flare

An observation carried out with a balloon-borne detector of an additional flux of secondary X-rays (E ≃ 30 keV) at large depths in the atmosphere is described. This excess is attributed to the emission of very hard X-rays during the solar flare of August 7, 1972. The propagation in the atmosphere of the secondary photons resulting from their electromagnetic interactions in the air is computed by utilizing the Monte Carlo method. The computations agree with the observed flux when a very hard solar X-ray spectrum is assumed.

Responses of a 30μm-diam tin granule to 60keV photons at a temperature of 30mK

We studied phase transitions of a superconducting tin granule of 30μm in diameter at a temperature of 30mK in an irradiation of 60keV. The spectrum of energies absorbed by the granule has two peaks at 60keV or less and at about 30keV. On the bases of the specific heat in the superconducting state and a hypothesis of global heating, the following are concluded. The former peak is due to energy deposits by electrons which are excited mainly from the L-shell by either primary gamma-rays or 20% of secondary X-rays produced by the filling of the K vacancies. However, 80% of the secondary X-rays pass out of the grain carrying an energy of more than 25keV. The latter peak is due to excited K-shell electrons accompanied by such escaping secondary X-rays.

Responses of a superheated superconducting tin granule to photons and neutrons at a temperature of 30mK

We measured responses of a 30µmφ tin SSG by irradiating 60keV photons at a temperature of 30mK. A spectrum of energy deposits is calculated by using the superconducting specific heat together with a global heating model. The resultant spectrum of energies absorbed by the tin granule has two peaks at 60keV or less and at about 30keV. The former peak is due to energy deposits by electrons which are excited mainly from the L-shell by either primary gamma-rays or 20% of secondary X-rays produced by the filling of the K vacancies. However, 80% of the secondary X-rays pass out of the grain carrying an energy of more than 25keV. The latter peak is due to excited K-shell electrons accompanied by such escaping secondary X-rays. The threshold of response energies was decreased down to 1keV. Therefore, an improvement in response energy was attained by three orders of magnitude in comparison with the result previously obtained in the α-ray irradiation experiment. A plan of an experimental study on the response of tin SSGs to irradiations of neutron-rays is briefly described.

Texture distributions imaged by energy dispersive X-ray diffraction

An X-ray scanning apparatus has been developed for the study of texture topography and element distributions on bulk sample surfaces. The set-up consists of a white X-ray source, a collimator system to produce a narrow primary beam, an x-y sample stage with stepper motors, and an EDX detecting system. The apparatus is controlled by a microcomputer. The spectrum of secondary X-rays is composed of broad diffraction peaks, sharp characteristic fluorescence lines, and a low background of scattered radiation. Peak separation and intensity measurement is performed by energy dispersive X-ray spectroscopy (EDX). The density distributions of selected crystallographic directions or elements in the sample surface are acquired spot by spot, and represented by false-colour images. Several texture distributions as well as element composition images can be obtained simultaneously. Local resolution is presently limited to 0.2 mm, due to the low intensity of a collimated primary X-ray beam. Es wurde eine Röntgen-Rasterapparatur zur Untersuchung der Texturtopographie und Elementverteilung an der Oberfläche massiver Proben entwickelt. Der Versuchsaufbau besteht aus einer weißen Röntgenquelle, einem Kollimatorsystem zur Erzeugung eines feinen Primärstrahls, einer x-y-Probenbühne mit Schrittmotoren und einem EDX-System. Die Apparatur wird von einem Mikrocomputer gesteuert. Das sekundäre Röntgenspektrum besteht aus breiten Beugungspeaks, scharfen charakteristischen Fluoreszenzlinien und einem niedrigen Streustrahlungsuntergrund. Die Peaktrennung und die Intensitätsmessung wird mittels energiedispersiver Röntgenspektroskopie (EDX) vorgenommen. Die Verteilung der Dichte ausgewählter kristallographischer Richtungen oder Elemente in der Probenoberfläche wird punktweise ermittelt und in Falschfarbenbildern dargestellt. Es können gleichzeitig mehrere Textur- und Element-Verteilungsbilder aufgenommen werden. Wegen der niedrigen Intensität, die man in einem durch Ausblenden kollimierten Primär-Röntgenstrahl erreicht, ist die Ortsauflösung gegenwärtig auf 0,2 mm beschränkt.

A complete inverse Monte Carlo model for energy-dispersive X-ray fluorescence analysis

A complete model for energy-dispersive X-ray fluorescence based on the Inverse Monte Carlo (IMC) method is obtained. The model accounts for primary, secondary, and tertiary X-rays excited by unscattered, single, and double scattered source photons. The elemental X-ray intensities are derived as functions of the difference in the elemental weight fractions between the unknown sample and a given reference sample to form a set of nonlinear equations. The coefficients of these equations are obtained from a Monte Carlo simulation in the reference sample and the system of equations is numerically solved for the unknown sample composition. The IMC model has been investigated for a radioisotope source excited EDXRF system consisting of a 109Cd source and a Si(Li) detector for a CuNi alloy sample (CDA Alloy 715) and a stainless steel sample (304 Stainless Steel) in addition to several other simulated cases. The results show that the IMC model is valid, accurate, and computationally efficient. The accuracy of the solution is found to be directly related to the accuracy with which the elemental intensities are known. On the average, the model takes about 5 min on a high speed personal computer to yield a relative error in the elemental weight fractions of about 3%.

Advances in Scanning Electron Microscopy

Scanning electron microscopes offer several unique advantages and they have evolved into complex integrated instruments that often incorporate several important accessories. Their principle advantage stems from the method of constructing an image from a highly focused electron beam that scans across the surface of a specimen. The beam generates backscattered electrons and excites secondary electrons and x-rays in a highly localized “spot.” These signals can be detected, and the results of the analysis are displayed as a specific intensity on a screen at a position that represents the position of the electron spot. As with a television image, after a given period, information about the entire field of view is displayed on the screen, resulting in a complete image. If the specimen is thin, the same type of information can be gathered from the transmitted electrons, and a scanning transmission image is thus constructed.The scanning electron microscope is highly versatile and widely used. The quality of the image is related to its resolution and contrast, which, in turn, depend on the diameter of the focused beam as well as its energy and current. Because electron lenses have inherently high aberrations, the usable aperture angles are much smaller than in a light microscope and, therefore, the electron beam remains focused over a relatively large distance, giving these instruments a very large depth of focus.Scanning electron microscopes are versatile in their ability to detect and analyze a lot of information. As a result, modern versions of these instruments are equipped with a number of detectors. Developments are sometimes related to placing the detectors in a geometrically attractive position close to the specimen.

Scanning X-Ray Analytical Microscope using X-Ray Guide Tube

AbstractA scanning X-ray analytical microscope was constructed using X-ray guide tube(XGT). XGT is a glass capillary which guides and focuses x-rays by total external reflection at the inner wall. The nature of X-ray beam passed through XGT is varied depending on the form of XGT. The cylindrical and conical types were used for the present setup. A small area (10μm × 10μm) of the sample was irradiated by the X-ray microbeam formed by XGT. Fluorescent and diffracted X-rays from the small area were detected by SSD. By scanning the sample in the plane normal to the X-ray microbeam, the intensity distributions of such secondary x-rays were measured and used as picture elements for constructing x-ray mapping images. The sample was a thin-section of an old chinaware. The images suggest a wide application of this instrument.

High Resolution Scanning Electron Microscopy of Surfaces

Electron beams of small diameter, generated with field emission guns may be used to investigate surfaces in many different ways. Images may be formed in the scanning mode by use of the elastically, or quasi-elastically scattered electrons or by the detection of secondary radiation including low energy secondary electrons, Auger electrons and X-rays. Except in the case of low-energy secondary electrons, high spatial resolution has not yet been achieved by detection of the secondary radiations so these imaging modes will not be discussed here.The scanning modes used with the detection of elastic or quasi-elastic electrons in a dedicated STEM instrument are analogous to those used in conventional TEM instruments for surface studies, such as profile imaging and reflection electron microscopy. In each case, the practical limitations of current STEM systems tend to limit the quality of the imaging but the flexibility of the STEM detector system has provided several important advantages. In scanning reflection microscopy (SREM) the resolution attained is comparable with that for REM. The important advantage over REM is that microdiffraction patterns may be obtained from any surface features as small as the resolution limit for imaging. Also it is relatively easy to make use of the surface channelling conditions in order to enhance the contrast of surface steps or other surface features.

A damage-free perfect planarization method using bias-sputtered SiO2

A novel bias-sputtered SiO 2 deposition process, which is suitable for depositing an interlevel insulator of an Al multilevel interconnection of submicrometer feature size, has been achieved. This process consists of damage-free technology and a perfect planarization method. It was found that during the bias-sputter deposition, damage was introduced into the gate oxides of MOS devices due to secondary X-rays generated by electrons coming from the sputter target, but that the presence of a grid electrode to absorb these electrons was quite effective to reduce damage introduction to an acceptable degree for practical use. Also, using a two-step bias-sputter deposition and an etch-back technique, a perfect planarization of bias-sputtered SiO 2 films was achieved.

The Mineral Composition of Intracellular Inclusions in Nematodes From Thiobiotic Mangrove Mud-Flats

Some marine nematodes from anoxic mangrove mud-flats contain densely packed intracellular inclusions within their tissues which are visible by light microscopy. Transmission electron microscopy of sections of Sabatieria wieseri, Terschellingia longicaudata and Sphaerolaimus papillatus shows these inclusions within the intestinal and other cells. Energy dispersive analysis of secondary X-rays by scanning electron microscopy of thick epoxy sections shows concentrations of Si, P, S, K, Ca and Fe in their tissues. EDS of secondary X-ray emissions from thin epoxy unstained sections by transmission electron microscopy shows these elements together with Na, Zn and Al concentrated in the intracellular inclusions. The physiological implications of these observations are discussed.