Small Exit Angles Research Articles

Collisionless jet expanding into vacuum from a circular aperture

Collisionless flows expanding into a vacuum from a circular slit are investigated using the gaskinetic theory. Both accurate and approximate expressions to the plume fields along a centerline and a constant radius are obtained, including the density, velocity components, and translational temperature. Special non-dimensional parameters such as the exit semi-opening angle, gas speed ratio at the exit, and positions are included in these expressions. Particle simulations with the direct simulation Monte Carlo method are performed to validate the above results. These expressions are complex and may need computers for evaluations; however, the cost is minor when compared to particle simulations. With the assumptions of a high or low exit speed ratio and small exit angle, simple explicit expressions for properties along the centerline and a constant radius are obtained. The investigations also find out that the cosine law relations can provide fast and crude estimations, but it is not recommended to use the cosine law relation to compute collisionless plume flowfields with a large exit speed.

A simulation study of sperm motility hydrodynamics near fish eggs and spheres

For teleost fish fertilisation, sperm must proceed through a small opening on the egg surface, referred to as the micropyle. In this paper, we have used boundary element simulations to explore whether the hydrodynamic attraction between sperm and a fish egg can be a sperm guidance cue. Hydrodynamical egg–sperm interactions alone do not increase the chances of an egg encounter, nor do they induce surface swimming for virtual turbot fish sperm across smooth spheres with a diameter of 1mm, which is representative of a turbot fish egg. When a repulsive surface force between the virtual turbot sperm and the egg is introduced, as motivated by surface charge and van-der-Waals interactions for instance, we find that extended surface swimming of the virtual sperm across a model turbot egg occurs, but ultimately the sperm escapes from the egg. This is due to the small exit angle of the scattering associated with the initial sperm–egg interaction at the egg surface, leading to a weak drift away from the egg, in combination with a weak hydrodynamical attraction between both gametes, though the latter is not sufficient to prevent eventual escape. The resulting transience is not observed experimentally but is a detailed quantitative difference between theory and observation in that stable surface swimming is predicted for eggs with radii larger than about 1.8mm. Regardless, the extended sperm swimming trajectory across the egg constitutes a two-dimensional search for the micropyle and thus the egg is consistently predicted to provide a guidance cue for sperm once they are sufficiently close. In addition, the observation that the virtual turbot sperm swims stably next to a flat plane given repulsive surface interactions, but does not swim stably adjacent to a turbot-sized egg, which is extremely large by sperm-lengthscales, also highlights that the stability of sperm swimming near a boundary is very sensitive to geometry.

Effect of multiple scattering on high-resolution Rutherford backscattering spectroscopy

The effect of multiple scattering on high-resolution Rutherford backscattering spectroscopy was studied for 450keV He+ ions incident on ultrathin HfO2 films on Si. There was a tail at the low energy Hf edge in the observed spectrum. The tail increases with increasing HfO2 thickness and decreasing exit angle (exit angle with respect to the surface). A notable tail was observed even for HfO2 films of 2nm thickness at a small exit angle of 7°. The observed tail was reproduced by Monte Carlo simulations showing that the origin of the tail is multiple scattering. An analytical model was developed to estimate the tail for practical use. The derived analytical formula roughly reproduced the observed tail.

Machined Workpiece Edge Shape Control by Laser Hardening —Optimizing Laser Scan Conditions and Cutter Paths—

Burring is a vital factor in metal cutting processes, since it may cause production-line problems that add unwanted time and cost required for deburring. We found that laser hardening of workpieces before face milling efficiently prevents burr formation. Our purpose here is to study optimum laser hardening conditions and cutter paths. Where no burring occurs, minimal chipping such as in chamfering is seen at the martensite layer on the workpiece exit face. The martensite layer thickens with laser power density, increasing chamfer height. The larger the exit angle, the more difficult it is to form a chamfer-like edge. Even for relatively small exit angles, the lower the feed rate, the more difficult it becomes to form a chamfer-like edge.

Polar exit angle distributions of slow H+ ions, related to the presence of a regular domain structure, calculated within the diffuse scattering approximation upon interaction of ions with the sample surface

The angular distributions of slow H ions scattered from the surface of a magnetic film with a stripe domain structure have been calculated. The calculations were performed within the models of specular and diffuse scattering upon collisions of ions with surface. It is shown that the magnetic fields of the stripe domain structure block the ions scattered at small exit angles. It is established that, within the more adequate model of diffuse scattering, the anisotropy of interaction of ions with the magnetic field of the stripe structure manifests itself in a wider angular range.

Effects of multiple scattering and surface roughness on medium energy backscattering spectra

The influence of multiple scattering and surface roughness on medium energy backscattering spectra was studied using Monte Carlo simulations. These factors can influence the shape of backscattering spectra, making it difficult to accurately determine composition profiles. Using near-normal and near-glancing ion exit angles, simulations were performed for 270keV 4He+ ions incident on targets of 33nm Ta on Si and 5nm ZrO2 on Si. The influence of both multiple scattering and surface roughness were found to increase with exit angle, which is measured towards the surface normal. Simulations showed that multiple scattering affected the shape of the Ta/Si spectrum even for a small exit angle of 15°, but did not significantly affect the shape of the ZrO2/Si spectrum. Monte Carlo simulated spectra from a 5nm ZrO2/Si target with a near glancing angle of 75° and a RMS roughness of 1nm resulted in a tail at the low energy edge of the Zr signal and the front edge of the Si signal.

Modeling low-coherence enhanced backscattering using Monte Carlo simulation

Constructive interference between coherent waves traveling time-reversed paths in a random medium gives rise to the enhancement of light scattering observed in directions close to backscattering. This phenomenon is known as enhanced backscattering (EBS). According to diffusion theory, the angular width of an EBS cone is proportional to the ratio of the wavelength of light lambda to the transport mean-free-path length l(s)* of a random medium. In biological media a large l(s)* approximately 0.5-2 mm >> lambda results in an extremely small (approximately 0.001 degrees ) angular width of the EBS cone, making the experimental observation of such narrow peaks difficult. Recently, the feasibility of observing EBS under low spatial coherence illumination (spatial coherence length Lsc << l(s)*) was demonstrated. Low spatial coherence behaves as a spatial filter rejecting longer path lengths and thus resulting in an increase of more than 100 times in the angular width of low coherence EBS (LEBS) cones. However, a conventional diffusion approximation-based model of EBS has not been able to explain such a dramatic increase in LEBS width. We present a photon random walk model of LEBS by using Monte Carlo simulation to elucidate the mechanism accounting for the unprecedented broadening of the LEBS peaks. Typically, the exit angles of the scattered photons are not considered in modeling EBS in the diffusion regime. We show that small exit angles are highly sensitive to low-order scattering, which is crucial for accurate modeling of LEBS. Our results show that the predictions of the model are in excellent agreement with the experimental data.

Quantitative analysis of metallic ultra‐thin films by grazing‐exit electron probe x‐ray microanalysis

AbstractGrazing‐exit electron probe x‐ray microanalysis (GE‐EPMA) was used for the quantitative analysis of films with thicknesses of 10 and 4 nm. First‐order calibration curves were obtained for the determination of Ti and Cr over a wide range of concentrations. The results confirmed that matrix effects are negligible when the film thickness is below some critical value. The minimum detection limits were obtained at the small exit angles (0.75° for the 10 nm thick film on the gold and 0.53° for the 4 nm thick film on the silicon substrate). Detection limits were improved by a factor of 6.5 under grazing exit conditions for the film with a thickness of 10 nm and by a factor of 2 for the film with a thickness of 4 nm, compared with detection limits obtained at 45°. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Grazing-exit electron probe X-ray microanalysis of ultra-thin films and single particles with high-angle resolution

Ultra-thin metallic films, artificial particles and aerosols were analyzed by grazing-exit electron probe X-ray microanalysis (GE-EPMA). It is beneficial to measure the characteristic intensity emitted from these specimens at very small exit angles. Such an approach reduces the high background originated from the substrate. The reduction of background X-rays is very important for thin film analysis. Therefore, it is shown that GE-EPMA is a powerful tool for localized analysis of thin-films and the surface of the sample. It is also found that GE-EPMA solves the problem of the overlapping of X-ray lines emitted from the substrate and the particle or the aerosol. Performing the measurement of the characteristic radiation from the particle under grazing exit conditions allows particles smaller than the electron beam diameter to be analyzed. Thus any limitations of the electron beam size can be removed.

Micro X-ray diffraction analysis of thin films using grazing-exit conditions

An X-ray diffraction technique using a hard X-ray microbeam for thin-film analysis has been developed. To optimize the spatial resolution and the surface sensitivity, the X-ray microbeam strikes the sample surface at a large glancing angle while the diffracted X-ray signal is detected with a small (grazing) exit angle. Kirkpatrick-Baez optics developed at the Photon Factory were used, in combination with a multilayer monochromator, for focusing X-rays. The focused beam size was about 10 x 10 micro m. X-ray diffraction patterns of Pd, Pt and their layered structure were measured. Using a small exit angle, the signal-to-background ratio was improved due to a shallow escape depth. Under the grazing-exit condition, the refraction effect of diffracted X-rays was observed, indicating the possibility of surface sensitivity.

A characterization of the β -glycidoxypropyltrimethoxysilane and aluminium interface by SIMS and XPS

Organosilanes are frequently applied as primers to oxide layers on aluminium and its alloys in order to improve adhesion to organic coatings, for example, for corrosion protection, although the bonding mechanism is not well understood [1, 2]. A common view has been that the adhesion involves formation of Si±O±Al type linkages, although direct evidence for this interfacial bonding has proved elusive [3±9]. Earlier work from this laboratory suggested that angle-dependent X-ray photoelectron spectroscopy (ADXPS), in combination with a bias-potential technique, may give a new way for probing the interfacial bonding between oxidized aluminium and silanes, and for aiding the identi®cation of relationships between atomic-level interfacial structure and macroscopic properties [10, 11]. For a thin layer of a-glycidoxypropyltrimethoxysilane (a-GPS) deposited on chemically etched aluminium, it was hypothesized that a new structure apparent in Al2p spectra for small exit angles in ADXPS, after applying a negative biasing potential, may indicate a ` chemical shift'' effect associated with the Si±O± Al bonding [10]. The evidence was indirect; it depended on the existence for some silane±aluminium systems of this additional structure in Al2p spectra, induced by differential charging, and an associated correlation with corrosion protection. This letter reports further observations on the same system, and includes an attempt at characterizing the interfacial bonding with secondary ion mass spectrometry (SIMS) in the static SIMS mode [12]. Following the earlier reports [10, 11], square panels of 7075-T6 aluminium (1 cm) were degreased and acid etched before coating with the silane solution (1 vol % formed by dissolving a-GPS monomer in an equi-volume mixture of distilled water and methanol). Three main samples are referred to below. Sample A was a blank sample prior to coating with aGPS (i.e. the alloy after etching); sample B was formed from sample A by applying the a-GPS solution drop-by-drop until a thick layer of polymer was formed; sample C gave the a-GPS=substrate interface formed by dipping sample A in the a-GPS solution for 5 min followed by air drying. X-ray photoelectron spectroscopy (XPS) spectra were measured with a Leybold MAX200 spectrometer [13] using the unmonochromatized AlKa source (1486.6 eV) operated at 15 kV, 20 mA with pressure in the analysis chamber around 6 3 10y7 Pa. The biased spectra were obtained by applying an external potential of y93 V through the sample holder, and then, after measurement, mathematically shifting the energy scale back by 93 eV [10]. Static SIMS was performed with a VG MM12-12S quadrupole mass spectrometer using a xenon primary beam (5 keV impact energy), for which a current of 0.2 nA irradiated a square area (6.25 mm) on the samples. XPS con®rms that the samples A, B and C had the expected compositions for the surface regions; also sample B was suf®ciently thick that Al signals were not detectable. Sample C showed the extra structure reported previously in the Al2p spectra from using the bias potential technique, and therefore it appeared to provide a suitable sample for probing the a-GPS=aluminium interface with SIMS. Relevant positive ion static SIMS spectra are reported in Fig. 1. Those for the acid-etched alloy (sample A) and the thick a-GPS layer (sample B) serve as references for interpreting that from the interface structure (sample C). The spectrum from sample A in Fig.1a is made up of Al‡ (mass 27) and CH fragments, the latter being indicative of the commonly observed hydrocarbon contamination. Since C2H3 ‡ and C2H5 ‡ fragments are usually comparable in intensity, only part of the mass 27 peak can be assigned to C2H3 ‡. The small peak at mass 28 may be AlH‡ (Si‡ is considered less likely since no Si was detected by XPS). Sample B experienced charging under ion bombardment, and the spectrum in Fig. 1b was obtained with operation of an electron ood gun (500 eV) to compensate. The signals obtained were fairly weak; nonetheless peaks from Si‡ and SiOH‡, and possibly SiCH3 ‡, were evident in the spectrum. The presence of SiOH‡ is consistent with expectation from the a-GPS polymerization [3]. There should be no contribution at mass 27 from Al‡ given the thickness of the a-GPS layer, but hydrocarbon fragments, in part from the a-GPS backbone, are clearly present. Fig. 1c shows the static SIMS spectrum for sample C. No sample charging was evident, thereby supporting the belief that the a-GPS layer was very thin. The most prominent peak was at mass 45 (SiOH‡ from the a-GPS polymerization), but there

切れ刃離脱時の過渡切削過程と欠損の発生 (第2報)

Fracture probability of an alumina ceramic tool during the exit of interrupted cutting is calculated using the transient distribution of tool face stresses, which was already obtained through the FEM simulation analysis in the previous paper. Contrary to expectation, the fracture probability reaches the maximum just before the downward crack initiation for making the chip with “foot”. The cutting edge becomes safe immediately after the crack initiation, because the cutting forces drop rapidly and the chip root pushes up the edge flank to yield a hydrostatic stress state. The fracture onset around this instant is proved experimentally. It is also revealed that the edge fracture is restrained by the early initiation of the crack with brittle workpiece and small exit angle, while the fracture is promoted by the delayed initiation with low friction on the tool face.