Angular Yield Research Articles

Absolute doubly differential angular sputtering yields for 20 keV Kr+ on polycrystalline Cu

We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr+ impacting a polycrystalline Cu slab at an incidence angle of θi = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θs, and azimuthal, ϕs, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 1018 ions/cm2. Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θs in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θs and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness.

Atomic structure and annealing-induced reordering of ε-Ga2O3: A Rutherford backscattering/channeling and spectroscopic ellipsometry study

The crystallographic structure of thin Ga2O3 layers grown by metal–organic vapour phase epitaxy on Al2O3 substrate was analyzed by Rutherford Backscattering Spectrometry/Channeling (RBS/C) angular yield scans performed around the c-axis of as-grown Ga2O3. The measured widths and minimum yields of the scan curves for the Ga and O component were compared to calculations based on the continuum steering potential model. The results obtained are consistent with a crystal structure containing oxygen atoms arranged in a 4H hexagonal closely packed lattice and Ga atoms preferentially occupying octahedral interstitial sites in the 4H cells - a structure closely related to the ε-Ga2O3 polymorph. After high-temperature annealing remarkable structural transformation is detected via significant changes in the RBS/C spectra. This effect is related to the hexagonal-monoclinic, i.e., ε-β phase transformation of Ga2O3. Spectroscopic ellipsometry spectra of as-grown and annealed samples can be best fitted using a vertically graded single-layer B-spline model. Significant differences in the dielectric functions were found, showing bandgap reduction for long term annealing. These features are related to the ε-β polymorphic transformation, variation of the preferred crystallographic orientation upon annealing, and differences in residual strain and defect structure determined by the annealing conditions.

Effect of heavy inert ion strikes on cell density-dependent profile variation and distortion during the etching process for high-aspect ratio features

Vertical scaling technique faces a physical limitation in 3D NAND device fabrication, even assuming superior etching technology. Another promising scaling technique to increase the storage density is lateral scaling, which increases the number of holes between slit and slit from four to nine and above. However, unpredictable small critical dimension, feature-to-feature variation, and distortion occur. To elucidate the profile deteriorations induced by the lateral scaling, we analyzed the effect of the angular etching yield dependency of the incident ion fluxes into a given feature using the multiscale technology computer-aided design methodology. As one of the inherent features of the gas, incident angle θmax in which the sputtering yield achieves its maximum value is a crucial factor for analyzing and modeling etching profiles. Moreover, the impact of the heavy inert ion strikes on the unpreferred etching profiles was investigated. In this study, the synergy of lower energy ions, larger fluxes, and larger θmax of heavy inert ions decrease the feature-to-feature variation, reducing hard mask distortion without the etch rate reduction.

A compact accelerator-driven deuterium–deuterium neutron source using heavy water jet target

A compact accelerator-driven deuterium–deuterium neutron source using a heavy water jet target is under development at the Institute of Nuclear Physics and Chemistry. The neutrons are generated by bombarding a 0.45 mm-thick heavy water jet target with 11 MeV/0.33 mA deuterons. The angular neutron yield between 10–14 MeV is about 6.5×1011 n/s/sr at 0 degree. The D(d,n)3 reaction is adopted to generate high energy neutrons for its relatively high angular neutron yield, outstanding forward directional characteristics and convenient for obtaining, operating and maintaining. To minimize the length of the neutron source, an IH-DTL is adopted for its high accelerating gradient, low input energy and low power consumption. The design of the deuteron accelerator, consisting of a deuteron injector, a four vane Radio-Frequency Quadrupole (RFQ) and an Interdigital H-mode Drift Tube Linac (IH-DTL), is introduced in this paper. The heavy water jet target, which suffers high deuteron beam power density, is also introduced in this paper.

Rheological Investigation of GO Doped p(APTMACl) Composite Hydrogel

Abstract The aim of the present work is an approach towards the exploration of comprehension of rheological work on polymer composites synthesized by ex-situ dispersion of graphene oxide (GO) in poly(3-acrylamidopropyl trimethyl ammonium chloride (APTMACl) cationic hydrogel template. FTIR was carried out for confirmation of polymer synthesis and existence of GO in hydrogel network. The rheological investigation via frequency sweep curve (shear measurement) and oscillatory sweep (dynamic mechanical analysis) at different temperature 20, 25, 30, 35, 40 and 45 °C was performed. The storage (G′) and loss (G′′) moduli as a function of angular frequency, yield stress, tangent loss, damping factor and retention property were also studied to confirm the visco-elastomeric nature of the GO@p(APTMACl) composite and their semi solid response at different range of temperature. Various rheological models like Bingham model, modified Bingham model and Ostwald’s power law were applied. The temperature dependency was further tested via Arrhenius-Frenkel-Eyring equation. The sample showed best fitting in the modified Bingham model, which justified the pseudo plastic semi solid behavior of GO@p(APTMACl) composite within the linear visco-elastic region (LVER). All the properties from rheological study show best mechanical property and make the composite hydrogel good for drug delivery and for other environmental applications.

Investigation of the graphene thermal motion by rainbow scattering

The thermal motion of graphene atoms was investigated using angular distributions of transmitted protons. The static proton-graphene interaction potential was constructed applying the Doyle-Turner's expression for the proton-carbon interaction potential. The effects of atom thermal motion were incorporated by averaging the static proton-graphene interaction potential over the distribution of atom displacements. The covariance matrix of graphene displacements was modeled according to the Debye theory, and calculated using Molecular Dynamics approach. Proton trajectories were used for construction of angular yields. We have found that there are lines, called rainbows, along which the angular yield is very large. Their evolution in respect to different sample orientation was examined in detail. Further we found that atom thermal motion has negligible influence on rainbows generated by protons experiencing distant collisions with the carbon atoms forming the graphene hexagon. On the other hand, rainbows generated by protons experiencing close collisions with the carbon atoms can be modeled by ellipses whose parameters are very sensitive to the structure of the covariance matrix. Numerical procedure was developed for extraction of the covariance matrix from the corresponding rainbow patterns in the general case, when atoms perform fully anisotropic and correlated motion.

Measurement and modeling of aluminum sputtering and ionization in the DIII-D divertor including magnetic pre-sheath effects

We present analysis and modeling of Al sputtering and ionization in attached, low-power L-mode plasmas near the outer divertor strike point of the DIII-D tokamak. Al serves as a useful proxy for Be, the low-Z main wall material for ITER and JET that will undergo significant divertor plasma contact upon migrating from the first wall to the divertor. Al is easily distinguishable from background sources in DIII-D (namely C and B), has a high physical sputtering yield similar to Be, and has a long ionization mean free path compared to its gyro radius (). Using neutral Al emission imaging techniques, we measured a toroidal and radial asymmetry in the shape of the photo-emission plumes of sputtered neutral Al that was consistent with previously observed asymmetry in the distribution of redeposited Al in these experiments. We propose that the main cause of the emission and redeposition asymmetry is due to a sputtering anisotropy caused by near-grazing angle incident ions. The observed emission asymmetry was reproduced using a simple emission/ionization model that included full angular distributions of sputtering yield and energy calculated by SDTRIM.SP, but not when symmetric, mono-energetic cosine sputtering distributions were assumed. We used an ion orbit tracking model to calculate the distributions of ion impact energies through the potential gradient in the magnetic pre-sheath and Debye sheath. We found that with the magnetic field pitch angle (1.5°–2° with respect to the surface plane), the majority of ions strike the surface at <15° with respect to the surface plane, leading to angular sputtering yield and energy distributions with significant forward-scattering bias. We also observed surface microstructure consistent with directional sputtering and ion flux shadowing expected from the calculated ion incidence angles.

Measurement of sputtered beryllium yield and angular distribution during nanostructure growth in a helium plasma

The angular distribution and sputtering yield of beryllium exposed to helium plasma are estimated from analysis of line-integrated 2D imaging of Be-I line emission in a steady-state linear plasma device. As the surface nanostructure forms during plasma exposure on a ∼100 s timescale (corresponding to a fluence of order 1020/cm2) from nearly mono-energetic ion bombardment, a narrowing of the beryllium sputtering angle and a significant (∼5×) drop in sputtering yield are observed. These trends are found to be qualitatively consistent with modeling taking into account the effect of the surface morphology on sputtering yield and angular distribution.

Second-order sliding mode attitude controller design of a small-scale helicopter

In this paper, the attitude control of a small-scale helicopter is investigated. The main rotor flapping dynamics is explicitly explored to improve the control performance. A two-layer control architecture is adopted: the inner loop controller is designed combining second-order sliding mode control with extended state observer to control the angular rates and yield good robustness properties with respect to model uncertainties; the outer loop controller is used to control the attitude. Experimental results show that the proposed controller yields excellent performance and robustness.

The calculation of vertical rolling force by using angular bisector yield criterion and Pavlov principle

The automatic width control of the strip that is used in vertical rolling is a key issue in the hot strip rolling process. It is the first time that the internal deformation power and the friction power are obtained by using angular bisector yield criterion and Pavlov projection principle in the vertical rolling. At the same time, the shear power is determined by use of the integral mean value theorem. Then the vertical rolling force and shape parameters are obtained by minimizing the total power functional. The relative error of rolling forces is less than 8.29 % compared with those measured on-line in a hot strip rolling plant. Moreover, the formula forms of the three powers mentioned above are greatly simplified and improved.

Diallel analysis to choose parents for black bean (Phaseolus vulgaris L.) breeding.

In this study, conducted in two different seasons, we aimed to choose parents to obtain promising segregating populations for the extraction of black bean (Phaseolus vulgaris L.) lines that are superior in terms of disease resistance, plant architecture, and grain yield. Twelve parents were arranged in two groups to compose a partial diallel in a 5 x 7 scheme. Group 1 was composed of parents with black grains and erect plant architecture, while group 2 was composed of parents that had carioca grains and were resistant to the main fungal diseases that occur in the common bean. The following traits were evaluated: severity of angular leaf spot (ALS), plant architecture (PAG), and grain yield (YIELD). The data were analyzed according to a partial diallel model using parents and F1 hybrids. In the genetic control of ALS and PAG, additive effects were predominant, while for YIELD, additive effects were predominant in one season and dominance effects were in another season, because it is a more complex trait than ALS and PAG. For YIELD, we observed an interaction between general combining ability and specific combining ability between seasons. The genes that control ALS, PAG, and YIELD were in eight of the 12 parents evaluated in the diallel. The cultivar 'BRS Estilo' is suitable to use as a parent in common bean breeding in terms of ALS, PAG and YIELD. Recurrent selection is the most recommended option for simultaneously breeding for PAG, YIELD, and resistance to angular leaf spot in bean culture.

Elastic-plastic transitional stresses distribution and displacement for transversely isotropic circular disc with inclusion subject to mechanical load

Seth's transition theory is applied to the problems of mechanical load in a thin rotating disc by finite deformation. Neither the yield criterion nor the associated flow rule is assumed here. The results obtained here are applicable to compressible materials. If the additional condition of incompressibility is imposed, then the expression for stresses corresponds to those arising from Tresca yield condition. It has been observed that rotating disc made of isotropic material required higher angular speed to yield at the internal surface as compared to disc made of transversely isotropic materials. Effect of mechanical load in a rotating disc with inclusion made of isotropic material as well as transversely isotropic materials increase the values of angular speed yield at the internal surface. With the introduction of mechanical load rotating disc made of Beryl material required maximum radial stress as compare to disc made of Mg and Brass materials at the internal surface.

Effect of Some Environmental Factors on Incidence and Severity of Angular Leaf Spot of Cotton in Yola and Mubi, Adamawa State, Nigeria

Environmental factors such as relative humidity and rainfall generally have been found to increase the incidence, rate of spread and severity of diseases thereby reducing yield of crops. Study was conducted on five cotton varieties, which were artificially inoculated with bacterial blight pathogen to determine the effects of rainfall and relative humidity on incidence and severity of angular leaf spot (ALS) and yield of seed cotton in Yola and Mubi. Results showed that the severity of ALS was higher in Yola (58.65%) at 13 WAS assumed to be due to higher relative humidity range of 76% - 87% and low rainfall of 2 - 40.6 mm. This is assumed to have favoured disease development as against that of Mubi location which recorded lower severity (51.11%) due to lower relative humidity (42% - 55%) and rainfall (37 - 73 mm). Results further revealed that at 13 WAS, SAMCOT-8 had low incidence (66%) and severity (39%) in Yola. This was against the much higher corresponding incidence and severity of 82% and 42% respectively that was observed in Mubi during the same period. SAMCOT-10 and SAMCOT-9 varieties were found to be highly susceptible to the disease at the same period. SAMCOT-8 recorded the highest yield of 390.00 kg?ha?1 in Yola and 868.09 kg?ha?1 in Mubi while the lowest yields of 227.17 kg?ha?1 was observed on SAMCOT-10 in Yola while 461.61 kg?ha?1 was obtained on SAMCOT-9 in Mubi. The variation in yield among these varieties might be due to the differences in their reactions to the disease. There is a need to conduct further trials in these locations to confirm the level of resistance or other aspects of these varieties to the disease.

A Semi-Empirical Model for Tilted-Gun Planar Magnetron Sputtering Accounting for Chimney Shadowing

Integrated computational materials engineering (ICME) approaches to composition and thickness profiles of sputtered thin-film samples are the key to expediting materials exploration for these materials. Here, an ICME-based semi-empirical approach to modeling the thickness of thin-film samples deposited via magnetron sputtering is developed. Using Yamamura’s dimensionless differential angular sputtering yield and a measured deposition rate at a point in space for a single experimental condition, the model predicts the deposition profile from planar DC sputtering sources. The model includes corrections for off-center, tilted gun geometries as well as shadowing effects from gun chimneys used in most state-of-the-art sputtering systems. The modeling algorithm was validated by comparing its results with experimental deposition rates obtained from a sputtering system utilizing sources with a multi-piece chimney assembly that consists of a lower ground shield and a removable gas chimney. Simulations were performed for gun-tilts ranging from 0° to 31.3° from the vertical with and without the gas chimney installed. The results for the predicted and experimental angular dependence of the sputtering deposition rate were found to have an average magnitude of relative error of $$ 4.14\% \pm 3.02\% $$ for a 0°–31.3° gun-tilt range without the gas chimney, and $$ 2.12\% \pm 1.71\% $$ for a 17.7°–31.3° gun-tilt range with the gas chimney. The continuum nature of the model renders this approach reverse-optimizable, providing a rapid tool for assisting in the understanding of the synthesis-composition-property space of novel materials.

Ion fluence dependence of the total sputtering yield and differential angular sputtering yield of bismuth due to 50 keV argon ion irradiation

The dependences of the total sputtering yield of Bi and the differential angular distribution of these sputtered Bi atoms on the fluence of 50keV Ar+ ions at normal incidence have been experimentally measured. Polycrystalline Bi targets were used for these purposes. The collector technique and accurate current integration methods were adopted for the determination of angular distributions of sputtered Bi atoms. The ion fluence was varied from 1.9×1019 to 3.1×1020ions/cm2. The sputtered atoms were collected on high purity aluminum foils under ultra-high vacuum (∼5×10−9Torr). The collector foils were subsequently analyzed using heavy ion Rutherford backscattering spectroscopy. The shape of the angular distribution of sputtered atoms was found not to change significantly with the fluence, but the sputtering yield increased significantly from 2.2±0.2 to 9.6±0.6atoms/ion over the fluence range studied.

Time-resolved and integrated angular distributions of plume ions from silver at low and medium laser fluence

Laser impact on metals in the UV regime results in a significant number of ablated plume ions even at moderate fluence (0.7–2.4 J/cm2). The ablated particles are largely neutrals at the lowest fluence, but the fraction of ions increases strongly with fluence. The ion flow in different directions from a silver target irradiated by a laser beam at a wavelength of 355 nm in vacuum was measured with a hemispherical array of Langmuir probes. The time-of-flight spectra in all directions, as well as the total angular yield were determined. The angular distribution peaks strongly in forward direction with increasing fluence and can be well approximated by Anisimov’s model. Typically, the spectra of silver ions peak from 70 eV up to 145 eV in a direction close to the normal of the target surface with increasing fluence. With increasing observation angle, the time-of-flight spectra exhibit a peak at longer flight times, i.e., at a lower kinetic energy. At the highest fluence, the ionized fraction of the ablated particles in the plume increases up to 0.5.

Feature Profile Evolution During Etching of SiO2 in Radio-Frequency or Direct-Current Plasmas

We have developed a plasma etching simulator to investigate the evolution of pattern profiles in SiO2 material under different plasma conditions. This model focuses on energy and angular dependent etching yield (physical sputtering in this paper), neutral and ion angular distributions, and reflection of ions or neutrals on the surface of a photoresist or SiO2. The effect of positive charge accumulation on the surface of insulated mask or SiO2 is studied and the charge accumulation contributes to a deflection of ion trajectory. The wafer profile evolution has been simulated using a cellular-automata-like method under radio-frequency (RF) bias and direct-current (DC) bias, respectively. On the basis of the critical role of angular distribution of ions or neutrals, the wafer profile evolution has been simulated for different variances of angles. Observed microtrenching has been well reproduced in the simulator. The ratio of neutrals to ions has been considered and the result shows that because the neutrals are not accelerated by an electric field, their energy is much lower compared with ions, so they are easily reflected on the surface of SiO2, which makes the trench shallower.

Determination of the density of ultrathin La films in La/B4C layered structures using X‐ray standing waves

AbstractUsing simultaneous analysis of both the grazing incidence X‐ray reflectivity (GIXR) and the angular dependent fluorescence yield from ultrathin layer structures, the densities of thin La and LaN layers of 2–6 nm thickness enclosed by B4C layers have been determined with approximately 5% precision. The density of the La layer in these systems is found to be reduced to the bulk La value. This is explained by LaB6 interlayers formation. The density of LaN layers were similar to the bulk LaN value, which favors this compound as the most energetically stable in LaN/B4C layered systems.

Effects of the relationship between area under disease progress curve of angular leaf spot and yield of seed cotton in northeastern Nigeria

Bacterial blight induced by Xanthomonas campestris pv. malvacearum causes substantial yield losses of cotton in Nigeria annually. A field study was carried out for two seasons to investigate the reaction of a selection of 10 different cotton genotypes to bacterial blight and to examine the relationship between the area under disease progress curve (AUDPC) and the yield of seed cotton in the northeastern cotton region of Nigeria. All 10 genotypes reacted positively to the disease with SAMCOT-13 having the highest incidence particularly at Dowaya and Kem locations during the two seasons. This investigation also revealed that SAMCOT-13 and Ex-Benin had the highest AUDPC while TX-CDP37HH-1-83, TAMCOT CAMD-E and TAMCOT SP-21S had the lowest AUDPC indicating relative susceptibility and resistance, respectively. However, it was observed that TX-CDP37HH-1-83, SAMCOT-11 and Ex-Benin had the highest mean yields of 1441.5 kg/ha and 1494.7 kg/ha at Dowaya, Kem and Ngurore, respectively. The results also show a highly significant (P = 0.01) negative correlation between AUDPC and yield in the three locations. These findings suggest that TX-CDP37HH-1-83, TAMCOT CAMD-E and TAMCOT SP-21S are moderately resistant to the disease in view of their lower AUDPC and are considered promising.

Evaluation of zinc interstitial in Si-ion implanted ZnO bulk single crystals by a Rutherford backscattering study: An origin of low resistivity

The relation between low resistivity and Zn interstitial in ZnO single crystals implanted with the peak Si atomic concentration of 2.62 × 1020 cm−3 is studied by combining Rutherford backscattering spectroscopy/channeling, photoluminescence, and Van der Pauw methods. The variation in resistivity from ∼104 Ω cm for un-implanted ZnO to ∼10−3 Ω cm for as-implanted ones is observed. The lattice displacement of Zn atoms of ∼0.10 Å from the 〈0 0 0 1〉 row is estimated from the normalized angular yield profiles, preserving the single crystallinity in as-implanted ZnO with a minimum yield (χmin) of ∼11%. The low resistance is maintained by the 1000 °C annealing, accompanied with the lattice displacement of Zn atoms of ∼0.07 Å. These results suggest the existence of the shallow donor consisting of Zn interstitial and/or Zn interstitial-related complex corresponding to a newly appeared 3.33 eV-emission located at ∼40 meV from the bottom of the conduction band.