Range Of Deposition Rates Research Articles

Monte Carlo simulation of planar GaAs nanowire growth

The Monte Carlo model for the planar GaAs nanowire growth via the vapor–liquid-solid mechanism on GaAs substrate using a gallium droplet as a catalyst is realized. The effect of temperature, Ga and As2 deposition rates, substrate orientation and surface properties on the morphology of planar GaAs nanowires is considered. It is shown, that at the initial stages of nanowire growth, a 3D GaAs crystal is formed under a gallium droplet, which sets the nanowire growth direction. The range of temperatures and deposition rates of gallium and arsenic, which ensure the planar nanowire formation on the GaAs(111)A surface, is determined. The investigation of surface properties influence on the nanowire morphology showed that the arsenic diffusion influx into a gallium droplet is of critical importance for the planar GaAs nanowire growth. Ways for achieving a unidirectional growth of planar nanowires on singular and vicinal GaAs surfaces are proposed.

Proton Bragg curve and energy reconstruction using an online scintillator stack detector.

Real-time measurement and characterization of laser-driven proton beams have become crucial with the advent of high-repetition-rate laser acceleration. Common passive diagnostics such as radiochromic film (RCF) are not suitable for real-time operation due to time-consuming post-processing; therefore, a novel approach is needed. Various scintillator-based detectors have recently gained interest as real-time substitutes to RCF-thanks to their fast response for a wide range of dose deposition rates. This work introduces a compact, scalable, and cost-effective scintillator-based device for proton beam measurements in real-time suitable for the laser-plasma environment. An advanced signal processing technique was implemented based on detailed Monte Carlo simulations, enabling an accurate unfolding of the proton energy and the depth-dose deposition curve. The quenching effect was accounted for based on Birks' law with the help of the Monte Carlo simulations. The detector was tested in a proof-of-principle experiment at a conventional cyclotron accelerating protons up to 35MeV of energy. The signal comparison with a standard RCF stack was also performed during the test of the device, showing an excellent agreement between the two diagnostics. Such devices would be suitable for both conventional and laser-driven proton beam characterization.

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

The structure and volume of large geysers in Yellowstone National Park, USA and the mineralogy and chemistry of their silica sinter deposits

Siliceous sinter is formed by biogenic and abiogenic opal deposition around hot springs and geysers. Using Structure-from-Motion photogrammetry we generated three-dimensional models of Giant and Castle Geysers from the Upper Geyser Basin of Yellowstone National Park. We use these models to calculate an approximate mass of sinter for each (~2 and ~ 5 kton, respectively) and estimate a range of plausible long-term deposition rates for Castle Geyser (470 to 940 kg·yr−1). We estimate ~2% of the silica discharged from Castle Geyser is deposited as sinter in the cone and proximal terraces. We collected 15 sinter samples following the stratigraphy of each geyser from the older terrace to the younger cone and examined them using a variety of analytical methods. We find that young opaline sinter with high water content (<12 wt% from loss on ignition) contains higher concentrations of major and trace elements, notably As, Sb, Rb, Ga and Cs, relative to older dehydrated sinter. Rare earth element (REE) concentrations in sinter are 2–3 orders of magnitude higher than in the thermal water from which they are deposited. Sinter deposits are enriched in light REE, Gd and Yb when normalized to concentrations in thermal water and enriched in Eu, Tm, and Yb when normalized to the underlying rhyolite. Sinter samples with the highest REE concentrations are also enriched in organic material, implying either microbial uptake of REE, or that organic molecules are efficient ligands that form metal complexes.

How fast do submarine fans grow? Insights from the Quaternary Golo fans, offshore Corsica

Abstract High-resolution seismic, core, and chronological data from the Quaternary Golo deep-sea fans, offshore Corsica, France, give new insights into rates of submarine fan growth. Average vertical deposition rates for units that represent the Late Pleistocene glacial periods are 0.1–0.5 m/k.y. Glacial-age deposits are sand rich; in contrast, post-glacial deposits lack a significant sand fraction and are dominated by carbonate-rich mud. As a result, seismically constrained volumetric rates of deposition for glacial periods with low sea level and a subaerially exposed shelf are ∼0.23 km3/k.y., 2×–5× higher than rates during interglacials when sea level is high, the shelf is submerged, and sand is trapped in shallow-marine environments. At millennial time scales, variations in deposition rate reflect climate-driven sea-level changes, autogenic avulsion of river channels that extend across the shelf during low sea level, and autogenic avulsion of submarine channels that shift the locus of deposition laterally. Short-term deposition rates range from 8.6 m/k.y. at proximal portions of submarine fans to 0.4 m/k.y. along the distal fringe. Our data show that submarine fans can be dynamic environments with formation and evolution of levee-confined channels and lobe complexes in 103–104 yr, comparable to the time scales needed to form fluvial channel belts and delta lobes.

Conformal Growth of Ultrathin Hydrophilic Coatings on Hydrophobic Surfaces Using Initiated Chemical Vapor Deposition.

Hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) was deposited onto hydrophobic polytetrafluoroethylene (PTFE) surfaces using initiated chemical vapor deposition. By tuning the reactor conditions, the reaction kinetics were varied to achieve a wide range of deposition rates that spanned over 2 orders of magnitude (∼0.1-10 nm/min). Depositions rates at >1 nm/min were successful in overcoming the interfacial energy and wettability barriers between the hydrophobic and hydrophilic polymers and were found to achieve both conformal and ultrathin coatings. PHEMA coatings as thin as ∼10 nm over PTFE were able to transform a hydrophobic surface with a water contact angle of ∼110° to a hydrophilic one with an angle of ∼20°.

Hierarchical morphologies in co-sputter deposited thin films

Co-depositions of immiscible alloy films at specific processing conditions have yielded hierarchical microstructures which consist of distinct features at multiple length scales, often agglomerates and concentration modulations on the submicrometer scale and fine nanoprecipitates in a matrix on the nanoscale. The present work examined a series of immiscible alloy systems: Cu-Mo, Cu-Ag, Cu-Fe, Cu-Ta, Mo-Ag, Cu-Mo-Ag, to determine the kinetic conditions favorable for hierarchical organization and the formation mechanism of such structures. Thin films of six immiscible systems were sputter co-deposited over a range of deposition rates from 0.12 to 2 nm/s and various temperatures from 400 to 800\ifmmode^\circ\else\textdegree\fi{}C. The resulting microstructures indicate that hierarchical structures form with sufficient disparity in kinetic energy between the constituent atoms, one species being highly mobile ($A$) and the other relatively immobile ($B$). This condition arises typically at elevated deposition temperatures and reduced deposition rates but is also alloy dependent. The hierarchical structures form during deposition via phase separation and self-organization processes across the multiple length scales. The adatoms diffuse on the film surface with the highly mobile species swiftly agglomerating into $A$-rich domains within which $B$-rich nanoprecipitates form, often self-organizing into periodic arrays. The smallest $B$-rich nanoprecipitates in the $A$-rich domains are found to be coherent and in a metastable crystal structure ($B$ taking the structure of $A$), but coarser precipitates exhibit the equilibrium structure of the $B$ element. The $A$-rich domains are surrounded by a $B$-rich matrix that phase-separates into a concentration modulated structure. The observations are interpreted via a model incorporating material properties and process parameters.

Influence of chloride deposition rate on rust layer protectiveness and corrosion severity of mild steel in tropical coastal atmosphere

A field exposure test of mild steel was conducted in a real tropical coastal atmosphere with the range of chloride deposition rate between 100–600 mg Cl−/m2 day. The effect of the chloride deposition rate on the atmospheric corrosion behavior of mild steel was investigated by weight loss measurement, confocal laser scanning microscope (CLSM), scanning electron microscope (SEM), X-ray diffraction (XRD) technique and Pearson correlation coefficient method. Results indicated that a high chloride deposition rate would reduce the protective ability of rust layer due to the increasing of detrimental akaganeite (β-FeOOH) and maghemite (γ-Fe2O3) in the corrosion products. Also, the existences of β-FeOOH and γ-Fe2O3 induced severe corrosion pits on the underlying mild steel surface. Quantitatively, strong positive correlations were obtained among the chloride deposition rate, the corrosion rate and the protective ability index (PAI) of rust layer by means of Pearson correlation coefficient. Thus chloride deposition rate could be directly related to the protectiveness of rust layer as well as corrosion severity of mild steel in the tropical coastal atmosphere.

Molecular Orientation for Vapor-Deposited Organic Glasses Follows Rate-Temperature Superposition: The Case of Posaconazole.

The anisotropic properties of organic glasses produced by physical vapor deposition (PVD) depend upon substrate temperature and deposition rate. In recent work, it was shown for a liquid crystalline system that the anisotropic structure of the glass was controlled by a single combined variable as indicated by the observation of deposition rate-substrate temperature superposition (RTS). Here we test the utility of RTS for posaconazole, a molecule that does not form liquid crystals. We prepare glasses of posaconazole utilizing a range of deposition rates covering 2 orders of magnitude and an 18 K range in substrate temperature. We characterize the glasses using ellipsometry and X-ray scattering. Consistent with RTS, we find that decreasing the deposition rate has the same effect upon molecular orientation as increasing the substrate temperature during deposition. Thus, RTS can be used to predict and control the structure of glasses prepared at a wide range of deposition conditions. We use RTS to infer a characteristic time for molecular reorientation at the surface of posaconazole.

Cracks in the 3D-printed conductive traces of silver nanoparticle ink

Printing conductive traces of sinterable metallic nanoparticle (NP) based inks is one of the key components of 3D additively manufactured (printed) electronic circuits. In this study, we employ 3D aerosol jet printing to print conductive traces of silver NP based ink and provide insights into the risk of cohesive longitudinal cracking inside the printed and sintered traces. This was investigated for a wide range of carrier and sheath gas flow rates, which implies a wide range of particle deposition rates and velocities. These cracks appear for both single and double pass traces that are several microns in height and hundreds of microns in width. We examine different sources of stress that could be the potential driver for the cracking and infer that the most likely source is the classical capillary-pressure-driven crack formation mechanism for the evaporating NP-based thin films. Most importantly, this hypothesis raises the possibility of crack formation at several locations of the NP-based conductive traces printed using an extremely popular recent technique for printed electronics, AJP.

Elektronenstrahlverdampfen von Silizium

SummaryElectron beam evaporation of siliconHigh rate electron beam evaporation of silicon is a versatile technique to deposit silicon layers with tailored properties on large areas in a cost effective manner. A unique feature of the process is the wide range of deposition rates that can be selected. This technique allows for the deposition of nanometer thin layers with high reproducibility on the one hand, on the other hand layers with thicknesses of several tens of micrometers and low film stress can be deposited within minutes. Due to the high quality of the deposited silicon it is possible to form ultra‐thin layers as contacts in solar cells or for TFT applications or several 10 micrometer thick films as absorbers in LPC solar cells or as “construction” material for MEMS. This article reports on the deposition process, the material properties and illustrates the applicability based on examples from our current research activities.

Limited surface mobility inhibits stable glass formation for 2-ethyl-1-hexanol.

Previous work has shown that vapor-deposition can prepare organic glasses with extremely high kinetic stabilities and other properties that would be expected from liquid-cooled glasses only after aging for thousands of years or more. However, recent reports have shown that some molecules form vapor-deposited glasses with only limited kinetic stability when prepared using conditions expected to yield a stable glass. In this work, we vapor deposit glasses of 2-ethyl-1-hexanol over a wide range of deposition rates and test several hypotheses for why this molecule does not form highly stable glasses under normal deposition conditions. The kinetic stability of 2-ethyl-1-hexanol glasses is found to be highly dependent on the deposition rate. For deposition at Tsubstrate = 0.90 Tg, the kinetic stability increases by 3 orders of magnitude (as measured by isothermal transformation times) when the deposition rate is decreased from 0.2 nm/s to 0.005 nm/s. We also find that, for the same preparation time, a vapor-deposited glass has much more kinetic stability than an aged liquid-cooled glass. Our results support the hypothesis that the formation of highly stable 2-ethyl-1-hexanol glasses is inhibited by limited surface mobility. We compare our deposition rate experiments to similar ones performed with ethylcyclohexane (which readily forms glasses of high kinetic stability); we estimate that the surface mobility of 2-ethyl-1-hexanol is more than 4 orders of magnitude less than that of ethylcyclohexane at 0.85 Tg.

Tailoring Si(100) substrate surfaces for GaP growth by Ga deposition: A low-energy electron microscopy study

For GaP-on-Si(100) heteroepitaxy, currently considered as a model system for monolithic integration of III–V semiconductors on Si(100), the surface steps of Si(100) have a major impact on the quality of the GaP film. Monoatomic steps cause antiphase domains in GaP with detrimental electronic properties. A viable route is to grow the III–V epilayer on single-domain Si(100) with biatomic steps, but preferably not at the expense of reduced terrace widths introduced by miscut substrates. We have performed in situ investigations of the influence of Ga deposition on the kinetics of surface steps and terraces of Si(100) at substrate temperatures above 600 °C by low-energy electron microscopy. Starting from nearly equally distributed TA and TB terraces of a two-domain Si(100) surface, submonolayer deposition of Ga results in a transformation into a surface dominated by TA terraces and biatomic DA steps. This transformation is reversible, and Si(100) with monoatomic steps is recovered upon termination of the Ga flux. Under conditions of higher coverages (but still below 0.25 monolayer), we observe restructuring into a surface with TB dominance, similar to the findings of Hara et al. [J. Appl. Phys. 98, 083515 (2005)]. The occurrence and mutual transformations of surface structures with different terrace and step structures in a narrow range of temperatures and Ga deposition rates is discussed.

Deposition of transparent indium tin oxide electrodes by magnetron sputtering of a metallic target on a cold substrate

Indium tin oxide layers with a surface resistance of 50 Ω/□ and a transmission in the visible range of up to 100% are obtained by magnetron sputtering of a metallic target on a cold substrate without ion enhancement of deposition and subsequent annealing. It is shown that the above parameters of the layers can be achieved in a wide range of oxygen partial pressures by controlling the deposition rate and in a wide range of deposition rates by controlling the oxygen partial pressure. An unambiguous dependence of the deposition rate on the oxygen partial pressure in the chamber is constructed.

Highly uniform arrays of epitaxial Ge quantum dots with interdot spacing of 50 nm

Abstract

Growth of shape controlled silicon nanowhiskers by electron beam evaporation

We investigated the effect of the deposition rate on the surface morphology of Si nanowhiskers (NW) deposited by e-beam evaporation using the vapor-liquid-solid growth mechanism. The roles of deposition rate and corresponding surface diffusion on the Si NW growth kinetics were examined. Two growth regimes were observed within the investigated range of deposition rates. Films belonging to these two regimes were found to have characteristically different formations and surface morphologies. We found that the length-diameter curves of NWs switch from decreasing to increasing at a certain critical evaporation rate. The surface morphology is composed of long whiskers (~1 μm) tapered with faceted sidewalls in the high deposition rate regimes (above 1.2 A/s) due to their length which is comparable with the adatom diffusion and the direct adsorption of Si atoms on the sidewalls. The characteristic morphology was composed of shorter straight whiskers in the low deposition rate regimes (0.6–1 A/s) because of the higher contribution of Si adatoms diffusing from the substrate to the NW growth.

Linking ice sheet and lake sediment archives of 10Be, 1468–1980 CE

As part of understanding and reconstructing our climate history it is important to investigate the link between climate and solar activity. Ice cores and ocean sediments have provided information on a range of timescales on atmospheric 10Be production, which is a proxy for past solar activity due to its cosmogenic nature of production. We here present results from the first, to our knowledge, multi-centennial and annual resolution study of 10Be in varved lake sediments.Varves were sampled over an interval covering the period 1468–2006 CE in sediment cored from Lake Lehmilampi in eastern Finland. The measured concentrations were converted into annual 10Be deposition rates by using the weights of dried samples as an estimation of sedimentation rates and scaling the result from sampling to catchment area size. We compare the lake catchment 10Be deposition rates to those derived from the Greenlandic ice cores NGRIP and Dye-3 along with past solar activity.Sediment 10Be concentrations range 2.1–17.6×108atomsg−1. The high end of this range is represented by a limited number of samples, and the average is near the lower end at 4.1×108atomsg−1. The deposition rates range 0.5–3.9×106atomscm−2year−1, with an average of 1.8×106atomscm−2year−1 (0.057atomscm−2s−1). We note higher 10Be deposition during the Spörer (∼1415–1535 CE) and Maunder (∼1645–1715 CE) solar minima, and also at the onset of the Dalton (∼1790–1830 CE) minimum. Equally high 10Be values in the 1840s and lower deposition during the Dalton minimum are not consistent with contemporaneous solar activity. Although this may in part be a result of incomplete measurements in the 19th century, it also shows the complexity of deposition and the intricacy of reconstructing past solar activity from sediment 10Be data. A comparison with ice core data reveals particularly good agreement between sediment and Dye-3 10Be flux around 1500–1750 CE.

Estimated range of black carbon dry deposition and the related snow albedo reduction over Himalayan glaciers during dry pre-monsoon periods

One of the major factors attributed to the accelerated melting of Himalayan glaciers is the snow darkening effect of atmospheric black carbon (BC). The BC is the result of incomplete fossil fuel combustion from sources such as open biomass burning and wood burning cooking stoves. One of the key challenges in determining the darkening effect is the estimation uncertainty of BC deposition (BCD) rate on surface snow cover. Here we analyze the variation of BC dry deposition in seven different estimates based on different dry deposition methods which include different atmospheric forcings (observations and global model outputs) and different spatial resolutions. The seven simulations are used to estimate the uncertainty range of BC dry deposition over the southern Himalayas during pre-monsoon period (March–May) in 2006. Our results show BC dry deposition rates in a wide range of 270–4700 μg m−2 during the period. Two global models generate higher BC dry deposition rates due to modeled stronger surface wind and simplification of complicated sub-grid surface conditions in this region. Using ice surface roughness and observation-based meteorological data, we estimate a better range of BC dry deposition rate of 900–1300 μg m−2. Under dry and highly polluted conditions, aged snow and sulfate-coated BC are expected to possibly reduce visible albedo by 4.2–5.1%. Our results suggest that for estimating aerosol-induced snow darkening effects of Himalaya snowpacks using global and regional models, realistic physical representation of ice or snow surface roughness and surface wind speed are critical in reducing uncertainties on the estimate of BC deposition over snow surface.

Sputter deposition of semicrystalline tin dioxide films

Tin dioxide is emerging as an important material for use in copper indium gallium diselenide based solar cells. Amorphous tin dioxide may be used as a glass overlayer for covering the entire device and protecting it against water permeation. Tin dioxide is also a viable semiconductor candidate to replace the wide band gap zinc oxide window layer to improve the long-term device reliability. The film properties required by these two applications are different. Amorphous films have superior water permeation resistance while polycrystalline films generally have better charge carrier transport properties. Thus, it is important to understand how to tune the structure of tin dioxide films between amorphous and polycrystalline. Using X-ray diffraction (XRD) and Hall-effect measurements, we have studied the structure and electrical properties of tin dioxide films deposited by magnetron sputtering as a function of deposition temperature, sputtering power, feed gas composition and film thickness. Films deposited at room temperature are semicrystalline with nanometer size SnO2 crystals embedded in an amorphous matrix. Film crystallinity increases with deposition temperature. When the films are crystalline, the X-ray diffraction intensity pattern is different than that of the powder diffraction pattern indicating that the films are textured with (101) and (211) directions oriented parallel to the surface normal. This texturing is observed on a variety of substrates including soda–lime glass (SLG), Mo-coated soda–lime glass and (100) silicon. Addition of oxygen to the sputtering gas, argon, increases the crystallinity and changes the orientation of the tin dioxide grains: (110) XRD intensity increases relative to the (101) and (211) diffraction peaks and this effect is observed both on Mo-coated SLG and (100) silicon wafers. Films with resistivities ranging between 8mΩ cm and 800mΩ cm could be deposited. The films are n-type with carrier concentrations in the 3×1018cm−3 to 3×1020cm−3 range. Carrier concentration decreases when the oxygen concentration in the feed gas is above 5%. Electron mobilities range from 1 to 7cm2/Vs and increase with increasing film thickness, oxygen addition to the feed gas and film crystallinity. Electron mobilities in the 1–3cm2/Vs range can be obtained even in semicrystalline films. Initial deposition rates range from 4nm/min at low sputtering power to 11nm/min at higher powers. However, deposition rate decreases with deposition time by as much as 30%.

The Deposition Rate of Ti Film by Plasma

Ti film on AISI 201 was prepared by plasma. The film was characterized by SEM. Their deposition rates were measured by measure the mess of Ti film(m) and the preparation time(t). SEM show that the more time is, the thicker Ti films is. The stronger power is, the thicker Ti films is. And the far the distance is, the more thin Ti films is. It was found that the deposition rates range from 0.02 mg.min-1 to 0.025 mg.min-1 at the area of 6.25cm2. The deposition rate of titanium film change with the deposition power range from 0.021 mg.min-1 to 0.163 mg.min-1. The deposition rate of titanium film change with the deposition power range from 0.096 mg.min-1 to 0.130 mg.min-1. The deposition rate of titanium film change with the deposition negative bias range from 0.008 mg.min-1 to 0.02mg.min-1 at the area of 6.25cm2.