Decrease In Deposition Rate Research Articles

Laboratory assessment of the mobility of water-dispersed engineered nanoparticles in a red soil (Ultisol)

Soils are major sinks of engineered nanoparticles (ENPs) as results of land applications of sewage sludge, accidental spills, or deliberate applications of ENPs (e.g., nano-pesticides). In this study, the transport behaviors of four widely used ENPs (i.e., titanium dioxide [TiO2], buckminsterfullerene [C60], single-walled carbon nanotube [SWNT], and elemental silver [Ag0]) were investigated in water-saturated columns packed with either a quartz sand, a red soil (Ultisol), or sand/soil mixtures with soil mass fraction (λ) from 0% to 100% at slightly acidic solution pH (4.0–5.0). The mobility of tested ENPs decreased significantly with increasing λ, which was attributed to increased surface area and/or retention sites imparted by iron oxides, clay minerals, and organic matter in the red soil. Breakthrough curves of all ENPs exhibited blocking effects (decreasing deposition rate over time) and were well-described using an unfavorable and favorable, two-site kinetic attachment model accounting for random sequential adsorption on the favorable site. Modeled maximum retention capacity and first-order attachment rate coefficient on the favorable site both increased linearly with increasing λ, suggesting that transport parameters of ENPs in natural soils may be accurately extrapolated from transport parameters in the sand/soil mixtures. In addition, the mobility of three negatively charged ENPs (C60, SWNT, and Ag0 NPs) was reversely correlated with their average hydrodynamic diameters, highlighting that the average hydrodynamic diameter of negatively charged ENPs is the dominant physicochemical characteristics controlling their mobility in the Ultisol.

Simulation of self-developed vertical HVPE system for growth of aluminium nitride

To understand the mechanism of aluminium nitride (AlN) film growth is of great importance for its potential applications. In this paper, we investigate the growth behaviour of the AlN film by using the computational fluid dynamics program FLUENT. It is found that the gas flow has a great impact on the temperature field. By equipping the aluminium boat area with a graphite ring and adjusting the heating power appropriately, the desired temperature field can be achieved. The simulation also shows that the V/III can have a significant impact on the deposition behaviour. With a V/III of 10, the trend of the curve is abnormal which is significantly different from the other curves. The distance between the inlet and the substrate is changed. It is found that with the increasing distance, AlN deposition rate decreases and the uniformity becomes better. Besides, when the operating pressure is changed, it is found that the operating pressure can also greatly affect the temperature field.

Coupled effects of hydrodynamic and solution chemistry on long-term nanoparticle transport and deposition in saturated porous media

This study aims to systematically explore the coupled effects of hydrodynamic and solution chemistry conditions on the long-term transport and deposition kinetics of nanoparticles (NPs) in saturated porous media. Column transport experiments were carried out at various solution ionic strengths (IS), ionic composition, and flow velocities utilizing negatively charged carboxyl-modified latex NPs of two different sizes (50 and 100nm). These experiments were designed to obtain the long-term breakthrough curves (BTCs) in order to unambiguously determine the full deposition kinetics and the fraction of the solid surface area (Sf) that was available for NP deposition. The BTCs exhibited a bimodal shape with increasing solution IS; i.e., BTCs were initially delayed, next they rapidly increased, and then they slowly approached the influent particle concentration. NP deposition was much more pronounced in the presence of Ca2+ than Na+ at any given solution IS. Deposition kinetic of NPs was successfully simulated using a two-site kinetic model that accounted for irreversible deposition and blocking on each site, i.e., a decreasing deposition rate as the site filled. Results showed that Sf values were controlled by the coupled effects of flow velocity, solution chemistry, and particle size. Data analyses further demonstrated that only a small fraction of sand surface area contributed in NP deposition even at the highest IS (60mM) and lowest flow velocity (1m/day) tested. Consistent with previous studies, our results imply that NP deposition is controlled by physicochemical interactions between the NPs and nanoscale physical and/or chemical heterogeneities on the sand surfaces that produce localized nanoscale favorable sites for deposition. Furthermore, our results suggest that the NP interactions with the collector surfaces tended to strengthen with increasing contact time.

N 2 流量对HIPIMS制备TiSiN涂层结构和力学性能的影响

Over the past years, TiSiN coatings have gained increasing importance in the field of cutting tool coatings due to its enhanced hardness and superior oxidation resistance properties produced by the nanocomposite microstructure of TiN nanocrystals embedded in an amorphous Si3N4 matrix. Many methods have been developed to prepare TiSiN coatings, typically named by the DC magnetron sputtering (DCMS) technique and cathodic arc ion plating (AIP), whereas limited studies have been carried out on the deposition of nanocomposite coatings using the high power impulse magnetron sputtering (HIPIMS) approach. The TiSiN coatings were reactively magnetron sputtered in mixed Ar/N-2 precursor gases in a new BERMS system with different flow rate of N-2 in this work. The deposition rate, crystal structure, composition, surface morphology, microstructure and mechanical properties were investigated systematically by surface profilometer, XRD, XPS, SPM, SEM, HRTEM and nano-indentation and the plasma discharge also was studied. The results show that increasing the flow rate of N-2 caused the decrease of deposition rate as expected, accompanying with the change of preferred orientation from (200) orientation to (220) orientation and the decreased compactness, discharge degree and ionization rate. Contrary to the changes of Ti content, Si content gradually increased with increasing the flow rate of N-2, but their changing scale were small. Combined with XRD and XPS analysis, the results indicated that the coatings were composed of crystalline TiN, amorphous Si3N4 and free Si. Besides, free Si disappeared with further increasing the flow rate of N-2. This nanocomposite structure can ultimately be assessed by HRTEM where individual grains and the amorphous regions can be distinguished. In addition, the grain size increased gradually with increasing the flow rate of N-2. Furthermore, both the hardness and elastic modulus linearly decreased with increasing the flow rate of N-2.

Liquid Ink Deposition from an Atomic Force Microscope Tip: Deposition Monitoring and Control of Feature Size

The controlled deposition of attoliter volumes of liquid inks may engender novel applications such as targeted drug delivery to single cells and localized delivery of chemical reagents at nanoscale dimensions. Although the deposition of small organic molecules from an atomic force microscope tip, known as dip-pen nanolithography (DPN), has been extensively studied, the deposition of liquid inks is little understood. In this work, we have used a set of model ink-substrate systems to develop an understanding of the deposition of viscous liquids using an unmodified AFM tip. First, the growth of dot size with increasing dwell time is characterized. The dynamics of deposition are found to vary for different ink-substrate systems, and the change in deposition rate over the course of an experiment limits our ability to quantify the ink-transfer dynamics in terms of liquid properties and substrate wettability. We find that the most critical parameter affecting the deposition rate is the volume of ink on the cantilever, an effect resulting in a 10-fold decrease in deposition rate (aL/s) over 2 h of printing time. We suggest that a driving force for deposition arises from the gradient in Laplace pressure set up when the tip touches the substrate. Second, the forces acting upon the AFM cantilever during ink deposition were measured in order to gain insight into the underlying ink-transfer mechanism. The force curve data and simple geometrical arguments were used to elucidate the shape of the ink meniscus at the instant of deposition, a methodology that may be used as an accurate and real-time means of monitoring the volume of deposited dots. Taken together, our results illustrate that liquid deposition involves a very different transfer mechanism than traditionally ascribed to DPN molecular transport.

Grain growth and complex stress evolution during Volmer–Weber growth of polycrystalline thin films

Volmer–Weber growth of polycrystalline thin films involves poorly understood kinetic processes that occur far from equilibrium and lead to complex co-evolution of the surface, microstructure and intrinsic stress of the films. Here we present a comprehensive study consisting of in situ stress measurements, microstructure characterization and analytical modeling for various metallic films that grow by the Volmer–Weber mechanism. We find that, under conditions of intermediate atomic mobility, stress evolution after coalescence involves a turnaround from a compressive to a tensile stress state. The thickness at which the stress turnaround is observed increases as the substrate temperature increases or the deposition rate decreases. We show that this phenomenon is associated with two competing mechanisms: grain growth during deposition (at homologous temperatures as low as 0.17) and adatom attachment to surface sites at grain boundaries. Grain growth during film deposition not only causes a tensile component of the intrinsic stress, but also leads to changes in the magnitude of the compressive stresses, from being independent of, to scaling with, the inverse of the grain size. Analyses of these phenomena lead to insights into stress evolution under conditions of low and high atomic mobility, as well as intermediate mobility, and are general for stress evolution during Volmer–Weber growth of polycrystalline films.

Effects of Bias on Optical and Chemical Bonding Properties of Germanium Carbon Films

Amorphous hydrogenated Ge1-xCx films are prepared by radio frequency (RF) magnetron cosputtering using Ge/graphite composite target and their composition, optical and chemical bonding properties as a function of bias have been investigated. The results show a decrease in the deposition rate with increasing bias, and the optical gap nearly keep constant due to effects of both composition and chemical bonding. Through the analysis of X-ray photoelectron spectroscopy, we find that the content of Ge-C bonds first increases and then decreases as increasing bias while the Ge-O bond decreases monotonically.

Asymptotic characteristics of particulate deposit formation in exhaust gas recirculation (EGR) coolers

The objective of this research is to shed some light into the asymptotic behavior of fouling process in EGR coolers based on a theoretical hypothesis that is verified experimentally. This is important for a successful simulation of particulate fouling in EGR coolers and to develop appropriate fouling mitigation approach. The experimental results showed that the development of fouling layer causes i) the thermal resistance of the fouling layer to increase as well as decreased temperature difference between the gas side and the fouling layer, which subsequently decreases the deposition rate, ii) the tube cross-sectional area to decrease thus the average gas-side temperature increases, consequently the gas velocity and deposit removal would increase. At a certain moment of time a balance occurs between the decreasing deposition rate and the increasing removal rate such that the fouling process ceases and an asymptotic behavior is approached.

Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)

Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films.

Simulation of a new style vertical HVPE system

In this paper, we simulate a new style vertical HVPE reactor by using computational fluid dynamics program FLUENT. In order to find the best parameter on the growth rate of Gallium nitride (GaN), we change the distance between the inlet and the substrate, GaCl and NH3 inlets, and also we add substrate rotation, separately. With the increase of the distance between the substrate and the gas inlet, GaN deposition rate decreases and the uniformity becomes better. The results show that the optimal distance in this new-style vertical hydride vapour phase epitaxy (HVPE) system is 4 cm. Besides, as the distance between the GaCl inlet and the NH3 inlet changes, the uniformity of GaN deposition varies. Our findings indicate that the optimal distance is 3 cm. Furthermore, it is found that substrate rotation also affects the growth rate of GaN.

Investigations on tailoring the deposition conditions in HIPIMS by varying the pulse durations and the argon partial pressure

In most cases HIPIMS is used to get the highest possible ionisation of the deposition particles, which is realised by pulse durations with short on- and very long off-times. These conditions are combined with a more or less pronounced decrease in deposition rate. In this work the pulse configuration has been varied. A three dimensional matrix of parameters was spanned, made of 3 on- and 3 off-times at 4 argon partial pressures. The average power was kept constant and the data achieved were additionally compared to DC-magnetron sputtering. The experiments were carried out using 50 mm diameter targets made of Ti, powered by a MELEC SPIK1000A pulser unit. The deposition rate was measured by quartz microbalance mounted in front of the target. Peak current density and target voltage were recorded and time averaged optical emission spectroscopy (t.a.OES) measurements provided information about the ionisation conditions in the plasma. The results of the data analysis provide a coherent overview of the impact of the HIPIMS parameters as well as of their complex interrelations.

Sequential recovery of uranium oxides by electrolysis of M2WO4-M2W2O7-UO2WO4 melts (M = Li, Na, K, Cs)

The effect of the electrolyte composition and solvent salt cation on the oxygen coefficient of the cathode product (O/U atomic ratio) and on the main characteristics of potentiostatic electrolytic deposition of UO2 (cathode current efficiency, current density, product deposition rate) in sequential recovery of uranium oxides from electrolytes of the system M2WO4-M2W2O7-UO2WO4 (M = Li, Na, K, Cs) in air was examined. The dependence of the oxygen coefficient of the cathode product on the electrolyte composition and solvent salt cation does not differ essentially from that observed previously in short experiments with low melt depletion of U. The current efficiency, initial current density, and product deposition rate decrease with the electrolyte depletion of U. The results obtained are satisfactorily accounted for in terms of the model of ionic composition of uranyl-containing oxide salt electrolytes, based on the concept of complexation and stepwise solvolysis of uranyl ions, taking into account formation of lower valence forms of U due to chemical corrosion of the cathode product.

Effects of Residence Time and Reaction Conditions on the Deposition of SiC from Methyltrichlorosilane and Hydrogen

The overall growth kinetics of silicon carbide films deposited from the mixture of methyltrichlorosilane (MTS) and hydrogen were determined by a magnetic suspension microbalance. The results show that three regions are distinguishable in the studied temperature range. In low temperatures (<1000°C), the deposition process is controlled by surface chemical reaction mechanism. The deposition rate has a weak dependence on temperature, and the activation energy is 188 kJ/mol. In mediate temperatures (1100°–1300°C), the deposition rate rapidly increases with increasing temperature, and the activation energy is 100 kJ/mol. The transition temperature of the above two deposition mechanisms lies in 1000°–1100°C. The complex relation between the deposition rate and total pressure can be explained by these two reaction mechanisms, depending on the competition between the residence time and concentrations of precursors. Both the flow rate and the distance into the chemical vapor deposition reactor strongly influence the reactivity. Longer residence time and larger distance of the substrate in reactor lead to decreasing deposition rate, mainly due to the reactant depletion on the wall, decomposition of MTS as well as the concentration of HCl.

Influence of pulsed substrate bias on the structure and properties of Ti–Al–N films deposited by cathodic vacuum arc

Ti–Al–N films were deposited by cathodic vacuum arc (CVA) technique in N2 atmosphere with different pulsed substrate bias. The influence of pulsed substrate bias (0 to −800V) on the deposition rate, surface morphology, crystal structure, and mechanical properties of the Ti–Al–N films were systematically investigated. Increasing pulsed bias voltage resulted in the decrease of deposition rate but the increase of surface roughness. It was found that there was a strong correlation between the pulsed bias and film structure. All the films studied in this paper were composed of TiN, AlN, and Ti–Al–N ternary phases. The grains changed from equiaxial to columnar and exhibited preferred orientation when the pulsed bias increased. With the increase of pulsed bias voltage, the atomic ratio of Ti to Al element increased gradually, while the N to (Ti+Al) ratio decreased. The composite films present an enhanced nanohardness compared with binary TiN and ZrN films. The film deposited with pulsed bias of −200V possessed the maximum scratch critical load and nanohardness. The minimum friction coefficient with pulsed bias of −300V was obtained.

Titanium nitride as promising gate electrode for MOS technology

AbstractTitanium nitride (TiN) films have been grown on Si (100) substrates by DC. reactive magnetron sputtering from a titanium (Ti) metallic target at different nitrogen partial pressures (80–10 sccm) and different power (500–1500 W). The effects of the nitrogen pressure and power on structural and electrical properties of TiN films were investigated by measuring their X‐ray diffraction (crystal orientation), Atomic Force Microscopy (surface roughness), four‐probe technique (electrical resistivity) and film thickness. It is show that deposition rate (13–65 nm/min) decrease with an increase of nitrogen pressure. The films have the grain size (0.001–0.027 μm2) along the sample surface and the size of the grain increase with an increase of nitrogen partial pressure. The X‐ray diffraction measurement show that films were crystalline (with preferred orientation (311)), but some of them were polycrystalline ((311) and (111) preferred orientation). These films have been used as gate electrodes in MOS capacitors, which were fabricated with TiN and SiNxOy as gate electrode and dielectric, respectively. With 20 minutes of annealing time, the extracted TiN work function and flat‐band voltage were about 4.65 eV and ‐0.29 V, which indicates that TiN can be used as mig‐gap electrode for MOS technology. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Anomaly of film porosity dependence on deposition rate

This letter reports an anomaly of film porosity dependence on deposition rate during physical vapor deposition – the porosity increases as deposition rate decreases. Using glancing angle deposition of Cu on SiO2 substrate, the authors show that the Cu film consists of well separated nanorods when the deposition rate is 1 nm/s, and that the Cu films consists of a more uniform film when the deposition rate is 6 nm/s; all other deposition conditions remain the same. This anomaly is the result of interplay among substrate non-wetting, density of Cu nuclei on the substrate, and the minimum diameter of nanorods.

EFFECTS OF INTERELECTRODE SPACING ON THE PROPERTIES OF MICROCRYSTALLINE SILICON ABSORBER AND SOLAR CELLS

ABSTRACTWe study the effect of the spacing between electrodes in very high frequency plasma enhanced chemical vapor deposition on the properties of microcrystalline silicon films and their related n-i-psolar cells. We vary the spacing from 0.2 to 1.0 cm to deposit microcrystalline silicon at 67.8 MHz while maintaining other growth parameters. The spacing between the electrodes significantly changes the plasma conditions, which govern film precursor chemistry as well as introduce etching and ion bombardment to the film; thereby, influencing nucleation and growth of the microcrystalline Si films. The resulting films were characterized by UV-Vis spectrometry, atomic force microscopy, X-ray diffraction, and transmission electron microscopy. We found that deposition rate decreases, while surface roughness and short circuit current density increase with smaller spacing.

Optical and Electrical Properties of Nitrogen-Doped Diamond-Like Carbon Films Prepared by a Bipolar-Type Plasma-Based Ion Implantation

Diamond-like carbon (DLC) films are prepared by a bipolar-type plasma-based ion implantation (PBII) technique using toluene and nitrogen gases (N2), and the optical and electrical properties are examined as a function of N2 flow rate. The N concentration in the films and structural changes are also examined by Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM), and Raman spectroscopy. It is found that the deposition rate decreases, but N concentration linearly increases with increasing N2 flow rate. Granular surfaces are observed and the grains decreases in size as N2 flow rate increases. In addition, Raman analysis suggests that aromatic ring clusters and the amorphous structure increase in amount. The optical band gap and conductivity increase with increasing N concentration up to about 11 at. %, and then decrease with further increase in N concentration.

Effect of circulating solution volume on codeposition process of two metals within porous electrode at high flow rate

The effect of the solution volume and deposition potential on the dynamics and final parameters of the deposition process was studied using a mathematical model of codeposition of the two metals within a one-dimensional flow porous electrode (PE). The initial PE characteristics, kinetic parameters of the overall polarization curve, and volume solution flow rate were fixed. It was found that a decrease in the solution volume at a high flow rate apart from the expected consequences (a decrease in the metal deposition rate in time and an increase in the time of the porous matrix filling by the deposit) results in a significant improvement of the uniformity of distribution of electropositive component M1 and a dramatic extension of the deposition region of electronegative component M2. The positive effect of a decrease in the solution volume is enhanced at an increase in the cathodic potential and the closing in of partial currents of the deposited metals. Eventually, these conditions provide simultaneously a high rate of metal recovery and maximum PE filling by the cathodic deposit.

Recent advances in modulated pulsed power magnetron sputtering for surface engineering

Over the past 10 years, the development of high-power pulsed magnetron sputtering (HPPMS) has shown considerable potential in improving the quality of sputtered films by generating a high degree of ionization of the sputtered species to achieve high plasma density by using pulsed, high peak target power for a short period of time. However, the early HPPMS technique showed a significantly decreased deposition rate as compared to traditional magnetron sputtering. Recently, an alternative HPPMS deposition technique known as modulated pulsed power (MPP) magnetron sputtering has been developed. This new sputtering technique is capable of producing a high ionization fraction of sputter target species and while at the same time achieving a high deposition rate. This paper is aimed at giving a review of recent advances in the MPP technique in terms of the plasma properties, the improvements in the structure and properties of the thin films, and the important advances in the high rate deposition of high quality thick coatings on the order of 20–100 μm in thickness.