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Radio Frequency Magnetron-Sputtered Germanium Nanoislands
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2019
Alireza Samavati, Ahmad Fauzi Ismail
The 3D AFM images of six different samples are illustrated in Figure 17.30. During sputtering process, the sputtering power and the gas pressure significantly effect the deposition rate and the properties of the deposited film. Gas pressure plays an important role in the probability of the collision between sputtered atom and background gas particles. Increasing the Ar flow rate causes the increment of ambient pressure, decrement of the self-bias potential on the substrate, and decrement of the average energy of the ion bombardment (Huang et al., 2009). In the extremely high pressure with high density of Ar atoms, the number of collisions between the Ar atoms and the sputtered atoms is increased. This causes to lose the energy of sputtered atoms and consequently a decrement in the growth rate. At a lower working pressure, atoms transport at a longer mean free path. Hence, at a higher working-gas pressure, the created film is expected to have a higher deposition rate. However, a lower sticking coefficient can be obtained in a lower working pressure. Thus, an optimal value of the pressure of working gas could be determined, under which the highest deposition rate, number density, and small size distribution occur.
Adhesion of Metal Films to Polyimides
Published in Malay K. Ghosh, K. L. Mittal, Polyimides Fundamentals and Applications, 2018
Luis J. Matienzo, William N. Unertl
Evaporation methods rely on the thermal evaporation of metal atoms and their condensation onto a substrate usually placed at ground potential. Since the distribution of evaporated atoms is Gaussian, the substrate must be rotated or moved in order to obtain a film with more uniform coverage. It is important to remember that each atom capable of landing on the substrate surface does not automatically adhere since it can also be reflected into the vacuum. Thus, evaporated atoms have a finite probability of sticking onto the substrate surface. This term is known as the sticking coefficient and it is dependent on some substrate characteristics such as its composition, crystal structure, temperature, and impurity level.
Sorption
Published in Igor Bello, Vacuum and Ultravacuum, 2017
Surface particles of solids exert attractive forces on gas molecules when they approach the surface. An incident molecule may be adsorbed by the surface, when its energy, in the direction of velocity normal to the surface, is given up to the surface, while the other portion of its energy may still be retained by molecules in the tangential velocity direction. At an incomplete energy exchange between the molecule and surface, the molecule can only be captured by physisorption in a shallow van der Waals potential well. In such a case, the molecule is not in its final adsorption site yet. The efficiency of capturing molecules in physisorption wells is expressed by the initial sticking coefficient, which is the ratio of the condensed molecular flux density and the molecular flux density impinging on the surface at the given temperature. The initial sticking coefficient on metal surfaces is close to one for most gases. Chemisorption, whose sorption efficiency is given by the sticking coefficient, is usually a successive process of physisorption. The sticking coefficient is the ratio of the capture rate of molecules on the surface chemisorption sites distributed over an area of unity and the total molecular flux density impinging on that surface area. The value of sticking coefficient is smaller than that of the initial sticking coefficient. The values of sticking coefficients may reduce with the increase in occupation of chemisorption sites. The initial sticking coefficients can have very different values,325 for example, it is 0.8 for O2–Ti, (0.98: O2–W), (0.95: O2–Ni), (0.3: N2–Ti), (0.95: N2–W), (0.06: H2–Ti), (0.5: H2–W), and 0.3 for H2–Ni. However, in addition to the temperature and chemical nature of interacting counterparts, the value of the initial sticking coefficients also depends on the crystallographic configuration of materials surfaces, availability of free chemisorption sites, and lifetime of the captured molecules on the surface. The lifetime of adsorbed molecules by physical adsorption may not be long enough for molecules to migrate to free chemisorption sites. These processes are related to the activation desorption energy of physisorbed molecules and activation migration energy over the surface.
Nanoscale zero-valent iron for remediation of toxicants and wastewater treatment
Published in Environmental Technology Reviews, 2023
On the other hand, doping metals on the surface of nZVI can increase the reaction rate and decrease the corrosion products due to the electroreduction of the metals and the role of hydrogen. The transformation of trivalent and two-valent iron occurred during the catalytic application of the nZVI, in which iron oxide layers are formed on the surface of the nZVI, increasing its thickness and preventing the contact of pollutants with the nZVI surface in the reaction [22]. The rapid aggregation of bare nZVI is attributed to the magnetic attraction between the particles. Thus, aggregation of nZVI causes decreases in mobility, surface area, reactivity, and fate. So, coating materials decrease the reactivity and increase the mobility of the nZVI by limiting the radius of influence. The mobility of nZVI in water treatment is affected by various factors such as pH, natural organic matter, ionic strength, water hardness, salinity, temperature, etc. The adsorption of natural organic matter on the surface of nZVI improves mobility due to a reduction in the sticking coefficient [23].
A critical overview of thin films coating technologies for energy applications
Published in Cogent Engineering, 2023
Mohammad Istiaque Hossain, Said Mansour
It is one of the several methods of depositing single crystals or monocrystals (Kim et al., 2022; Richards et al., 2022; Yao et al., 2022; Zhao et al., 2022; Zhu et al., 2022). MBE can be classified as a physical deposition, more specifically a PVD technique. In most of the cases, monocrystalline layers are expected due to the epitaxial growth in the chamber. The terminology “sticking coefficient” considers the ratio of the number of adsorb atoms and the total number of impinged atoms on the surface area. It is a suitable tool to deploy full-scale fabrication process of electronic devices related to energy and has gained tremendous attention in the recent days. The added advantage is the adaptability of such tool according to the research or manufacturing needs. Source guns can be chosen accordingly. MBE will continue to be source and means of basic research that will open up more horizons never ventured before (Kim et al., 2022; Richards et al., 2022; Yao et al., 2022; Zhao et al., 2022; Zhu et al., 2022).
A consistent soot nucleation model for improved prediction of strain rate sensitivity in ethylene/air counterflow flames
Published in Aerosol Science and Technology, 2022
Erica Quadarella, Junjun Guo, Hong G. Im
To facilitate the reader through the parametric analysis on strain rate sensitivity, a summary with specifications on the different characteristics used in the nucleation models adopted in this work (that, for brevity, will be referred to as reference models (RM)) is provided in Table 2. RM1 is the reference and the most comprehensive model, considering all PAH species with a heterogeneous collision model. RM2 is the same as RM1 but a limited set of precursors from A4 to A7 are considered. RM3 is the same as RM1 but the homogeneous collision model was used. RM4 is the same as RM1 but a different sticking coefficient without temperature dependence was employed. RM5 is the same as RM1 but the detailed mechanism was used. In addition, the dimer-less nucleation model following Wang and Chung (2016) was also considered, and finally, the approach by the RWTH group (Kruse et al. 2019) was also included for comparison. In the above, the A4–A7 PAH set includes a total of eight precursors (Wang and Chung 2016): pyrene, 1-ethylnyl pyrene, 2-ethynyl pyrene, 4-ethynyl pyrene, benzo(a)pyrene, benzo(e)pyrene, benzo(ghi)pyrene and coronene. For the A2–A7 PAH set, smaller species such as A2 and A2R5 were included. Moreover, recent studies reported that some additional long precursors are present in a considerable amount in sooting flames (Veshkini et al. 2016). Since there is no reason to exclude them, they are all included in the present model. They are A4R5 and anthanthrene (A6). SI provides the computational time comparison between RM1, RM2, RM3 and RM4.