Kinetics, deposition

As discussed before, the deposition during molecular combing is usually controlled by means of an energy barrier. Thus, deposition kinetics are governed by activated, or Arrhenius, kinetics and the flux, J, is given by 

We consider two models for deposition kinetics. The first (case I) assumes that depositing nanotubes increase surface charge homogeneously. The corresponding surface potential and potential barrier, AE, also increase. As AE increases, the deposition rate is reduced. This model is useful for cases where deposition is extensive or the salt concentration is very low, although as we will see below, it was not applicable to molecular combing of DNA-SWCNTs. 

The second kinetics formulation is applicable to cases where deposition density is low. In this case (case 11), we assume that the surface has a maximum number of sites that the DNA-SWCNT can occupy and that deposition gradually slows as sites are Tilled. The number of such sites is limited because deposited molecules, by virtue of not aggregating in solution, must necessarily repel other molecules and thus block part of the surface by depositing. Such processes are governed by random sequential absorption (RSA) theory. Kinetics formulations have been developed for some special geometries, but these are not applicable to molecular combing of long molecules. 

As noted above, we find that this kinetics formulation is applicable to cases where the salt concentration is low, and deposition extensive, so that the smeared charge approximation holds. Assuming that depositing DNA-SWCNTs form a homogenous layer on the surface implies that the surface charge will increase with deposited density Ps (in p.m of nanotubes per p.m of surface). As surface charge increases, surface potential relative to bulk solution will also increase. Within the linearized Debye-Hiickel approximation, the surface potential is related to surface charge as  

We start by finding Xpeak the location of the barrier, by setting dE/dx = 0. in Eq. 16.3 has two extrema, one at the barrier AE and a secondary minimum further away from the surface. For small Xpeak//d we find the location of the barrier to be  

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Ramsden J J 1993 Concentration scaling of protein deposition kinetics Phys. Rev. Lett. 71 295-8... 

Various plasma diagnostic techniques have been used to study the SiH discharges and results have helped in the understanding of the growth kinetics. These processes can be categorized as r-f discharge electron kinetics, plasma chemistry including transport, and surface deposition kinetics. 

The composition of the electrolyte is quite important in controlling the electrolytic deposition of the pertinent metal, the chemical interaction of the deposit with the electrolyte, and the electrical conductivity of the electrolyte. In the case of molten salts, the solvent cations and the solvent anions influence the electrodeposition process through the formation of complexes. The stability of these complexes determines the extent of the reversibility of the overall electroreduction process and, hence, the type of the deposit formed. By selecting a suitable mixture of solvent cations to produce a chemically stable solution with strong solute cation-anion interactions, it is possible to optimize the stability of the complexes so as to obtain the best deposition kinetics. In the case of refractory and reactive metals, the presence of a reasonably stable complex is necessary in order to yield a coherent deposition rather than a dendritic type of deposition. 

The different theoretical models for analyzing particle deposition kinetics from suspensions can be classified as either deterministic or stochastic. The deterministic methods are based on the formulation and solution of the equations arising from the application of Newton s second law to a particle whose trajectory is followed in time, until it makes contact with the collector or leaves the system. In the stochastic methods, forces are freed of their classic duty of determining directly the motion of particles and instead the probability of finding a particle in a certain place at a certain time is determined. A more detailed classification scheme can be found in an overview article [72]. 

Solution Composition Effect of Solution Stability, Deposition Kinetics, and Deposit... 

Electroless deposition as we know it today has had many applications, e.g., in corrosion prevention [5-8], and electronics [9]. Although it yields a limited number of metals and alloys compared to electrodeposition, materials with unique properties, such as Ni-P (corrosion resistance) and Co-P (magnetic properties), are readily obtained by electroless deposition. It is in principle easier to obtain coatings of uniform thickness and composition using the electroless process, since one does not have the current density uniformity problem of electrodeposition. However, as we shall see, the practitioner of electroless deposition needs to be aware of the actions of solution additives and dissolved O2 gas on deposition kinetics, which affect deposit thickness and composition uniformity. Nevertheless, electroless deposition is experiencing increased interest in microelectronics, in part due to the need to replace expensive vacuum metallization methods with less expensive and selective deposition methods. The need to find creative deposition methods in the emerging field of nanofabrication is generating much interest in electroless deposition, at the present time more so as a useful process however, than as a subject of serious research. 

Many factors influence the deposition kinetics of P and B, including metal ion and complexant concentrations, solution pH, and temperature. Though unavoidable side products of the electroless deposits, P and B impart unique properties to electroless deposits, e.g., good corrosion resistance in the case of Ni-P deposits, where the P content can exceed 30 at% in certain solutions [10, 11],... 

The O2 reduction reaction affects not only the steady-state deposition kinetics, but also the initiation of deposition, the so-called induction time [126, 127], At the beginning of the deposition process, the open circuit potential (Eoc) of either a uniformly catalytically active substrate, or a catalyst particle on an insulator, will be higher than that required for electroless deposition to occur. This is a consequence of the surface of the catalyst being covered with O or OH species which mask the catalytic activity of the surface the value of would be expected to be in the range of... 

As in earlier reported work (4), the present study has used a large-volume microwave plasma (IMP) facility. The choice is based on the favorable deposition kinetics at microwave frequencies, and on the relative ease of scaling experimental LMP apparatus to industrially useful size. 

The implied capability of these plasma deposits to inhibit corrosion at metal surfaces may be of practical as well as of basic importance. An important consideration in this respect is the rapid rate of deposition for such protective coatings attainable at micro-wave frequencies. Since plasma technology is still in a process of evolution, optimum deposition kinetics cannot yet be stated however, the marked effect of excitation frequency on the deposition of organo-silicones can be documented (10), as in Fig. 3. Here, using terminology and comparative data due to Yasuda et al. (2). it is shown that deposition rates in microwave plasmas exceed those at lower (e.g. radio) frequencies by about an order of magnitude. 

The book is divided into 18 chapters, presented in a logical and practical order as follows. After a brief introduction (Chapter 1) comes the discussion of ionic solutions (Chapter 2), followed by the subjects of metal surfaces (Chapter 3) and metal solution interphases (Chapter 4). Electrode potential, deposition kinetics, and thin-fihn nucleation are the themes of the next three chapters (5-7). Next come electroless and displacement-type depositions (Chapter 8 and 9), followed by the chapters dealing with the effects of additives and the science and technology of alloy deposition... 

A significant disadvantage of the bell jar configuration is that the monomer flow is not constrained to pass totally through the plasma formed between the electrodes. To overcome this problem, the electrodes can be mounted in a rectangular flow channel. By adding channel sections before and after the plasma zone, it is further possible to establish a well-developed flow profile for the gas as it enters the plasma zone. This reactor design is particularly well suited for studies of film deposition kinetics. 

The deposition of polymeric films by plasma polymerization of styrene in a 800 kHz discharge was investigated by Lam et al. . It was proposed that the observed deposition kinetics could be explained by a scheme in which the initiation of monomers by electron impact is followed by propagation and termination, as in conventional polymerization. This scheme is summarized by the following three reactions ... 

The number of attempts to model the kinetics of plasma-polymerization has been limited thus far. Nevertheless, these efforts have been useful in demonstrating the role of different processes in initiating polymerization and the manner in which the physical characteristics of the plasma affect the polymerization rate. It is anticipated that future modeling efforts will provide more detailed descriptions of the polymer deposition kinetics and thereby aid the development of a better understanding of the interactions between the physical characteristics of a plasma and the chemistry associated with polymer formation. 

The prepared solution will slowly deposit Se as a black precipitate over a period of weeks. Also, the solution is considerably less stable than thiourea. If kept out of excessive contact with air, it will be usable for about a month if high reproducibility of the deposition kinetics is not important. However, it is important to be aware of the slow decomposition and loss of reactivity of this reactant. If a freshly made NaiSeSOs solution is used to deposit CdSe, the reaction will proceed much faster than if an aged solution is used this fact should be taken into account in preparing the overall deposition solution. 

Based on this mechanism, a detailed theoretical model has recently been proposed for CdS deposition from the thiourea/ammonia bath [65a]. Prediction of different aspects of the deposition kinetics using this model provided a very good fit with the relevant experimental data. 

The main physicochemical processes in thin-film deposition are chemical reactions in the gas phase and on the film surface and heat-mass transfer processes in the reactor chamber. Laboratory deposition reactors have usually a simple geometry to reduce heat-mass transfer limitations and, hence, to simplify the study of film deposition kinetics and optimize process parameters. In this case, one can use simplified gas-dynamics reactor such as well stirred reactor (WSR), calorimetric bomb reactor (CBR, batch reactor), and plug flow reactor (PFR) models to simulate deposition kinetics and compare theoretical data with experimental results. 

The basic kinetic regularities of film growth must be considered to build the film deposition kinetic mechanism. In the case of Zr02 film growth from... 

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