Nucleation hemispherical growths

For simultaneous three-dimensional (3D) hemispherical growth and instantaneous nucleation. 

Schall et al. indented colloidal crystals using a needle with an almost hemispherical tip of diameter 40 dm, inducing a strain field in which tine maximum shear strain lies well below the contact surface. The tip diameter, particle radius and crystal thickness in their experiments were chosen to be similar to parameters in typical metallic nano-indentation experiments. The authors discussed their observations using a model that addresses the role played by thermal fluctuations in the nucleation and growth of dislocations. 

Thin layers of electrochemically deposited metals and thin polymer layers deposited on electrode surfaces can be conveniently studied by ellipsometry combined with other electrochemical experiments. Electrocrystallization of nickel was studied by Abyaneh, Visscher, and Barendrecht with ellipsometry and simultaneous amperometric measurements. The initial changes in A and ij/ showed nonlinear variations with the deposition time (Fig. 12), which is apparently abnormal, indicating a marked deviation of the optical properties of the deposited film from the bulk metal properties. The observed trend was explained by theoretical calculations using equations of effective medium theory (see Section IV.4 for effective medium theory) for hemispherical growth of the nucleation centers. The observed ellipsometry data clearly demonstrate that in the initial stage of nonuniform deposition the measured parameters, ij/ in particular, can change in a... 

In the second growth mechanism, carbon is first ejected from the catalyst particle in the form of a hemispherical dome that initiates the nucleation and growth of the cylindrical walls. 

For liquid metals the superiority of nucleate boiling heat transfer coefficients over those for forced-convection liquid-phase heat transfer is not as great as for ordinary liquids, primarily because the liquid-phase coefficients for liquid metals are already high, and the bubble growth period for liquid metals is a relatively short fraction of the total ebullition cycle compared with that for ordinary fluids. In the case of liquid metals, the initial shape of the bubbles is hemispheric, and it becomes spherical before leaving the heating surface. This is because of very rapid... 

Dwyer, O. E., and C. J. Hsu, 1976, Evaporation of the Microlayer in Hemispherical Bubble Growth in Nucleate Boiling of Liquid Metals, Int. J. Heat Mass Transfer 79 185. (2)... 

Si(lll) plane [300]. Because the redox potential of the Cd +/Cd couple is much lower than the flat band potential of Si substrate, the surface electron concentration is sufficiently high. Thus the process occurs similarly as on a metal surface at relatively low cathodic overpotentials. The initial stages of Cd deposition were explained by progressive nucleation and cluster growth controlled by hemispherical diffusion. CdTe deposition on Si was also studied due to interest in application in IR radiation detectors. Mechanisms of this process on different planes of n-Si(lOO) was also discussed ([203, 301, 302] and references given therein). 

On highly ordered pyrolytic graphite, HOPG(OOOl) electrodes, no UPD has been detected owing to weak carbon-lead interactions [311]. Deposition occurs by three-dimensional island growth according to Volmer-Weber mechanism. Initial steps are controlled by progressive nucleation on active sites and hemispherical diffusion. 

Indeed, the smallest tube that we measured had a diameter of 10 A, which is of the size of C o- predicted to be the limiting case of vapor-grown graphitic tubes with monolayer thickness (14). Our observation of hemispherically capped 10 A tubes suggests that an incomplete cluster is the nucleation seed for these tubes. The 60 derived tube could be the core of possible multilayer concentric graphitic tubes. After the fullerene-based tube has been formed, further concentric shells can be added by graphitic cylindrical layer growth. 

An analysis of potentiostatic current density transients indicates progressive nucleation and a cluster growth controlled by hemispherical diffusion (cf. Section 6.2), as shown in Fig. 6.37. From the initial part of the transients, the nucleation rate, /, as a function of rj was determined. The number of atoms forming the critical nuclei, Afcrit -2, was determined from the slope of the log/vs. t] plot in the overpotential range - 210 mV < T <- 100 mV. These results show that localized metal deposition under electrochemical conditions using in situ local probe techniques and appropriate poiarization routines seems to be realistic. 

The dehydration of chrome alum in vacuum [58] has an induction period, followed by nucleation at a constant rate. Surface nuclei were circular, but because the rate of bulk penetration was less than that of surface advance, the growth nuclei were flattened hemispheres. The rate of initial growth of each nucleus was exponential until a diameter of about 0.1 mm was attained and remained constant thereafter. Two fypes of nuclei were recognized [40], but in only one of these had the product undergone reorganization or recrystalhzation with the appearance of surface cracking. 

Indicates that the film does not grow uniformly. If one now assumes that growth proceeds by accretion of material as hemispherical bumps centered at nucleation sites scattered with some mean separation over the surface, the dielectric response of the film can be calculated by separations are shown as the dot-dashed curves. The results accurately represent the data until the hemispheres coalesce and the film begins to acquire the characteristics of a uniform layer. Thus not only is tbe growth mechanism identified, but the mean distance between nucleation centers is established to be of the order of 90A. Note that the growth mechanism can already be Identified after only two monolayers of material have been deposited. 

The first electrodeposition of aluminum from an ionic liquid was reported in 1994 by Carlin etal. [157], Two years later, Zhao et al. [158] smdied the aluminum deposition processes on tungsten electrodes in trimethylphenylanunonium chlo-ride/aluminum chloride with mole ratio 1 2. It was shown that the deposition of aluminum was instantaneous as a result of three-dimensional nucleation with hemispherical diffusion-controlled growth, underpotential deposition of aluminum, corresponding to several monolayers. Liao et al. investigated the constant current electrodeposition of bulk aluminum on copper substrates was in 1-methyl-... 

In this paper, we report on the electrochemical deposition of copper on a 30 nm TiN barrier film from pyrophosphate solution. We show that deposition occurs through the instantaneous nucleation of hemispherical clusters followed by diffusion-limited growth over a wide potential range. 

Analysis of deposition transients shows that deposition of copper on TiN from 50 mM copper (II) pyrophosphate solution proceeds through instantaneous nucleation of three dimensional hemispherical clusters and diffusion limited growth. Determination of the diffusion coefficient from the current maximum and analysis of the current decay using the Cotrell equation yielded values of 1 x 10 6 to 2 x 10 6 cm2 s, slightly lower than the value for Cu2t ions due to the presence of the pyrophosphate ligand. The potential dependence of inux and t,n suggest that the nucleus density is the only potential dependent parameter. 

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