Dynamics of carbon nanotube growth from fullerenes

The growth of double-walled carbon nanotubes from peapods was studied. The transformation was monitored by the decrease of fullerene Raman lines, the growth of inner tube Raman lines, and the development of X-ray diffraction patterns. A visual check of the growth process by HRTEM provided additional information. From the difference in time constants for the bleaching of fullerene Raman lines and for the growth of nanotube Raman lines, the existence of an intermediate phase was concluded that was eventually observed in X-ray diffraction and HRTEM. Time constants for the growth of large diameter inner tubes were up to a factor two larger than for small diameter inner tubes. The results fully support the fullerene coalescence growth model triggered by Stone-Wales transformations.     

Nucleation and growth of catalyst-free zinc oxide nanostructures

This paper deals with the investigations on the nucleation and growth of Zinc Oxide (ZnO) nanostructures in a catalyst free synthesis. The ZnO nanostructures have been formed by evaporation of Zn (99.99%) in O2 and Ar atmosphere in single zone furnace under two temperature regions, region A (approximately 1173-1073 K) and region B (approximately 873-773 K). Through application of XRD and TEM techniques, it has been shown that first ZnO is formed which changes to ZnOx through creation of oxygen vacancies. The ZnOx acts as self-catalyst and leads to formation of various nanostructures. Those observed in the present investigation are nanotetrapods (1 D, diameter approximately 70-450 nm, length approximately 2-4.5 approximatelym) nanorods (1 D, diameter approximately 45-95 nm, length approximately 2.5-4.5 microm), nanoflowers(2D, central core diameter approximately 90-185 nm, length of petals/nanorod approximately 1.0-3.5 microm) and nanoparticles (3D, size approximately 0.85-2.5 microm). These nanostructures have been revealed by SEM explorations. Attempts have been made to explain the formation of the various nanostructures in terms of the creation and distribution of the ZnOx, the temperature as well as oxygenation conditions.     

Nucleation and growth of a multicomponent metallic glass

The metallic glass samples of Fe ₆₇Co₁₈B₁₄Si₁ (2605CO), prepared by the melt spinning technique were procured from the Allied Corporation. The kinetics of crystallization of this multicomponent glassy alloy is studied using differential scanning calorimetry (DSC). The crystallization data have been examined in terms of modified Kissinger and Matusita equations for the nonisothermal crystallization. The results show enhanced bulk nucleation in general. At high heating rates added to it is surface induced abnormal grain growth resulting in fractal dimensionality. 5th IUMRS ICA98, October 1998, Bangalore.     

Nucleation,growth and orientation of bismuth films

The nucleation, growth and orientation of bismuth films vapour-deposited onto pure and bismuth-doped sodium chloride cleavages have been studied. The saturation nucleation density of bismuth on both pure and doped cleavages was found to be of the same order, i.e about 3.8 × 10¹¹ cm^?2 at 180 °C. It was observed that films deposited onto pure sodium chloride cleavages exhibit a (001) orientation whereas those deposited onto bismuth-doped cleavages exhibit a (012) orientation at a substrate temperature of 180 °C.     

Nucleation and growth of binary alloys on substrates

The nucleation and growth of silver-gold alloys on rock-salt cleavage surfaces was investigated systematically by evaporating the two metals from different sources so that the alloy was formed on the substrate surface. Measurements were carried out on the time dependences of the crystallite populations and size distributions and of the composition of the condensed material. It was found that the composition varies strongly with crystallite diameter and with the deposition time. The results were interpreted in terms of an extended kinetic nucleation model from the difference between the single atom adsorption energy and the activation energy for surface diffusion of the components. The adsorption energy for gold on rock-salt was found to be about 0.08 eV higher than for silver, whereas the activation energy for surface diffusion was about 0.02 eV lower for gold than for silver. These results were compared with data from other workers and show some discrepancies which may be due to different surface conditions.     

Nucleation and growth of condensate clusters on solid surfaces

The nucleation and growth of the condensate clusters during the early stages of the vapour deposition process were studied by depositing silver vapour on silicon, glass, mica, NaCl and KBr in a small coater. It was observed that the formation of the condensate film can be divided into four stages and the condensate clusters exhibit liquid-like behaviour during their early stage of growth. The mode of cluster growth is affected by the interfacial properties between the condensate and the substrate. The effect of surface roughness on the cluster growth is relatively insignificant and the experimental reproducibility is usually poor because of unavoidable contamination.     

Nucleation and growth of corrosion-fatigue cracks from semicircular notches

The initial stages of corrosion fatigue on the surfaces of semicircular notches are studied for the system of low-strength carbon steel and a 3% NaCl solution under different loading and electrochemical conditions on the notch surface. It is shown that the process of electrochemical dissolution of the metal plays the predominant role in the first stages of growth of short corrosion-fatigue crack. We suggest an expression for the prediction of the characteristic density of corrosion-fatigue cracks as a function of the synergistic action of cyclic stresses and parameters of the process of electrochemical dissolution on the notch surface. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Published in Fizyko-Khimichna Mekhanika Materialiv. Vol. 34, No. 5, pp. 53–60. September–October, 1998.     

Nucleation and anisotropic crystalline growth of polyethylene under shear

The crystallization of polyethylene was observed during shear experiments in isothermal conditions. The nucleation and the crystalline growth rates were measured from a microscopic observation of the growing morphologies. An unusual formation and development of row nuclei was observed throughout the experiment, followed by anisotropic growth. Three main growth rates were measured with respect to the main directions of the process. All these growth rates are enhanced differently by the shear rate. This result is interpreted first by an increase of the equilibrium melting temperature emanating from an entropy loss due to the chain orientation, second the anisotropy of growth is discussed as an effect of chain orientation with respect to the growth front of lamellae and of a local flow different from macroscopic shear-flow. An overall kinetic equation with shear effect has been proposed for this polyethylene and tested in a stimulation of crystallization during injection moulding of a polyethylene disc. The shear effect on the crystallization is necessary to predict the crystallization temperature and the thickness of polymer crystallized during the filling stage.     

Nucleation and growth of ion beam sputtered metal films

Transmission electron microscope observations have been made on ion beam sputtered (IBS) films of Cu, Au, Pt and Ni (of predetermined thicknesst 0.5 nm) deposited on amorphous carbon substrates. The influence of IBS parameters on particle size distribution and deposition rate has been measured, also the fractional substrate coveragef as a function oft which indicates three-dimensional island growth in Au, Cu films and two-dimensional growth in Pt, Ni films. Electron diffraction measurements appear to show that the f.c.c. metal particles grow with (1 1 0) parallel to the substrate with, in the case of Ni, a critical island thickness of 0.8 nm.     

Nucleation and growth of a macrocrack in tension and compression

Conclusions The general approach to analysis of the processes of nucleation and growth of radial separation macrocracks from the surface of a circular hole in sheets deformed in tension and compression was used to obtain new relations for calculating the characteristic values of compressive and tensile loads. The calculated results are in satisfactory agreement with the results of tests on sheets. At the same time, we detected unexpected fundamentally important aspects of the problem of brittle failure by separation.Firstly, it is justified to assume that the length of the region of the strong effect of the free surface of the hole on the state of the zone of development of the failure process in compression can be an order of magnitude higher than that in tensile loading. Secondly, with an increase of the distance of the crack tips from the hole the resistance of the material to failure in compressive loading gradually increases from the value close to minimum, at which k = 0, to its maximum value at k=-. If both these claims are valid, in future it would be necessary to revise greatly the methodology, results, and conclusions of a large number of investigations of brittle failure in compression, partially, in tension.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 5, pp. 62–66, September–October, 1991.     

Nucleation and growth of sputtered and evaporated trigonal selenium films

Critical nucleation temperature experiments, scanning electron microscopy and light microscopy were used to study the nucleation and growth of trigonal Se films deposited by evaporation and sputtering on both gold and anodized aluminum substrates. The major nucleation and growth processes were shown to be the condensation of Se₂ molecules followed by their polymerization into Se_n chains, where n can be very large. In sputtering, these chains have a higher surface mobility, due in part to their higher residual kinetic energy, and thus they can form large trigonal Se crystallites. The high incident kinetic energies also allow the Se to break through the surface contamination of the substrate. This is important since the Se chain mobility should also be dependent on the surface free energy and on the nucleation site density of the substrate. Very adherent large-grained trigonal Se films were grown by sputtering on Au substrates. It was shown that nucleation sites for the large trigonal Se crystallites were not created by the incident flux but are inherent on the substrate. The high energy incident flux did, however, increase nucleation probability for the initial Se₂ condensation. For sputtering on anodized aluminum substrates the combination of low surface energy and high nucleation site density decreased chain mobility and thus prevented formation of large crystallites.     

Nucleation and growth characteristics of spray- pyrolyzed CdS thin films

The nucleation, growth and microstructure of CdS films deposited by spray pyrolysis processing (SPP) was investigated. Comparisons of experimental data on films deposited by SPP were made with existing theories of deposition. Droplet impingement, surface pyrolysis and the incorporation of impurity phases were identified as the major mechanisms of film growth.     

Nucleation and growth of germanium on silicon (111)

The nucleation and growth of Ge on Si(111) substrates were investigated by transmission electron microscopy (TEM). It was found that growth is initiated by the formation of three-dimensional islands. At a very early stage of growth a polycrystalline layer was obtained. The orientation of this Ge film, however, improved as growth proceeded, resulting in an epitaxial film when the islands were fully coalesced. It was found that the major defects present in the Ge epilayer were microtwins (primary and secondary twins) occurring on the inclined {111} planes of Ge.