Formation Of Crystal Films Research Articles

Molecular Materials for Energy Storage

We map the requirements and design rules for dielectric materials that target large scale energy storage applications of electrostatic capacitors. The molecular unit (dielectrophore) must contain three main components: a polarizable subunit having large electric dipole, an isolating subunit which prevents current leakage, and a structural element that promotes self-assembly of molecules in solution and in mesophase and promotes crystallization in the process of film formation. This structural subunit is necessary for high molecular density and enhanced resistivity of film. The process engineering steps required for the supramolecular assembly and crystal film formation (cascade crystallization) are addressed.

Single-source macroporous hybrid materials by melt-shear organization of core–shell particles

The preparation of porous materials is an interesting field for a huge variety of potential applications. Herein we report an efficient and convenient strategy for the creation of inverse colloidal crystal structures based on soft core/shell polymer particle templating. This single-source strategy is based on starved-feed emulsion polymerization of hybrid core/shell particles consisting of a poly(methyl methacrylate-co-allyl methacrylate) (P(MMA-co-ALMA)) core and a poly(ethyl acrylate-co-(3-methacryloxypropyl-trimethoxysilane)) (PEA-co-PMEMO) shell. The resulting monodisperse particles are analyzed with respect to their size and distribution by transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. The hybrid monodisperse core/shell particles can be aligned to a colloidal crystal by using the convenient melt-shear organization technique. As a result, free-standing and crack-free hybrid polymer colloidal crystal films are accessible without the need of any solvent or dispersion medium. The processing step is investigated regarding different parameters comprising temperature and pressure for the influence on the colloidal crystal film formation. Furthermore, resulting core/shell ratio is tailored by starved-feed emulsion polymerization conditions, since the ratio affects the quality of the porous structure after thermal treatment of colloidal crystal films. The incorporation of alkoxysilane-containing monomers offers a unique crosslinking strategy that yields mechanically robust and thermally stable films. Due to the increased stability, a removal of PMMA cores is possible by thermal treatment of the templating colloidal crystal films leading to almost isoporous free-standing hybrid materials as determined by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM).

Effects of sputtering power on microstructure and mechanical properties of TiVCr films

We investigated the effects of sputtering power on the microstructure of direct-current magnetron sputter-deposited TiVCr films on silicon wafer grown at room temperature. When the sputtering power was 100 W, composite structure with amorphous and body-centered cubic (BCC) crystal phases can be observed. When sputtering power was increased to 200 W, the composite structure was almost transformed into crystal columnar structure. Apart from interface region, the amorphous zone was composed of bundles of fine fibrous structure, whereas the BCC crystal zone contained V-shaped columnar structures without significant element segregation. Results indicated that the high sputtering power favored the formation of crystal films and the decrease of intracolumnar voids. However, a significant crack occurred, thereby widening intercolumnar voids. The film deposited at high sputtering power demonstrates slight improvement of mechanical properties.

Micrometer–Range Pattern Formation of Crystal Films from Liquid Thin Films of Maleimide Methanol Solution

Crystal films of maleimide were produced from methanol solution liquid thin film climbing a vertical glass substrate. Optical microscopy and infrared (IR) spectroscopy were used to evaluate the crystal films. Maleimide methanol solution produced four banded crystal films with different thickness appearing alongside each other in horizontal position. Each band of crystal films had a uniform pattern different from the other bands. The differences of pattern among the banded crystal films were attributed to fluid dynamics, temperature and liquid film thickness as consequence of a particular experimental condition. Each band of crystal films also exhibited different sublimation nature and variations in IR spectra.

Micrometer–Range Pattern Formation of Crystal Films from Liquid Thin Films of Maleimide Methanol Solution

Micrometer–Range Pattern Formation of Crystal Films from Liquid Thin Films of Maleimide Methanol Solution

Relation between growth dynamics and the spatial distribution of intrinsic defects in self-assembled colloidal crystal films

Herein we establish a clear relation between the parameters that govern the growth dynamics and the structural quality of colloidal crystal films. We report an optical analysis of the spatial distribution of intrinsic defects in colloidal crystal films and correlate our results with a theoretical model describing the growth dynamics of such lattices. We find that the amount of defects fluctuates periodically and decreases along the growth direction of the lattice. We demonstrate that these spatial variations are a direct consequence of the temporal oscillations of the crystal film formation velocity, which are inherent to the colloidal particle deposition process.

Formation of Crystal Film at Interface in Process of Extraction of Rare Earth Metals by D2EHPA.

In the process of extraction of the rare earth metals europium and samarium by D2EHPA, we find that solid films form at the organic/aqueous interface. For extraction solution systems of europium and samarium, we specified concentration zones where the solid films should form, and show that the formation of the solid films occurs at the specific zones of hydrogen ion and extractant concentrations. We also determine the atomic constituents of the solid films by inductively coupled plasma emission spectroscopy, and find that the solid films are crystals composed of neutral 1:3 intermediate complexes. We further investigate film formation in the extraction solution system that contains two lanthanide elements, europium and samarium. We determine the atomic ratio of the solid film, and show that the atomic ratio takes the value which is near to that predicted from the separation coefficient in the organic/aqueous solution system.

Ion–surface interactions in low temperature silicon epitaxy by remote plasma enhanced chemical–vapor deposition

Epitaxial Si thin films have been deposited by remote plasma enhanced chemical–vapor deposition at temperatures below 450 °C and at pressures between 50 and 500 mTorr. Growth rate data reveal the presence of two pressure dependent regimes for deposition process activation. Sampling of the plasma afterglow by mass spectrometry indicates a correlation between enhanced rates for single crystal film formation and the onset of an ion-induced surface H abstraction processes below pressures of ∼200 mTorr. The role of low energy ions in the abstraction of chemisorbed H and its effects on the growth kinetics are discussed.

Ionized Cluster Beam Epitaxy of Single Crystal Metal Films on Semiconductors and Insulators

ABSTRACTOur experiments show that ionized cluster beams (ICB) can form epitaxial Al films on Si(111) and Si(100) substrates. This is unique because the lattice misfit of this material combination is more than 25%. Al can also be epitaxially grown on CaF2 films deposited on Si substrates. The initial stage of the film formation is measured by in-situ electron diffraction. In the case of Al(111) growth on Si(111) and CaF2, growth of mixed layers of different epitaxial islands of approximately 20–50 Angstrom thickness on the substrate surface is observed. With increase of thickness, the film shows the single crystal state with a flat surface, which indicates the epitaxial single crystal film formation on CaF2 or on Si substrates. It should be noted that in the Al/CaF2/Si (MIS) structure, the epitaxial CaF2 is a good insulating layer, which can be used to prepare three dimensional devices. These results show that the kinetic energy and the ionic charge of cluster ions have much influence on surface and interface modification, and that ICB is capable of producing films of good quality at low substrate temperatures.