Epitaxial structures

The fundamental physical properties of nanowire materials can be improved even more to surpass their bulk counterpart using precisely engineered NW heterostructures. It has been recently demonstrated that Si/Ge/Si core/shell nanowires exhibit electron mobility surpassing that of state-of-the-art technology.46 Group III-V nitride core/shell NWs of multiple layers of epitaxial structures with atomically sharp interfaces have also been demonstrated with well-controlled and tunable optical and electronic properties.47,48 Together, the studies demonstrate that semiconductor nanowires represent one of the best-defined nanoscale building block classes, with well-controlled chemical composition, physical size, and superior electronic/optical properties, and therefore, that they are ideally suited for assembly of more complex functional systems. 

Circular Bragg nanolasers (CBNLs) of several geometries and Bragg reflector orders were fabricated within a thin membrane of InGaAsP semiconductor material21. A cross-section of the semiconductor epitaxial structure used is illustrated... 

Molecular beam epitaxy (MBE) is an expensive yet widely used technique for producing epitaxial layers of metals, insulators and III-V and II-VI based semiconductors, both at the research and the industrial production level (Herman, 1996). It consists of deposition of molecular beams of atoms or clusters of atoms, which are produced by heating up a solid source, onto a heated crystalline substrate in ultra-high vacuum. MBE is characterized by low growth temperatures and low growth rates and thus enables producing high-precision epitaxial structures with monolayer... 

In general, unlike for the perfect epitaxial structures of fully strained materials, for nitride heteroepitaxial layers it is essential to perform not a single scan for a symmetrical reflection, but a set of two- or even three-dimensional maps of symmetrical and asymmetrical reflections. Additionally, for some applications, an intense beam is needed and therefore low-resolution X-ray diffractometry can be sometimes a preferable technique to the commonly used high-resolution XRD. For example, if we examine a heterostructural nitride superlattice, low resolution diffractometry will give us a broader zeroth-order peak (information on the whole layer) but more satellite peaks (information on the sublayers). Therefore, multipurpose diffractometers with variable configurations are the most desirable in nitride research. 

This field of research on the vapor-growth of ZnO has been reactivated from 1998 by the need of ZnO substrates for growing epitaxial structures in view of photonic applications. 

A number of factors can influence the behavior of ferroelectric thin films and multilayer stmctures with layer thickness at nanometer scale. One of the major factors is strain in epitaxial structures [15]. Recent demonstrations of huge strain effect on ferroelectric properties include changes in the phase diagram [16-22], dramatic enhancement of ferroelectric polarization, and increase of the ferroelectric phase transition temperature [23-27], induced ferroelectricity in non-ferroelectric materials like SrTi03 or KTa03 [28-33], or even simple rocksalt binary oxides like BaO ([34], theoretically predicted). 

Structural parameters for transition metal adsorption on transition metals epitaxial structures. The given bond length is the shortest distance between the adatom and a substrate atom. du is the spacing between the first and second layers of the epitaxial system, di3 is the spacing between the second and third layers, etc. The adatom-adatom and adatom-substrate bond lengths are derived from the determined structural paramaters. 

Transition metal adsorption results in one of two types of behavior alloy formation and the initial growth of epitaxial structures. Mn on Pd(100), Au and Pd on Cu(100) and Sn on Pt(lll) can result in substitutional structures in which the adatom replaces an host atom in the top layer of the substrate. This results in the formation of an ordered alloy which is confined to the first atomic layer of the surface. Because of the size difference between the adatom and host atom, this substitution can result in a buckling of the alloy monolayer (see table 11). 

In principle, epitaxial structures involve the deposition and growth of complete monolayers of the adatom which occupy the continuation sites of the substrate. Because of lattice mismatch, the epitaxial structure is subject to lateral stress which is relieved by defect formation. In reality, the distinction between alloy formation and epitaxy is often a function of the surface growth conditions and preparation. If grown at elevated temperatures, seemingly epitaxial structures can exhibit significant amounts of interdiffusion across the interfacial region. 

If a c = a sA then = 0 and the new phase C wets the interface. If nucleation barrier for the new phase C will vanish. On the other hand, if homogeneous nucleation. This would be the case if the original interface were nearly coherent, i.e., A/B is an epitaxial structure. Heterogeneous nucleation would be effectively suppressed in this case. In general, the nucleation barrier for C, AG UC depends on

0. These general features are applicable irrespective of whether C is a metastable... 

Apart from the (disordered and ordered) monolayer phases of tetraeene/ Ag(l 11), a second ordered phase is observed at higher coverage. This so-called (3-phase [69] is a bilayer with an extremely complex structure which is discussed elsewhere [49]. There are two notable facts about this phase. Firstly, the first layer of the bilayer is not the flat lying monolayer phase (a-phase). Rather, under the influence of the attractive intermolecular interactions with molecules in the seeond layer, the first layer re-orders and (partly) tilts up. This behaviour is markedly different from PTCDA, where the first layer forces the second layer into its epitaxial structure. This disparity indicates once more that for the two systems the weighting between intermolecular and interfacial interactions is different. Seeondly, a detailed analysis of single-molecule spectra in the (3-phase shows that the moleeular environment has a very strong influence on the electronic properties of individual molecules, even for molecules far away from the metal. 

The effect of SiN deposition conditions on the epitaxial structural quality was characterized first by the full width at half-maximum (FWFIM) values of X-ray diffraction (XRD) (0002) and (1012)rocking curves. 

Direct bandgap 11-VI semiconductors have opened up the blue-green region of the spectrum and a range of novel applications in optoelectronics. There are many potential applications for compact laser and Light Emitting Diodes (LED), but it is essential to minimize defects and imperfections which decrease the radiative yield of photons. This explains the interest of the construction of epitaxial structures between... 

The possibility of fabricating nanoobjects has been demonstrated using a series of epitaxial structures grown on GaAs, InP, InAs, Si substrates [2-19] (Fig. 2-4). 

A novel delta-doped by Si GaAs epitaxial structures were grown by a MBE method on vicinal... 

The structure of lead UPD films on silver (hkl) faces is a consequence of the significant lattice misfit. The atomic radius of Ag is 0.144 nm, the radius of lead 0.174. This prevents a complete epitaxial structure. One can expect that the forced layer structure has a high internal strain. The elastic strain in the film can be estimated from the deviation of the distance of the atoms in the film d from the distance dg in the bulk crystal. The elastic strain is given by the equation... 

Figure 3.17. Epitaxial structures on UHMWPE fiber obtained after annealing at 130°C. [Adapted, by permission, from McDaniel, P B Deitzel, J M wayS...

T. Mikami and H. Yanagi, Epitaxial structuring of blue light-emitting p-phenylene oligomers, Appl. Phys. Lett.. 73, 563-565 (1998). 

The idea of stabilization of an epitaxial structure by subsequent overgrowth has significant practical implications. The prospect of inserting material structures which are unstable or only weakly metastable into applications for which long life is required is undesirable. However, if material structures that are unstable as fabricated can be stabilized by overgrowth then the risk of material failure is diminished significantly. This issue plays a role in several quantum wire configurations, as discussed in Section 6.6, and... 

A coherent twin boundary in the jS-phase such as that shown above is by its stacking sequence an incipient a hexagonal nucleus. Because of their low stacking fault energy, such faults are present in abundance in the )8-phase. The tendency of complex epitaxial structures in SiC to persevere at temperatures where jS is metastable with respect to a is attributed to the small free energy difference between a- and jS-SiC and the low energy of the epitaxial -a interface. 

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