Molecular crystal substrates

Bonafede, S. J. and Ward, M. D. (1995). Selective nucleation and growth of an organic polymorph by ledge-directed epitaxy on a molecular crystal substrate. / Am. Chem. Soc., 117, 7853-61. [93]... 

Crystollization of Secondary Crystalline Phases on Molecular Crystal Substrates. 

However, all the receptors hitherto discussed are monomolecular species which possess a monomolecular cavity, pocket, cleft, groove or combination of it including the recognition sites to yield a molecular receptor—substrate complex. They can be assembled and preserved ia solution although there are dependences (see below). By way of contrast, molecular recognition demonstrated ia the foUowiag comes from multimolecular assembly and organization of a nonsolution phase such as polymer materials and crystals. 

A ZnS layer 11 is formed on an (001) face InSb single-crystal substrate. The ZnS layer, which is polycrystalline, is removed from islands where the detector elements will be formed. Molecular beam epitaxy is then used to form an HgCdTe layer on the structure, which will produce single crystal and polycrystalline layers on detector element regions 15 and the ZnS layer 14 respectively. The detector elements are separated by the polycrystalline layer, which is electrically insulating. 

Investigating 2D self-assembly at the molecular level provides new insight into complex inter molecular interactions. These model studies are usually performed under well-defined conditions in order to have more control on complicated surface processes [13]. This includes single-crystal substrates which allow the application of diffraction techniques. 

Experimental determinations of barrier heights on oxide semiconductor interfaces using photoelectron spectroscopy are rarely found in literature and no systematic data on interface chemistry and barrier formation on any oxide are available. So far, most of the semiconductor interface studies by photoelectron spectroscopy deal with interfaces with well-defined substrate surfaces and film structures. Mostly single crystal substrates and, in the case of semiconductor heterojunctions, lattice matched interfaces are investigated. Furthermore, highly controllable deposition techniques (typically molecular beam epitaxy) are applied, which lead to films and interfaces with well-known structure and composition. The results described in the following therefore, for the first time, provide information about interfaces with oxide semiconductors and about interfaces with sputter-deposited materials. Despite the rather complex situation, photoelectron spectroscopy studies of sputter-deposited... 

The non-volatile bubble memories used for data storage are based on the principle of formation of magnetic domains in thin films grown on a gadolinium gallium garnet crystal substrate. Molecular engineering creates the precise film compositions for optimum performance. 

Carter, P.W. Ward, M.D. Topographically directed nucleation of organic-crystals on molecular single-crystal substrates. J. Am. Chem. Soc. 1993, 115 (24), 11,521-11,535. 

In the present system adsorbed dye molecules are excited by picosecond laser light and electron transfer takes place from the valence band of the substrate molecular crystals to the excited dye and concomitantly quenches the fluorescence (6,7). We are able to determine the electron transfer rate by measuring the fluorescence decay dynamics of the adsorbed dye. Figure 2 shows the energy-gap (a) and temperature dependence (b) of the rate constant of electron transfer in the adsorption systems calculated according to eq.[1], which is Sarai s three-mode-variant (38) of Jortner s original equation (43) ... 

The nanostructuring is achieved by directing a pulse from a frequency-tripled Nd YAG laser with a pulse width of 35 ps, a wavelength of 355 nm, and up to 250 pj pulse energy through a near-field optical tip. The tip had a diameter aperture of around 170 nm, creating ablation craters with about the same diameter (see below). Molecular crystals (the same bis-triazene that was used as model compound for the triazene polymers in other studies, shown in Scheme 7) were applied as substrates, because the main goal of this study was the development of nanoscale atmospheric-pressure laser ablation-mass spectrometry [390]. 

The experiments are performed on Au/Co/Au sandwich structures grown by molecular beam epitaxy (MBE) on sapphire single crystal substrates [3] with Co... 

If, on the other hand, there is a stronger interaction between the substrate and the evaporated molecules than between the molecules themselves, then the molecules will tend to cover the substrate optimally, i.e. completely. Covalent bonds can also form between the molecules and the substrate, leading to changes in the molecular stmcture. One then refers to epitaxy, when the lattice parameter of the (single-crystal) substrate is commensurable with those which can exist in the crystalline phases formed by the evaporated molecules. Examples of epitaxy are shown in Figs. 2.23 and 1.9. 

The sample must be a single crystal semiconductor or metal and its surface should be smooth and flat so that the electron emission angle can be accurately determined. High surface sensitivity makes the technique vulnerable to contamination, necessitating the use of UHV procedures. However this surface sensitivity combined with the element specific crystallographic information that XPD provides makes the technique ideal for studying the structure of adsorbed molecular layers on single crystal substrates. 

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