Single crystal

About: Single crystal is a research topic. Over the lifetime, 59617 publications have been published within this topic receiving 870828 citations.

Structures of self-assembled monolayer films of organosulfur compounds adsorbed on gold single crystals: electron diffraction studies

Abstract: : Transmission electron microscopy and diffraction have been used to study the packing arrangements of docosyl thiol (RSH), didocosyl sulfide (RSR), and didocosyl disulfide (RSSR) on gold single crystal foils. The specimens include gold films in (100) and (111) orientations. Docosyl thiol and didocosyl disulfide adsorbed on (111) faces assemble in coincidence lattice structures yielding hexagonal overlayers c(7 x 7) in which the short interchain distance indicates freely rotating methylene chains. On a (100) surface both alkyl groups exhibit an in-plane structure consisting of a base-centered square array in which the interchain distance implies a hindered chain movement. We have presented evidence that substrate crystallography does control the packing of monolayer alkyl sulfides adsorbed from the solution phase.

Quasi-ideal strontium titanate crystal surfaces through formation of stontium hydroxide

Abstract: In recent years, well-defined and nearly perfect single crystal surfaces of oxide perovskites have become increasingly important. A single terminated surface is a prerequisite for reproducible thin film growth and fundamental growth studies. In this work, atomic and lateral force microscopy have been used to display different terminations of SrTiO3. We observe hydroxylation of the topmost SrO layer after immersion of SrTiO3 in water, which is used to enhance the etch-selectivity of SrO relative to TiO2 in a buffered HF solution. We reproducibly obtain perfect and single terminated surfaces, irrespective of the initial state of polished surfaces and the pH value of the HF solution. This approach to the problem might be used for a variety of multi-component oxide single crystals. True two-dimensional reflection high-energy electron diffraction intensity oscillations are observed during homo epitaxial growth using pulsed laser deposition on these surfaces.

Optical bandgap energy of wurtzite InN

Abstract: Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy. Growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction. We observed at room temperature strong photoluminescence (PL) at 0.76 eV as well as a clear absorption edge at 0.7–1.0 eV. In contrast, no PL was observed, even by high power excitation, at ∼1.9 eV, which had been reported as the band gap in absorption experiments on polycrystalline films. Careful inspection strongly suggests that a wurtzite InN single crystal has a true bandgap of 0.7–1.0 eV, and the discrepancy could be attributed to the difference in crystallinity.

Single-crystal x-ray diffraction structures of covalent organic frameworks

Abstract: The crystallization problem is an outstanding challenge in the chemistry of porous covalent organic frameworks (COFs). Their structural characterization has been limited to modeling and solutions based on powder x-ray or electron diffraction data. Single crystals of COFs amenable to x-ray diffraction characterization have not been reported. Here, we developed a general procedure to grow large single crystals of three-dimensional imine-based COFs (COF-300, hydrated form of COF-300, COF-303, LZU-79, and LZU-111). The high quality of the crystals allowed collection of single-crystal x-ray diffraction data of up to 0.83-angstrom resolution, leading to unambiguous solution and precise anisotropic refinement. Characteristics such as degree of interpenetration, arrangement of water guests, the reversed imine connectivity, linker disorder, and uncommon topology were deciphered with atomic precision—aspects impossible to determine without single crystals.

Growth of single-crystal TiN/VN strained-layer superlattices with extremely high mechanical hardness

Abstract: Single‐crystal TiN/VN strained‐layer superlattices (SLS’s) with layer thicknesses lTiN =lVN =λ/2 (where λ is the period of the superlattice) ranging from 0.75 to 16 nm have been grown on MgO(100 ) substrates by reactive magnetron sputtering. Cross‐sectional transmission electron microscopy (TEM) and x‐ray diffraction examinations showed that the films were single crystals exhibiting coherent interfaces and several orders of superlattice reflections. There was no evidence in either plan‐view or cross‐sectional TEM analyses of misfit interfacial dislocation arrays. The primary defects observed were dislocation loops with a diameter of 8–10 nm extending through several layers and small defects with a diameter of 1–2 nm that were confined within single layers. Microindentation hardness values H, measured as a function of λ in films with a total thickness of 2.5 μm, increased from 2035±280 kg mm−2 for Ti0.5V0.5N alloys (i.e., λ=0) to reach a maximum of 5560±1000 kg mm−2 at λ=5.2 nm and then decreased rapidly t...