Lipid monolayers on the surface of water have been studied for over a hundred years, but in last decade there has dramatic evolution our understanding structures and phase transitions these systems, driven by new experimental techniques theoretical advances. In this review, dense simple lipids are described detail, including revealed x-ray-diffraction experiments, computer simulations, molecular models, phenomenological theory transitions. The effects chirality phospholipid considered. Open...

The x-ray scattering from relaxed heteroepitaxial layers with the misfit dislocations randomly distributed at interface between layer and substrate is analyzed theoretically experimentally. profiles of x-ray-diffraction peaks reciprocal space maps intensity are measured simulated for several structures in a wide range dislocation densities. At large densities, peak position governed by mean distortions width due to mean-square variations distortions. widths calculated uncorrelated...

We analyze the line shape of x-ray diffraction profiles GaN epitaxial layers with large densities randomly distributed threading dislocations. The peaks are Gaussian only in central, most intense part peak, while tails obey a power law. ${q}^{\ensuremath{-}3}$ decay typical for random dislocations is observed rocking curves open detector. entire profile well fitted by restricted dislocation distribution. both edge and screw ranges correlations obtained.

We investigate the axial and radial growth of GaN nanowires upon a variation Ga flux during molecular beam epitaxial growth. An increase in promotes without affecting rate. In contrast, decrease reduces rate any change radius. These results are explained by kinetic model that accounts for both diffusion adatoms along side facets towards nanowire tip finite amount active N available The explains formation new equilibrium radius after increasing provides an explanation two well known but so...

X-ray diffraction data from water-supported monolayers of fatty acids with chain lengths 19 to 22 is presented. The structures the tilted mesophases L2′, L2, and Ov are characterized in detail. contributions unit cell distortion tilt ordering backbone planes molecules separated. It shown that at swiveling transition L2′–L2, not only azimuth but also packing change discontinuously. We demonstrate tilting LS–L2 accompanied by may be discontinuous. Evidence presented for a herringbone within L2...

We present experimental evidence of the equilibrium coexistence between crystalline phases in heteroepitaxial films MnAs on GaAs. The phases, which can coexist bulk system only at one temperature point, epitaxial film over a wide interval. An apparent contradiction with Gibbs phase rule is resolved by presence strain film.

The temperature-dependent phase coexistence between crystalline phases in heteroepitaxial films of MnAs on GaAs is studied. epitaxial constraints the film expansion are analyzed. x-ray-diffraction data fitted to a model periodic elastic domains. temperature dependencies fractions, domain sizes, and misfits simultaneously obtained. sizes correspond minimum energy, which proves equilibrium state system at each temperature.

The surface topography of epitaxial MnAs films on GaAs(001) is studied by scanning probe microscopy. We provide direct experimental evidence for temperature-dependent elastic domains the coexisting ferromagnetic αMnAs and paramagnetic βMnAs phases. results agree well with a theoretical model equilibrium periodic domains.

We investigate the nucleation, growth, and coalescence of spontaneously formed GaN nanowires in molecular beam epitaxy combining statistical analysis scanning electron micrographs with Monte Carlo growth models. find that (i) nanowire density is limited by shadowing substrate from impinging fluxes already existing nanowires, (ii) shortly after nucleation stage, radial becomes negligible, (iii) caused bundling nanowires. The latter phenomenon driven gain surface energy at expense elastic...

Condensed phases of Langmuir monolayers are treated in the framework Landau theory phase transitions as a result successive ordering hexatic phase. All types allowed by symmetry and couplings between them described. The diagrams x-ray structural data on various long-chain amphiphilic molecules can be explained using three coupled order parameters. One parameters governs collective tilt molecules, while other two describe one-dimensional ``weak crystallization'' involving herringbone...

We investigate the structural and optical properties of spontaneously formed GaN nanowires with different degrees coalescence. This quantity is determined by an analysis cross-sectional area perimeter obtained plan-view scanning electron microscopy. X-ray diffraction experiments are used to measure inhomogeneous strain in nanowire ensembles as well orientational distribution nanowires. The comparison results for prepared on bare Si AlN buffered 6H-SiC reveals that main source random...

We show that the growth kinetics of dense arrays self-induced GaN nanowires involves exchange Ga atoms between nanowires: desorbed from side surfaces readsorb on neighboring nanowires. This process favors shorter and gives rise to a narrow nanowire height distribution during late stages growth. propose stochastic differential equation model which describes ensembles. The calculations are in good agreement with experiments.

Single GaN nanowires formed spontaneously on a given substrate represent nanoscopic single crystals free of any extended defects. However, due to the high area density thus nanowire ensembles, individual coalesce with others in their immediate vicinity. This coalescence process may introduce strain and structural defects, foiling idea defect-free material geometry. To investigate consequences this process, quantitative measure ensembles is required. We derive objective criteria determine...

We investigate the impact of threading dislocations with an edge component ($a$ or $a+c$ type) on carrier recombination and diffusion in $\mathrm{Ga}\mathrm{N}$(0001) layers close to surface as well bulk. To this end, we utilize cathodoluminescence imaging top a layer deeply buried (In,$\mathrm{Ga}$)N quantum well. Varying acceleration voltage primary electrons comparing signal from enables us probe at depths ranging vicinity position Our experiments are accompanied by fully...

A combination of a molecular beam epitaxy (MBE) machine and six circle diffractometer has been constructed at dedicated wiggler beamline the storage ring BESSY II for in situ investigations III–V compound crystal growth. The growth conditions our system reach high MBE standard with noncooled base pressure 2×10−10 mbar. fast entry load lock is available sample exchange. Large-area Be windows ultrahigh vacuum chamber allow us to measure reflections entrance exit angles up 45°, i.e., large...

We theoretically analyze the contrast observed at outcrop of a threading dislocation GaN(0001) surface in cathodoluminescence and electron-beam induced current maps. consider exciton diffusion recombination including finite velocities both planar dislocation. Formulating reciprocity theorem for this general case enables us to provide rigorous analytical solution diffusion-recombination problem. The results calculations are applied an experimental example determine length strength...

Densities of a- and a+c-type threading dislocations for a series GaN films grown in different modes by metalorganic vapor phase epitaxy are determined from the x-ray diffraction profiles skew geometry. The reciprocal space maps also studied. Theory scattering crystals with is extended order to take into account contribution both misfit dislocations. broadening along surface normal rotation intensity distribution ellipse attributed at interface. We find that presence sharp AlN/GaN interface...

We compare the packing characteristics of alkyl chains in Langmuir monolayers nonchiral and racemic compounds as determined from available grazing incidence X-ray diffraction data. The analysis demonstrates a gradual change projected unit cell dimensions those hexagonal hydrocarbon chains, characteristic high-temperature monolayer phases, to one two more dense rectangular modes with 5.0 × 7.5 Å2 4.4 8.7 Å2, low-temperature phases. incorporates well-known herringbone arrangement, an ideally...

A theory of the formation X-ray images microdefects is developed. It shown that at sufficiently high collimation incident wave it possible not only to reveal such defects but also obtain their elastic fields almost without any additional diffraction within Borrmann fan typical conventional topography. The possibility observe displacement near with dimensions beyond limits topography resolution demonstrated aid computer simulation and analytical estimates. plane-wave give information on type,...

An analysis of the strain in an axial nanowire superlattice shows that dominating state can be defined arbitrarily between unstrained and maximum mismatch by choosing segment height ratios. We give experimental evidence for a successful design series GaN ensembles with InxGa1–xN quantum wells. vary barrier thickness determine wells Raman spectroscopy. A detailed calculation distribution LO phonon frequency shift uniform in-plane lattice constant segments satisfactorily describes resonant...

Lattice distortions in a cylindrical nanowire with nonuniform intrinsic strains arbitrarily varying along its axis are analyzed, special emphasis on heterostructures. We find that, as result of the elastic relaxation side surface, lateral mismatch does not change average longitudinal lattice period whole cylinder, but effects heterostructure. As consequence, positions x-ray diffraction peaks due to periodic axial heterostructure depend ratio total height cylinder diameter. The attain planar...

We investigate the origin of fast recombination dynamics bound and free excitons in GaN nanowire ensembles by temperature-dependent photoluminescence spectroscopy using both continuous-wave pulsed excitation. The exciton present nanowires is dominated a nonradiative channel between 10 300 K. Furthermore, NWs are strongly coupled even at low temperatures resulting common lifetime these states. By solving rate equations for two-level system, we show that one cannot, practice, distinguish...

We study the molecular beam epitaxy of rock-salt ScN on wurtzite GaN(11̅00) surface. To this end, is grown freestanding substrates and self-assembled GaN nanowires exhibiting (11̅00) sidewalls. On both substrates, crystallizes twin-free thanks to a specific epitaxial relationship, namely ScN(110)[001]∥GaN(11̅00)[0001], providing congruent, low-symmetry interface. The 13.1% uniaxial lattice mismatch occurring in orientation mostly relaxes within first few monolayers growth by forming...

A model of interacting rigid rods is proposed to describe tilting phase transitions in monolayers freely rotating long-chain molecules with hexatic in-plane order. The takes into account steric repulsion and van der Waals attraction between neighboring as well the orientational entropy individual rods, all within a mean field approximation limited unit cell. Two variants are proposed, different constraints on polar molecular headgroups. In first, headgroups grafted hexagonal close-packed...

Seven structurally distinct condensed phases in the phase diagram of water-supported Langmuir monolayers are explained framework Landau theory transitions. The present treatment, which covers two-dimensional hexatic and solid describes transitions between them, involves coupling three order parameters. One parameters governs collective tilt molecules, while other two describe one-dimensional ``weak crystallization'' along bond direction normal to it with herringbone ordering molecular...