(In1−xErx)2O3 ternary alloys are grown on A‐plane sapphire wafers by plasma‐assisted molecular beam epitaxy. The layers crystallize in the cubic bixbyite structure with axis aligned parallel to the substrate normal. The d‐spacing of the {111} lattice planes linearly increases with increasing the Er molar fraction in accordance with Vegard's law. Incorporation of Er in the In2O3 matrix is accompanied by the widening of the optical gap and linear increase of the peak absorption coefficient reaching 380 cm−1 at the telecommunication wavelength of 1.54 µm. The samples exhibit Er3+‐related emission at indirect excitation via the crystalline host at room temperature.

We demonstrate the use of a 3D printed radial collimator in X-ray powder diffraction and surface sensitive grazing incidence X-ray diffraction. We find a significant improvement in the overall signal to background ratio of up to 100 and a suppression of more than a factor 3 · 105 for undesirable Bragg reflections generated by the X-ray "transparent" windows of the sample environment. The background reduction and the removal of the high intensity signals from the windows, which limit the detector's dynamic range, enable significantly higher sensitivity in experiments within sample environments such as vacuum chambers and gas- or liquid-cells. Details of the additively manufactured steel collimator geometry, alignment strategies using X-ray fluorescence, and data analysis are also briefly discussed. The flexibility and affordability of 3D prints enable designs optimized for specific detectors and sample environments, without compromising the degrees of freedom of the diffractometer.

We present a combined experimental and theoretical study to solve the unit-cell and molecular arrangement of the tetracene thin film (TF) phase. TF phases, also known as substrate induced phases (SIPs), are polymorphs that exist at interfaces and decisively impact the functionality of organic thin films, e.g., in a transistor channel, but also change the optical spectra due to the different molecular packing. As SIPs only exist in textured ultrathin films, their structure determination remains challenging compared to bulk materials. Here, we use grazing incidence X-ray diffraction and atomistic simulations to extract the TF unit-cell parameters of tetracene together with the atomic positions within the unit-cell.

A novel strategy for direct photoalignment of molecular materials using optothermal re-orientation is introduced. Photoalignment for molecular materials such as the organic semiconductor tetracene is shown, without relying on additional photoreactive dopants or alignment layers. Patterning and polarized light emission, e.g., for polarized organic light emitting diodes is demonstrated.

We investigate the influence of light on the growth process and resulting phase coexistence of the organic semiconductor α-sexithiophene (6T). We demonstrate that 6T thin films deposited on potassium chloride (KCl) in dark environments exhibit a bimodal growth, with phase coexistence of both low-temperature (LT) and high-temperature (HT) polymorphs. In contrast, films grown under illumination with 532 nm light at 1.5 W/cm2 exhibit an increased purity of the LT phase, while the HT phase growth is slowed down by about a factor of 4. To understand the mechanism behind this optical control, we use in situ X-ray diffraction, atomic force microscopy, optical absorption measurements, as well as first-principles calculations for the optical absorption spectra of the HT and LT phase. We deduce that the phase purification is due to optical heating of the molecular film and lower cohesive energy of the HT phase compared to the LT phase, so that nucleation and growth of the HT phase are significantly reduced by light...

Sn-doped In-2 O-3 films with free-electron concentration varied up to 1.710cm are prepared by molecular beam epitaxy. In this way, a metallic Drude-type dielectric function with a negative real part extending beyond =1050nm is created. Despite essentially polycrystalline structure of the layers, the plasmonic damping is found not to exceed 70meV in the entire doping range making excitation of low-loss surface plasmon polaritons at frequencies fully covering the telecommunication band feasible. A monotonically increasing discrepancy between the carrier concentration obtained from Hall-effect and the concentration extracted from fitting the optical spectra hints at a change of the band-structure related parameters of In-2 O-3 with increasing Sn-doping.

We demonstrate a proof-of-concept refractive index sensor based on heavily doped ZnO:Ga nanostructured in a grating configuration, which supports free space excitation of propagating surface plasmons. The bulk sensitivity of the sensor of 4.9 × 103 nm per refractive index unit, achieved in the mid-infrared spectral range with the first grating prototype, surpasses that of the noble metal counterparts by three to four times. Sensing performance is discussed in the light of numerical simulations of the spatial profile of the near field of surface plasmon polaritons.

Thick AlxGa1−xN layers were grown by hydride vapor phase epitaxy on hexagonally patterned sapphire substrates. Non-c-planar growth is found inside the etched honeycombs which in part hinders coalescence of the c-plane AlGaN layer growing on top of the ridges. From X-ray diffraction, electron backscatter diffraction and scanning electron microscopy, the orientations of the parasitic crystallites were identified as {11–22} and {1–103} AlGaN growing on m-plane sapphire sidewalls as well as c-plane oriented AlGaN growing on n-plane sidewall facets which are located in the corners of the combs. According to the geometry of parasitic crystallites, it is further observed, that the semipolar growth occurring on sapphire m-plane sidewalls does not hinder the coalescence of c-plane AlGaN growing on top of the ridges, whereas fast propagation of parasitic crystallites nucleating on n-plane sidewall facets leads to delayed layer coalescence.

Heavily Ga-doped ZnO layers are grown on bulk ZnO wafers by molecular beam epitaxy. The layers grow in a two-dimensional pseudomorphic mode with high structural quality under increase of the c-lattice constant up to free-electron concentrations of 1021cm-3. Formation of Zn-polar inversion domains in the O-polar ZnO matrix is identified as the limiting factor for the incorporation of electrically active Ga. The domain formation can be inhibited by growing with larger excess of Zn. This results in a shift of surface plasmon frequency of =100meV and allows for covering the telecommunication wavelength range.

Doping of ZnO by Ga allows for generation of free electrons up to concentrations of about 1021 cm3 without significant deterioration of the crystal structure. In this way, a metallic dielectric function is formed with a negative real part tuneable from the mid infrared up to telecommunication wavelengths. The losses are about one order of magnitude lower than in traditional metals. We demonstrate surface plasmon polaritons with dispersion relations that can be engineered in a unique way by utilizing epitaxial multi-layer structures of different doping level. In contrast to the standard air/metal excitations, the surface-plasmon-polariton frequency approaches a finite value in the zero-wavevector limit at metal/metaltype interfaces. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Molecular semiconductors are increasingly used in devices, but understanding of elementary nanoscopic processes in molecular film growth is in its infancy. Here we use real-time in situ specular and diffuse X-ray scattering in combination with kinetic Monte Carlo simulations to study C 60 nucleation and multilayer growth. We determine a self-consistent set of energy parameters describing both intra- and interlayer diffusion processes in C 60 growth. This approach yields an effective Ehrlich–Schwoebel barrier of E ES =110 meV, diffusion barrier of E D =540 meV and binding energy of E B =130 meV. Analysing the particle-resolved dynamics, we find that the lateral diffusion is similar to colloids, but characterized by an atom-like Schwoebel barrier. Our results contribute to a fundamental understanding of molecular growth processes in a system, which forms an important intermediate case between atoms and colloids.

We demonstrate that Zn(Mg)O:Ga layers can be grown by molecular beam epitaxy in a two-dimensional mode with high structural perfection up to Ga mole fractions of about 6.5%. The doping efficiency is practically 100% so that free-carrier concentrations of almost 1021 cm−3 can be realized providing a zero-crossover wavelength of the real part of the dielectric function as short as 1.36 μm, while the plasmonic damping does not exceed 50 meV. Structural, electrical, and optical data consistently demonstrate a profound change of the Ga incorporation mode beyond concentrations of 1021 cm−3 attended by deterioration of the plasmonic features.

Arrays of crystalline and regularly spaced pentacene nanocolumns, with a typical diameter of ca. 150nm, were fabricated by glancing angle deposition on indium tin oxide substrates. The nanocolumn arrays were used to form large interface area organic heterojunction photovoltaic cells (OPVCs) by spin coating [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor material to fill the voids between nanocolumn. The light to electrical energy conversion efficiency of nanocolumn-based OPVCs was three times higher compared to planar heterojunction OPVCs of the same materials due to a significantly enlarged donor/acceptor interface area where exciton dissociation can occur. Further OPVC performance improvement was achieved through employing a thin pentacene electron-blocking layer before nanocolumn formation, which prevented electron current leakage to the anode.

The morphology of nanocolumns grown by glancing angle deposition is studied for molecular materials forming amorphous and crystalline solids. Amorphous tris(8-hydroxyquinoline)aluminum nanocolumn arrays were obtained at sample rotation speeds varying from 0.3 rpm (revolutions per minute) to 30 rpm. For crystalline pentacene, an array of regular nanocolumns formed at a rotation speed of 3 rpm, while higher and lower rotation speeds led to a wide distribution of column heights and shapes. The incoming molecular flux and the molecular diffusion length on column surfaces, both dependent on rotation speed, were found to govern the resulting morphology of crystalline pentacene nanocolumns.

Anisotropic surface diffusion and strain are used to explain the formation of three-dimensional (In,Ga)As quantum dot lattices. The diffusion characteristics of the surface, coupled with the elastic anisotropy of the matrix, provides an excellent opportunity to influence the dot positions. In particular, quantum dots that are laterally organized into long chains or chessboard two-dimensional arrays vertically organized with strict vertical ordering or vertical ordering that is inclined to the sample surface normal are accurately predicted and observed.

Grazing incidence small-angle x-ray scattering and grazing incidence x-ray diffraction from SiGe nanoscale islands grown on Si(001) substrate were investigated. Experiments and corresponding theoretical simulations based on the distorted-wave Born approximation were carried out. The strain field inside and in the vicinity of the SiGe islands was calculated in the framework of linear elasticity theory using the numerical finite element method. The diffuse intensity pattern in reciprocal space reveals a well-resolved fine structure with prominent maxima and a complicated fringe pattern. The distribution of diffuse intensity in reciprocal space strongly depends on the angle of incidence with respect to the sample surface. The results obtained substantiate the important role of basically five (grazing incidence small-angle x-ray) and nine (grazing incidence diffraction) scattering channels that have to be considered for a complete understanding of the scattering scenario. A refined island model concerning shape, size, and Ge composition was elaborated.

We report on a specific growth procedure combining low-temperature growth of ZnMgO and postgrowth annealing at intermediate temperatures. Despite the large lattice misfit induced by the sapphire substrate, layer-by-layer growth is accomplished up to the phase-separation limit found at a c-lattice constant of 0.5136 nm and Mg mole fraction of 0.40. The procedure allows us to grow quantum wells with atomically smooth interfaces in a wide range of structural designs exhibiting prominent emission features up to room temperature.