Electronics with semiconductors rely strongly on defect concentrations and on the properties of these defects. Here we study ZnO thin films which were grown by atomic layer deposition. An interesting mechanism of build-up and of self-healing of Zn interstitial defects as a function of layer thickness d was found, based on measurements of photoabsorption (PA), photoluminescence (PL) and x-ray diffraction as a function of d. The concentration of Zn interstitial defects increases up to d = 19 nm, coupled with a corresponding increase of the Urbach energy, Eu, in PA. At this layer thickness, the growth mode changes from the formation of a homogeneous layer to a layer of nano-crystals, where the nano-crystals grow in size with d. Surprisingly, the Zn interstitial concentration decreases spontaneously once the layer thickness exceeds d = 38 nm. We explain this behavior by a reduction of diffusion barriers for Zn interstitials as a function of average ZnO particle size leading to spontaneous diffusion to the particle surface and subsequent oxidation therein. At the same time, the concentration of oxygen vacancies, mostly located at the particle surface, is greatly reduced with increasing film thickness. The study is of importance in designing opto- and nano-electronic devices by means of appropriate selection of ZnO film thickness, for targeted quality, property and further practical applications.

In the large field of research on nanoplatelets (NPLs), their strong tendency to self‐assemble into ordered stacks and the resulting changes in their properties are of great interest. The assembly reveals new characteristics such as the charge carrier transport through the NPL assembly or altered optical properties. In particular, a reduced distance should enhance the charge carrier transport due to higher electronic coupling of neighboring NPLs, and therefore, is the focus of this work. To modify the inter‐particle distances, the straightforward method of ligand exchange is applied. Various CdSe and CdSe/CdX (hetero‐) NPLs serve as building blocks, which not only display different material combinations but also different types of heterostructures. The surface‐to‐surface distance between the stacked NPLs can be reduced to below 1 nm, thus, to less than the half compared to assemblies of pristine NPLs. Moreover, for certain NPLs stacking is only enabled by the ligand exchange. To characterize the ligand exchanges and to investigate the influences of the reduced distances, photo‐electrochemical measurements, fluorescence spectroscopy, energy dispersive X‐ray spectroscopy, nuclear magnetic resonance, and X‐ray photoelectron spectroscopy are performed. It is possible to show higher photocurrents for smaller distances, indicating enhanced charge transport ability within those stacks.

The Si(553) surface, covered with half a monolayer of gold, forms a double strand of well-ordered atomic Au chains in each miniterrace. It represents one of the smallest possible realizations of quasi-one-dimensional (1D) systems. In this prototype system, by combining DC conductance and low-energy electron diffraction measurements with density functional calculations and ab initio Monte Carlo simulations, we demonstrate that nonlocal electronic correlations, together with thermal excitations, lead to peculiar phase transitions without long-range order. They are characterized by marginal (average) geometric relaxations, but with huge variations of the electronic band structure and concomitant strong temperature-dependent modifications of the density of states close to the Fermi level. Similar phenomena are expected in the large class of quasi-1D conductors and open a wide range of possibilities for their controlled manipulation. It is the increasing hybridization between spin-polarized Au and Si edge states that makes the Si dangling bond states at the step edge conducting, first as a transient between two insulating phases and finally opening a permanent new 1D conduction channel at high temperatures.

Bi-layer epitaxial graphene (BLG) on 6H-SiC(0001) (EG/SiC) was grown and modified by thermal deposition of the molecular electron acceptor tetrafluoro-tetra cyano quinodimethane (F4-TCNQ). The surface-modified system, F4-TCNQ/EG/SiC, was studied by X-ray photoelectron spectroscopy (XPS) and angle-resolved polarized Raman spectroscopy (ARPRS). XPS results indicate that bonding of deposited F4-TCNQ molecules depends on their concentration. Although bonding through the cyano groups is present at all concentrations, charge transfer from graphene to fluorine is evident only at sub-monolayer concentrations. The corresponding change in bond character is coupled with a change in molecular orientation. Raman spectroscopy not only provides results consistent with the findings from the XPS study but also reveals a significant degree of molecular stacking above the monolayer concentration. Thus, both the variation of the acceptor concentration and the number of graphene layers provide further handles to manipulate charge and doping that may be useful in device applications.

The complex behavior of magnetoconductance of Bi films grown epitaxially on Si(111) with a thickness of 20-100 bilayers (BL) was measured at T= 9 K in magnetic fields up to B = 4 T, oriented in-plane parallel and perpendicular to the electric dc current I. Contributions to magnetoconductance (MC) by diffuse scattering, by weak localization (WL) as well as by weak antilocalization (WAL) were identified. All these components to MC turned out to be isotropic in two dimensions, i.e., no dependence on angle between B and I within the surface plane was found. Only for B perpendicular to I an increase of MC was detected that is, to first approximation, proportional to B-2. It is ascribed to ballistic scattering between the Rashba-split interfaces that allow Umklapp scattering without spin flip. While MC within the surface states, dominant at small thicknesses, d, shows negligible diffuse scattering under the chosen geometry, their quantum corrections are characterized by WAL with alpha = -0.3 and a coupling strength that decays alpha 1/d with layer thickness. The admixing of quantized bulk states, which dominates MC above 50 BL, not only increases diffuse scattering, it introduces WL in combination with WAL. Presumably due to hybridization with the surface states, it also modifies strongly the WAL component for d > 60 BL. Thus our findings suggest an intriguing interplay in magnetotransport between 2D and quantized 3D states at the Fermi surface of ultrathin bismuth quantum films and provide further deep insight into the electronic transport in quantized and partly spin split bands.

One-dimensional wires are known to be inherently unstable at finite temperature. Here, we show that long-range order of atomic Au double chains adsorbed on a Si(553) surface is not only stabilized by interaction with the substrate, but spontaneous self-healing of structural defects is actually enforced by the adsorption of atomic species such as Au or H. This is true even for random adsorbate distribution. Combining atomistic models within density functional theory with low energy electron diffraction and high-resolution electron energy loss spectroscopy, we demonstrate that this apparently counterintuitive behavior is mainly caused by adsorption-induced band filling of modified surface bands, i.e., by the strong electronic correlation throughout the whole terrace. Although adsorption preferably occurs at the step edge, it enhances the dimerization and the stiffness of the Au dimers. Thus, the intertwinement of quasi-1D properties with delocalized 2D effects enforces the atomic wire order.

Quantum size effects on interferons (electron-phonon bound states), confined in fractal silicon (Si) nanostructures (NSs), have been studied by using Raman spectromicroscopy. A paradoxical size dependence of Fano parameters, estimated from Raman spectra, has been observed as a consequence of longitudinal variation of nanocrystallite size along the Si wires leading to local variations in the dopants' density which actually starts governing the Fano coupling, thus liberating the interferons to exhibit the typical quantum size effect. These interferons are more dominated by the effective reduction in dopants' density rather than the quantum confinement effect. Detailed experimental and theoretical Raman line shape analyses have been performed to solve the paradox by establishing that the increasing size effect actually is accompanied by receding Fano coupling due to the weakened electronic continuum. The latter has been validated by observing a consequent variation in the Raman signal from dopants which was found to be consistent with the above conclusion.

Lithium-sulfur (Li-S) batteries have attracted widespread attention due to their high theoretical energy density. However, their practical application is still hindered by the shuttle effect and the sluggish conversion of lithium polysulfides (LiPSs). Herein, monodisperse molybdenum (Mo) nanoparticles embedded onto nitrogen-doped graphene (Mo@N-G) were developed and used as a highly efficient electrocatalyst to enhance LiPS conversion. The weight ratio of the electrocatalyst in the catalyst/sulfur cathode is only 9%. The unfilled d orbitals of oxidized Mo can attract the electrons of LiPS anions and form Mo-S bonds during the electrochemical process, thus facilitating fast conversion of LiPSs. Li-S batteries based on the Mo@N-G/S cathode can exhibit excellent rate performance, large capacity, and superior cycling stability. Moreover, Mo@N-G also plays an important role in room-temperature quasi-solid-state Li-S batteries. These interesting findings suggest the great potential of Mo nanoparticles in building high-performance Li-S batteries.

In this work, a closed loop recycling process is investigated, which allows polymerised bulk thermoplastic matrix (Elium 150) from production waste (also referred to as recyclate) to be reused as additive in composite manufacturing by vacuum assisted resin infusion (VARI) of virgin Elium 150 monomer. It is shown that this process can save up to 7.5 wt% of virgin material usage in each processing cycle. At the same time, the thermal stability and stiffness of the composite increases with the proportion of recyclate introduced. Contemporarily, the shear and bending properties have also been observed to improve. Gel permeation chromatography (GPC) showed that the changes observed are due to an increase in molecular weight with the recyclate content. In particular, a correlation between the molecular weight and the shear properties of the composite was discovered using single fibre push-out tests.

Even though there have been many experimental attempts and theoretical approaches to understand the process of electromigration (EM), it has not been quantitatively understood for ultrathin structures and at grain boundaries. Nevertheless, we showed recently that it can be used reliably for the formation of single atomic point contacts after careful pre-structuring of the initial Ag nanostructures. The process of formation of nanocontacts by EM down to a single-atom point contact was investigated for ultrathin (5 nm) Ag structures at 100 K by measuring the conductance as a function of the time during EM. In this paper, we compare the process of thinning by EM of structures with constrictions below the average grain size of Ag layers (15 nm) with that of structures with much larger initial constrictions of around 150 nm having multiple grains at the centre constriction prior to the formation of a point contact. Even though clear morphological differences exist between both types of structures, quantized conductance plateaus showing the formation of single point contacts have been observed for both. Here we put emphasis on the thinning process by EM, just before a point contact is formed. To understand this thinning process, the semi-classical regime before the contact reaches the quantum regime was analyzed in detail. For this purpose, we used experimental conductance histograms in the range between 2G 0 and 15G 0 and their corresponding Fourier transforms (FTs). The FT analysis of the conductance histograms exhibits a clear preference for thinning along the [100] direction. Using well-established models, both atom-by-atom steps and ranges of stability, presumably caused by electronic shell effects, can be discriminated. Although the directional motion of atoms during EM leads to specific properties such as the instabilities mentioned, similarities to mechanically opened contacts with respect to cross-sectional stability were found.

In this paper, we present a comprehensive investigation of the epitaxial growth of Ba2SiO4 on Si(001), a system in which neither crystal symmetry nor lattice constants match in a simple manner. In addition, it has the potential to become the first crystalline high-k gate dielectric. We combined x-ray photoelectron spectroscopy, low-energy electron diffraction, and aberration-corrected scanning transmission electron microscopy (STEM) in order to optimize the epitaxial growth by molecular beam epitaxy. Our focus was on the formation of a high quality crystalline interface. The films were grown by a co-deposition method that requires no diffusion of Si from the substrate. An annealing temperature of 400 degrees C turned out to be sufficient to form chemically homogeneous films. However, crystalline films require an annealing step to 670-690 degrees C for the formation of the epitaxial interface necessary for breaking Si-O bonds. STEM confirms that the interface is atomically sharp and that a single layer of the silicate is changed to a (2 x 3) structure at the interface from the (2 x 1.5) bulk structure. Based on our experimental results, we propose a geometrical model for the epitaxial interface. The growth of films with an understoichiometric Si flux leads to the formation of a near-surface Ba silicide that does not restrict the epitaxial silicate growth.

Several critical issues, such as the shuttling effect and the sluggish reaction kinetics, exist in the design of high‐performance lithium–sulfur (Li‐S) batteries. Here, it is reported that nitrogen doping can simultaneously and significantly improve both the immobilization and catalyzation effects of Co 9 S 8 nanoparticles in Li‐S batteries. Combining the theoretical calculations with experimental investigations, it is revealed that nitrogen atoms can increase the binding energies between LiPSs and Co 9 S 8 , and as well as alleviate the sluggish kinetics of Li‐S chemistry in the Li 2 S 6 cathode. The same effects are also observed when adding N‐Co 9 S 8 nanoparticles into the commercial Li 2 S cathode (which has various intrinsic advantages, but unfortunately a high overpotential). A remarkable improvement in the battery performances in both cases is observed. The work brings heteroatom‐doped Co 9 S 8 to the attention of designing high‐performance Li‐S batteries. A fundamental understanding of the inhibition of LiPSs shuttle and the catalytic effect of Li 2 S in the newly developed system may encourage more effort along this interesting direction.

Pictorial representation of the as-prepared device in ON and OFF states with itsin situabsorbance spectra at various applied biases.

A dense nanofilm of Co3O4 is synthesized using constant current electrodeposition on a conducting transparent electrode that works not only as a counter electrode but also shows electrochromic (EC) properties on its own. The isolated active nano‐Co3O4 electrode shows reduction in the redox potential and good color contrast between its yellowish transparent and dark states at different bias conditions. The electrode shows improved color contrast, stability, and cycle life. In situ spectroelectrochemical studies of the nanoelectrode reveals that the bias‐induced redox activity of the metal oxide leads to the color change between yellowish and opaque states. The bias‐induced color change makes it an active EC counter‐ion electrode for appropriate solid‐state EC devices.

3D nanoparticle assemblies offer a unique platform to enhance and extend the functionality and optical/electrical properties of individual nanoparticles. Especially, a self-supported, voluminous, and porous macroscopic material built up from interconnected semiconductor nanoparticles provides new possibilities in the field of sensing, optoelectronics, and photovoltaics. Herein, a method is demonstrated for assembling semiconductor nanoparticle systems containing building blocks possessing different composition, size, shape, and surface ligands. The method is based on the controlled destabilization of the particles triggered by trivalent cations (Y3+ , Yb3+ , and Al3+ ). The effect of the cations is investigated via X-ray photoelectron spectroscopy. The macroscopic, self-supported aerogels consist of the hyperbranched network of interconnected CdSe/CdS dot-in-rods, or CdSe/CdS as well as CdSe/CdTe core-crown nanoplatelets is used to demonstrate the versatility of the procedure. The non-oxidative assembly method takes place at room temperature without thermal activation in several hours and preserves the shape and the fluorescence of the building blocks. The assembled nanoparticle network provides longer exciton lifetimes with retained photoluminescence quantum yields, that make these nanostructured materials a perfect platform for novel multifunctional 3D networks in sensing. Various sets of photoelectrochemical measurements on the interconnected semiconductor nanorod structures also reveal the enhanced charge carrier separation.

The magnetoconductance of Bi films grown epitaxially on Si(111) for a film thickness between 10 and 100 bilayers (BL) was investigated at a temperature of T = 9 K in magnetic fields up to 4 T oriented perpendicular to the surface plane. The thickness dependence of magnetoconductance (MC) and Hall resistivity was investigated in order to derive thickness dependent charge carrier concentrations as well as their mobilities and to identify corrections by weak antilocalization (WAL) to magnetoconductance. While the electronic transport in ultrathin films up to 30 bilayers (BL) turned out to take place mainly within the surface states, contributions of (bulk derived) quantum well states mix in at larger thicknesses and dominate incoherent transport above 70 BL. On the contrary, for the WAL contribution at magnetic fields normal to the surface, scattering within the surface states dominates at all thicknesses, as evident from the gradual change from values of alpha = -0.35 to alpha = -1 as a function of thickness. This finding reflects the decrease of coupling between the two interfaces going from a single combined conduction channel to two independent channels at the highest film thickness. Quick changes of both parts of magnetoconductance as a function of film thickness at the thinnest films seem to be strain induced by the Bi/Si interface. These results will advance the understanding of the transport properties of Bi thin films and reveal exotic quantum phenomena.

Electronic properties of low dimensional structures on surfaces can be comprehensively explored by surface transport experiments. However, the surface sensitivity of this technique to atomic structures comes along with the control of bulk related electron paths and internal interfaces. Here we analyzed the role of Schottky-barriers and space charge layers for Si-surfaces. By means of a metal submonolayer coverage deposited on vicinal Si(1 1 1), we reliably accessed subsurface transport channels via angle- and temperature-dependent in situ transport measurements. In particular, high temperature treatments performed under ultra high vacuum conditions led to the formation of surface-near bulk defects, e.g. SiC-interstitials. Obviously, these defects act as p-type dopants and easily overcompensate lightly n-doped Si substrates.

Background:The process of electromigration is still not quantitatively understood. We showed recently that it can be used reliably for formation of single atomic point contacts in pre-structured Ag nanostructures. Results:The process of formation of nanocontacts by electromigration (EM) down to a single atomic point contact was investigated for ultrathin (5 nm) Ag structures at 100\,K. In this paper, we compare the structures with constrictions below the average grain size of Ag layers (15 nm), where the contribution of a single grain dominates, with structures of much larger constrictions of around 150 nm with multiple grains at the centre constriction during the initial steps of EM. The latter initially form filamentous structures. Despite these clear morphological differences, the conductance traces of both types of structures suggest that finally, i.e., in the quantized conduction regime, only one atomic point contact was formed. To analyse the thinning process within the semi-classical regime in detail, we used experimental conductance histograms in the range between 2 G0 and 15G0 and their corresponding Fourier transforms (FT). The FT analysis of the conductance histograms exhibits a clear preference for thinning along the [100] direction. Using well-established models, both atom-by-atom steps and ranges of stability, presumably caused by electronic shell effects, can be discriminated. A large range (5 to 14G0) of unstable conductance values was found in these electromigrated contacts that has not been reported by other techniques. It was observed irrespective of the initial geometry. Conclusion: Although the directional motion of atoms during EM leads to specific properties like the instabilities mentioned, similarities to mechanically opened contacts with respect to cross sectional stability were found.

In this study, the growth of Sn on Si(557) surfaces by means of scanning tunneling microscopy, low energy electron diffraction and angle resolved photoemission is analyzed. Depending on the Sn submonolayer coverage, various Sn‐nanowires are identified. For Sn‐coverages above 0.5 ML, ()‐ and ()‐reconstructions are found. In particular, these phases cover extended (111)‐areas, thus leading to an inhomogeneous refacetting of the Si(557) surface. The (223)‐facets between the mini‐(111) terraces reveal structures, which resemble a ×2 reconstruction along edges. The initial step structure of the Si(557) surface is maintained for Sn‐coverages below 0.5 ML, showing the α‐Sn phase on 3 nm wide (111)‐terraces. In contrast to the 2D Mott state of α‐Sn/Si(111), this confinement seems to quench the correlated electronic phase yielding metallic surface states at 40 K, in accordance with photoemission.