Tailoring the nature and strength of electron-phonon interactions in the SrTiO3(001) 2D electron liquid.

Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface to reveal a remarkably complex evolution of electron-phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron-phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs.

Transition from Reconstruction toward Thin Film on the (110) Surface of Strontium Titanate.

The surfaces of metal oxides often are reconstructed with a geometry and composition that is considerably different from a simple termination of the bulk. Such structures can also be viewed as ultrathin films, epitaxed on a substrate. Here, the reconstructions of the SrTiO3 (110) surface are studied combining scanning tunneling microscopy (STM), transmission electron diffraction, and X-ray absorption spectroscopy (XAS), and analyzed with density functional theory calculations. Whereas SrTiO3 (110) invariably terminates with an overlayer of titania, with increasing density its structure switches from n × 1 to 2 × n. At the same time the coordination of the Ti atoms changes from a network of corner-sharing tetrahedra to a double layer of edge-shared octahedra with bridging units of octahedrally coordinated strontium. This transition from the n × 1 to 2 × n reconstructions is a transition from a pseudomorphically stabilized tetrahedral network toward an octahedral titania thin film with stress-relief from octahedral strontia units at the surface.

Subsurface cation vacancy stabilization of the magnetite (001) surface.

Iron oxides play an increasingly prominent role in heterogeneous catalysis, hydrogen production, spintronics, and drug delivery. The surface or material interface can be performance-limiting in these applications, so it is vital to determine accurate atomic-scale structures for iron oxides and understand why they form. Using a combination of quantitative low-energy electron diffraction, scanning tunneling microscopy, and density functional theory calculations, we show that an ordered array of subsurface iron vacancies and interstitials underlies the well-known (√2 × âˆš2)R45° reconstruction of Fe3O4(001). This hitherto unobserved stabilization mechanism occurs because the iron oxides prefer to redistribute cations in the lattice in response to oxidizing or reducing environments. Many other metal oxides also achieve stoichiometry variation in this way, so such surface structures are likely commonplace.

The growth of ultra-thin zirconia films on Pd(3)Zr(0 0 0 1).

Despite its importance in many areas of industry, such as catalysis, fuel cell technology and microelectronics, the surface structure and physical properties of ZrO2 are not well understood. Following the successful growth of ultra-thin zirconia on Pt3Zr(0 0 0 1) (Antlanger et al 2012 Phys. Rev. B 86 035451), we report on recent progress into ZrO2 thin films, which were prepared by oxidation of a Pd3Zr(0 0 0 1) crystal. Results from scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS) as well as density-functional theory (DFT) are presented. Many sputter-annealing cycles are required for preparation of the clean Pd3Zr alloy surface, because oxygen easily dissolves in the bulk. By oxidation and post-annealing, a homogeneous ultra-thin ZrO2 film was obtained. This is an O-Zr-O trilayer based on cubic ZrO2(1 1 1). Using STM images corrected for distortion and creep of the piezo scanner the in-plane lattice parameter was determined as (351.2 ± 0.4) pm, slightly contracted with respect to the cubic ZrO2 bulk phase. The oxide forms an overlayer that is either incommensurate or has a very large superstructure cell (a = 8.3 nm); nevertheless its rotational orientation is always the same. In contrast to ultra-thin zirconia on Pt3Zr(0 0 0 1), where the uppermost substrate layer is pure (but reconstructed) Pt, STM and XPS suggest a stoichiometric Pd3Zr below the oxide. The oxide film binds to the substrate mainly via bonds between oxygen and the Zr atoms in the substrate. The ultra-thin oxide shows large buckling in STM, confirmed by DFT calculations, where the buckling of the Zr layer can exceed 100 pm. Compared to the ZrO2 film on Pt3Zr(0 0 0 1), the oxide on Pd3Zr(0 0 0 1) has the advantage that the substrate below does not reconstruct, leading to a homogeneous oxide film.

Imaging cluster surfaces with atomic resolution: the strong metal-support interaction state of Pt supported on TiO2(110)

Nanosized platinum clusters were grown on a TiO2(110) surface and annealed in ultrahigh vacuum at high temperatures. This leads to the so-called strong metal-support interaction (SMSI) state, characterized by a complete encapsulation of the clusters with a reduced titanium oxide layer. We present atomically resolved scanning tunneling microscopy measurements of the cluster surfaces and an atomic model of the SMSI state. The ability to resolve the cluster surface geometry with atomistic detail may help to identify the active sites responsible for the SMSI.

Benign childhood epilepsy with centrotemporal spikes and electroencephalography trait are not linked to EBN1 and EBN2 of benign neonatal familial convulsions.

PURPOSE: The electroencephalographic hallmark of benign childhood epilepsy with centrotemporal spikes (BECTS, or rolandic epilepsy) are characteristically shaped centrotemporal spikes and sharp waves (CTS). This EEG trait, but not BECTS itself, has been reported to follow an autosomal dominant mode of inheritance with incomplete penetrance and age dependence. CTS therefore represents a neurobiologic marker for the increased risk of developing BECTS. Benign neonatal familial convulsions (BNFC) like BECTS is an idiopathic age-dependent epilepsy with a benign course. Observations of benign neonatal seizures and BECTS in the same individual are well documented. Neonatal seizures with benign course were found in increased numbers in a series of CTS carriers. Two genetic loci, EBN1 and EBN2, have been mapped in families with BNFC, making these two loci strong candidates for the CTS trait underlying BECTS. The aim of this study was to determine whether these two epilepsy syndromes are allelic disorders. METHODS: Linkage analysis was performed in 12 families with probands with BECTS and one or more relatives with CTS in the EEG with or without BECTS by using polymorphic DNA markers. RESULTS: Assuming an autosomal mode of inheritance with penetrances of 0.9 and 0.45, respectively, both loci were consistently excluded. CONCLUSIONS: The CTS trait and EBN1 and EBN2 segregate independently. BECTS and BNFC therefore appear to be genetically distinct entities. Benign neonatal seizures may be a underrecognized symptom of the CTS trait itself.

Exclusion of linkage of genetic focal sharp waves to the HLA region on chromosome 6p in families with benign partial epilepsy with centrotemporal sharp waves.

Benign partial epilepsy with centrotemporal sharp waves (benign rolandic epilepsy, BRE) is a common form of idiopathic, localisation-related epilepsy of childhood. The characteristic age-dependent focal sharp wave (fsw) found on the EEG in this disorder segregates as an autosomal dominant trait in families with probands with BRE and acts as a neurobiological marker for the increased risk of developing BRE, other benign partial epilepsies of childhood, and other developmental disorders in these families. One of the genes for idiopathic generalised epilepsy (IGE), designated EJM1, has been mapped in families with probands with juvenile myoclonic epilepsy, by linkage to the HLA region on chromosome 6. As BRE and IGE are benign, idiopathic, age-dependent epilepsies, EJM1 is a candidate locus for the fsw underlying BRE and related disorders. Genetic linkage analysis was undertaken in 11 families with probands with BRE and one or more first degree relatives with fsw, with or without BRE, using a polymorphic DNA marker within the HLA region. Apparently unaffected individuals were classed as affection status unknown. Assuming autosomal dominant inheritance with a penetrance of 0.9 gave a lod score of -2.3 at zero recombination, excluding the candidate gene region around HLA. These observations exclude an important candidate gene for this common disorder, and suggest a fundamental molecular and genetic distinction between the benign partial epilepsies of childhood and the idiopathic generalised epilepsies.

Benign childhood epilepsy with centrotemporal spikes and the focal sharp wave trait is not linked to the fragile X region.

Benign childhood epilepsy with centrotemporal spikes (BCECS, benign rolandic epilepsy) is a common form of genetically determined localisation-related epilepsy of childhood. The characteristic age-dependent focal sharp wave (fsw) found on the EEG in this disorder segregates as a dominant trait in families with probands with BCECS. Seizures occur in a significant proportion of individuals with the fragile X syndrome in association with EEG abnormalities comparable to those found in BCECS. The possibility of a common genetic basis for these disorders was investigated by linkage analysis. Six pedigrees with probands with BCECS were analysed using a marker locus DXS548, close to the fragile X site, fra (X). Obligate recombinants between DXS548 and the fsw trait were observed in all six families. Assuming X-linked dominant inheritance and penetrance values of 0.4 (male) and 0.1 (female) a negative lod score of -6.823 was obtained at zero recombination and lod scores of -2.0 at 10cM either side of the fra (X) locus. These results exclude an important candidate gene for this common childhood disorder.

Importance of blood viscoelasticity in arteriosclerosis.

Corpuscular and biochemical components of blood create the viscoelastic nature of blood flow, which varies because of changes in flow velocity. The flow properties of blood are of special interest in arteriosclerotic diseases for vasoregulatory mechanisms are often disturbed in these states. The authors compared the rheologic properties of blood in patients with arteriosclerotic lesions (coronary heart disease: n = 56; cerebrovascular disease: n = 37; peripheral arterial occlusive disease: n = 29 and healthy controls: n = 42). With a new oscillating capillary rheometer imitating the physiologic pulsations of blood flow in an unbranched artery, the viscosity (eta') and elasticity (eta") of whole blood and plasma were measured (diameter of the capillary: 0.9928 mm; pulse rate: 2/s; shear rate: gamma = 0.03-200/s; temperature: 37 degrees C). In arteriosclerotic patients a statistically significant elevation of the viscoelasticity of whole blood and plasma was found. In addition, plasma fibrinogen levels were augmented in the patients' groups. Clotting parameters (Quick, partial thromboplastin time, platelet count) and total serum protein levels were in the normal range in all patients investigated. In conclusion the question arises whether the increase of blood viscoelasticity is an additional risk factor for patients with arteriosclerotic disease or if it is just a consequence of the underlying disease. The authors' observations concerning blood viscoelasticity support the clinical importance of improving blood rheology by appropriate therapeutic measures.