Titanium dioxide is one of the most widely investigated oxides. This is due to its broad range of applications, from catalysis to photocatalysis to photovoltaics. Despite this large interest, many of its bulk properties have been sparsely investigated using either experimental techniques or ab initio theory. Further, some of TiO2's most important properties, such as its electronic band gap, the localized character of excitons, and the localized nature of states induced by oxygen vacancies, are still under debate. We present a unified description of the properties of rutile and anatase phases, obtained from ab initio state of the art methods, ranging from density functional theory (DFT) to many body perturbation theory (MBPT) derived techniques. In so doing, we show how advanced computational techniques can be used to quantitatively describe the structural, electronic, and optical properties of TiO2 nanostructures, an area of fundamental importance in applied research. Indeed, we address one of the main challenges to TiO2-photocatalysis, namely band gap narrowing, by showing how to combine nanostructural changes with doping. With this aim we compare TiO2's electronic properties for 0D clusters, 1D nanorods, 2D layers, and 3D bulks using different approximations within DFT and MBPT calculations. While quantum confinement effects lead to a widening of the energy gap, it has been shown that substitutional doping with boron or nitrogen gives rise to (meta-)stable structures and the introduction of dopant and mid-gap states which effectively reduce the band gap. Finally, we report how ab initio methods can be applied to understand the important role of TiO2 as electron-acceptor in dye-sensitized solar cells. This task is made more difficult by the hybrid organic-oxide structure of the involved systems.
首次测量了Ba 8 Ga 16 Ge 30包合物-I的热电性能。采用溶胶-凝胶-煅烧法制备了非晶态纳米氧化物前驱体。氧化物的进一步还原导致晶体纳米尺寸的Ba 8 Ga 16 Ge 30笼形物-I的定量产率。TEM研究表明，笼形纳米粒子保留了前体氧化物的尺寸和形貌。包合物纳米颗粒主要包含薄片（约100 μ m）。300 nm x 300 nm x 50 nm）和少量纳米球（直径约10 nm）。SAED图案证实了两种形态的笼形物-I结构类型。通过火花等离子烧结（SPS）压实粉末以获得块状纳米结构材料。在低密度样品（δ x射线的53%）上测得的Seebeck系数S在375 °C时达到-145 μV/k。由于样品的高电阻率（比块体材料大两个数量级）和低样品密度，ZT值相当低（0.02）。S的温度依赖性的趋势是一致的电子结构计算和半经典玻尔兹曼输运理论在常数散射近似下得到的值。在高密度样品（δ x射线的93%）上测量的总热导率（1.61 W/mK）显示相对于块体材料（2.1 W/mK）降低20-25%。由于裂纹的存在，不可能对样品进行进一步成形以用于塞贝克系数和电导率测量。通过对压制工具的设计、样品的加载和施加压力的分布的改进，将提高样品的机械稳定性。这些调查目前正在进行中。
VO2 is a much-discussed material for oxide electronics and neuromorphic computing applications. Here, heteroepitaxy of vanadium dioxide (VO2) was realized on top of oxide nanosheets that cover either the amorphous silicon dioxide surfaces of Si substrates or X-ray transparent silicon nitride membranes. The out-of-plane orientation of the VO2 thin films was controlled at will between (011)M1/(110)R and (-402)M1/(002)R by coating the bulk substrates with Ti0.87O2 and NbWO6 nanosheets, respectively, prior to VO2 growth. Temperature dependent X-ray diffraction and automated crystal orientation map…
In contrast to bulk materials, nanoscale crystal growth is critically influenced by size- and shape-dependent properties. However, it is challenging to decipher how stoichiometry, in the realm of mixed-valence elements, can act to control physical properties, especially when complex bonding is implicated by short and long-range ordering of structural defects. Here, solution-grown iron-oxide nanocrystals (NCs) of the pilot wustite system are found to convert into iron-deficient rock-salt and ferro-spinel sub-domains, but attain a surprising tetragonally distorted local structure. Cationic vacan…
The Mott transistor is a paradigm for a new class of electronic devices---often referred to by the term Mottronics---, which are based on charge correlations between the electrons. Since correlation-induced insulating phases of most oxide compounds are usually very robust, new methods have to be developed to push such materials right to the boundary to the metallic phase in order to enable the metal-insulator transition to be switched by electric gating. Here we demonstrate that thin films of the prototypical Mott insulator LaTiO$_3$ grown by pulsed laser deposition under oxygen atmosphere are…
Understanding band alignment and charge transfer at complex oxide interfaces is critical to tailoring and utilizing their diverse functionality. Towards this goal, we design and experimentally validate both Ohmic- and Schottky-like charge transfers at oxide/oxide semiconductor/metal interfaces. We utilize a method for predicting band alignment and charge transfer in ABO3 perovskites, where previously established rules for simple semiconductors fail. The prototypical systems chosen are the rare class of oxide metals, SrBO3 with B=V-Ta, when interfaced with the multifaceted semiconducting oxide,…
Impact of Tailored Gamma Irradiation on Pore Size and Particle Size of Poly[Ethylene Oxide]Films: Correlation with Molecular Weight Distribution andMicrostructural Study
Impact of charge transition levels on grain boundary properties in acceptor doped oxide ceramics: A phase-field study
Technische Universität Darmstadt（达姆施塔特工业大学）；IMDEA Materials（IMDEA材料研究所）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；RWTH Aachen University（亚琛工业大学）；Max Planck Institute for Solid State Research（马克斯·普朗克固体的研究研究所）；University of Stuttgart（斯图加特大学）
In past few decades, Rashba spin-orbit coupling (SOC) has been successfully employed for the emergence of exotic phenomena at the quantum oxide interfaces. In these systems, the combined effect of charge transfer, broken symmetries and SOC yields intriguing interfacial magnetism and transport properties. Here, we provide an insight to control and tune interfacial phenomena in CaMnO3/CaIrO3 based 3d-5d oxide heterostructures by the charge transfer driven Rashba SOC. Anomalous Hall effect in these canted antiferromagnetic heterostructures originates from the intrinsic contribution associated wit…
Disentangling the contributions of individual cations to magnetic order in a spinel high entropy oxide
University of British Columbia（不列颠哥伦比亚大学）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；University of Saskatchewan（萨斯喀彻温大学）；Canadian Light Source（加拿大光源）
Polar discontinuities occurring at interfaces between two different materials constitute both a challenge and an opportunity in the study and application of a variety of devices. In order to cure the large electric field occurring in such structures, a reconfiguration of the charge landscape sets in at the interface via chemical modifications, adsorbates or charge transfer. In the latter case, one may expect a local electronic doping of one material: one sparkling example is the two-dimensional electron liquid (2DEL) appearing in SrTiO$_3$ once covered by a polar LaAlO$_3$ layer. Here we show …
Transition metal perovskite oxides display a variety of emergent phenomena which are tunable by tailoring the oxygen octahedral rotation. SrRuO$_3$, a ferromagnetic perovskite oxide, is well-known to have various atomic structures and octahedral rotations when grown as thin films. However, how the electronic structure changes with the film thickness has been hardly studied. Here, by using angle-resolved photoemission spectroscopy and electron diffraction techniques, we study the electronic structure of SrRuO$_3$ thin films as a function of the film thickness. Different reconstructed electronic…
Complex oxide heterointerfaces and van der Waals heterostructures present two versatile but intrinsically different platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between these two classes of materials, however, is yet to be charted. Here, we report an unconventional nonlinear optical filtering effect resulting from the interfacial polar alignment between monolayer MoS$_2$ and a neighboring ferroelectric oxide thin film. The second harmonic generation response at the heterointerface is either substantially enhan…
Engineering the electronic band structure of two-dimensional electron liquids (2DELs) confined at the surface or interface of transition metal oxides is key to unlocking their full potential. Here we describe a new approach to tailoring the electronic structure of an oxide surface 2DEL demonstrating the lateral modulation of electronic states with atomic scale precision on an unprecedented length scale comparable to the Fermi wavelength. To this end, we use pulsed laser deposition to grow anatase TiO2 films terminated by a (1 x 4) in-plane surface reconstruction. Employing photo-stimulated che…
Band Structure Modulation of ZrO2 Nanoparticles for Control of CO Adsorption Properties: A Combined Density Functional Theory - Density Functional Tight Binding Study
School of Materials and Chemical Technology, Institute of Science Tokyo（东京科学大学材料化学技术学院）；RIKEN Center for Computational Science（理化学研究所计算科学中心）；Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Gadjah Mada（加查马达大学数学与自然科学学院化学系）
