Matthew M. Hawkeye  Michael J. Brett 《physica status solidi (a)》2009,206(5):940-943

We have studied the optical properties of nanostructured TiO₂ films and demonstrated the ability to tune the refractive index of the material over a wide range. The nanostructured films are fabricated using glancing angle deposition, which provides the ability to precisely control the density of the deposited film. Film morphology was examined using scanning electron microscopy and the films were optically characterized by polarized‐reflectance measurements. A simple isotropic homogeneous model, which is shown to be a good approximation of the film, is used to determine the optical constants from the reflectance measurements. Improvements to the model are suggested. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

Toshio Kamiya  Kenji Nomura  Hideo Hosono 《physica status solidi (a)》2009,206(5):860-867

This paper discusses an optical model and subgap electronic states for a representative amorphous oxide semiconductor, InGaZnO₄ (a‐IGZO). Parameterized optical models were developed based on the Tauc–Lorentz model combined with a Lorentz‐type oscillator. The measured optical absorption spectra exhibit nearly linear dependences on photon energy (E) between 3 eV < E < 5 eV, which requires the transition energies in the Tauc–Lorentz model (E_0,TL) being around 4 eV. The optimized parameters for the fixed E_0,TL of 3.7 eV are provided for four different a‐IGZO films with root‐mean‐square errors less than 1%. Formation energies of crystalline IGZO, stoichiometric a‐IGZO, oxygen deficient a‐IGZO and their constituent oxides were calculated by the density functional theory using the local density approximation (LDA) and generalized gradient approximation with PBE96 functionals (PBE). PBE gives larger unit cell volumes at the ground states and better agreement in the formation energies than LDA does. The formation energies of an oxygen deficiency in a‐IGZO were calculated to be 3.2–3.5 eV. The calculated electronic structures of stoichiometric a‐IGZO models exhibit somewhat large dispersions for conduction bands (CB), which are not largely affected by the disordered structure in a‐IGZO, while the dispersions of the valence bands (VBs) are very small, unlike the crystalline IGZO, showing that a‐IGZO have strongly localized states at the VB maximums (VBMs). Oxygen‐deficient a‐IGZO models showed that oxygen deficiencies form both a deep localized state at 0.4–1 eV above VBM and a shallow donor state depending on local atomic configurations. An oxygen deficiency that forms a deep state breaks the dispersion of the CB, which could be an origin of the subgap states observed near CB. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

Jenifer L. Lawrie  Zhou Xu  Guoguang Rong  Paul E. Laibinis  Sharon M. Weiss 《physica status solidi (a)》2009,206(6):1339-1342

In‐situ oligonucleotide synthesis through an 8‐base sequence is demonstrated within 30 nm silicon mesopores utilizing sequential phosphoramidite reactions. Stepwise attachment of each base is confirmed by monitoring the porous silicon effective refractive index via a waveguide resonance angle. A linear increase in the effective refractive index is observed after the addition of each base, and the detection of oligonucleotides containing only a single thymine is possible. It is estimated that 50% of the available internal pore surface is occupied by the 8‐base oligonucleotides, which is a substantially greater coverage than obtained by using traditional methods of direct attachment of presynthesized DNA oligonucleotides. The greater surface coverage by DNA probes will enable more effective biosensing devices. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

J. Cheng  Z. Q. Yang 《physica status solidi b》2006,243(6):1151-1158

The electronic structures of double perovskites Ba₂MnWO₆ and Ba₂MnReO₆ are studied by using first‐principles linear muffin‐tin orbital method. The ground magnetic phases for the two compounds are found to be antiferromagnetic and ferrimagnetic, respectively, in agreement with experimental results. Barium atoms in both of the compounds show obvious ionic characters while very strong hybridizations are found among the states of Mn 3d–O 2p–W(Re) 5d. Metallic band structure is obtained for Ba₂MnReO₆ even though on‐site Coulomb interaction (LSDA+U method) is considered for Mn 3d and Re 5d states. A finite energy gap appears in the compound only when spin–orbital coupling on Re ions is also taken into account. This semiconducting band structure can explain well the curve of resistivity versus temperature observed in experiment for ferrimagnetic Ba₂MnReO₆. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

Yousef Saad  Yunkai Zhou  Constantine Bekas  Murilo L. Tiago  Jim Chelikowsky 《physica status solidi b》2006,243(9):2188-2197

The Pseudopotential Algorithm for Real‐Space Electronic Calculations (PARSEC) is a software package written by a team consisting of materials physicists and computer scientists over approximately one decade. During this period, the algorithms used in PARSEC have undergone a series of improvements. This paper reviews the nature of the eigenvalue problems encountered in solving the Kohn–Sham equations and discusses the evolution of the diagonalization methods used in PARSEC. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

Matías Nuez  M. Buongiorno Nardelli 《physica status solidi b》2006,243(9):2081-2084

Using calculations from first principles we have demonstrated that it is possible to tune the Schottky Barrier Height in a metal–alkaline earth oxide interface by manipulating the microscopic and macroscopic dipoles that naturally form at the junction between the two materials. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

R. A. Evarestov  A. V. Bandura  V. E. Alexandrov 《physica status solidi b》2006,243(12):2756-2763

Hybrid HF‐DFT LCAO simulations of SrZrO₃ and SrTiO₃(001) surface properties are performed in a single‐slab model framework. The SrZrO₃(001) surface was studied by an ab initio method for the first time. Three slab models with different surface terminations including up to 8 atomic planes were used for calculation of the various surface characteristics (surface energies, atomic charges, density of electronic states). The dependence of the results on the chosen model and on the kind of d ‐element is analyzed. The dissimilarity in the surface oxygen atom contributions to the total density of states of two crystals is attributed to the more ionic nature of Zr–O bonds compared to Ti–O bonds. It is found that in the case of SrZrO₃ the electronic density is biased towards the SrO‐terminated surface and this surface should be more basic in nature than the SrO surface of SrTiO₃ crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

L. Beji  T. Ben Jomaa  A. Ltaeif  A. Bouazizi 《physica status solidi (a)》2005,202(9):1763-1767

Poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene] (MEH‐PPV) was grown on porous GaAs (π‐GaAs) by spin coating and studied via scanning electron microscopy (SEM) and room temperature photoluminescence (PL). The SEM investigation revealed that MEH‐PPV was grown deeply in the porous structure and had a filament‐like shape. The PL result showed that a strong quenching effect occurred when using π‐GaAs. This effect was suggested to be due to photoinduced charge transfer at the MEH‐PPV/GaAs nanocrystallite interface. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

Luis Mancera  Jairo A. Rodríguez  Noboru Takeuchi 《physica status solidi b》2004,241(10):2424-2428

The relative stability of wurtzite, zinc‐blende, rock‐salt and CsCl structures and the possibility of high‐pressure phase transformations from wurtzite to rocksalt and from rocksalt to CsCl is of special interest. We present a comparative study of the stability of these phases for two Group IIIB‐nitrides (ScN, YN) and two Group IIIA‐nitrides (GaN, InN), in the framework of DFT. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

C. Nirmala Louis  K. Iyakutti  K. S. Hema Nandhini  M. Sivakumar  E. Palaniyandi 《physica status solidi b》2004,241(11):2489-2500

The electronic band structure, metallization, structural phase transition and superconductivity of cubic zinc blende‐type GaP and GaN are investigated. The equilibrium lattice constant, bulk modulus and pressure at which the compounds undergo a structural phase transition from ZnS structure to NaCl structure are predicted from the total energy calculations. The density of states at the Fermi level (N(E_F)) is enhanced after metallization, which leads to the superconductivity in GaP and GaN. The superconducting transition temperatures (T_c) of GaP and GaN are obtained as a function of pressure for both the ZnS and NaCl structures and GaP and GaN come under the category of pressure‐induced superconductors. When pressure is increased T_c increases in both the normal and high‐pressure structures. The dependence of T_c on the electron–phonon mass enhancement factor λ shows that GaP and GaN are electron–phonon‐mediated superconductors. Also, it is found that GaP and GaN retained in their normal structure under high pressure give appreciably high T_c. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献