Doping wide-gap materials p type is highly desirable but often difficult. This makes the recent discovery of p-type delafossite oxides, CuM(III)O2, very attractive. The CuM(III)O2 also show unique and unexplained physical properties: Increasing band gap from M(III) = Al,Ga, to In, not seen in conventional semiconductors. The largest gap CuInO2 can be mysteriously doped both n and p type but not the smaller gaps CuAlO2 and CuGaO2. Here, we show that both properties are results of a large disparity between the fundamental gap and the apparent optical gap, a finding that could lead to a breakthrough in the study of bipolarly dopable wide-gap semiconductor oxides.

A two-dimensional antiferromagnetic structure within a pseudomorphic monolayer film of chemically identical manganese atoms on tungsten(110) was observed with atomic resolution by spin-polarized scanning tunneling microscopy at 16 kelvin. A magnetic superstructure changes the translational symmetry of the surface lattice with respect to the chemical unit cell. It is shown, with the aid of first-principles calculations, that as a result of this, spin-polarized tunneling electrons give rise to an image corresponding to the magnetic superstructure and not to the chemical unit cell. These investigations demonstrate a powerful technique for the understanding of complicated magnetic configurations of nanomagnets and thin films engineered from ferromagnetic and antiferromagnetic materials used for magnetoelectronics.

Considerable evidence now exists to show that that the relative biological effectiveness (RBE) changes considerably along the proton depth-dose distribution, with progressively higher RBE values at the distal part of the modulated, or spread out Bragg peak (SOBP) and in the distal dose fall-off (DDF). However, the highly variable nature of the existing studies (with regards to cell lines, and to the physical properties and dosimetry of the various proton beams) precludes any consensus regarding the RBE weighting factor at any position in the depth-dose profile. We have thus conducted a systematic study on the variation in RBE for cell killing for two clinical modulated proton beams at Indiana University and have determined the relationship between the RBE and the dose-averaged linear energy transfer (LETd) of the protons at various positions along the depth-dose profiles. Clonogenic assays were performed on human Hep2 laryngeal cancer cells and V79 cells at various positions along the SOBPs of beams with incident energies of 87 and 200 MeV. There was a marked variation in the radiosensitivity of both cell lines along the SOBP depth-dose profile of the 87 MeV proton beam. Using Hep2 cells, the D(0.1) isoeffect dose RBE values (normalized against (60)Co) were 1.46 at the middle of SOBP, 2.1 at the distal end of the SOBP and 2.3 in the DDF. For V79 cells, the D(0.1) isoeffect RBE for the 87 MEV beam were 1.23 for the proximal end of the SOBP: 1.46 for the distal SOBP and 1.78 for the DDF. Similar D(0.1) isoeffect RBE values were found for Hep2 cells irradiated at various positions along the depth-dose profile of the 200 MeV beam. Our experimentally derived RBE values were significantly correlated (P = 0.001) with the mean LETd of the protons at the various depths, which confirmed that proton RBE is highly dependent on LETd. These in vitro data suggest that the RBE of the proton beam at certain depths is greater than 1.1, a value currently used in most treatment planning algorithms. Thus, the potential for increased cell killing and normal tissue damage in the distal regions of the proton SOBP may be greater than originally thought.

Scanning tunneling spectroscopy (STS) of thin Fe films on W(110) shows that the electronic structure of domains and domain walls is different. This experimental result is explained on the basis of first-principles calculations. A detailed analysis reveals that the spin-orbit induced mixing between minority d xyxz and minority d z 2 spin states depends on the magnetization direction and changes the local density of states in the vacuum detectable by STS. As a consequence nanometer-scale magnetic structure information is obtained even by using nonmagnetic probe tips. DOI: 10.1103/PhysRevLett.89.237205 PACS numbers: 75.90.+w, 07.79.Cz, 75.60.Ch Magnetism in reduced dimensions is one of the most active and innovative fields of solid-state physics. Recently, the effect of spin-orbit coupling onto spinpolarized electron wave functions has intensively been investigated as it is the physical basis of magnetic linear [1] and circular [2] x-ray dichroism which -in conjunction with relativistic ab initio calculations-yielded a detailed understanding of the electronic structure of ferromagnets [3]. As an important milestone towards a deeper understanding of magnetism on the nanometer scale, the combination of magnetic circular dichroism with photoemission electron microscopy allowed an imaging of magnetic domain structures at submicrometer resolution [4].Several authors have analyzed the spin-orbit induced changes in the band structure of thin ferromagnetic films in order to identify the electronic origin of the magnetic anisotropy energy [5,6], the energy difference between the easy and hard axes of the magnetization. It was found theoretically that the electronic structure of ferromagnetic transition metals depends on the magnetization direction. For example, 3d-band degeneracies can be lifted by the spin-orbit coupling (SOC) which is magnetization direction dependent [7]. However, the dependence of the electronic structure on the magnetization direction has never been confirmed experimentally by, e.g., angular resolved photoelectron spectroscopy (ARPES), due to (i) the incompatibility of the experimental setup with strong external magnetic fields which are necessary to force the sample magnetization into the hard directions, and (ii) the fact that ARPES can detect only occupied states while significant spin-orbit induced changes are also expected above the Fermi level (E F ).We have chosen a different approach: instead of changing the magnetization direction of the whole sample, we make use of the sample's virgin domain state and domain wall structure. In this Letter we show by scanning tunneling spectroscopy (STS) and first-principles calculations that the local surface electronic structure of a 20 nm stripe of an Fe double layer (DL) on W(110) -a sample with a well-known nanometer-scale domain structure [8,9] -depends on the local orientation of the magnetization. Since the tunneling current of a scanning tunneling microscope (STM), Iê e M r k ; r k ; U, depends on the electronic structure of the sample, we immedia...

This paper reviews recent investigations of the influence of dopants on the optical properties ofTiO2polymorphs. The common undoped polymorphs ofTiO2are discussed and compared. The results of recent doping efforts are tabulated, and discussed in the context of doping by elements of the same chemical group. Dopant effects on the band gap and photocatalytic activity are interpreted with reference to a simple qualitative picture of theTiO2electronic structure, which is supported with first-principles calculations.