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BaCuChF (Ch=S,Se,Te) surfaces and BaCuSeF interfaces with zinc phthalocyanine (ZnPc) were studied by photoelectron spectroscopy. BaCuChF compounds oxidize when exposed to ambient atmosphere. Se capping layers were studied as a means to produce representative surfaces for photoelectron spectroscopic measurements. Decapped BaCuSeF surfaces remain O-free and C-free when the Se layer is evaporated but they become F-deficient. The resulting surfaces have work functions of 4.85 eV and Fermi levels located 0.25 eV above the valence band maximum. In situ stepwise deposition of ZnPc on a BaCuSeF film surface produced a chemically inert interface with a hole-injection barrier of 0.11 eV.

A wide variety of brookite TiO2 synthesis methods have been published over the past several decades, but few studies discuss the underlying mechanism that stabilizes brookite over its stable counterparts, rutile and anatase. Here, we investigate of the effect of pulsed laser deposition parameters on the as-deposited amorphous precursor titania thin films, which subsequently crystallize into stable and metastable TiO2 polymorphs upon annealing. We find that oxygen pressure in the deposition chamber strongly influences the non-equilibrium state of the amorphous precursor, which ultimately allows for selective polymorph formation. Rutile forms as the dominant phase at low pO2 5 mTorr. Brookite forms primarily at intermediate pO2 (0.5–1.0 mTorr). Controlling the amorphous structure (i.e. Ti—O bonding and polyhedral arrangement) of the precursors via oxygen deficiency is therefore likely for the selective formation of crystalline TiO2 polymorphs from sub-stoichiometric amorphous precursors. Directing phase selectivity by manipulating the structure and internal energy of the precursor amorphous state may have tremendous potential for synthesis of metastable crystalline phases that exhibit more desirable properties in comparison to their stable counterparts.

Metastable inorganic materials with unique properties are important in many practical applications, but their synthesis is often challenging. In physics, epitaxial stabilization, also known as pseudomorphic growth, is used to synthesize metastable polymorphs, but usually only as very thin films and on expensive single-crystal substrates. In chemistry, the templated growth of inorganic solid-state materials on self-assembled monolayers of organic molecules is reported. Bridging these two fields, here, we show that the synthesis of metastable polymorphs is possible up to large film thickness on amorphous substrates covered with thin inorganic seed layers that serve as templates. The stabilization of a 500-nm-thick metastable wurtzite (WZ) $\mathrm{Mn}\mathrm{Te}$ film by a 5-nm-thick $\mathrm{Zn}\mathrm{Te}$ seed layer sputtered on amorphous glass substrates is experimentally demonstrated. Theoretical calculations explain this experimental observation by the small WZ polymorph energy relative to that of the ground-state nickeline (NC) structure of $\mathrm{Mn}\mathrm{Te}$ and a large lattice constant difference of the two. The resulting metastable WZ-$\mathrm{Mn}\mathrm{Te}$ polymorph exhibits a wide band gap of 2.7 eV and a low hole density of ${10}^{12}\phantom{\rule{0.25em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, which is relevant to optoelectronic applications. These properties are in sharp contrast to those of the narrow-band-gap highly doped NC-$\mathrm{Mn}\mathrm{Te}$ with 1.3 eV band gap and ${10}^{19}\phantom{\rule{0.25em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ hole density. The difference in hole density is due to the calculated difference in the formation energy of manganese vacancy acceptor defects. Overall, these results suggest that templated growth on amorphous substrates with seed layers can be used to synthesize metastable polymorphs of other materials, without the need for expensive single-crystal substrates.

Author(s): Tate, Janet P; Sterne, Jonathan AC; Justice, Amy C; Veterans Aging Cohort Study (VACS) and the Antiretroviral Therapy Cohort Collaboration (ART-CC) | Abstract: ObjectiveDespite viral suppression and immune response on antiretroviral therapy, people with HIV infection experience excess mortality compared with uninfected individuals. The Veterans Aging Cohort Study (VACS) Index incorporates clinical biomarkers of general health with age, CD4 cell count, and HIV-1 RNA to discriminate mortality risk in a variety of HIV-positive populations. We asked whether additional biomarkers further enhance discrimination.Design and methodsUsing patients from VACS for development and from the Antiretroviral Therapy Cohort Collaboration (ART-CC) for validation, we obtained laboratory values from a randomly selected visit from 2000 to 2014, at least 1 year after antiretroviral therapy initiation. Patients were followed for 5-year, all-cause mortality through September 2016. We fitted Cox models with established predictors and added new predictors based on model fit and Harrell's c-statistic. We converted all variables to continuous functional forms and selected the best model (VACS Index 2.0) for validation in ART-CC patients. We compared discrimination using c-statistics and Kaplan-Meier plots.ResultsAmong 28 390 VACS patients and 12 109 ART-CC patients, 7293 and 722 died, respectively. Nadir CD4, CD8, and CD4 : CD8 ratio did not improve discrimination. Addition of albumin, white blood count, and BMI, improved c-statistics in VACS from 0.776 to 0.805 and in ART-CC from 0.800 to 0.831. Results were robust in all nine ART-CC cohorts, all lengths of follow-up and all subgroups.ConclusionVACS Index 2.0, adding albumin, white blood count, and BMI to version 1.0 and using continuous variables, provides improved discrimination and is highly transportable to external settings.

We grow and kinetically stabilize the isotropic rocksalt phase of SnSe thin films by alloying SnSe with CaSe. Thin polycrystalline films of the metastable heterostructural alloy Sn1−xCaxSe are synthesized by pulsed laser deposition on amorphous SiO2 over the entire composition range 0 < x < 1. We observe the theoretically-predicted, composition-driven change from a layered, orthorhombic structure to an isotropic, cubic structure near x = 0.18, in reasonable agreement with the theoretical value of x = 0.13 calculated from first principles. The optical band gap is highly non-linear in x and the trend agrees with theory predictions. Compared to the layered end-member SnSe, the isotropic alloy near the orthorhombic-to-rocksalt transition has a p-type electrical resistivity three orders of magnitude lower, and a thermoelectric power factor at least ten times larger. Thus manipulation of the structure of a functional material like SnSe via alloying may provide a new path to enhanced functionality, in this case, improved thermoelectric performance.

Supplemental Digital Content is Available in the Text., Background: An increasing number of HIV-positive individuals now start antiretroviral therapy (ART) with high CD4 cell counts. We investigated whether this makes restoration of CD4 and CD8 cell counts and the CD4:CD8 ratio during virologically suppressive ART to median levels seen in HIV-uninfected individuals more likely and whether restoration depends on gender, age, and other individual characteristics. Methods: We determined median and quartile reference values for CD4 and CD8 cell counts and their ratio using cross-sectional data from 2309 HIV-negative individuals. We used longitudinal measurements of 60,997 HIV-positive individuals from the Antiretroviral Therapy Cohort Collaboration in linear mixed-effects models. Results: When baseline CD4 cell counts were higher, higher long-term CD4 cell counts and CD4:CD8 ratios were reached. Highest long-term CD4 cell counts were observed in middle-aged individuals. During the first 2 years, median CD8 cell counts converged toward median reference values. However, changes were small thereafter and long-term CD8 cell count levels were higher than median reference values. Median 8-year CD8 cell counts were higher when ART was started with

Exploratory synthesis in new chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation-from which we experimentally realized seven new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity and covalency of solid-state bonding from the density functional theory (DFT)-computed electron density, we reveal the complex interplay between chemistry, composition and electronic structure in governing large-scale stability trends in ternary nitride materials.

Exploratory synthesis in new chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation-from which we experimentally realized seven new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity and covalency of solid-state bonding from the density functional theory (DFT)-computed electron density, we reveal the complex interplay between chemistry, composition and electronic structure in governing large-scale stability trends in ternary nitride materials.

Structure-specific synthesis processes are of key importance to the growth of polymorphic functional compounds such as TiO2, where material properties strongly depend on structure as well as chemistry. The robust growth of the brookite polymorph of TiO2, a promising photocatalyst, has been difficult in both powder and thin-film forms due to the disparity of reported synthesis techniques, their highly specific nature, and lack of mechanistic understanding. In this work, we report the growth of high-fraction (~95%) brookite thin films prepared by annealing amorphous titania precursor films deposited by pulsed laser deposition. We characterize the crystallization process, eliminating the previously suggested roles of substrate templating and Na helper ions in driving brookite formation. Instead, we link phase selection directly to film thickness, offering a novel, generalizable route to brookite growth that does not rely on the presence of extraneous elements or particular lattice-matched substrates. In addition to providing a new synthesis route to brookite thin films, our results take a step towards resolving the problem of phase selection in TiO2 growth, contributing to the further development of this promising functional material.

Theoretically predicted metastable phases are realized in thin-film synthesis of Mn1−xZnxO and Sn1−xCaxS alloys., Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

Crystalline TiO2 films of anatase, brookite, and rutile are reproducibly made from amorphous precursors deposited by RF magnetron sputtering, producing large-area, single phase films of uniform thickness. Sputtered amorphous TiO2 precursor thin films follow the general behavior observed for amorphous precursor thin films generated by pulsed laser deposition, namely, that oxygen deficiency is necessary for the formation of brookite and rutile. We quantify the oxygen deficiency and correlate it with the long wavelength optical absorption. We find that the precursor deposition rate is also a contributing factor to phase selection and that brookite and rutile form from films deposited more rapidly and anatase from films deposited more slowly. Sputtered and pulsed laser deposited amorphous precursor films prepared with similar oxygen deficiency and similar thickness result in the same final state after annealing, but the rate for sputtered precursors is slower.

The thermal conductivity, measured by the 3ω method, of amorphous films of Al 2 P 1.2 O 6 (AlPO) deposited on Si substrates by an all-aqueous spin-coating technique is 0.93(3) W m − 1 K − 1 . The thermal conductivity of a degenerately doped n -Si substrate is 85(5) W m − 1 K − 1 and of a more lightly doped p -Si substrate is 139(7) W m − 1 K − 1 . The AlPO thermal conductivity is independent of film thickness in the range 45–200 nm. The total thermal resistance is dominated by the film contribution for film thicknesses above 50 nm, and for smaller thicknesses, interface contributions become significant.

Crystals of BiCuOSe were grown from a salt flux, and the crystal structure was determined by single-crystal X-ray diffraction. BiCuOSe adopts the tetragonal layered structure of LnCuOCh (Ln=lanthanide; Ch=S, Se, and Te) with bond lengths and bond angles in good agreement with those published for powders. Powders comprising mixed chalcogenides across the series BiCuOCh (Ch=S, Se, and Te) were made by reacting Bi2O2Ch and Cu2Ch. Band gaps determined via infrared diffuse reflectance from powders are Eg=0.82 eV for BiCuOSe, 0.89 eV for BiCuOS0.5Se0.5, and 1.07 eV for BiCuOS. The band gap of BiCuOSe inferred from infrared transmission measurements on single crystals is in good agreement with the value obtained from diffuse reflectance from the powder.

BaCuSeF/ZnTe is a model system to investigate physical and chemical properties of the interfaces of non-oxide wide-bandgap p-type semiconductors with materials used in chalcogenide solar cells. The BaCuSeF/ZnTe interface was studied using electron microscopy and photoelectron spectroscopy. Both techniques indicate that Se and Cu from BaCuSeF diffuse into ZnTe creating an interdiffused layer between these two materials. The interdiffusion may be attributed to the differences in materials formation enthalpies and to Fermi level pinning in BaCuSeF.

Undoped and 10% Ca-doped BiCuOSe thin films are prepared by pulsed laser deposition without ex-situ processing. The influence of the preparation conditions on structure and properties of Bi0.9Ca0.1CuOSe thin films on amorphous silica substrates is studied. The highest achieved concentration and mobility of free holes (3.9×1020 cm−3 and 3.5 cm2/Vs) was close to that measured in strongly c-axis oriented samples on SrTiO3 substrates (4.0×1020 cm−3 and 7.5 cm2/Vs). The Bi0.9Ca0.1CuOSe films on SrTiO3 show almost temperature-independent Seebeck coefficient and their resistivity increases with increasing temperature. The Seebeck coefficient of undoped BiCuOSe films on SrTiO3 increases below 150°K, and the resistivity shows a flat plateau centered at this temperature. Optical measurements suggest that BiCuOSe has an indirect bandgap of 0.8 eV and a strong absorption edge at 1.45 eV. Ab-initio calculations of the electronic band structure, effective masses and optical properties of BiCuOSe are also presented.

Thin-film solid solutions of BaCu(Ch1 − xChx′)F (Ch, Ch′ = S, Se, or Te) wide-band gap p-type semiconductors are obtained by pulsed laser deposition at elevated substrate temperatures from alternating layers of BaCuChF and BaCuCh′F. Adjusting the thickness of the component layers varies the relative chalcogen content, which allows tunability of the film transparency and results in a conductivity change of more than three orders of magnitude. The tunability of the physical properties makes these chalcogen-based semiconductors potentially useful for optoelectronics applications. Lattice parameters of BaCuChF calculated using density functional theory agree with those previously reported for the powders. Deviations from Vegard's law are observed in BaCu(S1 − xSex)F thin films with large sulfur content.

High-quality TiO2 thin films have been deposited from aqueous titanium-peroxo solutions via spin coating. The effects of precursor solution pH on the crystallization behavior, morphology, density, and refractive index of the films are reported. From X-ray diffraction measurements, the amorphous as-deposited films are found to crystallize in the anatase phase at 250 °C. Surface and cross-section SEM images reveal that films deposited from an acidic precursor are more uniform and denser than those deposited from a basic precursor. X-ray reflectivity measurements show that films with smooth surfaces and high densities (up to 87% of single-crystal anatase) can be produced at temperatures as low as 300 °C. Measured densities are consistent with high refractive indices at 633 nm of 2.24 and 2.11 for films derived from acidic and basic precursors, respectively. The uniformity and dense nature of the films have allowed fabrication of multilayer dielectric optical elements with thermal processing at only 300 °C. The distributed Bragg reflector with four bilayers exhibits a reflectance of 92% and a stop band width of 150 nm. The optical microcavity has a quality factor of 20. The optical properties of all elements agree well with theoretical models, indicating good optical quality. Use of the precursor chemistry for direct photopatterning of TiO2 films without a polymer resist is also demonstrated.

The simplest realization of a pin double-heterojunction thin-film solar cell would consist of a lightly doped, moderate-bandgap absorber i-layer; a heavily doped, wide-bandgap n-layer window (cathode); and a heavily doped, wide-bandgap p-layer window (anode) in which the anode and cathode are electrically contacted by at least one transparent conductor. The focus herein is on p-layer interfacial assessment, which is accomplished using modern Schottky barrier and heterojunction theory and is directed to the analysis of p-windows for copper indium gallium diselenide (CIGS) and cadmium telluride (CdTe) thin-film solar cells. A p-type window layer serves as an electron reflector and also aids in the formation of an ohmic anode contact. Ohmic anode contacts are particularly difficult to form in CIGS and CdTe thin-film solar cells since these materials have very large ionization potentials, i.e., IP S = 5.65 (CIGS) and 5.78 V (CdTe) and significant interfacial screening, characterized by extremely small Schottky barrier interface parameters, i.e., S = 0.14 (CIGS) and 0.21 (CdTe). An ideal p-type window material would be heavily doped, p-type, and would have a wide bandgap, a large ionization potential, and a smaller charge neutrality level energy than that of the absorber layer.

The structural, optical, and electronic properties of thin films of a family of wide band gap (Eg > 2.3 eV) p-type semiconductors Cu3TaQ4 (Q = S or Se) are presented. Thin films prepared by pulsed laser deposition of ceramic Cu3TaQ4 targets and ex-situ annealing of the as-deposited films in chalcogenide vapor exhibit mixed polycrystalline/[100]-directed growth on amorphous SiO2 substrates and strong (100) preferential orientation on single-crystal yttria-stabilized zirconia substrates. Cu3TaS4 (Eg = 2.70 eV) thin films are transparent over the entire visible spectrum while Cu3TaSe4 (Eg = 2.35 eV) thin films show some absorption in the blue. Thin film solid solutions of Cu3TaSe4 − xSx and Cu3TaSe4 − xTex can be prepared by annealing Cu3TaSe4 films in a mixed chalcogenide vapor. Powders and thin films of Cu3TaS4 exhibit visible photoluminescence when illuminated by UV light.

Transparent p-type conductive BaCuTeF thin films are reported. Epitaxial BaCuTeF films are obtained in situ by pulsed laser deposition in ultra-high vacuum and in Ar ambient up to 1 × 10−3 Torr on single-crystal MgO (100) substrates above 500 °C. Nominally undoped films exhibit hole carrier mobilities of 4–8 cm2/V s with a maximum conductivity of 167 S/cm. Polycrystalline films deposited under similar conditions on amorphous SiO2 substrates have hole mobilities of 0.2 cm2/V s and conductivities of 0.4–7 S/cm. The largest change in optical absorption occurs near 3 eV, with a weak feature near 2.4 eV in epitaxial films.

The Paradigms in Physics project at Oregon State University has reformed the entire upper-level physics curriculum. The reform has involved a rearrangement of content to better reflect the way physicists think about the field and the use of several new pedagogies that place responsibility for learning more firmly in the hands of the students. In particular, we employ a wide variety of computational examples and problems throughout the courses. Students use MAPLE, MATHEMATICA, JAVA, and other software packages to do calculations, visualizations, and simulations that develop their intuition and physical reasoning. These computational activities are indispensable to the success of the curriculum.

Zinc oxide powders prepared by decomposition of zinc peroxide and zinc nitrate show evidence of acceptor states from iodometric titrations. Chemical analysis also shows the presence of nitrogen in the samples prepared by nitrate decomposition. The evidence for acceptor states disappears on heating samples, eliminating the possibility of transport measurements on sintered samples. Complex impedance spectra suggest room temperature conductivities as high as 5 × 10−4 and 2 × 10−3 S/cm for these peroxide and nitrate derived zinc oxide powders, respectively. As zinc oxide particles become small there is an increase in unit cell dimensions and a red shift of the absorption edge. An even stronger red shift is observed in the case of N doping.

The compound BaCuTeF has been prepared by using high-temperature reaction methods, and its structure has been established via Rietveld refinement of powder X-ray diffraction data. It crystallizes in the tetragonal space group P4/nmm (No. 129) with Z=2, a=4.4297 (1), c=9.3706 (1) A, and V=183.87 (1) A{sup 3}; refinement residuals include R {sub p}/wR {sub p}/R {sub Bragg} (%)=6.72/4.42/5.72. A band gap of 2.3 eV is estimated from wavelength-dependent diffuse reflectance measurements. Room-temperature conductivities of pressed pellets are 6-8 S/cm, and variable-temperature Seebeck and electrical-conductivity measurements reveal p-type degenerate semiconductor behavior. - Graphical abstract: The telluride fluoride BaCuTeF has been synthesized and structurally characterized through Rietveld refinement of X-ray diffraction data. It crystallizes in the tetragonal structure of LaCuOS. Optical and transport measurements have been used to establish the material as a degenerate p-type semiconductor with a band gap near 2.3 eV.

Transport and structural properties of Mg-doped and O-intercalated sintered powders and polycrystalline films of CuSc1−xMgxO2+y are reported. Substitution of Mg for Sc systematically increases the p-type conductivity in CuSc1−xMgxO2 sintered powders, producing a maximum conductivity of 0.015S∕cm at x≈0.06. A similar level of conductivity is observed in transparent polycrystalline CuSc1−xMgxO2 films at the same doping level. Mg doping causes no significant increase in optical absorption at this level. Intercalation of oxygen into the delafossite structure leads to a much larger increase in p-type conductivity. In powders, the maximum conductivity is 0.5S∕cm at y=0.23 and x=0.05. In oxygen-intercalated films, the maximum conductivity was 25S∕cm, with the transparent films gradually darkening as oxygen is incorporated. Oxygen intercalation increases the a-axis lattice parameter of the delafossite structure in both films and powders, with a much smaller effect on the c-axis parameter. Two distinct phases with...

Thin films of CuSc 1− x Mg x O 2+ y have been rendered conducting by intercalation of oxygen. Hole conductivities up to of order 10 S/cm can be achieved at the expense of visible transparency, especially in the blue region of the spectrum. Hole conductivities up to 100 S/cm have been achieved in pressed pellets of K-doped BaCuSF, and a band-gap of 3.2 eV has been measured on undoped films.

Several p-type oxides of the delafossite structure have been investigated in the hope that the conductivity and transparency will be high enough to render them useful in the manufacture of transparent p–n junction diodes and other transparent devices. The highest conductivity achieved to date has been 220 S/cm in CuCr1−xMgxO2 thin films. Oxygen intercalation in CuSc1−xMgxO2+y films improves the conductivity at the expense of optical transparency. We have improved the conductivity of CuGaO2-based films from 0.02 to 1 S/cm by substitution of Fe for Ga. p-Type conductivity has been demonstrated in an Ag-based delafossite film. A sputter-deposited AgCoO2 film has a conductivity of 0.2 S/cm, a Seebeck coefficient of 230 μV/K and a band gap of 4.1 eV at room temperature. CuNi2/3Sb1/3O2 films have been produced that are p-type conductors when doped with Sn.

Transparent p–i–n heterojunction diodes are fabricated using heavily doped, p-type CuYO2 and semi-insulating i-ZnO thin films deposited onto a glass substrate coated with n-type indium tin oxide. Rectification is observed, with a ratio of forward-to-reverse current as high as 60 in the range −4–4 V. The forward-bias current–voltage characteristics are dominated by the flow of space-charge-limited current, which is ascribed to single-carrier injection into the i-ZnO layer. Capacitance measurements show strong frequency dispersion, which is attributed to i-ZnO traps. The diode structure has a total thickness of 0.75 μm and an optical transmission of ∼35%–65% in the visible region.

Thin films of CuY1−xCaxO2 that are p-type conductors have been prepared by thermal co-evaporation. The films are polycrystalline on amorphous substrates and c-axis oriented on crystalline substrates. Calcium doping was necessary to produce conductive films, and the highest conductivity recorded was 1.0 S cm−1. The average transparency in the visible region is approximately 40–50%, for conducting films approximately 250 nm thick, and in the infrared approximately 70% for a 350-nm conducting film. The optical spectra give evidence for a bandgap of 3.5 eV. We have demonstrated an all-oxide p–n diode using CuY1–xCaxO2/Zn1–xAlxO.

We describe a new curriculum for the final two years of a B.S. program in Physics. Case studies in the junior year provide concrete examples or Paradigms as pillars to support systematic Capstone lectures in the senior year. In each of nine three-week Paradigms, the junior progresses from a descriptive lower-division understanding to an advanced analysis of a topic defined by phenomenon rather than discipline. Students generally view the new format with favor. They are better at visualization and make important connections among physics disciplines. Independent assessment is ongoing.

CuCr1−xMgxO2, a wide band gap semiconductor with the delafossite structure, has been synthesized in bulk and thin-film form. Bulk undoped CuCrO2 is almost black and has moderate conductivity with p-type carriers. Upon doping with 5% Mg, the conductivity increases by a factor of 1000. In films, the best p-type conductivity is 220 S cm−1 in CuCr0.95Mg0.05O2, a factor of 7 higher than previously reported for Cu-based p-type delafossites. Undoped films have a conductivity of order 1 S cm−1. Films are usually polycrystalline on amorphous substrates, but undoped films can be c-axis oriented if deposited at or above 650 °C. Optical and ultraviolet transmission data indicate a direct band gap of 3.1 eV.

Compounds of the type CuMO2 and AgMO2 have been doped in various ways to induce p-type conductivity. Most of the compounds have the delafossite structure which can exist in 2H and 3R polytypes. Both the 2H and 3R forms of CuScO2 have been intercalated with oxygen up to a formula of CuScO2.5. p-Type conductivity can also be induced in CuScO2 by substitution of Mg for Sc. Thin films of CuScO2 prepared by rf sputtering are transparent and show a conductivity of 30 S cm−1. Thin films of Mg-doped CuCrO2 are transparent and show a room-temperature conductivity of 220 S cm−1. Doping of AgMO2 compounds with M=Sc, In, Cr, and Ga have produced p-type conductivity, but never higher than about 0.01 S cm−1 at room temperature.

ZnS:Mn, ZnGaS:Mn and ZnS:CuCl2 phosphor thin films for alternating-current thin-film electroluminescent (ACTFEL) devices were prepared by thermal evaporation from two and three sources, respectively. Films are polycrystalline, strongly oriented and stoichiometric or nearly stoichiometric with high optical transmission in the visible part of the spectrum. The band gap of ZnS:Mn, ZnGaS:Mn and ZnS:CuCl2 films was found to be 3.63, 3.86 and 3.56 eV, respectively. The sheet resistance of the ZnS:Mn and ZnGaS:Mn films was greater than 100 MΩ. The resistivity of ZnS:CuCl2 films was between 1.5–80 Ω cm. Photoluminescent (PL) and electroluminescent (EL) characteristics were also studied. The results indicate that after the optimization the investigated phosphor thin films will be suitable for ACTFEL device applications.

We have investigated epitaxial YBCO films by Perturbed γγ-Angular Correlation Spectroscopy (PAC) using 111In probe atoms. The probes substitute on the yttrium lattice site and hyperfine parameters have been determined unambiguously. Excellent agreement is achieved with full potential electric field gradient (efg) calculations. Good reproducibility has been achieved by our preparation method allowing us to study the influence of oxygen motion on the structural orthorhombic to tetragonal phase transition.

Oxygen-deficient, tetragonal thin films of YBa2Cu3O6+x with x ≈ 0.25, quenched from the deposition temperature, change to the oxygenated, orthorhombic phase with x ≈ 1, between 200 °C and 400 °C in flowing oxygen. The transition is not reversible in flowing oxygen, and cannot be completely reversed by cooling in flowing argon. We do not observe a transition of the orthorhombic films to the tetragonal phase up to 800 °C in flowing oxygen. We observe that the major impurity phases to appear under nonoptimal annealing conditions are oriented phases of YcuO2 and BaCu2O2, with Y2BaCu2O5 and Y2Cu2O5 conspicuously absent. These conclusions have been drawn from a study that uses perturbed angular correlation spectroscopy to probe the local microstructure of the films.

This is the publisher’s final pdf. The published article is copyrighted by The American Physical Society and can be found at: http://prb.aps.org/.

The local atomic order around very dilute indium impurities in c-axis-oriented YBa2Cu3O7 and YBa2Cu3O6.25 films at room temperature and in YBa2Cu3Ox bulk powders held in air or oxygen over a wide temperature range were investigated using 111In/Cd \gamma--\gamma perturbed angular correlation (PAC) spectroscopy. The probe atoms occupy a single substitutional lattice position in YBa2Cu3Ox, and evidence reported here strongly supports previous claims that this is the yttrium position. In YBa2Cu3Ox powders, the local atomic order changes continuously with temperature. At room temperature the electric field gradient measured by PAC in bulk YBa2Cu3Ox powder is indistinguishable from that in the fully oxygenated YBa2Cu3O7 film. Near the decomposition temperature, the bulk YBa2Cu3Ox powder data are semiquantitatively similar to data in the room temperature YBa2Cu3O6.25 film, with quantitative differences that we attribute to temperature averaging in the former. Other sites usually found in PAC spectra of YBa2Cu3Ox bulk samples arise from 111In dissolved in Y2BaCuO5 and Y2Cu2O5 impurity phases. The latter phase apparently arises because of significant barium loss during processing; the barium deficiency is clearly demonstrated by comparison of PAC data with the alloy phase diagram above the decomposition temperature. PAC data on pure Y2Cu2O5 are reported here also.

This is the publisher’s final pdf. The published article is copyrighted by The American Physical Society and can be found at: http://prb.aps.org/.

We have investigated a second-order phase transition of the vortex lattice in thin-film ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ from 1 mT to 1 T applied magnetic fields. The dc resistivity-current density data for each field exhibit critical scaling consistent with a second-order vortex-liquid to vortex-solid phase transition. The high-field data support the vortex-glass model and have the same critical exponents as thin-film ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. At low fields we observe a change in the critical exponents and universal functions. The critical regime diminishes as the field is decreased but remains nonzero even at 1 mT. These results suggest that the universality class of the transition changes at low fields.

BaCuQF (Q=S,Se) materials, candidate transparent p-type conductors, were prepared by solid-state reaction, and their bulk electrical and optical properties were evaluated. The room-temperature Seebeck coefficient and electrical conductivity of undoped BaCuQF pellets were +56 μV/K and 0.088 S/cm, respectively, for the sulfide fluoride, and +32 μV/K and 0.061 S/cm, respectively, for the selenide fluoride. The conductivity was greatly enhanced by the substitution of several percent of K for Ba; the highest conductivities were 82 S/cm for Ba0.9K0.1CuSF and 43 S/cm for Ba0.9K0.1SeF. The band gaps for Q=S and Q=Se were measured to be 3.2 and 3.0 eV, respectively. Undoped BaCuSF exhibits strong red luminescence near 630 nm under ultraviolet excitation.

Crystals of BiCuOSe were grown from a salt flux, and the crystal structure was determined by single-crystal X-ray diffraction. BiCuOSe adopts the tetragonal layered structure of LnCuOCh (Ln=lanthanide; Ch=S, Se, and Te) with bond lengths and bond angles in good agreement with those published for powders. Powders comprising mixed chalcogenides across the series BiCuOCh (Ch=S, Se, and Te) were made by reacting Bi2O2Ch and Cu2Ch. Band gaps determined via infrared diffuse reflectance from powders are Eg=0.82 eV for BiCuOSe, 0.89 eV for BiCuOS0.5Se0.5, and 1.07 eV for BiCuOS. The band gap of BiCuOSe inferred from infrared transmission measurements on single crystals is in good agreement with the value obtained from diffuse reflectance from the powder.

The electronic structure of the oxychalcogenides LaCuOSe and BiCuOSe has been studied using O K-edge x-ray emission spectroscopy, x-ray absorption spectroscopy, and density functional theory, in order to examine the effects of the M 3+ ion configurations. The known distortion of the BiO layers in BiCuOSe compared to the LaO layers in LaCuOCh; the significantly smaller band gap of BiCuOSe (0.9 eV) compared to LaCuOSe (2.8 eV); and similar hole transport properties of the two compounds are explained in terms of the electron lone pairs associated with the Bi d 10 s 2 p 0 electronic configuration. The Bi 6s orbitals are chemically active and form bonding and antibonding states with the oxygen 2p orbital. The structural distortion facilitates the interaction between the 6p orbital with 6s via the antibonding state. For BiCuOSe, the majority of the Bi 6s orbital character (i.e., the bonding state) lies below the valence band, with the antibonding state lying below the valence band maximum (VBM). The similar hole transport properties between the two compounds is a consequence of the Bi 6s contributing little to the Cu 3d‐Se 4p derived VBM. Finally, the band gap narrowing of BiCuOSe compared to LaCuOSe is mostly due to the low energy of the unoccupied Bi 6p orbitals along with the upshift of the VBM due to the presence of the O 2p‐Bi 6s antibonding states.

In the Paradigms in Physics Curriculum at Oregon State University, we take a spins-first approach to quantum mechanics using a java simulation of successive Stern-Gerlach experiments to explore the postulates. The experimental schematic is a diagrammatic representation that we use throughout our discussion of quantum measurements. With a spins-first approach, it is natural to start with Dirac bra-ket language for states, observables, and projection operators. We also use explicit matrix representations of operators and ask students to translate between the Dirac and matrix languages. The projection of the state onto a basis is represented with a histogram. When we subsequently introduce wave functions, the wave function attains a natural interpretation as the continuous limit of these discrete histograms or a projection of a Dirac ket onto position or momentum eigenstates. We are able to test the students' facility with moving between these representations in later modules.