Showing papers on "Doping published in 2012"
TL;DR: In this article, the authors describe the polycondensation of this structure, how to modify band positions and band gap by doping and copolymerization, and how to texture the organic solid to make it an effective photocatalyst.
Abstract: Polymeric graphitic carbon nitride (for simplicity, g-C3N4) is a layered material similar to graphene, being composed of only C, N, and some impurity H. Contrary to graphenes, g-C3N4 is a medium band gap semiconductor and an effective photocatalyst for a broad variety of reactions, and it possesses a high thermal and chemical stability In this Perspective, we describe the polycondensation of this structure, how to modify band positions and band gap by doping and copolymerization, and how to texture the organic solid to make it an effective photocatalyst. We then describe the photochemical splitting of water and some mild and selective photooxidation reactions catalyzed by g-C3N4.
1,449 citations
TL;DR: A large enhancement in the transition temperature Tc occurring at optimal doping in the chemically inaccessible low–carrier density regime is revealed, indicating that the superconducting dome may arise even in doped band insulators.
Abstract: A dome-shaped superconducting region appears in the phase diagrams of many unconventional superconductors. In doped band insulators, however, reaching optimal superconductivity by the fine-tuning of carriers has seldom been seen. We report the observation of a superconducting dome in the temperature-carrier density phase diagram of MoS(2), an archetypal band insulator. By quasi-continuous electrostatic carrier doping achieved through a combination of liquid and solid gating, we revealed a large enhancement in the transition temperature T(c) occurring at optimal doping in the chemically inaccessible low-carrier density regime. This observation indicates that the superconducting dome may arise even in doped band insulators.
1,010 citations
TL;DR: Using in situ Raman scattering from a single-layer MoS2 electrochemically top-gated field effect transistor (FET), this paper showed softening and broadening of the A(1g) phonon with electron doping, whereas the other Raman-active E2g(1) mode remains essentially inert.
Abstract: A strong electron-phonon interaction which limits the electronic mobility of semiconductors can also have significant effects on phonon frequencies. The latter is the key to the use of Raman spectroscopy for nondestructive characterization of doping in graphene-based devices. Using in situ Raman scattering from a single-layer MoS2 electrochemically top-gated field-effect transistor (FET), we show softening and broadening of the A(1g) phonon with electron doping, whereas the other Raman-active E-2g(1) mode remains essentially inert. Confirming these results with first-principles density functional theory based calculations, we use group theoretical arguments to explain why the A(1g) mode specifically exhibits a strong sensitivity to electron doping. Our work opens up the use of Raman spectroscopy in probing the level of doping in single-layer MoS2-based FETs, which have a high on-off ratio and are of technological significance.
916 citations
TL;DR: By identifying the regimes of junction doping concentration in which each mechanism dominates, this work was able to design and fabricate an independently confirmed 18.2%-efficient nanostructured 'black-silicon' cell that does not need the antireflection coating layer normally required to reach a comparable performance level.
Abstract: The efficiency of solar cells with high-area, nanostructured surfaces is limited by surface and Auger charge-recombination processes, which can be slowed through appropriate levels of junction doping
824 citations
TL;DR: In this paper, boron atoms are doped into graphene frameworks forming borton doped graphene (BG) via a catalyst-free thermal annealing approach in the presence of BORON oxide, which has a flake-like structure with an average thickness of ca. 2 nm.
Abstract: Boron atoms, with strong electron-withdrawing capability, are doped into graphene frameworks forming boron doped graphene (BG) via a catalyst-free thermal annealing approach in the presence of boron oxide. Atomic force microscopic (AFM) and transmission electron microscopic (TEM) characterizations reveal that the as-prepared BG has a flake-like structure with an average thickness of ca. 2 nm. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that boron atoms can be successfully doped into graphene structures with the atomic percentage of 3.2%. Due to its particular structure and unique electronic properties, the resultant BG exhibits excellent electrocatalytic activity towards oxygen reduction reaction (ORR) in alkaline electrolytes, similar to the performance of Pt catalysts. In addition, the non-metallic BG catalyst shows long-term stability and good CO tolerance superior to that of Pt-based catalysts. These results demonstrate that the BG, as a promising candidate in advanced electrode materials, may substitute Pt-based nanomaterials as a cathode catalyst for ORR in fuel cells as well as other electrochemical applications similar to the reported nitrogen doped graphene.
755 citations
TL;DR: Electrically pumped lasing from Germanium-on-Silicon pnn heterojunction diode structures is demonstrated and a Germanium gain spectrum of nearly 200nm is observed.
Abstract: Electrically pumped lasing from Germanium-on-Silicon pnn heterojunction diode structures is demonstrated. Room temperature multimode laser with 1mW output power is measured. Phosphorous doping in Germanium at a concentration over 4x1019cm-3 is achieved. A Germanium gain spectrum of nearly 200nm is observed.
746 citations
TL;DR: In this article, an effective structural doping approach has been described to modify the photoelectrochemical properties of g-C3N4 by doping with nonmetal (sulfur or phosphorus) impurities.
Abstract: An effective structural doping approach has been described to modify the photoelectrochemical properties of g-C3N4 by doping with nonmetal (sulfur or phosphorus) impurities. Here, the substitutional and interstitial doped models of g-C3N4 systems were constructed with different doped sites, and then their dopant formation energies and electronic properties were performed to study the stability and visible-light photoactivity using first-principles density functional theory, respectively. Our results have identified that an S atom preferentially substitutes for the edge N atom of g-C3N4; however, a P atom preferentially situates the interstitial sites of in-planar of g-C3N4. Furthermore, it is demonstrated that the doping with nonmetal impurities reduces the energy gap to enhance the visible-light absorption of g-C3N4. The increased dispersion of the contour distribution of the HOMO and LUMO brought by doping facilitates the enhancement of the carrier mobility, while the noncoplanar HOMO and LUMO favor the...
568 citations
TL;DR: It is demonstrated that a two-step process is an efficient way to dope graphene: create vacancies by high-energy atom/ion bombardment and fill these vacancies with desired dopants.
Abstract: Functionalized graphene has been extensively studied with the aim of tailoring properties for gas sensors, superconductors, supercapacitors, nanoelectronics, and spintronics. A bottleneck is the capability to control the carrier type and density by doping. We demonstrate that a two-step process is an efficient way to dope graphene: create vacancies by high-energy atom/ion bombardment and fill these vacancies with desired dopants. Different elements (Pt, Co, and In) have been successfully doped in the single-atom form. The high binding energy of the metal-vacancy complex ensures its stability and is consistent with in situ observation by an aberration-corrected and monochromated transmission electron microscope.
542 citations
TL;DR: Phos-phorus is a typical dopant for silicon or germanium to make itan n-type semiconductor, but it has been rarely used as anionic dopants for semiconductor photocatalysts to reduce their band-gap energies.
Abstract: Phos-phorus is a typical dopant for silicon or germanium to make itan n-type semiconductor. However, it has been rarely used asdopant for semiconductor photocatalysts. This is rathersurprising because other non-metallic elements, such as N,C, and S, have been widely used as anionic dopants forphotocatalysts to reduce their band-gap energies.
434 citations
TL;DR: The direct semiconductor bonding technique opens up a new pathway for realizing ultrahigh efficiency multijunction solar cells with ideal bandgap combinations that are free from lattice-match restrictions required in conventional heteroepitaxy, as well as enabling the creation of novel high performance and practical optoelectronic devices by III-V/Si hybrid integration.
Abstract: Monolithic integration of III-V compound semiconductors on silicon is highly sought after for high-speed, low-power-consumption silicon photonics and low-cost, light-weight photovoltaics. Here we present a GaAs/Si direct fusion bonding technique to provide highly conductive and transparent heterojunctions by heterointerfacial band engineering in relation to doping concentrations. Metal- and oxide-free GaAs/Si ohmic heterojunctions have been formed at 300°C; sufficiently low to inhibit active material degradation. We have demonstrated 1.3 μm InAs/GaAs quantum dot lasers on Si substrates with the lowest threshold current density of any laser on Si to date, and AlGaAs/Si dual-junction solar cells, by p-GaAs/p-Si and p-GaAs/n-Si bonding, respectively. Our direct semiconductor bonding technique opens up a new pathway for realizing ultrahigh efficiency multijunction solar cells with ideal bandgap combinations that are free from lattice-match restrictions required in conventional heteroepitaxy, as well as enabling the creation of novel high performance and practical optoelectronic devices by III-V/Si hybrid integration.
383 citations
TL;DR: In this article, the authors reported a red anatase TiO2 microsphere with a bandgap gradient varying from 1.94 eV on its surface to 3.22 eV in its core by a conceptually different doping approach.
Abstract: Narrowing the bandgap of wide-bandgap semiconductor photocatalysts (for instance, anatase TiO2) by introducing suitable heteroatoms has been actively pursued for increasing solar absorption, but usually suffers from a limited thermodynamic/kinetic solubility of substitutional dopants in bulk and/or dopant-induced recombination centres. Here we report a red anatase TiO2 microsphere with a bandgap gradient varying from 1.94 eV on its surface to 3.22 eV in its core by a conceptually different doping approach for harvesting the full spectrum of visible light. This approach uses a pre-doped interstitial boron gradient to weaken nearby Ti-O bonds for the easy substitution of oxygen by nitrogen, and consequently it substantially improves the nitrogen solubility. Furthermore, no nitrogen-related Ti3+ was formed in the red TiO2 due to a charge compensation effect by boron, which inevitably occurs in common nitrogen doped TiO2. The red anatase TiO2 exhibits photoelectrochemical water splitting activity under visible light irradiation. The results obtained may shed light on how to increase high visible light absorbance of wide-bandgap photocatalysts.
TL;DR: Bandlike transport in solution-deposited, CdSe QD thin-films with room temperature field-effect mobilities for electrons of 27 cm(2)/(V s) is reported with concomitant shift and broadening consistent with electron delocalization and measured electron mobilities.
Abstract: We report bandlike transport in solution-deposited, CdSe QD thin-films with room temperature field-effect mobilities for electrons of 27 cm2/(V s). A concomitant shift and broadening in the QD solid optical absorption compared to that of dispersed samples is consistent with electron delocalization and measured electron mobilities. Annealing indium contacts allows for thermal diffusion and doping of the QD thin-films, shifting the Fermi energy, filling traps, and providing access to the bands. Temperature-dependent measurements show bandlike transport to 220 K on a SiO2 gate insulator that is extended to 140 K by reducing the interface trap density using an Al2O3/SiO2 gate insulator. The use of compact ligands and doping provides a pathway to high performance, solution-deposited QD electronics and optoelectronics.
TL;DR: While Ag was expected to be a substitutional acceptor, nonmonotonic trends in the fluorescence and Fermi level suggest that Ag changes from an interstitial (n- type) to a subst institutional (p-type) impurity with increased doping.
Abstract: We dope CdSe nanocrystals with Ag impurities and investigate their optical and electrical properties. Doping leads not only to dramatic changes but surprising complexity. The addition of just a few Ag atoms per nanocrystal causes a large enhancement in the fluorescence, reaching efficiencies comparable to core–shell nanocrystals. While Ag was expected to be a substitutional acceptor, nonmonotonic trends in the fluorescence and Fermi level suggest that Ag changes from an interstitial (n-type) to a substitutional (p-type) impurity with increased doping.
TL;DR: It was found that Se increases the doping concentration of K in PbTe as a result of the balance of electronegativity and also lowers the lattice thermal conductivity because of the increased number of point defects.
Abstract: We present detailed studies of potassium doping in PbTe1–ySey (y = 0, 0.15, 0.25, 0.75, 0.85, 0.95, and 1). It was found that Se increases the doping concentration of K in PbTe as a result of the balance of electronegativity and also lowers the lattice thermal conductivity because of the increased number of point defects. Tuning the composition and carrier concentration to increase the density of states around the Fermi level results in higher Seebeck coefficients for the two valence bands of PbTe1–ySey. Peak thermoelectric figure of merit (ZT) values of ∼1.6 and ∼1.7 were obtained for Te-rich K0.02Pb0.98Te0.75Se0.25 at 773 K and Se-rich K0.02Pb0.98Te0.15Se0.85 at 873 K, respectively. However, the average ZT was higher in Te-rich compositions than in Se-rich compositions, with the best found in K0.02Pb0.98Te0.75Se0.25. Such a result is due to the improved electron transport afforded by heavy K doping with the assistance of Se.
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TSMC1
TL;DR: In this paper, a method for forming semiconductor contacts comprises forming a germanium fin structure over a silicon substrate, depositing a doped amorphous silicon layer over the first drain/source region and the second drain and source region at a first temperature, wherein the first temperature is lower than a melting point of the fin structure, and performing a solid phase epitaxial regrowth process on the doped silicon layer at a second temperature.
Abstract: A method for forming semiconductor contacts comprises forming a germanium fin structure over a silicon substrate, depositing a doped amorphous silicon layer over the first drain/source region and the second drain/source region at a first temperature, wherein the first temperature is lower than a melting point of the germanium fin structure and performing a solid phase epitaxial regrowth process on the amorphous silicon layer at a second temperature, wherein the second temperature is lower than the melting point of the germanium fin structure.
TL;DR: Mo or W doping enhanced the photocatalytic and photoelectrochemical water oxidation activity of monoclinic BiVO(4) by drastically reducing its charge-transfer resistance and thereby minimizing photoexcited electron-hole pair recombination.
Abstract: The visible-light-induced water oxidation ability of metal-ion-doped BiVO4 was investigated and of 12 metal ion dopants tested, only W and Mo dramatically enhanced the water photo-oxidation activity of bare BiVO4; Mo had the highest improvement by a factor of about six. Thus, BiVO4 and W- or Mo-doped (2 atom %) BiVO4 photoanodes about 1 μm thick were fabricated onto transparent conducting substrate by a metal–organic decomposition/spin-coating method. Under simulated one sun (air mass 1.5G, 100 mW cm−2) and at 1.23 V versus a reversible hydrogen electrode, the highest photocurrent density (JPH) of about 2.38 mA cm−2 was achieved for Mo doping followed by W doping (JPH≈1.98 mA cm−2), whereas undoped BiVO4 gave a JPH value of about 0.42 mA cm−2. The photoelectrochemical water oxidation activity of W- and Mo-doped BiVO4 photoanodes corresponded to the incident photon to current conversion efficiency of about 35 and 40 % respectively. Electrochemical impedance spectroscopy and Mott–Schottky analysis indicated a positive flat band shift of about 30 mV, a carrier concentration 1.6–2 times higher, and a charge-transfer resistance reduced by 3–4-fold for W- or Mo-doped BiVO4 relative to undoped BiVO4. Electronic structure calculations revealed that both W and Mo were shallow donors and Mo doping generated superior conductivity to W doping. The photo-oxidation activity of water on BiVO4 photoanodes (undoped
Posted Content•
TL;DR: Ab initio calculations have been performed to study the geometry and electronic structure of boron (B) and nitrogen (N) doped graphene sheet by varying the concentrations of dopants from 2 % to 12 % (six dopant atoms in 50 atoms host atoms) and also by considering different doping sites for the same concentration of substitutional doping as discussed by the authors.
Abstract: Ab-initio calculations have been performed to study the geometry and electronic structure of boron (B) and nitrogen (N) doped graphene sheet. The effect of doping has been investigated by varying the concentrations of dopants from 2 % (one atom of the dopant in 50 host atoms) to 12 % (six dopant atoms in 50 atoms host atoms) and also by considering different doping sites for the same concentration of substitutional doping. All the calculations have been performed by using VASP (Vienna Ab-initio Simulation Package) based on density functional theory. By B and N doping p-type and n-type doping is induced respectively in the graphene sheet. While the planar structure of the graphene sheet remains unaffected on doping, the electronic properties change from semimetal to semiconductor with increasing number of dopants. It has been observed that isomers formed differ significantly in the stability, bond length and band gap introduced. The band gap is maximum when dopants are placed at same sublattice points of graphene due to combined effect of symmetry breaking of sub lattices and the band gap is closed when dopants are placed at adjacent positions (alternate sublattice positions). These interesting results provide the possibility of tuning the band gap of graphene as required and its application in electronic devices such as replacements to Pt based catalysts in Polymer Electrolytic Fuel Cell (PEFC).
TL;DR: In this article, pure and Cu doped ZnO nanopowders (5, 10, 15, 20, 25 and 30 at% Cu) have been synthesized using co-precipitation method.
Abstract: Pure and Cu doped ZnO nanopowders (5, 10, 15, 20, 25 and 30 at% Cu) have been synthesized using co-precipitation method. Transmission Electron Microscopic analysis has shown the morphology of ZnO nanopowders to be quasi-spherical. Powder X-ray Diffraction studies have revealed the systematic doping of Cu into the ZnO lattice up to 10% Cu, though the peaks corresponding to CuO in 10% Cu are negligibly very small. Beyond this level, there was segregation of a secondary phase corresponding to the formation of CuO. Fourier Transform Infrared spectra have shown a broad absorption band at ∼490 cm −1 for all the samples, which corresponds to the stretching vibration of Zn–O bond. DC electrical resistivity has been found to decrease with increasing Cu content. The activation energy has also been observed to decrease with copper doping i.e. from ∼0.67 eV for pure ZnO to ∼0.41 eV for 30 at% Cu doped ZnO.
TL;DR: In this paper, La-doped BaSnO3 with the perovskite structure has an unprecedented high mobility at room temperature while retaining its optical transparency, and the maximum mobility reached 320 cm^2(Vs)^-1 at a doping level of 8x10^19 cm^-3, constituting the highest value among wideband gap semiconductors.
Abstract: We discovered that La-doped BaSnO3 with the perovskite structure has an unprecedentedly high mobility at room temperature while retaining its optical transparency. In single crystals, the mobility reached 320 cm^2(Vs)^-1 at a doping level of 8x10^19 cm^-3, constituting the highest value among wide-band-gap semiconductors. In epitaxial films, the maximum mobility was 70 cm^2(Vs)^-1 at a doping level of 4.4x10^20 cm^-3. We also show that resistance of (Ba,La)SnO3 changes little even after a thermal cycle to 530 Deg. C in air, pointing to an unusual stability of oxygen atoms and great potential for realizing transparent high-frequency, high-power functional devices.
TL;DR: In this paper, La-doped BaSnO3 with perovskite structure has an unprecedented high mobility at room temperature while retaining its optical transparency, reaching 320 cm2 V-1 s-1 at a doping level of 8×1019 cm-3, constituting the highest value among wideband-gap semiconductors.
Abstract: We discovered that La-doped BaSnO3 with the perovskite structure has an unprecedentedly high mobility at room temperature while retaining its optical transparency. In single crystals, the mobility reached 320 cm2 V-1 s-1 at a doping level of 8×1019 cm-3, constituting the highest value among wide-band-gap semiconductors. In epitaxial films, the maximum mobility was 70 cm2 V-1 s-1 at a doping level of 4.4×1020 cm-3. We also show that resistance of (Ba,La)SnO3 changes little even after a thermal cycle to 530 °C in air, pointing to an unusual stability of oxygen atoms and great potential for realizing transparent high-frequency, high-power functional devices.
TL;DR: In this paper, the bulk trap-induced component of current collapse (CC) in GaN/AlGaN heterojunction field effect transistors is studied in drift diffusion simulations, distinguishing between acceptor traps situated in the top and bottom half of the bandgap, with Fe and C used as specific examples.
Abstract: The bulk trap-induced component of current collapse (CC) in GaN/AlGaN heterojunction field-effect transistors is studied in drift diffusion simulations, distinguishing between acceptor traps situated in the top and the bottom half of the bandgap, with Fe and C used as specific examples. It is shown that Fe doping results in an inherent but relatively minor contribution to dispersion under pulse conditions. This simulation is in reasonable quantitative agreement with double pulse experiments. Simulations using deep-level intrinsic growth defects produced a similar result. By contrast, carbon can induce a strong CC which is dependent on doping density. The difference is attributed to whether the trap levels, whether intrinsic or extrinsic dopants, result in a resistive n-type buffer or a p-type floating buffer with bias-dependent depletion regions. This insight provides a key design concept for compensation schemes needed to ensure semi-insulating buffer doping for either RF or power applications.
Patent•
27 Apr 2012
TL;DR: In this article, the authors proposed a semiconductor light-emitting device (SLEEM) which consists of a substrate, an n-type semiconductor layer for providing electrons when voltage is applied thereto, a p-type electron hole when voltage was applied thereto; a conductive n- type electrode for applying voltage to the n-Type semiconductor layers, and an active layer which has a quantum well structure for activating electron-hole combination.
Abstract: The present invention relates to a semiconductor light-emitting device. The semiconductor light-emitting device comprises: a substrate; an n-type semiconductor layer for providing electrons when voltage is applied thereto; a p-type semiconductor layer for providing electron holes when voltage is applied thereto; a conductive n-type electrode for applying voltage to the n-type semiconductor layer; a conductive p-type electrode for applying voltage to the p-type semiconductor layer; an active layer which is interposed between the n-type semiconductor layer and the p-type semiconductor layer, and which has a quantum well structure for activating electron-hole combination; and a current-spreading and hole injection layer which is interposed between the p-type semiconductor layer and the p-type electrode, and in which both an n-type impurity and a p-type impurity are doped together for current-spreading and hole injection between the p-type electrode and the p-type semiconductor layer. Consequently, the semiconductor light-emitting device of the present invention is advantageous in that it not only reduces contact resistance between an electrode and a semiconductor layer, improving current flow and rendering current-spreading further uniform, but also improves hole injection performance, thereby achieving the maximized efficiency of the device.
TL;DR: The structural and microstructural properties as a function of Al and Ga concentrations through X-ray diffraction and scanning electron microscopy analysis and the optical bandgap and photoluminescence were estimated.
Abstract: We have investigated the influences of aluminum and gallium dopants (0 to 2.0 mol%) on zinc oxide (ZnO) thin films regarding crystallization and electrical and optical properties for application in transparent conducting oxide devices. Al- and Ga-doped ZnO thin films were deposited on glass substrates (corning 1737) by sol–gel spin-coating process. As a starting material, AlCl3⋅6H2O, Ga(NO3)2, and Zn(CH3COO)2⋅2H2O were used. A lowest sheet resistance of 3.3 × 103 Ω/□ was obtained for the GZO thin film doped with 1.5 mol% of Ga after post-annealing at 650°C for 60 min in air. All the films showed more than 85% transparency in the visible region. We have studied the structural and microstructural properties as a function of Al and Ga concentrations through X-ray diffraction and scanning electron microscopy analysis. In addition, the optical bandgap and photoluminescence were estimated.
TL;DR: A combination of resistive switching and magnetic modulation gives rise to the integration of room temperature ferromagnetism and electrical properties into a simple Pt/Co:ZnO/Pt structure due to the formation of oxygen vacancy-based conductive filaments, promising for broadening the applications of random access memories to encode quaternary information.
Abstract: A combination of resistive switching and magnetic modulation gives rise to the integration of room temperature ferromagnetism (spin) and electrical properties (charge) into a simple Pt/Co:ZnO/Pt structure due to the formation of oxygen vacancy-based conductive filaments. This is promising for broadening the applications of random access memories to encode quaternary information.
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21 Aug 2012TL;DR: In this article, a flowable silicon-carbon-and-nitrogen-containing layer is ion implanted to increase etch tolerance, prevent shrinkage, adjust film tension and/or adjust electrical characteristics.
Abstract: Methods are described for forming and treating a flowable silicon-carbon-and-nitrogen-containing layer on a semiconductor substrate. The silicon and carbon constituents may come from a silicon-and-carbon-containing precursor while the nitrogen may come from a nitrogen-containing precursor that has been activated to speed the reaction of the nitrogen with the silicon-and-carbon-containing precursor at lower deposition temperatures. The initially-flowable silicon-carbon-and-nitrogen-containing layer is ion implanted to increase etch tolerance, prevent shrinkage, adjust film tension and/or adjust electrical characteristics. Ion implantation may also remove components which enabled the flowability, but are no longer needed after deposition. Some treatments using ion implantation have been found to decrease the evolution of properties of the film upon exposure to atmosphere.
TL;DR: In this paper, a chemical approach to control the work function of few-layer graphene is investigated, where six metal chlorides, AuCl3, IrCl3 and MoCl3 are used as dopants.
Abstract: A chemical approach to controlling the work function of few-layer graphene is investigated. Graphene films are synthesized on Cu foil by chemical vapor deposition. Six metal chlorides, AuCl3, IrCl3, MoCl3, OsCl3, PdCl2, and RhCl3, are used as dopants. The sheet resistance of the doped graphene decreases from 1100 Ω/sq to ≈500–700 Ω/sq and its transmittance at 550 nm also decreases from 96.7% to 93% for 20 mM AuCl3 due to the formation of metal particles. The sheet resistance and transmittance are reduced with increasing metal chloride concentration. The G peak in the Raman spectra is shifted to a higher wavenumber after metal chloride doping, which indicates a charge transfer from graphene to metal ions. The intensity ratio of ICC/IC−C increases with doping, indicating an electron transfer from graphene sheets to metal ions. Ultraviolet photoemission spectroscopy data shows that the work function of graphene increases from 4.2 eV to 5.0, 4.9, 4.8, 4.68, 5.0, and 5.14 eV for the graphene with 20 mM AuCl3, IrCl3, MoCl3, OsCl3, PdCl2, and RhCl3, respectively. It is considered that spontaneous charge transfer occurs from the specific energy level of graphene to the metal ions, thus increasing the work function.
TL;DR: In this paper, the electronic properties of doped tungsten oxide (WO3) have been studied using DFT calculations with hybrid functionals, and the effect of substituting W with low-valent Ti, Zr, or Hf ions has been shown to narrow the energy gap by introducing localized occupied states above the valence band and shifting the conduction band minimum upward.
Abstract: The electronic properties of doped tungsten oxide (WO3) have been studied using DFT calculations with hybrid functionals. While the position of the top of the valence band (VB) in WO3 is good for O2 evolution in water splitting, the conduction band (CB) is too low for H2 production. Furthermore, the band gap should be reduced to improve activity with visible light. Doping can be used to alter the position of the energy levels, thus resulting in a more efficient photocatalyst. Replacing W in the lattice by isovalent Mo or Cr ions narrows the band gap but shifts the CB edge further down. Replacing O by S has the effect to narrow the energy gap by introducing localized occupied states above the VB and shifts the CB minimum upward—two effects that go in the right direction. Substitution of W with low-valent Ti, Zr, or Hf ions widens the band gap and shifts the CB edge to higher energies. However, a low-valent ion replacing W induces the formation of compensating defects: in Hf-doped WO3 oxygen vacancies (VO) ...
TL;DR: The robust p-type doping observed for quasi-free-standing graphene on hexagonal silicon carbide is explained by the spontaneous polarization of the substrate, and models based on hypothetical acceptor-type defects as they are discussed so far are obsolete.
Abstract: We explain the robust p-type doping observed for quasi-free-standing graphene on hexagonal silicon carbide by the spontaneous polarization of the substrate. This mechanism is based on a bulk property of SiC, unavoidable for any hexagonal polytype of the material and independent of any details of the interface formation. We show that sign and magnitude of the polarization are in perfect agreement with the doping level observed in the graphene layer. With this mechanism, models based on hypothetical acceptor-type defects as they are discussed so far are obsolete. The n-type doping of epitaxial graphene is explained conventionally by donorlike states associated with the buffer layer and its interface to the substrate that overcompensate the polarization doping. The basis for the unique electronic and optical properties of graphene is the linear dispersion relation of the � electrons, which is responsible for Dirac-type quasiparticles with many unusual properties. The band structure in the relevant energy range is made up by double cones in the corners of the two-dimensional hexagonal Brillouin zone; their opening angle is determined by the slope vF ¼ d! dk of the dispersion relation called the Fermi velocity, which is an intrinsic material parameter. The origin of these so-called Dirac cones defines the Fermi energy in an isolated and intrinsic graphene layer. At finite temperatures, the reservoir of mobile charge carriers is due to thermal excitation of equal concentrations n0 and p0 of electrons and holes. Evaluation of the Fermi statistics yields a value of n0 ¼ �k 2 B
TL;DR: Theoretical calculations of the lattice thermal conductivity based on the modified Callaway model reveal that both nanostructures and point defects (solid solution) effectively scatter phonons in this system, indicating the excellent thermal stability for these high performance thermoelectrics.
Abstract: We report high thermoelectric performance in nanostructured p-type PbS, a material consisting of highly earth abundant and inexpensive elements. The high level of Na doping switched intrinsic n-type PbS to p-type and substantially raised the power factor maximum for pure PbS to ∼9.0 μW cm–1 K–2 at >723 K using 2.5 at. % Na as the hole dopant. Contrary to that of PbTe, no enhancement in the Hall coefficient occurs at high temperature for heavily doped p-type PbS, indicating a single band model and no heavy hole band. We also report that the lattice thermal conductivity of PbS can be greatly reduced by adding SrS or CaS, which form a combination of a nanostructured/solid solution material as determined by transmission electron microscopy. We find that both nanoscale precipitates and point defects play an important role in reducing the lattice thermal conductivity, but the contribution from nanoscale precipitates of SrS is greater than that of CaS, whereas the contribution from point defects in the case of C...
TL;DR: Doping graphene with BN domains is an effective method to open a band gap for carbon-based next-generation microelectronic devices.
Abstract: Boron nitride (BN) domains are easily formed in the basal plane of graphene due to phase separation. With first-principles calculations, it is demonstrated theoretically that the band gap of graphene can be opened effectively around K (or K′) points by introducing small BN domains. It is also found that random doping with boron or nitrogen is possible to open a small gap in the Dirac points, except for the modulation of the Fermi level. The surface charges which belong to the π states near Dirac points are found to be redistributed locally. The charge redistribution is attributed to the change of localized potential due to doping effects. The band opening induced by the doped BN domain is found to be due to the breaking of localized symmetry of the potential. Therefore, doping graphene with BN domains is an effective method to open a band gap for carbon-based next-generation microelectronic devices.