Ab initio modelling of boron and nitrogen in diamond nanowires

In this study an analysis is presented of the bonding and structural properties of dehydrogenated and hydrogenated doped cylindrical diamond nanowires calculated using the Vienna Ab Initio Simulation Package, employing density functional theory within the generalized-gradient approximation. The dopants studied here have been inserted substitutionally along the axis of an infinite one-dimensional diamond nanowire and include the single-electron acceptor boron and the single-electron donor nitrogen. The doped nanowires have then been re-relaxed, and properties compared with the undoped structures. The structural properties of relaxed nanowires considered here include an examination bonding via the electron charge density, with the aim of providing a better understanding of the effects of dopants on the stability of diamond nanostructures and nanodevices.     

Ab initio modelling of band states in doped diamond

Presented in this study is an analysis of the electronic properties of doped diamond calculated using the Vienna ab initio simulation package, employing density functional theory within the generalized-gradient approximation. The dopants studied here have been inserted substitutionally into a 64-atom diamond supercell and include the single-electron acceptors boron and aluminium, the single-electron donors nitrogen and phosphorus and the double-electron donors oxygen and sulphur. Co-doping of diamond with sulphur and boron has also been briefly examined. The doped supercells have been relaxed, followed by calculation of electronic properties from the electronic density of states such as the indirect bandgap E _g, the valence bandwidth and an examination of the acceptor and donor states in the bandgap. It is anticipated that this study will provide a useful comparison of the third- and fourth-row donors and acceptors in diamond.     

From nanodiamond to diamond nanowires: structural properties affected by dimension

Although production of nanowires from various materials is proving very successful, the development of diamond nanowires has been slow. However, a significant amount of successful research has been conducted regarding zero-dimensional nanodiamond crystals, which may offer a basis for the development of one-dimensional diamond nanostructures. Observations of the structural transitions between nanodiamonds into carbon onions inevitably lead to questions as to whether a similar transformation occurs in one dimension and, if so, how it may be avoided. Presented here are ab initio investigations of dehydrogenated nanodiamond crystals and analogous diamond nanowires, to examine how the additional dimension effects structural properties.     

Scaling theory put into practice: first-principles modeling of transport in doped silicon nanowires

We combine the ideas of scaling theory and universal conductance fluctuations with density-functional theory to analyze the conductance properties of doped silicon nanowires. Specifically, we study the crossover from ballistic to diffusive transport in boron or phosphorus doped Si nanowires by computing the mean free path, sample-averaged conductance G, and sample-to-sample variations std(G) as a function of energy, doping density, wire length, and the radial dopant profile. Our main findings are (i) the main trends can be predicted quantitatively based on the scattering properties of single dopants, (ii) the sample-to-sample fluctuations depend on energy but not on doping density, thereby displaying a degree of universality, and (iii) in the diffusive regime the analytical predictions of the Dorokhov-Mello-Pereyra-Kumar theory are in good agreement with our ab initio calculations.     

Nanometric diamond delta doping with boron

Diamond is desired for active semiconducting device because of it high carrier mobility, high voltage breakdown resistance, and high thermal diffusivity. Exploiting diamond as a semiconductor is hampered by the lack of shallow dopants to create sufficient electronic carriers at room temperature. In this work, nanometer thick, heavily boron doped epitaxial diamond ‘delta doped’ layers have been grown on ultra smooth diamond surfaces which demonstrate p type conduction with enhanced Hall mobilities of up to 120 cm²/Vs and sheet carrier concentrations to 6 × 10¹³ cm^–2, thus enabling a new class of active diamond electronic devices. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Reactions and stresses in polycrystalline diamond-metal and diamond-carbide compacts

Abstract

The kind of bonding phase has a significant influence on the microstructure and mechanical properties of diamond compacts. Microstructural studies of diamond with 5% wt. Ti and 5%wt. Tic (and also 30%wt. Tic) were carried out with a Transmission Electron Microscope. The TEM microstructural observations show differences between the metal and metal carbide bonding phase in diamond compacts. The mismatch of thermal expansion coefficients between diamond and the bonding metal or the compound induces significant internal stresses and may generate micro-cracks in polycrystalline diamond compacts. Twins and dislocations are the important details of microstructures in diamond crystals after HPHT sintering. They can appear as a result of residual stress relaxation. Results of measurements of residual stresses on a diamond compact surface by means of the “sin²ψ X-ray diffraction method are reported.     

The formation of a diamond layer on a carbide substrate during diamond interaction with Si,WC and Co

Abstract

A diamond layer was formed on a carbide substrate in an irregular temperature field at high pressures (HP). A gradient scheme of HP cell set-up has been developed, which provides for a simultaneous impregnation of opposite planes of a diamond layer by components that differ in melting temperature. The cell temperature field has been calculated and physico-mechanical properties of the obtained composite material have been studied.     

Growth and comparison of physicochemical properties of pure,Ca and Sr doped NH4Sb3F10 single crystals for electro optic applications

Single crystals of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material.     

掺杂金刚石薄膜的缺陷研究

利用多普勒增宽谱和电子顺磁共振研究了掺硼和掺硫金刚石薄膜的缺陷状态.多普勒增宽谱的结果表明，不同杂质元素掺杂的金刚石薄膜，其中使正电子湮没的缺陷种类是相同的；正电子与不同杂质元素硼、硫之间的相互作用不明显；少量硼可使金刚石膜中的空位浓度减少.EPR结果表明，各掺杂样品的顺磁信号主要来自于金刚石的碳悬键. 关键词： 金刚石 掺杂 多普勒增宽谱 电子顺磁共振     

Modulation Mechanism of Transition Elements Fe and Mn on the Interface Bonding Performance of Bronze/Diamond Composites

The modulation mechanism of iron (Fe) and manganese (Mn) in transition-metal elements on the interface bonding and mechanical properties of bronze (Cu₃Sn)-based/diamond composites is investigated through first-principles calculations. Transition-elements-doping scenarios are investigated employing six-layer slab models. It is revealed that the doping of Fe or Mn can make the Cu₃Sn/diamond interface more stable, which effectively improves the wettability of the Cu₃Sn/diamond interface based on the calculation results and analysis of interface energy, differential charge density model, and density of states. However, co-doping with both Fe and Mn weakens the wettability of the Cu₃Sn/diamond interface. Finally, wettability tests and microstructure characterizations demonstrate that the doping of Fe and Mn represents an effective approach to controlling the interface bonding performance of bronze/diamond composites.     

First principles study of electronic structure and optical properties of CaTiO3

The electronic-energy band structure, site and angular momentum decomposed density of states (DOS) and charge-density contours of perovskite CaTiO ₃ are calculated by the first principles tight-binding linear muffin-tin orbitals method with atomic sphere approximation using density functional theory in its local density approximation. The calculated band structure shows an indirect (R-Γ) band gap of 1.5 eV. The total DOS as well as the partial density of states (PDOS) are compared with the experimental photoemission spectra. The calculated DOS are in reasonable agreement with the experimental energy spectra and the features in the spectra are interpreted by a comparison of the spectra with the PDOS. The origin of the various experimentally observed bands have been explained. From the DOS analysis, as well as charge-density studies, we conclude that the bonding between Ca and TiO ₃ is mainly ionic and that the TiO ₃ entities bond covalently. Using the projected DOS and band structure we have analyzed the interband contribution to the optical properties of CaTiO ₃ . The real and imaginary parts of the dielectric function and hence the optical constants such as refractive index and extinction coefficient are calculated. The calculated spectra are compared with the experimental results for CaTiO ₃ and are found to be in good agreement with the experimental results. The effective number of electrons per unit cell participating in the interband transitions are calculated. The role of band structure calculation as regards the optical properties of CaTiO ₃ is discussed. Received 1 February 2000 and Received in final form 21 July 2000     

Charge correlations in the weakly doped t-J model calculated by projection technique

We study frequency- and wave-vector dependent charge correlations in weakly doped antiferromagnets using Mori-Zwanzig projection technique. The system is described by the two-dimensional t-J model. The ground state is expressed within a cumulant formalism which has been successfully applied to study magnetic properties of the weakly doped system. Within this approach the ground state contains independent spin-bag quasiparticles (magnetic polarons). We present results for the charge-density response function and for the optical conductivity at zero temperature for different values of t / J. They agree well with numerical results calculated by exact diagonalization techniques. The density response function for intermediate and large momenta shows a broad continuum on energy scales of order of several t whereas the optical conductivity for is dominated by low energy excitations (at 1.5-2J). We show that these weak-doping properties can be well understood by transitions between excited states of spin-bag quasiparticles. Received: 10 July 1997 / Revised: 19 March 1998 / Accepted: 3 April 1998     

金刚石延(111)面生长的第一性原理研究

利用密度泛函理论(DFT)对碳原子在镍(111)表面吸附结构进行了计算，得到了吸附能以及态密度 (density of state, DOS)分布，分析了吸附在镍(111)面的碳原子和金刚石(111)面的碳原子的分波态密度(PDOS)，结果表明吸附在镍表面的碳原子具有与金刚石表面碳原子相类似的电子结构特点，即两者都存在孤对的和成键的sp³杂化电子,进而发现吸附在镍表面的碳原子极易与金刚石表面相互作用形成稳定的类金刚石几何结构. 关键词： 密度泛函理论 化学吸附 电子结构 金刚石生长     

Tunable electronic behavior in 3d transition metal doped 2H-WSe2

Structural and electronic properties of 3d transition metal Sc, Ti, Cr and Mn incorporated 2H-WSe₂ have been systematically investigated by first-principles calculations based on density functional theory. The calculated formation energies reveal that all the doped systems are thermodynamically more favorable under Se-rich condition than W-rich condition. The geometry structures almost hold that of the pristine 2H-WSe₂ albeit with slight lattice distortion. More importantly, the electronic properties have been significantly tuned by the dopants, i.e., metal and semimetal behavior has been found in Sc, Ti and Mn-doped 2H-WSe₂, respectively, semiconducting nature with narrowed band gap is expected in Cr-doped case, just as that of the pristine 2H-WSe₂. In particular, magnetic character is realized by incorporation of Mn impurity with a total magnetic moment of 0.96 μ_B. Our results suggest chemical doping is an effective way to precisely tailor the electronic structure of layered transition metal dichalcogenide 2H-WSe₂ for target technological applications.     

First-principles calculations of the monoclinic transition-metal doped NaMnO2 cathode material

ABSTRACT

Using spin-polarised generalised gradient approximation (GGA?+?U), I successfully investigate the electronic properties of the monoclinic NaMnO₂ doped with Cr, Fe and V atom to enhance the electrochemical performance. The expansion of volumes is induced by the dopants. The lowest conduction band and highest valence band are mostly from d orbital of Mn atom and transition-metal dopants which are responsible for the electronic conductivity. Na(Mn, Fe)O₂ is a semiconductor with the reduced band gap. Cr and V doping in NaMnO₂ compound reveal the half-metallic performance. The enhancement of the insertion potentials is induced by transition-metal dopants. The electronic conductivity of NaMnO₂ cathode material is improved by Cr-doping scheme. Finally, this research presents the new horizons for the expenditure of transition-metal doping for designing and improving the NaMnO₂ cathode materials in Na-ion rechargeable batteries.     

Effect of doping Zn atom on the structural stability,mechanical and thermodynamic properties of AlLi phase in Mg–Li alloys from first-principles calculations

ABSTRACT

This work uses first-principles total energy calculations on the basis of density functional theory to predict the structural stability, mechanical and thermodynamic properties of Zn atom doped AlLi phase in Mg–Li–Al–Zn alloy. The values of the equilibrium lattice parameters and the formation of enthalpy are highly consistent with the experimental and previous calculations results available. Negative enthalpies of formation ΔH are predicted for all AlLi phase doped concentrations which have positive consequences for its structural stability. The elastic modulus is deduced by Voigt–Reuss–Hill arithmetic approximation. The bulk modulus of the Al–Li–Zn compounds increases as the doping concentrations increase, which are larger than the value of the AlLi phase. In particular, the stability and mechanical anisotropy of the Al–Li–Zn compounds are discussed. The charge density cloud map is drawn to reveal the bonding characteristics of four compounds. The changes in thermodynamic properties are derived by the phonon frequencies within the quasi-harmonic approximation.     

Tuning electronic properties of In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires by doping control

We present two effective routes to tune the electronic properties of single-crystalline In₂O₃ nanowires by controlling the doping. The first method involves using different O₂ concentrations during the synthesis. Lightly (heavily) doped nanowires were produced by using high (low) O₂ concentrations, respectively, as revealed by the conductances and threshold voltages of nanowire-based field-effect transistors. Our second method exploits post-synthesis baking, as baking heavily doped nanowires in ambient air led to suppressed conduction and a positive shift of the threshold voltage, whereas baking lightly doped nanowires in vacuum displayed the opposite behavior. Our approaches offer viable ways to tune the electronic properties of many nonstoichiometric metal oxide systems such as In₂O₃, SnO₂, and ZnO nanowires for various applications. PACS 85.35.-p     

Electronic and structural properties of black phosphorene doped with Si,B and N

The electronic and structural properties of substitutional and doped phosphorene with B, N and Si were studied using first principles calculations based on density functional theory. Moreover, electronic and structural properties of functionalized phosphorene slowly increasing the concentration of doping was investigated. Phosphorene strongly binds with doped functionalization; B doped phosphorene is the most stable configuration studied. Si doped phosphorene maintains the semiconductor characteristic. B and N doped phosphorene present n-type and p-type semiconductors, respectively. Doped phosphorene with odd number of Si is a semiconductor material, doped phosphorene with an odd number of B has n-type semiconductor characteristic, and doped phosphorene with odd number of N atoms has a p-type semiconductor behaviour. Doped phosphorene with even number of Si has a metallic characteristic, while B and N doped phosphorene with even number present a semiconductor behaviour. This work reveals that phosphorene electronic properties could be changed by introducing the dopants on the system, and the properties are affected by the increasing number of dopants on phosphorene sheet.     

Effect of C doping on the structural and electronic properties of LiFePO4: A first-principles investigation

Using first-principles calculations within the generalized gradient approximation （GGA） ＋U framework, we inves- tigate the effect of C doping on the structural and electronic properties of LiFePO4. The calculated formation energies indicate that C doped at O sites is energetically favoured, and that C dopants prefer to occupy 03 sites. The band gap of the C doped material is much narrow than that of the undoped one, indicating better electro- conductive properties. To maintain charge balance, the valence of the Fe nearest to C appears as Fe3＋, and it will be helpful to the hopping of electrons.     

Alloying effects and site occupancies of Re in the C14 Cr-based Laves phases: a first-principles study

First-principles calculations based upon the density functional theory have been carried out to investigate the alloying effects and site occupancies of Re in the C14 XCr₂ (X?=?Nb, Ta, Ti, Zr, Hf) Laves phases. The calculated results indicate that Re tends to facilitate and participate in the formation of the Laves phases, generating X₈Cr₁₅Re accordingly. The partial density of states and charge density di?erence were analysed to re?ect the bonding characteristics. For X₈Cr₁₅Re, the bonding between the doped Re and its nearest neighbour Cr atoms all show covalent characteristics, which contribute to the phase stability. The substitution of Re on X sites is energetically unfavourable due to the weak bonding between Re and its nearest neighbour X atoms.