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The lattice constants of a diamond platelet and of large single, undoped, crystals of silicon and germanium have been determined from measurements of multiple diffraction patterns by the method described in Part I [Post (1975). J. Appl. Cryst. 8, 452–456]. The mean values, based on measurements of eight to twelve reflections, and their standard dev...
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... The optimized lattice constant for diamond is 3.57 Å, which matches the experimental value of 3.57 Å [23,24]. However, due to the inevitable bandgap narrowing by GGA-PBE, the bandgap is calculated to be 4.17 eV, smaller than the experimentally determined bandgap (5.47 eV) for diamond [25]. ...
With ultra-wide bandgap and outstanding thermal properties, diamond-based high-power devices have excellent application prospects. The crystal structure and electronic property of the metal/hydrogen-terminated diamond (H-diamond) interfaces have been extensively studied experimentally, but the Schottky barrier height (SBH) theory at the metal/H-diamond interface has not been systematically investigated yet. In this work, SBHs of interfaces formed by H-diamond (111) surfaces with 12 metals (Y, Sc, Mg, Ag, Al, Ti, Cu, Co, Pd, Ni, Au and Pt) are investigated using ab-initio calculations. The fitted curve of the SBH with respect to the metal work function is obtained with a Fermi pinning factor of 0.30, which is close to the empirical value of 0.36. Due to the negative electron affinity of H-diamond, Schottky contacts can be formed with low work function metals, which is useful in device design to regulate the SBH and it is relatively easier to form ohmic contacts with high work function metals, leading to low contact resistances. Our work sheds light on the rational design of diamond-based semiconductor devices with low contact resistances.
... Just for comparison, the theoretical lattice constant of Si (5.401 Å) matches the experimental one (5.431 Å [107]) quite well. To include the van-der-Waals functionals into the DFPT algorithm is part of our future plans. ...
Phonons are quantized vibrations of a crystal lattice that play a crucial role in understanding many properties of solids. Density functional theory (DFT) provides a state-of-the-art computational approach to lattice vibrations from first-principles. We present a successful software implementation for calculating phonons in the harmonic approximation, employing density-functional perturbation theory (DFPT) within the framework of the full-potential linearized augmented plane-wave (FLAPW) method as implemented in the electronic structure package FLEUR. The implementation, which involves the Sternheimer equation for the linear response of the wave function, charge density, and potential with respect to infinitesimal atomic displacements, as well as the setup of the dynamical matrix, is presented and the specifics due to the muffin-tin sphere centered LAPW basis-set and the all-electron nature are discussed. As a test, we calculate the phonon dispersion of several solids including an insulator, a semiconductor as well as several metals. The latter are comprised of magnetic, simple, and transition metals. The results are validated on the basis of phonon dispersions calculated using the finite displacement approach in conjunction with the FLEUR code and the phonopy package, as well as by some experimental results. An excellent agreement is obtained.
... First-principles calculations were performed using the Vienna Ab initio Simulation Package (VASP) 22 based on the density functional theory. Starting from 3.567 Å , the lattice constant relaxed to 3.57 Å after geometry optimization using the PBE (Perdew-Burke-Ernzerhof) functional, 23 which agreed well with the experimental value, 24 and this lattice constant was used for the subsequent N-doping calculations. The cutoff energy for the plane waves was set as 450 eV. ...
The development of diamond semiconductor devices has been hindered by the challenge of preparing n-type diamond with a shallow donor state. Recently, elastic strain engineering has emerged as a promising strategy for modulating the electrical properties of diamond. In this study, we used first-principles calculations to investigate the influence of large, uniaxial elastic strain on the electrical properties of nitrogen (N)-doped diamond, particularly the donor level. We found that both tensile and compressive strains can shift the donor level of N to a shallower state, but compressive strains of more than 9% along [100] appear more effective in making N a shallower donor in strained diamond. This study offers insights for future experimental design to combine strain engineering and doping toward practical diamond semiconductor devices.
... Wolfgang Zeier et al have provided a thorough understanding on the electronic properties, like bandgap, band degeneracy, and effective mass of carriers in relation with the bond length, bond energy, orbital overlap and electronegativity along with the dependency of thermal conductivity on the bond length, bond strength and crystal structure [32]. Diamond shows the thermal conductivity of 2000 Wm −1 K −1 because of strong carbon-carbon covalent bonding and the measured carbon-carbon bond length is 154 pm [39,40]. Octahedrallike chalcogenide compounds bonding mechanism is signalized by large anharmonicity and soft chemical bonds which reduce the lattice thermal conductivity and these compounds bring out strong band anisotropy and huge band degeneracy which accompany to power factor improvements [41,42]. ...
The continuous depletion of fossil fuels and the increasing demand for eco-friendly and sustainable energy sources have prompted researchers to look for alternative energy sources. The loss of thermal energy in heat engines (100-350 ºC), coal-based thermal plants (150-700 ºC), heated water pumping in the geothermal process (150-700 ºC), and burning of petrol in the automobiles (150-250 ºC) in form of untapped waste-heat can be directly and/or reversibly converted into usable electricity by means of charge carriers (electrons or holes) as moving fluids using thermoelectric (TE) technology, which works based on typical Seebeck effect. The enhancement in TE conversion efficiency has been a key challenge because of the coupled relation between thermal and electrical transport of charge carriers in a given material. In this review, we have deliberated the physical concepts governing the materials to device performance as well as key challenges for enhancing the TE performance. Moreover, the role of crystal structure in the form of chemical bonding, crystal symmetry, order-disorder and phase transition on charge carrier transport in the material has been explored. Further, this review has also emphasized some insights on various approaches employed recently to improve the TE performance, such as, (i). carrier engineering via band engineering, low dimensional effects, and energy filtering effects and (ii). Phonon engineering via doping/alloying, nano-structuring, embedding secondary phases in the matrix and microstructural engineering. Wehave also briefed the importance of magnetic elements on thermoelectric properties of the selected materials and spin Seebeck effect. Furthermore, the design and fabrication of TE modules and their major challenges are also discussed. As, thermoelectric figure of merit, zT does not have any theoretical limitation, an ideal high performance thermoelectric device should consist of low-cost, eco-friendly, efficient, n- or p-type materials that operate at wide- temperature range and similar coefficients of thermal expansion, suitable contact materials, less electrical/ thermal losses and constant source of thermal energy. Overall, this review provides the recent physical concepts adopted and fabrication procedures of TE materials and device so as to improve the fundamental understanding and to develop a promising TE device.
... The PBE functional is used for the relaxation of the diamond structure. After relaxation, the lattice parameter is 3.574 Å, compared with the experimental value of 3.567 Å [36] [37][38] [39], and the error is less than 0.2%. It shows that the calculation method 6 adopted is reliable and that the calculation parameters set during the calculation are correct. ...
... To gain insight into the stability of PtGe cluster structures, a phase diagram as a function of the chemical potential of Ge (μ Ge ) is built based on the ensemble-average of all thermally accessible isomers at 700 K. The chemical potentials of Ge in bulk germanium, [48] GeCl 4 (precursor used to prepare PtGe/Al 2 O 3 through ALD-like process), [31] and GeO 2 are used as references to calculate the ensemble-averaged formation energies. Pure Pt 4 is favored over a wide range of μ Ge . ...
Ethylene is a key molecule in the chemical industry and it can be obtained through the catalytic dehydrogenation of ethane. Pt‐based catalysts show high performance toward alkane dehydrogenation, but suffer from coke formation and sintering that deactivate the catalyst. Ge was recently discovered to be a promising alloying element that suppresses deactivation of Pt while preserving its catalytic activity toward alkane dehydrogenation. This work explores the effect of the Ge content in supported PtGe cluster alloys, on the activity toward ethane dehydrogenation, selectivity against deeper dehydrogenation and coking, and sintering resistance. The model proposed herein is a tetrameric Pt cluster supported on magnesia, with varying amounts of added Ge. The phase diagram for these clusters was computed using global optimization at the density functional theory level, and under the paradigm of a statistical ensemble of many states populated by clusters at catalytic temperatures. The phase diagram shows that various Ge contents should be synthetically accessible, with Pt4Ge/MgO and Pt4Ge4/MgO being the most likely phases. The subsequent adsorption and mechanistic studies show that the clusters with the 1 : 4 Ge to Pt ratio (Pt4Ge/MgO) feature the largest resistance to sintering and best selectivity in the ethane dehydrogenation toward ethylene. Clusters without Ge are too active and easily coke, whereas clusters with higher Ge content start losing the catalytic activity toward ethane dehydrogenation. Thus, Ge concentration is a lever of control of Pt cluster stability and selectivity, and of cluster catalyst design. The effect of the Ge concentration on the cluster properties is explained on the basis of the electronic structure.
... was constructed for test calculations and subsequent structure optimization based on crystal structure data. [17] To determine the pseudopotential for further calculations, we tested the non-empirical PZ (PerdewZunger) Ge pseudopotential based on the local density approximation parameterization [18] and the ultrasoft Perdew-Burke-Ernzerhof scalar-relativistic pseudopotential Ge.pbe-dn-rrkjus_psl.1.0.0.UPF. [19] As a result of testing, it was found that the PZ Ge pseudopotential better describes the electronic structure and band gap of bulk germanium. ...
... The results show that complete relaxation of the germanium unit cell leads to cell parameter values of a = b = c = 5.616191 Å (Figure 1a). These results agree well with the experimental data for the parameters a = b = c = 5.657820(5) Å. [17] This structure was then transformed by translation and trimming of the {1 0 5} group planes into a 14-atom Ge crystal layer, which then underwent further relaxation (Figure 1b). Figure 2 shows the structure of a 2D Ge layer with 56 atoms. We further used this structure to study the hole behavior and the effect of pressure on magnetization. ...
Designing stable quantum computers with the ability to correct errors responsibly requires a detailed understanding of the physical processes that underlie these devices. In this study, detailed quantum mechanical simulations of the atomic structure, charge distribution of electron density, and distribution and orientation of magnetic and quantum states as a function of applied external pressure performed for ultrathin layers of germanium. The results show that, even in the absence of holes, in the negative pressure range, the total spin is characterized by the quantum state |1〉 in the Bloch sphere. It found that the hole states predominantly localized in the volume structure of ultrathin germanium layers. In this structure, there is an ordering of magnetic states with a repetition period of 2a along the elongation axis of the slab.
... Due to the smaller size of Si atom, we observed that the addition of Si atom inside the system reduce the lattice constant effectively from 5.6770 Å for the pure Ge condition to the 5.4113 Å for the pure Si atom. Both of these two calculated parameters are very well matched with the known experimental data, with the error less than 0.3 % [19]. Now looking at the SiGe alloy, we also observed the reduction lattice parameter effect due to increasing Si atom composition. ...
The density functional theory (DFT) study on two variation of SiGe alloy (Si0.50Ge0.50 representing 50:50 ratio; Si0.25Ge0.75 representing 25:75 ratio) are reported in this study by utilizing a parameter-free functional named SCAN (strongly-constrained and appropriately normed). The SCAN functional is within meta-generalized gradient approximation (meta-GGA) level of accuracy. It was known from previous DFT studies based on LDA/GGA functional, germanium (Ge) system is predicted to be a metal instead of insulator, limiting the understanding on SiGe alloy without any parameterization included. By using the SCAN functional, we observed that the lattice parameter of SiGe alloy will increased with the reduction of Si-content inside the system. From the density of states figure we obtain an insulating gap value of 0.89 eV, while Si0.25Ge0.75 alloy shows a lower value of 0.75 eV. Our results indicate that the reduction gap effects caused by the increasing of Ge-content is captured properly and well-matched with the known experimental data.
... To gain insight into the stability of PtGe cluster structures, a phase diagram as a function of the chemical potential of Ge (μ Ge ) is built based on the ensemble-average of all thermally accessible isomers at 700 K. The chemical potentials of Ge in bulk germanium, 48 GeCl 4 (precursor used to prepare PtGe/Al 2 O 3 through ALD-like process) 31 , and GeO 2 are used as references to calculate the ensemble-averaged formation energies. Pure Pt 4 is favored over a wide range of μ Ge . ...
Ethylene is a key molecule in the chemical industry and it can be obtained through the catalytic dehydrogenation of ethane. Pt-based catalysts show high performance toward alkane dehydrogenation, but suffer from coke formation and sintering that deactivate the catalyst. Ge was recently discovered to be a promising alloying element that suppresses deactivation of Pt while preserving its catalytic activity toward alkane dehydrogenation. In this work we explore the effect of the Ge content in supported PtGe cluster alloys, on the activity toward ethane dehydrogenation, selectivity against deeper dehydrogenation and coking, and sintering resistance. Our model is a tetrameric Pt cluster supported on magnesia, with varying amounts of added Ge. The phase diagram for these clusters was computed using global optimization at the density functional theory level, and under the paradigm of a statistical ensemble of many states populated by clusters at catalytic temperatures. The phase diagram shows that various Ge contents should be synthetically accessible, with Pt4Ge/MgO and Pt4Ge4 /MgO being the most likely phases. The subsequent adsorption and mechanistic studies show that the clusters with the 1:4 Ge to Pt ratio (Pt4Ge/MgO) feature the largest resistance to sintering and best selectivity in the ethane dehydrogenation toward ethylene. Clusters without Ge are too active and easily coke, whereas clusters with higher Ge content start losing the catalytic activity toward ethane dehydrogenation. Thus, Ge concentration is a lever of control of Pt cluster stability and selectivity, and of cluster catalyst design. The effect of the Ge concentration on the cluster properties is explained on the basis of the electronic structure.
... 46 These internal interactions are held by strong covalent and ionic bonds. For silicon, we considered crystals in a cubic diamond structure with a lattice constant of 5.43 Å, 47 corresponding to the Fd3m space group. 48 Its structure can be seen as two interpenetrating face centered cubic sublattices with one sublattice displaced from the other by one-quarter of the distance along the body diagonal of the cube. ...
Thin films of transition metal oxides such as molybdenum oxide (MoOx) are attractive for application in silicon heterojunction solar cells for their potential to yield large short‐circuit current density. However, full control of electrical properties of thin MoOx layers must be mastered to obtain an efficient hole collector. Here, we show that the key to control the MoOx layer quality is the interface between the MoOx and the hydrogenated intrinsic amorphous silicon passivation layer underneath. By means of ab initio modelling, we demonstrate a dipole at such interface and study its minimization in terms of work function variation to enable high performance hole transport. We apply this knowledge to experimentally tailor the oxygen content in MoOx by plasma treatments (PTs). PTs act as a barrier to oxygen diffusion/reaction and result in optimal electrical properties of the MoOx hole collector. With this approach, we can thin down the MoOx thickness to 1.7 nm and demonstrate short‐circuit current density well above 40 mA/cm2 and a champion device exhibiting 23.83% conversion efficiency. In this paper, we demonstrate a method to reach a full control of electrical properties of molybdenum oxide (MoOx) thin‐films for an efficient hole collection. Ab initio simulations demonstrate the existence of dipole at the interface between silicon and MoOx. As postulated by our device modelling, we apply innovative plasma treatments (PTs) to such an interface to alleviate the detrimental effect of the dipole on the hole selectivity of the device. From TEM image, we observed the formation of a‐SiOx:H and a‐Si:H layers during PT with boron (PTB). Modifying the interface between (i)a‐Si:H and MoOx, these additional layers improved the passivation quality and carriers transport of the device resulting in a champion cell with certified efficiency of 23.83%.
