In this work, we present a first-principles density functional theory (DFT) computational investigation of the luminescence and absorption lineshapes associated with the neutral carbon-oxygen interstitial pair (CiOi) defect in silicon. We obtain the lineshapes of the defect in the dilute limit using a computational methodology that constructs dynamical matrices of supercells containing tens of thousands of atoms, utilizing systems directly accessible through DFT. Both perturbed bulk phonons and localized vibrations contribute to the phonon sideband. We achieve excellent agreement with experimental luminescence data. Our findings further reinforce the attribution of the well-known C-line in silicon to the neutral CiOi complex.
Silicon carbide with optically and magnetically active point defects offers unique opportunities for quantum technology applications. Since interaction with these defects commonly happens through optical excitation and de-excitation, a complete understanding of their light-matter interaction in general and optical signatures, in particular, is crucial. Here, we employ quantum mechanical density functional theory calculations to investigate the photoluminescence lineshapes of selected, experimentally observed color centers (including single vacancies, double vacancies, and vacancy impurity pair…
This letter introduces ab initio study of the full activation-volume tensor of crystalline defects as a means to make contact with mechanical response experiments. We present a theoretical framework for prediction of the internal friction associated with divacancy defects and give the first ab initio value for this quantity in silicon. Finally, making connection with defect alignment studies, we give the first unambiguous resolution of the debate surrounding ab initio verification of the ground-state structure of the defect.
The electronic structure and absorption spectrum of hydrogenated silicon carbide nanocrystals (SiCNC) have been determined by first principles calculations. We show that the reconstructed surface can significantly change not just the onset of absorption, but the \emph{shape} of the spectrum at higher energies. We found that the absorption treshold of the reconstructed SiCNs cannot be accurately predicted from traditional density functional theory calculations.
Using first principles molecular dynamics simulations, we have determined the threshold displacement energies and the associated created defects in cubic silicon carbide. Contrary to previous studies using classical molecular dynamics, we found values close to the experimental consensus, and also created defects in good agreement with recent works on interstitials stability in silicon carbide. We carefully investigated the limits of this approach. Our work shows that it is possible to calculate displacement energies with first principles accuracy in silicon carbide, and suggests that it may be…
Based on {\em ab initio} calculation, we propose a new structure for the fundamental excitation of the reconstructed 30$^\circ$ partial dislocation in silicon. This soliton has a rare structure involving a five-fold coordinated atom near the dislocation core. The unique electronic structure of this defect is consistent with the electron spin resonance signature of the hitherto enigmatic thermally stable R center of plastically deformed silicon. We present the first {\em ab initio} determination of the free energy of the soliton, which is also in agreement with the experimental observation. Thi…
Identification of carbon-related color centers in hBN by high-resolution ab initio photoluminescence modeling
University of Oslo（奥斯陆大学）；State Research Institute Center for Physical Sciences and Technology (FTMC)（立陶宛国家物理科学技术研究中心）；Warsaw University of Technology（华沙理工大学）
Using density-functional-theory calculations, we have identified new stable configurations for tri-, tetra-, and penta-vacancies in silicon. These new configurations consist of combinations of a ring-hexavacancy with three, two, or one interstitial atoms, respectively, such that all atoms remain fourfold. As a result, their formation energies are lower by 0.6, 1.0, and 0.6 eV, respectively, than the ``part of a hexagonal ring'' configurations, believed up to now to be the lowest-energy states.
The replacement of SiO2 by so-called high-k oxides is one of the major challenges for the semiconductor industry to date. Based on electronic structure calculations and ab-initio molecular dynamics simulations, we are able to provide a consistent picture of the growth process of a class of epitaxial oxides around SrO and SrTiO3. The detailed understanding of the interfacial binding principles has also allowed us to propose a way to engineer the band-offsets between the oxide and the silicon substrate.
The homogeneous shear of the {111} planes along the <110> direction of bulk silicon has been investigated using ab initio techniques, to better understand the strain properties of both shuffle and glide set planes. Similar calculations have been done with three empirical potentials, Stillinger-Weber, Tersoff and EDIP, in order to find the one giving the best results under large shear strains. The generalized stacking fault energies have also been calculated with these potentials to complement this study. It turns out that the Stillinger-Weber potential better reproduces the ab initio results, …
We describe a simple annealing procedure to obtain the Hugoniot locus (states accessible by a shock wave) for a given material in a computationally efficient manner. We apply this method to determine the Hugoniot locus in bulk silicon from ab initio molecular dynamics with forces from density-functional theory, up to 70 GPa. The fact that shock waves can split into multiple waves due to phase transitions or yielding is taken into account here by specifying the strength of any preceding waves explicitly based on their yield strain. Points corresponding to uniaxial elastic compression along thre…
We have used density functional theory to study the energetics and electronic structure of aluminium dopants in crystalline silicon. We present data regarding the atomic and electronic structure and properties of pairs of substitutional aluminium dopants. We find that pairs of dopants, when occupying nearest neighbouring subsitutional sites in a high spin state, can bond to form aluminium pairs. This suggests that such a configuration of dopants will be electrically active when made to occupy a high spin state, whereas in the low spin state the neighbouring dopant pairs are found to be self co…
We present a first-principles calculation of the electronic properties of crystalline silicon and gallium arsenide in a uniform electric field. Polarized Wannier-like functions which are confined in a finite region are obtained by minimizing a total-energy functional which depends explicitly on the macroscopic polarization of the solid. The polarization charge density and the electronic dielectric constant are computed via finite differences. The results coincide with those of the linear response approach in the limit of vanishing electric field and infinite localization region.
We present an ab initio calculation of the DC conductivity of amorphous silicon and hydrogenated amorphous silicon. The Kubo-Greenwood formula is used to obtain the DC conductivity, by thermal averaging over extended dynamical simulation. Its application to disordered solids is discussed. The conductivity is computed for a wide range of temperatures and doping is explored in a naive way by shifting the Fermi level. We observed the Meyer-Neldel rule for the electrical conductivity with E_MNR = 0.06 eV and a temperature coefficient of resistance, TCR ~ -2.0% K^-1 for a-Si:H. In general, experime…
We present a systematic methodology for the accurate calculation of defect structures in supercells which we illustrate with a study of the neutral vacancy in silicon. This is a prototypical defect which has been studied extensively using ab initio methods, yet remarkably there is still no consensus about the energy or structure of this defect, or even whether the nearest neighbour atoms relax inwards or outwards. In this paper we show that the differences between previous calculations can be attributed to supercell convergence errors, and we demonstrate how to systematically reduce each such …
In this paper we present kinetic properties such as migration and decomposition barriers of hydrogen defects in silicon calculated by Density Functional Theory (DFT) based methods. We study the following defects: H atoms (H) and ions (H+, H-), hydrogen molecules (H2) and hydrogen complexes (H2*). Our results show that the dominating migration species are H ions, their charge-independent migration barrier being 0.46 eV in excellent agreement with experimental value [1]. At higher temperatures H2 and H2* decompose with barriers of 1.2 and 1.5 eV respectively, while the migration barrier of H2 is…
Silicon telluride (Si2Te3) is a silicon-based 2D chalcogenide with potential applications in optoelectronics. It has a unique crystal structure where Si atoms form Si-Si dimers to occupy the "metal" sites. In this paper, we report an ab initio computational study of its optical dielectric properties using the GW approximation and the Bethe-Salpeter equation (BSE). Strong optical anisotropy is discovered. The imaginary part of the dielectric constant in the direction parallel to the Si-Si dimers is found to be much lower than that perpendicular to the dimers. We show this effect originates from…
We present fully ab-initio calculations of van der Waals coefficients for two different situations: i) the interaction between hydrogenated silicon clusters; and ii) the interactions between these nanostructures and a non metallic surface (a silicon or a silicon carbide surface). The methods used are very efficient, and allow the calculation of systems containing hundreds of atoms. The results obtained are further analyzed and understood with the help of simple models. These models can be of interest for molecular dynamics simulations of silicon nanostructures on surfaces, where they can give …
We present a new interpretation of measured Raman frequencies of a high-pressure structure of Silicon which was assigned previously to the beta-tin phase. Our results show that the beta-tin->Imma->sh phase transitions have been already indicated in this experiment which was performed before the discovery of the Imma phase. We have calculated phonon-dispersion curves for the beta-tin, Imma, and sh phases of silicon using the plane-wave pseudopotential approach to the density-functional theory and the density-functional perturbation theory within the local density approximation. With the new ass…
The split silicon-vacancy defect (SiV) in diamond is an electrically and optically active color center. Recently, it has been shown that this color center is bright and can be detected at the single defect level. In addition, the SiV defect shows a non-zero electronic spin ground state that potentially makes this defect an alternative candidate for quantum optics and metrology applications beside the well-known nitrogen-vacancy color center in diamond. However, the electronic structure of the defect, the nature of optical excitations and other related properties are not well-understood. Here w…
The thermal and lattice dynamical properties of seven silicon clathrate framework structures are investigated with ab initio density functional methods (frameworks I, II, IV, V, VII, VIII, and H). The negative thermal expansion (NTE) phenomenon is investigated by means of quasiharmonic approximation and applying it to equal time displacement correlation functions. The thermal properties of the studied clathrate frameworks, excluding the VII framework, resemble those of the crystalline silicon diamond structure. The clathrate framework VII was found to have anomalous NTE temperature range up to…
We have investigated the structural sequence of the high-pressure phases of silicon and germanium. We have focussed on the cd->beta-tin->Imma->sh phase transitions. We have used the plane-wave pseudopotential approach to the density-functional theory implemented within the Vienna ab-initio simulation package (VASP). We have determined the equilibrium properties of each structure and the values of the critical parameters including a hysteresis effect at the phase transitions. The order of the phase transitions has been obtained alternatively from the pressure dependence of the enthalpy and of t…
The formation of Ni(Pt)silicides on a Si(001) surface is investigated using an ab initio approach. After deposition of a Ni overlayer alloyed with Pt, the calculations reveal fast diffusion of Ni atoms into the Si lattice, which leads initially to the formation of Ni2Si. At the same time Si atoms are found to diffuse into the metallic overlayer. The transformation of Ni2Si into NiSi is likely to proceed via a vacancy-assisted diffusion mechanism. Silicon atoms are the main diffusing species in this transformation, migrating from the Si substrate through the growing NiSi layer into the Ni2Si. P…
The lattice thermal conductivities of silicon clathrate frameworks II and VIII are investigated by using ab initio lattice dynamics and iterative solution of the linearized Boltzmann transport equation(BTE) for phonons. Within the temperature range 100-350 K, the clathrate structures II and VIII were found to have lower lattice thermal conductivity values than silicon diamond structure (d-Si) by factors of 1/2 and 1/5, respectively. The main reason for the lower lattice thermal conductivity of the clathrate structure II in comparison to d-Si was found to be the harmonic phonon spectra, while i…
The diffusion of intrinsic defects in 3C-SiC is studied using an ab initio method based on density functional theory. The vacancies are shown to migrate on their own sublattice. The carbon split-interstitials and the two relevant silicon interstitials, namely the tetrahedrally carbon-coordinated interstitial and the <110>-oriented split-interstitial, are found to be by far more mobile than the vacancies. The metastability of the silicon vacancy, which transforms into a vacancy-antisite complex in p-type and compensated material, kinetically suppresses its contribution to diffusion processes. T…
Ab initio simulations are capable of providing detailed information of material behavior at the nanoscale. Simulating experimentally relevant situations is, however, often computationally intense. Using hybrid approaches between ab initio methods such as density functional theory (DFT) and machine learning, new models can be constructed which retain quantum accuracy while being computationally faster by several orders of magnitude. Two examples are discussed in this paper. The first is the computational search for low energy substitutional defect complexes in silicon. The second is the constru…
We investigate the pressure-induced metal-insulator transition from diamond to beta-tin in bulk Silicon, using quantum Monte Carlo (QMC) and density functional theory (DFT) approaches. We show that it is possible to efficiently describe many-body effects, using a variational wave function with an optimized Jastrow factor and a Slater determinant. Variational results are obtained with a small computational cost and are further improved by performing diffusion Monte Carlo calculations and an explicit optimization of molecular orbitals in the determinant. Finite temperature corrections and zero p…
Cubic silicon carbide is an excellent platform for integration of defect qubits into established wafer scale device architectures for quantum information and sensing applications, where divacancy qubit, that is similar to the negatively charged nitrogen-vacancy (NV) center in diamond, has favorable coherence properties. We demonstrate by means of density functional theory calculations that divacancy in 3C SiC has superior spin-stress coupling parameters and stress sensitivity for nanoscale, quantum enhanced photonic, optoelectronic and optomechanical devices.
We have combined the Boltzmann transport equation with an {\it ab initio} approach to compute the thermoelectric coefficients of semiconductors. Electron-phonon, ionized impurity, and electron-plasmon scattering rates have been taken into account. The electronic band structure and average intervalley deformation potentials for the electron-phonon coupling are obtained from the density functional theory. The linearized Boltzmann equation has then been solved numerically beyond the relaxation time approximation. Our approach has been applied to crystalline silicon. We present results for the mob…
Employing density functional theory calculations we explore initial stage of competitive alloying of co-deposited silver and indium atoms into a silicon surface. Particularly, we identify respective adsorption positions and activation barriers governing their diffusion on the dimer-reconstructed silicon surface. Further, we develop a growth model that properly describes diffusion mechanisms and silicon morphology with the account of silicon dimerization and the presence of C-type defects. Based on the surface kinetic Monte Carlo simulations we examine dynamics of bimetallic adsorption and elab…
The differences in energy between electronic bands due to valley splitting are of paramount importance in interpreting transport spectroscopy experiments on state-of-the-art quantum devices defined by scanning tunneling microscope lithography. We develop a plane-wave density functional theory description of these systems which is size-limited due to computational tractability. We then develop a less resource-intensive alternative via localized basis functions, retaining the physics of the plane-wave description, and extend this model beyond the capability of plane-wave methods to determine the…
Grain boundaries (GBs) are defects originating in multi-crystalline silicon during crystal growth for device Si solar cell fabrication. The presence of GBs changes the coordination of Si, making it advantageous for charge carriers to recombine, which brings a significant reduction of carrier lifetimes. Therefore, GBs can be highly detrimental for device performances. Furthermore, GBs easily form vacancies with deep defect electronic states and are also preferential segregation sites for various impurity species, such as C, N, and O. We studied from first principles the correlation between stru…
We develop an electronic-temperature dependent interatomic potential $Φ(T_\text{e})$ for unexcited and laser-excited silicon. The potential is designed to reproduce ab initio molecular dynamics simulations by requiring force- and energy matching for each time step. $Φ(T_\text{e})$ has a simple and flexible analytical form, can describe all relevant interactions and is applicable for any kind of boundary conditions (bulk, thin films, clusters). Its overall shape is automatically adjusted by a self-learning procedure, which finally finds the global minimum in the parameter space. We show that $Φ…
Motivated by the negative thermal expansion observed for silicon between 20 K and 120 K, we present first an ab initio study of the volume dependence of interatomic force constants, phonon frequencies of TA(X) and TA(L) modes, and of the associated mode Gruneisen parameters. The influence of successive nearest neighbors shells is analysed. Analytical formulas, taking into account interactions up to second nearest neighbors, are developped for phonon frequencies of TA(X) and TA(L) modes and the corresponding mode Gruneisen parameters. We also analyze the volume and pressure dependence of variou…
We fully implement the Aversa and Sipe sum-over-states formulism and make a full ab initio band structure analysis of interband and intraband contributions for the third-order nonlinear optical susceptibilities of bulk silicon. The band structure and momentum matrix elements were calculated by using the highly accurate all-electron full potential linearized augmented plane wave method within the local density approximation. The convergence tests including the scissor correction with different k-points meshes and empty states were performed. Both real and imaginary parts of susceptibility were …
Multi-crystalline silicon is widely used for producing low-cost and high-efficiency solar cells. During crystal growth and device fabrication, silicon solar cells contain grain boundaries (GBs) which are preferential segregation sites for atomic impurities such as oxygen atoms. GBs can induce charge carriers recombination significantly reducing carrier lifetimes and therefore they can be detrimental for Si device performance. We studied the correlation between structural, energetic and electronic properties of Σ3{111} Si GB in the presence of vacancies, strain and multiple O segregation. The s…
We study the temperature dependent dynamical processes of a Si10H16 cluster and obtain a blue shift of the Si-Si vibrational modes with transverse acoustic character and a red shift of the other vibrational modes with increasing temperature. We link this behavior to the bond length expansion and the varying sign of the Grueneisen parameter. We further present a computational approach able to extract the vibron-vibron coupling strength in clusters or molecules. Our approach is based on ab initio Born-Oppenheimer molecular dynamics and a projection formalism able to deliver the individual vibron…
On the basis of detailed first-principles calculations the anisotropic thermoelectric transport properties of biaxially strained silicon were studied with focus on a possible enhancement of the powerfactor. Electron as well as hole doping were examined in a broad doping and temperature range. In the low-temperature and low-doping regime an enhancement of the powerfactor was obtained for compressive and tensile strain in the electron-doped case and for compressive strain in the hole-doped case. In the thermoelectrically more important high-temperature and high- doping regime a slight enhancemen…
We present here a theory and a computational tool, Silicon-{\sc Qnano}, to describe atomic scale quantum dots in Silicon. The methodology is applied to model dangling bond quantum dots (DBQDs) created on a passivated H:Si-(100)-(2$\times$1) surface by removal of a Hydrogen atom. The electronic properties of DBQD are computed by embedding it in a computational box of Silicon atoms. The surfaces of the computational box were constructed by using DFT as implemented in {\sc Abinit} program. The top layer was reconstructed by the formation of Si dimers passivated with H atoms while the bottom layer…
We employ ab initio molecular dynamics to simulate the response of hydrogenated amorphous silicon to light exposure (Staebler-Wronski effect). We obtain improved microscopic understanding of PV operation, compute the motion of H atoms, and modes of light-induced degradation of photovoltaics. We clarify existing models of light-induced change in aSi:H and show that the Hydrogen collision model of Branz3 is correct in essentials.
Ab initio molecular dynamics calculations of deuterium desorbing from Si(100) have been performed in order to monitor the energy redistribution among the hydrogen and silicon degrees of freedom during the desorption process. The calculations show that part of the potential energy at the transition state to desorption is transferred to the silicon lattice. The deuterium molecules leave the surface vibrationally hot and rotationally cold, in agreement with experiments; the mean kinetic energy, however, is larger than found in experiments.
As the silicon industry continues to push the limits of device dimensions, tools such as Raman spectroscopy are ideal to analyze and characterize the doped silicon channels. The effect of inter-valence band transitions on the zone center optical phonon in heavily p-type doped silicon is studied by Raman spectroscopy for a wide range of excitation wavelengths extending from the red (632.8 nm) into the ultra-violet (325 nm). The asymmetry in the one-phonon Raman lineshape is attributed to a Fano interference involving the overlap of a continuum of electronic excitations with a discrete phonon st…
Studying the crystallization process of silicon is a challenging task since empirical potentials are not able to reproduce well the properties of both semiconducting solid and metallic liquid. On the other hand, nucleation is a rare event that occurs in much longer timescales than those achievable by ab-initio molecular dynamics. To address this problem, we train a deep neural network potential based on a set of data generated by Metadynamics simulations using a classical potential. We show how this is an effective way to collect all the relevant data for the process of interest. In order to d…
An extensive search for low-energy lithium defects in crystalline silicon using density-functional-theory methods and the ab initio random structure searching (AIRSS) method shows that the four-lithium-atom substitutional point defect is exceptionally stable. This defect consists of four lithium atoms with strong ionic bonds to the four under-coordinated atoms of a silicon vacancy defect, similar to the bonding of metal ions in Zintl phases. This complex is stable over a range of silicon environments, indicating that it may aid amorphization of crystalline silicon and form upon delithiation of…
The development of modern ab initio methods has rapidly increased our understanding of physics, chemistry and materials science. Unfortunately, intensive ab initio calculations are intractable for large and complex systems. On the other hand, empirical force fields are less accurate with poor transferability even though they are efficient to handle large and complex systems. The recent development of machine-learning based neural-network (NN) for local atomic environment representation of density functional theory (DFT) has offered a promising solution to this long-standing challenge. Si is on…
Density functional perturbation theory calculations of alpha-quartz using extended norm conserving pseudopotentials have been used to study the elastic properties and phonon dispersion relations along various high symmetry directions as a function of bulk, uniaxial and non-hydrostatic pressure. The computed equation of state, elastic constants and phonon frequencies are found to be in good agreement with available experimental data. A zone boundary (1/3, 1/3, 0) K-point phonon mode becomes soft for pressures above P=32 GPa. Around the same pressure, studies of the Born stability criteria revea…
A brief review of the SIESTA project is presented in the context of linear-scaling density-functional methods for electronic-structure calculations and molecular-dynamics simulations of systems with a large number of atoms. Applications of the method to different systems are reviewed, including carbon nanotubes, gold nanostructures, adsorbates on silicon surfaces, and nucleic acids. Also, progress in atomic-orbital bases adapted to linear-scaling methodology is presented.
Ab initio molecular dynamics calculations of deuterium desorbing from Si(100) have been performed in order to monitor the energy redistribution among the various D$_2$ and silicon degrees of freedom during the desorption process. The calculations show that a considerable part of the potential energy at the transition state to desorption is transferred to the silicon lattice. The deuterium molecules leave the surface vibrationally hot and rotationally cold, in agreement with thermal desorption experiments; the mean kinetic energy, however, is larger than found in a laser-induced desorption expe…
Based on ab initio calculation, we propose a new structure for the fundamental excitation of the reconstructed 30$^\circ$ partial dislocation in silicon. This soliton has a rare structure involving a five-fold coordinated atom near the dislocation core. The unique electronic structure of this defect is consistent with the electron spin resonance signature of the hitherto enigmatic thermally stable R center of plastically deformed silicon. This identification suggests the possibility of an experimental determination of the density of solitons, a key defect in understanding the plastic flow of t…
It is essential to know the arrangement of the atoms in a material in order to compute and understand its properties. Searching for stable structures of materials using first-principles electronic structure methods, such as density functional theory (DFT), is a rapidly growing field. Here we describe our simple, elegant and powerful approach to searching for structures with DFT which we call ab initio random structure searching (AIRSS). Applications to discovering structures of solids, point defects, surfaces, and clusters are reviewed. New results for iron clusters on graphene, silicon cluste…
This paper presents an $ab$ $initio$ study of hydrogen dynamics inside nanometer-size voids in $a$-Si within the framework of the density-functional theory for a varying hydrogen load of 10 to 30 H atoms/void at the low and high temperature of 400 K and 700 K, respectively. Using the local density approximation and its generalized-gradient counterpart, the dynamics of hydrogen atoms inside the voids are examined with an emphasis on the diffusion of H atoms/molecules, and the resulting nanostructural changes of the void surfaces. The results from simulations suggest that the microstructure of t…
We develop an empirical potential for silicon which represents a considerable improvement over existing models in describing local bonding for bulk defects and disordered phases. The model consists of two- and three-body interactions with theoretically motivated functional forms that capture chemical and physical trends as explained in a companion paper. The numerical parameters in the functional form are obtained by fitting to a set of ab initio results from quantum mechanical calculations based on density functional theory in the local density approximation, which include various bulk phases…
We theoretically investigate high harmonic generation (HHG) from silicon thin films with thicknesses from a few atomic layers to a few hundreds of nanometers, to determine the most efficient thickness for producing intense HHG in the reflected and transmitted pulses. For this purpose, we employ a few theoretical and computational methods. The most sophisticated method is the ab initio time-dependent density functional theory coupled with the Maxwell equations in a common spatial resolution. This enables us to explore such effects as the surface electronic structure and light propagation, as we…
Modeling point defects at an atomic scale requires careful treatment of the long-range atomic relaxations. This elastic field can strongly affect point defect properties calculated in atomistic simulations because of the finite size of the system under study. This is an important restriction for ab initio methods which are limited to a few hundred atoms. We propose an original approach coupling ab initio calculations and linear elasticity theory to obtain the properties of an isolated point defect for reduced supercell sizes. The reliability and benefit of our approach are demonstrated for thr…
We propose a di-interstitial model for the P6 center commonly observed in ion implanted silicon. The di-interstitial structure and transition paths between different defect orientations can explain the thermally activated transition of the P6 center from low-temperature C1h to room-temperature D2d symmetry. The activation energy for the defect reorientation determined by ab initio calculations is 0.5 eV in agreement with the experiment. Our di-interstitial model establishes a link between point defects and extended defects, di-interstitials providing the nuclei for the growth.
We report first principles ab initio density functional calculations of hydrogen dynam- ics in hydrogenated amorphous silicon. Thermal motion of the host Si atoms drives H diffusion, as we demonstrate by direct simulation and explain with simple models. Si-Si bond centers and Si ring centers are local energy minima as expected. We also describe a new mechanism for break- ing Si-H bonds to release free atomic H into the network: a fluctuation bond center detachment (FBCD) assisted diffusion. H dynamics in a-Si:H is dominated by structural fluctuations intrinsic to the amorphous phase not presen…
Accurate prediction of structural and mechanical properties on amorphous materials enabled through machine-learning potentials: a case study of silicon nitride
The ability to use photonic quasiparticles to control electromagnetic energy far below the diffraction limit is a defining paradigm in nanophotonics. An important recent development in this field is the measurement and manipulation of extremely confined phonon-polariton modes in polar dielectrics such as silicon carbide and hexagonal boron nitride, which pave the way for nanophotonics and extreme light-matter interactions in the mid-IR to THz frequency range. To further advance this promising field, it is of great interest to predict the optical response of recently discovered and yet-to-be-sy…
We investigated the stable silicon (113) surface with a 3x2ADI reconstruction by ab-initio methods. The ground state properties have been obtained using the density-functional theory. We present the dispersion of the electronic band structure, where the surface bands have been distinguished from the projected bulk bands by calculating their localization in the slab. The optical spectra, here the reflectance anisotropy (RAS), have been obtained within the independent particle random phase approximation. We identified surface features in the spectra tracing them back to the responsible electroni…
We present an ab-initio study of electron mobility and electron-phonon coupling in chemically modified graphene, considering fluorinated and hydrogenated graphene at different percentage coverage. Hexagonal Boron Carbon Nitrogen (h-BCN) is also investigated due the increased interest shown by the research community towards this material. In particular, the Deformation Potentials are computed by means of Density Functional Theory (DFT), while the carrier mobility is obtained according to the Takagi model (S. Takagi, A. Toriumi, and H. Tango, IEEE Trans. Electr. Dev. 41, 2363 (1994)). We will sh…
