The influence of substrate morphology on the Rashba band splitting at the Dirac point of graphene, has been theoretically investigated. More specifically, the possibility for this splitting to be caused by spin–orbit coupling (with the heavy metal substrate) was of a special interest to study. The model system consisted of a 4H-SiC (0 0 0 1)/graphene interface, with an intercalated metal layer (Ag and Au, respectively). These intercalating metal layers were built with two different types of morphologies; either flat or buckled (with different buckling positions). The results show that depending on the position of the buckled metal atom, the size of the bandgap and band splitting (at the Dirac point of graphene) will either increase (or decrease). Moreover, the enlargement of the buckling size was also shown to affect the electronic properties of graphene (i.e., by increasing the bandgap). The sizes of the bandgaps and band splitting for the different intercalating metals (Ag and Au), were also found to be different. Spin-projected band structures was also implemented in the present study, with the purpose to show the spin-texture of graphene. It was thereby shown that the spins pined to the x and y spin components for most of the cases.
The process of Au intercalation into a SiC/buffer interface has been theoretically investigated here by using density functional theory (DFT) and the nudged elastic band (NEB) method. Energy barriers were at first calculated (using NEB) for the transfer of an Au atom through a free-standing graphene sheet. The graphene sheet was either of a nondefect character or with a defect in the form of an enlarged hexagonal carbon ring. Defects in the form of single and double vacancies were also considered. Besides giving a qualitative prediction of the relative energy barriers for the corresponding SiC/buffer interfaces, some of the graphene calculations also proved evidence of energy minima close to the graphene sheet. The most stable Au positions within the SiC/buffer interface were, therefore, calculated by performing geometry optimization with Au in the vicinity of the buffer layer. Based on these NEB and DFT calculations, two factors were observed to have a great influence on the Au intercalation process: (i) energy barrier and (ii) preferential bonding of Au to the radical C atoms at the edges of the vacancies. The energy barriers were considerably smaller in the presence of vacancies. However, the Au atoms preferred to bind to the edge atoms of these vacancies when approaching the buffer layer. It can thereby be concluded that the Au intercalation will only occur for a nondefect buffer layer when using high temperature and/or by using high-energy impacts by Au atoms. For this type of Au intercalation, the buffer layer will become completely detached from the SiC surface, forming a single layer of graphene with an intact Dirac point.
This is a theoretical investigation where Density Functional Theory (DFT) has been used in studying the phenomenon of Au intercalation within the 4H-SiC/graphene interface. The electronic structure of some carefully chosen morphologies of the Au layer has then been of special interest to study. One of these specific Au morphologies is of a more hypothetical nature, whilst the others are, from an experimental point of view, realistic ones. The latter ones were also found to be energetically stable. Band structure calculations showed that intercalated Au layers with morphologies different from a planar Au layer will induce a band gap at the Dirac point of graphene (with up to 174 meV for the morphologies studied in the present work). It should here be mentioned that this bandgap size is four times larger than the energy of thermal motion at room temperature (26 meV). These findings reveal that a wide bandgap at the Dirac point of graphene comes from an inhomogeneous staggered potential on the Au layer, which non-uniformly breaks the sublattice symmetry. The presence of spin-orbit (SO) interactions have also been included in the present study, with the purpose to find out if SO will create a bandgap and/or band splitting of graphene.
Solvated electrons are among the most reductive species in an aqueous environment. Diamond materials have been proposed as a promising source of solvated electrons, but the underlying emission process in water remains elusive so far. Here, we show spectroscopic evidence for the emission of solvated electrons from detonation nanodiamonds upon excitation with both deep ultraviolet (225 nm) and visible (400 nm) light using ultrafast transient absorption. The crucial role of surface termination in the emission process is evidenced by comparing hydrogenated, hydroxylated and carboxylated nanodiamonds. In particular, a transient response that we attribute to solvated electrons is observed on hydrogenated nanodiamonds upon visible light excitation, while it shows a sub-ps recombination due to trap states when excited with deep ultraviolet light. The essential role of surface reconstructions on the nanodiamonds in these processes is proposed based on density functional theory calculations. These results open new perspectives for solar-driven emission of solvated electrons in an aqueous phase using nanodiamonds.
The effect of CH3 and Na on diamond nucleation on hexagonal boron nitride (h-BN) was investigated theoretically by using the DFT method. The methyl and sodium species were used as substituents on zigzag edge atoms of the basal plane. Outgrowths correspon
The process of adsorption of methanol on a Si(100)-2 × 1 surface has been investigated theoretically, using density functional theory and a periodic boundary condition. The methanol adsorption on Si(100)-2 × 1 is known to be dissociative, resulting in hydrogen(methanol)–oxygen(surface) and oxygen(methanol)–silicon(surface) bond formation. Adsorption energies have been calculated here for five different surface sites for the methoxy fragment (top, bridge, cave, valley-bridge and pedestal). The top site was found to be energetically most favourable. Surface sites bridging Si atoms from the first and second atomic layers were found to be energetically equivalent to the top site. The effects of the position of the hydrogen fragment on the methoxy adsorption energy for the various adsorption sites were also investigated. These various hydrogen positions only influenced the adsorption energies marginally
Diamond is a promising metal-free photocatalyst for nitrogen and carbon dioxide reduction in aqueous environment owing to the possibility of emitting highly reducing solvated electrons. However, the wide band gap of diamond necessitates the use of deep UV to trigger a photochemical reaction. Boron doping introduces acceptor levels within the band gap of diamonds, which may facilitate visible-light absorption through defect-based transitions. In this work, unoccupied electronic states from different boron-doped diamond materials, including single crystal, polycrystalline film, diamond foam, and nanodiamonds were probed by soft X-ray absorption spectroscopy at the carbon K edge. Supported by density functional theory calculations, we demonstrate that boron close to the surfaces of diamond crystallites induce acceptor levels in the band gap, which are dependent on the diamond morphology. Combining boron-doping with morphology engineering, this work thus demonstrates that electron acceptor states within the diamond band gap can be controlled.
Hydrogen terminated diamond is a very promising material for high energy photocatalytic reactions1 owing to its large band gap(5.5 eV) and a unique capability of generating solvated electrons due to its negative electron affinity.2 However, a major limitation to the photoexcitation process to create solvated electrons is the need for deep UV illumination. Introducing unoccupied electronic states within the band gap of diamonds by doping with boron could provide a potential pathway for photoexcitation using visible light.Previous reports on HRTEM and EELS study of B doped polycrystalline and nanocrystalline diamonds provide insights into the local B environment.4,5,6,7 However, since these are primarily electron in-electron out techniques, they do not provide sufficient information about the existence of acceptor levels in the band gap of diamonds that are associated with boron doping. X-ray spectroscopy techniques have been shown to be sensitive to the acceptor levels arising due to boron doping.3 However, their physical origin still remains unclear.Here we use soft X-ray absorption spectroscopy (XAS) to probe the unoccupied electronic states at the carbon K edge in different boron-doped diamond materials, ranging from single crystal and polycrystalline film to diamond foam and nanodiamonds with different sizes. XAS of carbon K edges for the different B doped diamonds were characterized using partial fluorescence yield at the BESSY II synchrotron facility. Combining these results with density functional theory calculations, here we elucidate the contribution of the environment of boron to these mid gap acceptor states that vary with the morphology of diamonds. These results could have important implications on the selection of a suitable diamond based visible-light photocatalysts.
Core-shell nanowire heterostructure is a new architecture for photodetector application with enlarged active surface area enhancing light absorption and photodetector performance. As an emanating coating material, SnS2 has a growing interest in next-generation optoelectronic materials. Here, we reported the enhanced optoelectronic performance of the hydrothermally grown SnS2 and Si nanowire (SiNWs) core-shell heterostructure. Hydrothermally grown SnS2 on Si nanowire creates a uniform coating over the entire surface of nanowires which enhances the heterostructure's effective junction area and improves optoelectronic performance over the broad spectral range (300 - 1100 nm). Specially, under 340 nm illumination, the core-shell photodetector exhibits large responsivity (-383 A/W) and extremely high external quantum efficiency (-2 x 105 %) at very low optical power (-20 nW/mm2). This SnS2/SiNWs core-shell heterostructure with significantly improved optoelectronic performance will be favourable for the development of photodetector with an ability to work with extremely high efficiency.
Nanocrystalline diamond with a porous-like morphology was used as the functional part of a semiconductor gas sensor. The device function is based on the two-dimensional p-type surface conductivity of intrinsic diamond with a H-terminated surface. Metallic electrodes are buried beneath the diamond film. Therefore, these electrodes are protected from harmful substances, and the electronic connection is facilitated by grain boundaries. The gas sensing properties of the sensor structure were examined using oxidising gases (i.e., phosgene, humid air) at various operating temperatures. A pronounced and selective increase by two orders of magnitude was found in the surface conductivity after sensor exposure to phosgene gas (20 ppm) at 140 degrees C. Density functional theory calculations indicated no direct charge transfer between the phosgene molecule and diamond. We present a model in which phosgene indirectly yet efficiently increases the H3O+ concentration, which consequently leads to multiplied electron transfer and a pronounced sensor response.
A platform for diagnostic applications showing signal-to-noise ratios that by far surpass those of traditional bioanalytical test formats has been developed. It combines the properties of modified nanocrystalline diamond (NCD) surfaces and those of polyethylene oxide and polypropylene oxide based block copolymers for surface passivation and binder conjugation with a new class of synthetic binders for proteins. The NCD surfaces were fluorine-, hydrogen-, or oxygen-terminated prior to further biofunctionalization and the surface composition was characterized by X-ray photoelectron spectroscopy. In a proof of principle demonstration targeting the C-reactive protein, an ELISA carried out using an F-terminated diamond surface showed a signal-to-noise ratio of 3,900 which compares well to the signal-to-noise of 89 obtained in an antibody-based ELISA on a polystyrene microtiter plate, a standard test format used in most life science laboratories today. The increase in signal-to-noise ratio is to a large extent the result of extremely efficient passivation of the diamond surface. The results suggest that significant improvements can be obtained in standardized test formats using new materials in combination with new types of chemical coatings and receptor molecules.
The combined effect of water adlayer composition and surface termination on diamond surface electrochemistyr, has been studied theoretically using Density Functional Theory (DFT) calculations. The terminating species included H, O(ontop), O(bridge), OH and NH2. The chemical composition of the water adlayer was altered by using a very thin layer of water only, or by introducing oxygen, ozone or hydroxonium ions (H3O+) into the adlayer. A partial electron transfer toward the atmospheric adlayer was observed for the situation with either an H- or NH2-terminated diamond surface. Corresponding calculations for oxygen-termination (O(ontop) or O(bridge)), did not render any significant amount of electron transfer. The situation was completely different for the situation with OH-termination. The degree of electron transfer was approximately of the same order as for H- and NH2-terminations. The presence of oxidative species like oxygen ozone and H(3)0(+) (or combinations thereof) were observed to significantly increase the degree of electron transfer for the situation with either NH2-, OH-, or H-terminated diamond (100)-2 x 1 surfaces. Adsorption energy calculations revealed, with some exceptions, a quite good correlation between diamond//adlayer adhesion strength and degree of interfacial electron transfer. The electron transfer process were further verified and analyzed by performing partial density of state (pDOS) calculations for some selected diamond//adlayer systems.
Interactions between ethanol-water mixtures and a hydrophobic hydrogen terminated nanocrystalline diamond surface, are investigated by sessile drop contact angle measurements. The surface free energy of the hydrophobic surface, obtained with pure liquids, differs strongly from values obtained by ethanol-water mixtures. Here, a model which explains this difference is presented. The model suggests that, due to a higher affinity of ethanol for the hydrophobic surface, when compared to water, a phase separation occurs when a mixture of both liquids is in contact with the H-terminated diamond surface. These results are supported by a computational study giving insight in the affinity and related interaction at the liquid-solid interface.
The nucleation of diamond on the zigzag and armchair edge atoms of the basal plane of hexagonal boron nitride (h-BN) has been investigated theoretically by using ab initio molecular orbital theory. The calculations have included the effects of electron co
The cubic phase of boron nitride (c-BN) is an extremely promising multifunctional material. However, to exploit all possible applications, a successful route for large area chemical vapor deposition (CVD) of c-BN films is required. Adsorption of gaseous growth species onto the c-BN surface is one of the key elementary reactions in CVD growth of c-BN. In the present work, the ability of BH(x), BF(x), and NH(x) species (x = 0, 1, 2, 3) to act as growth species for CVD of c-BN, in an H-, F-, or H/F-saturated gas-phase, has been investigated using density functional theory (DFT) calculations. It was found that the most optimal growth species for CVD growth of c-BN are B, BH, BH(2), BF, BF(2), N, NH, and NH(2) in an H/F-saturated gas-phase, i.e., decomposition of the incoming BH(3), BF(3), and NH(3) growth species is very crucial for CVD growth of c-BN. It was also found that it would be most preferable to use a CVD method where the incoming BH(3), BF(3), and NH(3) growth species are separately introduced into the reactor, e.g., by using an atomic layer deposition (ALD) type of method.
The cubic phase of boron nitride (c-BN) is an extremely promising multifunctional material. However, to exploit all possible applications, large area chemical vapor deposition (CVD) of c-BN films is required. To be successful in the CVD growth of high-quality c-BN films, one must be able to stabilize the sp(3) hybridization of the surface atoms; and in the present study, the surface stabilizing effect of F and Cl on the B- and N-terminated c-BN(100)-(1 x 1) surfaces has been investigated using density functional theory (DFT) calculations. It was found that Cl, most probably, will induce large sterical hindrance on both the B- and N-terminated c-BN(100) surface. F, on the other hand, was found to be a promising surface stabilizing agent for the B- and N-terminated c-BN(100) surface. However, the F atoms must be abstracted with H atoms. It can therefore be concluded that the optimal gas-phase composition for growth of c-BN consists of a mixture of H and F.
The cubic phase of boron nitride (c-BN) is an extremely promising multifunctional material. However, to exploit all possible applications, large area chemical vapor deposition (CVD) of c-BN films is required. For a successful CVD growth of high-quality c-BN films one must obtain a deeper understanding about the structural and electronic properties of the dominant c-BN growth surfaces under CVD conditions, that is, the (100), (110), and (111) surfaces, and their modification in the presence of surface stabilizing atomic hydrogen (H). In the present study, the surface stabilizing effect of H on the B- and N-terminated (1 × 1), (2 × 1), (2 × 4), (2 × 4(3)), and c(2 × 2) surfaces of c-BN(100) has therefore been investigated using density functional theory (DFT) calculations. It was found that a 100% surface coverage of on-top H on the B-terminated c-BN(100) surfaces is not able to uphold an ideal bulk-like (1 × 1) structure. However, the H atoms were able to uphold a bulk-like bond angle and bond length for the surface B atoms on the 100% H-covered B-terminated c-BN(100)-(2 × 1) surface. For the N-terminated c-BN(100) surfaces opposite observations were made. The H atoms were found to chemisorb strongly to both the B-terminated c-BN(100)-(2 × 1) surface and the N-terminated c-BN(100)-(1 × 1) surface. The process of H abstraction, with gaseous atomic H, was found to be significantly more favorable for the B-terminated c-BN(100)-(2 × 1) surface than for the N-terminated c-BN(100)-(1 × 1) surface. It was also found that N radical sites are more stable toward radical surface site collapse than B radical sites.
The cubic phase of boron nitride (c-BN) is an extremely promising multifunctional material. To exploit all possible applications, large area chemical vapor deposition (CVD) of c-BN films is required. To maintain the cubic (sp(3)) structure of the surface atoms, the growing surface is covered with surface stabilizing species. However, the surface stabilizing species must also be able to undergo abstraction reactions with gaseous species and, hence, leave room for an incoming B-or N-containing growth species for a continuous c-BN growth to occur. The abstraction process is therefore a central elementary reaction step in CVD growth of c-BN. Hydrogen, H, and fluorine, F, have earlier been found to be promising as surface stabilizing species for both the B-and N-terminated c-BN(100) surfaces - the sp(2) structure is maintained and both H and F bind strongly to the surface. In addition, of highest importance is the chemical capability to remove these terminating species from the surface, leaving a highly reactive surface site (i.e., gas-phase abstraction). The present study has therefore focused on, by using density functional theory (DFT), the kinetics of the H-or F-abstraction processes from the B-or N-terminated c-BN(100) surface. The energetic and structural evolution for gaseous F approaching a surface-binding F species, show that F radicals are not able to abstract chemisorbed F atoms, i.e., a gas-phase containing only F is unfavorable for growth of c-BN(100). On the other hand, H radicals are able to abstract chemisorbed H atoms. However, a minor barrier of energy was observed for the N-terminated surface (+ 13 kJ/mol). The abstraction of F from the B-terminated surface, with gaseous H radicals, was found to be highly probable from both thermodynamic and kinetic considerations, being also the situation for the F-covered N-terminated surface (with a minor energy barrier of + 8 kJ/mol). In addition, the energy evolution for the approaching F to a surface H, clearly shows that any abstraction reaction will never take place. Hence, the results within the present study clearly show that at realistic deposition temperatures, it is only gaseous H that will have the capacity to remove H or F from the c-BN(100) surface.
The cubic phase of boron nitride (c-BN) is an extremely promising multifunctional material. However, to exploit all possible applications, a successful route for large area chemical vapor deposition (CVD) of c-BN films is required. Adsorption of gaseous growth species onto the c-BN surface is one of the key elementary reactions in CVD growth of c-BN. In the present study, adsorption of BHx, BFx, and NHx species (x = 0, 1, 2, 3) onto the B- and N-terminated c-BN(100) surfaces has been investigated using density functional theory (DFT) calculations. It was found that adsorption of BHx is an activation less process.
Boosting the sensitivity of solid-state gas sensors by incorporating nanostructured materials as the active sensing element can be complicated by interfacial effects. Interfaces at nanoparticles, grains, or contacts may result in nonlinear current-voltage response, high electrical resistance, and ultimately, electric noise that limits the sensor read-out. This work reports the possibility to prepare nominally one atom thin, electrically continuous platinum layers by physical vapor deposition on the carbon zero layer (also known as the buffer layer) grown epitaxially on silicon carbide. With a 3-4 angstrom thin Pt layer, the electrical conductivity of the metal is strongly modulated when interacting with chemical analytes, due to charges being transferred to/from Pt. The strong interaction with chemical species, together with the scalability of the material, enables the fabrication of chemiresistor devices for electrical read-out of chemical species with sub part-per-billion (ppb) detection limits. The 2D system formed by atomically thin Pt on the carbon zero layer on SiC opens up a route for resilient and high sensitivity chemical detection, and can be the path for designing new heterogenous catalysts with superior activity and selectivity.
Global environmental issues, in addition to limited fossil fuel resources, are being addressed by quests in search of efficient visible-light-driven water splitting catalysts for hydrogen production. The photocatalytic water splitting activities of CdX/C2N (X = S, Se) heterostructures have been investigated here using hybrid density functional theory calculations. The calculated band gaps of CdS/C2N and CdSe/C2N heterostructures are 1.48 and 2.12 eV, respectively. These are ideal band gap values that make possible harvesting of more visible light from the solar spectrum, which will result in high solar to energy conversion efficiencies. Charge density difference analysis shows that the charge redistributions mainly occur in the interface regions and that the charges transfer from the C-2N to CdX layers. It is interesting to note that the CdX/C2N heterostructures possess a type-II band alignment, where the relative band alignment of the C2N and CdX monolayers promotes a spatial separation of the electrons (that resides in C2N) and holes (that resides in CdX). Importantly, the band edges of the heterostructures straddle the water redox potential under different pH conditions. This study demonstrates that the CdS/C2N and CdSe/C-2N heterostructures are suitable materials to split water (from various sources) in different ranges of pH values.
The search for an active, stable, and abundant semiconductor-based bifunctional catalysts for solar hydrogen production will make a substantial impact on the sustainable development of the society that does not rely on fossil reserves. The photocatalytic water splitting mechanism on a BeN2 monolayer has here been investigated by using state-of-the-art density functional theory calculations. For all possible reaction intermediates, the calculated changes in Gibbs free energy showed that the oxygen evolution reaction will occur at, and above, the potential of 2.06 V (against the NHE) as all elementary steps are exergonic. In the case of the hydrogen evolution reaction, a potential of 0.52 V, or above, was required to make the reaction take place spontaneously. Interestingly, the calculated valence band edge and conduction band edge positions for a BeN2 monolayer are located at the potential of 2.60 V and 0.56 V, respectively. This indicates that the photo-generated holes in the valence band can oxidize water to oxygen, and the photo-generated electrons in the conduction band can spontaneously reduce water to hydrogen. Hence, the results from the present theoretical investigation show that the BeN2 monolayer is an efficient bifunctional water-splitting catalyst, without the need for any co-catalyst.
Medical implants are increasingly often inserted into bone of frail patients, who are advanced in years. Due to age, severe trauma or pathology-related bone changes, osseous healing at the implant site is frequently limited. We were able to demonstrate that coating of endosseous implants with nanocrystalline diamond (NCD) allows stable functionalization by means of physisorption with BMP-2. Strong physisorption was shown to be directly related to the unique properties of NCD, and BMP-2 in its active form interacted strongly when NCD was oxygen-terminated. The binding of the protein was monitored under physiological conditions by single molecule force spectroscopy, and the respective adsorption energies were further substantiated by force-field-calculations. Implant surfaces refined in such a manner yielded enhanced osseointegration in vivo, when inserted into sheep calvaria. Our results further suggest that this technical advancement can be readily applied in clinical therapies with regard to bone healing, since primary human mesenchymal stromal cells strongly activated the expression of osteogenic markers when being cultivated on NCD physisorbed with physiological amounts of BMP-2.
The process of adsorption of H, CH3, CH2, C2H, and C2H2, on various steps on the diamond (111) surface, has been investigated theoretically. The first-principles density-functional theory was then used in order to calculate the binding energies and equili
Cubic boron nitride (c-BN) exhibits an extraordinary combination of physical and chemical properties (hardness, High thermal conductivity, transparency) which is comparable or even superior to diamond in what concerns its ability to be doped as both n- and p-type semiconductor, and its higher chemical stability and lower reactivity at high temperatures. All these properties strongly suggest that c-BN is an extremely promising multifunctional material, which could be tailored for a very large range of advanced applications, such as micro- and opto-electronics, electron emission devices, radiation detection, biosensing, high temperature and/or radiation resistant devices.
Similarities and dissimilarities in the growth of diamond vs. c-BN, in the present series of investigations, have been studied using quantum mechanical calculations. Hydrogen species have been observed to be very effective in stabilising both types of compounds. Very large similarities have also been observed when considering the adsorption of various growth species to these materials. However, it was found necessary to avoid mixtures of B- and N-containing species in the gas phase during c-BN growth, since they should most probably result in a mixture of these species also on the (111) and (110) surfaces. In addition, a careful gas phase design was found necessary in order to avoid a preferential initial growth of h-BN. These theoretical results can be used as guide lines in striving towards a thin film deposition of cubic boron nitride using gentle CVD methods like atomic layer deposition.
The stability of various cluster-sizes of H- and F-terminated c-BN, compared to corresponding clusters of h-BN, has been investigated theoretically using the ab initio molecular orbital method at the MP2 order of theory. For comparison, a corresponding in
The diamond material possesses very attractive properties, such as superior electronic properties (when doped), in addition to a controllable surface termination. During the process of diamond synthesis, the resulting chemical properties will mainly depend on the adsorbed species. These species will have the ability to influence both the chemical and electronic properties of diamond. All resulting (and interesting) properties of a terminated diamond surface, make it clear that surface termination is very important for especially those applications in which diamond can function as an electrode material. Theoretical modeling has during the last decades been proven to become highly valuable in the explanation and prediction of experimental results. Simulation of the dependence of various factors influencing the surface reactivity, will aid important information about surface processes including surface stability, modification and functionalization. Other examples include thin film growth mechanisms and surface electrochemistry.
The combined effects of geometrical structure and chemical composition on the diamond surface electronic structures have been investigated in the present study by using high-level theoretical calculations. The effects of diamond surface planes [(111) vs. (100)], surface terminations (H, F, OH, O-ontop, O-bridge, vs. NH2), and substitutional doping (B, N vs. P), were of the largest interest to study. As a measure of different electronic structures, the bandgaps, work functions, and electron affinities have been used. In addition to the effects by the doping elements, the different diamond surface planes [(111) vs. (100)] were also observed to cause large differences in the electronic structures. With few exceptions, this was also the case for the surface termination species. For example, O-ontop-termination was found to induce surface electron conductivities for all systems in the present study (except for a non-doped (100) surface). The other types of surface terminating species induced a reduction in bandgap values. The calculated bandgap ranges for the (111) surface were 3.4-5.7 (non-doping), and 0.9-5.3 (B-doping). For the (100) surface, the ranges were 0.9-5.3 (undoping) and 3.2-4.3 (B-doping). For almost all systems in the present investigation, it was found that photo-induced electron emission cannot take place. The only exception is the non-doped NH2-terminated diamond (111) surface, for which a direct photo-induced electron emission is possible.
The purpose with the present studies has been to support and explain the experimental observations made regarding the effect by N-, P-, S- and B-doping on the diamond (111), (100)−2 × 1 and (110) growth rate, respectively. All surfaces were assumed to be H-terminated. Density functional theory calculations were used, based on a plane wave approach under periodic boundary conditions. It was shown that the surface H abstraction reaction is most probably the rate-limiting step during diamond growth. Moreover, the results showed that it is N, substitutionally positioned within the upper diamond surface, that will cause the growth rate improvement, and not nitrogen chemisorbed onto the growing surface in the form of either NH (or NH2). These results coupled very strongly to experimental counterparts. For the situation with P doping, there were no visible energy barrier obtained for the approaching H radical to any of the diamond surface planes. Hence, the growth rate must be appreciably increased as a function of doping with P. It was furthermore observed that S and B doping will lead to anomalous changes in the diamond growth rate (i.e., either increase or decrease), depending on the position of these two dopants in the lattice. These phenomena are also strongly supported by experimental observations where there are both increasing and decreasing effects of the diamond growth rate by S and B doping.