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On‐surface synthesis has become a prominent method for growing low‐dimensional carbon‐based nanomaterials on metal surfaces. However, the necessity of decoupling organic nanostructures from metal substrates to exploit their properties requires either transfer methods or new strategies to perform reactions directly on inert surfaces. The use of on‐surface light‐induced reactions directly on semiconductor/insulating surfaces represents an alternative approach to address these challenges. Here, exploring the photochemical activity of different organic molecules on a SnSe semiconductor surface under ultra‐high vacuum, we present a novel on‐surface light‐induced reaction. The selective photodissociation of the anhydride group is observed, releasing CO and CO2. Moreover, we rationalize the relationship between the photochemical activity and the π‐conjugation of the molecular core. The different experimental behaviour of two model anhydrides was elucidated by theoretical calculations, showing how the molecular structure influences the distribution of the excited states. Our findings open new pathways for on‐surface synthesis directly on technologically relevant substrates. [ABSTRACT FROM AUTHOR]

Franz-Keldysh effect is expressed in the smearing of the absorption edge in semiconductors under high electric fields. While Franz [Z. Naturforsch. A 13, 484 (1958)] and Keldysh [Sov. Phys. JETP 7, 788 (1958)] considered a limited case of externally applied uniform electric field, the same effect may also be caused by built-in electric fields at semiconductor surfaces and interfaces. While in the first case, the bands are bent linearly, in the latter case, they are bent parabolically. This non-linear band bending poses an additional complexity that has not been considered previously. Here, we extend the linear model to treat the case of a non-linear band bending. We then show how this model may be used to quantitatively analyze photocurrent and photovoltage spectra to determine the built-in fields, the density of surface state charge, and the doping concentration of the material. We use the model on a GaN/AlGaN heterostructure and GaAs bulk. The results demonstrate that the same mechanism underlies the band-edge response both in photocurrent and photovoltage spectra and demonstrate the quantitative use of the model in contactless extraction of important semiconductor material parameters. [ABSTRACT FROM AUTHOR]

Indium metal is deposited on n-type Si (n-Si) samples with/without (NH4)2Sx treatment in order to experimentally study the mechanism for the transition from Schottky to ohmic contact. Indium metal that is deposited on a n-Si sample that is subject to (NH4)2Sx treatment shows ohmic behavior but indium metal that is deposited on a n-Si sample that is not subject to (NH4)2Sx treatment exhibits Schottky behavior. Using the transmission line method, the specific contact resistance of the In/(NH4)2Sx treated n-Si structure is calculated to be 283.3 mΩ cm2. Experimental identification confirms that the transformation to conduction behavior occurs because of the combined effect of broken Si–O bonds (i.e., the removal of the native oxide) and the formation of Si–Sx2− bonds at the Si surface, which results in a transition from upward to downward surface band bending for n-Si. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of Bi nanolines on the InAs (001) surface are investigated via density functional theory. Thereby, three models, Miki (M) (Miki et al. Phys. Rev. B 59 (1999)14,868), Naitoh (N) (M. Naitoh et al. Surf. Sci 377 (1997) 899), and Two Ad-Dimer (TAD) (J.H.G. Owen et al. Phys. Rev. Lett 22 (2002) 226,104) are implemented to simulate the formation of Bi nanolines and study their physical properties. The structural analysis reveals some differences in atomic arrangements, bond lengths, and surface organization among the different models. The comparison of our results with Bi nanolines on Si(001) highlights the substrate role in Bi nanostructure formation. The surface stability examination demonstrates that the M model is energetically the most favorable one. On the other hand, the electronic properties analysis reveals that M, TAD models exhibit semiconductor behavior, whereas, the N model show a metallic character. Moreover, the calculations of the partial electronic charge density of surface states provide valuable information about the electronic structure of Bi nanolines on InAs(001). Finally, this study constitutes a theoretical support that can open the way to experimentally produce Bi nanostructures on the InAs(001) surface as a beneficial solution for several applications. [ABSTRACT FROM AUTHOR]

In semiconductor manufacturing, the surface quality of silicon wafers has a significant impact on the subsequent processes that produce devices using the wafers as a component. The surface quality of a wafer is characterised by a two-dimensional (2-D) data structure: the geometric requirement for the wafer surface is smooth and flat and the thickness should fall within certain specification limits. Therefore, both low deviation and high uniformity are desirable for control over the wafer quality. In this work, we develop a run-to-run control algorithm for improving wafer quality. Considering the unique 2-D data structure, we first construct a model that encompasses the spatial correlation of the observations on the wafer surface to link the wafer quality with the process variables, and subsequently develop a recursive algorithm to generate optimal set points for the controllable factors. More specifically, a Gaussian-Kriging model is used to characterise the spatial dependence of the thickness measures of the wafer and a recursive least square method is employed to update the estimates of the model parameters. The performance of the new controller is studied via simulation and compared with existing controllers, which demonstrates that the newly proposed controller can effectively reduce the surface variations of the silicon wafers. [ABSTRACT FROM PUBLISHER]

Directly bonded ohmic InP/Si heterostructures are realized, overcoming the large (8%) lattice mismatch. By employing proper semiconductor surface pretreatments including cleaning and oxide removal, we obtain ohmic interfacial electrical characteristics at a bonding temperature as low as 200 °C. Among the doping-polarity combinations, ohmic interfacial electrical characteristics are observed for n-InP/n-Si and n-InP/p-Si bonded heterointerfaces, but not for p-InP/p-Si and p-InP/n-Si pairs. We numerically explain this polarity dependence in terms of energy band connections across the InP/Si heterointerfaces. The highly conductive III–V/Si direct bonding technique developed in this study is applicable for various heterostructured optoelectronic devices, such as multijunction solar cells and photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Abstract This work highlights the direct impact of selecting acceptor moiety for organic dyes on the electron dynamics at faster time scales, in which overlooked photo-physical properties are present on semiconductor surfaces with specific acceptor moieties. Four top-performing dyes of indoline family (D131, D102, D149, and D205) sharing the same donor moiety, but through different acceptor groups, were selected and compared with respect of electron injection process, using ultrafast transient-infrared probe. The presence of rhodanine moiety at the acceptor unit in D102, D149 and D205, shows an additional slow electron injection process, of picosecond time-scale, on the low band-gap semiconductor, TiO 2. This slow process is expected to be present due to a twisted intramolecular charge transfer/isomerized state of the excited dye prior to electron injection. This isomerized state reduces as well the detrimental electron recombination process rates, and results of high performance in solar cells based on these rhodanine dyes. Replacing the rhodanine moiety by a cyano-acrylic group in D131 dye shows faster electron injection and recombination processes, due to the lower dipole moment present in the excited state, hindering the formation of an isomerized state. These findings will aid to enhance the organic dyes design used in dye sensitized solar cells, in which designed photo-physical processes on semiconductor surfaces can increase the efficiencies of the solar cells. [ABSTRACT FROM AUTHOR]

The influence of annealing process on the structure of ultrathin gold films on the surfaces of glass substrates and substrates of CdS is investigated. The formation of nanoparticle arrays as a result of annealing the films on the glass surface was revealed, and analysis of average radii dependence for the formed particles on initial thickness of the film was carried out and shape of the particles analyzed. For annealed Au films on the surface of CdS, the destruction of the film for its initial thickness of 0.5 and 1 nm was noted, and small changes in the surface morphology for thicker films were observed. On the basis of elemental analysis, assumptions about the causes of such temperature behavior of films are made. [ABSTRACT FROM AUTHOR]

The effect of the chemical modification of Ge(1 0 0) semiconductor surfaces on their electronic structure was studied using density functional theory calculations. We have considered various possible adsorption configurations of phenylthiol molecule on Ge(1 0 0) with different spatial orientations relative to the dimer row. The most favorable configuration is that the H-dissociated phenylthiol molecule is located at the inter-dimer site with the covalent bonding between sulfur atom of H-dissociated phenylthiol molecule and down-Ge atom. Simulated STM images of the adsorption configurations reflect the change of the electronic charge density and agree well with the adsorption features observed in the experiment. The projected density of states of the germanium and the phenylthiol molecule could explain the change in surface electronic structures upon chemical adsorption. Moreover, organic functionalization affects the electronic structure like band gap. Band structure analysis shows that the different adsorption configurations of phenylthiol molecules could modify the band gap of clean Ge(1 0 0) surfaces. [ABSTRACT FROM AUTHOR]

Semiconductor surface plasmon polariton (SPP) waveguide has unique optical properties and compatibility with existing integrated circuit manufacturing technology; thus, SPP devices of semiconductor materials have wide application potential. In this study, a new integrated graphene SPP waveguide is designed using the bottom and top roles of graphene. Moreover, a T waveguide structure is designed by InGaAs of semiconductor gain, with rectangular GaAs material on both sides. The structure adopts light to stimulate the SPP, where its local area is enhanced by the interaction between two interface layers and a semiconductor gain and where its frequency can be adjusted by the thickness of the graphene. Characteristic analysis reveals the coupling between the T semiconductor gain and the SPP mode. The propagation distance of the waveguide can reach 75 cm, the effective mode field is approximately 0.0951λ2, the minimum of gain threshold is approximately 2992.7 cm−1, and the quality factor (FOM) can reach 180. The waveguide structure which provides stronger localization can be compatible with several optical and electronic nanoscale components. That means, it can provide light for surface plasmon circuit and also can provide a great development in the low-threshold nanolaser. [ABSTRACT FROM AUTHOR]

Self-assembled indium deposition-induced nanostructures are obtained on the UHV cleaved (100) surface of In4Se3 layered semiconductor crystals. The small indium-deposition rates and short deposition times are chosen to study growth orientation and origin of nanostructures observed by scanning tunnelling microscopy (STM) on the (100) surface of In4Se3 after indium deposition. The shape of these nanostructures strictly depends on the overstoichiometric indium concentration level in the melt during the crystal growth varying from 3D islands for low concentration to elongated shapes, i.e., nanowires, in the case of highly-indium-doped crystals. High-resolution STM study determines the self-assembled quasi-periodical nanowires' growth along c-axis of (100)In4Se3 substrate. The spatially resolved scanning tunnelling spectroscopy (STS) study revealed metallic nature of the surface of nanostructures grown on the semiconductor substrate. The growth mechanism of indium-deposited nanostructures is considered to be powered by anisotropic striated lattice structure of In4Se3 (100) surface with indium nuclei in concentration depending on the degree of overstoichiometric crystalgrowth indium subsequently intercalated into the interlayer gap. [ABSTRACT FROM AUTHOR]

The effect of surface phenomena caused by adsorption of NO2, CO2, and H2O vapor on the charge transport in thin films of chalcogenide glassy semiconductors (ChGS) of the As2S3Ge8–Te system has been studied. The investigations have been carried out by measuring the dynamic conductivity of these films in a large (5 to 107 Hz) frequency range, in both dry air and its mixture with controlled concentrations of the above mentioned gases at different temperatures. In addition to this, the temperature dependence of DC conductivity has also been measured for an unambiguous interpretation of the results. It is shown that depending on material's composition, the AC conductivity in dry air can either be frequency independent across the full range or be frequency independent until ≈104 Hz, with increasing σ(ω) ≈ ωn (n ≈ 0.7) at higher frequencies. This behavior demonstrates that for these glassy films there is a competition of several transport mechanisms, so that depending on frequency at normal temperatures the charge is carried: by free holes or by tunneling between localized states at either valence band edge or those near the Fermi level. An estimation has been made for the density of states at the Fermi level of As2S3Ge8Te13 that appears to be N(EF) ≈ 1.3 × 1021 eV−1 cm−3. Changes of environmental conditions either in air humidification or application of even very small (ppm) concentration of NO2 dramatically influence the spectra of dynamic conductivity that, on the other hand, remain nearly unaffected upon CO2 vapor application. This is evidence that for some chalcogenide materials the surface phenomena disturb the energetic distribution of states adjacent to surface, changing the transport mechanisms. [ABSTRACT FROM AUTHOR]

Thin films of chalcogenide vitreous semiconductors are characterized by a much higher resolving power than that of conventional optical focusing systems. The key interest is focused on the formation of elements with sizes significantly less than the values determined by the light diffraction limit. This process can be realized by using the nonlinear exposure characteristics of chalcogenide glass semiconductor films and a modification of their structure for the localization of exposing light to dimensions below the diffraction‐limited area. Appropriate conditions can be created by using the excitation of the plasmon resonance in nanoparticles of noble metals embedded into the chalcogenide glass semiconductor matrix. Near‐field methods of exposure by optical radiation open wide opportunities to produce nanoscale structures on the surface of chalcogenide glass semiconductors. The base limitation for the use of these systems is a low optical transmission, which leads to a slow exposure (∼100 μm per second). The transmission of near‐field probes can be sufficiently increased by fabricating these probes in the form of microstrip structures. [ABSTRACT FROM AUTHOR]

Electron gases (2DEG) confined in the quantum well (QW) of a semiconductor surface exhibit electronic properties with essentially two-dimensional (2D) character and quantized energies, directly observable by angle resolved photoemission spectroscopy (ARPES). Here, we present a simple formalism to extract the surface potential from the in-plane dispersion of the 2DEG and analytically derive the ARPES intensity in the damped free electron final state approximation. We find that the out-of-plane modulation of ARPES spectral weight explicitly encodes the shape and the bulk extent of the electronic wave function. Damping of the photoemission final state however leads to an underestimation of the wave function's bulk penetration. Our method provides a novel and universal way to deduce elusive information about the surface electronic structure from photon energy dependent ARPES measurements. [ABSTRACT FROM AUTHOR]

Halogen-containing plasmas are often used to form topological structures on semiconductor surfaces; therefore, spectral monitoring of the etching process is an important diagnostic tool in modern electronics. In this work, the emission spectra of gas discharges in mixtures of hydrogen chloride with argon, chlorine, and hydrogen in the presence of a semiconducting gallium arsenide plate were studied. Spectral lines and bands of the GaAs etching products appropriate for monitoring the etching rate were determined. It is shown that the emission intensity of the etching products is proportional to the GaAs etching rate in plasmas of HCl mixtures with Ar and Cl2, which makes it possible to monitor the etching process in real time by means of spectral methods. [ABSTRACT FROM AUTHOR]

Sodium dodecyl sulfate (SDS) effects at the electrified p- and n-GaAs(100)/H2SO4 interfaces were investigated by EIS, XPS and AFM. XPS data revealed that under the open circuit conditions, SDS adsorption on GaAs(100) results in a protective overlayer which prevents the further oxidation in air of both types of semiconductor surfaces. The dopant nature is, however, decisive for the way of bonding the surfactant molecule to the surface. At the p-doped substrate, SDS adsorbs mainly at As sites by its hydrocarbon tail and by the anion head to the Ga sites at the n-doped one. Although the surfactant behaves as a dipole under the applied potential control, the dopant type plays a key role in the SDS interaction with GaAs(100) electrodes too. EIS data evidenced that SDS interaction with n-GaAs(100) electrode brings a pronounced decrease of the capacitive contribution of the surface states and a shift of the flatband potential to less negative values, unlike the p-doped one, where no significant change in its electronic properties was observed. These results were rationalized in terms of surface states- and field-effects operating at the electrified interfaces under discussion. [ABSTRACT FROM AUTHOR]

The electrical characteristics of the Ni/Cd 1 − x Zn x Te/In structures with a metal–semiconductor rectifying contact are investigated. The diodes, fabricated on the base of In-doped n -type Cd 1 − x Zn x Te (CZT) crystals with resistivity of ∼ 10 10 Ω ⋅ cm, have low leakage current and can be used as X/ γ -ray detectors. The rectifying contact was obtained by vacuum deposition of Ni on the semiconductor surface pretreated with argon plasma. The high barrier rectifying contact allowed us to increase applied reverse bias voltage up to 2500 V at the CZT crystal thickness of 1 mm. Dark (leakage) currents of the diodes with the rectifying contact area of 4 mm 2 did not exceed 3–5 nA at bias voltage of 2000 V and room temperature. The charge transport mechanisms in the Ni/CZT/In structures have been interpreted as generation–recombination in the space charge region within the range of reverse bias of 5–100 V and as currents limited by space charge at both forward and reverse bias at V >100 V. [ABSTRACT FROM AUTHOR]

The temperature-dependent energetics of self-assembled Au nanowires on Ge(001) surfaces is studied with the help of density-functional theory (DFT) calculations: By calculating the surface phonon modes within harmonic approximation the surface vibrational free energy is obtained to complement the zero-temperature DFT total energies. We consider several previously suggested structural models for a Au coverage between 0.75 and 1.75 monolayer and investigate a temperature range between 0 and 900 K. The stability of the investigated surface models is found to depend clearly on temperature. We find that the extended Ge bridge dimer model previously predicted to be most stable for a large range of preparation conditions is less prominent in the phase diagrams for finite temperatures. On the other hand, a model derived previously from the giant missing row structure with a higher Au coverage gets stabilized by temperature. These findings explain, at least partially, the discrepancies between experimental data and previous theoretical investigations neglecting temperature effects. [ABSTRACT FROM AUTHOR]

It is demonstrated that plasma techniques can be used to detect various defects on a solid surface by a self-sustained discharge under atmospheric pressure. Special attention is paid to controlling surface defects and the end cleavages of semiconducting wafers and pinholes of layered structures. [ABSTRACT FROM AUTHOR]

Quantitative analysis of the electron accumulation layer formed near nonideal (actual) semiconductor surface causes considerable difficulties. In the present article, for the accumulation layers induced in the subsurface region at the real narrow-gap semiconductor-insulator interface, an effective algorithmic approach providing a simplified self-consistent solution of the Poisson and Schrödinger equations is proposed and discussed. The physical model takes into account the conduction band nonparabolicity, electron gas degeneration, and other dominant features of solids in question; special attention is paid to the existence of semiconductor-dielectric intermediate layer. A novel approximation for the surface electrostatic potential in the form of a modified Кratzer potential is proposed and substantiated. It allows us to obtain the electron wavefunctions and energy spectrum in the analytical form. It is shown that the modified Кratzer potential is a good approximation function applicable at least to subsurface electron accumulation layers induced at the A3B5 narrow-gap semiconductor boundary surface allowing for the existence of a semiconductor-insulator intermediate layer. For the n-InSb nonideal surface, as an example, spatial distribution of electron potential energy, discrete energy spectrum of electrons in the broad range of surface densities (up to 1013 cm-2), and some other physical characteristics are calculated using the proposed algorithm. [ABSTRACT FROM AUTHOR]

Hydrogen titanate (H 2 Ti 3 O 7 ) and TiO 2 -B polymorph are potential surfaces identified experimentally in the last years, which need to be analyzed. To study their performance as surfaces for dye sensitized solar cells (DSSC), a set of dye adsorption configurations were evaluated on them, as model dye the small and organic catechol molecule was used. We have calculated adsorption geometry, energy, electronic transfer from dye to semiconductor adsorbent and frontier orbitals by means of density functional theory (DFT). Results show that vacancy-like defected H 2 Ti 3 O 7 (100) and TiO 2 -B (100) surfaces present favorable adsorption energies. Finally, an adequate energy level alignment make both surfaces prone to be adequate for direct electron transfer upon excitation, from catechol to the conduction band of the semiconductors, with bands located in the Visible region of the electromagnetic spectrum. Additionally, the band structure alignment indicates an increase in the open circuit voltage, in reference to I 2 /I 3 − redox pair potential. All these characteristics make hydrogen titanate (H 2 Ti 3 O 7 ) and TiO 2 -B polymorph promising for DSSC applications. [ABSTRACT FROM AUTHOR]

Surface doping allows tuning the electronic structure of semiconductors at near-surface regime and is normally accomplished through the deposition of an ultrathin layer on top or below the host material. Surface doping is particularly appealing in organic field-effect transistors (OFETs) where charge transport takes place at the first monolayers close to the dielectric surface. However, due to fabrication restrictions that OFET architecture imparts, this is extremely challenging. Here, it is demonstrated that mercury cations, Hg2+, can be exploited to control doping levels at the top surface of a thin film of a p-type organic semiconductor blended with polystyrene. Electrolyte- or water-gated field-effect transistors, which have its conductive channel at the top surface of the organic thin film, turn out to be a powerful tool for monitoring the process. A positive shift of the threshold voltage is observed in the devices upon Hg2+ exposure. Remarkably, this interaction has been proved to be specific to Hg2+ with respect to other divalent cations and sensitive down to nanomolar concentrations. Hence, this work also opens new perspectives for employing organic electronic transducers in portable sensors for the detection of an extremely harmful water pollutant without the need of using specific receptors. [ABSTRACT FROM AUTHOR]

The article discusses role of surface preparation technology in providing pristine and stable hydrogen passivated semiconductor surfaces. It mentions that it enables thermal processes like epitaxy, chemical vapor deposition (CVD) and diffusion, without any semiconductor material consumption. It mentions that stable hydrogen passivated surface has been developed by APET Co. Ltd. in a system called TeraDox.

Most semiconductors have surface dynamics radically different from its bulk counterpart due to surface defect, doping level, and symmetry breaking. Because of the technical challenge of direct observation of the surface carrier dynamics, however, experimental studies have been allowed in severely shrunk structures including nanowires, thin films, or quantum wells where the surface-to-volume ratio is very high. Here, we develop a new type of terahertz (THz) nanoprobing system to investigate the surface dynamics of bulk semiconductors, using metallic nanogap accompanying strong THz field confinement. We observed that carrier lifetimes of InP and GaAs dramatically decrease close to the limit of THz time resolution (∼1 ps) as the gap size decreases down to nanoscale and that they return to their original values once the nanogap patterns are removed. Our THz nanoprobing system will open up pathways toward direct and nondestructive measurements of surface dynamics of bulk semiconductors. [ABSTRACT FROM AUTHOR]

In this paper, we carry out a theoretical calculation of quantum state and quantum energy structure in carbon nanotube embedded semiconductor surface. In this theoretical model, the electrons in the carbon nanotube are considered as in a two-dimensional cylindrical surface. Their motion, therefore, can be described by the Dirac equation. We solve the equation and find that the energy levels are quantized and are linearly dependent on the wave vectors along the -direction that is along the direction of the nanotube. This type of energy structure may have potential application for fabricating high efficiency solar cell or quantum bit in computer chips. [ABSTRACT FROM AUTHOR]

The localization behavior of a two-dimensional electron gas confined at the surface of a heavily doped semiconductor under conditions of the 'natural' size effect in the space-charge region is investigated. The scattering of low-energy electrons by the chaotic potential formed at the surface by point charges of ionized impurities is analyzed and the electron mean free path is determined. A criterion for strong localization in this two-dimensional electron system is obtained on the basis of the Ioffe-Regel criterion. [ABSTRACT FROM AUTHOR]

Understanding the physical and chemical processes in which local interactions lead to ordered structures is of particular relevance to the realization of supramolecular architectures on surfaces. While spectacular patterns have been demonstrated on metal surfaces, there have been fewer studies of the spontaneous organization of supramolecular networks on semiconductor surfaces, where the formation of covalent bonds between organics and adatoms usually hamper the diffusion of molecules and their subsequent interactions with each other. However, the saturation of the dangling bonds at a semiconductor surface is known to make them inert and offers a unique way for the engineering of molecular patterns on these surfaces. This review describes the physicochemical properties of the passivated B-Si(111)-(√3x√3) R30° surface, that enable the self-assembly of molecules into a rich variety of extended and regular structures on silicon. Particular attention is given to computational methods based on multi-scale simulations that allow to rationalize the relative contribution of the dispersion forces involved in the self-assembled networks observed with scanning tunneling microscopy. A summary of state of the art studies, where a fine tuning of the molecular network topology has been achieved, sheds light on new frontiers for exploiting the construction of supramolecular structures on semiconductor surfaces. [ABSTRACT FROM AUTHOR]

Photo detection of ultraviolet (UV) light remains a challenge since the penetration depth of UV light is limited to the nanometer scale. Therefore, the doping profile and electric field in the top nanometer range of the photo detection devices become critical. Traditional UV photodetectors usually use a constant doping profile near the semiconductor surface, resulting in a negligible electric field, which limits the photo-generated carrier collection efficiency of the photodetector. Here, we demonstrate, via the use of an optimized gradient boron doping technique, that the carrier collection efficiency and photo responsivity under the UV wavelength region have been enhanced. Furthermore, the ultrathin p+-i-n junction shows an avalanche gain of 2800 and an ultra-low junction capacitance (sub pico-farad), indicating potential applications in the low timing jitter single photon detection area. [ABSTRACT FROM AUTHOR]

Photoelectrochemical water-splitting is a promising carbon-free fuel production method for producing H2 and O2 gas from liquid water. These cells are typically composed of at least one semiconductor photoelectrode which is prone to degradation and/or oxidation. Various surface modifications are known for stabilizing semiconductor photoelectrodes, yet stabilization techniques are often accompanied by a decrease in photoelectrode performance. However, the impact of surface modification on charge transport and its consequence on performance is still lacking, creating a roadblock for further improvements. In this review, we discuss how density functional theory and finite-element device simulations are reliable tools for providing insight into charge transport across modified photoelectrodes. [ABSTRACT FROM AUTHOR]

Photoelectrochemical water-splitting is a promising carbon-free fuel production method for producing H2and O2gas from liquid water. These cells are typically composed of at least one semiconductor photoelectrode which is prone to degradation and/or oxidation. Various surface modifications are known for stabilizing semiconductor photoelectrodes, yet stabilization techniques are often accompanied by a decrease in photoelectrode performance. However, the impact of surface modification on charge transport and its consequence on performance is still lacking, creating a roadblock for further improvements. In this review, we discuss how density functional theory and finite-element device simulations are reliable tools for providing insight into charge transport across modified photoelectrodes. [ABSTRACT FROM AUTHOR]

A new type of atomic pseudopotential for passivation of semiconductors surfaces is presented. These pseudopotentials are intended to be used with empirical or effective pseudopotentials methods, where the main goal is to address nanostructures composed of thousands of atoms, but at low computational costs in comparison to density functional theory (DFT). It is shown that the spherical approximation, which is currently used for these potentials, is not suitable for describing passivants and that, instead, they have to be regarded as complex quantities in reciprocal space. A methodology to extract and implement the new pseudopotentials are described here based on an analytic formulation. Passivants for six different semiconductor compounds (GaAs, AlAs, Si, Ge, CdSe and ZnO) are generated, and their accuracy and high transferability are demonstrated by the calculation of the electronic states of different kinds of surfaces and structures and comparison to DFT calculations. The results show that the DFT results can be reproduced with high fidelity with the passivant potentials here presented. [ABSTRACT FROM AUTHOR]

Self organized nano-structure array on the surfaces of semiconductors have potential applications in photonics, magnetic devices, photovoltaics, and surface-wetting tailoring etc. Therefore, the control over their dimensions is gaining scientific interest in last couple of decades. In this work, fabrication of pits of nano-dimensions is carried out on the GaAs (1 0 0) surface using 50 keV Ar + at normal incidence. Variation in fluence from 3 × 10 17 ions/cm 2 to 5 × 10 18 ions/cm 2 does not make a remarkable variation in the dimension of pits such as size and depth, which is confirmed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). However the simultaneous dots formation is observed along with the pits at higher fluences. Average size of pits is found to be of 22 nm with depth of 1–5 nm for the used fluences. The importance of preferential sputtering of ‘As’ as compared to ‘Ga’ is estimated using energy dispersive X-ray analysis (EDX). The observed alteration in near surface composition shows the Ga enrichment of surface, which is not being much affected by variation in fluence. The growth evolution of pits and dots for the used experimental conditions is explained on the basis of ion beam induced preferential sputtering and surface diffusion. [ABSTRACT FROM AUTHOR]

Modification by electronic excitation of semiconductor surfaces and carbon-related quasi-two-dimensional (2D) nanostructured materials, namely graphene, carbon nanotubes is reviewed. Defect creation in these materials takes place not by low-intensity photoirradiation, but by laser or electron irradiation. The defect creation processes are different from ordinary photochemical processes in molecules or in some solids like alkali halides, which can be modified by a localized exciton. It is pointed out that there are common features in defect creation by electronic excitation in semiconductor surfaces and carbon-related quasi-2D nanomaterials: the yield-intensity relation shows strong superlinearity for laser irradiation near the bandgap energies and linearity or weak superlinearity for higher energy electron or photon irradiation. These results are explained in terms of multi-hole localization, in which bonds are weakened more strongly and more energy is available upon recombination with trapped electrons in comparison with excitons. The multi-hole localized state is considered to be realized by the creation of dense excitons or by cascade excitation for laser irradiation and by multiple excitations or multiple exciton generation by single impacts for electron irradiation. The review includes also polymerization of C films by electronic excitation, which is induced by low-intensity photoirradiation as well as by laser or electron irradiation. The experimental observation that laser or electron irradiation polymerize C films differently from low-intensity photoirradiation is explained in terms of multi-hole localization similar to the defect formation mechanism. Although fragmentation of C is due to electronic excitation of the molecule, it is included in the review because its yield is strongly superlinear for laser irradiation near bandgap energies and weakly superlinear for high-energy electron or photon irradiation as for other cases. Modification by electronic excitation of carbon-related quasi-two-dimensional nanostructured materials, namely graphene and carbon nanotubes, is reviewed with compare to the case of semiconductor surfaces. Modification in these materials exhibits two types of yield versus excitation intensity relations, depending on the excitation conditions and excitation sources: strongly and weakly superlinear relations. The results are reasonably explained in terms of excitation-induced multi-hole localization, in which bonds are strongly weakened and much energy is available upon recombination with trapped electrons. [ABSTRACT FROM AUTHOR]

We demonstrate on the basis of ab initio simulations how passivated semiconductor surfaces can be exploited to study bulklike interaction properties and wave functions of magnetic impurities on the atomic scale with conventional and spin-polarized scanning tunneling microscopy. By applying our approach to the case of 3d transition metal impurities close to the H/Si(111) surface, we show exemplarily that their wave functions in Si are less extended than for Mn in GaAs, thus obstructing ferromagnetism in Si. Finally, we discuss possible applications of this method to other dilute magnetic semiconductors. [ABSTRACT FROM AUTHOR]