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A new generation of two-dimensional (2D) material has captivated significant attention in the energy conversion field owing to their promising optoelectronics and thermoelectric applications. The present work involves the systematic investigation of fundamental properties of single-layered 2D carbon-based monochalcogenides (CS, CSe, CTe) with planar, buckled and puckered geometry within the framework of density functional theory (DFT). The structural and lattice dynamics analysis disclose that puckered and buckled configurations are energetically and dynamically stable whereas planar structures depict instability. The anisotropic group velocity of longitu-dinal acoustic (LA) and transverse acoustic (TA) phonon modes in puckered systems may render the charac-teristics thermal transport properties. Additionally, for the first time, we scrutinized the thermoelectric and optical properties of these materials. At room temperature, the electron carrier mobilities are 174.698 and 160.830 m(2)V(-1)s(-1) of puckered and buckled CS systems, respectively are highest among all structures. The computed Seebeck coefficient, electrical conductivity and power factor manifests the high thermoelectric transport properties of puckered CS material. Further, the calculated solar parameters demonstrate an excep-tionally high-power conversion efficiency of 19.61 % for puckered CTe. Present work indicates that puckered phase of CS and CTe show their potential for the heat and solar energy harvesting devices, respectively.

Organic semiconductors are an interesting class of materials for application in a wide range of emerging opto-electronics and electrical devices, such as light emitting diodes, thin-film transistors, solar cells, sensors, and thermoelectrics. However, despite the tremendous efforts on the development of the high-performance materials, device architectures, and manufacturing techniques; crucial challenges still persist and will need to be addressed in order to fully exploit the potential of this class of materials. In this respect, the underlying physics of charge transport in organic semiconductors is still not fully understood. Particularly, solution processed organic semiconductors have complex microstructures. In contrast to inorganic semiconductors, carrier transport in these partially ordered films cannot be described using models for either amorphous or crystalline semiconductors due to their uncontrolled morphology and alignment in the charge transport domain. Further, organic semiconductors are intrinsic and must be doped either with chemical or molecular dopants, carrier injection via external contacts, or photoexcitation in order to transport charge. In this regard, current flow may cause unwanted device heating in organic electrical devices due to high resistance of organic layers. Again, the low thermal conductivity of organic semiconductors prevents rapid heat dissipation from the device, which can have negative consequences on device lifetime and performance. Doping in organic semiconductors can significantly impact the molecular backbone, thin film morphology, and corresponding charge transport nature. The challenge is to experimentally untangle these intertwined physical and chemical phenomena. This thesis extensively investigates charge transport in conjugated organic semiconductors, with a focus on macromolecules such as conjugated polymers that are applied in opto-electronic and energy applications. The goal was to elucidate the impact of electric

Recently, electrically conducting heterointerfaces between dissimilar band insulators (such as lanthanum aluminate and strontium titanate) have attracted considerable research interest. Charge transport and fundamental aspects of conduction have been thoroughly explored. Perhaps surprisingly, similar studies on conceptually much simpler conducting homointerfaces, such as domain walls, are not nearly so well developed. Addressing this disparity, magnetoresistance is herein reported in approximately conical 180° charged domain walls, in partially switched ferroelectric thin-film single-crystal lithium niobate. This system is ideal for such measurements: first, the conductivity difference between domains and domain walls is unusually large (a factor of 1013) and hence currents driven through the thin film, between planar top and bottom electrodes, are overwhelmingly channeled along the walls; second, when electrical contact is made to the top and bottom of the domain walls and a magnetic field is applied along their cone axes, then the test geometry mirrors that of a Corbino disk: a textbook arrangement for geometric magnetoresistance measurement. Data imply carriers with extremely high room-temperature Hall mobilities of up to ≈3700 cm2 V−1 s−1. This is an unparalleled value for oxide interfaces (and for bulk oxides) comparable to mobilities in other systems seen at cryogenic, rather than at room, temperature.

Van der Waals (vdW) heterostructures identify the advantage of integrating excellent properties of the stacked two-dimensional (2-D) materials by vdW interactions, thereby have gained increasing attention in optoelectronic applications recently. However, heterostructures with type-II band aligning and direct bandgap are still scarce for optoelectronics. Herein, within the framework of density functional theory (DFT) calculations, we predict the indium selenide/antimonene heterostructure as a promising candidate for optoelectronic applications. The most energetically stable configuration of indium selenide/antimonene heterostructure presents a direct bandgap of 0.97 eV at HSE06 level. Remarkably, indium selenide/antimonene heterostructure exhibits a type-II band alignment, indicating its favorable capability of electron-hole separation. Carrier mobility computations show that indium selenide/antimonene heterostructure possesses both high electron mobility and hole mobility of up to 103 cm2 V-1 s-1, which are superior to that of any individual monolayer InSe and antimonene. The light absorption and photocurrent calculations reveal that InSe/antimonene heterostructure is sensitive to visible and ultraviolet light. The power conversion efficiency of an indium selenide/antimonene thin-film solar cell is up to 17.2%. The multifunctionality endows the indium selenide/antimonene heterostructure a potential candidate for photovoltaic devices and photodetectors.

Solar cells with the structure ZnO/CdS/Cu2ZnSnSe4/Mo/glass were studied by photoluminescence (PL) before and after irradiation with a dose of 1.8 × 1015 cm−2 and then 5.4 × 1015 cm−2 of 10 MeV electrons carried out at 77 K in liquid nitrogen bath. The low temperature PL spectra before irradiation revealed two bands, a broad and asymmetrical dominant band at 0.94 eV from the CZTSe layer and a lower intensity high energy band (HEB) at 1.3 eV, generated by defects in the CdS buffer layer. Analysis of the excitation intensity and temperature dependencies suggested that the dominant band is free-to-bound (FB): the recombination of free electrons with holes localised at acceptors whose energy levels are affected by potential fluctuations of the valence band due to high concentrations of randomly distributed charged defects. Irradiation did not induce any new band in the examined spectral range (from 0.5 μm to 1.65 μm) but reduced the intensity of both bands in the PL spectra measured at 77 K without warming the cells. The higher the dose the greater was the reduction. After this the cells were warmed to 300 K and moved to a variable temperature cryostat to measure temperature dependencies of the PL spectra. After irradiation the red shift rate of the FB band with temperature rise was found to increase. Electrons displace atoms in the lattice creating primary defects: interstitials and vacancies. These defects recombine during and shortly after irradiation forming secondary defect complexes which work as deep non-radiative traps of charge carriers reducing the PL intensity and increasing the rate of the temperature red shift. Irradiation did not affect the mean depth of the band tails estimated from the shape of the low energy side of the dominant PL band. © 2020 Elsevier Ltd

According to the Mott's relation, the figure-of-merit of a thermoelectric material depends on the charge carrier concentration and carrier mobility. This explains the observation that low thermoelectric properties of GeTe-based materials suffer from the degraded carrier mobility, on account of the fluctuation of electronegativity and ionicity of various elements. Here, high-performance CuBiSe2 alloyed GeTe with high carrier mobility due to the small electronegativity difference between Cu and Ge atoms and the weak ionicity of Cu-Te and Bi-Te bonds, is developed. Density functional theory calculations indicate that CuBiSe2 alloying increases the formation energy of Ge vacancies and correspondingly reduces the amount of Ge vacancies, leading to an optimized carrier concentration and a high power factor of 37.4 µW cm−1 K−2 at 723 K. Moreover, CuBiSe2 alloying induces dense point defects and triggers ubiquitous lattice distortions, leading to a reduced lattice thermal conductivity of 0.39 W m−1 K−1 at 723 K. These synergistic effects result in an optimization of the carrier mobility, the carrier concentration, and the lattice thermal conductivity, which favors an enhanced peak figure-of-merit of 2.2 at 723 K in (GeTe)0.94(CuBiSe2)0.06. This study provides guidance for the screening of GeTe-based thermoelectric materials with high carrier mobility.

Luminescent characteristics of K3Lu(PO4)2:Pr3+ (1 and 5 mol.%) microcrystalline powders, a promising optical material for scintillation applications, were investigated using various experimental techniques. The material shows emission features connected with both high intensity interconfigurational 4f15d→4f2 transitions (broad UV emission bands) and intraconfigurational 4f2→4f2 transitions (weak emission lines in the visible range). The output of X-ray excited 4f15d→4f2 emission of Pr3+ increases with a temperature rise from 90 K to room temperature and higher depending on the Pr3+ ions concentration. The high 5% concentration of Pr3+ ions is found to be favourable for the stabilization of a monoclinic phase (P21/m space group) over a trigonal one (P3‾ space group) while emission properties of the material reveal that a phase transition occurs at higher temperatures. Decay kinetics of Pr3+ 4f15d→4f2 emission are recorded upon excitation with high repetition rate X-ray synchrotron excitation and pulse cathode ray excitation. Issues related to a non-exponential decay of luminescence and presence of slow decay components are discussed in terms of energy transfer dynamics. The presence of defects was revealed with thermoluminescence measurements and these are suggested to be the mainly responsible for delayed recombination of charge carriers on the Pr3+ 4f15d states. Some peculiarities of host-to-impurity energy transfer are discussed. © 2020 Elsevier B.V.

Based on the first-principles calculations, the stability, elastic constants, electronic structure, and lattice thermal conductivity of monolayer XO2 (X = Ni, Pd, Pt) are investigated in this work. The results show that XO2 (X = Ni, Pd, Pt) have mechanical and dynamic stability at the same time. In addition, the Young's modulus of monolayer NiO2, PdO2 and PtO2 are 124.69 N.m(-1), 103.31 N.m(-1) and 116.51 N.m(-1), Poisson's ratio of monolayer NiO2, PdO2 and PtO2 are 0.25, 0.24 and 0.27, respectively, and each of them possesses high isotropy. The band structures show that monolayer XO2 (X = Ni, Pd, Pt) are indirect band-gap semiconductors with energy gap of 2.95 eV, 3.00 eV and 3.34 eV, respectively, and the energy levels near the valence band maximum and conduction band minimum are mainly composed of Ni-3d/Pd-4d/Pt-5d and O-2p orbital electrons. Based on deformation potential theory, the carrier mobility of each monolayer is calculated, and the results show that the effective mass and deformation potential of monolayer XO2 (X = Ni, Pd, Pt) along the armchair and zigzag directions show obvious anisotropy, and the highest electron and hole mobility are 13707.96 and 53.25 cm(2) .V-1.s(-1), 1288.12 and 19.18 cm(2).V-1.s(-1), and 404.71 and 270.60 cm(2) .V-1.s(-1) for NiO2, PdO(2 )and PtO2, respectively. Furthermore, the lattice thermal conductivity of monolayer XO2 (X = Ni, Pd, Pt) at 300 K are 53.55 W.m(-1).K-1, 19.06 W.m(-1).K-1 and 17.43 W.m(-1).K-1, respectively. These properties indicate that monolayer XO2 (X = Ni, Pd, Pt) have potential applications in nanometer electronic materials and thermal conductivity devices.

Parameters of the energy gap and, consequently, electronic, magnetic and galvanomagnetic properties in different X2YZ Heusler alloys can vary quite strongly. In particular, half-metallic ferromagnets (HMFs) and spin gapless semiconductors (SGSs) with almost 100% spin polarization of charge carriers are promising materials for spintronics. The changes in the electrical, magnetic and galvanomagnetic properties of the Co2YSi (Y = Ti, V, Cr, Mn, Fe) and Co2MnZ Heusler alloys (Z = Al, Si, Ga, Ge) in possible HMF- and/or SGS-states were followed and their interconnection was established. Significant changes in the values of the magnetization and residual resistivity were found. At the same time, the correlations between the changes in these electronic and magnetic characteristics depending on the number of valence electrons and spin polarization are observed. © 2021 Author(s).

Perovskite solar cells represent a highly promising third-generation photovoltaic tech-nology. However, their practical implementation is hindered by low device operational stability, mostly related to facile degradation of the absorber materials under exposure to light and elevated temperatures. Improving the intrinsic stability of complex lead halides is a big scientific challenge, which might be addressed using various “molecular modifiers”. These modifiers are usually rep-resented by some additives undergoing strong interactions with the perovskite absorber material, resulting in enhanced solar cell efficiency and/or operational stability. Herein, we present a deriva-tive of 1,4,6,10-tetraazaadamantane, NAdCl, as a promising molecular modifier for lead halide perovskites. NAdCl spectacularly improved both the thermal and photochemical stability of methy-lammonium lead iodide (MAPbI3 ) films and, most importantly, prevented the formation of metallic lead Pb0 as a photolysis product. NAdCl improves the electronic quality of perovskite films by healing the traps for charge carriers. Furthermore, it strongly interacts with the perovskite framework and most likely stabilizes undercoordinated Pb2+ ions, which are responsible for Pb0 formation under light exposure. The obtained results feature 1,4,6,10-tetraazaadamantane derivatives as highly promising molecular modifiers that might help to improve the operational lifetime of perovskite solar cells and facilitate the practical implementation of this photovoltaic technology. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

High photon conversion efficiencies and low-cost materials are crucial for implementing photocatalytic solutions in large scale applications. To improve the conversion efficiencies, knowledge on the lifetime and dynamics of photogenerated charge carriers is fundamental, for which transient absorption spectroscopy has provided important insights. Regarding the cost of the materials, one approach to decrease it is mixing the photocatalyst with cheaper additives while avoiding a significant loss in its activity. In this short review we summarize the findings of our group dealing with both aspects. A new model to fit transient absorption decays, based on fractal kinetics, is discussed. The model has been applied to the transient decays of TiO2 mixtures with binary particle size distributions and of TiO2 mixtures with a priori inert additives. In both cases, the insights obtained from the model were crucial to explain the photocatalytic activities of the mixtures. © 2020, The Author(s).

Herein, the hole transport in a quinoxaline–thiophene based conjugated polymer (PTQ1) mixed with an insulating polystyrene (PS) was studied by macroscopic and local current density−voltage characteristics measurements. As a result, we found that the hole conductivity in PTQ1 : PS blends increases as the weight ratio of PTQ1 is reduced down to 20 wt%. This is mainly ascribed to increases in mobility because the charge carrier density would be constant in the insulating PS matrix. With decreasing PTQ1 weight ratio in the blends, the absorption bandwidth of PTQ1 and additional emission due to excimer decreased, suggesting that interchain interactions are suppressed. By measuring the temperature‐dependent conductivity, we also found that the activation energy for the hole conductivity is smaller in PTQ1 : PS blends than in PTQ1 neat films. These findings suggest that trap sites decrease because of the suppressed interaction between PTQ1 chains in blend films. We also measured conductive atomic force microscope images of the blend films to clarify the local conductive property. For PTQ1 neat films, a low conductive image was observed over the entire film. For PTQ1 : PS blends, on the other hand, many highly conductive spots were locally found. We thus conclude that the dilution of PTQ1 chains in the PS matrix leads to a lower formation of trap sites, resulting in more conductive transport in PTQ1 : PS blends than in PTQ1 neat films.

The luminescent characteristics of the double phosphate KLuP2O7 doped with Pr3+ ions, a promising optical material for scintillator applications, were investigated using various experimental spectroscopic techniques. KLuP2O7:Pr3+ shows Pr3+ emission associated with interconfigurational 4f15d1→4f2 transitions located in the UV range (250–320 nm), intraconfigurational 4f2→4f2 transitions (weak lines in the visible spectral range) and defect-related luminescence. The light output of X-ray or cathode ray excited Pr3+ 4f15d1→4f2 luminescence is found to be nearly independent of temperature in the range of 90–400 K. The output of pulsed cathode luminescence shows thermal quenching above 450 K characterized by an activation energy of about 0.5 eV. Upon excitation with pulsed cathode rays or high-frequency (~8 MHz) X-ray synchrotron radiation, the luminescence decay kinetics of Pr3+ 4f15d1→4f2 transitions are dominated by a decay component with lifetime of about 20 ns. An additional slower decay component with lifetime of 75 ns was observed upon cathode ray excitation and was shown to result from delayed host-to-impurity energy transfer. The latter, in turn, originates from re-trapping of charge carriers at defect-related traps whose presence was demonstrated by thermoluminescence measurements. Parameters of the trapping centers were estimated. Peculiarities of host-to-impurity energy transfer are analysed and discussed. © 2020 Elsevier B.V.

One of the fundamental properties of semiconductors is their ability to support highly tunable electric currents in the presence of electric fields or carrier concentration gradients. These properties are described by transport coefficients such as electron and hole mobilities. Over the last decades, our understanding of carrier mobilities has largely been shaped by experimental investigations and empirical models. Recently, advances in electronic structure methods for real materials have made it possible to study these properties with predictive accuracy and without resorting to empirical parameters. These new developments are unlocking exciting new opportunities, from exploring carrier transport in quantum matter to in silico designing new semiconductors with tailored transport properties. In this article, we review the most recent developments in the area of ab initio calculations of carrier mobilities of semiconductors. Our aim is threefold: to make this rapidly-growing research area accessible to a broad community of condensed-matter theorists and materials scientists; to identify key challenges that need to be addressed in order to increase the predictive power of these methods; and to identify new opportunities for increasing the impact of these computational methods on the science and technology of advanced materials. The review is organized in three parts. In the first part, we offer a brief historical overview of approaches to the calculation of carrier mobilities, and we establish the conceptual framework underlying modern ab initio approaches. We summarize the Boltzmann theory of carrier transport and we discuss its scope of applicability, merits, and limitations in the broader context of manybody Green’s function approaches. We discuss recent implementations of the Boltzmann formalism within the context of density functional theory and many-body perturbation theory calculations, placing an emphasis on the key computational challenges and suggested solut

Halide perovskites have attracted substantial interest for their potential as disruptive display and lighting technologies. However, perovskite light-emitting diodes (PeLEDs) are still hindered by poor operational stability. A fundamental understanding of the degradation processes is lacking but will be key to mitigating these pathways. Here, a combination of in operando and ex situ measurements to monitor the performance degradation of (Cs0.06FA0.79MA0.15)Pb(I0.85Br0.15)3 PeLEDs over time is used. Through device, nanoscale cross-sectional chemical mapping, and optical spectroscopy measurements, it is revealed that the degraded performance arises from an irreversible accumulation of bromide content at one interface, which leads to barriers to injection of charge carriers and thus increased nonradiative recombination. This ionic segregation is impeded by passivating the perovskite films with potassium halides, which immobilizes the excess halide species. The passivated PeLEDs show enhanced external quantum efficiency (EQE) from 0.5% to 4.5% and, importantly, show significantly enhanced stability, with minimal performance roll-off even at high current densities (>200 mA cm−2). The decay half-life for the devices under continuous operation at peak EQE increases from <1 to ≈15 h through passivation, and ≈200 h under pulsed operation. The results provide generalized insight into degradation pathways in PeLEDs and highlight routes to overcome these challenges., QC 20210224

This work combines new and earlier obtained results on electron hole and oxygen-ion transport in the La2NiO4-based solid solutions. The effect of lanthanum substitution with Ca/Sr and nickel with Fe, Mn, Co or Cu on transport properties of La2-xAxNi1-yMeyO4+δ was analyzed and discussed at different substitution levels. Besides the changes in concentration and mobility of electron holes induced by the doping with cations of different nature, the partial transformation of Ni3+ from low-spin to high-spin state was shown to have a profound effect on transport properties of these materials leading to a notable decrease in mobility of electron holes, especially in the strontium-rich oxides. The obtained results suggested that the size factor was the main driving force behind the observed transformation of Ni3+. The oxygen-ion transport in La2-xAxNi1-yMeyO4+δ was characterized by significant surface exchange limitations, which can be reduced only at relatively high concentrations of strontium and iron, and should be taken into account while evaluating the ionic conductivity by means of oxygen permeation or the modified Hebb-Wagner polarization method. © 2019 IUPAC and De Gruyter.

Two-dimensional (2D) semiconductors are at the center of an intense research effort aimed at developing the next generation of flexible, transparent, and energy-efficient electronics. In these applications, the carrier mobility, that is the ability of electrons and holes to move rapidly in response to an external voltage, is a critical design parameter. Here, we show that the interlayer coupling between electronic wave functions in 2D semiconductors can be used to drastically alter carrier mobility and dynamics. We demonstrate this concept by performing state-of-the-art ab initio calculations for InSe, a prototypical 2D semiconductor that is attracting considerable attention, because of its exceptionally high electron mobility. We show that the electron mobility of InSe can be increased from 100 cm2 V−1 s−1 to 1000 cm2 V−1 s−1 by exploiting the dimensional crossover of the electronic density of states from two dimensions to three dimensions. By generalizing our results to the broader class of layered materials, we discover that dimensionality plays a universal role in the transport properties of 2D semiconductors.

We show that hole states in recently discovered single-layer InSe are strongly renormalized by the coupling with acoustic phonons. The coupling is enhanced significantly at moderate hole doping (∼1013 cm-2) due to hexagonal warping of the Fermi surface. While the system remains dynamically stable, its electron-phonon spectral function exhibits sharp low-energy resonances, leading to the formation of satellite quasiparticle states near the Fermi energy. Such many-body renormalization is predicted to have two important consequences. First, it significantly suppresses charge carrier mobility reaching ∼1 cm2 V-1 s-1 at 100 K in a freestanding sample. Second, it gives rise to unusual temperature-dependent optical excitations in the midinfrared region. Relatively small charge carrier concentrations and realistic temperatures suggest that these excitations may be observed experimentally. © 2019 American Physical Society.

Out-of-plane vibrations are considered as the dominant factor limiting the intrinsic carrier mobility of suspended two-dimensional materials at low carrier concentrations. Anharmonic coupling between in-plane and flexural phonon modes is usually excluded from the consideration. Here we present a theory for electron-phonon scattering, in which the anharmonic coupling between acoustic phonons is systematically taken into account. Our theory is applied to the typical group V two-dimensional semiconductors: hexagonal phosphorus, arsenic, and antimony. We find that the role of the flexural modes is essentially suppressed by their coupling with in-plane modes. At dopings lower than 1012cm-2 the mobility reduction does not exceed 30%, being almost independent of the concentration. Our findings suggest that compared to in-plane phonons, flexural phonons are considerably less important in the electronic transport of two-dimensional semiconductors, even at low carrier concentrations. © 2019 American Physical Society.

The Co2 YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys can manifest the properties of half-metallic ferromagnets. These compounds are promising materials for spintronics since almost 100 % spin polarization of charge carriers can be realized at room temperature. We measured the electroresistivity, magnetic and galvanomagnetic properties of the Co2 YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys from 4.2 K to 300 K and in magnetic fields up to 100 kOe. The type, concentration and mobility of charge carriers were estimated. The Y-component variation in the Co2 YSi Heusler alloys is found to affect strongly the number of current carriers and alter the electronic band structure near the Fermi level E F and, consequently, the electronic transport and magnetic properties of the Co2 YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys. © Published under licence by IOP Publishing Ltd.

Magnetotransport provides key experimental signatures in Weyl semimetals. The longitudinal magnetoresistance is linked to the chiral anomaly and the transversal magnetoresistance to the dominant charge relaxation mechanism. Axial magnetic fields that act with opposite sign on opposite chiralities facilitate new transport experiments that probe the low-energy Weyl nodes. As recently realized, these axial fields can be achieved by straining samples or adding inhomogeneities to them. Here, we identify a robust signature of axial magnetic fields: an anomalous scaling of the conductance in the diffusive ultraquantum regime. In particular, we demonstrate that the longitudinal conductivity in the ultraquantum regime of a disordered Weyl semimetal subjected to an axial magnetic field increases with both the field strength and sample width due to a spatial separation of charge carriers. We contrast axial magnetic with real magnetic fields to clearly distinguish the different behavior of the conductance. Our results rely on numerical tight-binding simulations and are supported by analytical arguments. We argue that the spatial separation of charge carriers can be used for directed currents in microstructured electronic devices., QC 20220614

Robotic technology helps humans in different areas such as manufacturing, health care and education. Due to the ubiquitous revolution, today's focus is on mobile robots and their applications in a variety of cyber-physical systems. ROS is a wll-known and powerful middleware that facilitates software development for mobile robots. However, this middleware does not support assuring properties such as timeliness and safety of ROS-based software. In this paper we present an integration of Timed Rebeca modeling language with ROS to synthesize verified robotic software. First, a conceptual model of robotic programs is developed using Timed Rebeca. After verifying a set of user-defined correctness properties on this model, it is translated to a ROS program automatically. Experiments on some small-scale case studies illustrates the applicability of the proposed integration method.

Here we report structural and electronic properties of a new family of two-dimensional covalent metal-free organic frameworks based on tetraoxa[8]circulene with different types of fusing. All nanosheets demonstrate high thermodynamic stability and unique electronic properties depending on the fusing type. Among three types of nanosheets, only two demonstrate semiconducting properties exhibiting 1.37 and 1.84 eV direct band gaps, while another one is found to be a semimetal, which hosts strong topological states and enhances the band gap (∼87 meV) induced by spin-orbit coupling that exceeds by several orders of magnitude that gap in graphene. Tetraoxa[8]circulene-based nanosheets are also predicted to be good organic semiconductors due to a clearly observable quantum confinement effect on the band gap size in oligomers and relatively low effective masses, which result in high carrier mobility. Owing to the versatility of chemical design, these materials have the potential to expand applications beyond those of graphene., QC 20181108

Here we develop a microscopic approach aimed at the description of a suite of physical effects related to carrier transport in, and the optical properties of, halide perovskites. Our theory is based on the description of the nuclear dynamics to all orders and goes beyond the common assumption of linear electron-phonon coupling in describing the carrier dynamics and band gap characteristics. When combined with first-principles calculations and applied to the prototypical MAPbI3 system, our theory explains seemingly disparate experimental findings associated with both the charge-carrier mobility and optical absorption properties, including their temperature dependencies. Our findings demonstrate that orbital-overlap fluctuations in the lead-halide structure plays a significant role in determining the optoelectronic features of halide perovskites.

The Multilevel Older Persons Transportation and Road Safety (MOTRS) model postulates a role for demographic, functional, and psychosocial factors in driving self-regulation. This study formally tested the constructs of the MOTRS model, and its ability to account for variation in older adult’s driving self-regulation. Four exogenous constructs dealing with sociodemographic and driving-related variables (driving space, dependency on other drivers, health, and driving performance) and three endogenous constructs of psychosocial appraisals (driving confidence, attitudes and beliefs towards driving) were used to predict driving self-regulation. A sample of 277 Australian drivers, aged 65 years or over, completed standardised questionnaires to assess these variables. Structural equation modelling was used to evaluate one of the model’s assumptions. Findings established that sociodemographic and driving-related factors influence older adults’ driving self-regulation by impacting psychosocial variables. A re-specified model accounted for 75% of the variance in self-reported driving self-regulation. When other variables were considered, attitude towards driving was the strongest single predictor of driving self-regulation. These findings provide an initial partial validation of the MOTRS model. The results indicate that psychosocial variables are important determinants of driving self-regulation by older adults. This model could guide future research into older adults’ driving self-regulation.

In this work, atomic layer deposition (ALD) has been employed to prepare high-mobility H-doped zinc oxide (ZnO:H) films. Hydrogen doping was achieved by interleaving the ZnO ALD cycles with H2 plasma treatments. It has been shown that doping with H2 plasma offers key advantages over traditional doping by Al and B, and enables a high mobility value up to 47 cm2/Vs and a resistivity of 1.8 mΩcm. By proper choice of a deposition regime where there is a strong competition between film growth and film etching by the H2 plasma treatment, a strongly enhanced grain size and hence increased carrier mobility with respect to undoped ZnO can be obtained. The successful incorporation of a significant amount of H from the H2 plasma has been demonstrated, and insights into the mobility-limiting scatter mechanisms have been obtained from temperature-dependent Hall measurements. A comparison with conventional TCOs has been made in terms of optoelectronic properties, and it has been shown that high-mobility ZnO:H has potential for use in various configurations of silicon heterojunction solar cells and silicon-perovskite tandem cells.

For higher device performances including low-power consumption and high-speed operation, functional materials in wide variety are actively studied. In particular, Si compatibility is regarded as one of the indispensable prerequisites owing to cost effectiveness and high maturity of Si platform and its process integration. SiGe is gaining much interest owing to Si compatibility, high carrier mobilities, and higher optical confinement capability compared with Si. In this work, SiGe layers have been epitaxially grown on Si substrate under different conditions and their structural and optical characteristics are analyzed in depth. Various analysis tools are used cooperatively, including high-resolution transmission electron microscopy (HR-TEM), dynamic secondary ion mass spectroscopy (SIMS), X-ray diffraction spectroscopy (XRD), and long-wavelength ellipsometer, in order to extract the thickness as the result of epitaxy condition, Ge fraction, interface status, lattice constant, and refractive index with extinction coefficient for setting up parameter database for electronic and photonic device applications., QC 20180131

We propose a method to investigate the carrier transport properties in the ultrathin wetting layer of a self-assembled quantum dot (QD) structure using low-voltage cathodoluminescence (CL) imaging. Measurements are performed on diluted InAs/InP QDs in order to spatially resolve them on CL images at temperature ranging from 5 to 300 K. The mean ambipolar diffusion length extracted from CL intensity profiles across different isolated bright spots is about 300 nm at 300 K. This gives an ambipolar carrier mobility of about 110 cm2/(V s)110 cm2/(V s). Temperature investigation reveals a maximum diffusion length near 120 K.

There has been a trend in car sharing and especially electric car sharing over the last decade. This study aims at developing knowledge of users and searching market opportunities for the electric car sharing service EVCARD in Shanghai, China. EVCARD originates in the suburban Jiading district and is planning on expanding the business to the centre of Shanghai. Survey methods and tools have been applied in the study to acquire user data. The analysis was designed to answer research questions related to users' attitudes and expectations about the EVCARD service and to provide suggestions for system improvement., Conference code: 125226

Twisted graphene is of particular interest due to several intriguing characteristics, such as its the Fermi velocity, van Hove singularities and electronic localization. Theoretical studies recently suggested the possible bandgap opening and tuning. Here, we report a novel approach to producing epitaxial twisted graphene on SiC (0001) and the observation of its intrinsic bandgap behaviour. The direct deposition of C60 on pre-grown graphene layers results in few-layer twisted graphene confirmed by angular resolved photoemission spectroscopy and Raman analysis. The strong enhanced G band in Raman and sp3 bonding characteristic in X-ray photoemission spectroscopy suggests the existence of interlayer interaction between adjacent graphene layers. The interlayer spacing between grapheme layers measured by transmission electron microscopy is 0.352 + or - 0.012 nm. Thermal activation behaviour and nonlinear current-voltage characteristics conclude that an intrinsic bandgap is opened in twisted graphene. Low sheet resistance (approximately 160 ohm square(exp1) at 10 K) and high mobility (approximately 2,000 cm(exp2)V 1s(exp1)1at 10 K) are observed., Published in Nature Communications, v6 n5677 p1-8, 6 January 2015. Prepared in collaboration with the Department of Physics at the University of Dayton, Dayton OH, the Department of Physics at Pusan National University, Republic of Korea and Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA.

The MOS technology using high-k dielectrics on high carrier mobility semiconductors of InGaAs leading to a faster speed at lower power is now at the International Technology Roadmap for Semiconductors (ITRS). Great efforts have been dedicated to understand the high k/InGaAs interface. This project involves an examination of interfacial electronic structure of in-situ HfO2 on In0.53Ga0.47As\(001)-4x2 probed by synchrotron radiation photoemission. The dielectric film was prepared by atomic layer deposition (ALD) with the precursors as tetrakis[ethylmethylamino] Hafnium (TEMAHf) and water. Samples were kept under ultra-high-vacuum (UHV) throughout from MBE/ALD preparation to data-acquisition photoemission chambers in the synchrotronradiation facility. The high-resolution work with a short inelastic mean-free path allowed for the first time identification of atom-toatom interaction at this interface. This work has elucidated the mechanism and nature of the bonding between the Hf atom in TEMAHf and In/As atoms of the reconstructed In0.53Ga0.47As(001)-4x2 surface. The TEMAHf precursor is either intact, or loses one ethylmethylamino ligand to become tri-EMAHf. The initial purge of the TEMAHf precursors effectively passivates all the edge As atoms in the top row. As a result, no oxygen bonding was found at either surface As or In atoms. The subsequent water purge reacts with tri-EMAHf to facilitate the growth of hafnium oxides there. The interface obtained by ALD in the present study found no evidence of oxygen bonding to any atom in the trough. The unpassivated surface In atoms may contribute to the frequency dispersion in the accumulation region of n-In0.53Ga0.47As MOSCAP.

Integration of a high-k interfacial layer (IL) is considered the leading technological solution to extend the scalability of Hf-based high-k/metal gate CMOS technology. We have previously shown that thulium silicate (TmSiO) IL can provide excellent electrical characteristics and enhanced channel mobility at sub-nm EOT. This paper presents a detailed analysis of channel mobility in TmSiO/HfO2/TiN MOSFETs, obtained through measurements at varying temperature and under constant voltage stress. We show experimentally for the first time that integration of a high-k IL can benefit mobility by attenuating remote phonon scattering. Specifically, integration of TmSiO results in attenuated remote phonon scattering compared to reference SiOx/HfO2 dielectric stacks having the same EOT, whereas it has no significant influence on remote Coulomb scattering., QC 20151207. QC 20160318

We study the impact of hot-carrier degradation (HCD) on the performance of graphene field-effect transistors (GFETs) for different polarities of HC and bias stress. Our results show that the impact of HCD consists in a change of both charged defect density and carrier mobility. At the same time, the mobility degradation agrees with an attractive/repulsive scattering asymmetry and can be understood based on the analysis of the defect density variation., QC 20150608

Fabrication of Si-As-Te chalcogenite amorphous semiconductor under microgravity in Spacelab-J is described. As Si-As-te system is constructed based on 4-3-2 coordinate bond network, it has wide vitrification area, in which various physical properties could be controlled. For example, in Si(x)(As2Te3)(1-x) system, variation of the composition rate x brings from 0.7 to 1.8 eV of variation of electrical bandgap. Systematic investigation on composite rate dependence of such physical constants is useful for research for both aspects of electronic and atomic properties of these random network materials. Moreover, this system is very interesting not only from view point of basic physics but also from technological aspect of application to electronic elements, photoelectric device etc. However, homogeneous amorphous semiconductors necessary for performing investigations in the field of basic or applied physics were difficult to produce on ground surface so far, due to difference of specific gravity, melting point and vapor pressure of constituent elements of materials. The main object of this flight experiments (First Material Production Test:FMPT) is to compare homogeneous multielement compound amorphous semiconductors produced under microgravity environment with samples obtained on ground surface on amorphous structure and electronic properties. This report introduce the reason of selecting Si(x)(As2Te3)(1-x) as FMPT material and the relative characteristics to basic and application technology. Further, the contents of FMPT experiments and samples are also described, and finally, material properties made clear so far is described in details by focussing on comparing with the samples produced on ground surface., Spacelab-Jの微小重力環境下において製造されたSi-As-Teカルコゲナイド系アモルファス半導体について報告する。Si-As-TeはIV-III-II配位結合ネットワークにより構成されているために、広い範囲のガラス化領域を有しており、その中で様々な物理的性質が制御可能となる。1例をあげると、Si(x)(As2Te3)(1-x)系において組成比xを変えることにより電気的バンドギャップは0.7eVから1.8eVまで可変である。このような物理定数の組成依存性の系統的研究は、この種のランダムネットワーク材料の電子的そして原子的物性の両面を合わせて探求する上で非常に有意義である。また、この系は基礎物理の観点のみならず、電子素子、光電素子への応用という工学的側面においても極めて魅力的な材料である。ところが、このような基礎また応用物理分野の研究を推進するために必要とされる均質なアモルファス半導体の作製は、材料を構成する各組成元素の比重、融点および蒸気圧の違いのため地上実験では困難であった。この飛行実験(FMPT)の主たる目的は、均質な多元素化合物アモルファス半導体を微小重力下において製造し、アモルファス構造またその電子物性を地上において作製した試料と比較評価することである。本報告では、まず、Si(x)(As2Te3)(1-x)系材料をFMPTに対して選定した理由、またその基礎物理および技術応用にかかわる特質を紹介する。次いで、FMPT実験の内容と試験材料について述べ、最後に、これまでに明らかとなった材料物性を地上試料との比較に焦点をおき詳述する。

Hydrogen-doped indium oxide (In2O3:H) has recently emerged as an enabling transparent conductive oxide for solar cells, in particular for silicon heterojunction solar cells because its high electron mobility (>100 cm2/(V s)) allows for a simultaneously high electrical conductivity and optical transparency. Here, we report on high-quality In2O3:H prepared by a low-temperature atomic layer deposition (ALD) process and present insights into the doping mechanism and the electron scattering processes that limit the carrier mobility in such films. The process consists of ALD of amorphous In2O3:H at 100 °C and subsequent solid-phase crystallization at 150–200 °C to obtain large-grained polycrystalline In2O3:H films. The changes in optoelectronic properties upon crystallization have been monitored both electrically by Hall measurements and optically by analysis of the Drude response. After crystallization, an excellent carrier mobility of 128 ± 4 cm2/(V s) can be obtained at a carrier density of 1.8 × 1020 cm–3, irrespective of the annealing temperature. Temperature-dependent Hall measurements have revealed that electron scattering is dominated by unavoidable phonon and ionized impurity scattering from singly charged H-donors. Extrinsic defect scattering related to material quality such as grain boundary and neutral impurity scattering was found to be negligible in crystallized films indicating that the carrier mobility is maximized. Furthermore, by comparison of the absolute H-concentration and the carrier density in crystallized films, it is deduced that

In this paper, we provide experimental evidence of the effects of unintentional p-type doping on the performance and the apparent recombination dynamics of bulk-heterojunction solar cells. By supporting these experimental observations with drift-diffusion simulations on two batches of the same efficient polymer-fullerene solar cells with substantially different doping levels and at different thicknesses, we investigate the way the presence of doping affects the interpretation of optoelectronic measurements of recombination and charge transport in organic solar cells. We also present experimental evidence on how unintentional doping can lead to excessively high apparent reaction orders. Our work suggests first that the knowledge of the level of dopants is essential in the studies of recombination dynamics and carrier transport and that unintentional doping levels need to be reduced below approximately 7 × 1015 cm-3 for full optimization around the second interference maximum of highly efficient polymer-fullerene solar cells.

The atomic mass ratio of ca. 2 between deuterium and hydrogen is the highest for any pair of stable isotopes and results in significant and measurable H/D isotope effects in high temperature proton conductors containing these species. This paper discusses H/D isotope effects manifested in O-H/O-D vibration frequencies, the mobility of H+/D+ carriers, the kinetics of the electrochemical oxidation of H2/D2, the solubilities of H2O/D2O and, finally, the spontaneous electromotive force that appears across H2/D2 cells with proton conducting electrolytes. Comparable work on tritium-exchanged materials is also discussed. The results highlight the usefulness of isotope effects in the study of high temperature proton conductors.

This article explores the growth of graphene under low-pressure Ar conditions. Carbon- and silicon-face 4H-SiC samples are subjected to epitaxial graphene growth at 1600 degrees C in vacuum, in 1 mbar argon, or in 10 mbar of argon. High-resolution x-ray scattering is used to characterize all graphene films. On the C-face, specular scans reveal a bimodal distribution of thicknesses that decrease with increasing Ar pressure. Thin and thick regions are approximately 15 and 46 monolayers in C-face graphene grown at high vacuum, 14 and 42 monolayers thick in graphene grown at 1 mbar, and 12 and 32 monolayers thick in graphene grown at 10 mbar. Azimuthal scans confirm in all cases that graphene layers are epitaxial and display expected crystallographic relationships with the underlying SiC substrate. In-plane azimuthal scans show the rotational disorder increases as pressure increases. Peaks in radial scans are asymmetric, suggesting the grain structure has a bimodal distribution of large and small domains. The sample displaying the lowest average Hall mobility (grown at 1 mbar) has the largest population of small crystallites (coherence length on the order of similar to 30 nm). Variations in structure and mobility of C-face graphene are attributed to inadequate control of Si sublimation during growth.

The growing need for large area display for home entertainment and the crossover to digital broadcasting has pushed the active matrix flat panel display industry to thrive over the past few years. The ability to make electronic devices that are transparent to visible and near infrared wavelengths with materials posing a high carrier mobility and high visual transparency is currently being researched. There has been a great interest in amorphous indium gallium zinc oxide (a-IGZO) as the active channel layer due to its promising electrical and photosensitive performance for thin film transistors with a high field-effect mobility, low drain off current and good uniformity that is compatible with the state-of-the-art Gen-8 substrate size. However, as indium resources are becoming scarce and expensive, replacing the a-IGZO TFT with a less expensive material such as gallium tin zinc oxide (GSZO) has shown a potential to have similar electrical behavior. One of the issues of the oxide TFT, in general, is the optical and electrical instability. Hence, we have carried out a systematic and detailed study on the electrical and optical stability of these TFTs as a function of annealing temperature, deposition pressure, film thickness and oxide thickness to gain better insight into the degradation mechanism of these transistors as well as to correlate to the initial performance of the device. The analysis of stability measurements indicated that the post deposition annealing temperature of 350 deg C has the dominant effect on the reduction of the deep and shallow states, thereby making the device more stable. This also explains the superior performance of the initial device. The low temperature annealed device at 140 C appears to be influenced by the deposition pressure. Thus, this work shows that there is considerable room for improvement in both the TFT performance as well as its stability by tailoring the deposition parameters., The original document contains color images.

Organic thin-film transistors (OTFTs) are the enablers of all organic circuitry but are severely limited by the paucity of high carrier mobility semiconductors (especially for electron transport), poor quality of compatible insulators, high power consumption, poor understanding of how critical material interfaces affect carrier injection and transport, limited understanding of charge carrier dynamics and trapping mechanisms, and poor understanding of circuit radiation hardness. In addition, current strategies fo OTFT integration and efficient printing, essential for organic complementary circuits, are an early stage of development. The objective of this program is to develop the understanding necessary to achieve high-performance polymeric and molecular materials enabling high speed electronic circuits. This report summarizes progress towards these goals describes what we have learned in terms of fundamental materials-property-device responses, unique molecular/polymeric materials sets, and process/device platforms to advance the field of organic electronics., The original document contains color images.

This grant was the first to the PI to use first principles quantum mechanics to characterize key atomic-scale elementary processes involved in photocatalysis by novel materials comprised of abundant elements. In particular, we performed computer simulations to evaluate the efficacy of doped and alloyed first-row transition metal oxides for use as catalysts for renewable fuels production. Our work began with extensive testing of methods to calculate properties of interest in photocatalytic production of fuels. These preliminary studies were necessary to establish a quantitatively accurate set of theories to employ when performing photocatalyst modeling, which entails a complicated series of events starting from sunlight absorption to produce electronic excited states (electron-hole pairs), subsequent electron-hole pair separation and transport, followed by redox chemistry at the surface of the catalyst to produce fuels. Properties to be optimized include the material s band gap (which determines the amount of sunlight absorbed), valence and conduction band edge positions (which control whether, e.g., photocatalytic water splitting is thermodynamically allowed), electron-hole pair lifetimes and charge carrier mobilities (which determine whether the charge carriers survive to reach an interface where they can react), and overpotentials for redox reactions at the surfaces of catalysts (which largely control the kinetics of the photoelectrocatalysis). We have examined all of these properties for a number of candidate catalyst materials, and have elucidated important design principles from these studies for future optimization of photocatalysts.

The growth of high-quality organic semiconductors on supporting substrates with minimal disorder is the key requirement for realizing high-performance organic electronics. However, the absence of an epitaxial relation and the presence of disorder make it particularly challenging to grow high-quality organic crystals having few defects and grain boundaries on conventional insulating substrates. Here, we report epitaxial growth of highly ordered, crystalline organic films on van der Waals (vdW) substrates and demonstrate high carrier mobility comparable to those of single-crystal counterparts. High quality rubrene films with large single-crystalline domains were grown on hexagonal boron nitride (h-BN) layers with an in-plane crystallographic registry. Furthermore, using graphene as the vdW electrical contacts, high field-effect mobility (11.5 sq cm V(exp 1) s(exp 1)) was achieved, attributable to an atomically sharp interface with low charge trap density between rubrene and h-BN. The ability to grow high-quality organic/inorganic epitaxial vdW heterostructures, combined with recent progress on large-area growth of layered materials, provides new opportunities for the scalable fabrication of high-performance organic electronic devices. Controlling the interface between organic films and inorganic substrates is of crucial importance for organic electronic applications, because this interface governs the initial nucleation during the growth of molecular films as well as the field-induced charge-carrier transport. In particular, charge transport is affected greatly by interfacial disorder, such as surface roughness and charge traps, as well as structural disorder of the molecular materials at the interface., Pub. in Advanced Materials, p1-6, 2014.

Our research activities during the last eight years from 2006 to 2013, with the grant supports from Nano National programs, NSC, Taiwan and AOARD, have been pushing the material limits of III-V InGaAs and GaN metal-oxide-semiconductor (MOS) systems using high-k dielectrics. In the third year of the funding, with the capabilities of atomic-scale probing and manipulating the high-k oxides/semiconductors interfaces, we have established the correlations between electronic structures and electrical properties essential to understand the Fermi level pinning/unpinning mechanism of the interfaces between metal/oxide and oxide/semiconductor. we have successfully continuously kept our world-leading expertise of high-k dielectric growth on InGaAs by achieving world record drain current of 1.8 mA/micro m, transconductance of 0.80 mS/micro m, and low sub-thresholds in a self-aligned inversion-channel InGaAs metal-oxide-semiconductor field-effect- transistor of 1 micro m gate length. In-situ ultrahigh vacuum deposited Y2O3 and HfO2 and atomic-layer-deposited (ALD) Al2O3 and HfO2 2-3 mono-layers thick on freshly grown In0.53Ga0.47As, with an Al2O3 cap, were employed as a gate dielectric., Prepared in collaboration with the Department of Physics, National Tsing Hua University, Hsinchu, Taiwan, Republic of China.

We applied the master equation method to investigate the anisotropic transport property of the 4,4'-bis((E)-2-(naphthalen-2-yl)vinyl)-1,1'-biphenyl molecular crystal based on first-principles calculation. It is found that the hole mobility has the largest value along the [100] direction, while electrons have the best transport property along the [010] direction. The anisotropic transport property was found to have close relationship with the charge transfer integral which is determined by the molecular stacking network in the crystals as well as the intermolecular frontier orbital overlap. In addition, the effect of the charge carrier density and the electronic field on the charge transport was also studied, and little effect was found except that the density is larger than 0.01 and the electronic field is increased to 1.0 x 106 V/cm. The kinetic Monte Carlo simulation method has also been used to study the anisotropic charge transport property, and consistent results were obtained as with the master equation method., QC 20140912

The performance of bulk heterojunction polymer solar cells is profoundly influenced by the spatial arrangements of microstructure at various length scales in its photo-active layer, referred to as morphology. Due to their complex chemical structures, polymers usually exhibits low crystallinity and carrier mobility, leading to a limited thickness ~100 nm of the active layer for a typical polymer solar cell. Such thin films are incompatible with the prevailing large-area coating techniques, thus increasing the difficulty to realize the high-throughput production of polymer-based photovoltaics in industry. On the other hand, for most high-performance low-band-gap polymers, during their film-casting process, processing solvent additives are usually essential for morphology optimization, which help boost device efficiency. However, most commonly-used solvent additives such as 1, 8-Diiodooctane (DIO), are disturbingly reactive to oxygen or water in air, leading to deteriorated performance of devices made under the ambient environment. Therefore, fabrication processes involving DIO have to be limited to an air-free environment, which is quite unfavorable for large-area fabrication techniques, as majority of them are carried on under the ambient environment. Therefore, an efficient air-stable solvent additive would be greatly appreciated in terms of OPV industrialization. As a result, in order to achieve thick active layers as well as to find an air-stable alternative additive for industrial applications, a thorough and systematic study on morphology is necessitated.First, via rational modification of polymer chemical structure(fine-tuning on side chains), new polymers with enhanced structure order (e.g., crystallite size increases from 35 � to 53 �) and higher hole mobility (from ~10-5 to ~10-4 cm2/(V*s)) are obtained, enabling thicker optimum active layers ~200 nm with a larger thickness tolerance up to ~350 nm for the corresponding bulk heterojunction devices. This r