Insulation Resistance Degradation in Ni-BaTiO3 Multilayer Ceramic Capacitors

NASA Technical Reports Server (NTRS)

Liu, Donhang David

2015-01-01

Insulation resistance (IR) degradation in NiBaTiO3 multilayer ceramic capacitors has been characterized by the measurement of both time to failure (TTF) and direct current leakage current as a function of stress time under highly accelerated life test conditions. The measured leakage current time dependence data fit well to an exponential form, and a characteristic growth time tau (sub SD) can be determined. A greater value of tau (sub SD) represents a slower IR degradation process. Oxygen vacancy migration and localization at the grain boundary region results in the reduction of the Schottky barrier height and has been found to be the main reason for IR degradation in NiBaTiO3 capacitors. The reduction of barrier height as a function oftime follows an exponential relation of phi (t ) = phi (0) e (exp -2Kt), where 13 the degradation rate constant K Koe (Ek/kT) is inversely proportional to the mean TTF (MTTF) and can be determined using an Arrhenius plot. For oxygen vacancy electromigration, a lower barrier height phi (0) will favor a slow IR degradation process, but a lower phi (0) will also promote electronic carrier conduction across the barrier and decrease the IR. As a result, a moderate barrier height phi (0) (and therefore a moderate IR value) with a longer MTTF (smaller degradation rate constant K) will result in a minimized IR degradation process and the most improved reliability in NiBaTiO3 multilayer ceramic capacitors.

Schottky barrier height of Ni to β-(AlxGa1-x)2O3 with different compositions grown by plasma-assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Ahmadi, Elaheh; Oshima, Yuichi; Wu, Feng; Speck, James S.

2017-03-01

Coherent β-(AlxGa1-x)2O3 films (x = 0, 0.038, 0.084, 0.164) were grown successfully on a Sn-doped β-Ga2O3 (010) substrate using plasma-assisted molecular beam epitaxy. Atom probe tomography, transmission electron microscopy, and high resolution x-ray diffraction were used to verify the alloy composition and high quality of the films. Schottky diodes were then fabricated using Ni as the Schottky metal. Capacitance-voltage measurements revealed a very low (<7 × 1015 cm-3) free charge density in the nominally undoped films. The barrier height and ideality factor were estimated by current-voltage (I-V) measurements performed at temperatures varying from 300 K to 500 K on the Schottky diodes. These measurements revealed that the apparent Schottky barrier height could have similar values for different compositions of β-(AlxGa1-x)2O3. We believe this is attributed to the lateral fluctuation in the alloy’s composition. This results in a lateral variation in the barrier height. Therefore, the average Schottky barrier height extracted from I-V measurements could be similar for β-(AlxGa1-x)2O3 films with different compositions.

Characterization of the inhomogeneous barrier distribution in a Pt/(100)β-Ga2O3 Schottky diode via its temperature-dependent electrical properties

NASA Astrophysics Data System (ADS)

Jian, Guangzhong; He, Qiming; Mu, Wenxiang; Fu, Bo; Dong, Hang; Qin, Yuan; Zhang, Ying; Xue, Huiwen; Long, Shibing; Jia, Zhitai; Lv, Hangbing; Liu, Qi; Tao, Xutang; Liu, Ming

2018-01-01

β-Ga2O3 is an ultra-wide bandgap semiconductor with applications in power electronic devices. Revealing the transport characteristics of β-Ga2O3 devices at various temperatures is important for improving device performance and reliability. In this study, we fabricated a Pt/β-Ga2O3 Schottky barrier diode with good performance characteristics, such as a low ON-resistance, high forward current, and a large rectification ratio. Its temperature-dependent current-voltage and capacitance-voltage characteristics were measured at various temperatures. The characteristic diode parameters were derived using thermionic emission theory. The ideality factor n was found to decrease from 2.57 to 1.16 while the zero-bias barrier height Φb0 increased from 0.47 V to 1.00 V when the temperature was increased from 125 K to 350 K. This was explained by the Gaussian distribution of barrier height inhomogeneity. The mean barrier height Φ ¯ b0 = 1.27 V and zero-bias standard deviation σ0 = 0.13 V were obtained. A modified Richardson plot gave a Richardson constant A* of 36.02 A.cm-2.K-2, which is close to the theoretical value of 41.11 A.cm-2.K-2. The differences between the barrier heights determined using the capacitance-voltage and current-voltage curves were also in line with the Gaussian distribution of barrier height inhomogeneity.

Negative tunnel magnetoresistance and spin transport in ferromagnetic graphene junctions.

PubMed

Zou, Jianfei; Jin, Guojun; Ma, Yu-Qiang

2009-03-25

We study the tunnel magnetoresistance (TMR) and spin transport in ferromagnetic graphene junctions composed of ferromagnetic graphene (FG) and normal graphene (NG) layers. It is found that the TMR in the FG/NG/FG junction oscillates from positive to negative values with respect to the chemical potential adjusted by the gate voltage in the barrier region when the Fermi level is low enough. Particularly, the conventionally defined TMR in the FG/FG/FG junction oscillates periodically from a positive to negative value with increasing the barrier height at any Fermi level. The spin polarization of the current through the FG/FG/FG junction also has an oscillating behavior with increasing barrier height, whose oscillating amplitude can be modulated by the exchange splitting in the ferromagnetic graphene.

Temperature dependent electrical characteristics of Zn/ZnSe/n-GaAs/In structure

NASA Astrophysics Data System (ADS)

Sağlam, M.; Güzeldir, B.

2016-04-01

We have reported a study of the I-V characteristics of Zn/ZnSe/n-GaAs/In sandwich structure in a wide temperature range of 80-300 K by a step of 20 K, which are prepared by Successive Ionic Layer Adsorption and Reaction (SILAR) method. The main electrical parameters, such as ideality factor and zero-bias barrier height determined from the forward bias I-V characteristics were found strongly depend on temperature and when the increased, the n decreased with increasing temperature. The ideality factor and barrier height values as a function of the sample temperature have been attributed to the presence of the lateral inhomogeneities of the barrier height. Furthermore, the series resistance have been calculated from the I-V measurements as a function of temperature dependent.

Fusion barrier characteristics of actinides

NASA Astrophysics Data System (ADS)

Manjunatha, H. C.; Sridhar, K. N.

2018-03-01

We have studied fusion barrier characteristics of actinide compound nuclei with atomic number range 89 ≤ Z ≤ 103 for all projectile target combinations. After the calculation of fusion barrier heights and positions, we have searched for their parameterization. We have achieved the empirical formula for fusion barrier heights (VB), positions (RB), curvature of the inverted parabola (ħω) of actinide compound nuclei with atomic number range 89 ≤ Z ≤ 103 for all projectile target combinations (6

Canonical Schottky barrier heights of transition metal dichalcogenide monolayers in contact with a metal

NASA Astrophysics Data System (ADS)

Szcześniak, Dominik; Hoehn, Ross D.; Kais, Sabre

2018-05-01

The transition metal dichalcogenide (M X2 , where M =Mo , W and X =S , Se, Te) monolayers are of high interest for semiconducting applications at the nanoscale level; this interest is due to both their direct band gaps and high charge mobilities. In this regard, an in-depth understating of the related Schottky barrier heights, associated with the incorporation of M X2 sheets into novel low-dimensional metal-semiconductor junctions, is of crucial importance. Herein, we generate and provide analysis of the Schottky barrier heights behavior to account for the metal-induced gap states concept as its explanation. In particular, the present investigations concentrate on the estimation of the charge neutrality levels directly by employing the primary theoretical model, i.e., the cell-averaged Green's function formalism combined with the complex band structure technique. The results presented herein place charge neutrality levels in the vicinity of the midgap; this is in agreement with previous reports and analogous to the behavior of three-dimensional semiconductors. The calculated canonical Schottky barrier heights are also found to be in agreement with other computational and experimental values in cases where the difference between electronegativities of the semiconductor and metal contact is small. Moreover, the influence of the spin-orbit effects is herein considered and supports that Schottky barrier heights have metal-induced gap state-derived character, regardless whether spin-orbit coupling interactions are considered. The results presented within this report constitute a direct and vital verification of the importance of metal-induced gap states in explaining the behavior of observed Schottky barrier heights at M X2 -metal junctions.

Theoretical studies of the potential surface for the F - H2 greater than HF + H reaction

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.; Walch, Stephen, P.; Langhoff, Stephen R.; Taylor, Peter R.; Jaffe, Richard L.

1987-01-01

The F + H2 yields HF + H potential energy hypersurface was studied in the saddle point and entrance channel regions. Using a large (5s 5p 3d 2f 1g/4s 3p 2d) atomic natural orbital basis set, a classical barrier height of 1.86 kcal/mole was obtained at the CASSCF/multireference CI level (MRCI) after correcting for basis set superposition error and including a Davidson correction (+Q) for higher excitations. Based upon an analysis of the computed results, the true classical barrier is estimated to be about 1.4 kcal/mole. The location of the bottleneck on the lowest vibrationally adiabatic potential curve was also computed and the translational energy threshold determined from a one-dimensional tunneling calculation. Using the difference between the calculated and experimental threshold to adjust the classical barrier height on the computed surface yields a classical barrier in the range of 1.0 to 1.5 kcal/mole. Combining the results of the direct estimates of the classical barrier height with the empirical values obtained from the approximation calculations of the dynamical threshold, it is predicted that the true classical barrier height is 1.4 + or - 0.4 kcal/mole. Arguments are presented in favor of including the relatively large +Q correction obtained when nine electrons are correlated at the CASSCF/MRCI level.

Using models to interpret the impact of roadside barriers on near-road air quality

NASA Astrophysics Data System (ADS)

Amini, Seyedmorteza; Ahangar, Faraz Enayati; Schulte, Nico; Venkatram, Akula

2016-08-01

The question this paper addresses is whether semi-empirical dispersion models based on data from controlled wind tunnel and tracer experiments can describe data collected downwind of a sound barrier next to a real-world urban highway. Both models are based on the mixed wake model described in Schulte et al. (2014). The first neglects the effects of stability on dispersion, and the second accounts for reduced entrainment into the wake of the barrier under unstable conditions. The models were evaluated with data collected downwind of a kilometer-long barrier next to the I-215 freeway running next to the University of California campus in Riverside. The data included measurements of 1) ultrafine particle (UFP) concentrations at several distances from the barrier, 2) micrometeorological variables upwind and downwind of the barrier, and 3) traffic flow separated by automobiles and trucks. Because the emission factor for UFP is highly uncertain, we treated it as a model parameter whose value is obtained by fitting model estimates to observations of UFP concentrations measured at distances where the barrier impact is not dominant. Both models provide adequate descriptions of both the magnitude and the spatial variation of observed concentrations. The good performance of the models reinforces the conclusion from Schulte et al. (2014) that the presence of the barrier is equivalent to shifting the line sources on the road upwind by a distance of about HU/u∗ where H is the barrier height, U is the wind velocity at half of the barrier height, and u∗ is the friction velocity. The models predict that a 4 m barrier results in a 35% reduction in average concentration within 40 m (10 times the barrier height) of the barrier, relative to the no-barrier site. This concentration reduction is 55% if the barrier height is doubled.

The Influence of High-Energy Electrons Irradiation on Surface of n-GaP and on Au/n-GaP/Al Schottky Barrier Diode

NASA Astrophysics Data System (ADS)

Demir, K. Çinar; Kurudirek, S. V.; Oz, S.; Biber, M.; Aydoğan, Ş.; Şahin, Y.; Coşkun, C.

We fabricated 25 Au/n-GaP/Al Schottky devices and investigated the influence of high electron irradiation, which has 12MeV on the devices, at room temperature. The X-ray diffraction patterns, scanning electron microscopic images and Raman spectra of a gallium phosphide (GaP) semiconductor before and after electron irradiation have been analyzed. Furthermore, some electrical measurements of the devices were carried out through the current-voltage (I-V) and capacitance-voltage (C-V) measurements. From the I-V characteristics, experimental ideality factor n and barrier height Φ values of these Schottky diodes have been determined before and after irradiation, respectively. The results have also been analyzed statically, and a gauss distribution has been obtained. The built-in potential Vbi, barrier height Φ, Fermi level EF and donor concentration Nd values have been determined from the reverse bias C-V and C-2-V curves of Au/n-GaP/Al Schottky barrier diodes at 100kHz before and after 12MeV electron irradiation. Furthermore, we obtained the series resistance values of Au/n-GaP/Al Schottky barrier diodes with the help of different methods. Experimental results confirmed that the electrical characterization of the device changed with the electron irradiation.

Monolayer graphene/SiC Schottky barrier diodes with improved barrier height uniformity as a sensing platform for the detection of heavy metals

PubMed Central

Eriksson, Jens; Khranovskyy, Volodymyr; Iakimov, Tihomir; Lloyd Spetz, Anita; Yakimova, Rositsa

2016-01-01

A vertical diode structure comprising homogeneous monolayer epitaxial graphene on silicon carbide is fabricated by thermal decomposition of a Si-face 4H-SiC wafer in argon atmosphere. Current–voltage characteristics of the graphene/SiC Schottky junction were analyzed by applying the thermionic-emission theory. Extracted values of the Schottky barrier height and the ideality factor are found to be 0.4879 ± 0.013 eV and 1.01803 ± 0.0049, respectively. Deviations of these parameters from average values are smaller than those of previously observed literature data, thereby implying uniformity of the Schottky barrier height over the whole diode area, a stable rectifying behaviour and a good quality of ohmic palladium–graphene contacts. Keeping in mind the strong sensitivity of graphene to analytes we propose the possibility to use the graphene/SiC Schottky diode as a sensing platform for the recognition of toxic heavy metals. Using density functional theory (DFT) calculations we gain insight into the nature of the interaction of cadmium, mercury and lead with graphene as well as estimate the work function and the Schottky barrier height of the graphene/SiC structure before and after applying heavy metals to the sensing material. A shift of the I–V characteristics of the graphene/SiC-based sensor has been proposed as an indicator of presence of the heavy metals. Since the calculations suggested the strongest charge transfer between Pb and graphene, the proposed sensing platform was characterized by good selectivity towards lead atoms and slight interferences from cadmium and mercury. The dependence of the sensitivity parameters on the concentration of Cd, Hg and Pb is studied and discussed. PMID:28144530

Monolayer graphene/SiC Schottky barrier diodes with improved barrier height uniformity as a sensing platform for the detection of heavy metals.

PubMed

Shtepliuk, Ivan; Eriksson, Jens; Khranovskyy, Volodymyr; Iakimov, Tihomir; Lloyd Spetz, Anita; Yakimova, Rositsa

2016-01-01

A vertical diode structure comprising homogeneous monolayer epitaxial graphene on silicon carbide is fabricated by thermal decomposition of a Si-face 4H-SiC wafer in argon atmosphere. Current-voltage characteristics of the graphene/SiC Schottky junction were analyzed by applying the thermionic-emission theory. Extracted values of the Schottky barrier height and the ideality factor are found to be 0.4879 ± 0.013 eV and 1.01803 ± 0.0049, respectively. Deviations of these parameters from average values are smaller than those of previously observed literature data, thereby implying uniformity of the Schottky barrier height over the whole diode area, a stable rectifying behaviour and a good quality of ohmic palladium-graphene contacts. Keeping in mind the strong sensitivity of graphene to analytes we propose the possibility to use the graphene/SiC Schottky diode as a sensing platform for the recognition of toxic heavy metals. Using density functional theory (DFT) calculations we gain insight into the nature of the interaction of cadmium, mercury and lead with graphene as well as estimate the work function and the Schottky barrier height of the graphene/SiC structure before and after applying heavy metals to the sensing material. A shift of the I - V characteristics of the graphene/SiC-based sensor has been proposed as an indicator of presence of the heavy metals. Since the calculations suggested the strongest charge transfer between Pb and graphene, the proposed sensing platform was characterized by good selectivity towards lead atoms and slight interferences from cadmium and mercury. The dependence of the sensitivity parameters on the concentration of Cd, Hg and Pb is studied and discussed.

Stability diagrams for the surface patterns of GaN(0001bar) as a function of Schwoebel barrier height

NASA Astrophysics Data System (ADS)

Krzyżewski, Filip; Załuska-Kotur, Magdalena A.

2017-01-01

Height and type of Schwoebel barriers (direct or inverse) decides about the character of the surface instability. Different surface morphologies are presented. Step bunches, double steps, meanders, mounds and irregular patterns emerge at the surface as a result of step (Schwoebel) barriers at some temperature or miscut values. The study was carried out on the two-component kinetic Monte Carlo (kMC) model of GaN(0001bar) surface grown in nitrogen rich conditions. Diffusion of gallium adatoms over N-polar surface is slow and nitrogen adatoms are almost immobile. We show that in such conditions surfaces remain smooth when gallium adatoms diffuse in the presence of low inverse Schwoebel barrier. It is illustrated by adequate stability diagrams for surface morphologies.

Thermoelectric properties of nano-granular indium-tin-oxide within modified electron filtering model with chemisorption-type potential barriers

NASA Astrophysics Data System (ADS)

Brinzari, V.; Nika, D. L.; Damaskin, I.; Cho, B. K.; Korotcenkov, G.

2016-07-01

In this work, an approach to the numerical study of the thermoelectric parameters of nanoscale indium tin oxide (ITO, Sn content<10 at%) based on an electron filtering model (EFM) was developed. Potential barriers at grain boundaries were assumed to be responsible for a filtering effect. In the case of the dominant inelastic scattering of electrons, the maximal distance between potential barriers was limited in this modified model. The algorithm for such characteristic length calculation was proposed, and its value was evaluated for ITO. In addition, the contributions of different scattering mechanisms (SMs) in electron transport were examined. It was confirmed that in bulk ITO, the scattering on polar optical phonons (POPs) and ionized impurities dominates, limiting electron transport. In the framework of the filtering model, the basic thermoelectric parameters (i.e., electrical conductivity, mobility, Seebeck coefficient, and power factor (PF)) were calculated for ITO in the temperature range of 100-500 °C as a function of potential barrier height. The results demonstrated a sufficient rise of the Seebeck coefficient with an increase in barrier height and specific behavior of PF. It was found that PF is very sensitive to barrier height, and at its optimal value for granular ITO, it may exceed the PF for bulk ITO by 3-5 times. The PF maximum was achieved by band bending, slightly exceeding Fermi energy. The nature of surface potential barriers in nano-granular ITO with specific grains is due to the oxygen chemisorption effect, and this can be observed despite of the degeneracy of the conduction band (CB). This hypothesis and the corresponding calculations are in good agreement with recent experimental studies [Brinzari et al. Thin Solid Films 552 (2014) 225].

Spin-dependent delay time in ferromagnet/insulator/ferromagnet heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, ZhengWei; Zheng Shi, De; Lv, HouXiang

2014-07-07

We study theoretically spin-dependent group delay and dwell time in ferromagnet/insulator/ferromagnet (FM/I/FM) heterostructure. The results indicate that, when the electrons with different spin orientations tunnel through the FM/I/FM junction, the spin-up process and the spin-down process are separated on the time scales. As the self-interference delay has the spin-dependent features, the variations of spin-dependent dwell-time and spin-dependent group-delay time with the structure parameters appear different features, especially, in low incident energy range. These different features show up as that the group delay times for the spin-up electrons are always longer than those for spin-down electrons when the barrier height ormore » incident energy increase. In contrast, the dwell times for the spin-up electrons are longer (shorter) than those for spin-down electrons when the barrier heights (the incident energy) are under a certain value. When the barrier heights (the incident energy) exceed a certain value, the dwell times for the spin-up electrons turn out to be shorter (longer) than those for spin-down electrons. In addition, the group delay time and the dwell time for spin-up and down electrons also relies on the comparative direction of magnetization in two FM layers and tends to saturation with the thickness of the barrier.« less

Growth and interface properties of Au Schottky contact on ZnO grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Asghar, M.; Mahmood, K.; Malik, Faisal; Hasan, M. A.

2013-06-01

In this paper, we have discussed the growth of ZnO by molecular beam epitaxy (MBE) and interface properties of Au Schottky contacts on grown sample. After the verification of structure and surface properties by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM), respectively, Au metal contact was fabricated by e-beam evaporation to study contact properties. The high value of ideality factor (2.15) and barrier height (0.61 eV) at room temperature obtained by current-voltage (I-V) characteristics suggested the presence of interface states between metal and semiconductor. To confirm this observation we carried out frequency dependent capacitance-voltage (C-V) and conductance-voltage (G-V) demonstrated that the capacitance of diode decreased with increasing frequency. The reason of this behavior is related with density of interface states, series resistance and image force lowering. The C-2-V plot drawn to calculate the carrier concentration and barrier height with values 1.4×1016 cm-3 and 0.92 eV respectively. Again, high value of barrier height obtained from C-V as compared to the value obtained from I-V measurements revealed the presence of interface states. The density of these interface states (Dit) was calculated by well known Hill-Coleman method. The calculated value of Dit at 1 MHz frequency was 2×1012 eV-1 cm-2. The plot between interface states and frequency was also drawn which demonstrated that density of interface states had inverse proportion with measuring frequency.

Process for preparing schottky diode contacts with predetermined barrier heights

DOEpatents

Chang, Y. Austin; Jan, Chia-Hong; Chen, Chia-Ping

1996-01-01

A process is provided for producing a Schottky diode having a preselected barrier height .phi..sub.Bn. The substrate is preferably n-GaAs, the metallic contact is derived from a starting alloy of the Formula [.SIGMA.M.sub..delta. ](Al.sub.x Ga.sub.1-x) wherein: .SIGMA.M is a moiety which consists of at least one M, and when more than one M is present, each M is different, M is a Group VIII metal selected from the group consisting of nickel, cobalt, ruthenium, rhodium, indium and platinum, .delta. is a stoichiometric coefficient whose total value in any given .SIGMA.M moiety is 1, and x is a positive number between 0 and 1 (that is, x ranges from greater than 0 to less than 1). Also, the starting alloy is capable of forming with the substrate a two phase equilibrium reciprocal system of the binary alloy mixture [.SIGMA.M.sub..delta. ]Ga-[.SIGMA.M.sub..delta. ]Al-AlAs-GaAs. When members of an alloy subclass within this Formula are each preliminarily correlated with the barrier height .phi..sub.Bn of a contact producable therewith, then Schottky diodes of predetermined barrier heights are producable by sputtering and annealing. Further provided are the product Schottky diodes that are produced according to this process.

Barrier height enhancement of metal/semiconductor contact by an enzyme biofilm interlayer

NASA Astrophysics Data System (ADS)

Ocak, Yusuf Selim; Gul Guven, Reyhan; Tombak, Ahmet; Kilicoglu, Tahsin; Guven, Kemal; Dogru, Mehmet

2013-06-01

A metal/interlayer/semiconductor (Al/enzyme/p-Si) MIS device was fabricated using α-amylase enzyme as a thin biofilm interlayer. It was observed that the device showed an excellent rectifying behavior and the barrier height value of 0.78 eV for Al/α-amylase/p-Si was meaningfully larger than the one of 0.58 eV for conventional Al/p-Si metal/semiconductor (MS) contact. Enhancement of the interfacial potential barrier of Al/p-Si MS diode was realized using enzyme interlayer by influencing the space charge region of Si semiconductor. The electrical properties of the structure were executed by the help of current-voltage and capacitance-voltage measurements. The photovoltaic properties of the structure were executed under a solar simulator with AM1.5 global filter between 40 and 100 mW/cm2 illumination conditions. It was also reported that the α-amylase enzyme produced from Bacillus licheniformis had a 3.65 eV band gap value obtained from optical method.

A three-dimensional semianalytical model of hydraulic fracture growth through weak barriers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luiskutty, C.T.; Tomutes, L.; Palmer, I.D.

1989-08-01

The goal of this research was to develop a fracture model for length/height ratio {le}4 that includes 2D flow (and a line source corresponding to the perforated interval) but makes approximations that allow a semianalytical solution, with large computer-time savings over the fully numerical mode. The height, maximum width, and pressure at the wellbore in this semianalytical model are calculated and compared with the results of the fully three-dimensional (3D) model. There is reasonable agreement in all parameters, the maximum discrepancy being 24%. Comparisons of fracture volume and leakoff volume also show reasonable agreement in volume and fluid efficiencies. Themore » values of length/height ratio, in the four cases in which agreement is found, vary from 1.5 to 3.7. The model offers a useful first-order (or screening) calculation of fracture-height growth through weak barriers (e.g., low stress contrasts). When coupled with the model developed for highly elongated fractures of length/height ratio {ge}4, which are also found to be in basic agreement with the fully numerical model, this new model provides the capability for approximating fracture-height growth through barriers for vertical fracture shapes that vary from penny to highly elongated. The computer time required is estimated to be less than the time required for the fully numerical model by a factor of 10 or more.« less

CURRENT-VOLTAGE CHARACTERISTICS OF THERMALLY ANNEALED Ni/n-GaAs SCHOTTKY CONTACTS

NASA Astrophysics Data System (ADS)

Yildirim, Nezir; Turut, Abdulmecit; Dogan, Hulya

The Schottky barrier type Ni/n-GaAs contacts fabricated by us were thermally annealed at 600∘C and 700∘C for 1min. The apparent barrier height Φap and ideality factor of the diodes were calculated from the forward bias current-voltage characteristic in 60-320K range. The Φap values for the nonannealed and 600∘C and 700∘C annealed diodes were obtained as 0.80, 0.81 and 0.67eV at 300K, respectively. Thus, it has been concluded that the reduced barrier due to the thermal annealing at 700∘C promises some device applications. The current preferentially flows through the lowest barrier height (BH) with the temperature due to the BH inhomogeneities. Therefore, it was seen that the Φap versus (2kT)‑1 plots for the nonannealed and annealed diodes showed the linear behavior according to Gaussian distributions.

Current-voltage characteristics of the semiconductor nanowires under the metal-semiconductor-metal structure

NASA Astrophysics Data System (ADS)

Wen, Jing; Zhang, Xitian; Gao, Hong; Wang, Mingjiao

2013-12-01

We present a method to calculate the I-V characteristics of semiconductor nanowires under the metal-semiconductor-metal (MSM) structure. The carrier concentration as an important parameter is introduced into the expression of the current. The subband structure of the nanowire has been considered for associating it with the position of the Fermi level and circumventing the uncertainties of the contact areas in the contacts. The tunneling and thermionic emission currents in the two Schottky barriers at the two metal-semiconductor contacts are discussed. We find that the two barriers have different influences on the I-V characteristics of the MSM structure, one of which under the forward bias plays the role of threshold voltage if its barrier height is large and the applied voltage is small, and the other under the reverse bias controls the shapes of I-V curves. Our calculations show that the shapes of the I-V curves for the MSM structure are mainly determined by the barrier heights of the contacts and the carrier concentration. The nearly identical I-V characteristics can be obtained by using different values of the barrier heights and carrier concentration, which means that the contact type conversion can be ascribed not only to the changes of the barrier heights but also that of the carrier concentration. We also discuss the mechanisms of the ohmic-Schottky conversions and clarify the ambiguity in the literature. The possibility about the variation of the carrier concentration under the applied fields has been confirmed by experimental results.

Detection of alpha particles using DNA/Al Schottky junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al-Ta'ii, Hassan Maktuff Jaber, E-mail: hassankirkukly@gmail.com, E-mail: vengadeshp@um.edu.my; Department of Physics, Faculty of Science, University of Al-Muthana, Al-Muthana 66001; Periasamy, Vengadesh, E-mail: hassankirkukly@gmail.com, E-mail: vengadeshp@um.edu.my

2015-09-21

Deoxyribonucleic acid or DNA can be utilized in an organic-metallic rectifying structure to detect radiation, especially alpha particles. This has become much more important in recent years due to crucial environmental detection needs in both peace and war. In this work, we fabricated an aluminum (Al)/DNA/Al structure and generated current–voltage characteristics upon exposure to alpha radiation. Two models were utilized to investigate these current profiles; the standard conventional thermionic emission model and Cheung and Cheung's method. Using these models, the barrier height, Richardson constant, ideality factor and series resistance of the metal-DNA-metal structure were analyzed in real time. The barriermore » height, Φ value calculated using the conventional method for non-radiated structure was 0.7149 eV, increasing to 0.7367 eV after 4 min of radiation. Barrier height values were observed to increase after 20, 30 and 40 min of radiation, except for 6, 8, and 10 min, which registered a decrease of about 0.67 eV. This was in comparison using Cheung and Cheung's method, which registered 0.6983 eV and 0.7528 eV for the non-radiated and 2 min of radiation, respectively. The barrier height values, meanwhile, were observed to decrease after 4 (0.61 eV) to 40 min (0.6945 eV). The study shows that conventional thermionic emission model could be practically utilized for estimating the diode parameters including the effect of series resistance. These changes in the electronic properties of the Al/DNA/Al junctions could therefore be utilized in the manufacture of sensitive alpha particle sensors.« less

Solitary wave runup and force on a vertical barrier

NASA Astrophysics Data System (ADS)

Liu, Philip L.-F.; Al-Banaa, Khaled

2004-04-01

In this paper we investigate the interaction between a solitary wave and a thin vertical barrier. A set of laboratory experiments was performed with different values of incident wave height to water depth ratio, H/h, and the draught of the barrier to water depth ratio, D/h. While wave gauges were used to measure the reflected and transmitted waves, pressure transducers were installed on both sides of the barrier, enabling the calculation of wave force. The particle image velocimetry (PIV) technique is also employed to measure the velocity field in the vicinity of the barrier. A numerical model, based on the Reynolds-averaged Navier Stokes (RANS) equations and the k - epsilon turbulence closure model, was first checked with experimental data and then employed to obtain additional results for the range of parameters where the laboratory experiments were not performed. Using both experimental data and numerical results, formulae for the maximum runup height, and the maximum wave force are derived in terms of H/h and D/h.

Electrical characteristics of multilayer MoS2 FET's with MoS2/graphene heterojunction contacts.

PubMed

Kwak, Joon Young; Hwang, Jeonghyun; Calderon, Brian; Alsalman, Hussain; Munoz, Nini; Schutter, Brian; Spencer, Michael G

2014-08-13

The electrical properties of multilayer MoS2/graphene heterojunction transistors are investigated. Temperature-dependent I-V measurements indicate the concentration of unintentional donors in exfoliated MoS2 to be 3.57 × 10(11) cm(-2), while the ionized donor concentration is determined as 3.61 × 10(10) cm(-2). The temperature-dependent measurements also reveal two dominant donor levels, one at 0.27 eV below the conduction band and another located at 0.05 eV below the conduction band. The I-V characteristics are asymmetric with drain bias voltage and dependent on the junction used for the source or drain contact. I-V characteristics of the device are consistent with a long channel one-dimensional field-effect transistor model with Schottky contact. Utilizing devices, which have both graphene/MoS2 and Ti/MoS2 contacts, the Schottky barrier heights of both interfaces are measured. The charge transport mechanism in both junctions was determined to be either thermionic-field emission or field emission depending on bias voltage and temperature. On the basis of a thermionic field emission model, the barrier height at the graphene/MoS2 interface was determined to be 0.23 eV, while the barrier height at the Ti/MoS2 interface was 0.40 eV. The value of Ti/MoS2 barrier is higher than previously reported values, which did not include the effects of thermionic field emission.

Effect of an InxGa1-xAs-GaAs blocking heterocathode metal contact on the GaAs TED operation

NASA Astrophysics Data System (ADS)

Arkusha, Yu. V.; Prokhorov, E. D.; Storozhenko, I. P.

2004-09-01

The frequency dependence of the generation efficiency of an mm- -nn:In:InxGaGa1-1-xAs- As-nn:GaAs-:GaAs-nn++:GaAs TED with the 2.5-mm long active region is calculated. The optimum values - which yield the diode maximum generation efficiency - for the :GaAs TED with the 2.5-mm long active region is calculated. The optimum values - which yield the diode maximum generation efficiency - for the nn:In:InxGaGa1-1-xAs cathode length, the cathode concentration of ionized impurities, and the height of the potential barrier on metal contact are determined.As cathode length, the cathode concentration of ionized impurities, and the height of the potential barrier on metal contact are determined.

Analysis of electronic parameters and frequency-dependent properties of Au/NiO/ n-GaN heterojunctions

NASA Astrophysics Data System (ADS)

Reddy, Varra Niteesh; Padma, R.; Gunasekhar, K. R.

2018-01-01

The electrical and frequency-dependent properties of ten Au/NiO/ n-GaN heterojunctions fabricated with similar conditions are assessed by I-V, C-V, and G-V measurement methods. In addition, C-f and G-f measurements are conducted in the frequency range of 1 kHz-1 MHz. The electronic parameters are changed from junction to junction even if they are fabricated in the similar way. The calculated barrier height and ideality factor values are fitted by the Gaussian distribution function. Statistical analysis of the data provides the mean barrier height and ideality factor values of 0.84 eV and 2.70 for the heterojunction. Besides, the mean barrier height ( V b), donor concentration ( N d), space charge layer width ( W D), and Fermi level ( E F) are determined from the C-V data and the corresponding values are 1.30 eV, 2.00 × 1017 cm-3, 8.222 × 10-6 cm, and 0.018 eV, respectively. The interface state density ( N SS) and relaxation time (τ) are assessed from C-f and G-f measurements. Moreover, the dielectric constant ( ɛ'), dielectric loss ( ɛ″), tangent loss (tan δ), and electrical conductivity ( σ ac) are determined from C-f and G-f data in the frequency range of 1 kHz-1 MHz with various biases (0.1-0.6 V). ɛ' and ɛ″ are decreased with increasing frequency.

Spin-Polarization in Quasi-Magnetic Tunnel Junctions

NASA Astrophysics Data System (ADS)

Xie, Zheng-Wei; Li, Ling

2017-05-01

Spin polarization in ferromagnetic metal/insulator/spin-filter barrier/nonmagnetic metal, referred to as quasi-magnetic tunnel junctions, is studied within the free-electron model. Our results show that large positive or negative spin-polarization can be obtained at high bias in quasi-magnetic tunnel junctions, and within large bias variation regions, the degree of spin-polarization can be linearly tuned by bias. These linear variation regions of spin-polarization with bias are influenced by the barrier thicknesses, barrier heights and molecular fields in the spin-filter (SF) layer. Among them, the variations of thickness and heights of the insulating and SF barrier layers have influence on the value of spin-polarization and the linear variation regions of spin-polarization with bias. However, the variations of molecular field in the SF layer only have influence on the values of the spin-polarization and the influences on the linear variation regions of spin-polarization with bias are slight. Supported by the Key Natural Science Fund of Sichuan Province Education Department under Grant Nos 13ZA0149 and 16ZA0047, and the Construction Plan for Scientific Research Innovation Team of Universities in Sichuan Province under Grant No 12TD008.

Study of barrier height and trap centers of Au/n-Hg{sub 3}In{sub 2}Te{sub 6} Schottky contacts by current-voltage (I-V) characteristics and deep level transient spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yapeng; Fu, Li, E-mail: fuli@nwpu.edu.cn; Sun, Jie

2015-02-28

The temperature-dependent electrical characteristics of the Au/n-Hg{sub 3}In{sub 2}Te{sub 6} Schottky contact have been studied at the temperature range of 140 K–315 K. Based on the thermionic emission theory, the ideality factor and Schottky barrier height were calculated to decrease and increase from 3.18 to 1.88 and 0.39 eV to 0.5 eV, respectively, when the temperature rose from 140 K to 315 K. This behavior was interpreted by the lateral inhomogeneities of Schottky barrier height at the interface of Au/n-Hg{sub 3}In{sub 2}Te{sub 6} contact, which was shown by the plot of zero-bias barrier heights Φ{sub bo} versus q/2kT. Meanwhile, it was found that the Schottky barriermore » height with a Gaussian distribution was 0.67 eV and the standard deviation σ{sub 0} was about 0.092 eV, indicating that the uneven distribution of barrier height at the interface region. In addition, the mean value of Φ{sup ¯}{sub b0} and modified Richardson constant was determined to be 0.723 eV and 62.8 A/cm{sup 2}K{sup 2} from the slope and intercept of the ln(I{sub o}/T{sup 2}) – (qσ{sub 0}{sup 2}/2k{sup 2}T{sup 2}) versus q/kT plot, respectively. Finally, two electron trap centers were observed at the interface of Au/n-Hg{sub 3}In{sub 2}Te{sub 6} Schottky contact by means of deep level transient spectroscopy.« less

Capacitance and conductance-frequency characteristics of In-pSi Schottky barrier diode

NASA Astrophysics Data System (ADS)

Dhimmar, J. M.; Desai, H. N.; Modi, B. P.

2015-06-01

The Schottky barrier height (SBH) values have been calculated by using the reverse bias capacitance-voltage (C-V) characteristics at temperature range of 120-360K. The forward bias capacitance-frequency (C-f) and conductance- frequency (G-f) measurement of In-pSi SBD have been carried out from 0-1.0 V with a step up 0.05 V whereby the energy distribution of the interface state has been determined from the forward bias I-V data taking the bias dependence of the effective barrier height and series resistance (RS) into account. The high value of ideality factor (n=2.12) was attributing to high density of interface states and interfacial oxide layer at metal semiconductor interface. The interface state density (NSS) shows a decrease with bias from bottom of conduction band toward the mid gap. In order to examine frequency dependence NSS, RS, C-V and G(ω)/ω-f measurement of the diode were performed at room temperature in the frequency range of 100Hz-100KHz. Experimental result confirmed that there is an influence in the electrical characteristic of Schottky diode.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, James B.

We report the third in a series of ’exact’ quantum Monte Carlo calculations for the potential energy of the saddle point of the barrier for the reaction H + H{sub 2} → H{sub 2} + H. The barrier heights determined are 9.61 ± 0.01 in 1992/94, 9.608 ± 0.001 in 2003, and 9.6089 ± 0.0001 in 2016 (this work), all in kcal/mole and successively a factor of ten more accurate. The new value is below the lowest value from explicitly correlated Gaussian calculations and within the estimated limits of extrapolated multireference configuration calculations.

ZnO quantum dot-doped graphene/h-BN/GaN-heterostructure ultraviolet photodetector with extremely high responsivity

NASA Astrophysics Data System (ADS)

Lu, Yanghua; Wu, Zhiqian; Xu, Wenli; Lin, Shisheng

2016-12-01

A ZnO quantum dot photo-doped graphene/h-BN/GaN-heterostructure ultraviolet photodetector with extremely high responsivity of more than 1915 A W-1 and detectivity of more than 1.02 × 1013 Jones (Jones = cm Hz1/2 W-1) has been demonstrated. The interfaced h-BN layer increases the barrier height at the graphene/GaN heterojunction, which decreases the dark current and improves the on/off current ratio of the device. The photo-doping effect increases the barrier height and carrier concentration at the graphene/h-BN/GaN heterojunction, thus the responsivity is improved from 1473 A W-1 to 1915 A W-1 and the detectivity is improved from 5.8 × 1012 to 1.0 × 1013 Jones. Moreover, all of the responsivity and detectivity values are the highest values among all the graphene-based ultraviolet photodetectors.

Conductance of graphene-based double-barrier nanostructures.

PubMed

Setare, M R; Jahani, D

2010-12-22

The effect of a mass gap on the conductance of graphene double-barrier heterojunctions is studied. By obtaining the 2D expression for the electronic transport of the low energy excitations of pure graphene through double-barrier systems, it is found that the conductivity of these structures does not depend on the type of charge carriers in the zones of the electric field. However, a finite induced gap in the graphene spectrum makes conductivity dependent on the energy band index. We also discuss a few controversies concerning double-barrier systems stemming from an improper choice of the scattering angle. Then it is observed that, for some special values of the incident energy and potential's height, graphene junctions behave like left-handed materials, resulting in a maximum value for the conductivity.

Effect of copper phthalocyanine thickness on surface morphology, optical and electrical properties of Au/CuPc/n-Si heterojunction

NASA Astrophysics Data System (ADS)

Reddy, P. R. Sekhar; Janardhanam, V.; Jyothi, I.; Harsha, Cirandur Sri; Reddy, V. Rajagopal; Lee, Sung-Nam; Won, Jonghan; Choi, Chel-Jong

2018-02-01

Effects of the thickness of copper phthalocyanine (CuPc) film (2, 5, 10, 15, 20, 30 and 40 nm) on the surface morphology, optical and electrical properties of Au/CuPc/n-Si heterojunction have been investigated. The optical band gap of CuPc film was increased with increase in the thickness of the CuPc film. The electrical properties of the Au/n-Si Schottky junction and Au/CuPc/n-Si heterojunctions were characterized by current-voltage ( I-V) and capacitance-voltage ( C-V) measurements. The barrier height, ideality factor and series resistance were estimated based on the I-V, Cheung's and Norde's methods. The barrier heights increased with increasing CuPc interlayer thickness up to 15 nm and remained constant for thickness above 20 nm, associated with the incapability of the generated carriers to reach the interface. The discrepancy in the barrier heights obtained from I-V and C-V measurements indicates the presence of barrier inhomogeneity at the interface as evidenced by higher ideality factor values. It can be concluded that the electrical properties of Au/n-Si Schottky junction can be significantly altered with the variation of CuPc thickness as interlayer.

Temperature dependent electrical properties of rare-earth metal Er Schottky contact on p-type InP

NASA Astrophysics Data System (ADS)

Rao, L. Dasaradha; Reddy, N. Ramesha; Kumar, A. Ashok; Reddy, V. Rajagopal

2013-06-01

The current-voltage (I-V) characteristics of the Er/p-InP Schottky barrier diodes (SBDs) have been investigated in the temperature range of 300-400K in steps of 25K. The electrical parameters such as ideality factor (n) and zero-bias barrier height (Φbo) are found to be strongly temperature dependent. It is observed that ΦI-V decreases whereas n increases with decreasing temperature. The series resistance is also calculated from the forward I-V characteristics of Er/p-InP SBD and it is found to be strongly dependent on temperature. Further, the temperature dependence of energy distribution of interface state density (NSS) profiles is determined from the forward I-V measurements by taking into account the bias dependence of the effective barrier height and ideality factor. It is observed that the NSS values increase with a decrease in temperature.

Towards a converged barrier height for the entrance channel transition state of the N( 2D) + CH 4 reaction and its implication for the chemistry in Titan's atmosphere

NASA Astrophysics Data System (ADS)

Ouk, Chanda-Malis; Zvereva-Loëte, Natalia; Bussery-Honvault, Béatrice

2011-10-01

The N( 2D) + CH 4 reaction appears to be a key reaction for the chemistry of Titan's atmosphere, opening the door to nitrile formation as recently observed by the Cassini-Huygens mission. Faced to the controversy concerning the existence or not of a potential barrier for this reaction, we have carried out accurate ab initio calculations by means of multi-state multi-reference configuration interaction (MS-MR-SDCI) method. These calculations have been partially corrected for the size-consistency errors (SCE) by Davidson, Pople or AQCC corrections. We suggest a barrier height of 3.86 ± 0.84 kJ/mol, including ZPE, for the entrance transition state, in good agreement with the experimental value. Its implication in Titan's atmopsheric chemistry is discussed.

Temperature and voltage dependence of barrier height and ideality factor in Au/0.07 graphene-doped PVA/n-Si structures

NASA Astrophysics Data System (ADS)

Altındal Yerişkin, S.; Balbaşı, M.; Demirezen, S.

2017-04-01

In this study, Au/0.07 graphene-doped PVA/n-Si structures were fabricated and current conduction mechanism in these structures were investigated in the temperature range of 80-380 K through forward bias current-voltage ( I- V) measurements. Main electrical parameters were extracted from I-V data. Zero-bias barrier height (\\overline{Φ}_{B0}) and ideality factor (n) were found strong functions of temperature and their values ranged from 0.234 eV and 4.98 (at 80 K) to 0.882 eV and 1.15 (at 380 K), respectively. Φ ap versus q/2k T plot was drawn to obtain an evidence of a Gaussian distribution of the barrier heights (BHs) and it revealed two distinct linear regions with different slopes and intercepts. The mean values of BH ( Φ Bo) and zero-bias standard deviation (σ s ) were obtained from the intercept and slope of the linear regions of this plot as 1.30 eV and 0.16 V for the first region (280-380 K) and 0.74 eV and 0.085 V for the second region (80-240 K), respectively. Thus, the values of \\overline{Φ}_{B0} and effective Richardson constant ( A*) were also found from the intercept and slope of the modified Richardson plot [ln( I s /T 2) - q 2 σ o 2 /2k 2 T 2 vs q/ kT] as 1.31 eV and 130 A/cm2 K2 for the first region and 0.76 eV and 922 A/cm2 K2 for the second region, respectively. The value of A* for the first region was very close to the theoretical value for n-Si (112 A/cm2 K2). The energy density distribution profile of surface states (Nss) was also extracted from the forward bias I-V data by taking into account voltage dependent effective BH (Φe) and n.

Development and fabrication of improved Schottky power diodes, phases I and II

NASA Technical Reports Server (NTRS)

Cordes, L. F.; Garfinkle, M.; Taft, E. A.

1974-01-01

Reproducible methods for the fabrication of silicon Schottky diodes were developed for the metals tungsten, aluminum, conventional platinum silicide and low temperature platinum silicide. Barrier heights and barrier lowering were measured permitting the accurate prediction of ideal forward and reverse diode performance. Processing procedures were developed which permit the fabrication of large area (approximately 1 sqcm) mesa-geometry power Schottky diodes with forward and reverse characteristics that approach theoretical values.

Ballistics-Electron-Microscopy and Spectroscopy of Metal/GaN Interfaces

NASA Technical Reports Server (NTRS)

Bell, L. D.; Smith, R. P.; McDermott, B. T.; Gertner, E. R.; Pittman, R.; Pierson, R. L.; Sullivan, G. J.

1997-01-01

BEEM spectroscopy and imaging have been applied to the Au/GaN interface. In contrast to previous BEEM measurements, spectra yield a Schottky barrier height of 1.04eV that agrees well with the highest values measured by conventional methods.

Fusion cross sections for reactions involving medium and heavy nucleus-nucleus systems

NASA Astrophysics Data System (ADS)

Atta, Debasis; Basu, D. N.

2014-12-01

Existing data on near-barrier fusion excitation functions of medium and heavy nucleus-nucleus systems have been analyzed by using a simple diffused-barrier formula derived assuming the Gaussian shape of the barrier-height distributions. The fusion cross section is obtained by folding the Gaussian barrier distribution with the classical expression for the fusion cross section for a fixed barrier. The energy dependence of the fusion cross section, thus obtained, provides good description to the existing data on near-barrier fusion and capture excitation functions for medium and heavy nucleus-nucleus systems. The theoretical values for the parameters of the barrier distribution are estimated which can be used for fusion or capture cross-section predictions that are especially important for planning experiments for synthesizing new superheavy elements.

Enhanced Thermionic Emission and Low 1/f Noise in Exfoliated Graphene/GaN Schottky Barrier Diode.

PubMed

Kumar, Ashutosh; Kashid, Ranjit; Ghosh, Arindam; Kumar, Vikram; Singh, Rajendra

2016-03-01

Temperature-dependent electrical transport characteristics of exfoliated graphene/GaN Schottky diodes are investigated and compared with conventional Ni/GaN Schottky diodes. The ideality factor of graphene/GaN and Ni/GaN diodes are measured to be 1.33 and 1.51, respectively, which is suggestive of comparatively higher thermionic emission current in graphene/GaN diode. The barrier height values for graphene/GaN diode obtained using thermionic emission model and Richardson plots are found to be 0.60 and 0.72 eV, respectively, which are higher than predicted barrier height ∼0.40 eV as per the Schottky-Mott model. The higher barrier height is attributed to hole doping of graphene due to graphene-Au interaction which shifts the Fermi level in graphene by ∼0.3 eV. The magnitude of flicker noise of graphene/GaN Schottky diode increases up to 175 K followed by its decrease at higher temperatures. This indicates that diffusion currents and barrier inhomogeneities dominate the electronic transport at lower and higher temperatures, respectively. The exfoliated graphene/GaN diode is found to have lower level of barrier inhomogeneities than conventional Ni/GaN diode, as well as earlier reported graphene/GaN diode fabricated using chemical vapor deposited graphene. The lesser barrier inhomogeneities in graphene/GaN diode results in lower flicker noise by 2 orders of magnitude as compared to Ni/GaN diode. Enhanced thermionic emission current, lower level of inhomogeneities, and reduced flicker noise suggests that graphene-GaN Schottky diodes may have the underlying trend for replacing metal-GaN Schottky diodes.

Assessing Controls on the Geometry and Dimensions of Modern Barrier Islands

NASA Astrophysics Data System (ADS)

Mulhern, J.; Johnson, C. L.; Martin, J. M.

2015-12-01

Barrier islands are highly ephemeral features, shaped by wave, tide, and storm energy. The processes that govern the size, shape, and motion of barrier islands are not well constrained, yet central to coastal dynamics. While the global distribution of barrier islands has been mapped and assessed, there is little consensus on the forces controlling barrier island formation, motion, or preservation. This study presents a new semi-global database of modern barrier islands to better understand their morphology and spatial distribution. We have mapped, in Google Earth, the subaerial extent of >350 barrier islands and spits, measuring spatial characteristic such as exposed area, perimeter, length, and width. These objects are cross-referenced with parameters that potentially control morphology, including tidal range, wave height, climate, distance from the continental shelf, proximity to fluvial output, and tectonic setting. This approach provides a more optimal framework to assess controls on coastal features, including barrier island morphology, and to investigate potential geometric scaling relationships. Preliminary analysis shows trends in the spatial characteristics of barrier islands. There is a strong linear relationship between the perimeter and length (y= -0.59 + 0.42x, R2=0.95). Linear trends also relate length to area when the data are separated by tidal range to wave height ratio. Assessment of barrier island shape supports the hypothesis of Hayes (1979) that barrier islands in wave-dominated settings are long and linear while those in mixed energy setting are more rounded. The barrier islands of the Texas Gulf of Mexico are larger than the global average for the database, with distinctly longer length values (41.16 km vs. 15.77 km respectively) and larger areas (103.81 km2 vs. 42.14 km2 respectively). Initial assessment shows that tidal range and wave height are primary controls barrier island dimensions. Future work will consider climate, latitude, fluvial input, and tectonic regime as additional factors. Assessing modern barrier islands will lend insight into potential paleomorphodynamic relationships and help determine how islands are transferred into the rock record, with implications for sequence stratigraphy, subsurface reservoirs, etc.

Graphene-insulator-semiconductor capacitors as superior test structures for photoelectric determination of semiconductor devices band diagrams

NASA Astrophysics Data System (ADS)

Piskorski, K.; Passi, V.; Ruhkopf, J.; Lemme, M. C.; Przewlocki, H. M.

2018-05-01

We report on the advantages of using Graphene-Insulator-Semiconductor (GIS) instead of Metal-Insulator-Semiconductor (MIS) structures in reliable and precise photoelectric determination of the band alignment at the semiconductor-insulator interface and of the insulator band gap determination. Due to the high transparency to light of the graphene gate in GIS structures large photocurrents due to emission of both electrons and holes from the substrate and negligible photocurrents due to emission of carriers from the gate can be obtained, which allows reliable determination of barrier heights for both electrons, Ee and holes, Eh from the semiconductor substrate. Knowing the values of both Ee and Eh allows direct determination of the insulator band gap EG(I). Photoelectric measurements were made of a series of Graphene-SiO2-Si structures and an example is shown of the results obtained in sequential measurements of the same structure giving the following barrier height values: Ee = 4.34 ± 0.01 eV and Eh = 4.70 ± 0.03 eV. Based on this result and results obtained for other structures in the series we conservatively estimate the maximum uncertainty of both barrier heights estimations at ± 0.05 eV. This sets the SiO2 band gap estimation at EG(I) = 7.92 ± 0.1 eV. It is shown that widely different SiO2 band gap values were found by research groups using various determination methods. We hypothesize that these differences are due to different sensitivities of measurement methods used to the existence of the SiO2 valence band tail.

Investigation of the CH3Cl + CN(-) reaction in water: Multilevel quantum mechanics/molecular mechanics study.

PubMed

Xu, Yulong; Zhang, Jingxue; Wang, Dunyou

2015-06-28

The CH3Cl + CN(-) reaction in water was studied using a multilevel quantum mechanics/molecular mechanics (MM) method with the multilevels, electrostatic potential, density functional theory (DFT) and coupled-cluster single double triple (CCSD(T)), for the solute region. The detailed, back-side attack SN2 reaction mechanism was mapped along the reaction pathway. The potentials of mean force were calculated under both the DFT and CCSD(T) levels for the reaction region. The CCSD(T)/MM level of theory presents a free energy activation barrier height at 20.3 kcal/mol, which agrees very well with the experiment value at 21.6 kcal/mol. The results show that the aqueous solution has a dominant role in shaping the potential of mean force. The solvation effect and the polarization effect together increase the activation barrier height by ∼11.4 kcal/mol: the solvation effect plays a major role by providing about 75% of the contribution, while polarization effect only contributes 25% to the activation barrier height. Our calculated potential of mean force under the CCSD(T)/MM also has a good agreement with the one estimated using data from previous gas-phase studies.

Investigation of the CH3Cl + CN- reaction in water: Multilevel quantum mechanics/molecular mechanics study

NASA Astrophysics Data System (ADS)

Xu, Yulong; Zhang, Jingxue; Wang, Dunyou

2015-06-01

The CH3Cl + CN- reaction in water was studied using a multilevel quantum mechanics/molecular mechanics (MM) method with the multilevels, electrostatic potential, density functional theory (DFT) and coupled-cluster single double triple (CCSD(T)), for the solute region. The detailed, back-side attack SN2 reaction mechanism was mapped along the reaction pathway. The potentials of mean force were calculated under both the DFT and CCSD(T) levels for the reaction region. The CCSD(T)/MM level of theory presents a free energy activation barrier height at 20.3 kcal/mol, which agrees very well with the experiment value at 21.6 kcal/mol. The results show that the aqueous solution has a dominant role in shaping the potential of mean force. The solvation effect and the polarization effect together increase the activation barrier height by ˜11.4 kcal/mol: the solvation effect plays a major role by providing about 75% of the contribution, while polarization effect only contributes 25% to the activation barrier height. Our calculated potential of mean force under the CCSD(T)/MM also has a good agreement with the one estimated using data from previous gas-phase studies.

ZnO quantum dot-doped graphene/h-BN/GaN-heterostructure ultraviolet photodetector with extremely high responsivity.

PubMed

Lu, Yanghua; Wu, Zhiqian; Xu, Wenli; Lin, Shisheng

2016-12-02

A ZnO quantum dot  photo-doped graphene/h-BN/GaN-heterostructure ultraviolet photodetector with extremely high responsivity of more than 1915 A W -1 and detectivity of more than 1.02 × 10 13 Jones (Jones = cm Hz 1/2 W -1 ) has been demonstrated. The interfaced h-BN layer increases the barrier height at the graphene/GaN heterojunction, which decreases the dark current and improves the on/off current ratio of the device. The photo-doping effect increases the barrier height and carrier concentration at the graphene/h-BN/GaN heterojunction, thus the responsivity is improved from 1473 A W -1 to 1915 A W -1 and the detectivity is improved from 5.8 × 10 12 to 1.0 × 10 13 Jones. Moreover, all of the responsivity and detectivity values are the highest values among all the graphene-based ultraviolet photodetectors.

Effect of inhomogeneous Schottky barrier height of SnO2 nanowires device

NASA Astrophysics Data System (ADS)

Amorim, Cleber A.; Bernardo, Eric P.; Leite, Edson R.; Chiquito, Adenilson J.

2018-05-01

The current–voltage (I–V) characteristics of metal–semiconductor junction (Au–Ni/SnO2/Au–Ni) Schottky barrier in SnO2 nanowires were investigated over a wide temperature range. By using the Schottky–Mott model, the zero bias barrier height Φ B was estimated from I–V characteristics, and it was found to increase with increasing temperature; on the other hand the ideality factor (n) was found to decrease with increasing temperature. The variation in the Schottky barrier and n was attributed to the spatial inhomogeneity of the Schottky barrier height. The experimental I–V characteristics exhibited a Gaussian distribution having mean barrier heights {\\overline{{{Φ }}}}B of 0.30 eV and standard deviation σ s of 60 meV. Additionally, the Richardson modified constant was obtained to be 70 A cm‑2 K‑2, leading to an effective mass of 0.58m 0. Consequently, the temperature dependence of I–V characteristics of the SnO2 nanowire devices can be successfully explained on the Schottky–Mott theory framework taking into account a Gaussian distribution of barrier heights.

Accelerated Adaptive Integration Method

PubMed Central

2015-01-01

Conformational changes that occur upon ligand binding may be too slow to observe on the time scales routinely accessible using molecular dynamics simulations. The adaptive integration method (AIM) leverages the notion that when a ligand is either fully coupled or decoupled, according to λ, barrier heights may change, making some conformational transitions more accessible at certain λ values. AIM adaptively changes the value of λ in a single simulation so that conformations sampled at one value of λ seed the conformational space sampled at another λ value. Adapting the value of λ throughout a simulation, however, does not resolve issues in sampling when barriers remain high regardless of the λ value. In this work, we introduce a new method, called Accelerated AIM (AcclAIM), in which the potential energy function is flattened at intermediate values of λ, promoting the exploration of conformational space as the ligand is decoupled from its receptor. We show, with both a simple model system (Bromocyclohexane) and the more complex biomolecule Thrombin, that AcclAIM is a promising approach to overcome high barriers in the calculation of free energies, without the need for any statistical reweighting or additional processors. PMID:24780083

Barrier scattering with complex-valued quantum trajectories: Taxonomy and analysis of isochrones

DOE Office of Scientific and Technical Information (OSTI.GOV)

David, Julianne K.; Wyatt, Robert E.

2008-03-07

To facilitate the search for isochrones when using complex-valued trajectory methods for quantum barrier scattering calculations, the structure and shape of isochrones in the complex plane were studied. Isochrone segments were categorized based on their distinguishing features, which are shared by each situation studied: High and low energy wave packets, scattering from both thick and thin Gaussian and Eckart barriers of varying height. The characteristic shape of the isochrone is a trifurcated system: Trajectories that transmit the barrier are launched from the lower branch (T), while the middle and upper branches form the segments for reflected trajectories (F and B).more » In addition, a model is presented for the curved section of the lower branch (from which transmitted trajectories are launched), and important features of the complex extension of the initial wave packet are identified.« less

Schottky barrier height measurements of Cu/Si(001), Ag/Si(001), and Au/Si(001) interfaces utilizing ballistic electron emission microscopy and ballistic hole emission microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balsano, Robert; Matsubayashi, Akitomo; LaBella, Vincent P., E-mail: vlabella@albany.edu

2013-11-15

The Schottky barrier heights of both n and p doped Cu/Si(001), Ag/Si(001), and Au/Si(001) diodes were measured using ballistic electron emission microscopy and ballistic hole emission microscopy (BHEM), respectively. Measurements using both forward and reverse ballistic electron emission microscopy (BEEM) and (BHEM) injection conditions were performed. The Schottky barrier heights were found by fitting to a linearization of the power law form of the Bell-Kaiser BEEM model. The sum of the n-type and p-type barrier heights are in good agreement with the band gap of silicon and independent of the metal utilized. The Schottky barrier heights are found to bemore » below the region of best fit for the power law form of the BK model, demonstrating its region of validity.« less

Fermi level de-pinning of aluminium contacts to n-type germanium using thin atomic layer deposited layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gajula, D. R., E-mail: dgajula01@qub.ac.uk; Baine, P.; Armstrong, B. M.

Fermi-level pinning of aluminium on n-type germanium (n-Ge) was reduced by insertion of a thin interfacial dielectric by atomic layer deposition. The barrier height for aluminium contacts on n-Ge was reduced from 0.7 eV to a value of 0.28 eV for a thin Al{sub 2}O{sub 3} interfacial layer (∼2.8 nm). For diodes with an Al{sub 2}O{sub 3} interfacial layer, the contact resistance started to increase for layer thicknesses above 2.8 nm. For diodes with a HfO{sub 2} interfacial layer, the barrier height was also reduced but the contact resistance increased dramatically for layer thicknesses above 1.5 nm.

Periodic Orbits and Semiclassical Form Factor in Barrier Billiards

NASA Astrophysics Data System (ADS)

Giraud, O.

2005-11-01

Using heuristic arguments based on the trace formulas, we analytically calculate the semiclassical two-point correlation form factor for a family of rectangular billiards with a barrier of height irrational with respect to the side of the billiard and located at any rational position p/q from the side. To do this, we first obtain the asymptotic density of lengths for each family of periodic orbits by a Siegel-Veech formula. The result obtained for these pseudo-integrable, non-Veech billiards is different but not far from the value of 1/2 expected for semi-Poisson statistics and from values of obtained previously in the case of Veech billiards.

Analysis of aging time dependent electrical characteristics of AuCu/n-Si/Ti Schottky type diode

NASA Astrophysics Data System (ADS)

Taser, Ahmet; Şenarslan, Elvan; Güzeldir, Betül; Saǧlam, Mustafa

2017-04-01

The purpose of this study is to fabricate AuCu/n-Si/Ti Schottky type diode and determine the effects of aging time on the diode parameters such as ideality factor, barrier height, series resistance, interface state density and rectification ratio. Gold and copper ratios in the gold-copper alloy used in making the Schottky contact were taken as equal. Schottky barrier contact using AuCu alloy and ohmic contact using Ti metal were made on n-Si by thermal evaporation. The electrical characterization of the AuCu/n-Si/Ti diode was made immediately based on the aging time at room temperature in dark conditions. The I-V measurements were also repeated 1, 7, 15, 30 and 90 days after fabrication of the diode in order to observe the effect of the aging time. The determined values of the ideality factor are in the range of 1,21 (for immediately)-1,075 (for 90 days). In the same way, values of the barrier height are also in the range of 0,566 eV (for immediately)-0,584 eV (for 90 days). From the I-V characteristics, it is seen that the diode appears to have a good rectification character.

Explanation of the barrier heights of graphene Schottky contacts by the MIGS-and-electronegativity concept

NASA Astrophysics Data System (ADS)

Mönch, Winfried

2016-09-01

Graphene-semiconductor contacts exhibit rectifying properties and, in this respect, they behave in exactly the same way as a "conventional" metal-semiconductor or Schottky contacts. It will be demonstrated that, as often assumed, the Schottky-Mott rule does not describe the reported barrier heights of graphene-semiconductor contacts. With "conventional" Schottky contacts, the same conclusion was reached already in 1940. The physical reason is that the Schottky-Mott rule considers no interaction between the metal and the semiconductor. The barrier heights of "conventional" Schottky contacts were explained by the continuum of metal-induced gap states (MIGSs), where the differences of the metal and semiconductor electronegativities describe the size and the sign of the intrinsic electric-dipoles at the interfaces. It is demonstrated that the MIGS-and-electronegativity concept unambiguously also explains the experimentally observed barrier heights of graphene Schottky contacts. This conclusion includes also the barrier heights reported for MoS2 Schottky contacts with "conventional" metals as well as with graphene.

Investigation of significantly high barrier height in Cu/GaN Schottky diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garg, Manjari, E-mail: meghagarg142@gmail.com; Kumar, Ashutosh; Singh, R.

2016-01-15

Current-voltage (I-V) measurements combined with analytical calculations have been used to explain mechanisms for forward-bias current flow in Copper (Cu) Schottky diodes fabricated on Gallium Nitride (GaN) epitaxial films. An ideality factor of 1.7 was found at room temperature (RT), which indicated deviation from thermionic emission (TE) mechanism for current flow in the Schottky diode. Instead the current transport was better explained using the thermionic field-emission (TFE) mechanism. A high barrier height of 1.19 eV was obtained at room temperature. X-ray photoelectron spectroscopy (XPS) was used to investigate the plausible reason for observing Schottky barrier height (SBH) that is significantlymore » higher than as predicted by the Schottky-Mott model for Cu/GaN diodes. XPS measurements revealed the presence of an ultrathin cuprous oxide (Cu{sub 2}O) layer at the interface between Cu and GaN. With Cu{sub 2}O acting as a degenerate p-type semiconductor with high work function of 5.36 eV, a high barrier height of 1.19 eV is obtained for the Cu/Cu{sub 2}O/GaN Schottky diode. Moreover, the ideality factor and barrier height were found to be temperature dependent, implying spatial inhomogeneity of barrier height at the metal semiconductor interface.« less

Investigation of the CH{sub 3}Cl + CN{sup −} reaction in water: Multilevel quantum mechanics/molecular mechanics study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Yulong; College of Physics and Electronics, Shandong Normal University, Jinan 250014; Zhang, Jingxue

2015-06-28

The CH{sub 3}Cl + CN{sup −} reaction in water was studied using a multilevel quantum mechanics/molecular mechanics (MM) method with the multilevels, electrostatic potential, density functional theory (DFT) and coupled-cluster single double triple (CCSD(T)), for the solute region. The detailed, back-side attack S{sub N}2 reaction mechanism was mapped along the reaction pathway. The potentials of mean force were calculated under both the DFT and CCSD(T) levels for the reaction region. The CCSD(T)/MM level of theory presents a free energy activation barrier height at 20.3 kcal/mol, which agrees very well with the experiment value at 21.6 kcal/mol. The results show thatmore » the aqueous solution has a dominant role in shaping the potential of mean force. The solvation effect and the polarization effect together increase the activation barrier height by ∼11.4 kcal/mol: the solvation effect plays a major role by providing about 75% of the contribution, while polarization effect only contributes 25% to the activation barrier height. Our calculated potential of mean force under the CCSD(T)/MM also has a good agreement with the one estimated using data from previous gas-phase studies.« less

Transport spectroscopy of low disorder silicon tunnel barriers with and without Sb implants

DOE PAGES

Shirkhorshidian, A.; Bishop, N. C.; Dominguez, J.; ...

2015-04-30

We present transport measurements of silicon MOS split gate structures with and without Sb implants. We observe classical point contact (PC) behavior that is free of any pronounced unintentional resonances at liquid He temperatures. The implanted device has resonances superposed on the PC transport indicative of transport through the Sb donors. We fit the differential conductance to a rectangular tunnel barrier model with a linear barrier height dependence on source–drain voltage and non-linear dependence on gate bias. Effects such as Fowler–Nordheim (FN) tunneling and image charge barrier lowering (ICBL) are considered. Barrier heights and widths are estimated for the entiremore » range of relevant biases. The barrier heights at the locations of some of the resonances for the implanted tunnel barrier are between 15–20 meV, which are consistent with transport through shallow partially hybridized Sb donors. The dependence of width and barrier height on gate voltage is found to be linear over a wide range of gate bias in the split gate geometry but deviates considerably when the barrier becomes large and is not described completely by standard 1D models such as FN or ICBL effects.« less

Temperature dependence of electrical characteristics of Pt/GaN Schottky diode fabricated by UHV e-beam evaporation.

PubMed

Kumar, Ashish; Arafin, Shamsul; Amann, Markus Christian; Singh, Rajendra

2013-11-15

Temperature-dependent electrical characterization of Pt/n-GaN Schottky barrier diodes prepared by ultra high vacuum evaporation has been done. Analysis has been made to determine the origin of the anomalous temperature dependence of the Schottky barrier height, the ideality factor, and the Richardson constant calculated from the I-V-T characteristics. Variable-temperature Hall effect measurements have been carried out to understand charge transport at low temperature. The modified activation energy plot from the barrier inhomogeneity model has given the value of 32.2 A/(cm2 K2) for the Richardson constant A** in the temperature range 200 to 380 K which is close to the known value of 26.4A/(cm2 K2) for n-type GaN.

Transition path time distribution and the transition path free energy barrier.

PubMed

Pollak, Eli

2016-10-19

The recent experimental measurement of the transition path time distributions of proteins presents several challenges to theory. Firstly, why do the fits of the experimental data to a theoretical expression lead to barrier heights which are much lower than the free energies of activation of the observed transitions? Secondly, there is the theoretical question of determining the transition path time distribution, without invoking the Smoluchowski limit. In this paper, we derive an exact expression for a transition path time distribution which is valid for arbitrary memory friction using the normal mode transformation which underlies Kramers' rate theory. We then recall that for low barriers, there is a noticeable difference between the transition path time distribution obtained with absorbing boundary conditions and free boundary conditions. For the former, the transition times are shorter, since recrossings of the boundaries are disallowed. As a result, if one uses the distribution based on absorbing boundary conditions to fit the experimental data, one will find that the transition path barrier will be larger than the values found based on a theory with free boundary conditions. We then introduce the paradigm of a transition path barrier height, and show that one should always expect it to be much smaller than the activation energy.

Electrical characteristics of n-GaN Schottky contacts on cleaved surfaces of free-standing substrates: Metal work function dependence of Schottky barrier height

NASA Astrophysics Data System (ADS)

Imadate, Hiroyoshi; Mishima, Tomoyoshi; Shiojima, Kenji

2018-04-01

We report the electrical characteristics of Schottky contacts with nine different metals (Ag, Ti, Cr, W, Mo, Au, Pd, Ni, and Pt) formed on clean m-plane surfaces by cleaving freestanding GaN substrates, compared with these of contacts on Ga-polar c-plane n-GaN surfaces grown on GaN substrates. The n-values from the forward current–voltage (I–V) characteristics are as good as 1.02–1.18 and 1.02–1.09 for the m- and c-plane samples, respectively. We found that the reverse I–V curves of both samples can be explained by the thermionic field emission theory, and that the Schottky barrier height of the cleaved m-plane contacts shows a metal work function dependence.

Experimental analysis of the Schottky barrier height of metal contacts in black phosphorus field-effect transistors

NASA Astrophysics Data System (ADS)

Chang, Hsun-Ming; Fan, Kai-Lin; Charnas, Adam; Ye, Peide D.; Lin, Yu-Ming; Wu, Chih-I.; Wu, Chao-Hsin

2018-04-01

Compared to graphene and MoS2, studies on metal contacts to black phosphorus (BP) transistors are still immature. In this work, we present the experimental analysis of titanium contacts on BP based upon the theory of thermionic emssion. The Schottky barrier height (SBH) is extracted by thermionic emission methods to analyze the properties of Ti-BP contact. To examine the results, the band gap of BP is extracted followed by theoretical band alignment by Schottky-Mott rule. However, an underestimated SBH is found due to the hysteresis in electrical results. Hence, a modified SBH extraction for contact resistance that avoids the effects of hysteresis is proposed and demonstrated, showing a more accurate SBH that agrees well with theoretical value and results of transmission electron microscopy and energy-dispersive x-ray spectroscopy.

Influence of the dynamic lattice strain on the transport behavior of oxide heterojunctions

NASA Astrophysics Data System (ADS)

Wang, J.; Hu, F. X.; Chen, L.; Zhao, Y. Y.; Lu, H. X.; Sun, J. R.; Shen, B. G.

2013-01-01

All-perovskite oxide heterojunctions composed of electron-doped titanate LaxSr1 - xTiO3 (x = 0.1, 0.15) and hole-doped manganite La0.67Ca0.33MnO3 films were fabricated on piezoelectric substrate of (001)-0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT). Taking advantage of the excellent converse piezoelectric effect of PMN-PT, we investigated the influence of the dynamic lattice strain on transport properties of the heterojunctions by applying external bias electric fields on the PMN-PT substrate. Photovoltaic experiments were carried out to characterize the interfacial barrier of the heterojunction. A linear reduction in the barrier height was observed with the increase of the bias field applied on PMN-PT. The value of the barrier height reduces from ˜1.55 (˜1.30) to 1.02 (1.08) eV as the bias field increases from 0 to 12 kV/cm for the junction of La0.10Sr0.9TiO3/La0.67Ca0.33MnO3 (La0.15Sr0.85TiO3/La0.67Ca0.33MnO3). The observed dependency of barrier height on external field can be ascribed to the increasing release of trapped carriers by strain modulation, which results in a suppression of the depletion layer and increases the opportunity for electron tunneling across the depletion area.

Identification of a barrier height threshold where brook trout population genetic diversity, differentiation, and relatedness are affected

Treesearch

Anne Timm; Eric Hallerman; Andy Dolloff; Mark Hudy; Randall Kolka

2016-01-01

The overall goal of the study was to evaluate effects of landscape features, barriers, on Brook Trout Salvelinus fontinalis population genetics and to identify a potential barrier height threshold where genetic diversity was reduced upstream of the barrier and differentiation and relatedness increase. We screened variation at eight...

Electrical properties and interface state energy distributions of Cr/n-Si Schottky barrier diode

NASA Astrophysics Data System (ADS)

Karataş, Şükrü; Yildirim, Nezir; Türüt, Abdülmecit

2013-12-01

In this study, the electrical characteristics of the Cr/n-type Si (MS) Schottky barrier diode have been investigated by the current-voltage (I-V) and capacitance-voltage (C-V) measurements at 300 K temperature. Using the thermionic emission theory, the values of ideality factor and the barrier height have been obtained to be 1.22, 0.71 and 1.01, 0.83 eV, from the results of the I-V and C-V measurements, respectively. The barrier height (Φb) and the series resistance (RS) obtained from Norde’s function have been compared with those obtained from Cheung functions, and a good agreement between the results of both methods was seen. The interface state density (NSS) calculated without the RS is obtained to be increasing exponentially with bias from 2.40 × 1012 cm-2 eV-1 in (EC-0.623) eV to 1.94 × 1014 cm-2 eV-1 in (EC-0.495) eV, also, the NSS obtained taking into account the RS has increased exponentially with bias from 2.07 × 1012 cm-2 eV-1 to 1.47 × 1014 cm-2 eV-1 in the same interval.

On the temperature dependent current transport mechanisms and barrier inhomogeneity in Au/SnO2-PVA/n-Si Schottky barrier diodes

NASA Astrophysics Data System (ADS)

Bilkan, Ç.; Badali, Y.; Fotouhi-Shablou, S.; Azizian-Kalandaragh, Y.; Altındal, Ş.

2017-08-01

In this paper, we report the preparation and characterization of SnO2-PVA nanocomposite film as interlayer for Schottky barrier diodes (SBDs). The possible current transport mechanisms (CTMs) of the prepared SBDs were investigated using the forward-bias current-voltage ( I- V) characteristics in the temperature range of 80-400 K. The structure of nanocomposite film was characterized by an X-ray diffractometer (XRD) and the surface morphology was investigated using a Scanning Electron Microscopy (SEM) at room temperature. The values of ideality factor ( n) and zero-bias barrier height (\\overline{Φ}_{Bo}) showed variation with temperature, such that they changed from 19.10 to 3.77 and 0.190 to 0.844 eV, respectively. \\overline{Φ}_{Bo}- n, \\overline{Φ}_{Bo}- q/2 kT, and n -1- q/2 kT plots were drawn to get evidence to the Gaussian Distribution (GD) of the barrier height (BH). These plots revealed two distinct linear regions with different slopes for low temperatures (80-160 K) (LTs) and high temperatures (180-400 K) (HTs). This behavior is an evidence to the existence double GD of BHs which provides an average value for BH (\\overline{Φ}_{Bo}) and a standard deviation (σs) for each region. The high value of n especially at low temperatures was attributed to the existence of interlayer: interface states ( N ss) and barrier inhomogeneity at Au/n-Si interface. The values of \\overline{Φ}_{Bo} and σs were obtained from the intercept and slope of mentioned plots as 0.588 and 0.0768 V for LTs and 1.183 eV and 0.158 V for HTs, respectively. Moreover, the modified ln( I s/ T 2)- q 2σ s 2 /2 k 2 T 2 vs q/ kT plot also showed two linear regions. The values of \\overline{Φ}_{Bo} and effective Richardson constant ( A *) were extracted from the slope and intercept of this plot as 0.610 eV and 93.13 A/cm2 K2 for LTs and 1.235 eV and 114.65 A/cm2 K2 for HTs, respectively. The value of A* for HTs is very close to the theoretical value (112 A/cm2 K2) of n-type Si. Thus, the forward-bias I- V- T characteristics of Au/SnO2-PVA/n-Si (SBDs) were successfully explained in terms of the thermionic-emission (TE) mechanism with a double GD of BHs.

Spatially inhomogeneous barrier height in graphene/MoS2 Schottky junctions

NASA Astrophysics Data System (ADS)

Tomer, Dushyant; Rajput, Shivani; Li, Lian

Graphene interfaced with a semiconductor forms a Schottky junction with rectifying properties. In this study, graphene Schottky junctions are fabricated by transferring CVD monolayer graphene on mechanically exfoliated MoS2 multilayers. The forward bias current-voltage characteristics are measured in the temperature range of 210-300 K. An increase in the zero bias barrier height and decrease in the ideality factor are observed with increasing temperature. Such behavior is attributed to Schottky barrier inhomogeneities possibly due to graphene ripples and ridges at the junction interface as suggested by atomic force microscopy. Assuming a Gaussian distribution of the barrier height, mean barrier of 0.97+/-0.10 eV is found for the graphene MoS2 junction. Our findings provide significant insight on the barrier height inhomogeneities in graphene/two dimensional semiconductor Schottky junctions. U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering Award No. DEFG02-07ER46228.

External electric field effects on Schottky barrier at Gd3N@C80/Au interface

NASA Astrophysics Data System (ADS)

Onishi, Koichi; Nakashima, Fumihiro; Jin, Ge; Eto, Daichi; Hattori, Hayami; Miyoshi, Noriko; Kirimoto, Kenta; Sun, Yong

2017-08-01

The effects of the external electric field on the height of the Schottky barrier at the Gd3N@C80/Au interface were studied by measuring current-voltage characteristics at various temperatures from 200 K to 450 K. The Gd3N@C80 sample with the conduction/forbidden/valence energy band structure had a face-centered cubic crystal structure with the average grain size of several nanometers. The height of the Gd3N@C80/Au Schottky barrier was confirmed to be 400 meV at a low electric field at room temperature. Moreover, the height decreases with the increasing external electric field through a change of permittivity in the Gd3N@C80 sample due to a polarization of the [Gd3] 9 +-[N3 -+("separators="|C80 ) 6 -] dipoles in the Gd3N@C80 molecule. The field-dependence of the barrier height can be described using a power math function of the electric field strength. The results of the field-dependent barrier height indicate that the reduction in the Schottky barrier is due to an image force effect of the transport charge carrier at the Gd3N@C80/Au interface.

Structural and electrical characterization of epitaxial Ge thin films on Si(001) formed by sputtering

NASA Astrophysics Data System (ADS)

Otsuka, Shintaro; Mori, Takahiro; Morita, Yukinori; Uchida, Noriyuki; Liu, Yongxun; O'uchi, Shin-ichi; Fuketa, Hiroshi; Migita, Shinji; Masahara, Meishoku; Matsukawa, Takashi

2017-04-01

We structurally and electrically characterize sub-10-nm-thick heteroepitaxial Ge films on Si(001), formed by heated sputtering and subsequent rapid thermal annealing (RTA). After RTA treatment at 720 °C, we find the heteroepitaxial Ge films to have smooth surfaces with a roughness root mean square value of 0.54 nm. Raman measurement reveals that the 720 °C RTA improves the crystallinity of Ge films while maintaining abrupt Ge/Si interfaces. Cross-sectional transmission electron microscopy confirms that the 720 °C RTA step effectively reduces stacking faults and dislocations in the Ge films. The Richardson plot of the TaN/Ge/n-Si diode indicates a Schottky barrier height (SBH) of 0.33 V, which is close to the height of 0.37 V measured from the capacitance-voltage measurement. These values are reasonable compared with the reported SBH of the TaN/bulk Ge Schottky barrier diode, indicating that the method involving heated sputtering and subsequent RTA provides adequate thin Ge films for Ge/Si heterostructures.

Effects of changes in effective rail height on barrier performance. Volume 1, Research report

DOT National Transportation Integrated Search

1987-04-01

The objective of this project was to determine the critical rail mounting heights to prevent underride and override for traffic barriers. W-beam guardrails, which are the most commonly specified barrier in the U. S., were used to develop criteria for...

Structural Consequences of Hydrogen Intercalation of Epitaxial Graphene on SiC(0001)

DTIC Science & Technology

2014-10-23

in barrier height at the graphene –silicon carbide Schottky junction,” Nat. Commun. 4, 2752 (2013). 31H. Yang, J. Heo, S. Park, H. J. Song, D. H. Seo, K...displacement. The shift of the Dirac point defines the Schottky barrier height and will determine the practicality of employing the wide-bandgap...are thought to critically influence technologi- cally relevant properties such as Dirac point shift and Schottky barrier height . Furthermore, this

Control of tunnel barriers in multi-wall carbon nanotubes using focused ion beam irradiation

NASA Astrophysics Data System (ADS)

Tomizawa, H.; Suzuki, K.; Yamaguchi, T.; Akita, S.; Ishibashi, K.

2017-04-01

We have formed tunnel barriers in individual multi-wall carbon nanotubes using the Ga focused ion beam irradiation. The barrier height was estimated by the temperature dependence of the current (Arrhenius plot) and the current-voltage curves (Fowler-Nordheim plot). It is shown that the barrier height has a strong correlation with the barrier resistance that is controlled by the dose. Possible origins for the variation in observed barrier characteristics are discussed. Finally, the single electron transistor with two barriers is demonstrated.

Correlation of film morphology and defect content with the charge-carrier transport in thin-film transistors based on ZnO nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polster, S.; Jank, M. P. M.; Frey, L.

2016-01-14

The correlation of defect content and film morphology with the charge-carrier transport in field-effect devices based on zinc oxide nanoparticles was investigated. Changes in the defect content and the morphology were realized by annealing and sintering of the nanoparticle thin films. Temperature-dependent electrical measurements reveal that the carrier transport is thermally activated for both the unsintered and sintered thin films. Reduced energetic barrier heights between the particles have been determined after sintering. Additionally, the energetic barrier heights between the particles can be reduced by increasing the drain-to-source voltage and the gate-to-source voltage. The changes in the barrier height are discussedmore » with respect to information obtained by scanning electron microscopy and photoluminescence measurements. It is found that a reduction of surface states and a lower roughness at the interface between the particle layer and the gate dielectric lead to lower barrier heights. Both surface termination and layer morphology at the interface affect the barrier height and thus are the main criteria for mobility improvement and device optimization.« less

Semantic 3d City Model to Raster Generalisation for Water Run-Off Modelling

NASA Astrophysics Data System (ADS)

Verbree, E.; de Vries, M.; Gorte, B.; Oude Elberink, S.; Karimlou, G.

2013-09-01

Water run-off modelling applied within urban areas requires an appropriate detailed surface model represented by a raster height grid. Accurate simulations at this scale level have to take into account small but important water barriers and flow channels given by the large-scale map definitions of buildings, street infrastructure, and other terrain objects. Thus, these 3D features have to be rasterised such that each cell represents the height of the object class as good as possible given the cell size limitations. Small grid cells will result in realistic run-off modelling but with unacceptable computation times; larger grid cells with averaged height values will result in less realistic run-off modelling but fast computation times. This paper introduces a height grid generalisation approach in which the surface characteristics that most influence the water run-off flow are preserved. The first step is to create a detailed surface model (1:1.000), combining high-density laser data with a detailed topographic base map. The topographic map objects are triangulated to a set of TIN-objects by taking into account the semantics of the different map object classes. These TIN objects are then rasterised to two grids with a 0.5m cell-spacing: one grid for the object class labels and the other for the TIN-interpolated height values. The next step is to generalise both raster grids to a lower resolution using a procedure that considers the class label of each cell and that of its neighbours. The results of this approach are tested and validated by water run-off model runs for different cellspaced height grids at a pilot area in Amersfoort (the Netherlands). Two national datasets were used in this study: the large scale Topographic Base map (BGT, map scale 1:1.000), and the National height model of the Netherlands AHN2 (10 points per square meter on average). Comparison between the original AHN2 height grid and the semantically enriched and then generalised height grids shows that water barriers are better preserved with the new method. This research confirms the idea that topographical information, mainly the boundary locations and object classes, can enrich the height grid for this hydrological application.

Barrier inhomogeneities limited current and 1/f noise transport in GaN based nanoscale Schottky barrier diodes

PubMed Central

Kumar, Ashutosh; Heilmann, M.; Latzel, Michael; Kapoor, Raman; Sharma, Intu; Göbelt, M.; Christiansen, Silke H.; Kumar, Vikram; Singh, Rajendra

2016-01-01

The electrical behaviour of Schottky barrier diodes realized on vertically standing individual GaN nanorods and array of nanorods is investigated. The Schottky diodes on individual nanorod show highest barrier height in comparison with large area diodes on nanorods array and epitaxial film which is in contrast with previously published work. The discrepancy between the electrical behaviour of nanoscale Schottky diodes and large area diodes is explained using cathodoluminescence measurements, surface potential analysis using Kelvin probe force microscopy and 1ow frequency noise measurements. The noise measurements on large area diodes on nanorods array and epitaxial film suggest the presence of barrier inhomogeneities at the metal/semiconductor interface which deviate the noise spectra from Lorentzian to 1/f type. These barrier inhomogeneities in large area diodes resulted in reduced barrier height whereas due to the limited role of barrier inhomogeneities in individual nanorod based Schottky diode, a higher barrier height is obtained. PMID:27282258

Diester Molecules for Organic-Based Electrical and Photoelectrical Devices

NASA Astrophysics Data System (ADS)

Topal, Giray; Tombak, Ahmet; Yigitalp, Esref; Batibay, Derya; Kilicoglu, Tahsin; Ocak, Yusuf Selim

2017-07-01

Diester derivatives of terephthalic acid molecules were synthesized according to the literature. Au/Diester derivatives/ n-Si organic-inorganic (OI) heterojunction-type devices were fabricated, and the current-voltage ( I- V) characteristics of the devices have been investigated at room temperature. I- V characteristics demonstrated that all diodes had excellent rectification properties. Primary diode parameters such as series resistance and barrier height were extracted by using semi-log I- V plots and Norde methods, and were compared. It was seen that there was a substantial agreement between results obtained from two methods. Calculated barrier height values were about the same with 0.02-eV differences that were attributed to the series resistance. Ideality factors, which show how the diode closes to ideal diodes, were also extracted from semi-log I- V plots. Thus, the modification of the Au/ n-Si diode potential barrier was accomplished using diester derivatives as an interlayer. The I- V measurements were repeated to characterize the devices at 100 mW/cm2 illumination intensity with the help of a solar simulator with an AM1.5G filter.

The effect of magnetic field on chiral transmission in p-n-p graphene junctions.

PubMed

Li, Yuan; Wan, Qi; Peng, Yingzi; Wang, Guanqing; Qian, Zhenghong; Zhou, Guanghui; Jalil, Mansoor B A

2015-12-18

We investigate Klein tunneling in graphene heterojunctions under the influence of a perpendicular magnetic field via the non-equilibrium Green's function method. We find that the angular dependence of electron transmission is deflected sideways, resulting in the suppression of normally incident electrons and overall decrease in conductance. The off-normal symmetry axis of the transmission profile was analytically derived. Overall tunneling conductance decreases to almost zero regardless of the potential barrier height V0 when the magnetic field (B-field) exceeds a critical value, thus achieving effective confinement of Dirac fermions. The critical field occurs when the width of the magnetic field region matches the diameter of the cyclotron orbit. The potential barrier also induces distinct Fabry-Pérot fringe patterns, with a "constriction region" of low transmission when V0 is close to the Fermi energy. Application of B-field deflects the Fabry-Pérot interference pattern to an off-normal angle. Thus, the conductance of the graphene heterojunctions can be sharply modulated by adjusting the B-field strength and the potential barrier height relative to the Fermi energy.

The effect of magnetic field on chiral transmission in p-n-p graphene junctions

NASA Astrophysics Data System (ADS)

Li, Yuan; Wan, Qi; Peng, Yingzi; Wang, Guanqing; Qian, Zhenghong; Zhou, Guanghui; Jalil, Mansoor B. A.

2015-12-01

We investigate Klein tunneling in graphene heterojunctions under the influence of a perpendicular magnetic field via the non-equilibrium Green’s function method. We find that the angular dependence of electron transmission is deflected sideways, resulting in the suppression of normally incident electrons and overall decrease in conductance. The off-normal symmetry axis of the transmission profile was analytically derived. Overall tunneling conductance decreases to almost zero regardless of the potential barrier height when the magnetic field (B-field) exceeds a critical value, thus achieving effective confinement of Dirac fermions. The critical field occurs when the width of the magnetic field region matches the diameter of the cyclotron orbit. The potential barrier also induces distinct Fabry-Pérot fringe patterns, with a “constriction region” of low transmission when is close to the Fermi energy. Application of B-field deflects the Fabry-Pérot interference pattern to an off-normal angle. Thus, the conductance of the graphene heterojunctions can be sharply modulated by adjusting the B-field strength and the potential barrier height relative to the Fermi energy.

Temperature Dependence Of Current-Voltage Characteristics Of Au/p-GaAsN Schottky Barrier Diodes, With Small N Content

NASA Astrophysics Data System (ADS)

Rangel-Kuoppa, Victor-Tapio; Reentilä, Outi; Sopanen, Markku; Lipsanen, Harri

2011-12-01

The temperature dependent current-voltage (IVT) measurements on Au Schottky barrier diodes made on intrinsically p-type GaAs1-xNx were carried out. Three samples with small N content (x = 0.5%, 0.7% and 1%) were studied. The temperature range was 10-320 K. All contacts were found to be of Schottky type. The ideality factor and the apparent barrier height calculated by using thermionic emission (TE) theory show a strong temperature dependence. The current voltage (IV) curves are fitted based on the TE theory, yielding a zero-bias carrier height (ΦB0) and a ideality factor (n) that decrease and increase with decreasing temperature, respectively. The linear fitting of ΦB0 vs n and its subsequent evaluation for n = 1 give a zero-bias ΦB0 in the order of 0.35-0.4 eV. From the reverse-bias IV study, it is found that the experimental carrier density (NA) values increase with increasing temperature and are in agreement with the intrinsic carrier concentration for GaAs.

Correlation between morphological defects, electron beam-induced current imaging, and the electrical properties of 4H-SiC Schottky diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Y.; Ali, G.N.; Mikhov, M.K.

2005-01-01

Defects in SiC degrade the electrical properties and yield of devices made from this material. This article examines morphological defects in 4H-SiC and defects visible in electron beam-induced current (EBIC) images and their effects on the electrical characteristics of Schottky diodes. Optical Nomarski microscopy and atomic force microscopy were used to observe the morphological defects, which are classified into 26 types based on appearance alone. Forward and reverse current-voltage characteristics were used to extract barrier heights, ideality factors, and breakdown voltages. Barrier heights decrease about linearly with increasing ideality factor, which is explained by discrete patches of low barrier heightmore » within the main contact. Barrier height, ideality, and breakdown voltage all degrade with increasing device diameter, suggesting that discrete defects are responsible. Electroluminescence was observed under reverse bias from microplasmas associated with defects containing micropipes. EBIC measurements reveal several types of features corresponding to recombination centers. The density of dark spots observed by EBIC correlates strongly with ideality factor and barrier height. Most morphological defects do not affect the reverse characteristics when no micropipes are present, but lower the barrier height and worsen the ideality factor. However, certain multiple-tailed defects, irregularly shaped defects and triangular defects with 3C inclusions substantially degrade both breakdown voltage and barrier height, and account for most of the bad devices that do not contain micropipes. Micropipes in these wafers are also frequently found to be of Type II, which do not run parallel to the c axis.« less

Correlation Between Morphological Defects, Electron Beam Induced Current Imaging, and the Electrical Properties of 4H-SiC Schottky Diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang,Y.; Ali, G.; Mikhov, M.

2005-01-01

Defects in SiC degrade the electrical properties and yield of devices made from this material. This article examines morphological defects in 4H-SiC and defects visible in electron beam-induced current (EBIC) images and their effects on the electrical characteristics of Schottky diodes. Optical Nomarski microscopy and atomic force microscopy were used to observe the morphological defects, which are classified into 26 types based on appearance alone. Forward and reverse current-voltage characteristics were used to extract barrier heights, ideality factors, and breakdown voltages. Barrier heights decrease about linearly with increasing ideality factor, which is explained by discrete patches of low barrier heightmore » within the main contact. Barrier height, ideality, and breakdown voltage all degrade with increasing device diameter, suggesting that discrete defects are responsible. Electroluminescence was observed under reverse bias from microplasmas associated with defects containing micropipes. EBIC measurements reveal several types of features corresponding to recombination centers. The density of dark spots observed by EBIC correlates strongly with ideality factor and barrier height. Most morphological defects do not affect the reverse characteristics when no micropipes are present, but lower the barrier height and worsen the ideality factor. However, certain multiple-tailed defects, irregularly shaped defects and triangular defects with 3C inclusions substantially degrade both breakdown voltage and barrier height, and account for most of the bad devices that do not contain micropipes. Micropipes in these wafers are also frequently found to be of Type II, which do not run parallel to the c axis.« less

Cumulative dose 60Co gamma irradiation effects on AlGaN/GaN Schottky diodes and its area dependence

NASA Astrophysics Data System (ADS)

Sharma, Chandan; Laishram, Robert; Rawal, Dipendra Singh; Vinayak, Seema; Singh, Rajendra

2018-04-01

Cumulative dose gamma radiation effects on current-voltage characteristics of GaN Schottky diodes have been investigated. The different area diodes have been fabricated on AlGaN/GaN high electron mobility transistor (HEMT) epi-layer structure grown over SiC substrate and irradiated with a dose up to the order of 104 Gray (Gy). Post irradiation characterization shows a shift in the turn-on voltage and improvement in reverse leakage current. Other calculated parameters include Schottky barrier height, ideality factor and reverse saturation current. Schottky barrier height has been decreased whereas reverse saturation current shows an increase in the value post irradiation with improvement in the ideality factor. Transfer length measurement (TLM) characterization shows an improvement in the contact resistance. Finally, diodes with larger area have more variation in the calculated parameters due to the induced local heating effect.

Intercalating cobalt between graphene and iridium (111): Spatially dependent kinetics from the edges

NASA Astrophysics Data System (ADS)

Vlaic, Sergio; Rougemaille, Nicolas; Kimouche, Amina; Burgos, Benito Santos; Locatelli, Andrea; Coraux, Johann

2017-10-01

Using low-energy electron microscopy, we image in real time the intercalation of a cobalt monolayer between graphene and the (111) surface of iridium. Our measurements reveal that the edges of a graphene flake represent an energy barrier to intercalation. Based on a simple description of the growth kinetics, we estimate this energy barrier and find small, but substantial, local variations. These local variations suggest a possible influence of the graphene orientation with respect to its substrate and of the graphene edge termination on the energy value of the barrier height. Besides, our measurements show that intercalated cobalt is energetically more favorable than cobalt on bare iridium, indicating a surfactant role of graphene.

Parameterization of fission barrier heights of medium, heavy and super heavy nuclei

NASA Astrophysics Data System (ADS)

Manjunatha, H. C.

2017-12-01

A new semi empirical formula is proposed for fission barrier heights of medium, heavy and super heavy nuclei in the atomic number region 50 ≤ Z ≤ 130. The fitting parameters for the proposed formula are obtained by making a polynomial fit to the available theoretical and experimental data. The calculated fission barrier heights are compared with that of experiments and other theoretical models such as SHF(SLy6) (Burvenich et al. in Phys Rev C 69:014307, 2004), SHFB(SkM) (Baran et al. in Nucl Phys A 944:442, 2015), FRLDM (Möller et al. in Phys Rev C 79:064304, 2009), ETFSI (SkSC4) with Skyrme SkSC4 force (Mamdouh et al. in Nucl Phys A 679:337, 2001), WS (Kowal et al. in Phys Rev C 82:014303, 2010) and CDFT(DD-ME2) (Abusara et al. in Phys Rev C 85:024314, 2012). The standard deviation for fission barrier heights produced by present formula is evaluated. The good agreement of present formula with the experiments and other models suggests that the present formula could be used to evaluate the fission barrier heights of medium, heavy and super heavy nuclei in the region 50 ≤ Z ≤ 130. This formula is a first of its kind that produces fission barrier heights of 2858 nuclei with the only simple inputs of only neutron number (N), proton number (Z) and mass number (A).

Parameterization of fission barrier heights of medium, heavy and super heavy nuclei

NASA Astrophysics Data System (ADS)

Manjunatha, H. C.

2018-04-01

A new semi empirical formula is proposed for fission barrier heights of medium, heavy and super heavy nuclei in the atomic number region 50 ≤ Z ≤ 130. The fitting parameters for the proposed formula are obtained by making a polynomial fit to the available theoretical and experimental data. The calculated fission barrier heights are compared with that of experiments and other theoretical models such as SHF(SLy6) (Burvenich et al. in Phys Rev C 69:014307, 2004), SHFB(SkM) (Baran et al. in Nucl Phys A 944:442, 2015), FRLDM (Möller et al. in Phys Rev C 79:064304, 2009), ETFSI (SkSC4) with Skyrme SkSC4 force (Mamdouh et al. in Nucl Phys A 679:337, 2001), WS (Kowal et al. in Phys Rev C 82:014303, 2010) and CDFT(DD-ME2) (Abusara et al. in Phys Rev C 85:024314, 2012). The standard deviation for fission barrier heights produced by present formula is evaluated. The good agreement of present formula with the experiments and other models suggests that the present formula could be used to evaluate the fission barrier heights of medium, heavy and super heavy nuclei in the region 50 ≤ Z ≤ 130. This formula is a first of its kind that produces fission barrier heights of 2858 nuclei with the only simple inputs of only neutron number (N), proton number (Z) and mass number (A).

Synchrotron Radiation and the Far-Infrared and Mid-Infrared Spectra of Ncncs

NASA Astrophysics Data System (ADS)

Winnewisser, Manfred; Winnewisser, Brenda P.; De Lucia, Frank C.; Tokaryk, Dennis; Ross, Stephen Cary; Billinghurst, Brant E.

2014-06-01

The large-amplitude in-plane bending vibration of NCNCS at 85 wn has a potential energy function which includes a barrier to linearity with a height of about 285 wn. The topology of the surface of the space defined by this two-dimensional potential function exhibits non-trivial monodromy. Therefore an energy/momentum map for a quantum system with its motion determined by such a potential takes the form of a lattice which contains a defect associated with the top of the barrier. In NCNCS, the wavenumber values of the fundamental vibrational excitation and the barrier height mean that easily accessible energy levels allow us to observe 3 bending vibrational levels below and 3 above the barrier, yet still below all of the other vibrational levels, allowing the study of all the levels in the neighborhood of the defect. In three measuring campaigns at the Canadian Light Source in May of the years 2011, 2012, and 2013 we have now obtained 8 of the 9 fundamental vibrational band systems of NCNCS in high resolution, in particular that of the large-amplitude bend in the FIR. So far only a-type spectra have been assigned. Thus we have now determined the Δvb = 1, and ΔKa = 0 vibrational intervals (using bent molecule notation) but do not yet have experimental values for either rotational ΔKa = +/- 1 intervals nor ro-vibrational Δvb = 1, ΔKa = +/- 1 intervals. In May of 2014 we will have our last measuring campaign and hope to observe the more elusive b-type transitions.

Electrical parameters of Au/n-GaN and Pt/n-GaN Schottky diodes

NASA Astrophysics Data System (ADS)

Kadaoui, Mustapha Amine; Bouiadjra, Wadi Bachir; Saidane, Abdelkader; Belahsene, Sofiane; Ramdane, Abderrahim

2015-06-01

Electrical properties of Si-doped GaN epitaxial layers, grown on a c-plane sapphire substrate by MOCVD to form Schottky diodes with Gold (Au) and platinum (Pt) and using Ti/Al/Au as Ohmic contact, are investigated. Characterization was performed through I-V and C-V-f measurements at room temperature. Schottky barrier height (Φb), ideality factor (n), and series resistance (Rs) were extracted from forward I-V characteriztics using Cheung and Lien methods. Φb, doping concentration (Nd) and Rs frequency dependence were extracted from C-V-f characteriztics. Pt/n-GaN shows a non-linear behavior with a barrier height of 0.63 eV, an ideality factor of 2.3, and series resistance of 63 Ω. Au/n-GaN behaves like two diodes in parallel with two barrier heights of (0.83 and 0.9 eV), two ideality factors of (5.8 and 3.18) and two series resistance of (10.6 and 68 Ω). Interface state properties in both samples have been investigated taking into account the bias dependence of the effective barrier height. The amount of stimulated traps along the energy-gap at the interface increases with voltage bias, which increases NSS exponentially from 4.24 ṡ 1013 to 3.67 ṡ 1014 eV-1 cm-2 in the range (Ec - 0.17) to (Ec - 0.61) eV for Pt/n-GaN, and from 2.3 ṡ 1013 to 1.14 ṡ 1014 eV-1 cm-2, in the range (Ec - 0.31) to (Ec - 0.82) eV for Au/n-GaN. The values of interface states density and series resistance for both samples are found to decrease with increasing frequency. Peak intensity was a measure of active interface states. C-V-f results confirm the model of the Schottky diode with a native interfacial insulator layer along the space charge region.

Interfacial Chemistry-Induced Modulation of Schottky Barrier Heights: In Situ Measurements of the Pt-Amorphous Indium Gallium Zinc Oxide Interface Using X-ray Photoelectron Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flynn, Brendan T.; Oleksak, Richard P.; Thevuthasan, Suntharampillai

A method to modulate the Schottky barrier heights for platinum and amorphous indium gallium zinc oxide (a-IGZO) interfaces is demonstrated through thermal processing and background ambient pressure control. The interfacial chemistries that modulate barrier heights for the Pt/a-IGZO system were investigated using in-situ X-ray photoelectron spectroscopy. A significant reduction of indium, from In3+ to In0, occurs during deposition of Pt on to the a-IGZO surface in ultra-high vacuum. Post-annealing and controlling the background ambient O2 pressure allows tuning the degree of indium reduction and the corresponding Schottky barrier height between 0.17 to 0.77 eV. Understanding the detailed interfacial chemistries atmore » Pt/a-IGZO interfaces may allow for improved electronic device performance, including Schottky diodes, memristors, and metalsemiconductor field-effect transistors.« less

Interfacial Chemistry-Induced Modulation of Schottky Barrier Heights: In Situ Measurements of the Pt–Amorphous Indium Gallium Zinc Oxide Interface Using X-ray Photoelectron Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flynn, Brendan T.; Oleksak, Richard P.; Thevuthasan, Suntharampillai

A method to modulate the Schottky barrier heights for platinum and amorphous indium gallium zinc oxide (a-IGZO) interfaces is demonstrated through thermal processing and background ambient pressure control. The interfacial chemistries that modulate barrier heights for the Pt/a-IGZO system were investigated using in-situ X-ray photoelectron spectroscopy. A significant reduction of indium, from In 3+ to In 0, occurs during deposition of Pt on to the a-IGZO surface in ultra-high vacuum. Post-annealing and controlling the background ambient O 2 pressure allows tuning the degree of indium reduction and the corresponding Schottky barrier height between 0.17 to 0.77 eV. Understanding the detailedmore » interfacial chemistries at Pt/a-IGZO interfaces may allow for improved electronic device performance, including Schottky diodes, memristors, and metalsemiconductor field-effect transistors.« less

Calculation of multidimensional potential energy surfaces for even-even transuranium nuclei: systematic investigation of the triaxiality effect on the fission barrier

NASA Astrophysics Data System (ADS)

Chai, Qing-Zhen; Zhao, Wei-Juan; Liu, Min-Liang; Wang, Hua-Lei

2018-05-01

Static fission barriers for 95 even-even transuranium nuclei with charge number Z = 94–118 have been systematically investigated by means of pairing self-consistent Woods-Saxon-Strutinsky calculations using the potential energy surface approach in multidimensional (β 2, γ, β 4) deformation space. Taking the heavier 252Cf nucleus (with the available fission barrier from experiment) as an example, the formation of the fission barrier and the influence of macroscopic, shell and pairing correction energies on it are analyzed. The results of the present calculated β 2 values and barrier heights are compared with previous calculations and available experiments. The role of triaxiality in the region of the first saddle is discussed. It is found that the second fission barrier is also considerably affected by the triaxial deformation degree of freedom in some nuclei (e.g., the Z=112–118 isotopes). Based on the potential energy curves, general trends of the evolution of the fission barrier heights and widths as a function of the nucleon numbers are investigated. In addition, the effects of Woods-Saxon potential parameter modifications (e.g., the strength of the spin-orbit coupling and the nuclear surface diffuseness) on the fission barrier are briefly discussed. Supported by National Natural Science Foundation of China (11675148, 11505157), the Project of Youth Backbone Teachers of Colleges and Universities of Henan Province (2017GGJS008), the Foundation and Advanced Technology Research Program of Henan Province (162300410222), the Outstanding Young Talent Research Fund of Zhengzhou University (1521317002) and the Physics Research and Development Program of Zhengzhou University (32410017)

A model to non-uniform Ni Schottky contact on SiC annealed at elevated temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pristavu, G.; Brezeanu, G.; Badila, M.

2015-06-29

Ni Schottky contacts on SiC have a nonideal behavior, with strong temperature dependence of the electrical parameters, caused by a mixed barrier on the contact area and interface states. A simple analytical model that establishes a quantitative correlation between Schottky contact parameter variation with temperature and barrier height non-uniformity is proposed. A Schottky contact surface with double Schottky barrier is considered. The main model parameters are the lower barrier (Φ{sub Bn,l}) and a p factor which quantitatively evaluates the barrier non-uniformity on the Schottky contact area. The model is validated on Ni/4H-SiC Schottky contacts, post metallization sintered at high temperatures.more » The measured I{sub F}–V{sub F}–T characteristics, selected so as not to be affected by interface states, were used for model correlation. An inhomogeneous double Schottky barrier (with both nickel silicide and Ni droplets at the interface) is formed by a rapid thermal annealing (RTA) at 750 °C. High values of the p parameter are obtained from samples annealed at this temperature, using the proposed model. A significant improvement in the electrical properties occurs following RTA at 800 °C. The expansion of the Ni{sub 2}Si phase on the whole contact area is evinced by an X-Ray diffraction investigation. In this case, the p factor is much lower, attesting the uniformity of the contact. The model makes it possible to evaluate the real Schottky barrier, for a homogenous Schottky contact. Using data measured on samples annealed at 800 °C, a true barrier height of around 1.73 V has been obtained for Ni{sub 2}Si/4H-SiC Schottky contacts.« less

Band-selective filter in a zigzag graphene nanoribbon.

PubMed

Nakabayashi, Jun; Yamamoto, Daisuke; Kurihara, Susumu

2009-02-13

Electric transport of a zigzag graphene nanoribbon through a steplike potential and a barrier potential is investigated by using the recursive Green's function method. In the case of the steplike potential, we demonstrate numerically that scattering processes obey a selection rule for the band indices when the number of zigzag chains is even; the electrons belonging to the "even" ("odd") bands are scattered only into the even (odd) bands so that the parity of the wave functions is preserved. In the case of the barrier potential, by tuning the barrier height to be an appropriate value, we show that it can work as the "band-selective filter", which transmits electrons selectively with respect to the indices of the bands to which the incident electrons belong. Finally, we suggest that this selection rule can be observed in the conductance by applying two barrier potentials.

Shingle system

DOEpatents

Dinwoodie, Thomas L [Piedmont, CA

2008-02-12

A barrier, such as a PV module, is secured to a base by a support to create a shingle assembly with a venting region defined between the barrier and base for temperature regulation. Water resistant junctions may be formed between the bases of adjacent shingle assemblies of an array of shingle assemblies. The base may include an insulation layer underlying a water barrier. The base may also include a waterproofing element; the width and height of the barrier may be shorter than the width and height of the waterproofing element.

Interface state density of free-standing GaN Schottky diodes

NASA Astrophysics Data System (ADS)

Faraz, S. M.; Ashraf, H.; Imran Arshad, M.; Hageman, P. R.; Asghar, M.; Wahab, Q.

2010-09-01

Schottky diodes were fabricated on the HVPE-grown, free-standing gallium nitride (GaN) layers of n- and p-types. Both contacts (ohmic and Schottky) were deposited on the top surface using Al/Ti and Pd/Ti/Au, respectively. The Schottky diode fabricated on n-GaN exhibited double barriers with values of 0.9 and 0.6 eV and better performance in the rectification factor together with reverse and forward currents with an ideality factor of 1.8. The barrier height for the p-GaN Schottky diode is 0.6 eV with an ideality factor of 4.16. From the capacitance-voltage (C-V) measurement, the net doping concentration of n-GaN is 4 × 1017 cm-3, resulting in a lower reverse breakdown of around -12 V. The interface state density (NSS) as a function of EC-ESS is found to be in the range 4.23 × 1012-3.87 × 1011 eV-1 cm-2 (below the conduction band) from Ec-0.90 to EC-0.99. Possible reasons responsible for the low barrier height and high ideality factor have been addressed.

Performance of RF sputtered p-Si/n-ZnO nanoparticle thin film heterojunction diodes in high temperature environment

NASA Astrophysics Data System (ADS)

Singh, Satyendra Kumar; Hazra, Purnima

2017-04-01

In this article, temperature-dependent current-voltage characteristics of n-ZnO/p-Si nanoparticle thin film heterojunction diode grown by RF sputtering technique are analyzed in the temperature range of 300-433 k to investigate the performance of the device in high temperature environment. The microstructural, morphological, optical and temptrature dependent electrical properties of as-grown nanoparticle thin film were characterized by X-ray diffractometer (XRD), atomic force microscopy (AFM), field emmision scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), variable angle ellipsometer and semiconductor device analyzer. XRD spectra of as-grown ZnO films are exhibited that highly c-axis oriented ZnO nanostructures are grown on p- Si〈100〉 substrate whereas AFM and FESEM images confirm the homogeneous deposition of ZnO nanoparticles on surface of Si substratewith minimum roughness.The optical propertiesof as-grown ZnO nanoparticles have been measured in the spectral range of 300-800 nm using variable angle ellipsometer.To measure electrical parameters of the device prototype in the temperature range of room temperature (300 K) to 433 K, large area ohmic contacts were fabricated on both side of the ZnO/Si heterostructure. From the current-voltage charcteristics of ZnO/Si heterojunction device, it is observed that the device exhibits rectifing nature at room temperature. However, with increase in temperature, reverse saturation current and barrier height are found to increase, whereas ideality factor is started decreasing. This phenomenon confirms that barrier inhomogeneities are present at the interface of ZnO/Si heterojunction, as a result of lattice constant and thermal coefficient mismatch between Si and ZnO. Therefore, a modified value of Richardson constant [33.06 Acm-2K-2] has been extracted from the temperature-dependent electrical characteristics after assuming the Gaussian distribution of special barrier height inhomogeneities across the Si/ZnO interface which is close to its theoretical value [32 Acm-2K-2]. This result indicates that regardless of presence of barrier height inmogeneities, ZnO/Si heterojunction diode still hasability to perform well in high temperature environment.

Calculation of the Electronic Parameters of an Al/DNA/p-Si Schottky Barrier Diode Influenced by Alpha Radiation

PubMed Central

Al-Ta’ii, Hassan Maktuff Jaber; Amin, Yusoff Mohd; Periasamy, Vengadesh

2015-01-01

Many types of materials such as inorganic semiconductors have been employed as detectors for nuclear radiation, the importance of which has increased significantly due to recent nuclear catastrophes. Despite the many advantages of this type of materials, the ability to measure direct cellular or biological responses to radiation might improve detector sensitivity. In this context, semiconducting organic materials such as deoxyribonucleic acid or DNA have been studied in recent years. This was established by studying the varying electronic properties of DNA-metal or semiconductor junctions when exposed to radiation. In this work, we investigated the electronics of aluminium (Al)/DNA/silicon (Si) rectifying junctions using their current-voltage (I-V) characteristics when exposed to alpha radiation. Diode parameters such as ideality factor, barrier height and series resistance were determined for different irradiation times. The observed results show significant changes with exposure time or total dosage received. An increased deviation from ideal diode conditions (7.2 to 18.0) was observed when they were bombarded with alpha particles for up to 40 min. Using the conventional technique, barrier height values were observed to generally increase after 2, 6, 10, 20 and 30 min of radiation. The same trend was seen in the values of the series resistance (0.5889–1.423 Ω for 2–8 min). These changes in the electronic properties of the DNA/Si junctions could therefore be utilized in the construction of sensitive alpha particle detectors. PMID:25730484

Effects of the temperature and pressure on the electronic and optical properties of an exciton in GaAs/Ga1-xAlxAs quantum ring

NASA Astrophysics Data System (ADS)

El-Bakkari, K.; Sali, A.; Iqraoun, E.; Rezzouk, A.; Es-Sbai, N.; Ouazzani Jamil, M.

2018-06-01

Using a variational approach, we have calculated the binding energies (E1s,2sb) and interband emission energy (Eph) of an exciton confined in GaAs / Ga1 - x Alx As quantum rings (QRs) structures under effects of the temperature and pressure, in the effective mass approximation. We have taken into consideration the difference in the effective masses of the charge carriers in two materials, well and barrier. The results that we have obtained show clearly that E1s,2sb and Eph are influenced by the structure geometries of QR (height H, radial thickness Δ R and potential barrier), the temperature and pressure. Indeed, with a smaller geometric parameter, E1s,2sb and Eph become higher due to the improvement in confinement of the charge carriers. We have also observed that for a given value of the temperature, the pressure leads to an increasing of the E1s,2sb and Eph , and the latter quantities are decreasing with temperature. In addition, these variations of the E1s,2sb and Eph under the external perturbations are more remarkable in small H for fixed Δ R , and for larger Δ R for a given value of the H, because for the choice of a finite height of the barrier in the z direction and an infinite confinement in ρ direction.

Experimental investigation of terahertz quantum cascade laser with variable barrier heights

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Aiting; Vijayraghavan, Karun; Belkin, Mikhail A., E-mail: mbelkin@ece.utexas.edu

2014-04-28

We report an experimental study of terahertz quantum cascade lasers with variable barrier heights based on the Al{sub x}Ga{sub 1–x}As/GaAs material system. Two new designs are developed based on semiclassical ensemble Monte Carlo simulations using state-of-the-art Al{sub 0.15}Ga{sub 0.85}As/GaAs three-quantum-well resonant phonon depopulation active region design as a reference. The new designs achieved maximum lasing temperatures of 188 K and 172 K, as compared to the maximum lasing temperature of 191 K for the reference structure. These results demonstrate that terahertz quantum cascade laser designs with variable barrier heights provide a viable alternative to the traditional active region designs with fixed barrier composition.more » Additional design space offered by using variable barriers may lead to future improvements in the terahertz quantum cascade laser performance.« less

Ideal MHD stability of double transport barrier plasmas in DIII-D

NASA Astrophysics Data System (ADS)

Li, G. Q.; Wang, S. J.; Lao, L. L.; Turnbull, A. D.; Chu, M. S.; Brennan, D. P.; Groebner, R. J.; Zhao, L.

2008-01-01

The ideal MHD stability for double transport barrier (DTB or DB) plasmas with varying edge and internal barrier width and height was investigated, using the ideal MHD stability code GATO. A moderate ratio of edge transport barriers (ETB) height to internal transport barriers (ITBs) height is found to be beneficial to MHD stability and the βN is limited by global low n instabilities. For moderate ITB width DB plasmas, if the ETB is weak, the stability is limited by n = 1 (n is the toroidal mode number) global mode; whereas if the ETB is strong it is limited by intermediate-n edge peeling-ballooning modes. Broadening the ITB can improve stability if the ITB half width wi lsim 0.3. For very broad ITB width plasmas the stability is limited by stability to a low n (n > 1) global mode.

Role of structural relaxations and chemical substitutions on piezoelectric fields and potential lineup in GaN/Al junctions

NASA Astrophysics Data System (ADS)

Picozzi, S.; Profeta, G.; Continenza, A.; Massidda, S.; Freeman, A. J.

2002-04-01

First-principles full-potential linearized augmented plane wave calculations are performed to clarify the role of the interface geometry on piezoelectric fields and potential lineups in [0001] wurtzite and [111]-zincblende GaN/Al junctions. The electric field (polarity and magnitude) is found to be strongly affected by atomic relaxations in the interface region. A procedure is used to evaluate the Schottky-barrier height in the presence of electric fields, showing that their effect is relatively small (a few tenths of an eV). These calculations assess the rectifying behavior of the GaN/Al contact, in agreement with experimental values for the barrier. We disentangle chemical and structural effects on the relevant properties (such as the potential discontinuity and the electric field) by studying unrelaxed ideal nitride/metal systems. Using simple electronegativity arguments, we outline the leading mechanisms that define the values of the electric field and Schottky barrier in these ideal systems. Finally, the transitivity rule is proved to be well satisfied.

Influence of temperature on Al/p-CuInAlSe2 thin-film Schottky diodes

NASA Astrophysics Data System (ADS)

Parihar, Usha; Ray, Jaymin; Panchal, C. J.; Padha, Naresh

2016-06-01

Al/p-CuInAlSe2 Schottky diodes were fabricated using the optimized thin layers of CuInAlSe2 semiconductor. These diodes were used to study their temperature-dependent current-voltage (I-V) and capacitance-voltage (C-V) analysis over a wide range of 233-353 K. Based on these measurements, diode parameters such as ideality factor ( η), barrier height (ϕbo) and series resistance ( R s) were determined from the downward curvature of I-V characteristics using Cheung and Cheung method. The extracted parameters were found to be strongly temperature dependent; ϕbo increases, while η and R s decrease with increasing temperature. This behavior of ϕbo and η with change in temperature has been explained on the basis of barrier inhomogeneities over the MS interface by assuming a Gaussian distribution (GD) of the ϕbo at the interface. GD of barrier height (BH) was confirmed from apparent BH (ϕap) versus q/2 kT plot, and the values of the mean BH and standard deviation (σs) obtained from this plot at zero bias were found to be 1.02 and 0.14 eV, respectively. Also, a modified ln ( {J_{{s}} /T2 } ) - q2 σ_{{s}}2 /2k2 T2 versus q/ kT plot for Al/p-CuInAlSe2 Schottky diodes according to the GD gives ϕbo and Richardson constant ( A ** ) as 1.01 eV and 26 Acm-2 K-2, respectively. The Richardson constant value of 26 Acm-2 K-2 is very close to the theoretical value of 30 Acm-2 K-2. The discrepancy between BHs obtained from I-V and C-V measurements has also been interpreted.

Exploratory Corrugated Infrared Hot-Electron Transistor Arrays

DTIC Science & Technology

2009-02-01

quantum well infrared photodetector ( QWIP ) structure. This improvement is consistent with the hot-electron distributions created by the thermal and...the designed value. This higher barrier height can be attributed to the finite p-type doping density in the material. 15. SUBJECT TERMS QWIP ...infrared photodetector ( QWIP ) sensor in a small exploratory array format, which is capable of suppressing the detector dark current. The new detector

Communication: An accurate calculation of the S{sub 1} C{sub 2}H{sub 2} cis-trans isomerization barrier height

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baraban, Joshua H.; Matthews, Devin A.; Stanton, John F.

2016-03-21

A high level ab initio calculation of the cis-trans isomerization barrier height in the first excited singlet electronic state of acetylene is found to agree very well with a recent experimental determination.

Communication: An accurate calculation of the S 1 C 2H 2 cis-trans isomerization barrier height

DOE PAGES

Baraban, Joshua H.; Matthews, Devin A.; Stanton, John F.

2016-03-16

In this study, a high level ab initio calculation of the cis-trans isomerization barrier height in the first excited singlet electronic state of acetylene is found to agree very well with a recent experimental determination.

Effect of barrier height on friction behavior of the semiconductors silicon and gallium arsenide in contact with pure metals

NASA Technical Reports Server (NTRS)

Mishina, H.; Buckley, D. H.

1984-01-01

Friction experiments were conducted for the semiconductors silicon and gallium arsenide in contact with pure metals. Polycrystalline titanium, tantalum, nickel, palladium, and platinum were made to contact a single crystal silicon (111) surface. Indium, nickel, copper, and silver were made to contact a single crystal gallium arsenide (100) surface. Sliding was conducted both in room air and in a vacuum of 10 to the minus 9th power torr. The friction of semiconductors in contact with metals depended on a Schottky barrier height formed at the metal semiconductor interface. Metals with a higher barrier height on semiconductors gave lower friction. The effect of the barrier height on friction behavior for argon sputtered cleaned surfaces in vacuum was more specific than that for the surfaces containing films in room air. With a silicon surface sliding on titanium, many silicon particles back transferred. In contrast, a large quantity of indium transferred to the gallium arsenide surface.

Interfacial Chemistry-Induced Modulation of Schottky Barrier Heights: In Situ Measurements of the Pt-Amorphous Indium Gallium Zinc Oxide Interface Using X-ray Photoelectron Spectroscopy.

PubMed

Flynn, Brendan T; Oleksak, Richard P; Thevuthasan, Suntharampillai; Herman, Gregory S

2018-01-31

A method to understand the role of interfacial chemistry on the modulation of Schottky barrier heights for platinum and amorphous indium gallium zinc oxide (a-IGZO) interfaces is demonstrated through thermal processing and background ambient pressure control. In situ X-ray photoelectron spectroscopy was used to characterize the interfacial chemistries that modulate barrier heights in this system. The primary changes were a significant chemical reduction of indium, from In 3+ to In 0 , that occurs during deposition of Pt on to the a-IGZO surface in ultrahigh vacuum. Postannealing and controlling the background ambient O 2 pressure allows further tuning of the reduction of indium and the corresponding Schottky barrier heights from 0.17 to 0.77 eV. Understanding the detailed interfacial chemistries at Pt/a-IGZO interfaces may allow for improved electronic device performance, including Schottky diodes, memristors, and metal-semiconductor field-effect transistors.

Effect of the δ-potential on spin-dependent electron tunneling in double barrier semiconductor heterostructure

NASA Astrophysics Data System (ADS)

Chandrasekar, L. Bruno; Gnanasekar, K.; Karunakaran, M.

2018-06-01

The effect of δ-potential was studied in GaAs/Ga0.6Al0·4As double barrier heterostructure with Dresselhaus spin-orbit interaction. The role of barrier height and position of the δ- potential in the well region was analysed on spin-dependent electron tunneling using transfer matrix method. The spin-separation between spin-resonances on energy scale depends on both height and position of the δ- potential, whereas the tunneling life time of electrons highly influenced by the position of the δ- potential and not on the height. These results might be helpful for the fabrication of spin-filters.

Effect of crystal size distribution on thermoelectric performance for Lanthanum-doped strontium titanate bulk material

NASA Astrophysics Data System (ADS)

Zhang, Boyu; Wang, Jun; Yaer, Xinba; Huo, Zhenzhen; Wu, Yin; Li, Yan; Miao, Lei; Liu, Chengyan; Zou, Tao; Ma, Wen

2015-07-01

Effect of crystal size distribution on thermoelectric performance of Lanthanum-doped strontium titanate (La-SrTiO3) ceramics are investigated in this study. Thermoelectric performance measurement, coupled with microstructure studies, shows that the electrical conductivity strongly depends on the crystal size, potential barrier on the grain boundary and porosity. Meantime, because the average potential barriers height are increased along with the reduction of crystal size, the Seebeck coefficients are increased by energy filtering effect at the large number of grain boundaries. As a result, by controlling of crystal size distribution, ZT value of La-SrTiO3 is improved.

Dependence of Fusion Barrier Heights on the Difference of Proton and Neutron Radii

NASA Astrophysics Data System (ADS)

Dobrowolski, A.; Pomorski, K.; Bartel, J.

2005-04-01

Using the Skyrme effective nucleon--nucleon interaction together with the semiclassical Extended Thomas--Fermi approach (ETF) we investigate the relative change of the fusion barrier heights for the reaction 16O+208Pb as function of the nuclear proton or neutron radii of the colliding nuclei.

Electrical conduction mechanism and dielectric characterization of MnTPPCl thin films

NASA Astrophysics Data System (ADS)

Meikhail, M. S.; Oraby, A. H.; El-Nahass, M. M.; Zeyada, H. M.; Al-Muntaser, A. A.

2018-06-01

The AC conductivity and dielectric properties of MnTPPCl sandwich structure as Au/MnTPPCl/Au were studied. The conductivity of the MnTPPCl thin films have been interpreted by the correlated barrier hopping (CBH) model. The dominant conduction process have found to be the single polaron hopping conduction. The values of the hopping distance, Rω, barrier height, W, and the localized-state density, N, are estimated at different frequencies. The behavior of dielectric constant and dielectric loss was discussed as a function of temperature and frequency. The dielectric constant was described in terms of polarization mechanism in materials. The spectral behavior of dielectric loss is interpreted on the basis of the Giuntini et al. model [1]. The value of WM is obtained as 0.32 eV. A non-Debye relaxation phenomenon was observed from the dielectric relaxation mechanism.

Railroad retarder noise reduction : study of acoustical barrier configurations

DOT National Transportation Integrated Search

1979-05-01

Field measurements of noise were made near a railroad retarder system without barriers and with acoustical barriers of various configurations. The configurations tested included acoustically reflective and acoustically absorptive barriers with height...

Realizing nanographene activated by a vacancy to solve hydrogen storage problem

NASA Astrophysics Data System (ADS)

Sunnardianto, Gagus Ketut; Maruyama, Isao; Kusakabe, Koichi

We found a triply hydrogenated vacancy (V111) in nanographene reduces an activation barrier of adsorption-desorption process in both ways in an equal manner from the known values for pristine graphene as well as those of other hydrogenated vacancies of graphene. This finding may give a key to overcome existing problems in the hydrogen uptake and release processes in known hydrogen storage materials, e.g. graphene and organic hydrides (OHs) in near ambient operation temperature. In this study, we used DFT-NEB simulation to estimate the barrier height, which is supported by realized real experiments. We consider a nanographene molecule (VANG) which contains V111 with armchair structure at the periphery. We found interesting feature in comparable values of energy barriers for both hydrogen uptake and release, where hydrogenation process is even a little bit endothermic and dehydrogenation is a little but exothermic nature. Thus, this material structure acts as ``self-catalytic properties'', which has an important role in reducing an energy barrier and as a trapping site for hydrogen serving a new material prevailing other hopeful candidates. The work is supported by JSPS KAKENHI in Science of Atomic Layers\\x9D.

Planar doped barrier subharmonic mixers

NASA Technical Reports Server (NTRS)

Lee, T. H.; East, J. R.; Haddad, G. I.

1992-01-01

The Planar Doped Barrier (PDB) diode is a device consisting of a p(+) doping spike between two intrinsic layers and n(+) ohmic contacts. This device has the advantages of controllable barrier height, diode capacitance and forward to reverse current ratio. A symmetrically designed PDB has an anti-symmetric current vs. voltage characteristic and is ideal for use as millimeter wave subharmonic mixers. We have fabricated such devices with barrier heights of 0.3, 0.5 and 0.7 volts from GaAs and InGaAs using a multijunction honeycomb structure with junction diameters between one and ten microns. Initial RF measurements are encouraging. The 0.7 volt barrier height 4 micron GaAs devices were tested as subharmonic mixers at 202 GHz with an IF frequency of 1 GHz and had 18 dB of conversion loss. The estimated mismatch loss was 7 dB and was due to higher diode capacitance. The LO frequency was 100.5 GHz and the pump power was 8 mW.

Modulation of Folding Internal Friction by Local and Global Barrier Heights.

PubMed

Zheng, Wenwei; de Sancho, David; Best, Robert B

2016-03-17

Recent experiments have revealed an unexpected deviation from a first power dependence of protein relaxation times on solvent viscosity, an effect that has been attributed to "internal friction". One clear source of internal friction in protein dynamics is the isomerization of dihedral angles. A key outstanding question is whether the global folding barrier height influences the measured internal friction, based on the observation that the folding rates of fast-folding proteins, with smaller folding free energy barriers, tend to exhibit larger internal friction. Here, by studying two alanine-based peptides, we find that systematic variation of global folding barrier heights has little effect on the internal friction for folding rates. On the other hand, increasing local torsion angle barriers leads to increased internal friction, which is consistent with solvent memory effects being the origin of the viscosity dependence. Thus, it appears that local torsion transitions determine the viscosity dependence of the diffusion coefficient on the global coordinate and, in turn, internal friction effects on the folding rate.

Comparison of nickel, cobalt, palladium, and tungsten Schottky contacts on n-4H-silicon carbide

NASA Astrophysics Data System (ADS)

Gora, V. E.; Chawanda, A.; Nyamhere, C.; Auret, F. D.; Mazunga, F.; Jaure, T.; Chibaya, B.; Omotoso, E.; Danga, H. T.; Tunhuma, S. M.

2018-04-01

We have investigated the current-voltage (I-V) characteristics of nickel (Ni), cobalt (Co), tungsten (W) and palladium (Pd) Schottky contacts on n-type 4H-SiC in the 300-800 K temperature range. Results extracted from I-V measurements of Schottky barrier diodes showed that barrier height (ФBo) and ideality factor (n) were strongly dependent on temperature. Schottky barrier heights for contacts of all the metals showed an increase with temperature between 300 K and 800 K. This was attributed to barrier inhomogeneities at the interface between the metal and the semiconductor, which resulted in a distribution of barrier heights at the interface. Ideality factors of Ni, Co and Pd decreased from 1.6 to 1.0 and for W the ideality factor decreased from 1.1 to 1.0 when the temperature was increased from 300 K to 800 K respectively. The device parameters were compared to assess advantages and disadvantages of the metals for envisaged applications.

Effect of graphene tunnel barrier on Schottky barrier height of Heusler alloy Co2MnSi/graphene/n-Ge junction

NASA Astrophysics Data System (ADS)

Gui-fang, Li; Jing, Hu; Hui, Lv; Zhijun, Cui; Xiaowei, Hou; Shibin, Liu; Yongqian, Du

2016-02-01

We demonstrate that the insertion of a graphene tunnel barrier between Heusler alloy Co2MnSi and the germanium (Ge) channel modulates the Schottky barrier height and the resistance-area product of the spin diode. We confirm that the Fermi level is depinned and a reduction in the electron Schottky barrier height (SBH) occurs following the insertion of the graphene layer between Co2MnSi and Ge. The electron SBH is modulated in the 0.34 eV-0.61 eV range. Furthermore, the transport mechanism changes from rectifying to symmetric tunneling following the insertion. This behavior provides a pathway for highly efficient spin injection from a Heusler alloy into a Ge channel with high electron and hole mobility. Project supported by the National Natural Science Foundation of China (Grant No. 61504107) and the Fundamental Research Funds for the Central Universities, China (Grant Nos. 3102014JCQ01059 and 3102015ZY043).

A Computational Methodology to Screen Activities of Enzyme Variants

PubMed Central

Hediger, Martin R.; De Vico, Luca; Svendsen, Allan; Besenmatter, Werner; Jensen, Jan H.

2012-01-01

We present a fast computational method to efficiently screen enzyme activity. In the presented method, the effect of mutations on the barrier height of an enzyme-catalysed reaction can be computed within 24 hours on roughly 10 processors. The methodology is based on the PM6 and MOZYME methods as implemented in MOPAC2009, and is tested on the first step of the amide hydrolysis reaction catalyzed by the Candida Antarctica lipase B (CalB) enzyme. The barrier heights are estimated using adiabatic mapping and shown to give barrier heights to within 3 kcal/mol of B3LYP/6-31G(d)//RHF/3-21G results for a small model system. Relatively strict convergence criteria (0.5 kcal/(molÅ)), long NDDO cutoff distances within the MOZYME method (15 Å) and single point evaluations using conventional PM6 are needed for reliable results. The generation of mutant structures and subsequent setup of the semiempirical calculations are automated so that the effect on barrier heights can be estimated for hundreds of mutants in a matter of weeks using high performance computing. PMID:23284627

Properties of GaP Schottky barrier diodes at elevated temperatures.

NASA Technical Reports Server (NTRS)

Nannichi, Y.; Pearson, G. L.

1969-01-01

Gallium phosphide Schottky barrier diodes, discussing construction and metals used, barrier height relationships to impurity concentration and temperature, rectifying characteristics and internal quantum efficiency

Intrinsic inhomogeneous barrier height at the n-TiO2/p-Si hole-blocking junction

NASA Astrophysics Data System (ADS)

Kumar, Mohit; Singh, Ranveer; Som, Tapobrata

2018-01-01

Using Kelvin probe force microscopy (KPFM) and temperature-dependent current-voltage characteristics, we study the charge transport across an n-TiO2/p-Si heterojunction. In particular, the KPFM result shows a variation in the work function at the TiO2 surface. On the other hand, temperature-dependent current-voltage characteristics depict a non-ideal hole-blocking behaviour of the same. In addition, the measured barrier height is found to decrease with temperature and does not follow the thermionic emission theory, strongly suggesting an inhomogeneous nature of the barrier. The observed barrier inhomogeneity is attributed to the nanoscale height modulation, arising due to the growth dynamics of TiO2 and corroborates well with the KPFM map. The presented results will open a new avenue to understand the charge transport in TiO2-based nanoscale devices.

Carrier Transport and Effective Barrier Height of Low Resistance Metal Contact to Highly Mg-Doped p-GaN

NASA Astrophysics Data System (ADS)

Park, Youngjun; Kim, Hyunsoo

2011-08-01

The effective barrier height and carrier transport mechanism of low resistance Ag-based contact to highly Mg-doped p-GaN were investigated. The specific contact resistance obtained was as low as 7.0×10-4 Ω cm2. The electrical resistivity of p-GaN was found to increase depending on ˜T-1/4, indicating variable-range hopping (VRH) conduction through Mg-related deep-level defects. Based on the VRH conduction model, the effective barrier height for carrier transport could be measured as 0.12 eV, which is low enough to explain the formation of excellent ohmic contact. The deep-level defects were also found to induce surface Fermi pinning.

Development and fabrication of improved Schottky power diodes

NASA Technical Reports Server (NTRS)

Cordes, L. F.; Garfinkel, M.; Taft, E. A.

1975-01-01

Reproducible methods for the fabrication of silicon Schottky diodes have been developed for tungsten, aluminum, conventional platinum silicide, and low temperature platinum silicide. Barrier heights and barrier lowering under reverse bias have been measured, permitting the accurate prediction of forward and reverse diode characteristics. Processing procedures have been developed that permit the fabrication of large area (about 1 sq cm) mesageometry power Schottky diodes with forward and reverse characteristics that approach theoretical values. A theoretical analysis of the operation of bridge rectifier circuits has been performed, which indicates the ranges of frequency and voltage for which Schottky rectifiers are preferred to p-n junctions. Power Schottky rectifiers have been fabricated and tested for voltage ratings up to 140 volts.

The dynamical conductance of graphene tunnelling structures.

PubMed

Zhang, Huan; Chan, K S; Lin, Zijing

2011-12-16

The dynamical conductances of graphene tunnelling structures were numerically calculated using the scattering matrix method with the interaction effect included in a phenomenological approach. The overall single-barrier dynamical conductance is capacitative. Transmission resonances in the single-barrier structure lead to dips in the capacitative imaginary part of the response. This is different from the ac responses of typical semiconductor nanostructures, where transmission resonances usually lead to inductive peaks. The features of the dips depend on the Fermi energy. When the Fermi energy is below half of the barrier height, the dips are sharper. When the Fermi energy is higher than half of the barrier height, the dips are broader. Inductive behaviours can be observed in a double-barrier structure due to the resonances formed by reflection between the two barriers.

Isotype InGaN/GaN heterobarrier diodes by ammonia molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fireman, Micha N.; Browne, David A.; Speck, James S.

The design of isotype InGaN/GaN heterobarrier diode structures grown by ammonia molecular beam epitaxy is presented. On the (0001) Ga-polar plane, a structure consisting of a surface n{sup +} GaN contact layer, followed by a thin InGaN layer, followed by a thick unintentionally doped (UID) GaN layer, and atop a buried n{sup +} GaN contact layer induces a large conduction band barrier via a depleted UID GaN layer. Suppression of reverse and subthreshold current in such isotype barrier devices under applied bias depends on the quality of this composite layer polarization. Sample series were grown under fixed InGaN growth conditionsmore » that varied either the UID GaN NH{sub 3} flow rate or the UID GaN thickness, and under fixed UID GaN growth conditions that varied InGaN growth conditions. Decreases in subthreshold current and reverse bias current were measured for thicker UID GaN layers and increasing InGaN growth rates. Temperature-dependent analysis indicated that although extracted barrier heights were lower than those predicted by 1D Schrödinger Poisson simulations (0.9 eV–1.4 eV for In compositions from 10% to 15%), optimized growth conditions increased the extracted barrier height from ∼11% to nearly 85% of the simulated values. Potential subthreshold mechanisms are discussed, along with those growth factors which might affect their prevalence.« less

An Evaluation of Structural, Topographic, Optical, and Temperature-Dependent Electrical Features of Sol-Gel Spin-Coated p-NiO/n-Si Heterojunction

NASA Astrophysics Data System (ADS)

Turgut, Güven; Duman, Songül; Özcelik, Fikriye Şeyma

2017-06-01

p-NiO/n-Si heterodiode was deposited with an easy and cheap sol-gel route using a spin coater. The XRD results revealed that NiO film had polycrystalline cubic bunsenite structure with (200) preferential direction. The AFM and SEM micrographs indicated that the film was composed of homogenously distributed nanoparticles on n-Si surface. The uniform scattering of Ni and O elements was also seen from EDX mapping pictures. The band gap value for NiO sample was found to be 3.74 eV. The current-voltage ( I- V) properties of Ag/p-NiO/n-Si heterojunction were inquired in the temperature range of 80 K to 300 K (-193 °C to 27 °C). The temperature coefficient of barrier height of the Ag/p-NiO/n-Si heterojunction was determined to be 2.6 meV/K. The I- V measurements showed that the barrier height of the heterojunction increased with an increment in the temperature.

Systematic study on the isotopic behavior of fusion barrier using the density-dependent nucleon-nucleon interactions

NASA Astrophysics Data System (ADS)

Ghodsi, O. N.; Khalaj, M.

By changing the neutron and nuclear matter incompressibility constant K, we investigate the isotopic behavior of the fusion barriers for the collision of large number of different isotopes with condition of 0.7 ≤ N/Z ≤ 1.36. Here, the double folding (DF) model which is accompanied by density-dependent (DD) versions of M3Y interactions is adopted as a basic heavy ion-ion potential. We show that the selected DD potentials predict a linear behavior for the calculated fusion barrier heights as a function of (N/Z - 1) for both proton- and neutron-rich systems. Moreover, the results indicate that the isotopic behavior of these values depend linearly on the change in the K constant. The isotopic studies conducted on the fusion cross-section also shows that the properties of the nuclear matter in the range of energy which is below the fusion barrier will quite affect the fusion process.

Nanoscale Electronics from a Molecular Perspective

DTIC Science & Technology

2012-01-19

Cyclohexanethiolate Self-Assembled Monolayers with Local Barrier Height Imaging, Journal of Physical Chemistry C, (07 2011): 0. doi: 2012/01/05 20:34:27...accepted for publication in the Journal of Physical Chemistry-C regarding the adsorption, ordering, and local work function measurements for...cyclohexanethiol on Au(111): Unveiling Molecular Adsorption Geometry in Cyclohexanethiolate Self-Assembled Monolayers with Local Barrier Height Imaging

Tunable reverse-biased graphene/silicon heterojunction Schottky diode sensor.

PubMed

Singh, Amol; Uddin, Ahsan; Sudarshan, Tangali; Koley, Goutam

2014-04-24

A new chemical sensor based on reverse-biased graphene/Si heterojunction diode has been developed that exhibits extremely high bias-dependent molecular detection sensitivity and low operating power. The device takes advantage of graphene's atomically thin nature, which enables molecular adsorption on its surface to directly alter graphene/Si interface barrier height, thus affecting the junction current exponentially when operated in reverse bias and resulting in ultrahigh sensitivity. By operating the device in reverse bias, the work function of graphene, and hence the barrier height at the graphene/Si heterointerface, can be controlled by the bias magnitude, leading to a wide tunability of the molecular detection sensitivity. Such sensitivity control is also possible by carefully selecting the graphene/Si heterojunction Schottky barrier height. Compared to a conventional graphene amperometric sensor fabricated on the same chip, the proposed sensor demonstrated 13 times higher sensitivity for NO₂ and 3 times higher for NH₃ in ambient conditions, while consuming ∼500 times less power for same magnitude of applied voltage bias. The sensing mechanism based on heterojunction Schottky barrier height change has been confirmed using capacitance-voltage measurements. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fusion reaction cross-sections using the Wong model within Skyrme energy density based semiclassical extended Thomas Fermi approach

NASA Astrophysics Data System (ADS)

Kumar, Raj; Sharma, Manoj K.; Gupta, Raj K.

2011-11-01

First, the nuclear proximity potential, obtained by using the semiclassical extended Thomas Fermi (ETF) approach in Skyrme energy density formalism (SEDF), is shown to give more realistic barriers in frozen density approximation, as compared to the sudden approximation. Then, taking advantage of the fact that, in ETF method, different Skyrme forces give different barriers (height, position and curvature), we use the ℓ-summed extended-Wong model of Gupta and collaborators (2009) [1] under frozen densities approximation for calculating the cross-sections, where the Skyrme force is chosen with proper barrier characteristics, not-requiring additional "barrier modification" effects (lowering or narrowing, etc.), for a best fit to data at sub-barrier energies. The method is applied to capture cross-section data from 48Ca + 238U, 244Pu, and 248Cm reactions and to fusion-evaporation cross-sections from 58Ni + 58Ni, 64Ni + 64Ni, and 64Ni + 100Mo reactions, with effects of deformations and orientations of nuclei included, wherever required. Interestingly, whereas the capture cross-sections in Ca-induced reactions could be fitted to any force, such as SIII, SV and GSkI, by allowing a small change of couple of units in deduced ℓ-values at below-barrier energies, the near-barrier data point of 48Ca + 248Cm reaction could not be fitted to ℓ-values deduced for below-barrier energies, calling for a check of data. On the other hand, the fusion-evaporation cross-sections in Ni-induced reactions at sub-barrier energies required different Skyrme forces, representing "modifications of the barrier", for the best fit to data at all incident center-of-mass energies E's, displaying a kind of fusion hindrance at sub-barrier energies. This barrier modification effect is taken into care here by using different Skyrme forces for reactions belonging to different regions of the periodic table. Note that more than one Skyrme force (with identical barrier characteristics) could equally well fit the same data.

Barrier heights, polarization switching, and electrical fatigue in Pb(Zr,Ti)O3 ceramics with different electrodes

NASA Astrophysics Data System (ADS)

Chen, Feng; Schafranek, Robert; Wachau, André; Zhukov, Sergey; Glaum, Julia; Granzow, Torsten; von Seggern, Heinz; Klein, Andreas

2010-11-01

The influence of Pt, tin-doped In2O3, and RuO2 electrodes on the electrical fatigue of bulk ceramic Pb(Zr,Ti)O3 (PZT) has been studied. Schottky barrier heights at the ferroelectric/electrode interfaces vary by more than one electronvolt for different electrode materials and do not depend on crystallographic orientation of the interface. Despite different barrier heights, hysteresis loops of polarization, strain, permittivity, and piezoelectric constant and the switching kinetics are identical for all electrodes. A 20% reduction in polarization after 106 bipolar cycles is observed for all the samples. In contrast to PZT thin films, the loss of remanent polarization with bipolar switching cycles does not significantly depend on the electrode material.

G3X-K theory: A composite theoretical method for thermochemical kinetics

NASA Astrophysics Data System (ADS)

da Silva, Gabriel

2013-02-01

A composite theoretical method for accurate thermochemical kinetics, G3X-K, is described. This method is accurate to around 0.5 kcal mol-1 for barrier heights and 0.8 kcal mol-1 for enthalpies of formation. G3X-K is a modification of G3SX theory using the M06-2X density functional for structures and zero-point energies and parameterized for a test set of 223 heats of formation and 23 barrier heights. A reduced perturbation-order variant, G3X(MP3)-K, is also developed, providing around 0.7 kcal mol-1 accuracy for barrier heights and 0.9 kcal mol-1 accuracy for enthalpies, at reduced computational cost. Some opportunities to further improve Gn composite methods are identified and briefly discussed.

Viscoelastic subdiffusion: from anomalous to normal.

PubMed

Goychuk, Igor

2009-10-01

We study viscoelastic subdiffusion in bistable and periodic potentials within the generalized Langevin equation approach. Our results justify the (ultra)slow fluctuating rate view of the corresponding bistable non-Markovian dynamics which displays bursting and anticorrelation of the residence times in two potential wells. The transition kinetics is asymptotically stretched exponential when the potential barrier V0 several times exceeds thermal energy k(B)T [V(0) approximately (2-10)k(B)T] and it cannot be described by the non-Markovian rate theory (NMRT). The well-known NMRT result approximates, however, ever better with the increasing barrier height, the most probable logarithm of the residence times. Moreover, the rate description is gradually restored when the barrier height exceeds a fuzzy borderline which depends on the power-law exponent of free subdiffusion alpha . Such a potential-free subdiffusion is ergodic. Surprisingly, in periodic potentials it is not sensitive to the barrier height in the long time asymptotic limit. However, the transient to this asymptotic regime is extremally slow and it does profoundly depend on the barrier height. The time scale of such subdiffusion can exceed the mean residence time in a potential well or in a finite spatial domain by many orders of magnitude. All these features are in sharp contrast with an alternative subdiffusion mechanism involving jumps among traps with the divergent mean residence time in these traps.

Optoelectronic properties of hybrid diodes based on vanadyl-phthalocyanine and zinc oxide

NASA Astrophysics Data System (ADS)

Kiran, M. Raveendra; Ulla, Hidayath; Satyanarayan, M. N.; Umesh, G.

2017-12-01

We report an investigation of the optoelectronic properties of a hybrid p-n diode device fabricated using ZnO film prepared by sol-gel technique on which a VOPc organic film is deposited by vacuum evaporation. The charge transport properties of devices having the configurations ITO/ZnO/Al and ITO/ZnO/VOPc/MoO3/Al were investigated at different annealing temperatures (150 °C, 250 °C, 350 °C and 450 °C) by Impedance Spectroscopy (IS). The structural, morphological, optical and electrical properties were also studied at different annealing temperatures. The parameters related to the ITO/ZnO and ZnO/VOPc interfaces such as ideality factor (n), barrier height (qϕB) and rectification ratio (RR) of the diodes were determined from current density-voltage (J-V) characteristics. IS measurements suggest that the large photocurrent generated is due to the decrease in bulk resistance of the device on account of the generation of electron-hole pairs in the organic active layer when exposed to light. The RR and the photocurrent responsivity (Rph) values obtained from the J-V characteristics compare well with those obtained from the IS measurements. It was observed that the absolute value of Rph (470 mA/W) for the p-n diode with ZnO annealed at 350 °C is high compared to that of diodes with different ZnO annealing temperatures. These values also agree well with the values obtained for p-n diodes of other phthalocyanines. Our studies clearly demonstrate that a p-n diode with ZnO film annealed at 350 °C exhibits much better optoelectronic characteristics on account of increased grain size, improved charge injection due to the reduction of barrier height and hence higher (up to 5 orders) charge carrier mobility.

Another Look at the Mechanisms of Hydride Transfer Enzymes with Quantum and Classical Transition Path Sampling.

PubMed

Dzierlenga, Michael W; Antoniou, Dimitri; Schwartz, Steven D

2015-04-02

The mechanisms involved in enzymatic hydride transfer have been studied for years, but questions remain due, in part, to the difficulty of probing the effects of protein motion and hydrogen tunneling. In this study, we use transition path sampling (TPS) with normal mode centroid molecular dynamics (CMD) to calculate the barrier to hydride transfer in yeast alcohol dehydrogenase (YADH) and human heart lactate dehydrogenase (LDH). Calculation of the work applied to the hydride allowed for observation of the change in barrier height upon inclusion of quantum dynamics. Similar calculations were performed using deuterium as the transferring particle in order to approximate kinetic isotope effects (KIEs). The change in barrier height in YADH is indicative of a zero-point energy (ZPE) contribution and is evidence that catalysis occurs via a protein compression that mediates a near-barrierless hydride transfer. Calculation of the KIE using the difference in barrier height between the hydride and deuteride agreed well with experimental results.

Time dependent changes in Schottky barrier mapping of the W/Si(001) interface utilizing ballistic electron emission microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durcan, Chris A.; Balsano, Robert; LaBella, Vincent P., E-mail: vlabella@albany.edu

2015-06-28

The W/Si(001) Schottky barrier height is mapped to nanoscale dimensions using ballistic electron emission microscopy (BEEM) over a period of 21 days to observe changes in the interface electrostatics. Initially, the average spectrum is fit to a Schottky barrier height of 0.71 eV, and the map is uniform with 98% of the spectra able to be fit. After 21 days, the average spectrum is fit to a Schottky barrier height of 0.62 eV, and the spatial map changes dramatically with only 27% of the spectra able to be fit. Transmission electron microscopy shows the formation of an ultra-thin tungsten silicide at themore » interface, which increases in thickness over the 21 days. This increase is attributed to an increase in electron scattering and the changes are observed in the BEEM measurements. Interestingly, little to no change is observed in the I-V measurements throughout the 21 day period.« less

Characterization technique for inhomogeneous 4H-SiC Schottky contacts: A practical model for high temperature behavior

NASA Astrophysics Data System (ADS)

Brezeanu, G.; Pristavu, G.; Draghici, F.; Badila, M.; Pascu, R.

2017-08-01

In this paper, a characterization technique for 4H-SiC Schottky diodes with varying levels of metal-semiconductor contact inhomogeneity is proposed. A macro-model, suitable for high-temperature evaluation of SiC Schottky contacts, with discrete barrier height non-uniformity, is introduced in order to determine the temperature interval and bias domain where electrical behavior of the devices can be described by the thermionic emission theory (has a quasi-ideal performance). A minimal set of parameters, the effective barrier height and peff, the non-uniformity factor, is associated. Model-extracted parameters are discussed in comparison with literature-reported results based on existing inhomogeneity approaches, in terms of complexity and physical relevance. Special consideration was given to models based on a Gaussian distribution of barrier heights on the contact surface. The proposed methodology is validated by electrical characterization of nickel silicide Schottky contacts on silicon carbide (4H-SiC), where a discrete barrier distribution can be considered. The same method is applied to inhomogeneous Pt/4H-SiC contacts. The forward characteristics measured at different temperatures are accurately reproduced using this inhomogeneous barrier model. A quasi-ideal behavior is identified for intervals spanning 200 °C for all measured Schottky samples, with Ni and Pt contact metals. A predictable exponential current-voltage variation over at least 2 orders of magnitude is also proven, with a stable barrier height and effective area for temperatures up to 400 °C. This application-oriented characterization technique is confirmed by using model parameters to fit a SiC-Schottky high temperature sensor's response.

Tracking the Effect of Adatom Electronegativity on Systematically Modified AlGaN/GaN Schottky Interfaces.

PubMed

Reiner, Maria; Pietschnig, Rudolf; Ostermaier, Clemens

2015-10-21

The influence of surface modifications on the Schottky barrier height for gallium nitride semiconductor devices is frequently underestimated or neglected in investigations thereof. We show that a strong dependency of Schottky barrier heights for nickel/aluminum-gallium nitride (0001) contacts on the surface terminations exists: a linear correlation of increasing barrier height with increasing electronegativity of superficial adatoms is observed. The negatively charged adatoms compete with the present nitrogen over the available gallium (or aluminum) orbital to form an electrically improved surface termination. The resulting modification of the surface dipoles and hence polarization of the surface termination causes observed band bending. Our findings suggest that the greatest Schottky barrier heights are achieved by increasing the concentration of the most polarized fluorine-gallium (-aluminum) bonds at the surface. An increase in barrier height from 0.7 to 1.1 eV after a 15% fluorine termination is obtained with ideality factors of 1.10 ± 0.05. The presence of surface dipoles that are changing the surface energy is proven by the sessile drop method as the electronegativity difference and polarization influences the contact angle. The extracted decrease in the Lifshitz-van-der-Waals component from 48.8 to 40.4 mJ/m(2) with increasing electronegativity and concentration of surface adatoms confirms the presence of increasing surface dipoles: as the polarizability of equally charged anions decreases with increasing electronegativity, the diiodomethane contact angles increase significantly from 14° up to 39° after the 15% fluorine termination. Therefore, a linear correlation between increasing anion electronegativity of the (Al)GaN termination and total surface energy within a 95% confidence interval is obtained. Furthermore, our results reveal a generally strong Lewis basicity of (Al)GaN surfaces explaining the high chemical inertness of the surfaces.

Band structure effects on resonant tunneling in III-V quantum wells versus two-dimensional vertical heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, Philip M., E-mail: philip.campbell@gatech.edu; Electronic Systems Laboratory, Georgia Tech Research Institute, Atlanta, Georgia 30332; Tarasov, Alexey

Since the invention of the Esaki diode, resonant tunneling devices have been of interest for applications including multi-valued logic and communication systems. These devices are characterized by the presence of negative differential resistance in the current-voltage characteristic, resulting from lateral momentum conservation during the tunneling process. While a large amount of research has focused on III-V material systems, such as the GaAs/AlGaAs system, for resonant tunneling devices, poor device performance and device-to-device variability have limited widespread adoption. Recently, the symmetric field-effect transistor (symFET) was proposed as a resonant tunneling device incorporating symmetric 2-D materials, such as transition metal dichalcogenides (TMDs),more » separated by an interlayer barrier, such as hexagonal boron-nitride. The achievable peak-to-valley ratio for TMD symFETs has been predicted to be higher than has been observed for III-V resonant tunneling devices. This work examines the effect that band structure differences between III-V devices and TMDs has on device performance. It is shown that tunneling between the quantized subbands in III-V devices increases the valley current and decreases device performance, while the interlayer barrier height has a negligible impact on performance for barrier heights greater than approximately 0.5 eV.« less

Gate-controlled tunneling of quantum Hall edge states in bilayer graphene

NASA Astrophysics Data System (ADS)

Zhu, Jun; Li, Jing; Wen, Hua

Controlled tunneling of integer and fractional quantum Hall edge states provides a powerful tool to probe the physics of 1D systems and exotic particle statistics. Experiments in GaAs 2DEGs employ either a quantum point contact or a line junction tunnel barrier. It is generally difficult to independently control the filling factors νL and νR on the two sides of the barrier. Here we show that in bilayer graphene both νL and νR as well as their Landau level structures can be independently controlled using a dual-split-gate structure. In addition, the height of the line-junction tunnel barrier implemented in our experiments is tunable via a 5th gate. By measuring the tunneling resistance across the junction RT we examine the equilibration of the edge states in a variety of νL/νR scenarios and under different barrier heights. Edge states from both sides are fully mixed in the case of a low barrier. As the barrier height increases, we observe plateaus in RT that correspond to sequential complete backscattering of edge states. Gate-controlled manipulation of edge states offers a new angle to the exploration of quantum Hall magnetism and fractional quantum Hall effect in bilayer graphene.

Physical aspects of colossal dielectric constant material CaCu3Ti4O12 thin films

NASA Astrophysics Data System (ADS)

Deng, Guochu; He, Zhangbin; Muralt, Paul

2009-04-01

The underlying physical mechanism of the so-called colossal dielectric constant phenomenon in CaCu3Ti4O12 (CCTO) thin films were investigated by using semiconductor theories and methods. The semiconductivity of CCTO thin films originated from the acceptor defect at a level ˜90 meV higher than valence band. Two contact types, metal-semiconductor and metal-insulator-semiconductor junctions, were observed and their barrier heights, and impurity concentrations were theoretically calculated. Accordingly, the Schottky barrier height of metal-semiconductor contact is about 0.8 eV, and the diffusion barrier height of metal-insulator-semiconductor contact is about 0.4-0.7 eV. The defect concentrations of both samples are quite similar, of the magnitude of 1019 cm-3, indicating an inherent feature of high defect concentration.

Very low Schottky barrier height at carbon nanotube and silicon carbide interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Inaba, Masafumi, E-mail: inaba-ma@ruri.waseda.jp; Suzuki, Kazuma; Shibuya, Megumi

2015-03-23

Electrical contacts to silicon carbide with low contact resistivity and high current durability are crucial for future SiC power devices, especially miniaturized vertical-type devices. A carbon nanotube (CNT) forest formed by silicon carbide (SiC) decomposition is a densely packed forest, and is ideal for use as a heat-dissipative ohmic contact in SiC power transistors. The contact resistivity and Schottky barrier height in a Ti/CNT/SiC system with various SiC dopant concentrations were evaluated in this study. Contact resistivity was evaluated in relation to contact area. The Schottky barrier height was calculated from the contact resistivity. As a result, the Ti/CNT/SiC contactmore » resistivity at a dopant concentration of 3 × 10{sup 18 }cm{sup −3} was estimated to be ∼1.3 × 10{sup −4} Ω cm{sup 2} and the Schottky barrier height of the CNT/SiC contact was in the range of 0.40–0.45 eV. The resistivity is relatively low for SiC contacts, showing that CNTs have the potential to be a good ohmic contact material for SiC power electronic devices.« less

The substitution reaction of (CNC)Fe-2N₂ with CO.

PubMed

Liu, Hongyan; Liu, Shuangshuang; Zhang, Xiang

2013-06-01

The substitution mechanism of two N₂ ligands in (CNC)Fe-2N₂ replaced by CO was studied theoretically at the B3LYP/LACVP* level. Both SN1 and SN₂ mechanisms were considered. The calculated results for the gas phase suggested that: 1) in SN1 mechanism, N₂ elimination, which involves S₀-T₁ PESs crossing, is the rate control step for both substitution stages. The barrier heights are 9.7 kcal mol(-1) and 13.05 kcal mol(-1), respectively. 2) In SN2 mechanism, the calculated barrier heights on LS PES are respectively 13.7 and 19.83 kcal mol(-1) for the two substitution steps, but S₀-T₁ PESs crossing lowers the two barriers to 10.7 and 15.7 kcal mol(-1), respectively. 3) Inclusion of solvation effect of THF by PCM model, the relative energies of all the key species (including minima, transition states and S₀-T₁ crossing points) do not have great difference from their gas phase relative energies. Considering that for each substitution step, SN1 barrier heights is slightly smaller than SN2 barrier, SN1 mechanism seems to be slightly preferable to SN2 mechanism.

Roadside barrier effectiveness : noise measurement program

DOT National Transportation Integrated Search

1978-04-01

A field noise measurement program was conducted to assess the performance of a variable height highway noise barrier with and without an acoustic lining material. The barrier site on Interstate I-93 in Andover MA was located adjacent to an acoustical...

Using a Bayesian network to predict barrier island geomorphologic characteristics

USGS Publications Warehouse

Gutierrez, Ben; Plant, Nathaniel G.; Thieler, E. Robert; Turecek, Aaron

2015-01-01

Quantifying geomorphic variability of coastal environments is important for understanding and describing the vulnerability of coastal topography, infrastructure, and ecosystems to future storms and sea level rise. Here we use a Bayesian network (BN) to test the importance of multiple interactions between barrier island geomorphic variables. This approach models complex interactions and handles uncertainty, which is intrinsic to future sea level rise, storminess, or anthropogenic processes (e.g., beach nourishment and other forms of coastal management). The BN was developed and tested at Assateague Island, Maryland/Virginia, USA, a barrier island with sufficient geomorphic and temporal variability to evaluate our approach. We tested the ability to predict dune height, beach width, and beach height variables using inputs that included longer-term, larger-scale, or external variables (historical shoreline change rates, distances to inlets, barrier width, mean barrier elevation, and anthropogenic modification). Data sets from three different years spanning nearly a decade sampled substantial temporal variability and serve as a proxy for analysis of future conditions. We show that distinct geomorphic conditions are associated with different long-term shoreline change rates and that the most skillful predictions of dune height, beach width, and beach height depend on including multiple input variables simultaneously. The predictive relationships are robust to variations in the amount of input data and to variations in model complexity. The resulting model can be used to evaluate scenarios related to coastal management plans and/or future scenarios where shoreline change rates may differ from those observed historically.

High Fill Factors of Si Solar Cells Achieved by Using an Inverse Connection Between MOS and PN Junctions.

PubMed

Wang, Liang-Xing; Zhou, Zhi-Quan; Zhang, Tian-Ning; Chen, Xin; Lu, Ming

2016-12-01

Fill factors (FFs) of ~0.87 have been obtained for crystalline Si (c-Si) solar cells based on Ag front contacts after rapid thermal annealing. The usual single PN junction model fails to explain the high FF result. A metal/oxide/semiconductor (MOS) junction at the emitter is found to be inversely connected to the PN one, and when its barrier height/e is close to the open-circuit voltage of the solar cell, very high FF is obtainable. In this work, although the open-circuit voltage (<580 mV) is not high here, the efficiency of c-Si solar cell still reaches the state-of-the-art value (>20 %) due to the high FF achieved.

An antithetic variate to facilitate upper-stem height measurements for critical height sampling with importance sampling

Treesearch

Thomas B. Lynch; Jeffrey H. Gove

2013-01-01

Critical height sampling (CHS) estimates cubic volume per unit area by multiplying the sum of critical heights measured on trees tallied in a horizontal point sample (HPS) by the HPS basal area factor. One of the barriers to practical application of CHS is the fact that trees near the field location of the point-sampling sample point have critical heights that occur...

Steric, Quantum, and Electrostatic Effects on SN2 Reaction Barriers in Gas Phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Shubin; Hu, Hao; Pedersen, Lee G.

2010-05-13

Biomolecular nucleophilic substitution reactions, S{sub N}2, are fundamental and commonplace in chemistry. It is the well-documented experimental finding in the literature that vicinal substitution with bulkier groups near the reaction center significantly slows the reaction due to steric hindrance, but theoretical understanding in the quantitative manner about factors dictating the S{sub N}2 reaction barrier height is still controversial. In this work, employing the new quantification approach that we recently proposed for the steric effect from the density functional theory framework, we investigate the relative contribution of three independent effects—steric, electrostatic, and quantum—to the S{sub N}2 barrier heights in gas phasemore » for substituted methyl halide systems, R{sub 1}R{sub 2}R{sub 3}CX, reacting with the fluorine anion, where R{sub 1}, R{sub 2}, and R{sub 3} denote substituting groups and X = F or Cl. We found that in accordance with the experimental finding, for these systems, the steric effect dominates the transition state barrier, contributing positively to barrier heights, but this contribution is largely compensated by the negative, stabilizing contribution from the quantum effect due to the exchange-correlation interactions. Moreover, we find that it is the component from the electrostatic effect that is linearly correlated with the S{sub N}2 barrier height for the systems investigated in the present study. In addition, we compared our approach with the conventional method of energy decomposition in density functional theory as well as examined the steric effect from the wave function theory for these systems via natural bond orbital analysis.« less

Comment on Chem. Phys. Lett. 371 (2003) 568: Barrier height for dissociation of acetaldehyde, CH 3CHO → CH 3 + HCO, in the triplet state T 1

NASA Astrophysics Data System (ADS)

Robert Huber, J.

2003-08-01

Based on recently reported experimental results from various groups, the barrier height (or transition state energy) for the T 1 dissociation of acetaldehyde, CH 3CHO → CH 3 + HCO, is determined to lie between 12.3 and 12.9 kcal mol -1. This result is compared with predictions from recent ab initio calculations.

Fission properties of Po isotopes in different macroscopic-microscopic models

NASA Astrophysics Data System (ADS)

Bartel, J.; Pomorski, K.; Nerlo-Pomorska, B.; Schmitt, Ch

2015-11-01

Fission-barrier heights of nuclei in the Po isotopic chain are investigated in several macroscopic-microscopic models. Using the Yukawa-folded single-particle potential, the Lublin-Strasbourg drop (LSD) model, the Strutinsky shell-correction method to yield the shell corrections and the BCS theory for the pairing contributions, fission-barrier heights are calculated and found in quite good agreement with the experimental data. This turns out, however, to be only the case when the underlying macroscopic, liquid-drop (LD) type, theory is well chosen. Together with the LSD approach, different LD parametrizations proposed by Moretto et al are tested. Four deformation parameters describing respectively elongation, neck-formation, reflectional-asymmetric, and non-axiality of the nuclear shape thus defining the so called modified Funny Hills shape parametrization are used in the calculation. The present study clearly demonstrates that nuclear fission-barrier heights constitute a challenging and selective tool to discern between such different macroscopic approaches.

Spatial inhomogeneous barrier heights at graphene/semiconductor Schottky junctions

NASA Astrophysics Data System (ADS)

Tomer, Dushyant

Graphene, a semimetal with linear energy dispersion, forms Schottky junction when interfaced with a semiconductor. This dissertation presents temperature dependent current-voltage and scanning tunneling microscopy/spectroscopy (STM/S) measurements performed on graphene Schottky junctions formed with both three and two dimensional semiconductors. To fabricate Schottky junctions, we transfer chemical vapor deposited monolayer graphene onto Si- and C-face SiC, Si, GaAs and MoS2 semiconducting substrates using polymer assisted chemical method. We observe three main type of intrinsic spatial inhomogeneities, graphene ripples, ridges and semiconductor steps in STM imaging that can exist at graphene/semiconductor junctions. Tunneling spectroscopy measurements reveal fluctuations in graphene Dirac point position, which is directly related to the Schottky barrier height. We find a direct correlation of Dirac point variation with the topographic undulations of graphene ripples at the graphene/SiC junction. However, no such correlation is established at graphene/Si and Graphene/GaAs junctions and Dirac point variations are attributed to surface states and trapped charges at the interface. In addition to graphene ripples and ridges, we also observe atomic scale moire patterns at graphene/MoS2 junction due to van der Waals interaction at the interface. Periodic topographic modulations due to moire pattern do not lead to local variation in graphene Dirac point, indicating that moire pattern does not contribute to fluctuations in electronic properties of the heterojunction. We perform temperature dependent current-voltage measurements to investigate the impact of topographic inhomogeneities on electrical properties of the Schottky junctions. We observe temperature dependence in junction parameters, such as Schottky barrier height and ideality factor, for all types of Schottky junctions in forward bias measurements. Standard thermionic emission theory which assumes a perfect smooth interface fails to explain such behavior, hence, we apply a modified emission theory with Gaussian distribution of Schottky barrier heights. The modified theory, applicable to inhomogeneous interfaces, explains the temperature dependent behavior of our Schottky junctions and gives a temperature independent mean barrier height. We attribute the inhomogeneous barrier height to the presence of graphene ripples and ridges in case of SiC and MoS2 while surface states and trapped charges at the interface is dominating in Si and GaAs. Additionally, we observe bias dependent current and barrier height in reverse bias regime also for all Schottky junctions. To explain such behavior, we consider two types of reverse bias conduction mechanisms; Poole-Frenkel and Schottky emission. We find that Poole-Frenkel emission explains the characteristics of graphene/SiC junctions very well. However, both the mechanism fails to interpret the behavior of graphene/Si and graphene/GaAs Schottky junctions. These findings provide insight into the fundamental physics at the interface of graphene/semiconductor junctions.

Barrier height modification and mechanism of carrier transport in Ni/in situ grown Si3N4/n-GaN Schottky contacts

NASA Astrophysics Data System (ADS)

Karpov, S. Y.; Zakheim, D. A.; Lundin, W. V.; Sakharov, A. V.; Zavarin, E. E.; Brunkov, P. N.; Lundina, E. Y.; Tsatsulnikov, A. F.

2018-02-01

In situ growth of an ultra-thin (up to 2.5 nm) Si3N4 film on the top of n-GaN is shown to reduce remarkably the height of the barrier formed by deposition of Ni-based Schottky contact. The reduction is interpreted in terms of polarization dipole induced at the Si3N4/n-GaN interface and Fermi level pinning at the Ni/Si3N4 interface. Detailed study of temperature-dependent current-voltage characteristics enables identification of the electron transport mechanism in such Schottky diodes under forward bias: thermal/field electron emission over the barrier formed in n-GaN followed by tunneling through the Si3N4 film. At reverse bias and room temperature, the charge transfer is likely controlled by Poole-Frenkel ionization of deep traps in n-GaN. Tunneling exponents at forward and reverse biases and the height of the Ni/Si3N4 Schottky barrier are evaluated experimentally and compared with theoretical predictions.

Electrical properties of nano-resistors made from the Zr-doped HfO2 high-k dielectric film

NASA Astrophysics Data System (ADS)

Zhang, Shumao; Kuo, Yue

2018-03-01

Electrical properties of nano-sized resistors made from the breakdown of the metal-oxide-semiconductor capacitor composed of the amorphous high-k gate dielectric have been investigated under different stress voltages and temperatures. The effective resistance of nano-resistors in the device was estimated from the I-V curve in the high voltage range. It decreased with the increase of the number of resistors. The resistance showed complicated temperature dependence, i.e. it neither behaves like a conductor nor a semiconductor. In the low voltage operation range, the charge transfer was controlled by the Schottky barrier at the nano-resistor/Si interface. The barrier height decreased with the increase of stress voltage, which was probably caused by the change of the nano-resistor composition. Separately, it was observed that the barrier height was dependent on the temperature, which was probably due to the dynamic nano-resistor formation process and the inhomogeneous barrier height distribution. The unique electrical characteristics of this new type of nano-resistors are important for many electronic and optoelectronic applications.

Interface state density distribution in Au/n-ZnO nanorods Schottky diodes

NASA Astrophysics Data System (ADS)

Faraz, S. M.; Willander, M.; Wahab, Q.

2012-04-01

Interface states density (NSS) distribution is extracted in Au/ ZnO Schottky diodes. Nanorods of ZnO are grown on silver (Ag) using aqueous chemical growth (ACG) technique. Well aligned hexagonal-shaped vertical nanorods of a mean diameter of 300 - 450 nm and 1.3 -1.9 μm high are revealed in SEM. Gold (Au) Schottky contacts of thickness 60 nm and 1.5mm diameter were evaporated. For electrical characterization of Schottky diodes current-voltage (I-V) and capacitance-Voltage (C-V) measurements are performed. The diodes exhibited a typical non-linear rectifying behavior with a barrier height of 0.62eV and ideality factor of 4.3. Possible reasons for low barrier height and high ideality factor have been addressed. Series resistance (RS) has been calculated from forward I-V characteristics using Chueng's function. The density of interfacial states (NSS) below the conduction band (EC-ESS) is extracted using I-V and C-V measured values. A decrease in interface states density (NSS) is observed from 3.74 × 1011 - 7.98 × 1010 eV-1 cm-2 from 0.30eV - 0.61eV below the conduction band edge.

Electrical properties of a novel 1,3-bis-(p-iminobenzoic acid) indane Langmuir-Blodgett films containing ZnS nanoparticles.

PubMed

Sari, H; Uzunoglu, T; Capan, R; Serin, N; Serin, T; Tarimci, C; Hassan, A K; Namli, H; Turhan, O

2007-08-01

ZnS nanoparticles have been formed in a newly synthesized 1,3-bis-(p-iminobenzoic acid) indane (IBI) by exposing Zn2+ doped multilayered Langmuir-Blodgett (LB) film to H2S gas after the growth. The formation of ZnS nanoparticles in the LB film structure was verified by measuring UV-Visible absorption spectra. DC electrical measurements were carried out for thin films of IBI prepared in a metal/LB films/metal sandwich structure with and without ZnS nanoparticles. It was observed that ZnS nanoparticles in the LB films cause a blue-shift in the absorption spectra as well as a decrease in both capacitance and conductivity values. By analysing I-V curves and assuming a Schottky conduction mechanism the barrier height was found to be about 1.13 eV and 1.21 eV for IBI LB films without and with ZnS nanoparticles, respectively. It is thought that the presence of ZnS nanoparticles influences the barrier height at the metal-organic film interface and causes a change in electrical conduction properties of LB films.

A multilayered-representation quantum mechanical/molecular mechanics study of the SN2 reaction of CH3Br + OH- in aqueous solution

NASA Astrophysics Data System (ADS)

Xu, Yulong; Wang, Tingting; Wang, Dunyou

2012-11-01

The bimolecular nucleophilic substitution (SN2) reaction of CH3Br and OH- in aqueous solution was investigated using a multilayered-representation quantum mechanical and molecular mechanics methodology. Reactant complex, transition state, and product complex are identified and characterized in aqueous solution. The potentials of mean force are computed under both the density function theory and coupled-cluster single double (triple) (CCSD(T)) levels of theory for the reaction region. The results show that the aqueous environment has a significant impact on the reaction process. The solvation effect and the polarization effect combined raise the activation barrier height by ˜16.2 kcal/mol and the solvation effect is the dominant contribution to the potential of mean force. The CCSD(T)/MM representation presents a free energy activation barrier height of 22.8 kcal/mol and the rate constant at 298 K of 3.7 × 10-25 cm3 molecule-1 s-1 which agree very well with the experiment values at 23.0 kcal/mol and 2.6 × 10-25 cm3 molecule-1 s-1, respectively.

Laterally inhomogeneous barrier analysis of cu/n-gap/al schottky devices

NASA Astrophysics Data System (ADS)

Çınar Demir, K.; Coşkun, C.; Kurudirek, S. V.; Öz, S.; Aydoğan, Ş.; Biber, M.

2016-04-01

In this study, we examined the electrical parameters of Cu/n-GaP/Al Schottky structures at room temperature and examined the electrical characterization of these devices depending on and Capacitance-Voltage (C-V) and Current-Voltage (I-V) measurements. A statistical study on the experimental ideality factor (n) and BHs(barrier heights) values of the devices was stated. The n and BHs of all contacts have been determined from the electrical characteristics. Even though all of the diodes were conformably prepared, there was a diode-todiode variation: the effective BHs changed from 0.988-0.07 to 1.216-0.07 eV, and the n from 1.01-0.299 to 2.16-0.299. The yielded results show that the mean electrical parameters of Schottky devices are different from one diode to another, even if they are identically prepared. It can be axplained that the lower BHs usher with the higher n values owing to inhomogeneities.

Fabrication and characterization of Au/n-CdTe Schottky barrier under illumination and dark

NASA Astrophysics Data System (ADS)

Bera, Swades Ranjan; Saha, Satyajit

2018-04-01

CdTe nanoparticles have been grown by chemical reduction method using EDA as capping agent. These are used to fabricate Schottky barrier in a simple cost-effective way at room temperature. The grown nanoparticles are structurally characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM). The optical properties of nano CdTe is characterized by UV-Vis absorption spectra, PL spectra. The band gap of the CdTe nanoparticles is increased as compared to CdTe bulk form indicating there is blue shift. The increase of band gap is due to quantum confinement. Photoluminescence spectra shows peak which corresponds to emission from surface state. CdTe nanofilm is grown on ITO coated glass substrate by dipping it on toluene containing dispersed CdTe nanoparticles. Schottky barrier of Au/n-CdTe is fabricated on ITO coated glass by vacuum deposition of gold. I- V and C- V characteristics of Au/n-CdTe Schottky barrier junction have been studied under dark and light condition. It is found that these characteristics are influenced by surface or interface traps. The values of barrier height, ideality factor, donor concentration and series resistance are obtained from the reverse bias capacitance-voltage measurements.

Assessing theoretical uncertainties in fission barriers of superheavy nuclei

DOE PAGES

Agbemava, S. E.; Afanasjev, A. V.; Ray, D.; ...

2017-05-26

Here, theoretical uncertainties in the predictions of inner fission barrier heights in superheavy elements have been investigated in a systematic way for a set of state-of-the-art covariant energy density functionals which represent major classes of the functionals used in covariant density functional theory. They differ in basic model assumptions and fitting protocols. Both systematic and statistical uncertainties have been quantified where the former turn out to be larger. Systematic uncertainties are substantial in superheavy elements and their behavior as a function of proton and neutron numbers contains a large random component. The benchmarking of the functionals to the experimental datamore » on fission barriers in the actinides allows to reduce the systematic theoretical uncertainties for the inner fission barriers of unknown superheavy elements. However, even then they on average increase on moving away from the region where benchmarking has been performed. In addition, a comparison with the results of non-relativistic approaches is performed in order to define full systematic theoretical uncertainties over the state-of-the-art models. Even for the models benchmarked in the actinides, the difference in the inner fission barrier height of some superheavy elements reaches $5-6$ MeV. This uncertainty in the fission barrier heights will translate into huge (many tens of the orders of magnitude) uncertainties in the spontaneous fission half-lives.« less

Tunneling barrier in nanoparticle junctions of La2/3(Ca,Sr)1/3MnO3: Nonlinear current-voltage characteristics

NASA Astrophysics Data System (ADS)

Niebieskikwiat, D.; Sánchez, R. D.; Lamas, D. G.; Caneiro, A.; Hueso, L. E.; Rivas, J.

2003-05-01

We study the nonlinear current-voltage (I-V) characteristics and analyze the voltage-dependent tunneling conductance in nanoparticles of La2/3A1/3MnO3 (A=Ca, Sr). The powders were prepared by different wet-chemical routes and low calcination temperatures were used to obtain an average particle size D≈30 nm. The data are comprehensively explained in terms of the tunneling picture, which allows one to estimate the height of the grain boundary insulating barrier (φ) for each sample. For constant D, our results show that the sample preparation route is mainly responsible for the value of φ in nanoparticles, while the Coulomb gap in the Coulomb blockade regime is ˜3 times higher for Sr- than for Ca-doping. We also show that a small fraction of the barriers contribute to the nonlinear transport, and the current is mainly carried through low-resistive percolated paths. In addition, despite the different barrier strengths, the low-field magnetoresistance (LFMR) is similar for all samples, implying that φ is not the fundamental parameter determining the LFMR.

Comparative study of I- V methods to extract Au/FePc/p-Si Schottky barrier diode parameters

NASA Astrophysics Data System (ADS)

Oruç, Çiğdem; Altındal, Ahmet

2018-01-01

So far, various methods have been proposed to extract the Schottky diode parameters from measured current-voltage characteristics. In this work, Schottky barrier diode with structure of Au/2(3),9(10),16(17),23(24)-tetra(4-(4-methoxyphenyl)-8-methylcoumarin-7 oxy) phthalocyaninatoiron(II) (FePc)/p-Si was fabricated and current-voltage measurements were carried out on it. In addition, current-voltage measurements were also performed on Au/p-Si structure, without FePc, to clarify the influence of the presence of an interface layer on the device performance. The measured current-voltage characteristics indicate that the interface properties of a Schottky barrier diode can be controlled by the presence of an organic interface layer. It is found that the room temperature barrier height of Au/FePc/p-Si structure is larger than that of the Au/p-Si structure. The obtained forward bias current-voltage characteristics of the Au/FePc/p-Si device was analysed by five different analytical methods. It is found that the extracted values of SBD parameters strongly depends on the method used.

Two Equivalent Methyl Internal Rotations in 2,5-DIMETHYLTHIOPHENE Investigated by Microwave Spectroscopy

NASA Astrophysics Data System (ADS)

Van, Vinh; Stahl, Wolfgang; Nguyen, Ha Vinh Lam

2016-06-01

The microwave spectrum of 2,5-dimethylthiophene, a sulfur-containing five-membered heterocyclic molecule with two conjugated double bonds, was recorded using two molecular beam Fourier transform microwave spectrometers operating in the frequency range from 2 to 40 GHz. Highly accurate molecular parameters were determined. The rotational constants obtained by geometry optimizations at different levels of theory are in good agreement with the experimental values. A C2v equilibrium structure was calculated, where one hydrogen atom of each methyl group is antiperiplanar to the sulfur atom, and the two methyl groups are thus equivalent. Transition states were optimized at different levels of theory using the Berny algorithm to calculate the barrier height of the two equivalent methyl rotors. The fitted experimental torsional barrier of 247.95594(30) wn is in reasonable agreement with the calculated barriers. Similar barriers to internal rotation were found for the monomethyl derivatives 2-methylthiophene (194.1 wn) and 3-methylthiophene (258.8 wn). A labeling scheme for the group G36 written as the semi-direct product (C3I x C3I) (x C2v was introduced.

The photovoltaic impact of atomic layer deposited TiO2 interfacial layer on Si-based photodiodes

NASA Astrophysics Data System (ADS)

Karabulut, Abdulkerim; Orak, İkram; Türüt, Abdulmecit

2018-06-01

In present work, photocurrent, current-voltage (I-V) and capacitance/conductance-voltage-frequency (C/G-V-f) measurements were analyzed for the photodiode and diode parameters of Al/TiO2/p-Si structure. The TiO2 thin film structure was deposited on p-Si by using atomic layer deposition technique (ALD) and its thickness was about 10 nm. The surface morphology of TiO2 coated on p-Si structure was observed via atomic force microscope (AFM). Barrier height (Φb) and ideality factor (n) values of device were found to be 0.80 eV, 0.70 eV, 0.56 eV and 1.04, 2.24, 10.27 under dark, 10 and 100 mW/cm2, respectively. Some photodiodes parameters such as fill factor (FF), power efficiency (%η), open circuit voltage (Voc), short circuit current (Isc) were obtained from I-V measurement under different light intensity. FF and η were accounted 49.2, 39,0 and 0.05, 0.45 under 10 and 100 mW/cm2 light power intensity, respectively. C-2-V graph was plotted from C-V-f measurements and zero bias voltage (V0), donor concentration (Nd), Fermi energy (EF), barrier height (Φb) and maximum electric field (Em) were determined from C-2-V data for different frequencies. The electrical and photocurrent values demonstrated that it can be used for photodiode, photo detector and photo sensing applications.

Debris flow runup on vertical barriers and adverse slopes

USGS Publications Warehouse

Iverson, Richard M.; George, David L.; Logan, Matthew

2016-01-01

Runup of debris flows against obstacles in their paths is a complex process that involves profound flow deceleration and redirection. We investigate the dynamics and predictability of runup by comparing results from large-scale laboratory experiments, four simple analytical models, and a depth-integrated numerical model (D-Claw). The experiments and numerical simulations reveal the important influence of unsteady, multidimensional flow on runup, and the analytical models highlight key aspects of the underlying physics. Runup against a vertical barrier normal to the flow path is dominated by rapid development of a shock, or jump in flow height, associated with abrupt deceleration of the flow front. By contrast, runup on sloping obstacles is initially dominated by a smooth flux of mass and momentum from the flow body to the flow front, which precedes shock development and commonly increases the runup height. D-Claw simulations that account for the emergence of shocks show that predicted runup heights vary systematically with the adverse slope angle and also with the Froude number and degree of liquefaction (or effective basal friction) of incoming flows. They additionally clarify the strengths and limitations of simplified analytical models. Numerical simulations based on a priori knowledge of the evolving dynamics of incoming flows yield quite accurate runup predictions. Less predictive accuracy is attained in ab initio simulations that compute runup based solely on knowledge of static debris properties in a distant debris flow source area. Nevertheless, the paucity of inputs required in ab initio simulations enhances their prospective value in runup forecasting.

Low p-type contact resistance by field-emission tunneling in highly Mg-doped GaN

NASA Astrophysics Data System (ADS)

Okumura, Hironori; Martin, Denis; Grandjean, Nicolas

2016-12-01

Mg-doped GaN with a net acceptor concentration (NA-ND) in the high 1019 cm-3 range was grown using ammonia molecular-beam epitaxy. Electrical properties of NiO contact on this heavily doped p-type GaN were investigated. A potential-barrier height of 0.24 eV was extracted from the relationship between NA-ND and the specific contact resistivity (ρc). We found that there is an optimum NA-ND value of 5 × 1019 cm-3 for which ρc is as low as 2 × 10-5 Ω cm2. This low ρc is ascribed to hole tunneling through the potential barrier at the NiO/p+-GaN interface, which is well accounted for by the field-emission model.

Perceived barriers to weight maintenance among university students in Kuwait: the role of gender and obesity.

PubMed

Musaiger, Abdulrahman O; Al-Kandari, Fawzia I; Al-Mannai, Mariam; Al-Faraj, Alaa M; Bouriki, Fajer A; Shehab, Fatima S; Al-Dabous, Lulwa A; Al-Qalaf, Wassin B

2014-05-01

To investigate the barriers to weight maintenance among university students in Kuwait by gender and obesity. A sample of 530 students was selected at convenience from four universities in Kuwait (2 public and 2 private). The age of students ranged from 19 to 26 years. A self-reported pretested questionnaire was used to obtain the barriers, which were divided into barriers to healthy eating and barriers to physical activity. Weight and height were based on self-reporting, and the students were grouped into non-obese and obese according to the WHO classification. The response options to barriers were: very important, somewhat important and not important. The main barriers to healthy eating for both genders were: "Do not have skills to plan, shop for, prepare or cook healthy foods" and "Not having time to prepare or eat healthy food". In general, there were no significant differences between men and women in barriers to healthy eating. There were highly significant differences between men and women regarding barriers to physical activity (P values ranged from <0.001 to <0.016). "Not having time to be physically active" and "The climate is not suitable for practising exercise" were the main barriers reported. Obese men were more likely to face barriers to healthy eating than non-obese men. There were no significant differences between obese and non-obese women regarding barriers to healthy eating and physical activity. The findings of this study can be utilized in intervention activities to promote a healthy lifestyle and to combat obesity in Kuwait, and maybe in other Arab countries.

Fabrication of single Ga-doped ZnS nanowires as high-gain photosensors by focused ion beam deposition

NASA Astrophysics Data System (ADS)

Yen, Shih-Hsiang; Hung, Yu-Chen; Yeh, Ping-Hung; Su, Ya-Wen; Wang, Chiu-Yen

2017-09-01

ZnS nanowires were synthesized via a vapor-liquid-solid mechanism and then fabricated into a single-nanowire field-effect transistor by focused ion beam (FIB) deposition. The field-effect electrical properties of the FIB-fabricated ZnS nanowire device, namely conductivity, mobility and hole concentration, were 9.13 Ω-1 cm-1, 13.14 cm2 V-1 s-1and 4.27 × 1018 cm-3, respectively. The photoresponse properties of the ZnS nanowires were studied and the current responsivity, current gain, response time and recovery time were 4.97 × 106 A W-1, 2.43 × 107, 9 s and 24 s, respectively. Temperature-dependent I-V measurements were used to analyze the interfacial barrier height between ZnS and the FIB-deposited Pt electrode. The results show that the interfacial barrier height is as low as 40 meV. The energy-dispersive spectrometer elemental line scan shows the influence of Ga ions on the ZnS nanowire surface on the FIB-deposited Pt contact electrodes. The results of temperature-dependent I-V measurements and the elemental line scan indicate that Ga ions were doped into the ZnS nanowire, reducing the barrier height between the FIB-deposited Pt electrodes and the single ZnS nanowire. The small barrier height results in the FIB-fabricated ZnS nanowire device acting as a high-gain photosensor.

Current Transport Properties of Monolayer Graphene/n-Si Schottky Diodes

NASA Astrophysics Data System (ADS)

Pathak, C. S.; Garg, Manjari; Singh, J. P.; Singh, R.

2018-05-01

The present work reports on the fabrication and the detailed macroscopic and nanoscale electrical characteristics of monolayer graphene/n-Si Schottky diodes. The temperature dependent electrical transport properties of monolayer graphene/n-Si Schottky diodes were investigated. Nanoscale electrical characterizations were carried out using Kelvin probe force microscopy and conducting atomic force microscopy. Most the values of ideality factor and barrier height are found to be in the range of 2.0–4.4 and 0.50–0.70 eV for monolayer graphene/n-Si nanoscale Schottky contacts. The tunneling of electrons is found to be responsible for the high value of ideality factor for nanoscale Schottky contacts.

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride

NASA Astrophysics Data System (ADS)

Lee, Gwan-Hyoung; Yu, Young-Jun; Lee, Changgu; Dean, Cory; Shepard, Kenneth L.; Kim, Philip; Hone, James

2011-12-01

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride (h-BN) on gold-coated mica was investigated using conductive atomic force microscopy. Low-bias direct tunneling was observed in mono-, bi-, and tri-layer h-BN. For all thicknesses, Fowler-Nordheim tunneling (FNT) occurred at high bias, showing an increase of breakdown voltage with thickness. Based on the FNT model, the barrier height for tunneling (3.07 eV) and dielectric strength (7.94 MV/cm) of h-BN are obtained; these values are comparable to those of SiO2.

Investigation of local tunneling current noise spectra on the silicon crystal surfaces by means of STM/STS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mantsevich, V. N., E-mail: vmantsev@spmlab.phys.msu.su; Maslova, N. S.; Cao, G. Y.

We report on a careful analysis of the local tunneling conductivity by means of ultra-high vacuum scanning tunneling microscopy/spectroscopy (STM/STS) technique in the vicinity of low-dimensional structures on the Si(111)–(7 × 7) and Si(110)–(16 × 2) surfaces. The power-law exponent α of low-frequency tunneling current noise spectra is investigated for different values of the tunneling contact parameters: relaxation rates, the localized state coupling, and the tunneling barrier width and height.

Investigation of local tunneling current noise spectra on the silicon crystal surfaces by means of STM/STS

NASA Astrophysics Data System (ADS)

Mantsevich, V. N.; Maslova, N. S.; Cao, G. Y.

2015-08-01

We report on a careful analysis of the local tunneling conductivity by means of ultra-high vacuum scanning tunneling microscopy/spectroscopy (STM/STS) technique in the vicinity of low-dimensional structures on the Si(111)-(7 × 7) and Si(110)-(16 × 2) surfaces. The power-law exponent α of low-frequency tunneling current noise spectra is investigated for different values of the tunneling contact parameters: relaxation rates, the localized state coupling, and the tunneling barrier width and height.

Gate-Controlled Transmission of Quantum Hall Edge States in Bilayer Graphene.

PubMed

Li, Jing; Wen, Hua; Watanabe, Kenji; Taniguchi, Takashi; Zhu, Jun

2018-02-02

The edge states of the quantum Hall and fractional quantum Hall effect of a two-dimensional electron gas carry key information of the bulk excitations. Here we demonstrate gate-controlled transmission of edge states in bilayer graphene through a potential barrier with tunable height. The backscattering rate is continuously varied from 0 to close to 1, with fractional quantized values corresponding to the sequential complete backscattering of individual modes. Our experiments demonstrate the feasibility to controllably manipulate edge states in bilayer graphene, thus opening the door to more complex experiments.

Gate-Controlled Transmission of Quantum Hall Edge States in Bilayer Graphene

NASA Astrophysics Data System (ADS)

Li, Jing; Wen, Hua; Watanabe, Kenji; Taniguchi, Takashi; Zhu, Jun

2018-02-01

The edge states of the quantum Hall and fractional quantum Hall effect of a two-dimensional electron gas carry key information of the bulk excitations. Here we demonstrate gate-controlled transmission of edge states in bilayer graphene through a potential barrier with tunable height. The backscattering rate is continuously varied from 0 to close to 1, with fractional quantized values corresponding to the sequential complete backscattering of individual modes. Our experiments demonstrate the feasibility to controllably manipulate edge states in bilayer graphene, thus opening the door to more complex experiments.

Hydrogen sensors based on electrophoretically deposited Pd nanoparticles onto InP

PubMed Central

2011-01-01

Electrophoretic deposition of palladium nanoparticles prepared by the reverse micelle technique onto InP substrates is addressed. We demonstrate that the substrate pre-deposition treatment and the deposition conditions can extensively influence the morphology of the deposited palladium nanoparticle films. Schottky diodes based on these films show notably high values of the barrier height and of the rectification ratio giving evidence of a small degree of the Fermi level pinning. Moreover, electrical characteristics of these diodes are exceptionally sensitive to the exposure to gas mixtures with small hydrogen content. PMID:21711912

Kinetics of polyelectrolyte adsorption

NASA Astrophysics Data System (ADS)

Cohen Stuart, M. A.; Hoogendam, C. W.; de Keizer, A.

1997-09-01

The kinetics of polyelectrolyte adsorption has been investigated theoretically. In analogy with Kramers' rate theory for chemical reactions we present a model which is based on the assumption that a polyelectrolyte encounters a barrier in its motion towards an adsorbing surface. The height of the barrier, which is of electrostatic origin, is calculated with a self-consistent-field (SCF) model. The salt concentration strongly affects the height of the barrier. At moderate salt concentrations (0953-8984/9/37/009/img1) equilibrium in the adsorption is attained; at low salt concentration (0953-8984/9/37/009/img2) equilibrium is not reached on the time scale of experiments. The attachment process shows resemblances to the classical DLVO theory.

Shear-transformation-zone theory of linear glassy dynamics.

PubMed

Bouchbinder, Eran; Langer, J S

2011-06-01

We present a linearized shear-transformation-zone (STZ) theory of glassy dynamics in which the internal STZ transition rates are characterized by a broad distribution of activation barriers. For slowly aging or fully aged systems, the main features of the barrier-height distribution are determined by the effective temperature and other near-equilibrium properties of the configurational degrees of freedom. Our theory accounts for the wide range of relaxation rates observed in both metallic glasses and soft glassy materials such as colloidal suspensions. We find that the frequency-dependent loss modulus is not just a superposition of Maxwell modes. Rather, it exhibits an α peak that rises near the viscous relaxation rate and, for nearly jammed, glassy systems, extends to much higher frequencies in accord with experimental observations. We also use this theory to compute strain recovery following a period of large, persistent deformation and then abrupt unloading. We find that strain recovery is determined in part by the initial barrier-height distribution, but that true structural aging also occurs during this process and determines the system's response to subsequent perturbations. In particular, we find by comparison with experimental data that the initial deformation produces a highly disordered state with a large population of low activation barriers, and that this state relaxes quickly toward one in which the distribution is dominated by the high barriers predicted by the near-equilibrium analysis. The nonequilibrium dynamics of the barrier-height distribution is the most important of the issues raised and left unresolved in this paper.

The barrier to ice nucleation in monatomic water

NASA Astrophysics Data System (ADS)

Prestipino, Santi

2018-03-01

Crystallization from a supercooled liquid initially proceeds via the formation of a small solid embryo (nucleus), which requires surmounting an activation barrier. This phenomenon is most easily studied by numerical simulation, using specialized biased-sampling techniques to overcome the limitations imposed by the rarity of nucleation events. Here, I focus on the barrier to homogeneous ice nucleation in supercooled water, as represented by the monatomic-water model, which in the bulk exhibits a complex interplay between different ice structures. I consider various protocols to identify solidlike particles on a computer, which perform well enough for the Lennard-Jones model, and compare their respective impact on the shape and height of the nucleation barrier. It turns out that the effect is stronger on the nucleus size than on the barrier height. As a by-product of the analysis, I determine the structure of the nucleation cluster, finding that the relative amount of ice phases in the cluster heavily depends on the method used for classifying solidlike particles. Moreover, the phase which is most favored during the earlier stages of crystallization may happen, depending on the nucleation coordinate adopted, to be different from the stable polymorph. Therefore, the quality of a reaction coordinate cannot be assessed simply on the basis of the barrier height obtained. I explain how this outcome is possible and why it just points out the shortcoming of collective variables appropriate to simple fluids in providing a robust method of particle classification for monatomic water.

Edge-induced Schottky barrier modulation at metal contacts to exfoliated molybdenum disulfide flakes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nouchi, Ryo, E-mail: r-nouchi@21c.osakafu-u.ac.jp

2016-08-14

Ultrathin two-dimensional semiconductors obtained from layered transition-metal dichalcogenides such as molybdenum disulfide (MoS{sub 2}) are promising for ultimately scaled transistors beyond Si. Although the shortening of the semiconductor channel is widely studied, the narrowing of the channel, which should also be important for scaling down the transistor, has been examined to a lesser degree thus far. In this study, the impact of narrowing on mechanically exfoliated MoS{sub 2} flakes was investigated according to the channel-width-dependent Schottky barrier heights at Cr/Au contacts. Narrower channels were found to possess a higher Schottky barrier height, which is ascribed to the edge-induced band bendingmore » in MoS{sub 2}. The higher barrier heights degrade the transistor performance as a higher electrode-contact resistance. Theoretical analyses based on Poisson's equation showed that the edge-induced effect can be alleviated by a high dopant impurity concentration, but this strategy should be limited to channel widths of roughly 0.7 μm because of the impurity-induced charge-carrier mobility degradation. Therefore, proper termination of the dangling bonds at the edges should be necessary for aggressive scaling with layered semiconductors.« less

Microstructural, electrical and frequency-dependent properties of Au/p-Cu2ZnSnS4/n-GaN heterojunction.

PubMed

Rajagopal Reddy, V; Janardhanam, V; Won, Jonghan; Choi, Chel-Jong

2017-08-01

An Au/Cu 2 ZnSnS 4 (CZTS)/n-GaN heterojunction (HJ) is fabricated with a CZTS interlayer and probed its chemical states, structural, electrical and frequency-dependent characteristics by XPS, TEM, I-V and C-V measurements. XPS and TEM results confirmed that the CZTS films are formed on the n-GaN surface. The band gap of deposited CZTS film is found to be 1.55eV. The electrical properties of HJ correlated with the Au/n-GaN Schottky junction (SJ). The Au/CZTS/n-GaN HJ reveals a good rectification nature with high barrier height (0.82eV) compared to the Au/n-GaN SJ (0.69eV), which suggests the barrier height is influenced by the CZTS interlayer. The barrier height values assessed by I-V, Cheung's and Norde functions are closely matched with one other, thus the methods used here are reliable and valid. The extracted interface state density (N SS ) of Au/CZTS/n-GaN HJ is lower compared to the Au/n-GaN SJ that suggests the CZTS interlayer plays an important role in the reduction of N SS . Moreover, the capacitance-frequency (C-f) and conductance-frequency (G-f) characteristics of SJ and HJ are measured in the range of 1kHz-1MHz, and found that the capacitance and conductance strappingly dependent on frequency. It is found that the N SS estimated from C-f and G-f characteristics is lower compared to those estimated from I-V characteristics. Analysis confirmed that Poole-Frenkel emission dominates the reverse leakage current in both SJ and HJ, probably related to the structural defects and trap levels in the CZTS interlayer. Copyright © 2017 Elsevier Inc. All rights reserved.

Analysis of photoconductive mechanisms of organic-on-inorganic photodiodes

NASA Astrophysics Data System (ADS)

Ocaya, R. O.; Dere, A.; Al-Sehemi, Abdullah G.; Al-Ghamdi, Ahmed A.; Soylu, M.; Yakuphanoglu, F.

2017-09-01

In this work, it is shown that choosing an organic-on-inorganic Schottky diode for photoconductive sensing by a using a power law exponent (PLE or γ) determined at a single bias point is a limited approach. The standard literature approach does not highlight any bias voltage effects on the distribution of interface state density and other operationally important parameters. In this paper we suggest a new empirical method that holistically highlights the variation of γ with voltage, irradiance and temperature to reach a more informed choice of photosensor for real applications. We obtain a simple, plausible relation of the variation of barrier height, Φ, with voltage, irradiance and temperature. The method is evaluated with data collected previously for Schottky diodes of structure Al/p-Si/organic-semiconductor (OSC)/Au, where OSC is Coumarin-doped with graphene oxide (GO), Cobalt Phthacyanine (CoPC) doped with GO or PCBM doped with GO, respectively. The method reproduces published data for the three diodes reported at specific bias and provides for the first time some qualitative evidence of barrier height variation with light intensity, for which a possible physical basis is also given. Typically, Schottky barrier height is characterized using dark current leading to an under reporting of the effect of illumination on barrier height. Finally, since recombination mechanisms are gauged on the basis of the magnitude of PLE, the method facilitates the identification of the recombination mechanism at a given bias.

Distributions of methyl group rotational barriers in polycrystalline organic solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beckmann, Peter A., E-mail: pbeckman@brynmawr.edu, E-mail: wangxianlong@uestc.edu.cn; Conn, Kathleen G.; Division of Education and Human Services, Neumann University, One Neumann Drive, Aston, Pennsylvania 19014-1298

We bring together solid state {sup 1}H spin-lattice relaxation rate measurements, scanning electron microscopy, single crystal X-ray diffraction, and electronic structure calculations for two methyl substituted organic compounds to investigate methyl group (CH{sub 3}) rotational dynamics in the solid state. Methyl group rotational barrier heights are computed using electronic structure calculations, both in isolated molecules and in molecular clusters mimicking a perfect single crystal environment. The calculations are performed on suitable clusters built from the X-ray diffraction studies. These calculations allow for an estimate of the intramolecular and the intermolecular contributions to the barrier heights. The {sup 1}H relaxation measurements,more » on the other hand, are performed with polycrystalline samples which have been investigated with scanning electron microscopy. The {sup 1}H relaxation measurements are best fitted with a distribution of activation energies for methyl group rotation and we propose, based on the scanning electron microscopy images, that this distribution arises from molecules near crystallite surfaces or near other crystal imperfections (vacancies, dislocations, etc.). An activation energy characterizing this distribution is compared with a barrier height determined from the electronic structure calculations and a consistent model for methyl group rotation is developed. The compounds are 1,6-dimethylphenanthrene and 1,8-dimethylphenanthrene and the methyl group barriers being discussed and compared are in the 2–12 kJ mol{sup −1} range.« less

Temperature dependent I-V characteristics of an Au/n-GaAs Schottky diode analyzed using Tung’s model

NASA Astrophysics Data System (ADS)

Korucu, Demet; Turut, Abdulmecit; Efeoglu, Hasan

2013-04-01

The current-voltage (I-V) characteristics of Au/n-GaAs contacts prepared with photolithography technique have been measured in the temperature range of 80-320 K. The ideality factor and barrier height (BH) values have remained almost unchanged between 1.04 and 1.10 and at a value of about 0.79 eV at temperatures above 200 K, respectively. Therefore, the ideality factor values near unity say that the experimental I-V data are almost independent of the sample temperature, that is, contacts have shown excellent Schottky diode behavior above 200 K. An abnormal decrease in the experimental BH Φb and an increase in the ideality factor with a decrease in temperature have been observed below 200 K. This behavior has been attributed to the barrier inhomogeneity by assuming a Gaussian distribution of nanometer-sized patches with low BH at the metal-semiconductor interface. The barrier inhomogeneity assumption is also confirmed by the linear relationship between the BH and the ideality factor. According to Tung’s barrier inhomogeneity model, it has been seen that the value of σT=7.41×10-5 cm2/3 V1/3from ideality factor versus (kT)-1 curve is in close agreement with σT=7.95×10-5 cm2/3 V1/3 value from the Φeff versus (2kT)-1 curve in the range of 80-200 K. The modified Richardson ln(J0/T2)-(qσT)2(Vb/η)2/3/[2(kT)2] versus (kT)-1 plot, from Tung’s Model, has given a Richardson constant value of 8.47 A cm-2 K-2which is in very close agreement with the known value of 8.16 A cm-2 K-2 for n-type GaAs; considering the effective patch area which is significantly lower than the entire geometric area of the Schottky contact, in temperature range of 80-200 K. Thus, it has been concluded that the use of Tung’s lateral inhomogeneity model is more appropriate to interpret the temperature-dependent I-V characteristics in the Schottky contacts.

Effect of annealing on the temperature dependence of inelastic tunneling contributions vis-à-vis tunneling magnetoresistance and barrier parameters in CoFe/MgO/NiFe magnetic tunnel junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhusan Singh, Braj; Chaudhary, Sujeet, E-mail: sujeetc@physics.iitd.ac.in

The effect of annealing on the changes in the inelastic tunneling contributions in tunneling conductance of ion beam sputtered CoFe/MgO/NiFe magnetic tunnel junctions (MTJs) is investigated. The inelastic contributions are evaluated using hopping conduction model of Glazman and Matveev in the temperature range of 25–300 K. The hopping through number of series of localized states present in the barrier due to structural defects increases from 9 (in as deposited MTJ) to 18 after annealing (at 200 °C/1 h); although no changes in the interface roughness of CoFe-MgO and MgO-NiFe interfaces are observed as revealed by the x-ray reflectance studies on planar MTJs. Themore » bias dependence of tunneling magnetoresistance (TMR) at 25 K is found to get improved after annealing as revealed by the value V{sub 1/2} (the bias value at which the TMR reaches to half of its value at nearly zero bias); which is 78 mV (in MTJ annealed at 200 °C/1 h) 2.5 times the value of 33 mV (in as deposited MTJ). At 25 K the inelastic tunneling spectra revealed the presence of zero bias anomaly and magnon excitations in the range of 10–15 mV. While the barrier height exhibited a strong temperature dependence with nearly 100% increase from the value at 300 K to 25 K, the temperature dependence of TMR becomes steep after annealing.« less

Dual-functional on-chip AlGaAs/GaAs Schottky diode for RF power detection and low-power rectenna applications.

PubMed

Hashim, Abdul Manaf; Mustafa, Farahiyah; Rahman, Shaharin Fadzli Abd; Rahman, Abdul Rahim Abdul

2011-01-01

A Schottky diode has been designed and fabricated on an n-AlGaAs/GaAs high-electron-mobility-transistor (HEMT) structure. Current-voltage (I-V) measurements show good device rectification, with a Schottky barrier height of 0.4349 eV for Ni/Au metallization. The differences between the Schottky barrier height and the theoretical value (1.443 eV) are due to the fabrication process and smaller contact area. The RF signals up to 1 GHz are rectified well by the fabricated Schottky diode and a stable DC output voltage is obtained. The increment ratio of output voltage vs input power is 0.2 V/dBm for all tested frequencies, which is considered good enough for RF power detection. Power conversion efficiency up to 50% is obtained at frequency of 1 GHz and input power of 20 dBm with series connection between diode and load, which also shows the device's good potential as a rectenna device with further improvement. The fabricated n-AlGaAs/GaAs Schottky diode thus provides a conduit for breakthrough designs for RF power detectors, as well as ultra-low power on-chip rectenna device technology to be integrated in nanosystems.

Temperature-dependent electrical characteristics and carrier transport mechanism of p-Cu2ZnSnS4/n-GaN heterojunctions

NASA Astrophysics Data System (ADS)

Niteesh Reddy, Varra; Reddy, M. Siva Pratap; Gunasekhar, K. R.; Lee, Jung-Hee

2018-04-01

This work explores the temperature-dependent electrical characteristics and carrier transport mechanism of Au/p-Cu2ZnSnS4/n-type GaN heterojunction (HJ) diodes with a CZTS interlayer. The electrical characteristics were examined by current-voltage-temperature, turn-on voltage-temperature and series resistance-temperature in the high-temperature range of 300-420 K. It is observed that an exponential decrease in the series resistance ( R S) and increase in the ideality factor ( n) and barrier height ( ϕ b) with increase in temperature. The thermal coefficient ( K j) is determined to be - 1.3 mV K-1 at ≥ 300 K. The effective ϕ b is determined to be 1.21 eV. This obtained barrier height is consistent with the theoretical one. The characteristic temperature ( T 0) resulting from the Cheung's functions [d V/d(ln I) vs. I and H( I) vs. I], is seen that there is good agreement between the T 0 values from both Cheung's functions. The relevant carrier transport mechanisms of Au/p-CZTS/n-type GaN HJ are explained based on the thermally decreased energy band gap of n-type GaN layers, thermally activated deep donors and increased further activated shallow donors.

Branch-point energies and the band-structure lineup at Schottky contacts and heterostrucures

NASA Astrophysics Data System (ADS)

Mönch, Winfried

2011-06-01

Empirical branch-point energies of Si, the group-III nitrides AlN, GaN, and InN, and the group-II and group-III oxides MgO, ZnO, Al2O3 and In2O3 are determined from experimental valance-band offsets of their heterostructures. For Si, GaN, and MgO, these values agree with the branch-point energies obtained from the barrier heights of their Schottky contacts. The empirical branch-point energies of Si and the group-III nitrides are in very good agreement with results of previously published calculations using quite different approaches such as the empirical tight-binding approximation and modern electronic-structure theory. In contrast, the empirical branch-point energies of the group-II and group-III oxides do not confirm the respective theoretical results. As at Schottky contacts, the band-structure lineup at heterostructures is also made up of a zero-charge-transfer term and an intrinsic electric-dipole contribution. Hence, valence-band offsets are not equal to the difference of the branch-point energies of the two semiconductors forming the heterostructure. The electric-dipole term may be described by the electronegativity difference of the two solids in contact. A detailed analysis of experimental Si Schottky barrier heights and heterostructure valence-band offsets explains and proves these conclusions.

Measurement and statistical analysis of single-molecule current-voltage characteristics, transition voltage spectroscopy, and tunneling barrier height.

PubMed

Guo, Shaoyin; Hihath, Joshua; Díez-Pérez, Ismael; Tao, Nongjian

2011-11-30

We report on the measurement and statistical study of thousands of current-voltage characteristics and transition voltage spectra (TVS) of single-molecule junctions with different contact geometries that are rapidly acquired using a new break junction method at room temperature. This capability allows one to obtain current-voltage, conductance voltage, and transition voltage histograms, thus adding a new dimension to the previous conductance histogram analysis at a fixed low-bias voltage for single molecules. This method confirms the low-bias conductance values of alkanedithiols and biphenyldithiol reported in literature. However, at high biases the current shows large nonlinearity and asymmetry, and TVS allows for the determination of a critically important parameter, the tunneling barrier height or energy level alignment between the molecule and the electrodes of single-molecule junctions. The energy level alignment is found to depend on the molecule and also on the contact geometry, revealing the role of contact geometry in both the contact resistance and energy level alignment of a molecular junction. Detailed statistical analysis further reveals that, despite the dependence of the energy level alignment on contact geometry, the variation in single-molecule conductance is primarily due to contact resistance rather than variations in the energy level alignment.

Dual-Functional On-Chip AlGaAs/GaAs Schottky Diode for RF Power Detection and Low-Power Rectenna Applications

PubMed Central

Hashim, Abdul Manaf; Mustafa, Farahiyah; Rahman, Shaharin Fadzli Abd; Rahman, Abdul Rahim Abdul

2011-01-01

A Schottky diode has been designed and fabricated on an n-AlGaAs/GaAs high-electron-mobility-transistor (HEMT) structure. Current-voltage (I–V) measurements show good device rectification, with a Schottky barrier height of 0.4349 eV for Ni/Au metallization. The differences between the Schottky barrier height and the theoretical value (1.443 eV) are due to the fabrication process and smaller contact area. The RF signals up to 1 GHz are rectified well by the fabricated Schottky diode and a stable DC output voltage is obtained. The increment ratio of output voltage vs input power is 0.2 V/dBm for all tested frequencies, which is considered good enough for RF power detection. Power conversion efficiency up to 50% is obtained at frequency of 1 GHz and input power of 20 dBm with series connection between diode and load, which also shows the device’s good potential as a rectenna device with further improvement. The fabricated n-AlGaAs/GaAs Schottky diode thus provides a conduit for breakthrough designs for RF power detectors, as well as ultra-low power on-chip rectenna device technology to be integrated in nanosystems. PMID:22164066

Introducing ionic and/or hydrogen bonds into the SAM//Ga2O3 top-interface of Ag(TS)/S(CH2)nT//Ga2O3/EGaIn junctions.

PubMed

Bowers, Carleen M; Liao, Kung-Ching; Yoon, Hyo Jae; Rappoport, Dmitrij; Baghbanzadeh, Mostafa; Simeone, Felice C; Whitesides, George M

2014-06-11

Junctions with the structure Ag(TS)/S(CH2)nT//Ga2O3/EGaIn (where S(CH2)nT is a self-assembled monolayer, SAM, of n-alkanethiolate bearing a terminal functional group T) make it possible to examine the response of rates of charge transport by tunneling to changes in the strength of the interaction between T and Ga2O3. Introducing a series of Lewis acidic/basic functional groups (T = -OH, -SH, -CO2H, -CONH2, and -PO3H) at the terminus of the SAM gave values for the tunneling current density, J(V) in A/cm(2), that were indistinguishable (i.e., differed by less than a factor of 3) from the values observed with n-alkanethiolates of equivalent length. The insensitivity of the rate of tunneling to changes in the terminal functional group implies that replacing weak van der Waals contact interactions with stronger hydrogen- or ionic bonds at the T//Ga2O3 interface does not change the shape (i.e., the height or width) of the tunneling barrier enough to affect rates of charge transport. A comparison of the injection current, J0, for T = -CO2H, and T = -CH2CH3--two groups having similar extended lengths (in Å, or in numbers of non-hydrogen atoms)--suggests that both groups make indistinguishable contributions to the height of the tunneling barrier.

Barrier inhomogeneities at vertically stacked graphene-based heterostructures.

PubMed

Lin, Yen-Fu; Li, Wenwu; Li, Song-Lin; Xu, Yong; Aparecido-Ferreira, Alex; Komatsu, Katsuyoshi; Sun, Huabin; Nakaharai, Shu; Tsukagoshi, Kazuhito

2014-01-21

The integration of graphene and other atomically flat, two-dimensional materials has attracted much interest and been materialized very recently. An in-depth understanding of transport mechanisms in such heterostructures is essential. In this study, vertically stacked graphene-based heterostructure transistors were manufactured to elucidate the mechanism of electron injection at the interface. The temperature dependence of the electrical characteristics was investigated from 300 to 90 K. In a careful analysis of current-voltage characteristics, an unusual decrease in the effective Schottky barrier height and increase in the ideality factor were observed with decreasing temperature. A model of thermionic emission with a Gaussian distribution of barriers was able to precisely interpret the conduction mechanism. Furthermore, mapping of the effective Schottky barrier height is unmasked as a function of temperature and gate voltage. The results offer significant insight for the development of future layer-integration technology based on graphene-based heterostructures.

Coastal vulnerability and the implications of sea level rise between the cities of Pescara and Ortona (Adriatic Sea - Central Italy)

NASA Astrophysics Data System (ADS)

Tarragoni, C.; Bellotti, P.; Caputo, C.; Davoli, L.; Evangelista, S.; Pugliese, F.; Raffi, R.; Lupia Palmieri, E.

2012-04-01

Geomorphic processes induce rapid environmental changes especially along the coast that is highly susceptible to them. In addiction, the effects of storm or wave may be amplified by the expected relative sea level rise. In a context, like Italian coast, where the almost part of coast is densely populated and many infrastructures are presents, it is very important to have adequate tools to urban planning like the coastal vulnerability map. In this study the preliminary results of the ongoing SECOA project (Solution for Environmental contrasts in COastal Areas; 7th Framework Program) are presented, with reference to the Adriatic coast between Pescara and Ortona cities, in the Abruzzo region. In this work the same analytical model applied in the Venice Lagoon has been employed (Fontolan, 2001; 2005) involving the evaluation of the effective vulnerability (Ve). Ve is calculated as the difference between the potential vulnerability (Vp) and the defence elements present along the coast (D). (Ve = Vp - D) The data used to measure quantitative features are: high-resolution DEM (LiDAR), satellite images, aero photos, bathymetric profiles and topographic maps. The variables that contribute to the evaluation are: beach amplitude, berm height, seafloor gradient, seafloor evolution, recent and historical shorelines evolution for Vp; height, slope, vegetation cover, presence of passages, incipient dunes and windbreak barriers for the dune and anthropic barriers height. In this context, the potential vulnerability results from the sum of each variable (Vn) per the relative efficacy coefficient (Kn): Vp = V1K1+V2K2+ …VnKn In the same way the defences result from the sum of each kind of defence per the relative efficacy coefficient: D = D1K1+ …. DnKn The coastal area between Pescara and Ortona cities has been segmented in different sectors characterized by homogeneous values of the considered variables and for each of these the Ve values have been calculated and referred to one of the five corresponding standard vulnerability classes. In long-term vulnerability analyses (year 2100) the following aspects have been taken into account: sea level rise expected according to the IPCC and Rahmstorf hypothesis, local tectonic movement (compaction and sedimentary load) and local vertical movement due to isostasy. The height of defences have been decreased of relative sea level rise value and the efficacy coefficients have been modified according to the different long-term weight of morphological and morphodynamics variables. A coastal vulnerability map has been drawn both for the short-term (present day) and long-term; the vulnerability classes values have been represented by different colours from green to red respectively from lowest to highest values. In conclusion, the short-term results show Ve values belonging to the lowest class due to the considerable presence of the defence works, even if Vp values falling in the medium and medium-low classes. Similar results are obtained from the long-term analysis in the case of both the IPCC and Rahmstorf hypothesis, further evidencing the overwhelming employment of defence structures.

Self-organization and forcing templates in coastal barrier response to storms

NASA Astrophysics Data System (ADS)

Lazarus, E.

2015-12-01

When a storm event pushes water up and over a coastal barrier, cross-shore flow transports sediment from the barrier face to the back-barrier environment. This natural physical process is called "overwash", and "washover" is the sedimentary deposit it forms. Overwash and washover support critical coastal habitats, and enable barriers to maintain their height and width relative to rising sea level. On developed barrier coasts, overwash constitutes a natural hazard, which sea-level rise will exacerbate. Overwash is also a prerequisite for barrier breaching and coastal flooding. Predicting occurrence and characteristics of overwash and washover has significant societal value. Hazard models typically assume that pre-storm barrier morphology determines how the barrier changes during a storm. However, classic work has documented the absence of a relationship between pre/post-storm topography in some cases, and has also identified rhythmic patterns in washover alongshore. Previous explanations for these spatial patterns have looked to forcing templates, forms that get imprinted in the barrier shape. An alternative explanation is that washover patterns self-organize, emerging from feedbacks between water flow and sediment transport. Self-organization and forcing templates are often framed as mutually exclusive, but patterns likely form across a continuum of conditions. Here, I use data from a new physical experiment to suggest that spatial patterns in washover can self-organize within the limit of a forcing template of some critical "strength", beyond which pre/post-storm morphologies are highly correlated. Quantifying spatial patterns in washover deposits opens exciting questions regarding coastal morphodynamic response to storms. Measurement of relative template strength over extended spatial (and temporal) scales has the potential to improve hazard assessment and prediction, particularly where template strength is low and self-organization dominates barrier change.

The effects of gamma irradiation on electrical characteristics of Zn/ZnO/n-Si/Au-Sb structure

NASA Astrophysics Data System (ADS)

Salari, M. Abdolahpour; Güzeldir, B.; Saǧlam, M.

2018-02-01

In this research, we have investigated the electrical characteristics of Zn/ZnO/n-Si/Au-Sb structure before and after 60Co gamma (γ)-ray source irradiation with the total dose range of 0-500 kGy at room temperature. Electrical measurements of this structure have been performed using current-voltage (I-V) and capacitance-voltage (C-V) techniques. Experimental results show that the values of the ideality factor obtained from I-V measurements increased and the values of the barrier height obtained from reverse-bias C-V measurements decreased after gamma-irradiation. The results show that the main effect of the radiation is the generation of laterally inhomogeneous defects near the semiconductor surface.

Liquid junction schottky barrier solar cell

DOEpatents

Williams, Richard

1980-01-01

A mixture of ceric ions (Ce.sup.+4) and cerous ions (Ce.sup.+3) in an aqueous electrolyte solution forms a Schottky barrier at the interface between an active region of silicon and the electrolyte solution. The barrier height obtained for hydrogenated amorphous silicon using the Ce.sup.+4 /Ce.sup.+3 redox couple is about 1.7 eV.

Accuracy of AHOF400 with a moment-measuring load cell barrier.

DOT National Transportation Integrated Search

2011-06-13

Several performance measures derived from rigid : barrier crash testing have been proposed to assess : vehicle-to-vehicle crash compatibility. One such : measure, the Average Height of Force 400 (AHOF400) : [1], has been proposed to estimate the heig...

Electronic Properties of Grain Boundaries in GaAs: A Study of Oriented Bicrystals Prepared by Epitaxial Lateral Overgrowth.

DTIC Science & Technology

1984-05-10

overgrowth from a spoke 90 pattern of radial stripe openings at 1 intervals on an Si0 2 coated (110) surface. Bright regions are GaAs and dark regions are Si0...the dark current for such an ideal device is given by Idark - Io[exp(eVbi/AokT) - 1] , (11-l) where Io is a proportionality constant describing the...recombination and leakage currents which contribute to an increased dark current. The value of Voc is determined by the built-in junction barrier height and the

Bimolecular reactions of carbenes: Proton transfer mechanism

NASA Astrophysics Data System (ADS)

Abu-Saleh, Abd Al-Aziz A.; Almatarneh, Mansour H.; Poirier, Raymond A.

2018-04-01

Here we report the bimolecular reaction of trifluoromethylhydroxycarbene conformers and the water-mediated mechanism of the 1,2-proton shift for the unimolecular trans-conformer by using quantum chemical calculations. The CCSD(T)/cc-pVTZ//MP2/cc-pVDZ potential-energy profile of the bimolecular reaction of cis- and trans-trifluoromethylhydroxycarbene, shows the lowest gas-phase barrier height of 13 kJ mol-1 compared to the recently reported value of 128 kJ mol-1 for the unimolecular reaction. We expect bimolecular reactions of carbene's stereoisomers will open a valuable field for new and useful synthetic strategies.

Effect of interfacial composition on Ag-based Ohmic contact of GaN-based vertical light emitting diodes

NASA Astrophysics Data System (ADS)

Wu, Ning; Xiong, Zhihua; Qin, Zhenzhen

2018-02-01

By investigating the effect of a defective interface structure on Ag-based Ohmic contact of GaN-based vertical light-emitting diodes, we found a direct relationship between the interfacial composition and the Schottky barrier height of the Ag(111)/GaN(0001) interface. It was demonstrated that the Schottky barrier height of a defect-free Ag(111)/GaN(0001) interface was 2.221 eV, and it would be dramatically decreased to 0.375 eV with the introduction of one Ni atom and one Ga vacancy at the interface structure. It was found that the tunability of the Schottky barrier height can be attributed to charge accumulations around the interfacial defective regions and an unpinning of the Fermi level, which explains the experimental phenomenon of Ni-assisted annealing improving the p-type Ohmic contact characteristic. Lastly, we propose a new method of using Cu as an assisted metal to realize a novel Ag-based Ohmic contact. These results provide a guideline for the fabrication of high-quality Ag-based Ohmic contact of GaN-based vertical light-emitting diodes.

Schottky Barrier Height Tuning via the Dopant Segregation Technique through Low-Temperature Microwave Annealing.

PubMed

Fu, Chaochao; Zhou, Xiangbiao; Wang, Yan; Xu, Peng; Xu, Ming; Wu, Dongping; Luo, Jun; Zhao, Chao; Zhang, Shi-Li

2016-04-27

The Schottky junction source/drain structure has great potential to replace the traditional p/n junction source/drain structure of the future ultra-scaled metal-oxide-semiconductor field effect transistors (MOSFETs), as it can form ultimately shallow junctions. However, the effective Schottky barrier height (SBH) of the Schottky junction needs to be tuned to be lower than 100 meV in order to obtain a high driving current. In this paper, microwave annealing is employed to modify the effective SBH of NiSi on Si via boron or arsenic dopant segregation. The barrier height decreased from 0.4-0.7 eV to 0.2-0.1 eV for both conduction polarities by annealing below 400 °C. Compared with the required temperature in traditional rapid thermal annealing, the temperature demanded in microwave annealing is ~60 °C lower, and the mechanisms of this observation are briefly discussed. Microwave annealing is hence of high interest to future semiconductor processing owing to its unique capability of forming the metal/semiconductor contact at a remarkably lower temperature.

Schottky Barrier Height Tuning via the Dopant Segregation Technique through Low-Temperature Microwave Annealing

PubMed Central

Fu, Chaochao; Zhou, Xiangbiao; Wang, Yan; Xu, Peng; Xu, Ming; Wu, Dongping; Luo, Jun; Zhao, Chao; Zhang, Shi-Li

2016-01-01

The Schottky junction source/drain structure has great potential to replace the traditional p/n junction source/drain structure of the future ultra-scaled metal-oxide-semiconductor field effect transistors (MOSFETs), as it can form ultimately shallow junctions. However, the effective Schottky barrier height (SBH) of the Schottky junction needs to be tuned to be lower than 100 meV in order to obtain a high driving current. In this paper, microwave annealing is employed to modify the effective SBH of NiSi on Si via boron or arsenic dopant segregation. The barrier height decreased from 0.4–0.7 eV to 0.2–0.1 eV for both conduction polarities by annealing below 400 °C. Compared with the required temperature in traditional rapid thermal annealing, the temperature demanded in microwave annealing is ~60 °C lower, and the mechanisms of this observation are briefly discussed. Microwave annealing is hence of high interest to future semiconductor processing owing to its unique capability of forming the metal/semiconductor contact at a remarkably lower temperature. PMID:28773440

Electron and hole photoemission detection for band offset determination of tunnel field-effect transistor heterojunctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Wei; Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871; Zhang, Qin

2014-11-24

We report experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as an optically transparent electrode, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. For a Al{sub 2}O{sub 3}/InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al{sub 2}O{sub 3} conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al{sub 2}O{sub 3} valence band to the bottom ofmore » the InAs and GaSb conduction bands. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to facilitate the development of predicted models of electron quantum tunneling efficiency and transistor performance.« less

Rotational Spectrum and Internal Rotation Barrier of 1-Chloro-1,1-difluoroethane

NASA Astrophysics Data System (ADS)

Alonso, José L.; López, Juan C.; Blanco, Susana; Guarnieri, Antonio

1997-03-01

The rotational spectra of 1-chloro-1,1-difluoroethane (HCFC-142b) has been investigated in the frequency region 8-115 GHz with Stark, waveguide Fourier transform (FTMW), and millimeter-wave spectrometers. Assignments in large frequency regions with the corresponding frequency measurements have been made for the ground andv18= 1 (CH3torsion) vibrational states of the35Cl isotopomer and for the ground state of the37Cl species. Accurate rotational, quartic centrifugal distortion, and quadrupole coupling constants have been determined from global fits considering all these states. SmallA-Einternal rotation splittings have been observed for thev18= 1 vibrational state using FTMW spectroscopy. The barrier height for the internal rotation of the methyl group has been determined to be 3751 (4) cal mol-1, in disagreement with the previous microwave value of 4400 (100) cal mol-1reported by G. Graner and C. Thomas [J. Chem. Phys.49,4160-4167 (1968)].

Many-body design of highly strained GaInNAs electroabsorption modulators on GaInAs ternary substrates

NASA Astrophysics Data System (ADS)

Fujisawa, Takeshi; Arai, Masakazu; Kano, Fumiyoshi

2010-05-01

Electroabsorption in highly strained GaInAs and GaInNAs quantum wells (QWs) grown on GaInAs or quasi-GaInAs substrates is investigated by using microscopic many-body theory. The effects of various parameters, such as strain, barrier height, substrate composition, and temperature are thoroughly examined. It is shown that the value of the absorption coefficient strongly depends on the depth of the QWs under large bias electric field due to the small overlap integral of wave functions between the conduction and valence bands. The use of GaInNAs QWs makes the strain in the well layer very small. Further, the effective quantum-well depth is increased in GaInNAs QWs due to the anticrossing interaction between the conduction and N-resonant bands, making it possible to obtain larger absorption coefficient under large bias electric fields without using wide-band gap materials for barriers.

Temperature-Dependent Electrical Characteristics of Au/Si3N4/4H n-SiC MIS Diode

NASA Astrophysics Data System (ADS)

Yigiterol, F.; Güllü, H. H.; Bayraklı, Ö.; Yıldız, D. E.

2018-03-01

Electrical characteristics of the Au/Si3N4/4H n-SiC metal-insulator-semiconductor (MIS) diode were investigated under the temperature, T , interval of 160-400 K using current-voltage (I-V), capacitance-voltage ( C {-} V ) and conductance-voltage ( G/ω {-} V ) measurements. Firstly, the Schottky diode parameters as zero-bias barrier height ( Φ_{B0} ) and ideality factor ( n ) were calculated according to the thermionic emission (TE) from forward bias I-V analysis in the whole working T . Experimental results showed that the values of Φ_{B0} were in increasing behavior with increasing T while n values decreased with inverse proportionality in n versus Φ_{{{{B}}0}} plot. Therefore, the non-ideal I-V behavior with inhomogeneous barrier height (BH) formation has been discussed under the assumption of Gaussian distribution (GD). From the GD of BHs, the mean BH was found to be about 1.40 eV with 0.1697 standard deviation and the modified Richardson constant A^{*} of this diode was obtained as 141.65 A/cm2 K2 in good agreement with the literature (the theoretical value of A^{*} is 137.21 A/cm2 K2). The relationship between Φ_{B0} and n showed an abnormal I-V behavior depending on T , and it was modeled by TE theory with GD of BH due to the effect in inhomogeneous BH at the interface. Secondly, according to Cheung's model, series resistance, R_{{S}} values were calculated in the T range of 160-400 K and these values were found to decrease with increasing T . Finally, the density of interface states, D_{{it}} was calculated and the T dependence of energy distribution of D_{{it}} profiles determined the forward I {-} V measurements by taking into account the bias dependence of the effective BH, Φ_{{e}} and n . D_{{it}} were also calculated according to the Hill-Coleman method from C {-} V and G/ω {-} V analysis. Furthermore, the variation of D_{{it}} as a function of frequency, f and T were determined.

Boltzmann-distribution-equivalent for Lévy noise and how it leads to thermodynamically consistent epicatalysis

NASA Astrophysics Data System (ADS)

Bier, Martin

2018-02-01

Nonequilibrium systems commonly exhibit Lévy noise. This means that the distribution for the size of the Brownian fluctuations has a "fat" power-law tail. Large Brownian kicks are then more common as compared to the ordinary Gaussian distribution. We consider a two-state system, i.e., two wells and a barrier in between. The barrier is sufficiently high for a barrier crossing to be a rare event. When the noise is Lévy, we do not get a Boltzmann distribution between the two wells. Instead we get a situation where the distribution between the two wells also depends on the height of the barrier that is in between. Ordinarily, a catalyst, by lowering the barrier between two states, speeds up the relaxation to an equilibrium, but does not change the equilibrium distribution. In an environment with Lévy noise, on the other hand, we have the possibility of epicatalysis, i.e., a catalyst effectively altering the distribution between two states through the changing of the barrier height. After deriving formulas to quantitatively describe this effect, we discuss how this idea may apply in nuclear reactors and in the biochemistry of a living cell.

Gas phase hydrolysis of formaldehyde to form methanediol: impact of formic acid catalysis.

PubMed

Hazra, Montu K; Francisco, Joseph S; Sinha, Amitabha

2013-11-21

We find that formic acid (FA) is very effective at facilitating diol formation through its ability to reduce the barrier for the formaldehyde (HCHO) hydrolysis reaction. The rate limiting step in the mechanism involves the isomerization of a prereactive collision complex formed through either the HCHO···H2O + FA and/or HCHO + FA···H2O pathways. The present study finds that the effective barrier height, defined as the difference between the zero-point vibrational energy (ZPE) corrected energy of the transition state (TS) and the HCHO···H2O + FA and HCHO + FA···H2O starting reagents, are respectively only ∼1 and ∼4 kcal/mol. These barriers are substantially lower than the ∼17 kcal/mol barrier associated with the corresponding step in the hydrolysis of HCHO catalyzed by a single water molecule (HCHO + H2O + H2O). The significantly lower barrier heights for the formic acid catalyzed pathway reveal a new important role that organic acids play in the gas phase hydrolysis of atmospheric carbonyl compounds.

Characterization of WB/SiC Schottky Barrier Diodes Using I-V-T Method

NASA Astrophysics Data System (ADS)

Aldridge, James; Oder, Tom

2009-04-01

The importance of silicon carbide (SiC) semiconductor for high temperature and high power microelectronic device applications has long been established. We have fabricated SiC Schottky barrier diodes using tungsten boride (WB) as the Schottky contact. The diodes were characterized using the current-voltage-temperature method. The sample was mounted on a heated stage and the temperature varied from about 25 ^oC to 300 ^oC at intervals of 25 ^oC. From the Richardson's plot, we obtained an energy barrier height of 0.96 eV and a Richardson's constant of 71.2 AK-1cm-2. Using the modified Richardson's plot, we obtained a barrier height of 1.01 eV. From the variation of the ideality factor and the temperature, we determined a characteristic energy of 0.02 eV to 0.04 eV across the range of the measurement temperature. This implies that thermionic emission is dominant in the low measurement temperature range. Our results confirm the excellent thermal stability of WB/SiC Schottky barrier diodes.

Evaluation of Schottky barrier height on 4H-SiC m-face \\{ 1\\bar{1}00\\} for Schottky barrier diode wall integrated trench MOSFET

NASA Astrophysics Data System (ADS)

Kobayashi, Yusuke; Ishimori, Hiroshi; Kinoshita, Akimasa; Kojima, Takahito; Takei, Manabu; Kimura, Hiroshi; Harada, Shinsuke

2017-04-01

We proposed an Schottky barrier diode wall integrated trench MOSFET (SWITCH-MOS) for the purposes of shrinking the cell pitch and suppressing the forward degradation of the body diode. A trench Schottky barrier diode (SBD) was integrated into a trench gate MOSFET with a wide shielding p+ region that protected the trench bottoms of both the SBD and the MOS gate from high electrical fields in the off state. The SBD was placed on the trench sidewall of the \\{ 1\\bar{1}00\\} plane (m-face). Static and transient simulations revealed that SWITCH-MOS sufficiently suppressed the bipolar current that induced forward degradation, and we determined that the optimum Schottky barrier height (SBH) was from 0.8 to 2.0 eV. The SBH depends on the crystal planes in 4H-SiC, but the SBH of the m-face was unclear. We fabricated a planar m-face SBD for the first time, and we obtained SBHs from 1.4 to 1.8 eV experimentally with titanium or nickel as a Schottky metal.

Utilizing Schottky barriers to suppress short-channel effects in organic transistors

NASA Astrophysics Data System (ADS)

Fernández, Anton F.; Zojer, Karin

2017-10-01

Transistors with short channel lengths exhibit profound deviations from the ideally expected behavior. One of the undesired short-channel effects is an enlarged OFF current that is associated with a premature turn on of the transistor. We present an efficient approach to suppress the OFF current, defined as the current at zero gate source bias, in short-channel organic transistors. We employ two-dimensional device simulations based on the drift-diffusion model to demonstrate that intentionally incorporating a Schottky barrier for injection enhances the ON-OFF ratio in both staggered and coplanar transistor architectures. The Schottky barrier is identified to directly counteract the origin of enlarged OFF currents: Short channels promote a drain-induced barrier lowering. The latter permits unhindered injection of charges even at reverse gate-source bias. An additional Schottky barrier hampers injection for such points of operations. We explain how it is possible to find the Schottky barrier of the smallest height necessary to exactly compensate for the premature turn on. This approach offers a substantial enhancement of the ON-OFF ratio. We show that this roots in the fact that such optimal barrier heights offer an excellent compromise between an OFF current diminished by orders of magnitude and an only slightly reduced ON current.

Diffusion of One-Dimensional Crystals in Channels of Single-Walled Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Zhigalina, V. G.; Kumskov, A. S.; Falaleev, N. S.; Vasiliev, A. L.; Kiselev, N. A.

2018-05-01

The transport of one-dimensional CuI crystals in channels of single-walled carbon nanotubes (SWCNTs) has been studied by high resolution electron microscopy. The diffusion kinetics has been investigated by counting the number of CuI atoms escaping from the nanotube channel. The diffusivity is calculated to be 6.8 × 10-21 m2/s, which corresponds to an activation-barrier height of 1 eV/atom. A comparison with the theoretically estimated height of the energy barrier for molecular transport through a graphene layer is indicative of mass transfer through vacancy defects in graphene.

The dissociative chemisorption of water on Ni(111): Mode- and bond-selective chemistry on metal surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farjamnia, Azar; Jackson, Bret, E-mail: jackson@chem.umass.edu

A fully quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore the dissociative chemisorption of H{sub 2}O, HOD, and D{sub 2}O on Ni(111). For this late barrier system, excitation of both the bending and stretching modes significantly enhances dissociative sticking. The vibrational efficacies vary somewhat from mode-to-mode but are all relatively close to one, in contrast to methane dissociation, where the behavior is less statistical. Similar to methane dissociation, the motion of lattice atoms near the dissociating molecule can significantly modify the height of the barrier to dissociation, leading to a strong variation in dissociativemore » sticking with substrate temperature. Given a rescaling of the barrier height, our results are in reasonable agreement with measurements of the dissociative sticking of D{sub 2}O on Ni(111), for both laser-excited molecules with one or two quanta of excitation in the antisymmetric stretch and in the absence of laser excitation. Even without laser excitation, the beam contains vibrationally excited molecules populated at the experimental source temperature, and these make significant contributions to the sticking probability. At high collision energies, above the adiabatic barrier heights, our results correlate with these barrier heights and mode softening effects. At lower energies, dissociative sticking occurs primarily via vibrationally nonadiabatic pathways. We find a preference for O–H over O–D bond cleavage for ground state HOD molecules at all but the highest collision energies, and excitation of the O–H stretch gives close to 100% O–H selectivity at lower energies. Excitation of the O–D stretch gives a lower O–D cleavage selectivity, as the interaction with the surface leads to energy transfer from the O–D stretch into the O–H bond, when mode softening makes these vibrations nearly degenerate.« less

Spatial fluctuations in barrier height at the graphene-silicon carbide Schottky junction.

PubMed

Rajput, S; Chen, M X; Liu, Y; Li, Y Y; Weinert, M; Li, L

2013-01-01

When graphene is interfaced with a semiconductor, a Schottky contact forms with rectifying properties. Graphene, however, is also susceptible to the formation of ripples upon making contact with another material. Here we report intrinsic ripple- and electric field-induced effects at the graphene semiconductor Schottky junction, by comparing chemical vapour-deposited graphene transferred on semiconductor surfaces of opposite polarization-the hydrogen-terminated silicon and carbon faces of hexagonal silicon carbide. Using scanning tunnelling microscopy/spectroscopy and first-principles calculations, we show the formation of a narrow Schottky dipole barrier approximately 10 Å wide, which facilitates the observed effective electric field control of the Schottky barrier height. We further find atomic-scale spatial fluctuations in the Schottky barrier that directly follow the undulation of ripples on both graphene-silicon carbide junctions. These findings reveal fundamental properties of the graphene/semiconductor Schottky junction-a key component of vertical graphene devices that offer functionalities unattainable in planar device architecture.

Energy shift and conduction-to-valence band transition mediated by a time-dependent potential barrier in graphene

NASA Astrophysics Data System (ADS)

Chaves, Andrey; da Costa, D. R.; de Sousa, G. O.; Pereira, J. M.; Farias, G. A.

2015-09-01

We investigate the scattering of a wave packet describing low-energy electrons in graphene by a time-dependent finite-step potential barrier. Our results demonstrate that, after Klein tunneling through the barrier, the electron acquires an extra energy which depends on the rate of change of the barrier height with time. If this rate is negative, the electron loses energy and ends up as a valence band state after leaving the barrier, which effectively behaves as a positively charged quasiparticle.

Effects of fluorine incorporation into β-Ga2O3

NASA Astrophysics Data System (ADS)

Yang, Jiangcheng; Fares, Chaker; Ren, F.; Sharma, Ribhu; Patrick, Erin; Law, Mark E.; Pearton, S. J.; Kuramata, Akito

2018-04-01

β-Ga2O3 rectifiers fabricated on lightly doped epitaxial layers on bulk substrates were exposed to CF4 plasmas. This produced a significant decrease in Schottky barrier height relative to unexposed control diodes (0.68 eV compared to 1.22 eV) and degradation in ideality factor (2.95 versus 1.01 for the control diodes). High levels of F (>1022 cm-3) were detected in the near-surface region by Secondary Ion Mass Spectrometry. The diffusion of fluorine into the Ga2O3 was thermally activated with an activation energy of 1.24 eV. Subsequent annealing in the range 350-400 °C brought recovery of the diode characteristics and an increase in barrier height to a value larger than in the unexposed control diodes (1.36 eV). Approximately 70% of the initial F was removed from the Ga2O3 by 400 °C, with the surface outgas rate also being thermally activated with an activation energy of 1.23 eV. Very good fits to the experimental data were obtained by integrating physics of the outdiffusion mechanisms into the Florida Object Oriented Process Simulator code and assuming that the outgas rate from the surface was mediated through fluorine molecule formation. The fluorine molecule forward reaction rate had an activation energy of 1.24 eV, while the reversal rate of this reaction had an activation energy of 0.34 eV. The net carrier density in the drift region of the rectifiers decreased after CF4 exposure and annealing at 400 °C. The data are consistent with a model in which near-surface plasma-induced damage creates degraded Schottky barrier characteristics, but as the samples are annealed, this damage is removed, leaving the compensation effect of Si donors by F- ions. The barrier lowering and then enhancement are due to the interplay between surface defects and the chemical effects of the fluorine.

Kinetics of Deliquescence

NASA Astrophysics Data System (ADS)

McGraw, R. L.; Lewis, E.

2009-12-01

We examine deliquescence phase transformation for inorganic salt particles ranging from bulk down to several nanometers in size. Thermodynamic properties of the particles, coated with aqueous solution layers of varying thickness and surrounded by vapor, are analyzed. A thin layer criterion is introduced to define a limiting deliquescence relative humidity (DRH). Nano-size particles are predicted to deliquesce at relative humidity just below the DRH on crossing a nucleation barrier, located at a critical solution layer thickness. This barrier vanishes precisely at the DRH defined by the criterion. For a population of particles, the inherent random nature of the nucleation process is predicted to result in a distribution of RH values over which deliquescence will be seen to occur. Measurement of this (apparent) non-abrupt deliquescence of the population should provide both a validation of the nucleation mechanism and a quantitative determination of nucleation rate. This paper presents calculations of crossing (i.e. deliquescence) rate using the theory of mean first passage times (MFPT). MFPT theory is shown to provide a generalization of Becker-Döring nucleation kinetics especially useful for barrier heights much lower than those typically encountered in vapor-liquid nucleation. Barrier heights for deliquescence depend on the concentration of pre-deliquesced particles and observation time, but are typically in the 5-15kT range. Calculations use the tandem nano-differential mobility analyzer setup of Biskos et al. [1] as a model framework. In their experiment, a concentration of dry salt particles is subject to a higher RH for some observation time, after which is measured the (well-separated) populations of un-deliquesced particles and those that have deliquesced. Theoretical estimates for the conversion kinetics are presented as a function of dry particle size, DRH, and salt properties. [1] G. Biskos, A. Malinowski, L. M. Russell, P. R. Buseck, and S. T. Martin, Aerosol Sci. and Technol. 40, 97 (2006).

Schottky barrier parameters and low frequency noise characteristics of graphene-germanium Schottky barrier diode

NASA Astrophysics Data System (ADS)

Khurelbaatar, Zagarzusem; Kil, Yeon-Ho; Shim, Kyu-Hwan; Cho, Hyunjin; Kim, Myung-Jong; Lee, Sung-Nam; Jeong, Jae-chan; Hong, Hyobong; Choi, Chel-Jong

2016-03-01

We investigated the electrical properties of chemical vapor deposition-grown monolayer graphene/n-type germanium (Ge) Schottky barrier diodes (SBD) using current-voltage (I-V) characteristics and low frequency noise measurements. The Schottky barrier parameters of graphene/n-type Ge SBDs, such as Schottky barrier height (VB), ideality factor (n), and series resistance (Rs), were extracted using the forward I-V and Cheung's methods. The VB and n extracted from the forward ln(I)-V plot were found to be 0.63 eV and 1.78, respectively. In contrast, from Cheung method, the VB and n were calculated to be 0.53 eV and 1.76, respectively. Such a discrepancy between the values of VB calculated from the forward I-V and Cheung's methods indicated a deviation from the ideal thermionic emission of graphene/n-type Ge SBD associated with the voltage drop across graphene. The low frequency noise measurements performed at the frequencies in the range of 10 Hz-1 kHz showed that the graphene/n-type Ge SBD had 1/f γ frequency dependence, with γ ranging from 1.09 to 1.12, regardless of applied forward biases. Similar to forward-biased SBDs operating in the thermionic emission mode, the current noise power spectral density of graphene/n-type Ge SBD was linearly proportional to the forward current.

Forward- and reverse-bias tunneling effects in n/+/p silicon solar cells

NASA Technical Reports Server (NTRS)

Garlick, G. F. J.; Kachare, A. H.

1980-01-01

Excess currents due to field-assisted tunneling in both forward and reverse bias directions have been observed in n(+)-p silicon solar cells. These currents arise from the effect of conducting paths produced in the depletion layer by n(+) diffusion and cell processing. Forward-bias data indicate a small potential barrier with height of 0.04 eV at the n(+) end of conducting paths. Under reverse bias, excess tunneling currents involve a potential barrier at the p end of the conducting paths, the longer paths being associated with smaller barrier heights and dominating at the lower temperatures. Low-reverse-bias data give energy levels of 0.11 eV for lower temperatures (253-293 K) and 0.35 eV for higher temperatures (293-380 K). A model is suggested to explain the results.

Electric field modulation of Schottky barrier height in graphene/MoSe{sub 2} van der Waals heterointerface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sata, Yohta; Moriya, Rai, E-mail: moriyar@iis.u-tokyo.ac.jp, E-mail: tmachida@iis.u-tokyo.ac.jp; Morikawa, Sei

2015-07-13

We demonstrate a vertical field-effect transistor based on a graphene/MoSe{sub 2} van der Waals (vdW) heterostructure. The vdW interface between the graphene and MoSe{sub 2} exhibits a Schottky barrier with an ideality factor of around 1.3, suggesting a high-quality interface. Owing to the low density of states in graphene, the position of the Fermi level in the graphene can be strongly modulated by an external electric field. Therefore, the Schottky barrier height at the graphene/MoSe{sub 2} vdW interface is also modulated. We demonstrate a large current ON-OFF ratio of 10{sup 5}. These results point to the potential high performance ofmore » the graphene/MoSe{sub 2} vdW heterostructure for electronics applications.« less

Structure, vibrational spectrum, and ring puckering barrier of cyclobutane.

PubMed

Blake, Thomas A; Xantheas, Sotiris S

2006-09-07

We present the results of high level ab initio calculations for the structure, harmonic and anharmonic spectroscopic constants, and ring puckering barrier of cyclobutane (C4H8) in an effort to establish the minimum theoretical requirements needed for their accurate description. We have found that accurate estimates for the barrier between the minimum (D(2d)) and transition state (D(4h)) configurations require both higher levels of electron correlation [MP4, CCSD(T)] and orbital basis sets of quadruple-zeta quality or larger. By performing CCSD(T) calculations with basis sets as large as cc-pV5Z, we were able to obtain, for the first time, a value for the puckering barrier that lies within 10 cm(-1) (or 2%) from experiment, whereas the best previously calculated values were in errors exceeding 40% of experiment. Our best estimate of 498 cm(-1) for the puckering barrier is within 10 cm(-1) of the experimental value proposed originally, but it lies approximately 50 cm(-1) higher than the revisited value, which was obtained more recently using different assumptions regarding the coupling between the various modes. It is therefore suggested that revisiting the analysis of the experimental data might be warranted. Our best computed values (at the CCSD(T)/aug-cc-pVTZ level of theory) for the equilibrium structural parameters of C4H8 are r(C-C) = 1.554 A, r(C-H(alpha)) = 1.093 A, r(C-H(beta)) = 1.091 A, phi(C-C-C) = 88.1 degrees , alpha(H(alpha)-C-H(beta)) = 109.15 degrees , and theta = 29.68 degrees for the puckering angle. We have found that the puckering angle theta is more sensitive to the level of electron correlation than to the size of the basis set for a given method. We furthermore present anharmonic calculations that are based on a second-order perturbative evaluation of rovibrational parameters and their effects on the vibrational spectra and average structure. We have found that the anharmonic calculations predict the experimentally measured fundamental band origins within 1% (< or =30 cm(-1)) for most vibrations. The results of the current study can serve as a guide for future calculations on the substituted four-member ring hydrocarbon compounds. To this end we present a method for estimating the puckering barrier height at higher levels of electron correlation [MP4, CCSD(T)] from the MP2 results that can be used in chemically similar compounds.

Temperature dependent electrical properties of pulse laser deposited Au/Ni/β-(AlGa)2O3 Schottky diode

NASA Astrophysics Data System (ADS)

Feng, Qian; Feng, Zhaoqing; Hu, Zhuangzhuang; Xing, Xiangyu; Yan, Guangshuo; Zhang, Jincheng; Xu, Yongkuan; Lian, Xiaozheng; Hao, Yue

2018-02-01

We have demonstrated the epitaxial growth of a β-(Al0.08Ga0.92)2O3 film on a β-Ga2O3 (010) substrate through pulsed laser deposition. The temperature-dependent electrical characteristics of Au/Ni/β-(Al0.08Ga0.92)2O3 Schottky diodes were investigated in the temperature range of 300-573 K, using thermionic emission theory to calculate the Schottky diode parameters. The barrier height ϕb was found to increase, while the ideality factor n and the series resistance Rs were found to decrease with increasing temperatures. The calculated values of ϕb and n varied from 0.81 eV and 2.29 at 300 K to 1.02 eV and 1.65 at 573 K. The temperature-dependent I-V characteristics of the Schottky diode have shown the Gaussian distribution, yielding a mean barrier height of 1.23 eV and a standard deviation of 0.147 V, respectively. A modified Richardson plot of ln (Is /T2 )-(q2σs2 /2 k2T2 ) versus q/2kT gives ϕb 0 ¯ and A* as 1.24 eV and 44.3 A cm-2 K-2, showing the promise of Ni/β-(AlGa)2O3 as a Schottky diode rectifier.

Hydrogen-abstraction reactions of fully hydrogenated fullerene cages with the amino radical: a density functional study

NASA Astrophysics Data System (ADS)

Anafcheh, Maryam

2018-01-01

We have applied density functional theory calculations to study the reactions of NH2 + CnHn (n = 20, 40, 50, 60, 70 and 80). Due to the hard curvature in C20 cage, the NH2• + C20H20 → NH3 + C20H19• reaction is nearly thermoneutral with a high potential barrier height. For the CnHn fulleranes with n > 20 the transition states appear earlier on the reaction paths, as can be anticipated for exothermic reactions. Using the spherical excess parameter, we distinguished different curvatures on the surfaces of fullerane cages. The reaction enthalpies ΔH°298 and potential barrier heights ΔETS of the considered reactions indicate good correlation with the values of ϕi parameter, showing an upward trend with the curvature increasing at carbon sites. We have also investigated the H-abstraction of the chemical derivatives of the C20H20 cage (C20H19-CH3, C20H19-CH2CH3 and C20H19-CH2CH2CH3) in comparison to the corresponding isolated alkanes (CH4, C2H6 and C3H8). Overall, it could be inferred that the H-abstraction from the primary and secondary C-H bonds of isolated alkanes could occur more easily than fullarane derivatives.

Microwave Spectroscopy of 2-PENTANONE

NASA Astrophysics Data System (ADS)

Andresen, Maike; Nguyen, Ha Vinh Lam; Kleiner, Isabelle; Stahl, Wolfgang

2017-06-01

Methyl propyl ketone (MPK) or 2-Pentanone is known to be an alarm pheroromone released by the mandibular glands of the bees. It is a highly volatile compound. This molecule was studied by a combination of quantum chemical calculations and microwave spectroscopy in order to get informations about the lowest energy conformers and their structures.The rotational spectrum of 2-pentanone was measured using the molecular beam Fourier transform microwave spectrometer in Aachen operating between 2 and 26.5 GHz. Ab initio calculations determine 4 conformers but only two of them are observed in our jet-beam conditions.The lowest conformer has a C_{1} structure and its spectrum shows internal rotation splittings arising from two methyl groups. The internal splittings of 305 transitions for this conformer were analyzed using the XIAM code It led to the determination of the values for the barrier heights hindering the internal rotation of two methyl groups of 239 cm^{-1} and 980 cm^{-1} respectively. The next energy conformer has a C_{s} structure and the analysis of the internal splittings of 134 transitions using the XIAM code and the BELGI code led to the determination of internal rotation barrier height of 186 cm^{-1}. Comparisons of quantum chemistry and experimental results will be discussed. H. Hartwig, H. Dreizler, Z. Naturforsch. 51a, 923 (1996). J. T. Hougen, I. Kleiner and M. Godefroid, J. Mol. Spectrosc., 163, 559-586 (1994).

Potential barrier heights at metal on oxygen-terminated diamond interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muret, P., E-mail: pierre.muret@neel.cnrs.fr; Traoré, A.; Maréchal, A.

2015-11-28

Electrical properties of metal-semiconductor (M/SC) and metal/oxide/SC structures built with Zr or ZrO{sub 2} deposited on oxygen-terminated surfaces of (001)-oriented diamond films, comprised of a stack of lightly p-doped diamond on a heavily doped layer itself homoepitaxially grown on an Ib substrate, are investigated experimentally and compared to different models. In Schottky barrier diodes, the interfacial oxide layer evidenced by high resolution transmission electron microscopy and electron energy losses spectroscopy before and after annealing, and barrier height inhomogeneities accounts for the measured electrical characteristics until flat bands are reached, in accordance with a model which generalizes that by Tung [Phys.more » Rev. B 45, 13509 (1992)] and permits to extract physically meaningful parameters of the three kinds of interface: (a) unannealed ones, (b) annealed at 350 °C, (c) annealed at 450 °C with the characteristic barrier heights of 2.2–2.5 V in case (a) while as low as 0.96 V in case (c). Possible models of potential barriers for several metals deposited on well defined oxygen-terminated diamond surfaces are discussed and compared to experimental data. It is concluded that interface dipoles of several kinds present at these compound interfaces and their chemical evolution due to annealing are the suitable ingredients that are able to account for the Mott-Schottky behavior when the effect of the metal work function is ignored, and to justify the reverted slope observed regarding metal work function, in contrast to the trend always reported for all other metal-semiconductor interfaces.« less

Morphological evolution of protective works by Genetic Algorithms: An application to Mt Etna

NASA Astrophysics Data System (ADS)

Marocco, Davide; Spataro, William; D'Ambrosio, Donato; Filippone, Giuseppe; Rongo, Rocco; Iovine, Giulio; Neri, Marco

2013-04-01

The hazard induced by dangerous flow-type phenomena - e.g. lava flows, earth flows, debris flows, and debris avalanches - has increased in recent years due to continuous urbanization. In many cases, the numerical simulation of hypothetical events can help to forecast the flow path in advance and therefore give indications about the areas that can be considered for the construction of protective works - e.g. earth barriers or channels. In this way, urbanized areas, as well as cultural heritage sites or even important infrastructures, can be protected by diverting the flow towards lower interest regions. Here, we have considered the numerical Cellular Automata model Sciara-fv2 for simulating lava flows at Mt Etna and Genetic Algorithms for optimizing the position, orientation and extension of an earth barrier built to protect the Rifugio Sapienza, a well-known touristic facility located near the summit of the volcano. The Rifugio Sapienza area was in fact interested by a lava flow in 2003, which destroyed a Service Center, a parking area and a Cafeteria. In this study, a perimeter was devised around the Rifugio (i.e., security perimeter), which delimitates the area that has to be protected by the flow. Furthermore, another perimeter was devised (i.e., work perimeter), specifying the area in which the earth barrier can be located. The barrier is specified by three parameters, namely the two geographic coordinates of the vertex and the height. In fact, in this preliminary analysis the barrier was modeled as a segment (in plant) having a constant height. Though preliminary, the study has produced extremely positive results. Among different alternatives generated by the genetic algorithm, an interesting scenario consists of a 35 meters barrier high solution, which completely deviates the flow avoiding that the lava reaches the inhabited area. The relative elevated height of the barrier is high due to the fact that the crater is located close to the area to be protected and, consequently, the lava rate is very high.

Activated dynamics in dense fluids of attractive nonspherical particles. II. Elasticity, barriers, relaxation, fragility, and self-diffusion

NASA Astrophysics Data System (ADS)

Tripathy, Mukta; Schweizer, Kenneth S.

2011-04-01

In paper II of this series we apply the center-of-mass version of Nonlinear Langevin Equation theory to study how short-range attractive interactions influence the elastic shear modulus, transient localization length, activated dynamics, and kinetic arrest of a variety of nonspherical particle dense fluids (and the spherical analog) as a function of volume fraction and attraction strength. The activation barrier (roughly the natural logarithm of the dimensionless relaxation time) is predicted to be a rich function of particle shape, volume fraction, and attraction strength, and the dynamic fragility varies significantly with particle shape. At fixed volume fraction, the barrier grows in a parabolic manner with inverse temperature nondimensionalized by an onset value, analogous to what has been established for thermal glass-forming liquids. Kinetic arrest boundaries lie at significantly higher volume fractions and attraction strengths relative to their dynamic crossover analogs, but their particle shape dependence remains the same. A limited universality of barrier heights is found based on the concept of an effective mean-square confining force. The mean hopping time and self-diffusion constant in the attractive glass region of the nonequilibrium phase diagram is predicted to vary nonmonotonically with attraction strength or inverse temperature, qualitatively consistent with recent computer simulations and colloid experiments.

Effect of dissolved hydrogen on Schottky barrier height of Fe-Cr alloy heterojunction

NASA Astrophysics Data System (ADS)

Berahim, A. N.; Zaharudin, M. Z.; Ani, M. H.; Arifin, S. K.

2018-01-01

The presence of water vapour at high temperature oxidation has certain effects on ferritic alloy in comparison to dry environment. It is hypothesized that at high temperature; water vapour provides hydrogen, which will dissolve into ferritic alloy substrate and altering their electronic state at the metal-oxide interface. This work aimed to clarify the change in electronic state of metal-oxide heterojunction with the presence of hydrogen/water vapour. In this study, the Schottky Barrier (SB) was created by sputtering Cr2O3 onto prepared samples by using RF Magnetron sputtering machine. The existence of Fe/Cr2O3 junction was characterized by using XRD. The surfaces were observed by using Optical Microscope (OM) and Scanning Electron Microscope (SEM). The samples were then exposed in dry and humid condition at temperature of 473 K and 1073 K. In dry condition, 100% Ar is flown inside the furnace, while in wet condition mixture of 95% Ar and 5% H was used. I-V measurement of the junction was done to determine the Schottky Barrier Height(SBH) of the samples in the corresponding ambient. The results show that in Fe/Cr2O3 junction, with presence of hydrogen at temperature 473 K; the SBH was reduced by the scale factor of 1.054 and at 1073 K in wet ambient by factor of 1.068. Meanwhile, in Fe-Cr/Cr2O3 junction with presence of hydrogen, the value of SBH was increased by scale factor of 1.068 at temperature 473 K while at 1073 K, the SBH also increased by factor of 1.009.

Quasiclassical trajectory study of the Cl+CH4 reaction dynamics on a quadratic configuration interaction with single and double excitation interpolated potential energy surface.

PubMed

Castillo, J F; Aoiz, F J; Bañares, L

2006-09-28

An ab initio interpolated potential energy surface (PES) for the Cl+CH(4) reactive system has been constructed using the interpolation method of Collins and co-workers [J. Chem. Phys. 102, 5647 (1995); 108, 8302 (1998); 111, 816 (1999); Theor. Chem. Acc. 108, 313 (2002)]. The ab initio calculations have been performed using quadratic configuration interaction with single and double excitation theory to build the PES. A simple scaling all correlation technique has been used to obtain a PES which yields a barrier height and reaction energy in good agreement with high level ab initio calculations and experimental measurements. Using these interpolated PESs, a detailed quasiclassical trajectory study of integral and differential cross sections, product rovibrational populations, and internal energy distributions has been carried out for the Cl+CH(4) and Cl+CD(4) reactions, and the theoretical results have been compared with the available experimental data. It has been shown that the calculated total reaction cross sections versus collision energy for the Cl+CH(4) and Cl+CD(4) reactions is very sensitive to the barrier height. Besides, due to the zero-point energy (ZPE) leakage of the CH(4) molecule to the reaction coordinate in the quasiclassical trajectory (QCT) calculations, the reaction threshold falls below the barrier height of the PES. The ZPE leakage leads to CH(3) and HCl coproducts with internal energy below its corresponding ZPEs. We have shown that a Gaussian binning (GB) analysis of the trajectories yields excitation functions in somehow better agreement with the experimental determinations. The HCl(v'=0) and DCl(v'=0) rotational distributions are as well very sensitive to the ZPE problem. The GB correction narrows and shifts the rotational distributions to lower values of the rotational quantum numbers. However, the present QCT rotational distributions are still hotter than the experimental distributions. In both reactions the angular distributions shift from backward peaked to sideways peaked as collision energy increases, as seen in the experiments and other theoretical calculations.

Quasiclassical trajectory study of the Cl +CH4 reaction dynamics on a quadratic configuration interaction with single and double excitation interpolated potential energy surface

NASA Astrophysics Data System (ADS)

Castillo, J. F.; Aoiz, F. J.; Bañares, L.

2006-09-01

An ab initio interpolated potential energy surface (PES) for the Cl +CH4 reactive system has been constructed using the interpolation method of Collins and co-workers [J. Chem. Phys. 102, 5647 (1995); 108, 8302 (1998); 111, 816 (1999); Theor. Chem. Acc. 108, 313 (2002)]. The ab initio calculations have been performed using quadratic configuration interaction with single and double excitation theory to build the PES. A simple scaling all correlation technique has been used to obtain a PES which yields a barrier height and reaction energy in good agreement with high level ab initio calculations and experimental measurements. Using these interpolated PESs, a detailed quasiclassical trajectory study of integral and differential cross sections, product rovibrational populations, and internal energy distributions has been carried out for the Cl +CH4 and Cl +CD4 reactions, and the theoretical results have been compared with the available experimental data. It has been shown that the calculated total reaction cross sections versus collision energy for the Cl +CH4 and Cl +CD4 reactions is very sensitive to the barrier height. Besides, due to the zero-point energy (ZPE) leakage of the CH4 molecule to the reaction coordinate in the quasiclassical trajectory (QCT) calculations, the reaction threshold falls below the barrier height of the PES. The ZPE leakage leads to CH3 and HCl coproducts with internal energy below its corresponding ZPEs. We have shown that a Gaussian binning (GB) analysis of the trajectories yields excitation functions in somehow better agreement with the experimental determinations. The HCl(v'=0) and DCl(v'=0) rotational distributions are as well very sensitive to the ZPE problem. The GB correction narrows and shifts the rotational distributions to lower values of the rotational quantum numbers. However, the present QCT rotational distributions are still hotter than the experimental distributions. In both reactions the angular distributions shift from backward peaked to sideways peaked as collision energy increases, as seen in the experiments and other theoretical calculations.

Assessment of Orbital-Optimized MP2.5 for Thermochemistry and Kinetics: Dramatic Failures of Standard Perturbation Theory Approaches for Aromatic Bond Dissociation Energies and Barrier Heights of Radical Reactions.

PubMed

Soydaş, Emine; Bozkaya, Uğur

2015-04-14

An assessment of orbital-optimized MP2.5 (OMP2.5) [ Bozkaya, U.; Sherrill, C. D. J. Chem. Phys. 2014, 141, 204105 ] for thermochemistry and kinetics is presented. The OMP2.5 method is applied to closed- and open-shell reaction energies, barrier heights, and aromatic bond dissociation energies. The performance of OMP2.5 is compared with that of the MP2, OMP2, MP2.5, MP3, OMP3, CCSD, and CCSD(T) methods. For most of the test sets, the OMP2.5 method performs better than MP2.5 and CCSD, and provides accurate results. For barrier heights of radical reactions and aromatic bond dissociation energies OMP2.5-MP2.5, OMP2-MP2, and OMP3-MP3 differences become obvious. Especially, for aromatic bond dissociation energies, standard perturbation theory (MP) approaches dramatically fail, providing mean absolute errors (MAEs) of 22.5 (MP2), 17.7 (MP2.5), and 12.8 (MP3) kcal mol(-1), while the MAE values of the orbital-optimized counterparts are 2.7, 2.4, and 2.4 kcal mol(-1), respectively. Hence, there are 5-8-folds reductions in errors when optimized orbitals are employed. Our results demonstrate that standard MP approaches dramatically fail when the reference wave function suffers from the spin-contamination problem. On the other hand, the OMP2.5 method can reduce spin-contamination in the unrestricted Hartree-Fock (UHF) initial guess orbitals. For overall evaluation, we conclude that the OMP2.5 method is very helpful not only for challenging open-shell systems and transition-states but also for closed-shell molecules. Hence, one may prefer OMP2.5 over MP2.5 and CCSD as an O(N(6)) method, where N is the number of basis functions, for thermochemistry and kinetics. The cost of the OMP2.5 method is comparable with that of CCSD for energy computations. However, for analytic gradient computations, the OMP2.5 method is only half as expensive as CCSD.

Intramolecular H-transfer reactions in Si 2H n (for n=3-5)

NASA Astrophysics Data System (ADS)

Ernst, M. C.; Sax, A. F.; Kalcher, J.

1993-12-01

Intramolecular rearrangement reactions for doublet Si 2H 5 and Si 2H 3, quartet Si 2H 3, and singlet Si 2H 4 have been studied. aim of the study was to characterize a series of intramolecular H-transfer reactions in silicon hydrides with vrying degrees of saturation. The transition states belonging to the reactions presented in this work possess a monobridged Si 2H moiety. Structural features of the transition states and relative barrier heights have been examined; the geometry optimizations were performed with the use of CAS-SCF wavefunctions and the barrier height estimates were obtained with single-point CI calculations.

Allylic amination reactivity of Ni, Pd, and Pt heterobimetallic and monometallic complexes.

PubMed

Carlsen, Ryan W; Ess, Daniel H

2016-06-14

Transition metal heterobimetallic complexes with dative metal-metal interactions have the potential for novel fast reactivity. There are few studies that both compare the reactivity of different metal centers in heterobimetallic complexes and compare bimetallic reactivity to monometallic reactivity. Here we report density-functional calculations that show the reactivity of [Cl2Ti(N(t)BuPPh2)2M(II)(η(3)-methallyl)] heterobimetallic complexes for allylic amination follows M = Ni > Pd > Pt. This reactivity trend was not anticipated since the amine addition transition state involves M(II) to M(0) reduction and this could disadvantage Ni. Comparison of heterobimetallic complexes to the corresponding monometallic (CH2)2(N(t)BuPPh2)2M(II)(η(3)-methallyl) complexes reveals that this reactivity trend is due to the bimetallic interaction and that the bimetallic interaction significantly lowers the barrier height for amine addition by >10 kcal mol(-1). The impact of the early transition metal center on the amination addition barrier height depends on the late transition metal center. The lowest barrier heights for this reaction occur when late and early transition metal centers are from the same periodic table row.

The 6-31B(d) basis set and the BMC-QCISD and BMC-CCSD multicoefficient correlation methods.

PubMed

Lynch, Benjamin J; Zhao, Yan; Truhlar, Donald G

2005-03-03

Three new multicoefficient correlation methods (MCCMs) called BMC-QCISD, BMC-CCSD, and BMC-CCSD-C are optimized against 274 data that include atomization energies, electron affinities, ionization potentials, and reaction barrier heights. A new basis set called 6-31B(d) is developed and used as part of the new methods. BMC-QCISD has mean unsigned errors in calculating atomization energies per bond and barrier heights of 0.49 and 0.80 kcal/mol, respectively. BMC-CCSD has mean unsigned errors of 0.42 and 0.71 kcal/mol for the same two quantities. BMC-CCSD-C is an equally effective variant of BMC-CCSD that employs Cartesian rather than spherical harmonic basis sets. The mean unsigned error of BMC-CCSD or BMC-CCSD-C for atomization energies, barrier heights, ionization potentials, and electron affinities is 22% lower than G3SX(MP2) at an order of magnitude less cost for gradients for molecules with 9-13 atoms, and it scales better (N6 vs N,7 where N is the number of atoms) when the size of the molecule is increased.

Tuning the electronic properties and Schottky barrier height of the vertical graphene/MoS2 heterostructure by an electric gating

NASA Astrophysics Data System (ADS)

Nguyen, Chuong V.

2018-04-01

In this paper, the electronic properties and Schottky contact in graphene/MoS2 (G/MoS2) heterostructure under an applied electric field are investigated by means of the density functional theory. It can be seen that the electronic properties of the G/MoS2 heterostructure are preserved upon contacting owing to the weak van der Waals interaction. We found that the n-type Schottky contact is formed in the G/MoS2 heterostructure with the Schottky barrier height of 0.49 eV. Furthermore, both Schottky contact and Schottky barrier height in the G/MoS2 heterostructure could be controlled by the applied electric field. If a positive electric field of 4 V/nm is applied to the system, a transformation from the n-type Schottky contact to the p-type one was observed, whereas the system keeps an n-type Schottky contact when a negative electric field is applied. Our results may provide helpful information to design, fabricate, and understand the physics mechanism in the graphene-based two-dimensional van der Waals heterostructures like as G/MoS2 heterostructure.

Direct control and characterization of a Schottky barrier by scanning tunneling microscopy

NASA Technical Reports Server (NTRS)

Bell, L. D.; Kaiser, W. J.; Hecht, M. H.; Grunthaner, F. J.

1988-01-01

Scanning tunneling microscopy (STM) methods are used to directly control the barrier height of a metal tunnel tip-semiconductor tunnel junction. Barrier behavior is measured by tunnel current-voltage spectroscopy and compared to theory. A unique surface preparation method is used to prepare a low surface state density Si surface. Control of band bending with this method enables STM investigation of semiconductor subsurface properties.

Analysis of the Temperature Dependence of the Capacitance-Voltage and Conductance-Voltage Characteristics of Au/TiO2(rutile)/ n-Si Structures

NASA Astrophysics Data System (ADS)

KInacI, BarIş; Özçelik, Süleyman

2013-06-01

The capacitance-voltage-temperature ( C- V- T) and the conductance/angular frequency-voltage-temperature ( G/ω- V- T) characteristics of Au/TiO2(rutile)/ n-Si Schottky barrier diodes (SBDs) were investigated over the temperature range from 200 K to 380 K by considering the series resistance effect. Titanium dioxide (TiO2) was deposited on n-type silicon (Si) substrate using a direct-current (DC) magnetron sputtering system at 200°C. To improve the crystal quality, the deposited film was annealed at 900°C to promote a phase transition from the amorphous to rutile phase. The C -2 versus V plots gave a straight line in the reverse-bias region. The main electrical parameters, such as the doping concentration ( N D), Fermi energy level ( E F), depletion layer width ( W D), barrier height ( ф CV), and series resistance ( R S), of Au/TiO2(rutile)/ n-Si SBDs were calculated from the C- V- T and the G/ω- V- T characteristics. The obtained results show that ф CV, R S, and W D values decrease, while E F and N D values increase, with increasing temperature.

Characterisation of temperature dependent parameters of multi-quantum well (MQW) Ti/Au/n-AlGaAs/n-GaAs/n-AlGaAs Schottky diodes

NASA Astrophysics Data System (ADS)

Filali, Walid; Sengouga, Nouredine; Oussalah, Slimane; Mari, Riaz H.; Jameel, Dler; Al Saqri, Noor Alhuda; Aziz, Mohsin; Taylor, David; Henini, Mohamed

2017-11-01

Forward and reverse current-voltage (Isbnd V) of Ti/Au/n-Al0.33Ga0.67As/n-GaAs/n-Al0.33Ga0.67As multi-quantum well (MQW) Schottky diodes were measured over a range of temperatures from 20 to 400 K by a step of 20 K. The Schottky diodes parameters were then extracted from these characteristics. The Cheung method is used for this purpose, assuming a thermionic conduction mechanism. The extracted ideality factor decrease with increasing temperatures. But their values at low temperatures were found to be unrealistic. In order to explain this uncertainty, three assumptions were explored. Firstly an assumed inhomogeneous barrier height gave better parameters especially the Richardson constant but the ideality factor is still unrealistic at low temperatures. Secondly, by using numerical simulation, it was demonstrated that defects including interface states are not responsible for the apparent unrealistic Schottky diode parameters. The third assumption is the tunnelling mechanism through the barrier in the low temperature range. At these lower temperatures, the tunnelling mechanism was more suitable to explain the extracted parameters values.

New ab initio potential surfaces and three-dimensional quantum dynamics for transition state spectroscopy in ozone photodissociation

NASA Astrophysics Data System (ADS)

Yamashita, Koichi; Morokuma, Keiji; Le Quéré, Frederic; Leforestier, Claude

1992-04-01

New ab initio potential energy surfaces (PESs) of the ground and B ( 1B 2) states of ozone have been calculated with the CASSCF-SECI/DZP method to describe the three-dimensional photodissociation process. The dissociation energy of the ground state and the vertical barrier height of the B PES are obtained to be 0.88 and 1.34 eV, respectively, in better agreement with the experimental values than the previous calculation. The photodissociation autocorrelation function, calculated on the new B PES, based on exact three-dimensional quantum dynamics, reproduces well the main recurrence feature extracted from the experimental spectra.

Effects of a Single Water Molecule on the Reaction Barrier of Interstellar CO2 Formation Reaction.

PubMed

Tachikawa, Hiroto; Kawabata, Hiroshi

2016-08-25

The mechanism by which CO2 is formed in the interstellar space remains a mystery. The most likely reaction is collision between CO and OH; however, previous theoretical works have shown that the activation barrier for CO2 formation is high enough to prevent the reaction at the low thermal conditions of space (∼10 K). The effects of single water molecule on the reaction barrier of CO2 formation from reaction between CO and OH have been investigated here by means of ab initio calculation. The barrier height along the lowest-energy pathway in the reaction between CO and OH in the absence of the H2O molecule was calculated to be 2.3 kcal/mol when CCSD(T) energy corrections are combined with the MP2 basis set limit. In the case of the hydrated (H2O-CO-OH) system, the inclusion of a single H2O molecule into the system significantly decreased the barrier height to 0.2 kcal/mol. This suggests that CO2 can be formed when CO and OH react in the presence of H2O, even under thermal conditions as low as 10 K.

Effect of contact barrier on electron transport in graphene.

PubMed

Zhou, Yang-Bo; Han, Bing-Hong; Liao, Zhi-Min; Zhao, Qing; Xu, Jun; Yu, Da-Peng

2010-01-14

The influence of the barrier between metal electrodes and graphene on the electrical properties was studied on a two-electrode device. A classical barrier model was used to analyze the current-voltage characteristics. Primary parameters including barrier height and effective resistance were achieved. The electron transport properties under magnetic field were further investigated. An abnormal peak-valley-peak shape of voltage-magnetoresistance curve was observed. The underlying mechanisms were discussed under the consideration of the important influence of the contact barrier. Our results indicate electrical properties of graphene based devices are sensitive to the contact interface.

The Impact of Roadside Barriers and Buildings on Near Road Concentrations of Vehicle Emissions

NASA Astrophysics Data System (ADS)

Schulte, Nico

Exposure to elevated concentrations of vehicle emitted pollutants is associated with negative health effects. Elevated concentrations are typically found within several hundred meters of high traffic roads, where atmospheric dispersion has not sufficiently diluted pollutants. Tall buildings next to roads reduce dispersion, thereby creating pollutant hot spots and increasing exposure to vehicle emissions for city residents. Roadside barriers enhance dispersion of roadway emissions and thus can be used to mitigate elevated concentrations next to large roads. The work in this thesis develops semi-empirical dispersion models that are useful for estimating near road concentrations of vehicle emissions when there are buildings or barriers next to the road. Dispersion models that account for the effect of near road barriers on concentrations are developed and evaluated with data from a wind tunnel and a field tracer study. The model evaluation shows that the primary effect of roadside barriers is enhancement of the vertical mixing by an amount proportional to the barrier height. Additionally, turbulence is enhanced in the barrier's wake, resulting in more rapid growth of the pollutant plume. The models perform well during neutral and stable atmospheric conditions. During unstable conditions the models overestimate concentrations. A model that accounts for reduction of the mean wind speed in the barrier wake is unbiased for all stabilities. Models of the impact of tall buildings next to the road on near road concentrations of vehicle emissions are developed. The models are evaluated with data from field measurements conducted in Los Angeles and Riverside counties, CA, and with data from an urban area in Hannover, Germany. The study specifically investigates dispersion in cities with significant building height variability. Model evaluation shows that vertical turbulent transport dominates dispersion in cities. The primary variables governing near road concentrations of vehicle emissions in cities are the ratio of area weighted building height to street width and the vertical averaged standard deviation of vertical velocity fluctuations. The model informs design of transit oriented developments, dense residential areas located in close proximity to transportation infrastructure, which are used to reduce pollution and greenhouse gas emissions due to transportation.

Ideal MHD Stability Prediction and Required Power for EAST Advanced Scenario

NASA Astrophysics Data System (ADS)

Chen, Junjie; Li, Guoqiang; Qian, Jinping; Liu, Zixi

2012-11-01

The Experimental Advanced Superconducting Tokamak (EAST) is the first fully superconducting tokamak with a D-shaped cross-sectional plasma presently in operation. The ideal magnetohydrodynamic (MHD) stability and required power for the EAST advanced tokamak (AT) scenario with negative central shear and double transport barrier (DTB) are investigated. With the equilibrium code TOQ and stability code GATO, the ideal MHD stability is analyzed. It is shown that a moderate ratio of edge transport barriers' (ETB) height to internal transport barriers' (ITBs) height is beneficial to ideal MHD stability. The normalized beta βN limit is about 2.20 (without wall) and 3.70 (with ideal wall). With the scaling law of energy confinement time, the required heating power for EAST AT scenario is calculated. The total heating power Pt increases as the toroidal magnetic field BT or the normalized beta βN is increased.

Transport gap of organic semiconductors in organic modified Schottky contacts

NASA Astrophysics Data System (ADS)

Zahn, Dietrich R. T.; Kampen, Thorsten U.; Méndez, Henry

2003-05-01

Two different organic molecules with similar structure, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and N, N'-dimethyl-3,4,9,10-perylenetetracarboxylic diimide (DiMe-PTCDI), were used for the modification of Ag Schottky contacts on sulphur passivated GaAs(1 0 0) (S-GaAs). Such diodes were investigated recording in situ current-voltage ( I- V) characteristics. As a function of the PTCDA thickness the effective barrier height of Ag/PTCDA/S-GaAs contacts initially increases from 0.59±0.01 to 0.72±0.01 eV, and then decreases to 0.54±0.01 eV, while only a decrease in barrier height from 0.54±0.01 to 0.45±0.01 eV is observed for DiMe-PTCDI interlayers. The initial increase and decrease in effective barrier height for PTCDA and DiMe-PTCDI respectively, is correlated with the energy level alignment of the lowest unoccupied molecular orbital (LUMO) with respect to the conduction band minimum (CBM) of S-GaAs at the organic/inorganic semiconductor interface. Whilst there is an additional barrier for electrons at the PTCDA/S-GaAs interface of about 150 meV, i.e. the LUMO lies above CBM, the LUMO is aligned or below CBM in the DiMe-PTCDI case. The results also shine light on the important issue of the transport gap in organic semiconductors for which an estimation can be obtained.

Study of hydrogen-molecule guests in type II clathrate hydrates using a force-matched potential model parameterised from ab initio molecular dynamics

NASA Astrophysics Data System (ADS)

Burnham, Christian J.; Futera, Zdenek; English, Niall J.

2018-03-01

The force-matching method has been applied to parameterise an empirical potential model for water-water and water-hydrogen intermolecular interactions for use in clathrate-hydrate simulations containing hydrogen guest molecules. The underlying reference simulations constituted ab initio molecular dynamics (AIMD) of clathrate hydrates with various occupations of hydrogen-molecule guests. It is shown that the resultant model is able to reproduce AIMD-derived free-energy curves for the movement of a tagged hydrogen molecule between the water cages that make up the clathrate, thus giving us confidence in the model. Furthermore, with the aid of an umbrella-sampling algorithm, we calculate barrier heights for the force-matched model, yielding the free-energy barrier for a tagged molecule to move between cages. The barrier heights are reasonably large, being on the order of 30 kJ/mol, and are consistent with our previous studies with empirical models [C. J. Burnham and N. J. English, J. Phys. Chem. C 120, 16561 (2016) and C. J. Burnham et al., Phys. Chem. Chem. Phys. 19, 717 (2017)]. Our results are in opposition to the literature, which claims that this system may have very low barrier heights. We also compare results to that using the more ad hoc empirical model of Alavi et al. [J. Chem. Phys. 123, 024507 (2005)] and find that this model does very well when judged against the force-matched and ab initio simulation data.

A Bayesian Network to Predict Barrier Island Geomorphologic Characteristics

NASA Astrophysics Data System (ADS)

Gutierrez, B.; Plant, N. G.; Thieler, E. R.; Turecek, A.; Stippa, S.

2014-12-01

Understanding how barrier islands along the Atlantic and Gulf coasts of the United States respond to storms and sea-level rise is an important management concern. Although these threats are well recognized, quantifying the integrated vulnerability is challenging due to the range of time and space scalesover which these processes act. Developing datasets and methods to identify the physical vulnerabilities of coastal environments due to storms and sea-level rise thus is an important scientific focus that supports land management decision making. Here we employ a Bayesian Network (BN) to model the interactions between geomorphic variables sampled from existing datasets that capture both storm-and sea-level rise related coastal evolution. The BN provides a means of estimating probabilities of changes in specific geomorphic characteristics such as foredune crest height, beach width, beach height, given knowledge of barrier island width, maximum barrier island elevation, distance from an inlet, the presence of anthropogenic modifications, and long-term shoreline change rates, which we assume to be directly related to sea-level rise. We evaluate BN skill and explore how different constraints, such as shoreline change characteristics (eroding, stable, accreting), distance to nearby inlets and island width, affect the probability distributions of future morphological characteristics. Our work demonstrates that a skillful BN can be constructed and that factors such as distance to inlet, shoreline change rate, and the presence of human alterations have the strongest influences on network performance. For Assateague Island, Maryland/Virginia, USA, we find that different shoreline change behaviors affect the probabilities of specific geomorphic characteristics, such as dune height, which allows us to identify vulnerable locations on the barrier island where habitat or infrastructure may be vulnerable to storms and sea-level rise.

Conductance and refraction across a Barrier in Phosphorene

NASA Astrophysics Data System (ADS)

Dahal, Dipendra; Gumbs, Godfrey

The transmission coefficient and ballistic conductance for monolayer black phosphorene is calculated when a potential step or square barrier is present. The Landauer-B¨uttiker formalism is employed in our calculations of the conductance. We obtain the refractive index for the step potential barrier when an incident beam of electron travel along different paths so as to observe what role the anisotropy of the energy bands plays. Numerical results are presented for various potential heights and barrier widths and these are compared with those for gapless and gapped graphene.

Spray particle drift mitigation using field corn (Zea mays L.) as a drift barrier.

PubMed

Vieira, Bruno C; Butts, Thomas R; Rodrigues, Andre O; Golus, Jeffrey A; Schroeder, Kasey; Kruger, Greg R

2018-04-24

Herbicide particle drift reduces application efficacy and can cause severe impacts on nearby vegetation depending on the herbicide mode-of-action, exposure level, and tolerance to the herbicide. A particle drift mitigation effort placing windbreaks or barriers on the field boundaries to reduce off-target movement of spray particles has been utilized in the past. The objective of this research was to evaluate the effectiveness of field corn (Zea mays L.) at different heights as a particle drift barrier. Applications with a non-air inclusion flat fan nozzle (ER11004) resulted in greater particle drift when compared to an air inclusion nozzle (TTI11004). Eight rows of corn were used as barriers (0.91, 1.22, and 1.98 m height) which reduced the particle drift for both nozzles, especially at shorter downwind distances. Applications with the ER11004 nozzle without corn barriers had 1% of the applied rate (D 99 ) predicted to deposit at 14.8 m downwind, whereas this distance was reduced (up to 7-fold) when applications were performed with corn barriers. The combination of corn drift barriers and nozzle selection (TTI11004) provided satisfactory particle drift reduction when the D 99 estimates were compared to applications with the ER11004 nozzle without corn barriers (up to 10-fold difference). The corn drift barriers were effective in reducing particle drift from applications with the ER11004 and the TTI11004 nozzles (Fine and Ultra Coarse spray classifications, respectively). The corn drift barrier had appropriate porosity and width as the airborne spray was captured within its canopy instead of deflecting up and over it. This article is protected by copyright. All rights reserved.

Vertical field effect tunneling transistor based on graphene-ultrathin Si nanomembrane heterostructures

NASA Astrophysics Data System (ADS)

Das, Tanmoy; Jang, Houk; Bok Lee, Jae; Chu, Hyunwoo; Kim, Seong Dae; Ahn, Jong-Hyun

2015-12-01

Graphene-based heterostructured vertical transistors have attracted a great deal of research interest. Herein we propose a Si-based technology platform for creating graphene/ultrathin semiconductor/metal (GSM) junctions, which can be applied to large-scale and low-power electronics compatible with a variety of substrates. We fabricated graphene/Si nanomembrane (NM)/metal vertical heterostructures by using a dry transfer technique to transfer Si NMs onto chemical vapor deposition-grown graphene layers. The resulting van der Waals interfaces between graphene and p-Si NMs exhibited nearly ideal Schottky barrier behavior. Due to the low density of states of graphene, the graphene/Si NM Schottky barrier height can be modulated by modulating the band profile in the channel region, yielding well-defined current modulation. We obtained a maximum current on/off ratio (Ion/Ioff) of up to ˜103, with a current density of 102 A cm-2. We also observed significant dependence of Schottky barrier height Δφb on the thickness of the Si NMs. We confirmed that the transport in these devices is dominated by the effects of the graphene/Si NM Schottky barrier.

Oscillations in MOS tunneling

NASA Technical Reports Server (NTRS)

Lewicki, G.; Maserjian, J.

1975-01-01

Oscillatory deviations from Fowler-Nordheim tunneling currents were measured in MOS capacitors with oxide thicknesses ranging from 30 to 75 A. The observed variation of oscillation phases and amplitudes with oxide thickness indicates that the Si-SiO2 interface is independent of oxide thickness only for thicknesses greater than 65 A. At lower thicknesses, the barrier height at the interface decreases gradually with oxide thickness at a rate on the order of 10 mV/A. At higher thicknesses, the barrier height is 4.08 eV. The energy dispersion relation with the SiO2 conduction band is parabolic. The mean free path within the SiO2 conduction band is on the order of 13 A.

The effectiveness of platform screen doors for the prevention of subway suicides in South Korea.

PubMed

Chung, Yong Woon; Kang, Sung Jin; Matsubayashi, Tetsuya; Sawada, Yasuyuki; Ueda, Michiko

2016-04-01

Subway suicide can significantly impact the general public. Platform Screen Doors (PSDs) are considered to be an effective strategy to prevent suicides at subway stations, but the evidence on their effectiveness is limited. We assessed the effectiveness of installing half- and full-height platform screen doors in reducing subway suicides using Poisson regression analysis. Ten-year monthly panel data for 121 subway stations between 2003 and 2012 in the Seoul metropolitan area were used for the analysis. We found that installing PSDs decreases fatal suicide cases by 89% (95% CI: 57-97%). We also found that the installation of full-height PSDs resulted in the elimination of subway suicides by completely blocking access to the track area; however, half-height PSDs, which do not extend to the ceiling of the platform, were not as effective as full-height ones. Our findings were based on the data from a single subway operator for a limited period of time. Accordingly, we did not consider the possibility that some passengers choose to die at a station run by other operators. Our study did not examine the potential substitution effects of other suicide methods. Installing physical barriers at subway stations can be an effective strategy to reduce the number of subway suicides; however, half-height PSDs are not as effective as full-height ones, even when they are as high as the height of an adult. Thus, these barriers should be made high enough so that nobody can climb over them. Copyright © 2016 Elsevier B.V. All rights reserved.

Energy barriers, entropy barriers, and non-Arrhenius behavior in a minimal glassy model.

PubMed

Du, Xin; Weeks, Eric R

2016-06-01

We study glassy dynamics using a simulation of three soft Brownian particles confined to a two-dimensional circular region. If the circular region is large, the disks freely rearrange, but rearrangements are rarer for smaller system sizes. We directly measure a one-dimensional free-energy landscape characterizing the dynamics. This landscape has two local minima corresponding to the two distinct disk configurations, separated by a free-energy barrier that governs the rearrangement rate. We study several different interaction potentials and demonstrate that the free-energy barrier is composed of a potential-energy barrier and an entropic barrier. The heights of both of these barriers depend on temperature and system size, demonstrating how non-Arrhenius behavior can arise close to the glass transition.

Decay analysis of compound nuclei with masses A ≈30 - 200 formed in reactions involving loosely bound projectiles

NASA Astrophysics Data System (ADS)

Kaur, Mandeep; Singh, BirBikram; Sharma, Manoj K.; Gupta, Raj K.

2015-08-01

The dynamics of compound nuclei formed in the reactions using loosely bound projectiles are analyzed within the framework of the dynamical cluster-decay model (DCM) of Gupta and Collaborators. We have considered the reactions with neutron-rich and neutron-deficient projectiles, respectively, as 7Li , 9Be , and 7Be , on various targets at three different Elab energies, forming compound nuclei in the mass region A ˜30 - 200. For these reactions, the contributions of light-particle (LP, A ≤4 ) cross sections σLP, energetically favored intermediate-mass-fragment (IMF, 5 ≤A2≤20 ) cross sections σIMF, as well as the fusion-fission ff cross sections σff constitute the σfus(=σLP+σIMF+σff ), i.e., the contributions of the emitted LPs, IMFs, and ff fragments are added for all the angular momenta up to the ℓmax value for the respective reactions. Interestingly, we find that the empirically fitted neck-length parameter Δ Remp , the only parameter of the DCM, is uniquely fixed to address σfus for all the reactions having the same loosely bound projectile at a chosen incident laboratory energy. It may be noted that, in DCM, the dynamical collective mass motion of preformed LPs, IMFs, and ff fragments or clusters, through the modified interaction potential barrier, are treated on parallel footing. The modification of the barrier is due to nonzero Δ Remp , and the values of corresponding modified interaction-barrier heights Δ VBemp for such reactions are almost of the same order, specifically at the respective ℓmax value.

Interfacial layer thickness dependent electrical characteristics of Au/(Zn-doped PVA)/n-4H-SiC (MPS) structures at room temperature

NASA Astrophysics Data System (ADS)

Lapa, Havva Elif; Kökce, Ali; Al-Dharob, Mohammed; Orak, İkram; Özdemir, Ahmet Faruk; Altındal, Semsettin

2017-10-01

Au/(Zn-doped PVA)/n-4H-SiC metal/polymer/semiconductor (MPS) structures with different interfacial layer thickness values (50, 150, 500 nm) were fabricated and their electrical characteristics were compared. Their electrical parameters (i.e. reverse-bias saturation current (Io), ideality factor (n), zero-bias barrier height (BH) (Φbo), series and shunt resistances (Rs, Rsh)) were calculated from the forward bias current-voltage (IF-VF) data whereas other parameters (i.e. Fermi energy level (EF), BH (Vb) and donor concentration (Nd)) were calculated from the linear part of C-2-V characteristics at room temperature. Obtained results confirmed that the values of n, Φbo, Rs and Rsh increase with increasing interlayer thickness, and linear correlation between n and Φbo was observed. The high values of n for three structures can be ascribed to the presence of an interlayer, surface states (Nss) and barrier inhomogeneities. The energy density distribution profile of Nss was obtained from the IF-VF data by taking into account voltage-dependent effective BH (Ve) and n for each structure. The Ri vs V plot for these structures was obtained using both Ohm's law and Nicollian-Brews method. All these experimental results show that the interfacial layer and its thickness play an important role in main electric parameters of these structures.

Alternating current characterization of nano-Pt(II) octaethylporphyrin (PtOEP) thin film as a new organic semiconductor

NASA Astrophysics Data System (ADS)

M, Dongol; M, M. El-Nahass; A, El-Denglawey; A, A. Abuelwafa; T, Soga

2016-06-01

Alternating current (AC) conductivity and dielectric properties of thermally evaporated Au/PtOEP/Au thin films are investigated each as a function of temperature (303 K-473 K) and frequency (50 Hz-5 MHz). The frequency dependence of AC conductivity follows the Jonscher universal dynamic law. The AC-activation energies are determined at different frequencies. It is found that the correlated barrier hopping (CBH) model is the dominant conduction mechanism. The variation of the frequency exponent s with temperature is analyzed in terms of the CBH model. Coulombic barrier height W m , hopping distance R ω , and the density of localized states N(E F) are valued at different frequencies. Dielectric constant ɛ 1(ω,T) and dielectric loss ɛ 2(ω,T) are discussed in terms of the dielectric polarization process. The dielectric modulus shows the non-Debye relaxation in the material. The extracted relaxation time by using the imaginary part of modulus (M″) is found to follow the Arrhenius law.

[Relocation of Espeletia grandiflora (Asteraceae) plants as a strategy for enrichment of disturbed paramo areas (PNN Chingaza, Colombia)].

PubMed

Rojas-Zamora, Oscar; Insuasty-Torres, Jennyfer; de Cardenas, Camilo los Angeles; Ríos, Orlando Vargas

2013-03-01

Ecological restoration of the Andean paramos faces several ecological barriers mainly at the phase of dispersal and establishment of native species. With the aim to contribute to the enrichment of degraded areas, different strategies have to be developed to overcome those barriers. In this work we studied the response of individuals of Espeletia grandiflora (Asteraceae) to the relocation as a strategy for ecological restoration programs. We also evaluated the effect of size of relocated individuals on their survival and development. The work was carried out in an experimental plot at 3 424m altitude in the sector "Lagunas de Siecha" of Chingaza National Park, Colombia. We relocated 200 plants that belonged to three different size classes: 5, 10 and 15cm of initial height. The following variables were registered: survival, plant height, number of living leaves and stem diameter of each individual. We also evaluated the differences between individuals in survival and development. In terms of survival the most efficient size classes corresponded to 15cm high; the survival was 85% after two years. The relative growth rates for height and stem diameter decreases with the increase in size, but the absolute increase in height did not show significant differences between the three sizes tested. Since the stem diameter was found the strongest survival predictor after two years of relocation activities, we suggest its use as a criterion for selection of relocation individuals. The relocation of individuals of E. grandiflora had a positive side effect, carrying other species that may contribute to the enrichment and restoration of degraded areas. Among these, we found species of the genus Hypericum, as well as Arcytophyllum nitidum and Calamagrostis effusa, which should be evaluated in terms of survival and development for the subsequent implementation of the relocation strategy. In this study we verified the successful relocation of individuals of E. grandiflora as a strategy for enrichment of paramos, and provided values of survival and growth, which should be useful for planning and predicting with greater certainty the success of restoration programs in the paramo.

Constant pH Molecular Dynamics in Explicit Solvent with Enveloping Distribution Sampling and Hamiltonian Exchange

PubMed Central

2015-01-01

We present a new computational approach for constant pH simulations in explicit solvent based on the combination of the enveloping distribution sampling (EDS) and Hamiltonian replica exchange (HREX) methods. Unlike constant pH methods based on variable and continuous charge models, our method is based on discrete protonation states. EDS generates a hybrid Hamiltonian of different protonation states. A smoothness parameter s is used to control the heights of energy barriers of the hybrid-state energy landscape. A small s value facilitates state transitions by lowering energy barriers. Replica exchange between EDS potentials with different s values allows us to readily obtain a thermodynamically accurate ensemble of multiple protonation states with frequent state transitions. The analysis is performed with an ensemble obtained from an EDS Hamiltonian without smoothing, s = ∞, which strictly follows the minimum energy surface of the end states. The accuracy and efficiency of this method is tested on aspartic acid, lysine, and glutamic acid, which have two protonation states, a histidine with three states, a four-residue peptide with four states, and snake cardiotoxin with eight states. The pKa values estimated with the EDS-HREX method agree well with the experimental pKa values. The mean absolute errors of small benchmark systems range from 0.03 to 0.17 pKa units, and those of three titratable groups of snake cardiotoxin range from 0.2 to 1.6 pKa units. This study demonstrates that EDS-HREX is a potent theoretical framework, which gives the correct description of multiple protonation states and good calculated pKa values. PMID:25061443

Effect of nanodimensional polyethylenimine layer on surface potential barriers of hybrid structures based on silicon single crystal

NASA Astrophysics Data System (ADS)

Malyar, Ivan V.; Gorin, Dmitry A.; Stetsyura, Svetlana V.

2013-01-01

In this report we present the analysis of I-V curves for MIS-structures like silicon substrate / nanodimensional polyelectrolyte layer / metal probe (contact) which is promising for biosensors, microfluidic chips, different devices of molecular electronics, such as OLEDs, solar cells, where polyelectrolyte layers can be used to modify semiconductor surface. The research is directed to investigate the contact phenomena which influence the resulting signal of devices mentioned above. The comparison of I-V characteristics of such structures measured by scanning tunnel microscopy (contactless technique) and using contact areas deposited by thermal evaporation onto the organic layer (the contact one) was carried out. The photoassisted I-V measurements and complex analysis based on Simmons and Schottky models allow one to extract the potential barriers and to observe the changes of charge transport in MIS-structures under illumination and after polyelectrolyte adsorption. The direct correlation between the thickness of the deposited polyelectrolyte layer and both equilibrium tunnel barrier and Schottky barrier height was observed for hybrid structures with polyethylenimine. The possibility of control over the I-V curves of hybrid structure and the height of the potential barriers (for different charge transports) by illumination was confirmed. Based on experimental data and complex analysis the band diagrams were plotted which illustrate the changes of potential barriers for MIS-structures due to the polyelectrolyte adsorption and under the illumination.

Analysis of high reverse currents of 4H-SiC Schottky-barrier diodes

NASA Astrophysics Data System (ADS)

Okino, Hiroyuki; Kameshiro, Norifumi; Konishi, Kumiko; Shima, Akio; Yamada, Ren-ichi

2017-12-01

Nickel (Ni), titanium (Ti), and molybdenum (Mo) 4H-silicon carbide Schottky-barrier diodes (SiC SBDs) were fabricated and used to investigate the relation between forward and reverse currents. Temperature dependence of reverse current follows a theory that includes tunneling in regard to thermionic emission, namely, temperature dependence is weak at low temperature but strong at high temperatures. On the other hand, the reverse currents of the Ni and Mo SBDs are higher than their respective currents calculated from their Schottky barrier heights (SBHs), whereas the reverse current of the Ti SBD agrees well with that calculated from its SBH. The cause of the high reverse currents was investigated from the viewpoints of low barrier patch, Gaussian distribution of barrier height (GD), thin surface barrier, and electron effective mass. The high reverse current of the Ni and Mo SBDs can be explained not in terms of a low-barrier patch, GD, or thin surface barrier but in terms of small effective masses. Investigation of crystal structures at the Schottky interface revealed a large lattice mismatch between the metals (Ni, Ti, or Mo) and SiC for the Ni and Mo SBDs. The small effective mass is possibly attributed to the large lattice mismatch, which might generate transition layers at the Schottky interface. It is concluded from these results that the lattice constant as well as the work function is an important factor in selecting the metal species as the Schottky metal for wide band-gap SBDs, for which tunneling current dominates reverse current.

[Practice of engineering management and its effect on schistosomiasis control in Hankou marshland, Wuhan City].

PubMed

Zhi-Qing, Deng; Xiao-Dong, Tan; Shi-Bo, Kong; Kai, Wu; Ming-Xing, Xu; Hua-Tang, Luo

2017-01-06

To investigate the Oncomelania hupensis snail control effect of schistosomiasis control engineering in marshland within Wuhan City. The engineering measures including surface barrier removal, molluscicide, flatting surface, topsoil stripping, topsoil covering and ditch renovation were applied to transform Hankou marshland. Then the corresponding technical parameters of engineering measures were put forward. The situation of snails was analyzed before and after the transform project. The total length and area of the project were 6 015 m and 87.21 hm 2 , respectively, including 17.44 hm 2 of topsoil landfill, 52.08 hm 2 of topsoil covering and 23 new ditches. After the transformation, the average length of the new groove, the groove top width, groove depth, height difference, and the average values of slopes and ditch bottom slope were all increased, while the average values of the width and height of the ditch were decreased. At the same time, the marshland beach surface had a new slope that the embankment was higher than the river and no living O. hupensis snails were found then. The snail breeding environment in Hankou marshland has been effectively changed by the project. However, the constant monitoring and engineering management are still needed to consolidate the effect.

Electronic Characterization of Au/DNA/ITO Metal-Semiconductor-Metal Diode and Its Application as a Radiation Sensor.

PubMed

Al-Ta'ii, Hassan Maktuff Jaber; Periasamy, Vengadesh; Amin, Yusoff Mohd

2016-01-01

Deoxyribonucleic acid or DNA molecules expressed as double-stranded (DSS) negatively charged polymer plays a significant role in electronic states of metal/silicon semiconductor structures. Electrical parameters of an Au/DNA/ITO device prepared using self-assembly method was studied by using current-voltage (I-V) characteristic measurements under alpha bombardment at room temperature. The results were analyzed using conventional thermionic emission model, Cheung and Cheung's method and Norde's technique to estimate the barrier height, ideality factor, series resistance and Richardson constant of the Au/DNA/ITO structure. Besides demonstrating a strongly rectifying (diode) characteristic, it was also observed that orderly fluctuations occur in various electrical parameters of the Schottky structure. Increasing alpha radiation effectively influences the series resistance, while the barrier height, ideality factor and interface state density parameters respond linearly. Barrier height determined from I-V measurements were calculated at 0.7284 eV for non-radiated, increasing to about 0.7883 eV in 0.036 Gy showing an increase for all doses. We also demonstrate the hypersensitivity phenomena effect by studying the relationship between the series resistance for the three methods, the ideality factor and low-dose radiation. Based on the results, sensitive alpha particle detectors can be realized using Au/DNA/ITO Schottky junction sensor.

Electronic Characterization of Au/DNA/ITO Metal-Semiconductor-Metal Diode and Its Application as a Radiation Sensor

PubMed Central

Al-Ta’ii, Hassan Maktuff Jaber; Periasamy, Vengadesh; Amin, Yusoff Mohd

2016-01-01

Deoxyribonucleic acid or DNA molecules expressed as double-stranded (DSS) negatively charged polymer plays a significant role in electronic states of metal/silicon semiconductor structures. Electrical parameters of an Au/DNA/ITO device prepared using self-assembly method was studied by using current–voltage (I-V) characteristic measurements under alpha bombardment at room temperature. The results were analyzed using conventional thermionic emission model, Cheung and Cheung’s method and Norde’s technique to estimate the barrier height, ideality factor, series resistance and Richardson constant of the Au/DNA/ITO structure. Besides demonstrating a strongly rectifying (diode) characteristic, it was also observed that orderly fluctuations occur in various electrical parameters of the Schottky structure. Increasing alpha radiation effectively influences the series resistance, while the barrier height, ideality factor and interface state density parameters respond linearly. Barrier height determined from I–V measurements were calculated at 0.7284 eV for non-radiated, increasing to about 0.7883 eV in 0.036 Gy showing an increase for all doses. We also demonstrate the hypersensitivity phenomena effect by studying the relationship between the series resistance for the three methods, the ideality factor and low-dose radiation. Based on the results, sensitive alpha particle detectors can be realized using Au/DNA/ITO Schottky junction sensor. PMID:26799703

Surface morphological, electrical and transport properties of rapidly annealed double layers Ru/Cr Schottky structure on n-type InP

NASA Astrophysics Data System (ADS)

Shanthi Latha, K.; Rajagopal Reddy, V.

2017-07-01

The electrical and transport properties of a fabricated bilayer Ru/Cr/ n-InP Schottky diode (SD) have been investigated at different annealing temperatures. Atomic force microscopy results have showed that the overall surface morphology of the Ru/Cr/ n-InP SD is fairly smooth at elevated temperatures. High barrier height is achieved for the diode annealed at 300 °C compared to the as-deposited, annealed at 200 and 400 °C diodes. The series resistance and shunt resistance of the Ru/Cr/ n-InP SD are estimated by current-voltage method at different annealing temperatures. The barrier heights and series resistance are also determined by Cheung's and modified Norde functions. The interface state density of the Ru/Cr/ n-InP SD is found to be decreased after annealing at 300 °C and then slightly increased upon annealing at 400 °C. The difference between barrier heights obtained from current-voltage and capacitance-voltage is also discussed. Experimental results have showed that the Poole-Frenkel emission is found to be dominant in the lower bias region whereas Schottky emission is dominant in the higher bias region for the Ru/Cr/ n-InP SDs irrespective of annealing temperatures.

Forward Current Transport Mechanisms of Ni/Au—InAlN/AlN/GaN Schottky Diodes

NASA Astrophysics Data System (ADS)

Wang, Xiao-Feng; Shao, Zhen-Guang; Chen, Dun-Jun; Lu, Hai; Zhang, Rong; Zheng, You-Dou

2014-05-01

We fabricate two Ni/Au-In0.17Al0.83N/AlN/GaN Schottky diodes on substrates of sapphire and Si, respectively, and investigate their forward-bias current transport mechanisms by temperature-dependent current-voltage measurements. In the temperature range of 300-485 K, the Schottky barrier heights (SBHs) calculated by using the conventional thermionic-emission (TE) model are strongly positively dependent on temperature, which is in contrast to the negative-temperature-dependent characteristic of traditional semiconductor Schottky diodes. By fitting the forward-bias I-V characteristics using different current transport models, we find that the tunneling current model can describe generally the I-V behaviors in the entire measured range of temperature. Under the high forward bias, the traditional TE mechanism also gives a good fit to the measured I-V data, and the actual barrier heights calculated according to the fitting TE curve are 1.434 and 1.413 eV at 300K for InAlN/AlN/GaN Schottky diodes on Si and the sapphire substrate, respectively, and the barrier height shows a slightly negative temperature coefficient. In addition, a formula is given to estimate SBHs of Ni/Au—InAlN/AlN/GaN Schottky diodes taking the Fermi-level pinning effect into account.

Modulating the Surface State of SiC to Control Carrier Transport in Graphene/SiC.

PubMed

Jia, Yuping; Sun, Xiaojuan; Shi, Zhiming; Jiang, Ke; Liu, Henan; Ben, Jianwei; Li, Dabing

2018-05-28

Silicon carbide (SiC) with epitaxial graphene (EG/SiC) shows a great potential in the applications of electronic and photoelectric devices. The performance of devices is primarily dependent on the interfacial heterojunction between graphene and SiC. Here, the band structure of the EG/SiC heterojunction is experimentally investigated by Kelvin probe force microscopy. The dependence of the barrier height at the EG/SiC heterojunction to the initial surface state of SiC is revealed. Both the barrier height and band bending tendency of the heterojunction can be modulated by controlling the surface state of SiC, leading to the tuned carrier transport behavior at the EG/SiC interface. The barrier height at the EG/SiC(000-1) interface is almost ten times that of the EG/SiC(0001) interface. As a result, the amount of carrier transport at the EG/SiC(000-1) interface is about ten times that of the EG/SiC(0001) interface. These results offer insights into the carrier transport behavior at the EG/SiC heterojunction by controlling the initial surface state of SiC, and this strategy can be extended in all devices with graphene as the top layer. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Schottky junction interfacial properties at high temperature: A case of AgNWs embedded metal oxide/p-Si

NASA Astrophysics Data System (ADS)

Mahala, Pramila; Patel, Malkeshkumar; Gupta, Navneet; Kim, Joondong; Lee, Byung Ha

2018-05-01

Studying the performance limiting parameters of the Schottky device is an urgent issue, which are addressed herein by thermally stable silver nanowire (AgNW) embedded metal oxide/p-Si Schottky device. Temperature and bias dependent junction interfacial properties of AgNW-ITO/Si Schottky photoelectric device are reported. The current-voltage-temperature (I-V-T), capacitance-voltage-temperature (C-V-T) and impedance analysis have been carried out in the high-temperature region. The ideality factor and barrier height of Schottky junction are assessed using I-V-T characteristics and thermionic emission, to reveal the decrease of ideality factor and increase of barrier height by the increasing of temperature. The extracted values of laterally homogeneous Schottky (ϕb) and ideality factor (n) are approximately 0.73 eV and 1.58, respectively. Series resistance (Rs) assessed using Cheung's method and found that it decreases with the increase of temperature. A linear response of Rs of AgNW-ITO/Si Schottky junction is observed with respect to change in forward bias, i.e. dRS/dV from 0 to 0.7 V is in the range of 36.12-36.43 Ω with a rate of 1.44 Ω/V. Impedance spectroscopy is used to study the effect of bias voltage and temperature on intrinsic Schottky properties which are responsible for photoconversion efficiency. These systematic analyses are useful for the AgNWs-embedding Si solar cells or photoelectrochemical cells.

Topological Insulator Bi2Se3/Si-Nanowire-Based p-n Junction Diode for High-Performance Near-Infrared Photodetector.

PubMed

Das, Biswajit; Das, Nirmalya S; Sarkar, Samrat; Chatterjee, Biplab K; Chattopadhyay, Kalyan K

2017-07-12

Chemically derived topological insulator Bi 2 Se 3 nanoflake/Si nanowire (SiNWs) heterojunctions were fabricated employing all eco-friendly cost-effective chemical route for the first time. X-ray diffraction studies confirmed proper phase formation of Bi 2 Se 3 nanoflakes. The morphological features of the individual components and time-evolved hybrid structures were studied using field emission scanning electron microscope. High resolution transmission electron microscopic studies were performed to investigate the actual nature of junction whereas elemental distributions at junction, along with overall stoichiometry of the samples were analyzed using energy dispersive X-ray studies. Temperature dependent current-voltage characteristics and variation of barrier height and ideality factor was studied between 50 and 300 K. An increase in barrier height and decrease in the ideality factor were observed with increasing temperature for the sample. The rectification ratio (I + /I - ) for SiNWs substrate over pristine Si substrate under dark and near-infrared (NIR) irradiation of 890 nm was found to be 3.63 and 10.44, respectively. Furthermore, opto-electrical characterizations were performed for different light power intensities and highest photo responsivity and detectivity were determined to be 934.1 A/W and 2.30 × 10 13 Jones, respectively. Those values are appreciably higher than previous reports for topological insulator based devices. Thus, this work establishes a hybrid system based on topological insulator Bi 2 Se 3 nanoflake and Si nanowire as the newest efficient candidate for advanced optoelectronic materials.

Number-squeezed and fragmented states of strongly interacting bosons in a double well

NASA Astrophysics Data System (ADS)

Corbo, Joel C.; DuBois, Jonathan L.; Whaley, K. Birgitta

2017-11-01

We present a systematic study of the phenomena of number squeezing and fragmentation for a repulsive Bose-Einstein condensate (BEC) in a three-dimensional double-well potential over a range of interaction strengths and barrier heights, including geometries that exhibit appreciable overlap in the one-body wave functions localized in the left and right wells. We compute the properties of the condensate with numerically exact, full-dimensional path-integral ground-state (PIGS) quantum Monte Carlo simulations and compare with results obtained from using two- and eight-mode truncated basis models. The truncated basis models are found to agree with the numerically exact PIGS simulations for weak interactions, but fail to correctly predict the amount of number squeezing and fragmentation exhibited by the PIGS simulations for strong interactions. We find that both number squeezing and fragmentation of the BEC show nonmonotonic behavior at large values of interaction strength a . The number squeezing shows a universal scaling with the product of number of particles and interaction strength (N a ), but no such universal behavior is found for fragmentation. Detailed analysis shows that the introduction of repulsive interactions not only suppresses number fluctuations to enhance number squeezing, but can also enhance delocalization across wells and tunneling between wells, each of which may suppress number squeezing. This results in a dynamical competition whose resolution shows a complex dependence on all three physical parameters defining the system: interaction strength, number of particles, and barrier height.

Dietary l-threonine supplementation attenuates lipopolysaccharide-induced inflammatory responses and intestinal barrier damage of broiler chickens at an early age.

PubMed

Chen, Yueping; Zhang, Hao; Cheng, Yefei; Li, Yue; Wen, Chao; Zhou, Yanmin

2018-06-01

This study was conducted to investigate the protective effects of l-threonine (l-Thr) supplementation on growth performance, inflammatory responses and intestinal barrier function of young broilers challenged with lipopolysaccharide (LPS). A total of 144 1-d-old male chicks were allocated to one of three treatments: non-challenged broilers fed a basal diet (control group), LPS-challenged broilers fed a basal diet without l-Thr supplementation and LPS-challenged broilers fed a basal diet supplemented with 3·0 g/kg l-Thr. LPS challenge was performed intraperitoneally at 17, 19 and 21 d of age, whereas the control group received physiological saline injection. Compared with the control group, LPS challenge impaired growth performance of broilers, and l-Thr administration reversed LPS-induced increase in feed/gain ratio. LPS challenge elevated blood cell counts related to inflammation, and pro-inflammatory cytokine concentrations in serum (IL-1β and TNF-α), spleen (IL-1β and TNF-α) and intestinal mucosa (jejunal interferon-γ (IFN-γ) and ileal IL-1β). The concentrations of intestinal cytokines in LPS-challenged broilers were reduced by l-Thr supplementation. LPS administration increased circulating d-lactic acid concentration, whereas it reduced villus height, the ratio between villus height and crypt depth and goblet density in both jejunum and ileum. LPS-induced decreases in jejunal villus height, intestinal villus height:crypt depth ratio and ileal goblet cell density were reversed with l-Thr supplementation. Similarly, LPS-induced alterations in the intestinal mRNA abundances of genes related to intestinal inflammation and barrier function (jejunal toll-like receptor 4, IFN- γ and claudin-3, and ileal IL-1 β and zonula occludens-1) were normalised with l-Thr administration. It can be concluded that l-Thr supplementation could attenuate LPS-induced inflammatory responses and intestinal barrier damage of young broilers.

How Accurate Are the Minnesota Density Functionals for Noncovalent Interactions, Isomerization Energies, Thermochemistry, and Barrier Heights Involving Molecules Composed of Main-Group Elements?

DOE PAGES

Mardirossian, Narbe; Head-Gordon, Martin

2016-08-18

The 14 Minnesota density functionals published between the years 2005 and early 2016 are benchmarked on a comprehensive database of 4986 data points (84 data sets) involving molecules composed of main-group elements. The database includes noncovalent interactions, isomerization energies, thermochemistry, and barrier heights, as well as equilibrium bond lengths and equilibrium binding energies of noncovalent dimers. Additionally, the sensitivity of the Minnesota density functionals to the choice of basis set and integration grid is explored for both noncovalent interactions and thermochemistry. By and large, the main strength of the hybrid Minnesota density functionals is that the best ones provide verymore » good performance for thermochemistry (e.g., M06-2X), barrier heights (e.g., M08-HX, M08-SO, MN15), and systems heavily characterized by self-interaction error (e.g., M06-2X, M08-HX, M08-SO, MN15), while the main weakness is that none of them are state-of-the-art for the full spectrum of noncovalent interactions and isomerization energies (although M06-2X is recommended from the 10 hybrid Minnesota functionals). Similarly, the main strength of the local Minnesota density functionals is that the best ones provide very good performance for thermochemistry (e.g., MN15-L), barrier heights (e.g., MN12-L), and systems heavily characterized by self-interaction error (e.g., MN12-L and MN15-L), while the main weakness is that none of them are state-of-the-art for the full spectrum of noncovalent interactions and isomerization energies (although M06-L is clearly the best from the four local Minnesota functionals). Finally, as an overall guide, M06-2X and MN15 are perhaps the most broadly useful hybrid Minnesota functionals, while M06-L and MN15-L are perhaps the most broadly useful local Minnesota functionals, although each has different strengths and weaknesses.« less

FIBER AND INTEGRATED OPTICS: Problems involved in the profiling of quantum wells and barriers for optoelectronic applications

NASA Astrophysics Data System (ADS)

Eliseev, P. G.; Zakhar'ev, B. N.

1992-10-01

Some important problems concerning the profiling of the potential energy in quantum-well lasers are discussed. The goals being sought are to introduce a relative shift of the levels of localized states, to introduce an energy gap, and to reduce the transmission of barriers without increasing their height.

Calculation of the Schottky barrier and current–voltage characteristics of metal–alloy structures based on silicon carbide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Altuhov, V. I., E-mail: altukhovv@mail.ru; Kasyanenko, I. S.; Sankin, A. V.

2016-09-15

A simple but nonlinear model of the defect density at a metal–semiconductor interface, when a Schottky barrier is formed by surface defects states localized at the interface, is developed. It is shown that taking the nonlinear dependence of the Fermi level on the defect density into account leads to a Schottky barrier increase by 15–25%. The calculated barrier heights are used to analyze the current–voltage characteristics of n-M/p-(SiC){sub 1–x}(AlN){sub x} structures. The results of calculations are compared to experimental data.

Enhancing the effective energy barrier of a Dy(III) SMM using a bridged diamagnetic Zn(II) ion.

PubMed

Upadhyay, Apoorva; Singh, Saurabh Kumar; Das, Chinmoy; Mondol, Ranajit; Langley, Stuart K; Murray, Keith S; Rajaraman, Gopalan; Shanmugam, Maheswaran

2014-08-18

Field induced single-molecule-magnet behaviour is observed for both a heterodinuclear [ZnDy(L(-))2](3+) complex (1) and a mononuclear [Dy(HL)2](3+) complex (2), with effective energy barriers of 83 cm(-1) and 16 cm(-1), respectively. Insights into the relaxation mechanism(s) and barrier heights are provided via ab initio and DFT calculations. Our findings reveal an interesting observation that the U(eff) of SMMs can be enhanced by incorporating diamagnetic metal ions.

Two-diode behavior in metal-ferroelectric-semiconductor structures with bismuth titanate interfacial layer

NASA Astrophysics Data System (ADS)

Durmuş, Perihan; Altindal, Şemsettin

2017-10-01

In this study, electrical parameters of the Al/Bi4Ti3O12/p-Si metal-ferroelectric-semiconductor (MFS) structure and their temperature dependence were investigated using current-voltage (I-V) data measured between 120 K and 300 K. Semi-logarithmic I-V plots of the structure revealed that fabricated structure presents two-diode behavior that leads to two sets of ideality factor, reverse saturation current and zero-bias barrier height (BH) values. Obtained results of these parameters suggest that current conduction mechanism (CCM) deviates strongly from thermionic emission theory particularly at low temperatures. High values of interface states and nkT/q-kT/q plot supported the idea of deviation from thermionic emission. In addition, ln(I)-ln(V) plots suggested that CCM varies from one bias region to another and depends on temperature as well. Series resistance values were calculated using Ohm’s law and Cheungs’ functions, and they decreased drastically with increasing temperature.

Pressure effect on hydrogen tunneling and vibrational spectrum in α-Mn

DOE PAGES

Kolesnikov, Alexander I; Podlesnyak, Andrey A; Sadykov, Ravil A.; ...

2016-10-03

Here in this paper, the pressure effect on the tunneling mode and vibrational spectra of hydrogen in α-MnH0.07 has been studied by inelastic neutron scattering. Applying hydrostatic pressure of up to 30 kbar is shown to shift both the hydrogen optical modes and the tunneling peak to higher energies. First-principles calculations show that the potential for hydrogen in α-Mn becomes overall steeper with increasing pressure. At the same time, the barrier height and its extent in the direction of tunneling decrease and the calculations predict significant changes of the dynamics of hydrogen in α-Mn at 100 kbar, when the estimatedmore » tunneling splitting of the hydrogen ground state exceeds the barrier height.« less

Sputter deposition of indium tin oxide onto zinc pthalocyanine: Chemical and electronic properties of the interface studied by photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Gassmann, Jürgen; Brötz, Joachim; Klein, Andreas

2012-02-01

The interface chemistry and the energy band alignment at the interface formed during sputter deposition of transparent conducting indium tin oxide (ITO) onto the organic semiconductor zinc phtalocyanine (ZnPc), which is important for inverted, transparent, and stacked organic light emitting diodes, is studied by in situ photoelectron spectroscopy (XPS and UPS). ITO was sputtered at room temperature and a low power density with a face to face arrangement of the target and substrate. With these deposition conditions, no chemical reaction and a low barrier height for charge injection at this interface are observed. The barrier height is comparable to those observed for the reverse deposition sequence, which also confirms the absence of sputter damage.

Pressure effect on hydrogen tunneling and vibrational spectrum in α-Mn

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kolesnikov, Alexander I; Podlesnyak, Andrey A; Sadykov, Ravil A.

Here in this paper, the pressure effect on the tunneling mode and vibrational spectra of hydrogen in α-MnH0.07 has been studied by inelastic neutron scattering. Applying hydrostatic pressure of up to 30 kbar is shown to shift both the hydrogen optical modes and the tunneling peak to higher energies. First-principles calculations show that the potential for hydrogen in α-Mn becomes overall steeper with increasing pressure. At the same time, the barrier height and its extent in the direction of tunneling decrease and the calculations predict significant changes of the dynamics of hydrogen in α-Mn at 100 kbar, when the estimatedmore » tunneling splitting of the hydrogen ground state exceeds the barrier height.« less

Electronic transport and Schottky barrier heights of p-type CuAlO2 Schottky diodes

NASA Astrophysics Data System (ADS)

Lin, Yow-Jon; Luo, Jie; Hung, Hao-Che

2013-05-01

A CuAlO2 Schottky diode was fabricated and investigated using current density-voltage (J-V) and capacitance-voltage (C-V) methods. It is shown that the barrier height (qϕB) determined from J-V measurements is lower than that determined from C-V measurements and qϕB determined from C-V measurements is close to the Schottky limit. This is due to a combined effect of the image-force lowering and tunneling. Time domain measurements provide evidence of the domination of electron trapping with long-second lifetime in CuAlO2. Carrier capture and emission from charge traps may lead to the increased probability of tunneling, increasing the ideality factor.

A sensitivity-based approach to optimize the surface treatment of a low-height tramway noise barrier

NASA Astrophysics Data System (ADS)

Jolibois, Alexandre

Transportation noise has become a main nuisance in urban areas, in the industrialized world and across the world, to the point that according to the World Health Organization 65% of the European population is exposed to excessive noise and 20% to night-time levels that may harm their health. There is therefore a need to find new ways to mitigate transportation noise in urban areas. In this work, a possible device to achieve this goal is studied: a low-height noise barrier. It consists of a barrier typically less than one meter high placed close to the source, designed to decrease significantly the noise level for nearby pedestrians and cyclists. A numerical method which optimizes the surface treatment of a low-height barrier in order to increase its insertion loss is presented. Tramway noise barriers are especially studied since the noise sources are in this case close to the ground and would be attenuated more by the barrier. The acoustic behavior of the surface treatment is modeled via its admittance. It can be itself described by a few parameters (flow resistivity, geometrical dimensions...), which can then be optimized. It is proposed to couple porous layers and micro-perforated panel (MPP) resonators in order to take advantage of their different acoustic properties. Moreover, the optimization is achieved using a sensitivity-based method, since in this framework the gradient of the attenuation can be evaluated accurately and efficiently. Several shapes are considered: half-cylinder, quarter-cylinder, straight wall, T-shape and square shape. In the case of a half-cylindrical geometry, a semi-analytical solution for the sound field in terms of a series of cylindrical waves is derived, which simplifies the sensitivity calculation and optimization process. The boundary element method (BEM) is used to evaluate the attenuation for the remaining shapes, and in this case the sensitivity is evaluated using the adjoint state approach. For all considered geometries, it is found that placing an absorbing treatment close to the source is indeed necessary to attenuate the multiple re ections happening between the tramway and the barrier, and that a tuned MPP resonator on the top of the barrier can yield better performance than a uniform absorbent treatment. More advanced numerical modeling and scale model measurements seem to confirm these results.

The structure and dynamics of barrier jets along the southeast Alaskan coast

NASA Astrophysics Data System (ADS)

Olson, Joseph Benjamin

Coastal barrier jets along the complex orography of southeastern Alaska were investigated using high resolution observations and model simulations. Barrier jet events were sampled with the Wyoming King-Air research aircraft during the Southeastern Alaskan Regional Jet (SARJET) field experiment in 2004. These observations, combined with simulations of select cases by the Penn State-NCAR Mesoscale Model (MM5), were used to better understand barrier jet structure and dynamics. A suite of idealized simulations were used to put the case studies in perspective with a larger set of atmospheric conditions, while also evaluating previous theoretical and observational results. Two SARJET case studies were investigated along the tall and steep Fairweather Mountains near Juneau, Alaska. The first case (24 September 2004) was a classical barrier jet forced primarily by onshore flow and upslope adiabatic cooling, with maximum winds >30 m s-1 at the coast between 600-800 m ASL and an offshore extent of ˜60 km. In contrast, the hybrid jet (12 October 2004) was influenced by an offshore-directed gap flow at the coast, which produced a warm anomaly over the coast associated with downslope flow and a wind maximum (˜30 m s-1) that was displaced 30-40 km offshore at 500 m ASL. A sensitivity experiment in which the coastal mountain gap was filled led to a ˜40% reduction in the jet width, and the position of the jet maximum shifted ˜40 km to the coast, but the overall jet intensity remained approximately the same. The generality of these SARJET results was tested by generating a set of three-dimensional idealized MM5 simulations by varying wind speeds, wind directions, and static stabilities for the classical jet simulations, while incrementing the magnitude of the inland cold pool (instead of static stability) for hybrid jet simulations. The broad inland terrain was shown to impact the upstream winds by rotating them cyclonically to become more terrain-parallel within 500-1000 km of the coast. This reduced cross-barrier component acted to reduce the local Froude number of the impinging flow, thus enhancing the potential for flow blocking. Thus, the enhancement of the large-scale mountain anticyclone by the inland terrain acts to "precondition" the impinging flow for barrier jet development. The largest simulated wind speed enhancements (˜1.9-2.0) for the classic and hybrid jets occurred for low Froude numbers ( Fr), with a maximum at Fr ˜0.3-0.4. Low ambient wind speeds (10--15 m s-1) and southerly (170-180°) wind directions (˜30-45° from coast-parallel) were also ingredients for the largest wind speed enhancements. The widest barrier jets were found in simulations with ambient winds oriented nearly terrain-parallel (˜160°) with strong static stability (N > 0.01 s-1). Hybrid barrier jets were slightly wider than the classical, with the gap outflows acting to shift the position of the jet maximum further away from the coast. During periods of maximal gap outflow (hrs 6-18), the height of the jet maximums were typically lower than the classical simulations, since the hybrid jet maximum was located at the top of the shallow gap outflow. The jet height was most correlated with total wind speed, Utotal, and negatively correlated with static stability, N, suggesting that the height of the jet maximum approximately scales as U total/N, which is proportional to the vertical wavelength of a mountain wave. Finally, a detailed assessment of the usefulness of the previous linear theory and scale analysis on barrier jets was performed. The high Fr relationship (L = Nhm/ f) performed better than the low Fr relationship (L = Un/f) in determining the offshore extent of the barrier jet. The implementation of the dividing streamline concept of Sheppard's model for determining the proper blocking height (hd) resulted in a modified form (L = Nhd/ f), which improved the predictive skill. For the determination of maximum wind speeds, the high Fr relationship (DeltaV = Nhm) was found to be better correlated with the measured values than the low Fr relationship ( DeltaV = Un) throughout the full range of Fr. Two-dimensional linear theory performed poorly for Fr < 0.5. Modifications were made to these previous relationships to better account for the three dimensional winds, which helped to improve the estimated wind speed enhancements.

Richardson constant and electrostatics in transfer-free CVD grown few-layer MoS2/graphene barristor with Schottky barrier modulation >0.6eV

NASA Astrophysics Data System (ADS)

Jahangir, Ifat; Uddin, M. Ahsan; Singh, Amol K.; Koley, Goutam; Chandrashekhar, M. V. S.

2017-10-01

We demonstrate a large area MoS2/graphene barristor, using a transfer-free method for producing 3-5 monolayer (ML) thick MoS2. The gate-controlled diodes show good rectification, with an ON/OFF ratio of ˜103. The temperature dependent back-gated study reveals Richardson's coefficient to be 80.3 ± 18.4 A/cm2/K and a mean electron effective mass of (0.66 ± 0.15)m0. Capacitance and current based measurements show the effective barrier height to vary over a large range of 0.24-0.91 eV due to incomplete field screening through the thin MoS2. Finally, we show that this barristor shows significant visible photoresponse, scaling with the Schottky barrier height. A response time of ˜10 s suggests that photoconductive gain is present in this device, resulting in high external quantum efficiency.

Improved transfer of graphene for gated Schottky-junction, vertical, organic, field-effect transistors.

PubMed

Lemaitre, Maxime G; Donoghue, Evan P; McCarthy, Mitchell A; Liu, Bo; Tongay, Sefaattin; Gila, Brent; Kumar, Purushottam; Singh, Rajiv K; Appleton, Bill R; Rinzler, Andrew G

2012-10-23

An improved process for graphene transfer was used to demonstrate high performance graphene enabled vertical organic field effect transistors (G-VFETs). The process reduces disorder and eliminates the polymeric residue that typically plagues transferred films. The method also allows for purposely creating pores in the graphene of a controlled areal density. Transconductance observed in G-VFETs fabricated with a continuous (pore-free) graphene source electrode is attributed to modulation of the contact barrier height between the graphene and organic semiconductor due to a gate field induced Fermi level shift in the low density of electronic-states graphene electrode. Pores introduced in the graphene source electrode are shown to boost the G-VFET performance, which scales with the areal pore density taking advantage of both barrier height lowering and tunnel barrier thinning. Devices with areal pore densities of 20% exhibit on/off ratios and output current densities exceeding 10(6) and 200 mA/cm(2), respectively, at drain voltages below 5 V.

Tunneling Characteristics Depending on Schottky Barriers and Diffusion Current in SiOC.

PubMed

Oh, Teresa; Kim, Chy Hyung

2016-02-01

To obtain a diffusion current in SiOC, the aluminum doped zinc oxide films were deposited on SiOC/Si wafer by a RF magnetron sputtering. All the X-ray patterns of the SiOC films showed amorphous phases. The level of binding energy of Si atoms will lead to an additional potential modulation by long range Coulombic and covalent interactions with oxygen ions. The growth of the AZO film was affected by the characteristics of SiOC, resulting in similar trends in XPS spectra and a shift to higher AZO lattice d values than the original AZO d values in XRD analyses. The charges trapped by the defects at the interlayer between AZO and SiOC films induced the decreased mobility of carriers. In the absence of trap charges, AZO grown on SiOC film such as the sample prepared at O2 = 25 or 30 sccm, which has low charge carrier concentration and high mobility, showed high mobility in an ambipolar characteristic of oxide semiconductor due to the tunneling effect and diffusion current. The structural matching of an interface between AZO and amorphous SiOC enhanced the height of Schottky Barrier (SB), and then the mobility was increased by the tunneling effect from band to band through the high SB.

Performing a local barrier operation

DOEpatents

Archer, Charles J; Blocksome, Michael A; Ratterman, Joseph D; Smith, Brian E

2014-03-04

Performing a local barrier operation with parallel tasks executing on a compute node including, for each task: retrieving a present value of a counter; calculating, in dependence upon the present value of the counter and a total number of tasks performing the local barrier operation, a base value, the base value representing the counter's value prior to any task joining the local barrier; calculating, in dependence upon the base value and the total number of tasks performing the local barrier operation, a target value of the counter, the target value representing the counter's value when all tasks have joined the local barrier; joining the local barrier, including atomically incrementing the value of the counter; and repetitively, until the present value of the counter is no less than the target value of the counter: retrieving the present value of the counter and determining whether the present value equals the target value.

Performing a local barrier operation

DOEpatents

Archer, Charles J; Blocksome, Michael A; Ratterman, Joseph D; Smith, Brian E

2014-03-04

Performing a local barrier operation with parallel tasks executing on a compute node including, for each task: retrieving a present value of a counter; calculating, in dependence upon the present value of the counter and a total number of tasks performing the local barrier operation, a base value of the counter, the base value representing the counter's value prior to any task joining the local barrier; calculating, in dependence upon the base value and the total number of tasks performing the local barrier operation, a target value, the target value representing the counter's value when all tasks have joined the local barrier; joining the local barrier, including atomically incrementing the value of the counter; and repetitively, until the present value of the counter is no less than the target value of the counter: retrieving the present value of the counter and determining whether the present value equals the target value.

Ferroelectric-field-effect-enhanced electroresistance in metal/ferroelectric/semiconductor tunnel junctions

NASA Astrophysics Data System (ADS)

Wen, Zheng; Li, Chen; Wu, Di; Li, Aidong; Ming, Naiben

2013-07-01

Ferroelectric tunnel junctions (FTJs), composed of two metal electrodes separated by an ultrathin ferroelectric barrier, have attracted much attention as promising candidates for non-volatile resistive memories. Theoretical and experimental works have revealed that the tunnelling resistance switching in FTJs originates mainly from a ferroelectric modulation on the barrier height. However, in these devices, modulation on the barrier width is very limited, although the tunnelling transmittance depends on it exponentially as well. Here we propose a novel tunnelling heterostructure by replacing one of the metal electrodes in a normal FTJ with a heavily doped semiconductor. In these metal/ferroelectric/semiconductor FTJs, not only the height but also the width of the barrier can be electrically modulated as a result of a ferroelectric field effect, leading to a greatly enhanced tunnelling electroresistance. This idea is implemented in Pt/BaTiO3/Nb:SrTiO3 heterostructures, in which an ON/OFF conductance ratio above 104, about one to two orders greater than those reported in normal FTJs, can be achieved at room temperature. The giant tunnelling electroresistance, reliable switching reproducibility and long data retention observed in these metal/ferroelectric/semiconductor FTJs suggest their great potential in non-destructive readout non-volatile memories.

Tunable Schottky barrier and high responsivity in graphene/Si-nanotip optoelectronic device

NASA Astrophysics Data System (ADS)

Di Bartolomeo, Antonio; Giubileo, Filippo; Luongo, Giuseppe; Iemmo, Laura; Martucciello, Nadia; Niu, Gang; Fraschke, Mirko; Skibitzki, Oliver; Schroeder, Thomas; Lupina, Grzegorz

2017-03-01

We demonstrate tunable Schottky barrier height and record photo-responsivity in a new-concept device made of a single-layer CVD graphene transferred onto a matrix of nanotips patterned on n-type Si wafer. The original layout, where nano-sized graphene/Si heterojunctions alternate to graphene areas exposed to the electric field of the Si substrate, which acts both as diode cathode and transistor gate, results in a two-terminal barristor with single-bias control of the Schottky barrier. The nanotip patterning favors light absorption, and the enhancement of the electric field at the tip apex improves photo-charge separation and enables internal gain by impact ionization. These features render the device a photodetector with responsivity (3 {{A}} {{{W}}}-1 for white LED light at 3 {{mW}} {{{cm}}}-2 intensity) almost an order of magnitude higher than commercial photodiodes. We extensively characterize the voltage and the temperature dependence of the device parameters, and prove that the multi-junction approach does not add extra-inhomogeneity to the Schottky barrier height distribution. We also introduce a new phenomenological graphene/semiconductor diode equation, which well describes the experimental I-V characteristics both in forward and reverse bias.

Current-induced changes of migration energy barriers in graphene and carbon nanotubes

NASA Astrophysics Data System (ADS)

Obodo, J. T.; Rungger, I.; Sanvito, S.; Schwingenschlögl, U.

2016-05-01

An electron current can move atoms in a nanoscale device with important consequences for the device operation and breakdown. We perform first principles calculations aimed at evaluating the possibility of changing the energy barriers for atom migration in carbon-based systems. In particular, we consider the migration of adatoms and defects in graphene and carbon nanotubes. Although the current-induced forces are large for both the systems, in graphene the force component along the migration path is small and therefore the barrier height is little affected by the current flow. In contrast, the same barrier is significantly reduced in carbon nanotubes as the current increases. Our work also provides a real-system numerical demonstration that current-induced forces within density functional theory are non-conservative.An electron current can move atoms in a nanoscale device with important consequences for the device operation and breakdown. We perform first principles calculations aimed at evaluating the possibility of changing the energy barriers for atom migration in carbon-based systems. In particular, we consider the migration of adatoms and defects in graphene and carbon nanotubes. Although the current-induced forces are large for both the systems, in graphene the force component along the migration path is small and therefore the barrier height is little affected by the current flow. In contrast, the same barrier is significantly reduced in carbon nanotubes as the current increases. Our work also provides a real-system numerical demonstration that current-induced forces within density functional theory are non-conservative. Electronic supplementary information (ESI) available. See DOI: 10.1039/C6NR00534A

Experimental study of a wake behind a barrier

NASA Astrophysics Data System (ADS)

Tomáš, Dufek; Katarína, Ratkovská

2017-09-01

This article describes in detail an experiment which was carried out on a wind tunnel in the Laboratory of the Department of Power Machines, Faculty of Mechanical Engineering, at the University of West Bohemia (UWB), using Particle Image Velocimetry and Stereo Particle Image Velocimetry. PIV is a non-invasive method that allows you to simultaneously measure the flow velocity across the entire field under investigation. In the experiment, the field was located behind the exit of the wind tunnel. The experiment dealt with the measurement of the wake behind a barrier. Measurement with Stereo PIV was carried out in several vertical parallel planes perpendicular to the axis of the tunnel. Conventional PIV method was then used for a horizontal plane passing through the axis of the tunnel at half the height of the barrier. The velocities in the measured plane are expressed by a vector map. In areas not affected by the wake, the speed in the w direction is about 16 m / s. The wake is formed behind the barrier. A shear layer is formed at the boundary between the flowing air and the braked air. A backflow occurs in the area just behind the barrier. The highest speed in the area is achieved in places just behind the exit of the tunnel, where the current is not affected by the barrier. In the direction from the axis and the obstacle, the speed gradually rises from the negative values of the return flow through the zero speed. In addition to the velocity fields, the output from the experimental measurement was also the distribution of the sum of variances, standard deviation and correlation coefficient in the measured planes.

Analytical modeling of trilayer graphene nanoribbon Schottky-barrier FET for high-speed switching applications.

PubMed

Rahmani, Meisam; Ahmadi, Mohammad Taghi; Abadi, Hediyeh Karimi Feiz; Saeidmanesh, Mehdi; Akbari, Elnaz; Ismail, Razali

2013-01-30

Recent development of trilayer graphene nanoribbon Schottky-barrier field-effect transistors (FETs) will be governed by transistor electrostatics and quantum effects that impose scaling limits like those of Si metal-oxide-semiconductor field-effect transistors. The current-voltage characteristic of a Schottky-barrier FET has been studied as a function of physical parameters such as effective mass, graphene nanoribbon length, gate insulator thickness, and electrical parameters such as Schottky barrier height and applied bias voltage. In this paper, the scaling behaviors of a Schottky-barrier FET using trilayer graphene nanoribbon are studied and analytically modeled. A novel analytical method is also presented for describing a switch in a Schottky-contact double-gate trilayer graphene nanoribbon FET. In the proposed model, different stacking arrangements of trilayer graphene nanoribbon are assumed as metal and semiconductor contacts to form a Schottky transistor. Based on this assumption, an analytical model and numerical solution of the junction current-voltage are presented in which the applied bias voltage and channel length dependence characteristics are highlighted. The model is then compared with other types of transistors. The developed model can assist in comprehending experiments involving graphene nanoribbon Schottky-barrier FETs. It is demonstrated that the proposed structure exhibits negligible short-channel effects, an improved on-current, realistic threshold voltage, and opposite subthreshold slope and meets the International Technology Roadmap for Semiconductors near-term guidelines. Finally, the results showed that there is a fast transient between on-off states. In other words, the suggested model can be used as a high-speed switch where the value of subthreshold slope is small and thus leads to less power consumption.

Fission barriers at the end of the chart of the nuclides

NASA Astrophysics Data System (ADS)

Möller, Peter; Sierk, Arnold J.; Ichikawa, Takatoshi; Iwamoto, Akira; Mumpower, Matthew

2015-02-01

We present calculated fission-barrier heights for 5239 nuclides for all nuclei between the proton and neutron drip lines with 171 ≤A ≤330 . The barriers are calculated in the macroscopic-microscopic finite-range liquid-drop model with a 2002 set of macroscopic-model parameters. The saddle-point energies are determined from potential-energy surfaces based on more than 5 000 000 different shapes, defined by five deformation parameters in the three-quadratic-surface shape parametrization: elongation, neck diameter, left-fragment spheroidal deformation, right-fragment spheroidal deformation, and nascent-fragment mass asymmetry. The energy of the ground state is determined by calculating the lowest-energy configuration in both the Nilsson perturbed-spheroid (ɛ ) and the spherical-harmonic (β ) parametrizations, including axially asymmetric deformations. The lower of the two results (correcting for zero-point motion) is defined as the ground-state energy. The effect of axial asymmetry on the inner barrier peak is calculated in the (ɛ ,γ ) parametrization. We have earlier benchmarked our calculated barrier heights to experimentally extracted barrier parameters and found average agreement to about 1 MeV for known data across the nuclear chart. Here we do additional benchmarks and investigate the qualitative and, when possible, quantitative agreement and/or consistency with data on β -delayed fission, isotope generation along prompt-neutron-capture chains in nuclear-weapons tests, and superheavy-element stability. These studies all indicate that the model is realistic at considerable distances in Z and N from the region of nuclei where its parameters were determined.

Quantifying reactivity for electrophilic aromatic substitution reactions with Hirshfeld charge.

PubMed

Liu, Shubin

2015-03-26

An electrophilic aromatic substitution is a process where one atom or group on an aromatic ring is replaced by an incoming electrophile. The reactivity and regioselectivity of this category of reactions is significantly impacted by the group that is already attached to the aromatic ring. Groups promoting substitution at the ortho/para and meta position are called ortho/para and meta directing groups, respectively. Earlier, we have shown that regioselectivity of the electrophilic aromatic substitution is dictated by the nucleophilicity of the substituted aromatic ring, which is proportional to the Hirshfeld charge on the regioselective site. Ortho/para directing groups have the largest negative charge values at the ortho/para positions, whereas meta directing groups often have the largest negative charge value at the meta position. The electron donation or acceptance feature of a substitution group is irrelevant to the regioselectivity. In this contribution, we extend our previous study by quantifying the reactivity for this kind of reactions. To that end, we examine the transition-state structure and activation energy of an identity reaction for a series of monosubstituted-benzene molecules reacting with hydrogen fluoride using BF3 as the catalyst in the gas phase. A total of 18 substitution groups will be considered, nine of which are ortho/para directing and the other nine groups meta directing. From this study, we found that the barrier height of these reactions strongly correlates with the Hirshfeld charge on the regioselective site for both ortho/para and meta directing groups, with the correlation coefficient R(2) both better than 0.96. We also discovered a less accurate correlation between the barrier height and HOMO energy. These results reconfirm the validity and effectiveness of employing the Hirshfeld charge as a reliable descriptor of both reactivity and regioselectivity for this vastly important category of chemical transformations.

Global height datum unification: a new approach in gravity potential space

NASA Astrophysics Data System (ADS)

Ardalan, A. A.; Safari, A.

2005-12-01

The problem of “global height datum unification” is solved in the gravity potential space based on: (1) high-resolution local gravity field modeling, (2) geocentric coordinates of the reference benchmark, and (3) a known value of the geoid’s potential. The high-resolution local gravity field model is derived based on a solution of the fixed-free two-boundary-value problem of the Earth’s gravity field using (a) potential difference values (from precise leveling), (b) modulus of the gravity vector (from gravimetry), (c) astronomical longitude and latitude (from geodetic astronomy and/or combination of (GNSS) Global Navigation Satellite System observations with total station measurements), (d) and satellite altimetry. Knowing the height of the reference benchmark in the national height system and its geocentric GNSS coordinates, and using the derived high-resolution local gravity field model, the gravity potential value of the zero point of the height system is computed. The difference between the derived gravity potential value of the zero point of the height system and the geoid’s potential value is computed. This potential difference gives the offset of the zero point of the height system from geoid in the “potential space”, which is transferred into “geometry space” using the transformation formula derived in this paper. The method was applied to the computation of the offset of the zero point of the Iranian height datum from the geoid’s potential value W 0=62636855.8 m2/s2. According to the geometry space computations, the height datum of Iran is 0.09 m below the geoid.

The 1,2-hydrogen shift reaction for monohalogenophosphanes PH2X and HPX (X = F, Cl)

NASA Astrophysics Data System (ADS)

Viana, Rommel B.; Varela, Jaldyr J. G., Jr.; Tello, Ana C. M.; Savedra, Ranylson M. L.; da Silva, Albérico B. F.

2016-10-01

The aim of the present study was to perform a quantum chemical investigation in the 1,2-hydrogen shift reaction for the PH2X and HPX molecules (X = F,Cl). Several phosphorus-halogen-bearing molecules were studied, including PH2F, PH2Cl, HPF, HPCl, HPFH, HPClH, PFH and PClH. The energies of stationary and saddle points on the ground electronic potential energy surface were investigated with post-Hartree-Fock methods [CCSD(T), MP2, QCISD] and different DFT functionals. The PH2F 1,2-hydrogen shift energy barrier was 75 kcal mol-1 at the CCSD(T) level and only a small increase in this value was observed for the HPF isomerisation. In contrast, the HPCl 1,2-hydrogen shift barrier is higher than the PH2Cl one, which presented a barrier height of 69 kcal mol-1 among CCSD(T) and composite methods. The rate constants of these unimolecular rearrangements varied from 10-44 to 10-38 s-1, and these isomerisation channels exhibited large half-lives. In addition, the heat of formation of each monohalogenophosphane was also calculated. The Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) analysis were also employed to characterise the differences between the phosphorous-halogen bonds.

Proton Transfer Dynamics at the Membrane/Water Interface: Dependence on the Fixed and Mobile pH Buffers, on the Size and Form of Membrane Particles, and on the Interfacial Potential Barrier

PubMed Central

Cherepanov, Dmitry A.; Junge, Wolfgang; Mulkidjanian, Armen Y.

2004-01-01

Crossing the membrane/water interface is an indispensable step in the transmembrane proton transfer. Elsewhere we have shown that the low dielectric permittivity of the surface water gives rise to a potential barrier for ions, so that the surface pH can deviate from that in the bulk water at steady operation of proton pumps. Here we addressed the retardation in the pulsed proton transfer across the interface as observed when light-triggered membrane proton pumps ejected or captured protons. By solving the system of diffusion equations we analyzed how the proton relaxation depends on the concentration of mobile pH buffers, on the surface buffer capacity, on the form and size of membrane particles, and on the height of the potential barrier. The fit of experimental data on proton relaxation in chromatophore vesicles from phototropic bacteria and in bacteriorhodopsin-containing membranes yielded estimates for the interfacial potential barrier for H+/OH− ions of ∼120 meV. We analyzed published data on the acceleration of proton equilibration by anionic pH buffers and found that the height of the interfacial barrier correlated with their electric charge ranging from 90 to 120 meV for the singly charged species to >360 meV for the tetra-charged pyranine. PMID:14747306

Determination of Torsional Barriers of Itaconic Acid and N-Acetylethanolamine Using Chirped-Pulsed Ftmw Spectroscopy

NASA Astrophysics Data System (ADS)

Bailey, Josiah R.; McMahon, Timothy J.; Bird, Ryan G.; Pratt, David

2015-06-01

The ground state rotational spectrum of itaconic acid (methylenesuccinic acid) and N-acetylethanolamine (AEA) have been collected and analyzed over the frequency range of 7-17.5 GHz. Both molecules displayed an unexpected tunneling splitting pattern caused by a V2 and V3 barriers, respectively. AEA's methyl rotor is directly connected to a carbonyl and is expected to have too high of a barrier to internal motion. Itaconic acid contains no methyl groups or any symmetry, yet a torsional splitting was observed. The origin of this motion as well their barrier heights and lowest energy conformations will be discussed.

Evaluation of screen barriers on redbay trees to protect them from Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae) and distribution of initial attacks in relation to stem moisture content, diameter, and height

Treesearch

M. Lake Maner; James Hanula; S. Kristine Braman

2013-01-01

Fine mesh screen was used to create a physical barrier to prevent redbay ambrosia beetles, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), from accessing various parts of the boles of redbay trees, Persea borbonia (L.) Sprengel, and infecting them with the laurel wilt fungus, Raffaelea lauricola...

Five-class height-weight mean and SD system applying Estonian reference values of height-weight mean and SD for systematization of seventeen-year-old conscripts' anthropometric data.

PubMed

Lintsi, Mart; Kaarma, Helje; Aunapuu, Marina; Arend, Andres

2007-03-01

A study of 739 conscripts aged 17 years from the town of Tartu and from the Tartu county was performed. Height, weight, 33 anthropometric measurements and 12 skinfolds were measured. The data were classified into five height-weight mean and SD-classes applying the Estonian reference values for this age and sex (Grünberg et al. 1998). There were 3 classes with conformity between height and weight class: 1--small (small height and small weight), 2--medium (medium height and medium weight), 3--large (large height and large weight), 4--weight class dominating (pyknomorphic) and 5--height class dominating (leptomorphic). It was found, that in classes 1, 2 and 3 the height and weight increase was in accordance with the increase in all heights, breadths and depths, circumferences, skinfolds, body fat, muscle and bone mass. In class 4 circumferences, skinfolds, body fat and muscle mass were bigger. In class 5 all heights and the relative bone mass were bigger. The present investigation confirms the assumption that the five height-weight mean and SD five-class system applying the Estonian reference values for classifying the anthropometric variables is suitable for seventeen-year-old conscripts. As well the border values of 5%, 50% and 95% for every anthropometrical variable in the five-classes were calculated, which may be helpful for practical classifying.

Effects of ageing on the electrical characteristics of Zn/ZnS/n-GaAs/In structure

NASA Astrophysics Data System (ADS)

Güzeldir, B.; Sağlam, M.

2016-04-01

Zn/ZnS/n-GaAs/In structure has been fabricated by the Successive Ionic Layer Adsorption and Reaction (SILAR) method and the influence of the time dependent or ageing on the characteristic parameters are examined. The current-voltage (I-V) of the structure have been measured immediately, 1, 3, 5, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150 and 165 days after fabrication of this structure. The characteristics parameters of this structure such as barrier height, ideality factor, series resistance are calculated from the I-V measurements. It has been seen that the changes of characteristic parameters such as barrier height, ideality factor and series resistance of Zn/ZnS/n-GaAs/In structure have lightly changed with increasing ageing time.

Capacitance-voltage characterization of Al/Al2O3/PVA-PbSe MIS diode

NASA Astrophysics Data System (ADS)

Gawri, Isha; Sharma, Mamta; Jindal, Silky; Singh, Harpreet; Tripathi, S. K.

2018-05-01

The present paper reports the capacitance-voltage characterization of Al/Al2O3/PVA-PbSe MIS diode using chemical bath deposition method. Here anodic alumina layer prepared using electrolytic deposition method on Al substrate is used as insulating material. Using the capacitance-voltage variation at a fixed frequency, the different parameters such as Depletion layer width, Barrier height, Built-in voltage and Carrier concentration has been calculated at room temperature as well as at temperature range from 123 K to 323 K. With the increase in temperature the barrier height and depletion layer width follow a decreasing trend. Therefore, the capacitance-voltage characterization at different temperatures characterization provides strong evidence that the properties of MIS diode are primarily affected by diode parameters.

Electrical characterization of n/p-type nickel silicide/silicon junctions by Sb segregation.

PubMed

Jun, Myungsim; Park, Youngsam; Hyun, Younghoon; Choi, Sung-Jin; Zyung, Taehyung; Jang, Moongyu

2011-08-01

In this paper, n/p-type nickel-silicided Schottky diodes were fabricated by incorporating antimony atoms near the nickel silicide/Si junction interface and the electrical characteristics were studied through measurements and simulations. The effective Schottky barrier height (SBH) for electron, extracted from the thermionic emission model, drastically decreased from 0.68 to less than 0.1 eV while that for hole slightly increased from 0.43 to 0.53 eV. In order to identify the current conduction mechanisms, the experimental current-temperature-voltage characteristics for the n-type diode were fitted based on various models for transport of charge carrier in Schottky diodes. As the result, the large change in effective SBH for electron is ascribed to trap-assisted tunneling rather than barrier height inhomogeneity.

Densely-packed ZnTPPs Monolayer on the Rutile TiO2(110)-(1×1) Surface: Adsorption Behavior and Energy Level Alignment

PubMed Central

Rangan, Sylvie; Ruggieri, Charles; Bartynski, Robert; Martínez, José Ignacio; Flores, Fernando; Ortega, José

2016-01-01

The adsorption of a densely packed Zinc(II) tetraphenylporphyrin monolayer on a rutile TiO2(110)-(1×1) surface has been studied using a combination of experimental and theoretical methods, aimed at analyzing the relation between adsorption behavior and barrier height formation. The adsorption configuration of ZnTPP was determined from scanning tunnel microscopy (STM) imaging, density functional theory (DFT) calculations and STM image simulation. The corresponding energy alignment was experimentally determined from X-ray and UV-photoemission spectroscopies and inverse photoemission spectroscopy. These results were found in good agreement with an appropriately corrected DFT model, pointing to the importance of local bonding and intermolecular interactions in the establishment of barrier heights. PMID:26998188

Step edge influence on barrier height and contact area in vertical heterojunctions between epitaxial graphene and n-type 4H-SiC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tadjer, M. J., E-mail: marko.tadjer.ctr@nrl.navy.mil; Nyakiti, L. O.; Robinson, Z.

2014-02-17

Vertical rectifying contacts of epitaxial graphene grown by Si sublimation on the Si-face of 4H-SiC epilayers were investigated. Forward bias preferential conduction through the step edges was correlated by linear current density normalization. This phenomenon was observed on samples with 2.7–5.8 monolayers of epitaxial graphene as determined by X-ray photoelectron spectroscopy. A modified Richardson plot was implemented to extract the barrier height (0.81 eV at 290 K, 0.99 eV at 30 K) and the electrically dominant SiC step length of a Ti/Al contact overlapping a known region of approximately 0.52 μm wide SiC terraces.

Generation of valley-polarized electron beam in bilayer graphene

NASA Astrophysics Data System (ADS)

Park, Changsoo

2015-12-01

We propose a method to produce valley-polarized electron beams using a bilayer graphene npn junction. By analyzing the transmission properties of electrons through the junction with zigzag interface in the presence of trigonal warping, we observe that there exist a range of incident energies and barrier heights in which transmitted electrons are well polarized and collimated. From this observation and by performing numerical simulations, it is demonstrated that valley-dependent electronic currents with nearly perfect polarization can be generated. We also show that the peak-to-peak separation angle between the polarized currents is tunable either by incident energy or by barrier height each of which is controlled by using top and back gate voltages. The results can be used for constructing an electron beam splitter to produce valley-polarized currents.

Uncertainties in derived temperature-height profiles

NASA Technical Reports Server (NTRS)

Minzner, R. A.

1974-01-01

Nomographs were developed for relating uncertainty in temperature T to uncertainty in the observed height profiles of both pressure p and density rho. The relative uncertainty delta T/T is seen to depend not only upon the relative uncertainties delta P/P or delta rho/rho, and to a small extent upon the value of T or H, but primarily upon the sampling-height increment Delta h, the height increment between successive observations of p or delta. For a fixed value of delta p/p, the value of delta T/T varies inversely with Delta h. No limit exists in the fineness of usable height resolution of T which may be derived from densities, while a fine height resolution in pressure-height data leads to temperatures with unacceptably large uncertainties.

Formic acid catalyzed hydrolysis of SO3 in the gas phase: a barrierless mechanism for sulfuric acid production of potential atmospheric importance.

PubMed

Hazra, Montu K; Sinha, Amitabha

2011-11-02

Computational studies at the B3LYP/6-311++G(3df,3pd) and MP2/6-311++G(3df,3pd) levels are performed to explore the changes in reaction barrier height for the gas phase hydrolysis of SO(3) to form H(2)SO(4) in the presence of a single formic acid (FA) molecule. For comparison, we have also performed calculations for the reference reaction involving water assisted hydrolysis of SO(3) at the same level. Our results show that the FA assisted hydrolysis of SO(3) to form H(2)SO(4) is effectively a barrierless process. The barrier heights for the isomerization of the SO(3)···H(2)O···FA prereactive collision complex, which is the rate limiting step in the FA assisted hydrolysis, are found to be respectively 0.59 and 0.08 kcal/mol at the B3LYP/6-311++G(3df,3pd) and MP2/6-311++G(3df,3pd) levels. This is substantially lower than the ~7 kcal/mol barrier for the corresponding step in the hydrolysis of SO(3) by two water molecules--which is currently the accepted mechanism for atmospheric sulfuric acid production. Simple kinetic analysis of the relative rates suggests that the reduction in barrier height facilitated by FA, combined with the greater stability of the prereactive SO(3)···H(2)O···FA collision complex compared to SO(3)···H(2)O···H(2)O and the rather plentiful atmospheric abundance of FA, makes the formic acid mediated hydrolysis reaction a potentially important pathway for atmospheric sulfuric acid production.

Stability and bistability in a one-dimensional model of coastal foredune height

NASA Astrophysics Data System (ADS)

Goldstein, Evan B.; Moore, Laura J.

2016-05-01

On sandy coastlines, foredunes provide protection from coastal storms, potentially sheltering low areas—including human habitat—from elevated water level and wave erosion. In this contribution we develop and explore a one-dimensional model for coastal dune height based on an impulsive differential equation. In the model, coastal foredunes continuously grow in a logistic manner as the result of a biophysical feedback and they are destroyed by recurrent storm events that are discrete in time. Modeled dunes can be in one of two states: a high "resistant-dune" state or a low "overwash-flat" state. The number of stable states (equilibrium dune heights) depends on the value of two parameters, the nondimensional storm frequency (the ratio of storm frequency to the intrinsic growth rate of dunes) and nondimensional storm magnitude (the ratio of total water level during storms to the maximum theoretical dune height). Three regions of phase space exist (1) when nondimensional storm frequency is small, a single high resistant-dune attracting state exists; (2) when both the nondimensional storm frequency and magnitude are large, there is a single overwash-flat attracting state; (3) within a defined region of phase space model dunes exhibit bistable behavior—both the resistant-dune and the low overwash-flat states are stable. Comparisons to observational studies suggest that there is evidence for each state to exist independently, the coexistence of both states (i.e., segments of barrier islands consisting of overwash-flats and segments of islands having large dunes that resist erosion by storms), as well as transitions between states.

The Use of Arm Span as a Substitute for Height in Calculating Body Mass Index (BMI) for Spine Deformity Patients.

PubMed

Opoku, Harriet; Yirerong, Theresa; Osei-Onwona, Belinda; Boachie-Adjei, Oheneba

To compare arm span and height in body mass index (BMI) calculation in patients with spinal curvature and investigate their impact on interpretation of BMI. Prospective case-control cohorts. The BMI value is based on weight to height ratio. Spine deformity patients experience height loss and its use in calculating BMI is likely to produce errors. A surrogate for height should therefore be sought in BMI determination. Ninety-three spine deformity patients were matched with 64 normal children. Anthropometric values (height, arm span, and weight) and spinal curve were obtained. BMIs using arm span and height were calculated, and statistical analysis performed to assess the relationship between BMI/height and BMI/arm span in both groups as well as the relationship between these values and Arm Span to Height difference (Delta AH). There were 46 males and 47 females, the average age was 15.5 years in Group 1 versus 33 males and 31 females, average age 14.8 years in Group 2. Major scoliosis in Group 1 averaged 125.7° (21° to 252°). The extreme curves show vertebral transposition, with overlapping segments making it more than 180°. A logistic regression showed that there was linearity in BMI scores (R 2 = 0.97) for both arm span and height (R 2 = 0.94) in group 2 patients. For group 1 patients there was a significant difference in the BMI values when comparing BMI/arm span versus BMI/height (p < .0001). Mean BMI values using height was overstated by 2.8 (18.6%). The threshold at which BMI score must be calculated using arm span as opposed to the height (Delta AH) was determined to be 3 cm. Spine deformity patients experience height loss, which can impact their true BMI values thereby giving an erroneous impression of their nutritional status. The arm span should be used in patients with Delta AH >3 cm to properly assess nutritional status. Copyright © 2017 Scoliosis Research Society. Published by Elsevier Inc. All rights reserved.

Urban sound energy reduction by means of sound barriers

NASA Astrophysics Data System (ADS)

Iordache, Vlad; Ionita, Mihai Vlad

2018-02-01

In urban environment, various heating ventilation and air conditioning appliances designed to maintain indoor comfort become urban acoustic pollution vectors due to the sound energy produced by these equipment. The acoustic barriers are the recommended method for the sound energy reduction in urban environment. The current sizing method of these acoustic barriers is too difficult and it is not practical for any 3D location of the noisy equipment and reception point. In this study we will develop based on the same method a new simplified tool for acoustic barriers sizing, maintaining the same precision characteristic to the classical method. Abacuses for acoustic barriers sizing are built that can be used for different 3D locations of the source and the reception points, for several frequencies and several acoustic barrier heights. The study case presented in the article represents a confirmation for the rapidity and ease of use of these abacuses in the design of the acoustic barriers.

Characterization of a SiC MIS Schottky diode as RBS particle detector

NASA Astrophysics Data System (ADS)

Kaufmann, I. R.; Pick, A. C.; Pereira, M. B.; Boudinov, H. I.

2018-02-01

A 4H-SiC Schottky diode was investigated as a particle detector for Rutherford Backscattering Spectroscopy (RBS) experiment. The device was fabricated on a commercial 4H-SiC epitaxial n-type layer grown onto a 4H-SiC n+ type substrate wafer doped with nitrogen. Hafnium oxide with thickness of 1 nm was deposited by Atomic Layer Deposition and 10 nm of Ni were deposited by sputtering to form the Ni/HfO2/4H-SiC MIS Schottky structure. Current-Voltage curves with variable temperature were measured to extract the real Schottky Barrier Height (0.32 V) and ideality factor values (1.15). Reverse current and Capacitance-Voltage measurements were performed on the 4H-SiC detector and compared to a commercial Si barrier detector acquired from ORTEC. RBS data for four alpha energies (1, 1.5, 2 and 2.5 MeV) were collected from an Au/Si sample using the fabricated SiC and the commercial Si detectors simultaneously. The energy resolution for the fabricated detector was estimated to be between 75 and 80 keV.

Metal-organic semiconductor interfacial barrier height determination from internal photoemission signal in spectral response measurements

NASA Astrophysics Data System (ADS)

Kumar, Sandeep; Iyer, S. Sundar Kumar

2017-04-01

Accurate and convenient evaluation methods of the interfacial barrier ϕb for charge carriers in metal semiconductor (MS) junctions are important for designing and building better opto-electronic devices. This becomes more critical for organic semiconductor devices where a plethora of molecules are in use and standardised models applicable to myriads of material combinations for the different devices may have limited applicability. In this paper, internal photoemission (IPE) from spectral response (SR) in the ultra-violet to near infra-red range of different MS junctions of metal-organic semiconductor-metal (MSM) test structures is used to determine more realistic MS ϕb values. The representative organic semiconductor considered is [6, 6]-phenyl C61 butyric acid methyl ester, and the metals considered are Al and Au. The IPE signals in the SR measurement of the MSM device are identified and separated before it is analysed to estimate ϕb for the MS junction. The analysis of IPE signals under different bias conditions allows the evaluation of ϕb for both the front and back junctions, as well as for symmetric MSM devices.

Computational Study of Chemical Reactivity Using Information-Theoretic Quantities from Density Functional Reactivity Theory for Electrophilic Aromatic Substitution Reactions.

PubMed

Wu, Wenjie; Wu, Zemin; Rong, Chunying; Lu, Tian; Huang, Ying; Liu, Shubin

2015-07-23

The electrophilic aromatic substitution for nitration, halogenation, sulfonation, and acylation is a vastly important category of chemical transformation. Its reactivity and regioselectivity is predominantly determined by nucleophilicity of carbon atoms on the aromatic ring, which in return is immensely influenced by the group that is attached to the aromatic ring a priori. In this work, taking advantage of recent developments in quantifying nucleophilicity (electrophilicity) with descriptors from the information-theoretic approach in density functional reactivity theory, we examine the reactivity properties of this reaction system from three perspectives. These include scaling patterns of information-theoretic quantities such as Shannon entropy, Fisher information, Ghosh-Berkowitz-Parr entropy and information gain at both molecular and atomic levels, quantitative predictions of the barrier height with both Hirshfeld charge and information gain, and energetic decomposition analyses of the barrier height for the reactions. To that end, we focused in this work on the identity reaction of the monosubstituted-benzene molecule reacting with hydrogen fluoride using boron trifluoride as the catalyst in the gas phase. We also considered 19 substituting groups, 9 of which are ortho/para directing and the other 9 meta directing, besides the case of R = -H. Similar scaling patterns for these information-theoretic quantities found for stable species elsewhere were disclosed for these reactions systems. We also unveiled novel scaling patterns for information gain at the atomic level. The barrier height of the reactions can reliably be predicted by using both the Hirshfeld charge and information gain at the regioselective carbon atom. The energy decomposition analysis ensued yields an unambiguous picture about the origin of the barrier height, where we showed that it is the electrostatic interaction that plays the dominant role, while the roles played by exchange-correlation and steric effects are minor but indispensable. Results obtained in this work should shed new light for better understanding of the factors governing the reactivity for this class of reactions and assisting ongoing efforts for the design of new and more efficient catalysts for such kind of transformations.

Fission barriers at the end of the chart of the nuclides

DOE PAGES

Möller, Peter; Sierk, Arnold J.; Ichikawa, Takatoshi; ...

2015-02-12

We present calculated fission-barrier heights for 5239 nuclides for all nuclei between the proton and neutron drip lines with 171 ≤ A ≤ 330. The barriers are calculated in the macroscopic-microscopic finite-range liquid-drop (FRLDM) with a 2002 set of macroscopic-model parameters. The saddle-point energies are determined from potential-energy surfaces based on more than five million different shapes, defined by five deformation parameters in the three-quadratic-surface shape parametrization: elongation, neck diameter, left-fragment spheroidal deformation, right-fragment spheroidal deformation, and nascent-fragment mass asymmetry. The energy of the ground state is determined by calculating the lowest-energy configuration in both the Nilsson perturbed-spheroid (ϵ) andmore » the spherical-harmonic (β) parametrizations, including axially asymmetric deformations. The lower of the two results (correcting for zero-point motion) is defined as the ground-state energy. The effect of axial asymmetry on the inner barrier peak is calculated in the (ϵ,γ) parametrization. We have earlier benchmarked our calculated barrier heights to experimentally extracted barrier parameters and found average agreement to about one MeV for known data across the nuclear chart. Here we do additional benchmarks and investigate the qualitative and, when possible, quantitative agreement and/or consistency with data on β-delayed fission, isotope generation along prompt-neutron-capture chains in nuclear-weapons tests, and superheavy-element stability. In addition these studies all indicate that the model is realistic at considerable distances in Z and N from the region of nuclei where its parameters were determined.« less

Contact doping, Klein tunneling, and asymmetry of shot noise in suspended graphene

NASA Astrophysics Data System (ADS)

Laitinen, Antti; Paraoanu, G. S.; Oksanen, Mika; Craciun, Monica F.; Russo, Saverio; Sonin, Edouard; Hakonen, Pertti

2016-01-01

The inherent asymmetry of the electric transport in graphene is attributed to Klein tunneling across barriers defined by p n interfaces between positively and negatively charged regions. By combining conductance and shot noise experiments, we determine the main characteristics of the tunneling barrier (height and slope) in a high-quality suspended sample with Au/Cr/Au contacts. We observe an asymmetric resistance Rodd=100 -70 Ω across the Dirac point of the suspended graphene at carrier density | nG|=(0.3 -4 ) × 1011cm-2 , while the Fano factor displays a nonmonotonic asymmetry in the range Fodd˜0.03 -0.1. Our findings agree with analytical calculations based on the Dirac equation with a trapezoidal barrier. Comparison between the model and the data yields the barrier height for tunneling, an estimate of the thickness of the p n interface d <20 nm, and the contact region doping corresponding to a Fermi level offset of ˜-18 meV. The strength of pinning of the Fermi level under the metallic contact is characterized in terms of the contact capacitance Cc=19 ×10-6 F/cm2 . Additionally, we show that the gate voltage corresponding to the Dirac point is given by the difference in work functions between the backgate material and graphene.

Successful application of the DBLOC method to the hydroxylation of camphor by cytochrome p450

PubMed Central

Jerome, Steven V.; Hughes, Thomas F.

2015-01-01

Abstract The activation barrier for the hydroxylation of camphor by cytochrome P450 was computed using a mixed quantum mechanics/molecular mechanics (QM/MM) model of the full protein‐ligand system and a fully QM calculation using a cluster model of the active site at the B3LYP/LACVP*/LACV3P** level of theory, which consisted of B3LYP/LACV3P** single point energies computed at B3LYP/LACVP* optimized geometries. From the QM/MM calculation, a barrier height of 17.5 kcal/mol was obtained, while the experimental value was known to be less than or equal to 10 kcal/mol. This process was repeated using the D3 correction for hybrid DFT in order to investigate whether the inadequate treatment of dispersion interaction was responsible for the overestimation of the barrier. While the D3 correction does reduce the computed barrier to 13.3 kcal/mol, it was still in disagreement with experiment. After application of a series of transition metal optimized localized orbital corrections (DBLOC) and without any refitting of parameters, the barrier was further reduced to 10.0 kcal/mol, which was consistent with the experimental results. The DBLOC method to C—H bond activation in methane monooxygenase (MMO) was also applied, as a second, independent test. The barrier in MMO was known, by experiment, to be 15.4 kcal/mol.1 After application of the DBLOC corrections to the MMO barrier compute by B3LYP, in a previous study, and accounting for dispersion with Grimme's D3 method, the unsigned deviation from experiment was improved from 3.2 to 2.3 kcal/mol. These results suggested that the combination of dispersion plus localized orbital corrections could yield significant quantitative improvements in modeling the catalytic chemistry of transition‐metal containing enzymes, within the limitations of the statistical errors of the model, which appear to be on the order of approximately 2 kcal/mole. PMID:26441133

Reference values for airway resistance in newborns, infants and preschoolers from a Latin American population.

PubMed

Gochicoa, Laura G; Thomé-Ortiz, Laura P; Furuya, María E Y; Canto, Raquel; Ruiz-García, Martha E; Zúñiga-Vázquez, Guillermo; Martínez-Ramírez, Filiberto; Vargas, Mario H

2012-05-01

Several studies have determined reference values for airway resistance measured by the interrupter technique (Rint) in paediatric populations, but only one has been done on Latin American children, and no studies have been performed on Mexican children. Moreover, these previous studies mostly included children aged 3 years and older; therefore, information regarding Rint reference values for newborns and infants is scarce. Rint measurements were performed on preschool children attending eight kindergartens (Group 1) and also on sedated newborns, infants and preschool children admitted to a tertiary-level paediatric hospital due to non-cardiopulmonary disorders (Group 2). In both groups, Rint values were inversely associated with age, weight and height, but the strongest association was with height. The linear regression equation for Group 1 (n = 209, height 86-129 cm) was Rint = 2.153 - 0.012 × height (cm) (standard deviation of residuals 0.181 kPa/L/s). The linear regression equation for Group 2 (n = 55, height 52-113 cm) was Rint = 4.575 - 0.035 × height (cm) (standard deviation of residuals 0.567 kPa/L/s). Girls tended to have slightly higher Rint values than boys, a difference that diminished with increasing height. In this study, Rint reference values applicable to Mexican children were determined, and these values are probably also applicable to other paediatric populations with similar Spanish-Amerindian ancestries. There was an inverse relationship between Rint and height, with relatively large between-subject variability. © 2012 The Authors. Respirology © 2012 Asian Pacific Society of Respirology.

Energy Levels in Quantum Wells.

NASA Astrophysics Data System (ADS)

Zang, Jan Xin

Normalized analytical equations for eigenstates of an arbitrary one-dimensional configuration of square potentials in a well have been derived. The general formulation is used to evaluate the energy levels of a particle in a very deep potential well containing seven internal barriers. The configuration can be considered as a finite superlattice sample or as a simplified model for a sample with only several atom layers. The results are shown in graphical forms as functions of the height and width of the potential barriers and as functions of the ratio of the effective mass in barrier to the mass in well. The formation of energy bands and surface eigenstates from eigenstates of a deep single well, the coming close of two energy bands and a surface state which are separate ordinarily, and mixing of the wave function of a surface state with the bulk energy bands are seen. Then the normalized derivation is extended to study the effect of a uniform electric field applied across a one-dimensional well containing an internal configuration of square potentials The general formulation is used to calculate the electric field dependence of the energy levels of a deep well with five internal barriers. Typical results are shown in graphical forms as functions of the barrier height, barrier width, barrier effective mass and the field strength. The formation of Stark ladders and surface states from the eigenstates of a single deep well in an electric field, the localization process of wave functions with changing barrier height, width, and field strength and their anticrossing behaviors are seen. The energy levels of a hydrogenic impurity in a uniform medium and in a uniform magnetic field are calculated with variational methods. The energy eigenvalues for the eigenstates with major quantum number less than or equal to 3 are obtained. The results are consistent with previous results. Furthermore, the energy levels of a hydrogenic impurity at the bottom of a one-dimensional parabolic quantum well with a magnetic field normal to the plane of the well are calculated with the finite-basis-set variational method. The limit of small radial distance and the limit of great radial distance are considered to choose a set of proper basis functions. It is found that the energy levels increase with increasing parabolic parameter alpha and increase with increasing normalized magnetic field strength gamma except those levels with magnetic quantum number m < 0 at small gamma.

Application of dimensional analysis to predict the performance of rockfall barrier

NASA Astrophysics Data System (ADS)

Spadari, M.; Giacomini, A.; Buzzi, O.; Hambleton, J.

2012-04-01

Natural hazards involving rocks or rock slopes are responsible for loss of life and damage to infrastructure and are consequently widely studied. Rock fall barriers are a common type of protection structures that is usually designed on the basis of total impact energy. However, the systems are usually tested in free fall where the predominant component of energy is kinematic and it has been shown that there is not a unique relationship between the response of a barrier and the kinetic energy of the impacting block. In particular, recent studies have discussed the so called "bullet effect" i.e. relatively small blocks traveling at high speed can perforate the barriers yet having acceptable level of energy. This effect compromises the use of kinetic energy as an adequate design criterion since there is not a threshold value defining clearly acceptable and unacceptable values of energy. This issue can be addressed empirically by using different block sizes when it comes to test a system. However, the literature still lacks a characterization of a rockfall barrier performance regarding the bullet effect. This note presents the results of the application of dimensional analysis to the physical problem of the bullet effect. This latter has been formulated as a function involving eight key variables: v = f(ρ, K, σy, H, A, Db,Dw) where v is the minimum speed of a given block to break the barrier, ρgs the density of the block, Kis the stiffness of the system, σy is the strength of the wires, H is the height of the barrier, A is the aperture of the mesh, Db is the dimension of the block and Dw is the diameter of the wire. Applying the Buckingham Pi theorem allows reducing the equation above to a simpler problem involving only three dimensionless parameters: E*=F(S*, G*) Where E* is the performance parameter, S* is the strength-stiffness parameter and G* is the geometrical parameters defined as: E*= (ρ.v2.H)/K S*=K/(H.gσy) And G*=A-0.25.Db-0.75.Db F in the simplified equation is referred to as the Rockfall Barrier Performance, or RoBaP, Model. Results suggest that the dimensional analysis can satisfactorily be used to assess the performance of a barrier when impacted by variable block size. A calibration-prediction exercise has been conducted using data form the literature to assess the predictive capability of the RoBaP model. It has been found that the RoBaP model gives satisfactory results. In particular, the progressive loss of performance of the rock fall barrier as the block size diminishes has been well captured.

Observation of quantum oscillation of work function in ultrathin-metal/semiconductor junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takhar, Kuldeep; Meer, Mudassar; Khachariya, Dolar

2015-09-15

Quantization in energy level due to confinement is generally observed for semiconductors. This property is used for various quantum devices, and it helps to improve the characteristics of conventional devices. Here, the authors have demonstrated the quantum size effects in ultrathin metal (Ni) layers sandwiched between two large band-gap materials. The metal work function is found to oscillate as a function of its thickness. The thermionic emission current bears the signature of the oscillating work function, which has a linear relationship with barrier heights. This methodology allows direct observation of quantum oscillations in metals at room temperature using a Schottkymore » diode and electrical measurements using source-measure-units. The observed phenomena can provide additional mechanism to tune the barrier height of metal/semiconductor junctions, which are used for various electronic devices.« less

A numerical model for explaining the role of the interface morphology in composite solar cells

NASA Astrophysics Data System (ADS)

Martin, C. M.; Burlakov, V. M.; Assender, H. E.; Barkhouse, D. A. R.

2007-11-01

We have developed a numerical model that simulates the operation of organic/inorganic photovoltaic devices. Using this model, we have investigated the effect of the interface morphology and have shown that for a given system, there is both a most efficient device thickness and the interfacial feature size for overall power conversion. The variation of current-voltage (I-V) curves with differing recombination rates, anode barrier height, and light intensity has been simulated with reducing the recombination rate and lowering the anode barrier height shown to lead to improved open circuit voltages and fill factors. Through this model, we show that the increase in fill factor observed when the lithium salt Li[CF3SO2]2N is added to devices can be explained by an increase in the polymer hole mobility.

Perspective analysis of tri gate germanium tunneling field-effect transistor with dopant segregation region at source/drain

NASA Astrophysics Data System (ADS)

Liu, Liang-kui; Shi, Cheng; Zhang, Yi-bo; Sun, Lei

2017-04-01

A tri gate Ge-based tunneling field-effect transistor (TFET) has been numerically studied with technology computer aided design (TCAD) tools. Dopant segregated Schottky source/drain is applied to the device structure design (DS-TFET). The characteristics of the DS-TFET are compared and analyzed comprehensively. It is found that the performance of n-channel tri gate DS-TFET with a positive bias is insensitive to the dopant concentration and barrier height at n-type drain, and that the dopant concentration and barrier height at a p-type source considerably affect the device performance. The domination of electron current in the entire BTBT current of this device accounts for this phenomenon and the tri-gate DS-TFET is proved to have a higher performance than its dual-gate counterpart.

Internal Dynamics of Water Attached to a Photoacidic Substrate: High Resolution Electronic Spectroscopy of β-NAPHTHOL-WATER in the Gas Phase.

NASA Astrophysics Data System (ADS)

Fleisher, Adam J.; Young, Justin W.; Pratt, David W.

2010-06-01

An understanding of the structure and internal dynamics of water attached to the photoacid β-naphthol is attainable through rotationally resolved electronic spectroscopy. Here, we present rotational constants for the 1:1 acid-base cluster in both S0 and S1, which provide the location of water within the cluster, as well as the barrier height to internal rotation of water in each electronic state. The barrier height decreases slightly upon excitation, from 206 wn in S0, to 182 wn in S1. There is also little evidence of a large change in water location, orientation, or overall hydrogen bond length upon irradiation with UV light. Thus, a single water molecule has relatively little affect on the substrate photo-acidity measured in the liquid phase.

Integrating millennial and interdecadal shoreline changes: Morpho-sedimentary investigation of two prograded barriers in southeastern Australia

NASA Astrophysics Data System (ADS)

Oliver, T. S. N.; Tamura, T.; Hudson, J. P.; Woodroffe, C. D.

2017-07-01

Prograded barriers are distinctive coastal landforms preserving the position of past shorelines as low relief, shore-parallel ridges composed of beach sediments and commonly adorned with variable amounts of dune sand. Prograded barriers have been valued as coastal archives which contain palaeoenvironmental information, however integrating the millennial timescale geological history of barriers with observed inter-decadal modern beach processes has proved difficult. Technologies such as airborne LiDAR, ground penetrating radar (GPR) and optically stimulated luminescence dating (OSL) were utilised at Boydtown and Wonboyn, in southeastern Australia, and combined with previously reported radiocarbon dates and offshore seismic and sedimentological data to reconstruct the morpho-sedimentary history of prograded barrier systems. These technologies enabled reconstruction of geological timescale processes integrated with an inter-decadal model of ridge formation explaining the GPR-imaged subsurface character of the barriers. Both the Boydtown and Wonboyn barriers began prograding 7500-8000 years ago when sea level attained at or near present height along this coastline and continued prograding until the present-day with an initially slower rate of shoreline advancement. Sources of sediment for progradation appear to be the inner shelf and shoreface with a large shelf sand body likely contributing to progradation at Wonboyn. The Towamba River seems to have delivered sediment to Twofold Bay during flood events after transitioning to a mature estuarine system sometime after 4000 cal. yr BP. Some of this material appears to have been reworked onto the Boydtown barrier, increasing the rate of progradation in the seaward 50% of the barrier deposited over the past 1500 years. The GPR imaged beachfaces are shown to have similar geometry to beach profiles following recent storm events and a model of ridge formation involving cut and fill of the beachface, and dune building in the backshore, explains the character of the preserved beachface record and the morphology of the ridges. This model is applicable to future management of individual beaches where such beaches are subject to ongoing cut and fill, dune building processes and inherited sediment budget conditions.

An Updated Equilibrium Machine

NASA Astrophysics Data System (ADS)

Schultz, Emeric

2008-08-01

A device that can demonstrate equilibrium, kinetic, and thermodynamic concepts is described. The device consists of a leaf blower attached to a plastic container divided into two chambers by a barrier of variable size and form. Styrofoam balls can be exchanged across the barrier when the leaf blower is turned on and various air pressures are applied. Equilibrium can be approached from different distributions of balls in the container under different conditions. The Le Châtelier principle can be demonstrated. Kinetic concepts can be demonstrated by changing the nature of the barrier, either changing the height or by having various sized holes in the barrier. Thermodynamic concepts can be demonstrated by taping over some or all of the openings and restricting air flow into container on either side of the barrier.

Effects of ultrathin oxides in conducting MIS structures on GaAs

NASA Technical Reports Server (NTRS)

Childs, R. B.; Ruths, J. M.; Sullivan, T. E.; Fonash, S. J.

1978-01-01

Schottky barrier-type GaAs baseline devices (semiconductor surface etched and then immediately metalized) and GaAs conducting metal oxide-semiconductor devices are fabricated and characterized. The baseline surfaces (no purposeful oxide) are prepared by a basic or an acidic etch, while the surface for the MIS devices are prepared by oxidizing after the etch step. The metallizations used are thin-film Au, Ag, Pd, and Al. It is shown that the introduction of purposeful oxide into these Schottky barrier-type structures examined on n-type GaAs modifies the barrier formation, and that thin interfacial layers can modify barrier formation through trapping and perhaps chemical reactions. For Au- and Pd-devices, enhanced photovoltaic performance of the MIS configuration is due to increased barrier height.

A simple strategy to realize biomimetic surfaces with controlled anisotropic wetting

NASA Astrophysics Data System (ADS)

Wu, Dong; Chen, Qi-Dai; Yao, Jia; Guan, Yong-Chao; Wang, Jian-Nan; Niu, Li-Gang; Fang, Hong-Hua; Sun, Hong-Bo

2010-02-01

The study of anisotropic wetting has become one of the most important research areas in biomimicry. However, realization of controlled anisotropic surfaces remains challenging. Here we investigated anisotropic wetting on grooves with different linewidth, period, and height fabricated by laser interference lithography and found that the anisotropy strongly depended on the height. The anisotropy significantly increased from 9° to 48° when the height was changed from 100 nm to 1.3 μm. This was interpreted by a thermodynamic model as a consequence of the increase of free energy barriers versus the height increase. According to the relationship, controlled anisotropic surfaces were rapidly realized by adjusting the grooves' height that was simply accomplished by changing the resin thickness. Finally, the perpendicular contact angle was further enhanced to 131°±2° by surface modification, which was very close to 135°±3° of a common grass leaf.

Influence of Ag, Cd or Pb Addition on Electrical and Dielectric Properties of Bulk Glassy Se-Ge

NASA Astrophysics Data System (ADS)

El-Metwally, E. G.; Shakra, A. M.

2018-05-01

Bulk glassy samples of Se0.7Ge0.3 and Se0.7Ge0.25 X 0.05 (X = Ag, Cd or Pb) chalcogenide glass have been prepared by melt-quenching method. The studied compositions were examined in powder form by x-ray diffraction analysis. The direct-current (dc) conductivity σ_{{dc}} was measured for bulk samples in the temperature range from 303 K to 433 K, revealing enhancement with temperature for all samples. The results indicate two values of activation energy ( Δ E_{{σ1 }} and Δ E_{{σ2 }} ) due to two conduction mechanisms. Measurements of the alternating-current (ac) conductivity σ_{{ac}} ( ω ) and dielectric properties for bulk samples were carried out in the temperature range from 303 K to 433 K and frequency range from 1 kHz to 1 MHz. The ac conductivity σ_{{ac}} ( ω ) was temperature dependent and proportional to ωS , where S is the frequency exponent, which reduced with rising temperature, and ω is the angular frequency. These results are discussed based on a correlated barrier hopping model. The calculated values of the maximum height of the barrier W_{{M}} for each composition are consistent with carrier hopping over a potential barrier. The density of localized states N( {E_{{F}} } ) at the Fermi level lay in the range from 1019 eV-1 cm-3 to 1020 eV-1 cm-3, and increased with temperature. The dielectric constant ɛ1 ( ω ) and loss ɛ2 ( ω ) increased with temperature but decreased with frequency. The values of σ_{{dc}} , σ_{{ac}} ( ω ) , ɛ1 ( ω ) , and ɛ2 ( ω ) increased with temperature and with addition of Ag, Cd or Pb. The observed increase was greater for Se0.7Ge0.25Pb0.05 than for Se0.7Ge0.25Cd0.05, which was greater than for Se0.7Ge0.25Ag0.05.

Influence of interface inhomogeneities in thin-film Schottky diodes

NASA Astrophysics Data System (ADS)

Wilson, Joshua; Zhang, Jiawei; Li, Yunpeng; Wang, Yiming; Xin, Qian; Song, Aimin

2017-11-01

The scalability of thin-film transistors has been well documented, but there have been very few investigations into the effects of device scalability in Schottky diodes. Indium-gallium-zinc-oxide (IGZO) Schottky diodes were fabricated with IGZO thicknesses of 50, 150, and 250 nm. Despite the same IGZO-Pt interface and Schottky barrier being formed in all devices, reducing the IGZO thickness caused a dramatic deterioration of the current-voltage characteristics, most notably increasing the reverse current by nearly five orders of magnitude. Furthermore, the forward characteristics display an increase in the ideality factor and a reduction in the barrier height. The origins of this phenomenon have been elucidated using device simulations. First, when the semiconductor layer is fully depleted, the electric field increases with the reducing thickness, leading to an increased diffusion current. However, the effects of diffusion only offer a small contribution to the huge variations in reverse current seen in the experiments. To fully explain this effect, the role of inhomogeneities in the Schottky barrier height has been considered. Contributions from lower barrier regions (LBRs) are found to dominate the reverse current. The conduction band minimum below these LBRs is strongly dependent upon thickness and bias, leading to reverse current variations as large as several orders of magnitude. Finally, it is demonstrated that the thickness dependence of the reverse current is exacerbated as the magnitude of the inhomogeneities is increased and alleviated in the limit where the LBRs are large enough not to be influenced by the adjacent higher barrier regions.

Current transient spectroscopy for trapping analysis on Au-free AlGaN/GaN Schottky barrier diode

NASA Astrophysics Data System (ADS)

Hu, J.; Stoffels, S.; Lenci, S.; Bakeroot, B.; Venegas, R.; Groeseneken, G.; Decoutere, S.

2015-02-01

This paper presents a combined technique of high voltage off-state stress and current transient measurements to investigate the trapping/de-trapping characteristics of Au-free AlGaN/GaN Schottky barrier diodes. The device features a symmetric three-terminal structure with a central anode contact surrounded by two separate cathodes. Under the diode off-state stress conditions, the two separate cathodes were electrically shorted. The de-trapping dynamics was studied by monitoring the recovery of the two-dimensional electron gas (2DEG) current at different temperatures by applying 0.5 V at cathode 2 while grounding cathode 1. During the recovery, the anode contact acts as a sensor of changes in diode leakage current. This leakage variation was found to be mainly due to the barrier height variation. With this method, the energy level and capture cross section of different traps in the AlGaN/GaN Schottky barrier diode can be extracted. Furthermore, the physical location of different trapping phenomena is indicated by studying the variation of the diode leakage current during the recovery. We have identified two distinct trapping mechanisms: (i) electron trapping at the AlGaN surface in the vicinity of the Schottky contact which results in the leakage reduction (barrier height ϕB increase) together with RON degradation; (ii) the electron trapping in the GaN channel layer which partially depletes the 2DEG. The physical origin of the two different traps is discussed in the text.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Möller, Peter; Sierk, Arnold J.; Ichikawa, Takatoshi

We present calculated fission-barrier heights for 5239 nuclides for all nuclei between the proton and neutron drip lines with 171 ≤ A ≤ 330. The barriers are calculated in the macroscopic-microscopic finite-range liquid-drop (FRLDM) with a 2002 set of macroscopic-model parameters. The saddle-point energies are determined from potential-energy surfaces based on more than five million different shapes, defined by five deformation parameters in the three-quadratic-surface shape parametrization: elongation, neck diameter, left-fragment spheroidal deformation, right-fragment spheroidal deformation, and nascent-fragment mass asymmetry. The energy of the ground state is determined by calculating the lowest-energy configuration in both the Nilsson perturbed-spheroid (ϵ) andmore » the spherical-harmonic (β) parametrizations, including axially asymmetric deformations. The lower of the two results (correcting for zero-point motion) is defined as the ground-state energy. The effect of axial asymmetry on the inner barrier peak is calculated in the (ϵ,γ) parametrization. We have earlier benchmarked our calculated barrier heights to experimentally extracted barrier parameters and found average agreement to about one MeV for known data across the nuclear chart. Here we do additional benchmarks and investigate the qualitative and, when possible, quantitative agreement and/or consistency with data on β-delayed fission, isotope generation along prompt-neutron-capture chains in nuclear-weapons tests, and superheavy-element stability. In addition these studies all indicate that the model is realistic at considerable distances in Z and N from the region of nuclei where its parameters were determined.« less

Sensitivity of the nuclear deformability and fission barriers to the equation of state

NASA Astrophysics Data System (ADS)

Seif, W. M.; Anwer, Hisham

2018-07-01

The model-dependent analysis of the fission data impacts the extracted fission-related quantities, which are not directly observables, such as the super- and hyperdeformed isomeric states and their energies. We investigated the model dependence of the deformability of a nucleus and its fission barriers on the nuclear equation of state. Within the microscopic-macroscopic model based on a large number of Skyrme nucleon-nucleon interactions, the total energy surfaces and the double-humped fission barrier of 230Th are calculated in a multidimensional deformation space. In addition to the ground-state (GS) and the superdeformed (SD) minima, all the investigated forces yielded a hyperdeformed (HD) minimum. The contour map of the shell-plus-pairing energy clearly displayed the three minima. We found that the GS binding energy and the deformation energy of the different deformation modes along the fission path increase with the incompressibility coefficient K0, while the fission barrier heights and the excitation energies of the SD and HD modes decrease with it. Conversely, the surface-energy coefficient asurf, the symmetry-energy, and its density-slope parameter decrease the GS energy and the deformation energies, but increase the fission barrier heights and the excitation energies. The obtained deformation parameters of the different deformation modes exhibit almost independence on K0, and on the symmetry-energy and its density-slope. The principle deformation parameters of the SD and HD isomeric states tend to decrease with asurf.

Tunable negative differential resistance in planar graphene superlattice resonant tunneling diode

NASA Astrophysics Data System (ADS)

Sattari-Esfahlan, S. M.; Fouladi-Oskuei, J.; Shojaei, S.

2017-04-01

Here, we study the negative differential resistance (NDR) of Dirac electrons in biased planar graphene superlattice (PGSL) and investigate the transport characteristics by adopted transfer matrix method within Landauer-Buttiker formalism. Our model device is based on one-dimensional Kronig-Penney type electrostatic potential in monolayer graphene deposited on a substrate, where the bias voltage is applied by two electrodes in the left and right. At Low bias voltages, we found that NDR appears due to breaking of minibands to Wannier-Stark ladders (WSLs). At the critical bias voltage, delocalization appeared by WS states leads to tunneling peak current in current-voltage (I-V) characteristics. With increasing bias voltage, crossing of rungs from various WSL results in multi-peak NDR. The results demonstrate that the structure parameters like barrier/well thickness and barrier height have remarkable effect on I-V characteristics of PGSL. In addition, Dirac gap enhances peak to valley (PVR) value due to suppressing Klein tunneling. Our results show that the tunable PVR in PGSL resonant tunneling diode can be achievable by structure parameters engineering. NDR at ultra-low bias voltages, such as 100 mV, with giant PVR of 20 is obtained. In our device, the multiple same NDR peaks with ultra-low bias voltage provide promising prospect for multi-valued memories and the low power nanoelectronic tunneling devices.

Delay time and Hartman effect in strain engineered graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xi, E-mail: xchen@shu.edu.cn; Deng, Zhi-Yong; Ban, Yue, E-mail: yban@shu.edu.cn

2014-05-07

Tunneling times, including group delay and dwell time, are studied for massless Dirac electrons transmitting through a one-dimensional barrier in strain-engineered graphene. The Hartman effect, the independence of group delay on barrier length, is induced by the strain effect, and associated with the transmission gap and the evanescent mode. The influence of barrier height/length and strain modulus/direction on the group delay is also discussed, which provides the flexibility to control the group delay with applications in graphene-based devices. The relationship between group delay and dwell time is finally derived to clarify the nature of the Hartman effect.

Determining when a set of compute nodes participating in a barrier operation on a parallel computer are ready to exit the barrier operation

DOEpatents

Blocksome, Michael A [Rochester, MN

2011-12-20

Methods, apparatus, and products are disclosed for determining when a set of compute nodes participating in a barrier operation on a parallel computer are ready to exit the barrier operation that includes, for each compute node in the set: initializing a barrier counter with no counter underflow interrupt; configuring, upon entering the barrier operation, the barrier counter with a value in dependence upon a number of compute nodes in the set; broadcasting, by a DMA engine on the compute node to each of the other compute nodes upon entering the barrier operation, a barrier control packet; receiving, by the DMA engine from each of the other compute nodes, a barrier control packet; modifying, by the DMA engine, the value for the barrier counter in dependence upon each of the received barrier control packets; exiting the barrier operation if the value for the barrier counter matches the exit value.

Micro heat barrier

DOEpatents

Marshall, Albert C.; Kravitz, Stanley H.; Tigges, Chris P.; Vawter, Gregory A.

2003-08-12

A highly effective, micron-scale micro heat barrier structure and process for manufacturing a micro heat barrier based on semiconductor and/or MEMS fabrication techniques. The micro heat barrier has an array of non-metallic, freestanding microsupports with a height less than 100 microns, attached to a substrate. An infrared reflective membrane (e.g., 1 micron gold) can be supported by the array of microsupports to provide radiation shielding. The micro heat barrier can be evacuated to eliminate gas phase heat conduction and convection. Semi-isotropic, reactive ion plasma etching can be used to create a microspike having a cusp-like shape with a sharp, pointed tip (<0.1 micron), to minimize the tip's contact area. A heat source can be placed directly on the microspikes. The micro heat barrier can have an apparent thermal conductivity in the range of 10.sup.-6 to 10.sup.-7 W/m-K. Multiple layers of reflective membranes can be used to increase thermal resistance.

Phi-value analysis of a linear, sequential reaction mechanism: theory and application to ion channel gating.

PubMed

Zhou, Yu; Pearson, John E; Auerbach, Anthony

2005-12-01

We derive the analytical form of a rate-equilibrium free-energy relationship (with slope Phi) for a bounded, linear chain of coupled reactions having arbitrary connecting rate constants. The results confirm previous simulation studies showing that Phi-values reflect the position of the perturbed reaction within the chain, with reactions occurring earlier in the sequence producing higher Phi-values than those occurring later in the sequence. The derivation includes an expression for the transmission coefficients of the overall reaction based on the rate constants of an arbitrary, discrete, finite Markov chain. The results indicate that experimental Phi-values can be used to calculate the relative heights of the energy barriers between intermediate states of the chain but provide no information about the energies of the wells along the reaction path. Application of the equations to the case of diliganded acetylcholine receptor channel gating suggests that the transition-state ensemble for this reaction is nearly flat. Although this mechanism accounts for many of the basic features of diliganded and unliganded acetylcholine receptor channel gating, the experimental rate-equilibrium free-energy relationships appear to be more linear than those predicted by the theory.

An analysis of the errors associated with the determination of atmospheric temperature from atmospheric pressure and density data

NASA Technical Reports Server (NTRS)

Minzner, R. A.

1976-01-01

A graph was developed for relating delta T/T, the relative uncertainty in atmospheric temperature T, to delta p/p, the relative uncertainty in the atmospheric pressure p, for situations, when T is derived from the slope of the pressure-height profile. A similar graph relates delta T/T to delta roh/rho, the relative uncertainty in the atmospheric density rho, for those cases when T is derived from the downward integration of the density-height profile. A comparison of these two graphs shows that for equal uncertainties in the respective basic parameters, p or rho, smaller uncertainties in the derived temperatures are associated with density-height rather than with pressure-height data. The value of delta T/T is seen to depend not only upon delta p or delta rho, and to a small extent upon the value of T or the related scale height H, but also upon the inverse of delta h, the height increment between successive observations of p or rho. In the case of pressure-height data, delta T/T is dominated by 1/delta h for all values of delta h; for density-height data, delta T/T is dominated by delta rho/rho for delta h smaller than about 5 km. In the case of T derived from density-height data, this inverse relationship between delta T/T and delta h applies only for large values of delta h, that is, for delta h 35 km. No limit exists in the fineness of usable height resolution of T which may be derived from densities, while a fine height resolution in pressure-height data leads to temperature with unacceptably large uncertainties.

Quantum Chemical Evaluation of the Astrochemical Significance of Reactions between S Atom and Acetylene or Ethylene

NASA Technical Reports Server (NTRS)

Woon, David E.

2007-01-01

Addition-elimination reactions of S atom in its P-3 ground state with acetylene (C2H2) and ethylene (C2H4) were characterized with both molecular orbital and density functional theory calculations employing correlation consistent basis sets in order to assess the likelihood either reaction might play a general role in astrochemistry or a specific role in the formation of S2 (X (sup 3 SIGMA (sub g) (sup -)) via a mechanism proposed by Saxena and Misra (Mon. Not. R. Astron. Soc. 1995, 272, 89). The acetylene and ethylene reactions proceed through C2H2S ((sup 3)A")) and C2H4S ((sup 3)A")) intermediates, respectively, to yield HCCS ((sup 2)II)) and C2H3S ((sup 2)A')). Substantial barriers were found in the exit channels for every combination of method and basis set considered in this work, which effectively precludes hydrogen elimination pathways for both S + C2H2 and S + C2H4 in the ultracold interstellar medium where only very modest barriers can be surmounted and processes without barriers tend to predominate. However, if one or both intermediates is formed and stabilized efficiently under cometary or dense interstellar cloud conditions, they could serve as temporary reservoirs for S atom and participate in reactions such as S + C2H2S (right arrow) S2 = C2H2 or S + C2H4S (right arrow) S2 + C2H4. For formation and stabilization to be efficient, the reaction must possess a barrier height small enough to be surmountable at low temperatures yet large enough to prevent redissociation to reactants. Barrier heights computed with B3LYP and large basis sets are very low, but more rigorous QCISD(T) and RCCSD(T) results indicate that the barrier heights are closer to 3-4 kcal/mol. The calculations therefore indicate that S + C2H2 or S + C2H4 could contribute to the formation of S2 in comets and may serve as a means to gauge coma temperature. The energetics of the ethylene reaction are more favorable.

InGaP/InGaAs field-effect transistor typed hydrogen sensor

NASA Astrophysics Data System (ADS)

Tsai, Jung-Hui; Liou, Syuan-Hao; Lin, Pao-Sheng; Chen, Yu-Chi

2018-02-01

In this article, the Pd-based mixture comprising silicon dioxide (SiO2) is applied as sensing material for the InGaP/InGaAs field-effect transistor typed hydrogen sensor. After wet selectively etching the SiO2, the mixture is turned into Pd nanoparticles on an interlayer. Experimental results depict that hydrogen atoms trapped inside the mixture could effectively decrease the gate barrier height and increase the drain current due to the improved sensing properties when Pd nanoparticles were formed by wet etching method. The sensitivity of the gate forward current from air (the reference) to 9800 ppm hydrogen/air environment approaches the high value of 1674. Thus, the studied device shows a good potential for hydrogen sensor and integrated circuit applications.

[Effects of mulberry/soybean intercropping on the plant growth and rhizosphere soil microbial number and enzyme activities].

PubMed

Hu, Ju-Wei; Zhu, Wen-Xu; Zhang, Hui-Hui; Xu, Nan; Li, Xin; Yue, Bing-Bing; Sun, Guang-yu

2013-05-01

A root separation experiment was conducted to investigate the plant growth and rhizosphere soil microbes and enzyme activities in a mulberry/soybean intercropping system. As compared with those in plastic barrier and nylon mesh barrier treatments, the plant height, leaf number, root length, root nodule number, and root/shoot ratio of mulberry and soybean in non-barrier treatment were significantly higher, and the soybean's effective nodule number was larger. The available phosphorous content in the rhizosphere soils of mulberry and soybean in no barrier and nylon mesh barrier treatments was increased by 10.3% and 11.1%, and 5.1% and 4.6%, respectively, as compared with that in plastic barrier treatment. The microbial number, microbial diversity, and enzyme activities in the rhizosphere soils of mulberry and soybean were higher in the treatments of no barrier and nylon mesh barrier than in the treatment of plastic barrier. All the results indicated that there was an obvious interspecific synergistic effect between mulberry and soybean in the mulberry/soybean intercropping system.

Escape driven by alpha-stable white noises.

PubMed

Dybiec, B; Gudowska-Nowak, E; Hänggi, P

2007-02-01

We explore the archetype problem of an escape dynamics occurring in a symmetric double well potential when the Brownian particle is driven by white Lévy noise in a dynamical regime where inertial effects can safely be neglected. The behavior of escaping trajectories from one well to another is investigated by pointing to the special character that underpins the noise-induced discontinuity which is caused by the generalized Brownian paths that jump beyond the barrier location without actually hitting it. This fact implies that the boundary conditions for the mean first passage time (MFPT) are no longer determined by the well-known local boundary conditions that characterize the case with normal diffusion. By numerically implementing properly the set up boundary conditions, we investigate the survival probability and the average escape time as a function of the corresponding Lévy white noise parameters. Depending on the value of the skewness beta of the Lévy noise, the escape can either become enhanced or suppressed: a negative asymmetry parameter beta typically yields a decrease for the escape rate while the rate itself depicts a non-monotonic behavior as a function of the stability index alpha that characterizes the jump length distribution of Lévy noise, exhibiting a marked discontinuity at alpha=1. We find that the typical factor of 2 that characterizes for normal diffusion the ratio between the MFPT for well-bottom-to-well-bottom and well-bottom-to-barrier-top no longer holds true. For sufficiently high barriers the survival probabilities assume an exponential behavior versus time. Distinct non-exponential deviations occur, however, for low barrier heights.

Doping enhanced barrier lowering in graphene-silicon junctions

NASA Astrophysics Data System (ADS)

Zhang, Xintong; Zhang, Lining; Chan, Mansun

2016-06-01

Rectifying properties of graphene-semiconductor junctions depend on the Schottky barrier height. We report an enhanced barrier lowering in graphene-Si junction and its essential doping dependence in this paper. The electric field due to ionized charge in n-type Si induces the same type doping in graphene and contributes another Schottky barrier lowering factor on top of the image-force-induced lowering (IFIL). We confirm this graphene-doping-induced lowering (GDIL) based on well reproductions of the measured reverse current of our fabricated graphene-Si junctions by the thermionic emission theory. Excellent matching between the theoretical predictions and the junction data of the doping-concentration dependent barrier lowering serves as another evidence of the GDIL. While both GDIL and IFIL are enhanced with the Si doping, GDIL exceeds IFIL with a threshold doping depending on the as-prepared graphene itself.

Study of Fission Barrier Heights of Uranium Isotopes by the Macroscopic-Microscopic Method

NASA Astrophysics Data System (ADS)

Zhong, Chun-Lai; Fan, Tie-Shuan

2014-09-01

Potential energy surfaces of uranium nuclei in the range of mass numbers 229 through 244 are investigated in the framework of the macroscopic-microscopic model and the heights of static fission barriers are obtained in terms of a double-humped structure. The macroscopic part of the nuclear energy is calculated according to Lublin—Strasbourg-drop (LSD) model. Shell and pairing corrections as the microscopic part are calculated with a folded-Yukawa single-particle potential. The calculation is carried out in a five-dimensional parameter space of the generalized Lawrence shapes. In order to extract saddle points on the potential energy surface, a new algorithm which can effectively find an optimal fission path leading from the ground state to the scission point is developed. The comparison of our results with available experimental data and others' theoretical results confirms the reliability of our calculations.

Effect of non-parabolicity and confinement potential on exciton binding energy in a quantum well

NASA Astrophysics Data System (ADS)

Vignesh, G.; Nithiananthi, P.

2018-04-01

The effect of non-parabolicity(NP) (both conduction and valance band) on the binding energy(EB) of a ground state exciton in GaAs/AlxGa1-xAs single Quantum Well(QW) has been calculated using variational method. Confinement of a light hole(LH-CB1-X) and heavy hole(HH-CB1-X) exciton have been numerically evaluated as a function of well width and barrier heights by imposing three different confinement potentials such as square(SQW), parabolic(PQW) and triangular(TQW). Due to NP effects, EB of exciton is increasedin the narrow well region irrespective of the type of exciton, barrier height and nature of the confinement potentials applied. Non-parabolicity effect is prominent in abrupt(SQW) and linearlyvarying(TQW) confinement potentials. All these effects are attributed to be an inter-play between the Coulombic interaction and NP effects among the subband structures.

Computational study of the reactions of methanol with the hydroperoxyl and methyl radicals. 1. Accurate thermochemistry and barrier heights.

PubMed

Alecu, I M; Truhlar, Donald G

2011-04-07

The reactions of CH(3)OH with the HO(2) and CH(3) radicals are important in the combustion of methanol and are prototypes for reactions of heavier alcohols in biofuels. The reaction energies and barrier heights for these reaction systems are computed with CCSD(T) theory extrapolated to the complete basis set limit using correlation-consistent basis sets, both augmented and unaugmented, and further refined by including a fully coupled treatment of the connected triple excitations, a second-order perturbative treatment of quadruple excitations (by CCSDT(2)(Q)), core-valence corrections, and scalar relativistic effects. It is shown that the M08-HX and M08-SO hybrid meta-GGA density functionals can achieve sub-kcal mol(-1) agreement with the high-level ab initio results, identifying these functionals as important potential candidates for direct dynamics studies on the rates of these and homologous reaction systems.

Ferroelectric-Domain-Patterning-Controlled Schottky Junction State in Monolayer MoS 2

DOE PAGES

Xiao, Zhiyong; Song, Jingfeng; Ferry, David K.; ...

2017-06-08

Here, we exploit scanning probe controlled domain patterning in a ferroelectric top-layer to induce nonvolatile modulation of the conduction characteristic of monolayer MoS 2 between a transistor and a junction state. In the presence of a domain wall, MoS 2 exhibits rectified I-V that is well described by the thermionic emission model. The induced Schottky barrier height Φ eff Β varies from 0.38 eV to 0.57 eV and is tunabe by a SiO 2 global back-gate, while the tuning range of Φ eff Β the barrier height depends sensitively on the conduction band tail trapping states. Our work points tomore » a new route to achieve programmable functionalities in van der Waals materials and sheds light on the critical performance limiting factors in these hybrid systems.« less

Ferroelectric-Domain-Patterning-Controlled Schottky Junction State in Monolayer MoS 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, Zhiyong; Song, Jingfeng; Ferry, David K.

Here, we exploit scanning probe controlled domain patterning in a ferroelectric top-layer to induce nonvolatile modulation of the conduction characteristic of monolayer MoS 2 between a transistor and a junction state. In the presence of a domain wall, MoS 2 exhibits rectified I-V that is well described by the thermionic emission model. The induced Schottky barrier height Φ eff Β varies from 0.38 eV to 0.57 eV and is tunabe by a SiO 2 global back-gate, while the tuning range of Φ eff Β the barrier height depends sensitively on the conduction band tail trapping states. Our work points tomore » a new route to achieve programmable functionalities in van der Waals materials and sheds light on the critical performance limiting factors in these hybrid systems.« less

Temperature-dependent radiative and non-radiative dynamics of photo-excited carriers in extremely high-density and small InGaN nanodisks fabricated by neutral-beam etching using bio-nano-templates

NASA Astrophysics Data System (ADS)

Chen, Yafeng; Kiba, Takayuki; Takayama, Junichi; Higo, Akio; Tanikawa, Tomoyuki; Chen, Shula; Samukawa, Seiji; Murayama, Akihiro

2018-05-01

Temperature-dependent radiative and non-radiative dynamics of photoexcited carriers were studied in In0.3Ga0.7N nanodisks (NDs) fabricated from quantum wells (QWs) by neutral-beam etching using bio-nano-templates. The NDs had a diameter of 5 nm, a thickness of 2 and 3 nm, and a sheet density of 2 × 1011 cm-2. The radiative decay time, reflecting the displacement between the electron and hole wavefunctions, is about 0.2 ns; this value is almost constant as a function of temperature in the NDs and not dependent on their thickness. We observed non-exponential decay curves of photoluminescence (PL) in the NDs, particularly at temperatures above 150 K. The thermal activation energies of PL quenching in the NDs are revealed to be about 110 meV, corresponding to the barrier heights of the valence bands in the disks. Therefore, hole escape is deemed responsible for the PL quenching, while thermal activation energies of 12 meV due to the trapping of carriers by defects were dominant in the mother QWs. The above-mentioned non-exponential PL decay curves can be attributed to variations in the rate of hole escape in the NDs because of fluctuations in the valence-band barrier height, which, in turn, is possibly due to compositional fluctuations in the QWs. We found that non-radiative trapping, characteristic of the original QW, also exists in about 1% of the NDs in a form that is not masked by other newly formable defects. Therefore, we suggest that additional defect formation is not significant during our ND fabrication process.

Fabrication and characterization of tunnel barriers in a multi-walled carbon nanotube formed by argon atom beam irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomizawa, H.; Department of Applied Physics, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585; Yamaguchi, T., E-mail: tyamag@riken.jp

We have evaluated tunnel barriers formed in multi-walled carbon nanotubes (MWNTs) by an Ar atom beam irradiation method and applied the technique to fabricate coupled double quantum dots. The two-terminal resistance of the individual MWNTs was increased owing to local damage caused by the Ar beam irradiation. The temperature dependence of the current through a single barrier suggested two different contributions to its Arrhenius plot, i.e., formed by direct tunneling through the barrier and by thermal activation over the barrier. The height of the formed barriers was estimated. The fabrication technique was used to produce coupled double quantum dots withmore » serially formed triple barriers on a MWNT. The current measured at 1.5 K as a function of two side-gate voltages resulted in a honeycomb-like charge stability diagram, which confirmed the formation of the double dots. The characteristic parameters of the double quantum dots were calculated, and the feasibility of the technique is discussed.« less

Scale-dependent behavior of the foredune: Implications for barrier island response to storms and sea-level rise

NASA Astrophysics Data System (ADS)

Houser, Chris; Wernette, Phil; Weymer, Bradley A.

2018-02-01

The impact of storm surge on a barrier island tends to be considered from a single cross-shore dimension, dependent on the relative elevations of the storm surge and dune crest. However, the foredune is rarely uniform and can exhibit considerable variation in height and width at a range of length scales. In this study, LiDAR data from barrier islands in Texas and Florida are used to explore how shoreline position and dune morphology vary alongshore, and to determine how this variability is altered or reinforced by storms and post-storm recovery. Wavelet analysis reveals that a power law can approximate historical shoreline change across all scales, but that storm-scale shoreline change ( 10 years) and dune height exhibit similar scale-dependent variations at swash and surf zone scales (< 1000 m). The in-phase nature of the relationship between dune height and storm-scale shoreline change indicates that areas of greater storm-scale shoreline retreat are associated with areas of smaller dunes. It is argued that the decoupling of storm-scale and historical shoreline change at swash and surf zone scales is also associated with the alongshore redistribution of sediment and the tendency of shorelines to evolve to a more diffusive (or straight) pattern with time. The wavelet analysis of the data for post-storm dune recovery is also characterized by red noise at the smallest scales characteristic of diffusive systems, suggesting that it is possible that small-scale variations in dune height can be repaired through alongshore recovery and expansion if there is sufficient time between storms. However, the time required for dune recovery exceeds the time between storms capable of eroding and overwashing the dune. Correlation between historical shoreline retreat and the variance of the dune at swash and surf zone scales suggests that the persistence of the dune is an important control on transgression through island migration or shoreline retreat with relative sea-level rise.

Phase-Space Approach to the Tunnel Effect: A New Semiclassical Traversal Time

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xavier, A.L. Jr.; de Aguiar, M.A.

1997-11-01

We determine the semiclassical coherent-state propagator for a particle going through one-dimensional evolution in a simple barrier potential. The described semiclassical method makes use of complex trajectories which, by its turn, enables the definition of (real) traversal times in the complexified phase space. We then discuss the behavior of this time for a wave packet whose average energy is below the barrier height. {copyright} {ital 1997} {ital The American Physical Society}

Droplets on liquid surfaces: Dual equilibrium states and their energy barrier

NASA Astrophysics Data System (ADS)

Shabani, Roxana; Kumar, Ranganathan; Cho, Hyoung J.

2013-05-01

Floating aqueous droplets were formed at oil-air interface, and two stable configurations of (i) non-coalescent droplet and (ii) cap/bead droplet were observed. General solutions for energy and force analysis were obtained for both configurations and were shown to be in good agreement with the experimental observations. The energy barrier obtained for transition from configuration (i) to configuration (ii) was correlated to the droplet release height and the probability of non-coalescent droplet formation.

Control of GaAs Microwave Schottky Diode Electrical Characteristics by Contact Geometry: The Gap Diode.

DTIC Science & Technology

1982-05-01

semiconductor Schottky-barrier contacts are used in many semiconductor devices, including switches, rectifiers, varactors , IMPATTs, mixer and detector...ionic materials such as most of the II-VI compound semiconductors (e.g. ZnS and ZnO) and the transition-metal oxides , the barrier height is strongly...the alloying process described above is nonuniformity, due to the incomplete removal of residual surface oxides prior to the evaporation of the metal

Origin of hydrogen-inclusion-induced critical current deviation in Nb/AlOx/Al/Nb Josephson junctions

NASA Astrophysics Data System (ADS)

Hinode, Kenji; Satoh, Tetsuro; Nagasawa, Shuichi; Hidaka, Mutsuo

2010-04-01

We investigated the mechanisms that change the critical current density (Jc) of Nb/AlOx/Al/Nb Josephson junctions due to the inclusion of hydrogen in the Nb electrodes. Our investigations were performed according to three aspects: the superconductivity change, the change in thickness of the barrier layer, and the change in the barrier height due to the electronic effect. The results are as follows: (a) the hydrogen-inclusion-accompanied changes in the superconductivity parameters, such as the junction gap voltage, were much less than those of the critical current density, (b) the effect of hydrogen inclusion on Jc varied depending on the electrodes, i.e., the upper electrode above the barrier layer was the most affected, (c) the junctions with increased Ics due to hydrogen exclusion showed the identical amount of decrease in the junction resistance measured at room temperature, and (d) the hydrogen exclusion from the junction electrodes had no influence on the Nb/Al/AlOx/Al/Nb junctions, which had an extra Al layer. Based on these results we conclude that the Jc change is mainly caused by the change in junction resistance. A one order of magnitude smaller effect is caused by the superconductivity change. We believe the Jc change is caused by a Nb work function increase due to the hydrogen inclusion, resulting in an increase in barrier height.

Influence of Asymmetric Contact Form on Contact Resistance and Schottky Barrier, and Corresponding Applications of Diode.

PubMed

Zhao, Yudan; Xiao, Xiaoyang; Huo, Yujia; Wang, Yingcheng; Zhang, Tianfu; Jiang, Kaili; Wang, Jiaping; Fan, Shoushan; Li, Qunqing

2017-06-07

We have fabricated carbon nanotube and MoS 2 field-effect transistors with asymmetric contact forms of source-drain electrodes, from which we found the current directionality of the devices and different contact resistances under the two current directions. By designing various structures, we can conclude that the asymmetric electrical performance was caused by the difference in the effective Schottky barrier height (Φ SB ) caused by the different contact forms. A detailed temperature-dependent study was used to extract and compare the Φ SB for both contact forms of CNT and MoS 2 devices; we found that the Φ SB for the metal-on-semiconductor form was much lower than that of the semiconductor-on-metal form and is suitable for all p-type, n-type, or ambipolar semiconductors. This conclusion is meaningful with respect to the design and application of nanomaterial electronic devices. Additionally, using the difference in barrier height caused by the contact forms, we have also proposed and fabricated Schottky barrier diodes with a current ratio up to 10 4 ; rectifying circuits consisting of these diodes were able to work in a wide frequency range. This design avoided the use of complex chemical doping or heterojunction methods to achieve fundamental diodes that are relatively simple and use only a single material; these may be suitable for future application in nanoelectronic radio frequency or integrated circuits.

Frontal facial proportions of 12-year-old southern Chinese: a photogrammetric study.

PubMed

Yeung, Charles Yat Cheong; McGrath, Colman Patrick; Wong, Ricky Wing Kit; Hägg, Erik Urban Oskar; Lo, John; Yang, Yanqi

2015-08-14

This study aimed to establish norm values for facial proportion indices among 12-year-old southern Chinese children, to determine lower facial proportion, and to identify gender differences in facial proportions.A random population sample of 514 children was recruited. Fifteen facial landmarks were plotted with ImageJ (V1.45) on standardized photos and 22 Facial proportion index values were obtained. Gender differences were analyzed by 2-sample t-test with 95% confidence interval. Repeated measurements were conducted on approximately 10% of the cases.The rate of adopted subjects was 52.5% (270/514). Intraclass correlation coefficient values (ICC) for intra- examiner reliability were >0.87. Population facial proportion index values were derived. Gender differences in 11 of the facial proportion indices were evident (P < 0.05).Upper face-face height (N- Sto/ N- Gn), vermilion height (Ls-Sto/Sto-Li), upper face height-biocular width (N-Sto/ExR-ExL) and nose -face height (N-Sn/N-Gn) indices were found to be larger among girls (P < 0.01). Males had larger lower face-face height (Sn -Gn/ N-Gn), mandibulo-face height (Sto-Gn/N-Gn), mandibulo-upper face height (Sto-Gn/N-Sto), nasal (AlR-AlL/N-Sn), upper lip height-mouth width (Sn-Sto/ChR-ChL), upper lip-upper face height (Sn-Sto/N-Sto) and upper lip-nose height (Sn-Sto/N-Sn) indices (P < 0.05).Population norm of facial proportion indices for 12-year-old Southern Chinese were derived and mean lower facial proportion were obtained. Sexual dimorphism is apparent.

Temperature dependent electrical characterisation of Pt/HfO{sub 2}/n-GaN metal-insulator-semiconductor (MIS) Schottky diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shetty, Arjun, E-mail: arjun@ece.iisc.ernet.in; Vinoy, K. J.; Roul, Basanta

2015-09-15

This paper reports an improvement in Pt/n-GaN metal-semiconductor (MS) Schottky diode characteristics by the introduction of a layer of HfO{sub 2} (5 nm) between the metal and semiconductor interface. The resulting Pt/HfO{sub 2}/n-GaN metal-insulator-semiconductor (MIS) Schottky diode showed an increase in rectification ratio from 35.9 to 98.9(@ 2V), increase in barrier height (0.52 eV to 0.63eV) and a reduction in ideality factor (2.1 to 1.3) as compared to the MS Schottky. Epitaxial n-type GaN films of thickness 300nm were grown using plasma assisted molecular beam epitaxy (PAMBE). The crystalline and optical qualities of the films were confirmed using high resolutionmore » X-ray diffraction and photoluminescence measurements. Metal-semiconductor (Pt/n-GaN) and metal-insulator-semiconductor (Pt/HfO{sub 2}/n-GaN) Schottky diodes were fabricated. To gain further understanding of the Pt/HfO{sub 2}/GaN interface, I-V characterisation was carried out on the MIS Schottky diode over a temperature range of 150 K to 370 K. The barrier height was found to increase (0.3 eV to 0.79 eV) and the ideality factor decreased (3.6 to 1.2) with increase in temperature from 150 K to 370 K. This temperature dependence was attributed to the inhomogeneous nature of the contact and the explanation was validated by fitting the experimental data into a Gaussian distribution of barrier heights.« less

Exploring the energy landscape of resistive switching in antiferromagnetic S r3I r2O7

NASA Astrophysics Data System (ADS)

Williamson, Morgan; Shen, Shida; Cao, Gang; Zhou, Jianshi; Goodenough, John B.; Tsoi, Maxim

2018-04-01

We study the resistive switching triggered by an applied electrical bias in the antiferromagnetic Mott insulator S r3I r2O7 . The switching was previously associated with an electric-field-driven structural transition. Here we use time-resolved measurements to probe the thermal activation behavior of the switching process and acquire information about the energy barrier associated with the transition. We quantify the changes in the energy-barrier height with respect to the applied bias and find a linear decrease of the barrier with increasing bias. Our observations support the potential of antiferromagnetic transition-metal oxides for spintronic applications.

Conformational relaxation dynamics in the excited electronic states of benzil in solution

NASA Astrophysics Data System (ADS)

Singh, Ajay K.; Palit, Dipak K.; Mittal, Jai P.

2002-07-01

Relaxation dynamics in the excited singlet (S1) state of benzil have been studied in solution using pico and subpicosecond transient absorption spectroscopic techniques. The triple exponential decay dynamics of the S1 state indicates that the process of conformational change from the cis-skewed to the trans-planar form takes place via the formation of a meta-stable intermediate conformer resulting the involvement of two consequent barrier crossing processes. The barrier crossing dynamics is governed by both the polarity of the solvent, which alters the barrier heights by `static' interactions, as well as the viscosity of the solvent via `dynamical' interactions.

Interferometry of Klein tunnelling electrons in graphene quantum rings

NASA Astrophysics Data System (ADS)

de Sousa, D. J. P.; Chaves, Andrey; Pereira, J. M.; Farias, G. A.

2017-01-01

We theoretically study a current switch that exploits the phase acquired by a charge carrier as it tunnels through a potential barrier in graphene. The system acts as an interferometer based on an armchair graphene quantum ring, where the phase difference between interfering electronic wave functions for each path can be controlled by tuning either the height or the width of a potential barrier in the ring arms. By varying the parameters of the potential barriers, the interference can become completely destructive. We demonstrate how this interference effect can be used for developing a simple graphene-based logic gate with a high on/off ratio.

Graphite based Schottky diodes formed semiconducting substrates

NASA Astrophysics Data System (ADS)

Schumann, Todd; Tongay, Sefaattin; Hebard, Arthur

2010-03-01

We demonstrate the formation of semimetal graphite/semiconductor Schottky barriers where the semiconductor is either silicon (Si), gallium arsenide (GaAs) or 4H-silicon carbide (4H-SiC). The fabrication can be as easy as allowing a dab of graphite paint to air dry on any one of the investigated semiconductors. Near room temperature, the forward-bias diode characteristics are well described by thermionic emission, and the extracted barrier heights, which are confirmed by capacitance voltage measurements, roughly follow the Schottky-Mott relation. Since the outermost layer of the graphite electrode is a single graphene sheet, we expect that graphene/semiconductor barriers will manifest similar behavior.

First-Principles Study of the Band Diagrams and Schottky-Type Barrier Heights of Aqueous Ta3N5 Interfaces.

PubMed

Watanabe, Eriko; Ushiyama, Hiroshi; Yamashita, Koichi

2017-03-22

The photo(electro)chemical production of hydrogen by water splitting is an efficient and sustainable method for the utilization of solar energy. To improve photo(electro)catalytic activity, a Schottky-type barrier is typically useful to separate excited charge carriers in semiconductor electrodes. Here, we focused on studying the band diagrams and the Schottky-type barrier heights of Ta 3 N 5 , which is one of the most promising materials as a photoanode for water splitting. The band alignments of the undoped and n-type Ta 3 N 5 with adsorbents in a vacuum were examined to determine how impurities and adsorbents affect the band positions and Fermi energies. The band edge positions as well as the density of surface states clearly depended on the density of O N impurities in the bulk and surface regions. Finally, the band diagrams of the n-type Ta 3 N 5 /water interfaces were calculated with an improved interfacial model to include the effect of electrode potential with explicit water molecules. We observed partial Fermi level pinning in our calculations at the Ta 3 N 5 /water interface, which affects the driving force for charge separation.

Enhancing photoresponsivity using MoTe2-graphene vertical heterostructures

NASA Astrophysics Data System (ADS)

Kuiri, Manabendra; Chakraborty, Biswanath; Paul, Arup; Das, Subhadip; Sood, A. K.; Das, Anindya

2016-02-01

MoTe2 with a narrow band-gap of ˜1.1 eV is a promising candidate for optoelectronic applications, especially for the near-infrared photo detection. However, the photo responsivity of few layers MoTe2 is very small (<1 mA W-1). In this work, we show that a few layer MoTe2-graphene vertical heterostructures have a much larger photo responsivity of ˜20 mA W-1. The trans-conductance measurements with back gate voltage show on-off ratio of the vertical transistor to be ˜(0.5-1) × 105. The rectification nature of the source-drain current with the back gate voltage reveals the presence of a stronger Schottky barrier at the MoTe2-metal contact as compared to the MoTe2-graphene interface. In order to quantify the barrier height, it is essential to measure the work function of a few layers MoTe2, not known so far. We demonstrate a method to determine the work function by measuring the photo-response of the vertical transistor as a function of the Schottky barrier height at the MoTe2-graphene interface tuned by electrolytic top gating.

Effects of glutamine alone or in combination with zinc and vitamin A on growth, intestinal barrier function, stress and satiety-related hormones in Brazilian shantytown children.

PubMed

Lima, Aldo A M; Anstead, Gregory M; Zhang, Qiong; Figueiredo, Ítalo L; Soares, Alberto M; Mota, Rosa M S; Lima, Noélia L; Guerrant, Richard L; Oriá, Reinaldo B

2014-01-01

To determine the impact of supplemental zinc, vitamin A, and glutamine alone or in combination on growth, intestinal barrier function, stress and satiety-related hormones among Brazilian shantytown children with low median height-for-age z-scores. A randomized, double-blind, placebo-controlled trial was conducted in children aged two months to nine years from the urban shanty compound community of Fortaleza, Brazil. Demographic and anthropometric information was assessed. The random treatment groups available for testing (a total of 120 children) were as follows: (1) glutamine alone, n = 38; (2) glutamine plus vitamin A plus zinc, n = 37; and a placebo (zinc plus vitamin A vehicle) plus glycine (isonitrogenous to glutamine) control treatment, n = 38. Leptin, adiponectin, insulin-like growth factor (IGF-1), and plasma levels of cortisol were measured with immune-enzymatic assays; urinary lactulose/mannitol and serum amino acids were measured with high-performance liquid chromatography. ClinicalTrials.gov: NCT00133406. Glutamine treatment significantly improved weight-for-height z-scores compared to the placebo-glycine control treatment. Either glutamine alone or all nutrients combined prevented disruption of the intestinal barrier function, as measured by the percentage of lactulose urinary excretion and the lactulose:mannitol absorption ratio. Plasma leptin was negatively correlated with plasma glutamine (p = 0.002) and arginine (p = 0.001) levels at baseline. After glutamine treatment, leptin was correlated with weight-for-age (WAZ) and weight-for-height z-scores (WHZ) (p≤0.002) at a 4-month follow-up. In addition, glutamine and all combined nutrients (glutamine, vitamin A, and zinc) improved the intestinal barrier function in these children. Taken together, these findings reveal the benefits of glutamine alone or in combination with other gut-trophic nutrients in growing children via interactions with leptin.

Large-scale field testing on flexible shallow landslide barriers

NASA Astrophysics Data System (ADS)

Bugnion, Louis; Volkwein, Axel; Wendeler, Corinna; Roth, Andrea

2010-05-01

Open shallow landslides occur regularly in a wide range of natural terrains. Generally, they are difficult to predict and result in damages to properties and disruption of transportation systems. In order to improve the knowledge about the physical process itself and to develop new protection measures, large-scale field experiments were conducted in Veltheim, Switzerland. Material was released down a 30° inclined test slope into a flexible barrier. The flow as well as the impact into the barrier was monitored using various measurement techniques. Laser devices recording flow heights, a special force plate measuring normal and shear basal forces as well as load cells for impact pressures were installed along the test slope. In addition, load cells were built in the support and retaining cables of the barrier to provide data for detailed back-calculation of load distribution during impact. For the last test series an additional guiding wall in flow direction on both sides of the barrier was installed to achieve higher impact pressures in the middle of the barrier. With these guiding walls the flow is not able to spread out before hitting the barrier. A special constructed release mechanism simulating the sudden failure of the slope was designed such that about 50 m3 of mixed earth and gravel saturated with water can be released in an instant. Analysis of cable forces combined with impact pressures and velocity measurements during a test series allow us now to develop a load model for the barrier design. First numerical simulations with the software tool FARO, originally developed for rockfall barriers and afterwards calibrated for debris flow impacts, lead already to structural improvements on barrier design. Decisive for the barrier design is the first dynamic impact pressure depending on the flow velocity and afterwards the hydrostatic pressure of the complete retained material behind the barrier. Therefore volume estimation of open shallow landslides by assessing the thickness of the failure layer and the width of the possible failure are essential for the required barrier design parameter height and width. First results of the calculated drag coefficients of dynamic impact pressure measurements showed that the dynamic coefficient cw is much lower than 1.0 which is contradictory to most of existing dimensioning property protection guidelines. It appears to us that special adaptation to the system like smaller mesh sizes and special ground-barrier interface compared to normal rock-fall barriers and channelised debris flow barriers are necessary to improve the retention behavior of shallow landslide barriers. Detailed analysis of the friction coefficient in relationship with pore water pressure measurements gives interesting insights into the dynamic of fluid-solid mixed flows. Impact pressures dependencies on flow features are analyzed and discussed with respect to existing models and guidelines for shallow landslides.

Site index, height growth, normal yields and stocking levels for larch in Oregon and Washington.

Treesearch

P.H. Cochran

1985-01-01

Even-aged stands of larch in Oregon and Washington have cubic volume yields similar to yields from larch in Idaho and Montana. Site index values derived from the heights of the single tallest tree on 1/5-acre plots at an age at breast height of 50 years range from 50 to 110 feet. These values have the same index to productivity as the site index values of 30 to 90 feet...

Hydraulic properties of fronds from palms of varying height and habitat.

PubMed

Renninger, Heidi J; Phillips, Nathan

2011-12-01

Because palms grow in highly varying climates and reach considerable heights, they present a unique opportunity to evaluate how environment and plant size impact hydraulic function. We studied hydraulic properties of petioles from palms of varying height from three species: Iriartea deltoidea, a tropical rainforest species; Mauritia flexuosa, a tropical rainforest, swamp species; and Washingtonia robusta, a subtropical species. We measured leaf areas, petiole cross-sectional areas, specific conductivity (K(S)), petiole anatomical properties, vulnerability to embolism and leaf water potentials and calculated petiole Huber values and leaf-specific conductivities (K(L)). Leaf and petiole cross-sectional areas varied widely with height. However, hydraulic properties including Huber values, K(S) and K(L), remained constant. The two palmate species, M. flexuosa and W. robusta, had larger Huber values than I. deltoidea, a pinnately-compound species which exhibited the highest K(S). Metaxylem vessel diameters and vascular bundle densities varied with height in opposing patterns to maintain petiole conductivities. I. deltoidea and W. robusta petioles had similar P(50) values (the point at which 50% of hydraulic conductivity is lost) averaged over all crown heights, but W. robusta exhibited more negative P(50) values in taller palms. Comparison of P (50) values with transpiring midday leaf water potentials, as well as a double-dye staining experiment in a 1-m-tall palm, suggested that a fairly significant amount of embolisms were occurring and refilled on a diurnal basis. Therefore, across palms differing widely in height and growing environments, we found convergence in water transport per unit leaf area (K(L)) with individuals exhibiting differing strategies for achieving this.

Nature of Dielectric Properties, Electric Modulus and AC Electrical Conductivity of Nanocrystalline ZnIn2Se4 Thin Films

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Attia, A. A.; Ali, H. A. M.; Salem, G. F.; Ismail, M. I.

2018-02-01

The structural characteristics of thermally deposited ZnIn2Se4 thin films were indexed utilizing x-ray diffraction as well as scanning electron microscopy techniques. Dielectric properties, electric modulus and AC electrical conductivity of ZnIn2Se4 thin films were examined in the frequency range from 42 Hz to 106 Hz. The capacitance, conductance and impedance were measured at different temperatures. The dielectric constant and dielectric loss decrease with an increase in frequency. The maximum barrier height was determined from the analysis of the dielectric loss depending on the Giuntini model. The real part of the electric modulus revealed a constant maximum value at higher frequencies and the imaginary part of the electric modulus was characterized by the appearance of dielectric relaxation peaks. The AC electrical conductivity obeyed the Jonscher universal power law. Correlated barrier hopping model was the appropriate mechanism for AC conduction in ZnIn2Se4 thin films. Estimation of the density of states at the Fermi level and activation energy, for AC conduction, was carried out based on the temperature dependence of AC electrical conductivity.

On-site infiltration of a copper roof runoff: role of clinoptilolite as an artificial barrier material.

PubMed

Athanasiadis, Konstantinos; Helmreich, Brigitte; Horn, Harald

2007-08-01

On-site infiltration may be considered as a promising way of managing rainwater runoffs in urban areas, provided the hydrological and ecological conditions allow infiltration, and provided there is adequate treatment of the contaminants to avoid a risk of soil and groundwater pollution. The aim of this study was to evaluate the feasibility of the application of a new technical infiltration system equipped with clinoptilolite as an artificial barrier material for the treatment of the copper roof runoff of the Academy of Fine Arts in Munich, Germany. During the 2-yr sampling period, 30 rain events were examined. The cover material of the roof and the drainage system was responsible for the high copper concentrations in the roof runoff. The rain height and the rain intensity were of great significance regarding the establishment of the copper runoff rate. The technical infiltration system applied was able to reduce the copper from the roof runoff by a factor up to 96%. The mean measured copper concentration in percolation water was lower than the critical value of 50 microg/l set by the German Federal Soil Protection Act and Ordinance, indicating no risk for soil and groundwater contamination.

Reactivity of Criegee Intermediates toward Carbon Dioxide.

PubMed

Lin, Yen-Hsiu; Takahashi, Kaito; Lin, Jim Jr-Min

2018-01-04

Recent theoretical work by Kumar and Francisco suggested that the high reactivity of Criegee intermediates (CIs) could be utilized for designing efficient carbon capture technologies. Because the anti-CH 3 CHOO + CO 2 reaction has the lowest barrier in their study, we chose to investigate it experimentally. We probed anti-CH 3 CHOO with its strong UV absorption at 365 nm and measured the rate coefficient to be ≤2 × 10 -17 cm 3 molecule -1 s -1 at 298 K, which is consistent with our theoretical value of 2.1 × 10 -17 cm 3  molecule -1 s -1 at the QCISD(T)/CBS//B3LYP/6-311+G(2d,2p) level but inconsistent with their results obtained at the M06-2X/aug-cc-pVTZ level, which tends to underestimate the barrier heights. The experimental result indicates that the reaction of a Criegee intermediate with atmospheric CO 2 (400 ppmv) would be inefficient (k eff < 0.2 s -1 ) and cannot compete with other decay processes of Criegee intermediates like reactions with water vapor (∼10 3 s -1 ) or thermal decomposition (∼10 2 s -1 ).

Surface roughness measuring system. [synthetic aperture radar measurements of ocean wave height and terrain peaks

NASA Technical Reports Server (NTRS)

Jain, A. (Inventor)

1978-01-01

Significant height information of ocean waves, or peaks of rough terrain is obtained by compressing the radar signal over different widths of the available chirp or Doppler bandwidths, and cross-correlating one of these images with each of the others. Upon plotting a fixed (e.g., zero) component of the cross-correlation values as the spacing is increased over some empirically determined range, the system is calibrated. To measure height with the system, a spacing value is selected and a cross-correlation value is determined between two intensity images at a selected frequency spacing. The measured height is the slope of the cross-correlation value used. Both electronic and optical radar signal data compressors and cross-correlations are disclosed for implementation of the system.

GaN Schottky diodes with single-crystal aluminum barriers grown by plasma-assisted molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tseng, H. Y.; Yang, W. C.; Lee, P. Y.

2016-08-22

GaN-based Schottky barrier diodes (SBDs) with single-crystal Al barriers grown by plasma-assisted molecular beam epitaxy are fabricated. Examined using in-situ reflection high-energy electron diffractions, ex-situ high-resolution x-ray diffractions, and high-resolution transmission electron microscopy, it is determined that epitaxial Al grows with its [111] axis coincident with the [0001] axis of the GaN substrate without rotation. In fabricated SBDs, a 0.2 V barrier height enhancement and 2 orders of magnitude reduction in leakage current are observed in single crystal Al/GaN SBDs compared to conventional thermal deposited Al/GaN SBDs. The strain induced piezoelectric field is determined to be the major source of themore » observed device performance enhancements.« less

Spin-resolved conductance of Dirac electrons through multibarrier arrays

NASA Astrophysics Data System (ADS)

Dahal, Dipendra; Gumbs, Godfrey; Iurov, Andrii

We use a transfer matrix method to calculate the transmission coefficient of Dirac electrons through an arbitrary number of square potential barrier in gapped monolayer graphene(MLG) and bilayer graphene (BLG). The widths of barriers may not be chosen equal. The shift in the angle of incidence and the width of the barrier required for resonance are investigated numerically for both MLG and BLG. We compare the effects due to energy gap on these two transmission coefficient for each of these two structures (MLG and BLG). We present our results as functions of barrier width, height as well as incoming electron energy as well as band gap and examine the conditions for which perfect reflection or transmission occurs. Our transmission data are further used to calculate conductivity.

Current-induced changes of migration energy barriers in graphene and carbon nanotubes.

PubMed

Obodo, J T; Rungger, I; Sanvito, S; Schwingenschlögl, U

2016-05-21

An electron current can move atoms in a nanoscale device with important consequences for the device operation and breakdown. We perform first principles calculations aimed at evaluating the possibility of changing the energy barriers for atom migration in carbon-based systems. In particular, we consider the migration of adatoms and defects in graphene and carbon nanotubes. Although the current-induced forces are large for both the systems, in graphene the force component along the migration path is small and therefore the barrier height is little affected by the current flow. In contrast, the same barrier is significantly reduced in carbon nanotubes as the current increases. Our work also provides a real-system numerical demonstration that current-induced forces within density functional theory are non-conservative.

Flexible nonlinear estimates of the association between height and mental ability in early life.

PubMed

Murasko, Jason E

2014-01-01

To estimate associations between early-life mental ability and height/height-growth in contemporary US children. Structured additive regression models are used to flexibly estimate the associations between height and mental ability at approximately 24 months of age. The sample is taken from the Early Childhood Longitudinal Study-Birth Cohort, a national study whose target population was children born in the US during 2001. A nonlinear association is indicated between height and mental ability at approximately 24 months of age. There is an increasing association between height and mental ability below the mean value of height, but a flat association thereafter. Annualized growth shows the same nonlinear association to ability when controlling for baseline length at 9 months. Restricted growth at lower values of the height distribution is associated with lower measured mental ability in contemporary US children during the first years of life. Copyright © 2013 Wiley Periodicals, Inc.

Height and body mass index values of nineteenth-century New York legislators.

PubMed

Bodenhorn, Howard

2010-03-01

Previous studies of mid-nineteenth-century American BMI values have used data created by military academies and penitentiaries. This paper uses an alternative data set, constructed from legislative documents in which the heights and weights of New York State legislators were recorded. The results reveal that middle- to upper-middle class Americans maintained BMI values closer to the modern standard than did students and prisoners. The average BMI value among this group was 24 and their height-weight combinations did not greatly diverge from historical mortality risk optima. Copyright 2009 Elsevier B.V. All rights reserved.

Atomically Thin Al2O3 Films for Tunnel Junctions

NASA Astrophysics Data System (ADS)

Wilt, Jamie; Gong, Youpin; Gong, Ming; Su, Feifan; Xu, Huikai; Sakidja, Ridwan; Elliot, Alan; Lu, Rongtao; Zhao, Shiping; Han, Siyuan; Wu, Judy Z.

2017-06-01

Metal-insulator-metal tunnel junctions are common throughout the microelectronics industry. The industry standard AlOx tunnel barrier, formed through oxygen diffusion into an Al wetting layer, is plagued by internal defects and pinholes which prevent the realization of atomically thin barriers demanded for enhanced quantum coherence. In this work, we employ in situ scanning tunneling spectroscopy along with molecular-dynamics simulations to understand and control the growth of atomically thin Al2O3 tunnel barriers using atomic-layer deposition. We find that a carefully tuned initial H2O pulse hydroxylated the Al surface and enabled the creation of an atomically thin Al2O3 tunnel barrier with a high-quality M -I interface and a significantly enhanced barrier height compared to thermal AlOx . These properties, corroborated by fabricated Josephson junctions, show that atomic-layer deposition Al2O3 is a dense, leak-free tunnel barrier with a low defect density which can be a key component for the next generation of metal-insulator-metal tunnel junctions.

Methods for fabricating a micro heat barrier

DOEpatents

Marshall, Albert C.; Kravitz, Stanley H.; Tigges, Chris P.; Vawter, Gregory A.

2004-01-06

Methods for fabricating a highly effective, micron-scale micro heat barrier structure and process for manufacturing a micro heat barrier based on semiconductor and/or MEMS fabrication techniques. The micro heat barrier has an array of non-metallic, freestanding microsupports with a height less than 100 microns, attached to a substrate. An infrared reflective membrane (e.g., 1 micron gold) can be supported by the array of microsupports to provide radiation shielding. The micro heat barrier can be evacuated to eliminate gas phase heat conduction and convection. Semi-isotropic, reactive ion plasma etching can be used to create a microspike having a cusp-like shape with a sharp, pointed tip (<0.1 micron), to minimize the tip's contact area. A heat source can be placed directly on the microspikes. The micro heat barrier can have an apparent thermal conductivity in the range of 10.sup.-6 to 10.sup.-7 W/m-K. Multiple layers of reflective membranes can be used to increase thermal resistance.

Analysing black phosphorus transistors using an analytic Schottky barrier MOSFET model.

PubMed

Penumatcha, Ashish V; Salazar, Ramon B; Appenzeller, Joerg

2015-11-13

Owing to the difficulties associated with substitutional doping of low-dimensional nanomaterials, most field-effect transistors built from carbon nanotubes, two-dimensional crystals and other low-dimensional channels are Schottky barrier MOSFETs (metal-oxide-semiconductor field-effect transistors). The transmission through a Schottky barrier-MOSFET is dominated by the gate-dependent transmission through the Schottky barriers at the metal-to-channel interfaces. This makes the use of conventional transistor models highly inappropriate and has lead researchers in the past frequently to extract incorrect intrinsic properties, for example, mobility, for many novel nanomaterials. Here we propose a simple modelling approach to quantitatively describe the transfer characteristics of Schottky barrier-MOSFETs from ultra-thin body materials accurately in the device off-state. In particular, after validating the model through the analysis of a set of ultra-thin silicon field-effect transistor data, we have successfully applied our approach to extract Schottky barrier heights for electrons and holes in black phosphorus devices for a large range of body thicknesses.

Analysing black phosphorus transistors using an analytic Schottky barrier MOSFET model

PubMed Central

Penumatcha, Ashish V.; Salazar, Ramon B.; Appenzeller, Joerg

2015-01-01

Owing to the difficulties associated with substitutional doping of low-dimensional nanomaterials, most field-effect transistors built from carbon nanotubes, two-dimensional crystals and other low-dimensional channels are Schottky barrier MOSFETs (metal-oxide-semiconductor field-effect transistors). The transmission through a Schottky barrier-MOSFET is dominated by the gate-dependent transmission through the Schottky barriers at the metal-to-channel interfaces. This makes the use of conventional transistor models highly inappropriate and has lead researchers in the past frequently to extract incorrect intrinsic properties, for example, mobility, for many novel nanomaterials. Here we propose a simple modelling approach to quantitatively describe the transfer characteristics of Schottky barrier-MOSFETs from ultra-thin body materials accurately in the device off-state. In particular, after validating the model through the analysis of a set of ultra-thin silicon field-effect transistor data, we have successfully applied our approach to extract Schottky barrier heights for electrons and holes in black phosphorus devices for a large range of body thicknesses. PMID:26563458

Oscillations above the barrier in the fusion of 28Si + 28Si

DOE PAGES

Montagnoli, G.; Stefanini, A.M.; Esbensen, H.; ...

2015-05-13

Fusion cross sections of 28Si+ 28Si have been measured in a range above the barrier with a very small energy step (Delta E lab=0.5 MeV). Regular oscillations have been observed, best evidenced in the first derivative of the energy-weighted excitation function. For the first time, quite different behaviors (the appearance of oscillations and the trend of sub-barrier cross sections) have been reproduced within the same theoretical frame, i.e., the coupled-channel model using the shallow M3Y+repulsion potential. The calculations suggest that channel couplings play an important role in the appearance of the oscillations, and that the simple relation between a peakmore » in the derivative of the energy-weighted cross section and the height of a centrifugal barrier is lost, and so is the interpretation of the second derivative of the excitation function as a barrier distribution for this system, at energies above the Coulomb barrier.« less

Wave Overtopping of a Barrier Beach

DTIC Science & Technology

2009-09-01

but can result in increased dune erosion along Scenic Road as occurred in 1993, 1997, and 2005 (James, 2005). Field data and observations for...factors are equal to 1. The equations for these run-up formulas are parameterized on significant wave height at the toe of the structure as measured in...3 exp C r SS RQ C D HgH γ ⎛ ⎞ = −⎜ ⎟ ⎝ ⎠ 2pξ > where the significant wave height at the toe of the structure, SH and pT are used. Again the

Post-storm beach and dune recovery: Implications for barrier island resilience

NASA Astrophysics Data System (ADS)

Houser, Chris; Wernette, Phil; Rentschlar, Elizabeth; Jones, Hannah; Hammond, Brianna; Trimble, Sarah

2015-04-01

The ability of beaches and dunes to recover following an extreme storm is a primary control of barrier island response to sea-level rise and changes in the frequency and/or magnitude of storm surges. Whereas erosion of the beach and dune occurs over hours and days, it can be years to decades before the beach and dune are able to recover to their pre-storm state. As a consequence, there are numerous descriptions of near-instantaneous beach and dune erosion due to storms, the immediate onshore transport of sand, and the initial phases of beach and dune recovery following a storm, but a paucity of data on long-term beach and dune recovery. A combination of previously published data from Galveston Island, Texas and new remotely sensed data from Santa Rosa Island, Florida is used in the present study to quantify the rate of dune recovery for dissipative and intermediate beach types, respectively. Recovery of the dune height and volume on Galveston Island was observed within two years following Hurricane Alicia (1983) and was largely complete within six years of the storm, despite extensive washover. In contrast, the dunes on Santa Rosa Island in Northwest Florida began to recover four years after Hurricane Ivan (2004), and only after the profile approached its pre-storm level and the rate of vegetation recovery (regrowth) was at a maximum. Results show that complete recovery of the largest dunes (in height and volume) will take approximately 10 years on Santa Rosa Island, which suggests that these sections of the island are particularly vulnerable to significant change in island morphology if there is also a change in the frequency and magnitude of storm events. In contrast, the areas of the island with the smallest dunes before Hurricane Ivan exhibited a rapid recovery, but no further growth in profile volume and dune height beyond the pre-storm volume and height, despite continued recovery of the largest dunes to their pre-storm height. A change in storm magnitude and/or frequency is a potential threat to barrier island resilience, particularly for those sections of the island where dune recovery has historically taken the longest time. Further study is required to determine how and why dune recovery varies for the dissipative and intermediate beaches of Galveston Island and Santa Rosa Island, respectively.

Small Barriers Trigger Liftoff of Unconfined Dilute Heated Laboratory Density Currents

NASA Astrophysics Data System (ADS)

Fauria, K.; Andrews, B. J.; Manga, M.

2015-12-01

Dilute pyroclastic density currents (PDCs) are hot, turbulent, particle-laden flows that propagate because they are denser than air. PDCs can traverse tens to hundreds of kilometers and surmount ridges 100s of m tall, yet the effects of complex topography on PDC liftoff and runout distance are uncertain. Here we used scaled laboratory experiments to explore how barriers affect dilute density current dynamics and the occurrence of liftoff. We created dilute density currents by heating and suspending 20 μm diameter talc in air in an 8.5 x 6.1 x 2.6 m tank. We scaled the currents with respect to Froude, densimetric and thermal Richardson, particle Stokes and Settling numbers such that they were dynamically similar to natural PDCs. While currents were fully turbulent, their Reynolds numbers were not as high as those for natural PDCs. We performed the first set of experiments in a laterally unconfined volume, used laser sheets to illuminate the currents, measured bulk sedimentation rates down the current centerlines, and positioned four to twenty-four cm tall ridge-like barriers in the path of the currents. We found that relatively small barriers (~ half the current height) caused PDC liftoff. By comparison, conservation of kinetic and potential energy predicts that incompressible density currents are able to surmount barriers twice their height. Furthermore, we observed increased sedimentation immediately upstream of barriers and conclude that small barriers initiated buoyancy reversal through a combination of increased air entrainment and sedimentation. We conducted a second set of experiments with the same thermal scaling and mass flux rates but where the currents were laterally confined within a 0.6 m wide channel. We found that small barriers also triggered liftoff of confined currents, but that the body of these currents reattached after liftoff. Those results suggest that lateral confinement inhibits buoyancy reversal by limiting the surface area of the current-air interface and air entrainment. Real dilute PDCs that originate in confined valleys may therefore have different fates and longer runout distances than those on unconfined planes.

Electrical Characterization of Graphite/InP Schottky Diodes by I-V-T and C-V Methods

NASA Astrophysics Data System (ADS)

Tiagulskyi, Stanislav; Yatskiv, Roman; Grym, Jan

2018-02-01

A rectifying junction was prepared by casting a drop of colloidal graphite on the surface of an InP substrate. The electrophysical properties of graphite/InP junctions were investigated in a wide temperature range. Temperature-dependent I-V characteristics of the graphite/InP junctions are explained by the thermionic emission mechanism. The Schottky barrier height (SBH) and the ideality factor were found to be 0.9 eV and 1.47, respectively. The large value of the SBH and its weak temperature dependence are explained by lateral homogeneity of the junction, which is related to the structure of the graphite layer. The moderate disagreement between the current-voltage and capacitance-voltage measurements is attributed to the formation of interfacial native oxide film on the InP surface.

Microinhomogeneities in Semi-Insulating Cd(Zn)Te

DOE PAGES

Fochuk, P.; Nykoniuk, Y.; Zakharuk, Z.; ...

2017-09-04

Here, we investigated the temperature dependences (TDs) in the range of 290-423 K for the Hall constant R H and the Hall carrier mobility μn (σ R H) in semi-insulating Cd 0.9 Zn 0.1 Te:In (CZT) crystals. As-grown, CZT material has nonequilibrium distributions of native and impurity-related defects. Thus, before taking any measurements, the samples were kept inside the test chamber in the dark at 423 K to reach an equilibrium state at T <; 423 K. For all the tested samples, the R H TD could be described by two activation energies. At the transitional point, the TD ofmore » the carrier mobility also changes from “normal” at high temperatures to “exponential” at low temperatures. The latter is a result of the collective effect of drift barriers due to microinhomogeneity. Therefore, only the high-temperature activation energies can be assigned to the ionization energies of the compensated deep donors (ε D). For different samples, the values for ε D 0 (at absolute zero) were found to be in the range of 0.50-0.78 eV, and the degree of donor compensation [D +]/[D] is between 0.3 and 0.98. The low-temperature region, where there are strong effects of crystal microinhomogeneities, cannot be used to characterize the ionization energy of donors. Therefore, we describe the activation energy as ε 1 = ε D - αε b, where ε b is the drift barrier height found from the TD of the carrier mobility and α takes a value close to unity. Values of ε b for our studied samples lie within (0.05-0.35) eV.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fochuk, P.; Nykoniuk, Y.; Zakharuk, Z.

Here, we investigated the temperature dependences (TDs) in the range of 290-423 K for the Hall constant R H and the Hall carrier mobility μn (σ R H) in semi-insulating Cd 0.9 Zn 0.1 Te:In (CZT) crystals. As-grown, CZT material has nonequilibrium distributions of native and impurity-related defects. Thus, before taking any measurements, the samples were kept inside the test chamber in the dark at 423 K to reach an equilibrium state at T <; 423 K. For all the tested samples, the R H TD could be described by two activation energies. At the transitional point, the TD ofmore » the carrier mobility also changes from “normal” at high temperatures to “exponential” at low temperatures. The latter is a result of the collective effect of drift barriers due to microinhomogeneity. Therefore, only the high-temperature activation energies can be assigned to the ionization energies of the compensated deep donors (ε D). For different samples, the values for ε D 0 (at absolute zero) were found to be in the range of 0.50-0.78 eV, and the degree of donor compensation [D +]/[D] is between 0.3 and 0.98. The low-temperature region, where there are strong effects of crystal microinhomogeneities, cannot be used to characterize the ionization energy of donors. Therefore, we describe the activation energy as ε 1 = ε D - αε b, where ε b is the drift barrier height found from the TD of the carrier mobility and α takes a value close to unity. Values of ε b for our studied samples lie within (0.05-0.35) eV.« less

Nanocrystals with linear and branched topology

DOEpatents

Alivisatos, A. Paul; Milliron, Delia; Manna, Liberato; Hughes, Steven M.

2007-12-04

Disclosed herein are nanostructures comprising distinct dots and rods coupled through potential barriers of tuneable height and width, and arranged in three dimensional space at well defined angles and distances. Such control allows investigation of potential applications ranging from quantum information processing to artificial photosynthesis.

1-kV vertical Ga2O3 field-plated Schottky barrier diodes

NASA Astrophysics Data System (ADS)

Konishi, Keita; Goto, Ken; Murakami, Hisashi; Kumagai, Yoshinao; Kuramata, Akito; Yamakoshi, Shigenobu; Higashiwaki, Masataka

2017-03-01

Ga2O3 field-plated Schottky barrier diodes (FP-SBDs) were fabricated on a Si-doped n--Ga2O3 drift layer grown by halide vapor phase epitaxy on a Sn-doped n+-Ga2O3 (001) substrate. The specific on-resistance of the Ga2O3 FP-SBD was estimated to be 5.1 mΩ.cm2. Successful field-plate engineering resulted in a high breakdown voltage of 1076 V. A larger-than-expected effective barrier height of 1.46 eV, which was extracted from the temperature-dependent current-voltage characteristics, could be caused by the effect of fluorine atoms delivered in a hydrofluoric acid solution process.

Electrostatic and magnetic fields in bilayer graphene

NASA Astrophysics Data System (ADS)

Jellal, Ahmed; Redouani, Ilham; Bahlouli, Hocine

2015-08-01

We compute the transmission probability through rectangular potential barriers and p-n junctions in the presence of a magnetic and electric fields in bilayer graphene taking into account contributions from the full four bands of the energy spectrum. For energy E higher than the interlayer coupling γ1 (E >γ1) two propagation modes are available for transport giving rise to four possible ways for transmission and reflection coefficients. However, when the energy is less than the height of the barrier the Dirac fermions exhibit transmission resonances and only one mode of propagation is available for transport. We study the effect of the interlayer electrostatic potential denoted by δ and variations of different barrier geometry parameters on the transmission probability.

Electron Excess Doping and Effective Schottky Barrier Reduction on the MoS2/h-BN Heterostructure.

PubMed

Joo, Min-Kyu; Moon, Byoung Hee; Ji, Hyunjin; Han, Gang Hee; Kim, Hyun; Lee, Gwanmu; Lim, Seong Chu; Suh, Dongseok; Lee, Young Hee

2016-10-12

Layered hexagonal boron nitride (h-BN) thin film is a dielectric that surpasses carrier mobility by reducing charge scattering with silicon oxide in diverse electronics formed with graphene and transition metal dichalcogenides. However, the h-BN effect on electron doping concentration and Schottky barrier is little known. Here, we report that use of h-BN thin film as a substrate for monolayer MoS 2 can induce ∼6.5 × 10 11 cm -2 electron doping at room temperature which was determined using theoretical flat band model and interface trap density. The saturated excess electron concentration of MoS 2 on h-BN was found to be ∼5 × 10 13 cm -2 at high temperature and was significantly reduced at low temperature. Further, the inserted h-BN enables us to reduce the Coulombic charge scattering in MoS 2 /h-BN and lower the effective Schottky barrier height by a factor of 3, which gives rise to four times enhanced the field-effect carrier mobility and an emergence of metal-insulator transition at a much lower charge density of ∼1.0 × 10 12 cm -2 (T = 25 K). The reduced effective Schottky barrier height in MoS 2 /h-BN is attributed to the decreased effective work function of MoS 2 arisen from h-BN induced n-doping and the reduced effective metal work function due to dipole moments originated from fixed charges in SiO 2 .

Infrared spectra of molecules and materials of astrophysical interest

NASA Technical Reports Server (NTRS)

Durig, J. R.

1978-01-01

The Raman spectra of gaseous, liquid and solid, and infrared spectra of gaseous and solid isopropylamine-d sub 0 and -d sub 2 was investigated between 4000 and 50 cm superscript -1. Differences between the spectrum of the solid phase and that of the fluid phases were interpreted in terms of an equilibrium between low energy s-trans and high energy gauche conformers, and a complete vibrational assignment was proposed for the s-trans conformer. The far infrared spectra of the gaseous compounds contained bands due to the asymmetric amino and coupled methyl torsions; the assignment of these bands was aided by observation of a number of two quantum transitions for each vibrational mode. The asymmetric potential functions were calculated, which resulted in values for the enthalpy differences between conformers in the gaseous phase of 446 and 523 callmole for the sub 0 -d and -d sub 2 compounds, respectively. The methyl torsional potential function of isopropylamine-d sub 0 was calculated which led to a value for the barrier height to internal rotation of the methyl rotors of 4.23 + or - 0.06 kcal/mole. Values for the ideal gas thermodynamic functions were calculated over a range of temperatures.

Possibilities for LWIR detectors using MBE-grown Si(/Si(1-x)Ge(x) structures

NASA Technical Reports Server (NTRS)

Hauenstein, Robert J.; Miles, Richard H.; Young, Mary H.

1990-01-01

Traditionally, long wavelength infrared (LWIR) detection in Si-based structures has involved either extrinsic Si or Si/metal Schottky barrier devices. Molecular beam epitaxially (MBE) grown Si and Si/Si(1-x)Ge(x) heterostructures offer new possibilities for LWIR detection, including sensors based on intersubband transitions as well as improved conventional devices. The improvement in doping profile control of MBE in comparison with conventional chemical vapor deposited (CVD) Si films has resulted in the successful growth of extrinsic Si:Ga, blocked impurity-band conduction detectors. These structures exhibit a highly abrupt step change in dopant profile between detecting and blocking layers which is extremely difficult or impossible to achieve through conventional epitaxial growth techniques. Through alloying Si with Ge, Schottky barrier infrared detectors are possible, with barrier height values between those involving pure Si or Ge semiconducting materials alone. For both n-type and p-type structures, strain effects can split the band edges, thereby splitting the Schottky threshold and altering the spectral response. Measurements of photoresponse of n-type Au/Si(1-x)Ge(x) Schottky barriers demonstrate this effect. For intersubband multiquntum well (MQW) LWIR detection, Si(1-x)Ge(x)/Si detectors grown on Si substrates promise comparable absorption coefficients to that of the Ga(Al)As system while in addition offering the fundamental advantage of response to normally incident light as well as the practical advantage of Si-compatibility. Researchers grew Si(1-x)Ge(x)/Si MQW structures aimed at sensitivity to IR in the 8 to 12 micron region and longer, guided by recent theoretical work. Preliminary measurements of n- and p-type Si(1-x)Ge(x)/Si MQW structures are given.

Double-inversion mechanisms of the X⁻ + CH₃Y [X,Y = F, Cl, Br, I] SN2 reactions.

PubMed

Szabó, István; Czakó, Gábor

2015-03-26

The double-inversion and front-side attack transition states as well as the proton-abstraction channels of the X(-) + CH3Y [X,Y = F, Cl, Br, I] reactions are characterized by the explicitly correlated CCSD(T)-F12b/aug-cc-pVTZ(-PP) level of theory using small-core relativistic effective core potentials and the corresponding aug-cc-pVTZ-PP bases for Br and I. In the X = F case the double-inversion classical(adiabatic) barrier heights are 28.7(25.6), 15.8(13.4), 13.2(11.0), and 8.6(6.6) kcal mol(-1) for Y = F, Cl, Br, and I, respectively, whereas the barrier heights are in the 40-90 kcal mol(-1) range for the other 12 reactions. The abstraction channels are always above the double-inversion saddle points. For X = F, the front-side attack classical(adiabatic) barrier heights, 45.8(44.8), 31.0(30.3), 24.7(24.2), and 19.5(19.3) kcal mol(-1) for Y = F, Cl, Br, and I, respectively, are higher than the corresponding double-inversion ones, whereas for the other systems the front-side attack saddle points are in the 35-70 kcal mol(-1) range. The double-inversion transition states have XH···CH2Y(-) structures with Cs point-group symmetry, and the front-side attack saddle points have either Cs (X = F or X = Y) or C1 symmetry with XCY angles in the 78-88° range. On the basis of the previous reaction dynamics simulations and the minimum energy path computations along the inversion coordinate of selected XH···CH2Y(-) systems, we suggest that the double inversion may be a general mechanism for SN2 reactions.

Lab Experiments Probe Interactions Between Dilute Pyroclastic Density Currents and 3D Barriers

NASA Astrophysics Data System (ADS)

Fauria, K.; Andrews, B. J.; Manga, M.

2014-12-01

We conducted scaled laboratory experiments of unconfined dilute pyroclastic density currents (PDCs) to examine interactions between three - dimensional obstacles and dilute PDCs. While it is known that PDCs can surmount barriers by converting kinetic energy into potential energy, the signature of topography on PDC dynamics is unclear. To examine the interplay between PDCs and topography, we turbulently suspended heated and ambient-temperature 20 μm talc powder in air within an 8.5 x 6.1 x 2.6 m tank. Experimental parameters (Froude number, densimetric and thermal Richardson number, particle Stokes and Settling numbers) were scaled such that the experimental currents were dynamically similar to natural PCS. The Reynolds number, however, is much smaller than in natural currents, but still large enough for the flows to be turbulent. We placed cylindrical and ridge-like objects in the path of the currents, illuminated the currents with orthogonal laser sheets, and recorded each experiment with high definition cameras. We observed currents surmounting ridge-like barriers (barrier height = current height). Slanted ridges redirected the currents upward and parallel to the upstream face of the ridges (~45° from horizontal). Down stream of the slanted ridges, ambient-temperature currents reattached to the floor. By comparison, hot currents reversed buoyancy and lifted off. These observations suggest that obstacles enhance air entrainment, a process key to affecting runout distance and the depletion of fine particles in ignimbrites. Moreover, we observed vortex shedding in the wake of cylinders. Our experiments demonstrate that barriers of various shapes affect PDC dynamics and can shorten PDC runout distances. Understanding the effects of topography on PDCs is required for interpreting many deposits because processes such as vortex shedding and topographically-induced changes in turbulent length scales and entrainment likely leave depositional signatures.

Extreme storms, sea level rise, and coastal change: implications for infrastructure reliability in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Anarde, K.; Kameshwar, S.; Irza, N.; Lorenzo-Trueba, J.; Nittrouer, J. A.; Padgett, J.; Bedient, P. B.

2016-12-01

Predicting coastal infrastructure reliability during hurricane events is important for risk-based design and disaster planning, such as delineating viable emergency response routes. Previous research has focused on either infrastructure vulnerability to coastal flooding or the impact of changing sea level and landforms on surge dynamics. Here we investigate the combined impact of sea level, morphology, and coastal flooding on the reliability of highway bridges - the only access points between barrier islands and mainland communities - during future extreme storms. We forward model coastal flooding for static projections of geomorphic change using ADCIRC+SWAN. First-order parameters that are adjusted include sea level and elevation. These are varied for each storm simulation to evaluate relative impact on the reliability of bridges surrounding Freeport, TX. Simulated storms include both synthetic and historical events, which are classified by intensity using the storm's integrated kinetic energy, a metric for surge generation potential. Reliability is estimated through probability of failure - given wave and surge loads - and time inundated. Findings include that: 1) bridge reliability scales inversely with surge height, and 2) sea level rise reduces bridge reliability due to a monotonic increase in surge height. The impact of a shifting landscape on bridge reliability is more complex: barrier island rollback can increase or decrease inundation times for storms of different intensity due to changes in wind-setup and back-barrier bay interactions. Initial storm surge readily inundates the coastal landscape during large intensity storms, however the draining of inland bays following storm passage is significantly impeded by the barrier. From a coastal engineering standpoint, we determine that to protect critical infrastructure, efforts now implemented that nourish low-lying barriers may be enhanced by also armoring back-bay coastlines and elevating bridge approach ramps.

Proton and hydrogen transport through two-dimensional monolayers

NASA Astrophysics Data System (ADS)

Seel, Max; Pandey, Ravindra

2016-06-01

Diffusion of protons and hydrogen atoms in representative two-dimensional materials is investigated. Specifically, density functional calculations were performed on graphene, hexagonal boron nitride (h-BN), phosphorene, silicene, and molybdenum disulfide (MoS2) monolayers to study the surface interaction and penetration barriers for protons and hydrogen atoms employing finite cluster models. The calculated barrier heights correlate approximately with the size of the opening formed by the three-fold open sites in the monolayers considered. They range from 1.56 eV (proton) and 4.61 eV (H) for graphene to 0.12 eV (proton) and 0.20 eV (H) for silicene. The results indicate that only graphene and h-BN monolayers have the potential for membranes with high selective permeability. The MoS2 monolayer behaves differently: protons and H atoms become trapped between the outer S layers in the Mo plane in a well with a depth of 1.56 eV (proton) and 1.5 eV (H atom), possibly explaining why no proton transport was detected, suggesting MoS2 as a hydrogen storage material instead. For graphene and h-BN, off-center proton penetration reduces the barrier to 1.38 eV for graphene and 0.11 eV for h-BN. Furthermore, Pt acting as a substrate was found to have a negligible effect on the barrier height. In defective graphene, the smallest barrier for proton diffusion (1.05 eV) is found for an oxygen-terminated defect. Therefore, it seems more likely that thermal protons can penetrate a monolayer of h-BN but not graphene and defects are necessary to facilitate the proton transport in graphene.

Novel attributes of bandstructure effect on the performance of germanium Schottky barrier MOSFET

NASA Astrophysics Data System (ADS)

Ahangari, Zahra

2018-07-01

A detailed study of the bandstructure effect on the performance of a double-gate germanium Schottky barrier MOSFET (Ge-SBFET) is investigated. An accurate calculation of the thickness-dependent 2D bandstructure is employed within a 20 orbital sp 3 d 5 s* tight-binding formalism, and the quantum transport of the carriers is elucidated based on the non-equilibrium Green’s function formalism. Quantum confinement considerably changes the bandstructure profile of the Ge-SBFET and causes the energy difference of the | {{Γ }}-L| valleys to rearrange. For a channel thickness of about 1.5 nm, the two-fold X 2 type valleys with major axes at the {{Γ }} point form a subband with minimum energy, and the | {{Γ }}-L| energy split is reduced to 13 meV, which compensates for the lack of density of states in the nanoscale regime. Moreover, the strong transverse confinement of the ultra-thin body Ge-SBFET increases the effective Schottky barrier height and a parabolic potential profile with discrete resonant states is formed along the current transport direction, mainly at low drain voltages. Resonant tunnelling creates oscillations in the transfer characteristic, especially at low temperatures and at a reduced value of drain voltages. The impact of the physical and structural parameters, which may affect the resonant tunnelling in a Ge-SBFET, is thoroughly analysed. The results in this paper pave the way towards elucidating the applications of nanoscale Ge-SBFETs.

Modelling the influence of high currents on the cutoff frequency in Si/SiGe/Si heterojunction transistors

NASA Astrophysics Data System (ADS)

Briggs, P. J.; Walker, A. B.; Herbert, D. C.

1998-05-01

A one-dimensional self-consistent bipolar Monte Carlo simulation code has been used to model carrier mobilities in strained doped SiGe and the base-collector region of Si/SiGe/Si and SiC/Si heterojunction bipolar transistors (HBTs) with wide collectors, to study the variation of the cutoff frequency 0268-1242/13/5/005/img6 with collector current density 0268-1242/13/5/005/img7. Our results show that while the presence of strain enhances the electron mobility, the scattering from alloy disorder and from ionized impurities reduces the electron mobility so much that it is less than that of Si at the same doping level, leading to larger base transit times 0268-1242/13/5/005/img8 and hence poorer 0268-1242/13/5/005/img6 performance for large 0268-1242/13/5/005/img7 for an Si/SiGe/Si HBT than for an SiC/Si HBT. At high values of 0268-1242/13/5/005/img7, we demonstrate the formation of a parasitic electron barrier at the base-collector interface which causes a sharp increase in 0268-1242/13/5/005/img8 and hence a dramatic reduction in 0268-1242/13/5/005/img6. Based on a comparison of the height of this parasitic barrier with estimates from an analytical model, we suggest a physical mechanism for base pushout after barrier formation that differs somewhat from that given for the analytical model.

Validity of parent-reported weight and height of preschool children measured at home or estimated without home measurement: a validation study

PubMed Central

2011-01-01

Background Parental reports are often used in large-scale surveys to assess children's body mass index (BMI). Therefore, it is important to know to what extent these parental reports are valid and whether it makes a difference if the parents measured their children's weight and height at home or whether they simply estimated these values. The aim of this study is to compare the validity of parent-reported height, weight and BMI values of preschool children (3-7 y-old), when measured at home or estimated by parents without actual measurement. Methods The subjects were 297 Belgian preschool children (52.9% male). Participation rate was 73%. A questionnaire including questions about height and weight of the children was completed by the parents. Nurses measured height and weight following standardised procedures. International age- and sex-specific BMI cut-off values were employed to determine categories of weight status and obesity. Results On the group level, no important differences in accuracy of reported height, weight and BMI were identified between parent-measured or estimated values. However, for all 3 parameters, the correlations between parental reports and nurse measurements were higher in the group of children whose body dimensions were measured by the parents. Sensitivity for underweight and overweight/obesity were respectively 73% and 47% when parents measured their child's height and weight, and 55% and 47% when parents estimated values without measurement. Specificity for underweight and overweight/obesity were respectively 82% and 97% when parents measured the children, and 75% and 93% with parent estimations. Conclusions Diagnostic measures were more accurate when parents measured their child's weight and height at home than when those dimensions were based on parental judgements. When parent-reported data on an individual level is used, the accuracy could be improved by encouraging the parents to measure weight and height of their children at home. PMID:21736757

Super-giant magnetoresistance at room-temperature in copper nanowires due to magnetic field modulation of potential barrier heights at nanowire-contact interfaces

NASA Astrophysics Data System (ADS)

Hossain, Md I.; Maksud, M.; Palapati, N. K. R.; Subramanian, A.; Atulasimha, J.; Bandyopadhyay, S.

2016-07-01

We have observed a super-giant (∼10 000 000%) negative magnetoresistance at 39 mT field in Cu nanowires contacted with Au contact pads. In these nanowires, potential barriers form at the two Cu/Au interfaces because of Cu oxidation that results in an ultrathin copper oxide layer forming between Cu and Au. Current flows when electrons tunnel through, and/or thermionically emit over, these barriers. A magnetic field applied transverse to the direction of current flow along the wire deflects electrons toward one edge of the wire because of the Lorentz force, causing electron accumulation at that edge and depletion at the other. This lowers the potential barrier at the accumulated edge and raises it at the depleted edge, causing a super-giant magnetoresistance at room temperature.

The triaxiality and Coriolis effects on the fission barrier in isovolumic nuclei with mass number A = 256 based on multidimensional total Routhian surface calculations

NASA Astrophysics Data System (ADS)

Chai, Qing-Zhen; Zhao, Wei-Juan; Wang, Hua-Lei; Liu, Min-Liang; Xu, Fu-Rong

2018-05-01

The triaxiality and Coriolis effects on the first fission barrier in even-even nuclei with A=256 have been studied in terms of the approach of multidimensional total Routhian surface calculations. The present results are compared with available data and other theories, showing a good agreement. Based on the deformation energy or Routhian curves, the first fission barriers are analyzed, focusing on their shapes, heights, and evolution with rotation. It is found that, relative to the effect on the ground-state minimum, the saddle point, at least the first one, can be strongly affected by the triaxial deformation degree of freedom and Coriolis force. The evolution trends of the macroscopic and microscopic (shell and pairing) contributions as well as the triaxial fission barriers are briefly discussed.

Super-giant magnetoresistance at room-temperature in copper nanowires due to magnetic field modulation of potential barrier heights at nanowire-contact interfaces.

PubMed

Hossain, Md I; Maksud, M; Palapati, N K R; Subramanian, A; Atulasimha, J; Bandyopadhyay, S

2016-07-29

We have observed a super-giant (∼10 000 000%) negative magnetoresistance at 39 mT field in Cu nanowires contacted with Au contact pads. In these nanowires, potential barriers form at the two Cu/Au interfaces because of Cu oxidation that results in an ultrathin copper oxide layer forming between Cu and Au. Current flows when electrons tunnel through, and/or thermionically emit over, these barriers. A magnetic field applied transverse to the direction of current flow along the wire deflects electrons toward one edge of the wire because of the Lorentz force, causing electron accumulation at that edge and depletion at the other. This lowers the potential barrier at the accumulated edge and raises it at the depleted edge, causing a super-giant magnetoresistance at room temperature.

Zitterbewegung and symmetry switching in Klein’s four-group

NASA Astrophysics Data System (ADS)

Chotorlishvili, L.; Zięba, P.; Tralle, I.; Ugulava, A.

2018-01-01

Zitterbewegung is the exotic phenomenon associated either with relativistic electron-positron rapid oscillation or to electron-hole transitions in narrow gap semiconductors. In the present work, we enlarge the concept of Zitterbewegung and show that trembling motion may occur due to dramatic changes in the symmetry of the system. In particular, we exploit a paradigmatic model of quantum chaos, the quantum mathematical pendulum (universal Hamiltonian). The symmetry group of this system is Klein’s four-group that possesses three invariant subgroups. The energy spectrum of the system parametrically depends on the height of the potential barrier, and contains degenerate and non-degenerate areas, corresponding to the different symmetry subgroups. Change in the height of the potential barrier switches the symmetry subgroup and leads to trembling motion. We analyzed mean square fluctuations of the velocity operator and observed that trembling is enhanced in highly excited states. We observed a link between the phenomena of trembling motion and the uncertainty relations of noncommutative operators of the system.

Temperature dependent transport characteristics of graphene/n-Si diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parui, S.; Ruiter, R.; Zomer, P. J.

2014-12-28

Realizing an optimal Schottky interface of graphene on Si is challenging, as the electrical transport strongly depends on the graphene quality and the fabrication processes. Such interfaces are of increasing research interest for integration in diverse electronic devices as they are thermally and chemically stable in all environments, unlike standard metal/semiconductor interfaces. We fabricate such interfaces with n-type Si at ambient conditions and find their electrical characteristics to be highly rectifying, with minimal reverse leakage current (<10{sup −10} A) and rectification of more than 10{sup 6}. We extract Schottky barrier height of 0.69 eV for the exfoliated graphene and 0.83 eV for themore » CVD graphene devices at room temperature. The temperature dependent electrical characteristics suggest the influence of inhomogeneities at the graphene/n-Si interface. A quantitative analysis of the inhomogeneity in Schottky barrier heights is presented using the potential fluctuation model proposed by Werner and Güttler.« less

Computational Study of the Reactions of Methanol with the Hydroperoxyl and Methyl Radicals. Part I: Accurate Thermochemistry and Barrier Heights

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alecu, I. M.; Truhlar, D. G.

2011-04-07

The reactions of CH 3OH with the HO 2 and CH 3 radicals are important in the combustion of methanol and are prototypes for reactions of heavier alcohols in biofuels. The reaction energies and barrier heights for these reaction systems are computed with CCSD(T) theory extrapolated to the complete basis set limit using correlation-consistent basis sets, both augmented and unaugmented, and further refined by including a fully coupled treatment of the connected triple excitations, a second-order perturbative treatment of quadruple excitations (by CCSDT(2) Q), core–valence corrections, and scalar relativistic effects. It is shown that the M08-HX and M08-SO hybrid meta-GGAmore » density functionals can achieve sub-kcal mol -1 agreement with the high-level ab initio results, identifying these functionals as important potential candidates for direct dynamics studies on the rates of these and homologous reaction systems.« less

On the effect of local barrier height in scanning tunneling microscopy: Measurement methods and control implications

NASA Astrophysics Data System (ADS)

Tajaddodianfar, Farid; Moheimani, S. O. Reza; Owen, James; Randall, John N.

2018-01-01

A common cause of tip-sample crashes in a Scanning Tunneling Microscope (STM) operating in constant current mode is the poor performance of its feedback control system. We show that there is a direct link between the Local Barrier Height (LBH) and robustness of the feedback control loop. A method known as the "gap modulation method" was proposed in the early STM studies for estimating the LBH. We show that the obtained measurements are affected by controller parameters and propose an alternative method which we prove to produce LBH measurements independent of the controller dynamics. We use the obtained LBH estimation to continuously update the gains of a STM proportional-integral (PI) controller and show that while tuning the PI gains, the closed-loop system tolerates larger variations of LBH without experiencing instability. We report experimental results, conducted on two STM scanners, to establish the efficiency of the proposed PI tuning approach. Improved feedback stability is believed to help in avoiding the tip/sample crash in STMs.

Schottky Barrier Height of Pd/MoS2 Contact by Large Area Photoemission Spectroscopy.

PubMed

Dong, Hong; Gong, Cheng; Addou, Rafik; McDonnell, Stephen; Azcatl, Angelica; Qin, Xiaoye; Wang, Weichao; Wang, Weihua; Hinkle, Christopher L; Wallace, Robert M

2017-11-08

MoS 2 , as a model transition metal dichalcogenide, is viewed as a potential channel material in future nanoelectronic and optoelectronic devices. Minimizing the contact resistance of the metal/MoS 2 junction is critical to realizing the potential of MoS 2 -based devices. In this work, the Schottky barrier height (SBH) and the band structure of high work function Pd metal on MoS 2 have been studied by in situ X-ray photoelectron spectroscopy (XPS). The analytical spot diameter of the XPS spectrometer is about 400 μm, and the XPS signal is proportional to the detection area, so the influence of defect-mediated parallel conduction paths on the SBH does not affect the measurement. The charge redistribution by Pd on MoS 2 is detected by XPS characterization, which gives insight into metal contact physics to MoS 2 and suggests that interface engineering is necessary to lower the contact resistance for the future generation electronic applications.

Substrate Vibrations as Promoters of Chemical Reactivity on Metal Surfaces.

PubMed

Campbell, Victoria L; Chen, Nan; Guo, Han; Jackson, Bret; Utz, Arthur L

2015-12-17

Studies exploring how vibrational energy (Evib) promotes chemical reactivity most often focus on molecular reagents, leaving the role of substrate atom motion in heterogeneous interfacial chemistry underexplored. This combined theoretical and experimental study of methane dissociation on Ni(111) shows that lattice atom motion modulates the reaction barrier height during each surface atom's vibrational period, which leads to a strong variation in the reaction probability (S0) with surface temperature (Tsurf). State-resolved beam-surface scattering studies at Tsurf = 90 K show a sharp threshold in S0 at translational energy (Etrans) = 42 kJ/mol. When Etrans decreases from 42 kJ/mol to 34 kJ/mol, S0 decreases 1000-fold at Tsurf = 90 K, but only 2-fold at Tsurf = 475 K. Results highlight the mechanism for this effect, provide benchmarks for DFT calculations, and suggest the potential importance of surface atom induced barrier height modulation in heterogeneously catalyzed reactions, particularly on structurally labile nanoscale particles and defect sites.

Catalytic mechanism of human N-acetylserotonin methyltransferase: a theoretical investigation

NASA Astrophysics Data System (ADS)

Wang, Li; Zhang, Ting; Li, Jieqiong; He, Chaozheng; He, Hongqing; Zhang, Jinglai

2015-11-01

The methyl-transfer mechanism of human N-acetylserotonin methyltransferase and the roles of several residues around the active sites are investigated by density function theory method. This enzyme will catalyse the conversion of N-acetylserotonin and S-adenosyl-L-methionine (SAM) into melatonin and S-asenosylhomocysteine, which is the terminal step in the melatonin (N-acetyl-5-methoxytryptamine) biosynthesis. The calculated results confirm that the methyl transfer and proton transfer will take place via a SN2 step with a concerted mechanism, which is different from the experimental estimation via a water bridge. The residues H255, D256, E311, and R252 play an important role in reducing the barrier height and inducing methyl transfer. In addition, a full SAM molecule is considered in this work, which is never explored in previous reports. We find that some residues around the SAM in the centre of active site are essential factors to influence the mechanism and barrier height. So a truncated SAM model may not be suitable for all reactions.

Stochastic Spiking Neural Networks Enabled by Magnetic Tunnel Junctions: From Nontelegraphic to Telegraphic Switching Regimes

NASA Astrophysics Data System (ADS)

Liyanagedera, Chamika M.; Sengupta, Abhronil; Jaiswal, Akhilesh; Roy, Kaushik

2017-12-01

Stochastic spiking neural networks based on nanoelectronic spin devices can be a possible pathway to achieving "brainlike" compact and energy-efficient cognitive intelligence. The computational model attempt to exploit the intrinsic device stochasticity of nanoelectronic synaptic or neural components to perform learning or inference. However, there has been limited analysis on the scaling effect of stochastic spin devices and its impact on the operation of such stochastic networks at the system level. This work attempts to explore the design space and analyze the performance of nanomagnet-based stochastic neuromorphic computing architectures for magnets with different barrier heights. We illustrate how the underlying network architecture must be modified to account for the random telegraphic switching behavior displayed by magnets with low barrier heights as they are scaled into the superparamagnetic regime. We perform a device-to-system-level analysis on a deep neural-network architecture for a digit-recognition problem on the MNIST data set.

Graphene/h-BN/GaAs sandwich diode as solar cell and photodetector.

PubMed

Li, Xiaoqiang; Lin, Shisheng; Lin, Xing; Xu, Zhijuan; Wang, Peng; Zhang, Shengjiao; Zhong, Huikai; Xu, Wenli; Wu, Zhiqian; Fang, Wei

2016-01-11

In graphene/semiconductor heterojunction, the statistic charge transfer between graphene and semiconductor leads to decreased junction barrier height and limits the Fermi level tuning effect in graphene, which greatly affects the final performance of the device. In this work, we have designed a sandwich diode for solar cells and photodetectors through inserting 2D hexagonal boron nitride (h-BN) into graphene/GaAs heterostructure to suppress the static charge transfer. The barrier height of graphene/GaAs heterojunction can be increased from 0.88 eV to 1.02 eV by inserting h-BN. Based on the enhanced Fermi level tuning effect with interface h-BN, through adopting photo-induced doping into the device, power conversion efficiency (PCE) of 10.18% has been achieved for graphene/h-BN/GaAs compared with 8.63% of graphene/GaAs structure. The performance of graphene/h-BN/GaAs based photodetector is also improved with on/off ratio increased by one magnitude compared with graphene/GaAs structure.

Weight gain as a barrier to smoking cessation among military personnel.

PubMed

Russ, C R; Fonseca, V P; Peterson, A L; Blackman, L R; Robbins, A S

2001-01-01

To assess the relationships between active-duty military status, military weight standards, concern about weight gain, and anticipated relapse after smoking cessation. Cross-sectional study. Hospital-based tobacco cessation program. Two hundred fifty-two enrollees, of 253 eligible, to a tobacco cessation program in 1999 (135 men, 117 women; 43% on active duty in the military). Independent variables included gender, body mass index (weight/height2), and military status. Dependent variables included about weight gain with smoking cessation and anticipated relapse. In multivariate regression analyses that controlled for gender and body mass index, active-duty military status was associated with an elevated level of concern about weight gain (1.9-point increase on a 10-point scale; 95% confidence interval [CI], 1.0- to 2.8-point increase), as well as higher anticipated relapse (odds ratio [OR] = 3.6; 95% CI, 1.3 to 9.8). Among subjects who were close to or over the U.S. Air Force maximum allowable weight for height, the analogous OR for active-duty military status was 6.9 (p = .02). Occupational weight standards or expectations may pose additional barriers for individuals contemplating or attempting smoking cessation, as they do among active-duty military personnel. These barriers are likely to hinder efforts to decrease smoking prevalence in certain groups.

Gate tunable spin transport in graphene with Rashba spin-orbit coupling

NASA Astrophysics Data System (ADS)

Tan, Xiao-Dong; Liao, Xiao-Ping; Sun, Litao

2016-10-01

Recently, it attracts much attention to study spin-resolved transport properties in graphene with Rashba spin-orbit coupling (RSOC). One remarkable finding is that Klein tunneling in single layer graphene (SLG) with RSOC (SLG + R for short below) behaves as in bi-layer graphene (BLG). Based on the effective Dirac theory, we reconsider this tunneling problem and derive the analytical solution for the transmission coefficients. Our result shows that Klein tunneling in SLG + R and BLG exhibits completely different behaviors. More importantly, we find two new transmission selection rules in SLG + R, i.e., the single band to single band (S → S) and the single band to multiple bands (S → M) transmission regimes, which strongly depend on the relative height among Fermi level, RSOC, and potential barrier. Interestingly, in the S → S transmission regime, only normally incident electrons have capacity to pass through the barrier, while in the S → M transmission regime the angle-dependent tunneling becomes very prominent. Using the transmission coefficients, we also derive spin-resolved conductance analytically, and conductance oscillation with the increasing barrier height and zero conductance gap are found in SLG + R. The present study offers new insights and opportunities for developing graphene-based spin devices.

New Global Calculation of Nuclear Masses and Fission Barriers for Astrophysical Applications

NASA Astrophysics Data System (ADS)

Möller, P.; Sierk, A. J.; Bengtsson, R.; Ichikawa, T.; Iwamoto, A.

2008-05-01

The FRDM(1992) mass model [1] has an accuracy of 0.669 MeV in the region where its parameters were determined. For the 529 masses that have been measured since, its accuracy is 0.46 MeV, which is encouraging for applications far from stability in astrophysics. We are developing an improved mass model, the FRDM(2008). The improvements in the calculations with respect to the FRDM(1992) are in two main areas. (1) The macroscopic model parameters are better optimized. By simulation (adjusting to a limited set of now known nuclei) we can show that this actually makes the results more reliable in new regions of nuclei. (2) The ground-state deformation parameters are more accurately calculated. We minimize the energy in a four-dimensional deformation space (ɛ2, V3, V4, V6,) using a grid interval of 0.01 in all 4 deformation variables. The (non-finalized) FRDM (2008-a) has an accuracy of 0.596 MeV with respect to the 2003 Audi mass evaluation before triaxial shape degrees of freedom are included (in progress). When triaxiality effects are incorporated preliminary results indicate that the model accuracy will improve further, to about 0.586 MeV. We also discuss very large-scale fission-barrier calculations in the related FRLDM (2002) model, which has been shown to reproduce very satisfactorily known fission properties, for example barrier heights from 70Se to the heaviest elements, multiple fission modes in the Ra region, asymmetry of mass division in fission and the triple-humped structure found in light actinides. In the superheavy region we find barriers consistent with the observed half-lives. We have completed production calculations and obtain barrier heights for 5254 nuclei heavier than A = 170 for all nuclei between the proton and neutron drip lines. The energy is calculated for 5009325 different shapes for each nucleus and the optimum barrier between ground state and separated fragments is determined by use of an ``immersion'' technique.

Electrical and dielectric properties of (barium, strontium) titanium trioxide thin film capacitors for ultra-high density dynamic random access memories

NASA Astrophysics Data System (ADS)

Basceri, Cem

The electrical and dielectric properties of fiber-textured, MOCVD (Basb{0.7}Srsb{0.3})TiOsb3 (BST) thin film capacitors appropriate for ultra-large scale integration (ULSI) dynamic random access memory (DRAM) applications have been analyzed. Dielectric relaxation, leakage, resistance degradation, and dielectric response phenomena, within a comprehensive matrix of external and material parameters, have been investigated. The phenomenology of the dielectric response of our BST films has been shown to be well-described by Curie-von Schweidler behavior, although the microscopic origin of this behavior has not been presently agreed upon. The time-dependent polarization behavior has been linked to the dispersion in permittivity with respect to frequency. The leakage current through our BST films has been found to be primarily limited by interfacial Schottky barriers whose properties depend on the electrode material, interface microstructure, and deposition conditions. Its temperature and voltage dependence have been interpreted via a thermionic emission model. Analysis in terms of Schottky-barrier limited current flow gave acceptable values for the cathode barrier height. The results have indicated that our BST films, appropriate for DRAM applications, do not possess depletion layers at the film-electrode interfaces. Instead, they must be considered as depleted of charge carriers across their entire thickness. Resistance degradation has been found to be thermally activated and voltage/field dependent. The results have indicated that there is a film thickness effect, which manifests itself as a decrease in the activation energy with respect to temperature for thicker films. A significant stoichiometry effect on the measured resistance degradation lifetimes has been observed. The analyses of the leakage and capacitance-voltage behaviors for the degraded samples have indicated that a demixing of oxygen vacancies occurs during resistance degradation, which causes the Schottky barrier height to decrease, in agreement with the observed relative shift of the peak capacitance as a function of voltage. For all the film thicknesses and compositions studied, extrapolated resistance degradation lifetimes of our BST films, which were obtained by using an appropriate form, are well above the current benchmark of 10 years at the DRAM operating conditions of 1.6 V and 85sp°C. Above the bulk Curie point (˜300 K), the phenomenological approach, i.e., Landau-Ginzburg-Devonshire (LGD) theory, has been demonstrated to account very well for the observed C-V behavior in our BST films. Furthermore, temperature dependent measurements gave evidence that, as expected, the form of the dielectric behavior changes near the bulk Curie point, but that the phase transition appears for some reason to be frustrated. Film thickness has been established to impact primarily the zero-bias permittivity through a thickness dependence of the first order coefficient of the LGD power series. Our analysis does indicate that if it results from a series-connected interfacial layer, that layer must be a nonlinear dielectric, as must the bulk of the film. The dielectric constant has been found to be composition dependent, reaching its highest values for compositions near the stoichiometric values. Furthermore, film stoichiometry has been established to strongly effect both the first order and third order coefficients of the LGD power series.

Energy band and transport properties in magnetic aperiodic graphene superlattices of Thue-Morse sequence

NASA Astrophysics Data System (ADS)

Yin, Yiheng; Niu, Yanxiong; Zhang, Huiyun; Zhang, Yuping; Liu, Haiyue

2016-02-01

Utilizing the transfer matrix method, we develop the electronic band structure and transport properties in Thue-Morse aperiodic graphene superlattices with magnetic barriers. It is found that the normal transmission is blocked and the position of the Dirac point can be shifted along the wavevector axis by changing the height and width ratio of magnetic barriers, which is intrinsic different from electronic field modulated superlattices. In addition, the angular threshold property of the transmission spectra and the oscillatory property of the conductance have been studied.

Effects of monochromatic light on mucosal mechanical and immunological barriers in the small intestine of broilers.

PubMed

Xie, D; Li, J; Wang, Z X; Cao, J; Li, T T; Chen, J L; Chen, Y X

2011-12-01

Our previous studies demonstrated that green and blue monochromatic lights were effective to stimulate immune response of the spleen in broilers. This study was designed to investigate the effects of monochromatic light on both gut mucosal mechanical and immunological barriers. A total of 120 Arbor Acre male broilers on post-hatching day (P) 0 were exposed to red light, green light (GL), blue light (BL), and white light (WL) for 49 d, respectively. As compared with broilers exposed to WL, the broilers exposed to GL showed that the villus height of small intestine was increased by 19.5% (P = 0.0205) and 38.8% (P = 0.0149), the crypt depth of small intestine was decreased by 15.1% (P = 0.0049) and 10.1% (P = 0.0005), and the ratios of villus height to crypt depth were increased by 39.3% (P < 0.0001) and 52.5% (P < 0.0001) at P7 and P21, respectively. Until P49, an increased villus height (33.6%, P = 0.0076), a decreased crypt depth (15.4%, P = 0.0201), and an increased villus height-to-crypt depth ratio (58.5%, P < 0.0001) were observed in the BL group as compared with the WL group. On the other hand, the numbers of intestinal intraepithelial lymphocytes (27.9%, P < 0.0001 and 37.0%, P < 0.0001), goblet cells (GC, 22.1%, P < 0.0001 and 18.1%, P < 0.0001), and IgA(+) cells (14.8%, P = 0.0543 and 47.9%, P = 0.0377) in the small intestine were significantly increased in the GL group as compared with the WL group at P7 and P21, respectively. The numbers of intestinal intraepithelial lymphocytes (36.2%, P < 0.0001), GC (26.5%, P < 0.0001), and IgA(+) cells (68.0%, P = 0.0177) in the BL group were also higher than those in the WL group at P49. These results suggest that both mucosal mechanical and immunological barriers of the small intestine may be improved by rearing broilers under GL at an early age and under BL at an older age.

Determination of minimum height and lateral design load for MASH test level 4 bridge rails.

DOT National Transportation Integrated Search

2011-12-01

The Manual for Assessing Safety Hardware (MASH) prescribes higher design vehicle impact speed and mass for test level 4 barriers compared to its predecessor National Cooperative Highway Research Program (NCHRP) Report 350. This has resulted in a 56 p...

Height, weight and body mass index values of mid-19th century New York legislative officers.

PubMed

Bodenhorn, Howard

2010-07-01

Previous studies of mid-19th century American heights and body mass index values have used potentially unrepresentative groups-students in military academies, prisoners, and African Americans. This paper uses an alternative source with heights and weights of ordinary people employed in a wide variety of occupations. The results reveal the operation of the antebellum paradox in that average heights declined between men born circa 1820 and those born circa 1840. Average weights also declined for adult males, suggesting a decline in mid-19th century nutritional status. 2010 Elsevier B.V. All rights reserved.

Type of adsorbent and column height in adsorption process of used cooking oil

NASA Astrophysics Data System (ADS)

Hasnelly, Hervelly, Taufik, Yusman; Melany, Ivo Nila

2015-12-01

The purpose of this research was to find out the best adsorbent and column height that can adsorb color and soluble impurities substances in used cooking oil. This research was meant for knowledge development of refined cooking oil technology. The used of this research was giving out information on the recycling process of used cooking oil. Research design used 2 × 2 factorial pattern in randomized group design with 6 repetitions. The first factor is adsorbent type (J) that consist of activated carbon (J1) and Zeolit (J2). The second factor is column height (K) with variations of 15 cm (k1) and 20 cm (k2). Chemical analysis parameter are free fatty acid, water content and saponification value. Physical parameter measurement was done on color with Hunter Lab system analysis and viscosity using viscometer method. Chemical analysis result of preliminary research on used cooking oil showed water content of 1,9%, free fatty acid 1,58%, saponification value 130,79 mg KOH/g oil, viscosity 0,6 d Pas and color with L value of -27,60, a value 1,04 and b value 1,54. Result on main research showed that adsorbent type only gave effect on water content whereas column height and its interaction was not gave significant effect on water content. Interaction between adsorbent type (J) and column height (K) gave significant effect to free fatty acid, saponification value, viscosity and color for L, a and b value of recycled cooking oil.

Double Barriers and Magnetic Field in Bilayer Graphene

NASA Astrophysics Data System (ADS)

Redouani, Ilham; Jellal, Ahmed; Bahlouli, Hocine

2015-12-01

We study the transmission probability in an AB-stacked bilayer graphene of Dirac fermions scattered by a double-barrier structure in the presence of a magnetic field. We take into account the full four bands structure of the energy spectrum and use the suitable boundary conditions to determine the transmission probability. Our numerical results show that for energies higher than the interlayer coupling, four ways for transmission are possible while for energies less than the height of the barrier, Dirac fermions exhibit transmission resonances and only one transmission channel is available. We show that, for AB-stacked bilayer graphene, there is no Klein tunneling at normal incidence. We find that the transmission displays sharp peaks inside the transmission gap around the Dirac point within the barrier regions while they are absent around the Dirac point in the well region. The effect of the magnetic field, interlayer electrostatic potential, and various barrier geometry parameters on the transmission probabilities is also discussed.

SETs: stand evaluation tools: II. tree value conversion standards for hardwood sawtimber

Treesearch

Joseph J. Mendel; Paul S. DeBald; Martin E. Dale

1976-01-01

Tree quatity index tables are presented for 12 important hardwood species of the oak-hickory forest. From these, tree value conversion standards are developed for each species, log grade, merchantable height, and diameter at breast height. The method of calculating tree value conversion standards and adapting them to different conditions is explained. A computer...

Estimation of Return Values of Wave Height: Consequences of Missing Observations

ERIC Educational Resources Information Center

Ryden, Jesper

2008-01-01

Extreme-value statistics is often used to estimate so-called return values (actually related to quantiles) for environmental quantities like wind speed or wave height. A basic method for estimation is the method of block maxima which consists in partitioning observations in blocks, where maxima from each block could be considered independent.…

Debris flow impact estimation on a rigid barrier

NASA Astrophysics Data System (ADS)

Vagnon, Federico; Segalini, Andrea

2016-07-01

The aim of this paper is to analyse debris flow impact against rigid and undrained barrier in order to propose a new formulation for the estimation of acting force after the flow impact to safe design protection structures. For this reason, this work concentrates on the flow impact, by performing a series of small scale tests in a specifically created flume. Flow characteristics (flow height and velocity) and applied loads (dynamic and static) on barrier were measured using four ultrasonic devices, four load cells and a contact surface pressure gauge. The results obtained were compared with main existing models and a new equation is proposed. Furthermore, a brief review of the small scale theory was provided to analyse the scale effects that can affect the results.

Nonaxial hexadecapole deformation effects on the fission barrier

NASA Astrophysics Data System (ADS)

Kardan, A.; Nejati, S.

2016-06-01

Fission barrier of the heavy nucleus 250Cf is analyzed in a multi-dimensional deformation space. This space includes two quadrupole (ɛ2,γ) and three hexadecapole deformation (ɛ40,ɛ42,ɛ44) parameters. The analysis is performed within an unpaired macroscopic-microscopic approach. Special attention is given to the effects of the axial and non-axial hexadecapole deformation shapes. It is found that the inclusion of the nonaxial hexadecapole shapes does not change the fission barrier heights, so it should be sufficient to minimize the energy in only one degree of freedom in the hexadecapole space ɛ4. The role of hexadecapole deformation parameters is also discussed on the Lublin-Strasbourg drop (LSD) macroscopic and the Strutinsky shell energies.

Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope

PubMed Central

Nazin, G. V.; Wu, S. W.; Ho, W.

2005-01-01

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends. PMID:15956189

Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope.

PubMed

Nazin, G V; Wu, S W; Ho, W

2005-06-21

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends.

Modulating emission intensity of GaN-based green light emitting diodes on c-plane sapphire

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Chunhua; Ma, Ziguang; Zhou, Junming

2014-04-14

The asymmetric dual-wavelength (green/blue) coupled InGaN/GaN multiple quantum wells were proposed to modulate the green emission intensity. Electroluminescent measurements demonstrate the conspicuous increment of the green light intensity by decreasing the coupled barrier thickness. This was partly attributed to capture of more carriers when holes tunnel across the thinner barrier from the blue quantum wells, as a hole reservoir, to the green quantum wells. While lower effective barrier height of the blue quantum wells benefits improved hole transportation from p-GaN to the active region. Efficiency droop of the green quantum wells was partially alleviated due to the enhanced injection efficiencymore » of holes.« less

An aggregation-volume-bias Monte Carlo investigation on the condensation of a Lennard-Jones vapor below the triple point and crystal nucleation in cluster systems: an in-depth evaluation of the classical nucleation theory.

PubMed

Chen, Bin; Kim, Hyunmi; Keasler, Samuel J; Nellas, Ricky B

2008-04-03

The aggregation-volume-bias Monte Carlo based simulation technique, which has led to our recent success in vapor-liquid nucleation research, was extended to the study of crystal nucleation processes. In contrast to conventional bulk-phase techniques, this method deals with crystal nucleation events in cluster systems. This approach was applied to the crystal nucleation of Lennard-Jonesium under a wide range of undercooling conditions from 35% to 13% below the triple point. It was found that crystal nucleation in these model clusters proceeds initially via a vapor-liquid like aggregation followed by the formation of crystals inside the aggregates. The separation of these two stages of nucleation is distinct except at deeper undercooling conditions where the crystal nucleation barrier was found to diminish. The simulation results obtained for these two nucleation steps are separately compared to the classical nucleation theory (CNT). For the vapor-liquid nucleation step, the CNT was shown to provide a reasonable description of the critical cluster size but overestimate the barrier heights, consistent with previous simulation studies. On the contrary, for the crystal nucleation step, nearly perfect agreement with the barrier heights was found between the simulations and the CNT. For the critical cluster size, the comparison is more difficult as the simulation data were found to be sensitive to the definition of the solid cluster, but a stringent criterion and lower undercooling conditions generally lead to results closer with the CNT. Additional simulations at undercooling conditions of 40% or above indicate a nearly barrierless transition from the liquid to crystalline-like structure for sufficiently large clusters, which leads to further departure of the barrier height predicted by the CNT from the simulation data for the aggregation step. This is consistent with the latest experimental results on argon that show an unusually large underestimation of the nucleation rate by the CNT toward deep undercooling conditions.

Metal-semiconductor barrier modulation for high photoresponse in transition metal dichalcogenide field effect transistors.

PubMed

Li, Hua-Min; Lee, Dae-Yeong; Choi, Min Sup; Qu, Deshun; Liu, Xiaochi; Ra, Chang-Ho; Yoo, Won Jong

2014-02-10

A gate-controlled metal-semiconductor barrier modulation and its effect on carrier transport were investigated in two-dimensional (2D) transition metal dichalcogenide (TMDC) field effect transistors (FETs). A strong photoresponse was observed in both unipolar MoS2 and ambipolar WSe2 FETs (i) at the high drain voltage due to a high electric field along the channel for separating photo-excited charge carriers and (ii) at the certain gate voltage due to the optimized barriers for the collection of photo-excited charge carriers at metal contacts. The effective barrier height between Ti/Au and TMDCs was estimated by a low temperature measurement. An ohmic contact behavior and drain-induced barrier lowering (DIBL) were clearly observed in MoS2 FET. In contrast, a Schottky-to-ohmic contact transition was observed in WSe2 FET as the gate voltage increases, due to the change of majority carrier transport from holes to electrons. The gate-dependent barrier modulation effectively controls the carrier transport, demonstrating its great potential in 2D TMDCs for electronic and optoelectronic applications.

Determination of ionospheric electron content from the Faraday rotation of geostationary satellite signals.

NASA Technical Reports Server (NTRS)

Titheridge, J. E.

1972-01-01

Observation that calculations of the integrated electron content up to the height of the satellite, using a wide range of model ionospheres (with a peak at 300 km) could be up to four times the value deduced from Faraday rotation measurements. However, using a fixed mean field height of 400 km, the observed Faraday rotation gives the electron content up to a height h sub F of 2000 km with an accuracy of plus or minus 3%. For observations at different magnetic and geographic latitudes, and geostationary satellites at different longitudes, the optimum value of h sub F varies by only plus or minus 200 km. Nighttime increases in the height of the ionosphere have little effect on h sub F, but increase the mean field height to about 470 km. Using a fixed value of 420 km, with h sub F = 2000 km, gives an accuracy of plus or minus 5% under most conditions.

Influence of in doping in GaN barriers on luminescence properties of InGaN/GaN multiple quantum well LEDs

NASA Astrophysics Data System (ADS)

Wang, Xiaowei; Yang, Jing; Zhao, Degang; Jiang, Desheng; Liu, Zongshun; Liu, Wei; Liang, Feng; Liu, Shuangtao; Xing, Yao; Wang, Wenjie; Li, Mo

2018-02-01

Room-temperature photoluminescence (RT PL) spectra of InGaN/GaN multiple quantum well (MQW) structures grown by metalorganic chemical vapor deposition (MOCVD) was investigated. It is found that with increasing In content in GaN barriers, the FWHM and emission intensity decreases, and the emission wavelength is first red shift and then blue shift. The shrinkage of FWHM and emission wavelength blue shift can be attributed to the reduction of piezoelectric field, and the lower height of potential barrier will make carrier confinement weaker and ground state level lower, which resulting in emission intensity decreasing and wavelength red shift. In addition, doping the barrier with In will induce more inhomogeneous and deeper localized states in InGaN QWs, which also contribute to a red shift of PL emission wavelength.

Planar edge Schottky barrier-tunneling transistors using epitaxial graphene/SiC junctions.

PubMed

Kunc, Jan; Hu, Yike; Palmer, James; Guo, Zelei; Hankinson, John; Gamal, Salah H; Berger, Claire; de Heer, Walt A

2014-09-10

A purely planar graphene/SiC field effect transistor is presented here. The horizontal current flow over one-dimensional tunneling barrier between planar graphene contact and coplanar two-dimensional SiC channel exhibits superior on/off ratio compared to conventional transistors employing vertical electron transport. Multilayer epitaxial graphene (MEG) grown on SiC(0001̅) was adopted as the transistor source and drain. The channel is formed by the accumulation layer at the interface of semi-insulating SiC and a surface silicate that forms after high vacuum high temperature annealing. Electronic bands between the graphene edge and SiC accumulation layer form a thin Schottky barrier, which is dominated by tunneling at low temperatures. A thermionic emission prevails over tunneling at high temperatures. We show that neglecting tunneling effectively causes the temperature dependence of the Schottky barrier height. The channel can support current densities up to 35 A/m.

Doubly charged coronene clusters—Much smaller than previously observed

NASA Astrophysics Data System (ADS)

Mahmoodi-Darian, Masoomeh; Raggl, Stefan; Renzler, Michael; Goulart, Marcelo; Huber, Stefan E.; Mauracher, Andreas; Scheier, Paul; Echt, Olof

2018-05-01

The smallest doubly charged coronene cluster ions reported so far, Cor152+, were produced by charge exchange between bare coronene clusters and He2+ [H. A. B. Johansson et al., Phys. Rev. A 84, 043201 (2011)]. These dications are at least five times larger than the estimated Rayleigh limit, i.e., the size at which the activation barrier for charge separation vanishes. Such a large discrepancy is unheard of for doubly charged atomic or molecular clusters. Here we report the mass spectrometric observation of doubly charged coronene trimers, produced by electron ionization of helium nanodroplets doped with coronene. The observation implies that Cor32+ features a non-zero fission barrier too large to overcome under the present experimental conditions. The height of the barriers for the dimer and trimer has been estimated by means of density functional theory calculations. A sizeable barrier for the trimer has been revealed in agreement with the experimental findings.

Multi-barrier field-emission behavior in PBTTT thin films at low temperatures

PubMed Central

Kang, Evan S. H.; Kim, Eunseong

2015-01-01

We investigated the low-temperature transport mechanism for poly[2,5-bis(3-alkylthiophen-2-yl)thieno(3,2-b)thiophene] (PBTTT). The temperature-dependent transport behavior was studied by varying the drain–source electric field and gate bias. The results suggest that low-temperature charge transport is dominated by direct tunneling at low electric fields, while field emission is prevailing for high electric fields with high carrier densities. However, the obtained barrier heights are remarkably greater than expected in a conventional field emission. We propose a simplified model of field emission through quasi-one-dimensional path with multiple barriers which shows good agreement with the results more clearly. Field emission across the domain boundaries may assist in overcoming the transport barriers induced by the interchain disorder, which results in the weak temperature dependence of conductivities and nonlinear current–voltage relation at low temperatures. PMID:25670532

Graphene barristor, a triode device with a gate-controlled Schottky barrier.

PubMed

Yang, Heejun; Heo, Jinseong; Park, Seongjun; Song, Hyun Jae; Seo, David H; Byun, Kyung-Eun; Kim, Philip; Yoo, InKyeong; Chung, Hyun-Jong; Kim, Kinam

2012-06-01

Despite several years of research into graphene electronics, sufficient on/off current ratio I(on)/I(off) in graphene transistors with conventional device structures has been impossible to obtain. We report on a three-terminal active device, a graphene variable-barrier "barristor" (GB), in which the key is an atomically sharp interface between graphene and hydrogenated silicon. Large modulation on the device current (on/off ratio of 10(5)) is achieved by adjusting the gate voltage to control the graphene-silicon Schottky barrier. The absence of Fermi-level pinning at the interface allows the barrier's height to be tuned to 0.2 electron volt by adjusting graphene's work function, which results in large shifts of diode threshold voltages. Fabricating GBs on respective 150-mm wafers and combining complementary p- and n-type GBs, we demonstrate inverter and half-adder logic circuits.

Does disc space height of fused segment affect adjacent degeneration in ALIF? A finite element study.

PubMed

Tang, Shujie; Meng, Xueying

2011-01-01

The restoration of disc space height of fused segment is essential in anterior lumbar interbody fusion, while the disc space height in many cases decreased postoperatively, which may adversely aggravate the adjacent segmental degeneration. However, no literature available focused on the issue. A normal healthy finite element model of L3-5 and four anterior lumbar interbody fusion models with different disc space height of fused segment were developed. 800 N compressive loading plus 10 Nm moments simulating flexion, extension, lateral bending and axial rotation were imposed on L3 superior endplate. The intradiscal pressure, the intersegmental rotation, the tresca stress and contact force of facet joints in L3-4 were investigated. Anterior lumbar interbody fusion with severely decreased disc space height presented with the highest values of the four parameters, and the normal healthy model presented with the lowest values except, under extension, the contact force of facet joints in normal healthy model is higher than that in normal anterior lumbar interbody fusion model. With disc space height decrease, the values of parameters in each anterior lumbar interbody fusion model increase gradually. Anterior lumbar interbody fusion with decreased disc space height aggravate the adjacent segmental degeneration more adversely.

Genetic variation in GPR133 is associated with height: genome wide association study in the self-contained population of Sorbs.

PubMed

Tönjes, Anke; Koriath, Moritz; Schleinitz, Dorit; Dietrich, Kerstin; Böttcher, Yvonne; Rayner, Nigel W; Almgren, Peter; Enigk, Beate; Richter, Olaf; Rohm, Silvio; Fischer-Rosinsky, Antje; Pfeiffer, Andreas; Hoffmann, Katrin; Krohn, Knut; Aust, Gabriela; Spranger, Joachim; Groop, Leif; Blüher, Matthias; Kovacs, Peter; Stumvoll, Michael

2009-12-01

Recently, associations of several common genetic variants with height have been reported in different populations. We attempted to identify further variants associated with adult height in a self-contained population (the Sorbs in Eastern Germany) as discovery set. We performed a genome wide association study (GWAS) (approximately 390,000 genetic polymorphisms, Affymetrix gene arrays) on adult height in 929 Sorbian individuals. Subsequently, the best SNPs (P < 0.001) were taken forward to a meta-analysis together with two independent cohorts [Diabetes Genetics Initiative, British 1958 Birth Cohort, (58BC, publicly available)]. Furthermore, we genotyped our best signal for replication in two additional German cohorts (Leipzig, n = 1044 and Berlin, n = 1728). In the primary Sorbian GWAS, we identified 5 loci with a P-value < 10(-5) and 455 SNPs with P-value < 0.001. In the meta-analysis on those 455 SNPs, only two variants in GPR133 (rs1569019 and rs1976930; in LD with each other) retained a P-value at or below 10(-6) and were associated with height in the three cohorts individually. Upon replication, the SNP rs1569019 showed significant effects on height in the Leipzig cohort (P = 0.004, beta = 1.166) and in 577 men of the Berlin cohort (P = 0.049, beta = 1.127) though not in women. The combined analysis of all five cohorts (n = 6,687) resulted in a P-value of 4.7 x 10(-8) (beta = 0.949). In conclusion, our GWAS suggests novel loci influencing height. In view of the robust replication in five different cohorts, we propose GPR133 to be a novel gene associated with adult height.

Systematic analysis of hot Yb* isotopes using the energy density formalism

NASA Astrophysics Data System (ADS)

Jain, Deepika; Sharma, Manoj K.; Rajni; Kumar, Raj; Gupta, Raj K.

2014-10-01

A systematic study of the spin-orbit density interaction potential is carried out, with spherical as well as deformed choices of nuclei, for a variety of near-symmetric and asymmetric colliding nuclei leading to various isotopes of the compound nucleus Yb*, using the semiclassical extended Thomas-Fermi formulation (ETF) of the Skyrme energy density formalism (SEDF). We observe that the spin-orbit density interaction barrier height ( and barrier position ( increase systematically with the increase in number of neutrons in both the projectile and target, for spherical systems. On allowing deformation effects with optimum orientations, the barrier-height increases by a large order of magnitude, as compared to the spherical case, in going from 156Yb* to 172Yb* nuclear systems formed via near-symmetric Ni+Mo or asymmetric O+Sm colliding nuclei, except that for the oblate-shaped nuclei, the is the highest and shifts towards a smaller (compact) interaction radius. The temperature does not change the behavior of spin-orbit density dependent ( and independent ( interaction potentials, except for some minor changes in the magnitude. The orientation degree of freedom also plays an important role in modifying the barrier characteristics and hence produces a large effect on the fusion cross section. The fusion excitation function of the compound nuclei 160, 164Yb* formed in different incoming channels, show clearly that the new forces GSkI and KDE0v1 respond better than the old SIII force. Among the first two, KDE0v1 seems to perform better. The fusion cross-sections are also predicted for a few other isotopes of Yb*.

Naturalizing supersymmetry with a two-field relaxion mechanism

DOE PAGES

Evans, Jason L.; Gherghetta, Tony; Nagata, Natsumi; ...

2016-09-26

We present a supersymmetric version of a two-field relaxion model that naturalizes tuned versions of supersymmetry. This arises from a relaxion mechanism that does not depend on QCD dynamics and where the relaxion potential barrier height is controlled by a second axion-like field. During the cosmological evolution, the relaxion rolls with a nonzero value that breaks supersymmetry and scans the soft supersymmetric mass terms. Electroweak symmetry is broken after the soft masses become of order the supersymmetric Higgs mass term and causes the relaxion to stop rolling for superpartner masses up to ~10 9 GeV. This can explain the tuningmore » in supersymmetric models, including split-SUSY models, while preserving the QCD axion solution to the strong CP problem. Furthermore, besides predicting two very weakly-coupled axion-like particles, the supersymmetric spectrum may contain an extra Goldstino, which could be a viable dark matter candidate.« less

Crosstalk and transitions between multiple spatial maps in an attractor neural network model of the hippocampus: Collective motion of the activity

NASA Astrophysics Data System (ADS)

Monasson, R.; Rosay, S.

2014-03-01

The dynamics of a neural model for hippocampal place cells storing spatial maps is studied. In the absence of external input, depending on the number of cells and on the values of control parameters (number of environments stored, level of neural noise, average level of activity, connectivity of place cells), a "clump" of spatially localized activity can diffuse or remains pinned due to crosstalk between the environments. In the single-environment case, the macroscopic coefficient of diffusion of the clump and its effective mobility are calculated analytically from first principles and corroborated by numerical simulations. In the multienvironment case the heights and the widths of the pinning barriers are analytically characterized with the replica method; diffusion within one map is then in competition with transitions between different maps. Possible mechanisms enhancing mobility are proposed and tested.

Organic/Inorganic Hybrid p-n Junction with PEDOT Nanoparticles for Light-Emitting Diode

NASA Astrophysics Data System (ADS)

Kim, M. S.; Jin, S. M.; Cho, M. Y.; Choi, H. Y.; Kim, G. S.; Jeon, S. M.; Yim, K. G.; Kim, H. G.; Shim, K. B.; Kang, B. K.; Kim, Y.; Lee, D. Y.; Kim, J. S.; Kim, J. S.; Leem, J. Y.

2011-12-01

A heavily Si-doped GaN/polymer hybrid structure with p-type poly(3,4-ethylene-dioxythiophene):beta-1,3-glucan (PEDOT nanoparticle) interface layer has been fabricated. The Si-doped GaN thin film with carrier concentration of 1×1019 cm-3 was grown by metal-organic chemical vapor deposition (MOCVD). The PEDOT nanoparticle with various sizes ranging from 60 to 120 nm was synthesized via a miniemulsion polymerization process. The electrical conductivity of the PEDOT nanoparticle is less than 1.2 S/cm. The current-voltage (I-V) characteristic of the hybrid structure shows diode-like behavior. The I-V characteristic was examined in the framework of the thermionic emission model. The ideality factor and barrier height of the hybrid structure were obtained as 5.6 and 0.41 eV, respectively. The value of ideality factor is decreased by inserting the PEDOT nanoparticle interface layer.

Direct ab initio dynamics study of the reaction of C 2(A 3Π u) radical with C 2H 6

NASA Astrophysics Data System (ADS)

Li, Na; Huo, Rui-Ping; Zhang, Xiang; Huang, Xu-Ri; Li, Ji-Lai; Sun, Chia-Chung

2011-02-01

The reaction of C 2 (A 3Π u) with C 2H 6 has been investigated at the BMC-CCSD//BB1K/6-311+G(2d, 2p) level. The classical barrier height for H-abstraction reaction is calculated to be 3.32 kcal/mol and the electron transfer behavior is also analyzed in detail. The rate constants are calculated by TST, CVT, and CVT/SCT over a wide temperature range 50-3000 K. The results indicate: (1) variational effect is small and nonclassical reflection effect is important to the H abstraction in high temperature region; and (2) variational effect is negligible and tunneling effect cooperating with the nonclassical reflection effect makes the rate constant temperature independence in low-temperature range. The CVT/SCT rate constants are in excellent agreement with experimental values.

Growth and Characterization of CuO Nanostructures on Si for the Fabrication of CuO/p-Si Schottky Diodes

PubMed Central

Çetinkaya, S.; Çetinkara, H. A.; Bayansal, F.; Kahraman, S.

2013-01-01

CuO interlayers in the CuO/p-Si Schottky diodes were fabricated by using CBD and sol-gel methods. Deposited CuO layers were characterized by SEM and XRD techniques. From the SEM images, it was seen that the film grown by CBD method is denser than the film grown by sol-gel method. This result is compatible with XRD results which show that the crystallization in CBD method is higher than it is in sol-gel method. For the electrical investigations, current-voltage characteristics of the diodes have been studied at room temperature. Conventional I-V and Norde's methods were used in order to determine the ideality factor, barrier height, and series resistance values. It was seen that the morphological and structural analysis are compatible with the results of electrical investigations. PMID:23766670

36 CFR 1192.105 - Priority seating signs.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 36 Parks, Forests, and Public Property 3 2010-07-01 2010-07-01 false Priority seating signs. 1192.105 Section 1192.105 Parks, Forests, and Public Property ARCHITECTURAL AND TRANSPORTATION BARRIERS...” spacing (generally, the space between letters shall be 1/16 the height of upper case letters), and shall...

36 CFR 1192.105 - Priority seating signs.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 36 Parks, Forests, and Public Property 3 2011-07-01 2011-07-01 false Priority seating signs. 1192.105 Section 1192.105 Parks, Forests, and Public Property ARCHITECTURAL AND TRANSPORTATION BARRIERS...” spacing (generally, the space between letters shall be 1/16 the height of upper case letters), and shall...

36 CFR 1192.39 - Destination and route signs.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 36 Parks, Forests, and Public Property 3 2010-07-01 2010-07-01 false Destination and route signs. 1192.39 Section 1192.39 Parks, Forests, and Public Property ARCHITECTURAL AND TRANSPORTATION BARRIERS... (generally, the space between letters shall be 1/16 the height of upper case letters), and shall contrast...

36 CFR 1192.55 - Priority seating signs.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 36 Parks, Forests, and Public Property 3 2011-07-01 2011-07-01 false Priority seating signs. 1192.55 Section 1192.55 Parks, Forests, and Public Property ARCHITECTURAL AND TRANSPORTATION BARRIERS... 5/8 inch, with “Wide” spacing (generally, the space between letters shall be 1/16 the height of...

36 CFR 1192.55 - Priority seating signs.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 36 Parks, Forests, and Public Property 3 2010-07-01 2010-07-01 false Priority seating signs. 1192.55 Section 1192.55 Parks, Forests, and Public Property ARCHITECTURAL AND TRANSPORTATION BARRIERS... 5/8 inch, with “Wide” spacing (generally, the space between letters shall be 1/16 the height of...

36 CFR 1192.27 - Priority seating signs.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 36 Parks, Forests, and Public Property 3 2011-07-01 2011-07-01 false Priority seating signs. 1192.27 Section 1192.27 Parks, Forests, and Public Property ARCHITECTURAL AND TRANSPORTATION BARRIERS..., the space between letters shall be 1/16 the height of upper case letters), and shall contrast with the...

36 CFR 1192.39 - Destination and route signs.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 36 Parks, Forests, and Public Property 3 2011-07-01 2011-07-01 false Destination and route signs. 1192.39 Section 1192.39 Parks, Forests, and Public Property ARCHITECTURAL AND TRANSPORTATION BARRIERS... (generally, the space between letters shall be 1/16 the height of upper case letters), and shall contrast...

Apolipoprotein E4 influences growth and cognitive responses to micronutrient supplementation in shantytown children from northeast Brazil.

PubMed

Mitter, Sumeet S; Oriá, Reinaldo B; Kvalsund, Michelle P; Pamplona, Paula; Joventino, Emanuella Silva; Mota, Rosa M S; Gonçalves, Davi C; Patrick, Peter D; Guerrant, Richard L; Lima, Aldo A M

2012-01-01

Apolipoprotein E4 may benefit children during early periods of life when the body is challenged by infection and nutritional decline. We examined whether apolipoprotein E4 affects intestinal barrier function, improving short-term growth and long-term cognitive outcomes in Brazilian shantytown children. A total of 213 Brazilian shantytown children with below-median height-for-age z-scores (HAZ) received 200,000 IU of retinol (every four months), zinc (40 mg twice weekly), or both for one year, with half of each group receiving glutamine supplementation for 10 days. Height-for-age z-scores, weight-for-age z-scores, weight-for-height z-scores, and lactulose:mannitol ratios were assessed during the initial four months of treatment. An average of four years (range 1.4-6.6) later, the children underwent cognitive testing to evaluate non-verbal intelligence, coding, verbal fluency, verbal learning, and delayed verbal learning. Apolipoprotein E4 carriage was determined by PCR analysis for 144 children. Thirty-seven children were apolipoprotein E4(+), with an allele frequency of 13.9%. Significant associations were found for vitamin A and glutamine with intestinal barrier function. Apolipoprotein E4(+) children receiving glutamine presented significant positive Pearson correlations between the change in height-for-age z-scores over four months and delayed verbal learning, along with correlated changes over the same period in weight-for-age z-scores and weight-for-height z-scores associated with non-verbal intelligence quotients. There was a significant correlation between vitamin A supplementation of apolipoprotein E4(+) children and improved delta lactulose/mannitol. Apolipoprotein E4(-) children, regardless of intervention, exhibited negative Pearson correlations between the change in lactulose-to-mannitol ratio over four months and verbal learning and non-verbal intelligence. During development, apolipoprotein E4 may function concomitantly with gut-tropic nutrients to benefit immediate nutritional status, which can translate into better long-term cognitive outcomes.

A Temporal Assessment of Barrier Island Vulnerability to Extreme Wave Events, Virginia Coast Reserve

NASA Astrophysics Data System (ADS)

Oster, D. J.; Moore, L. J.; Doran, K. J.; Stockdon, H. F.

2010-12-01

Barrier island vulnerability to storm-generated waves is directly related to interactions between shoreface morphology and surf-zone dynamics. During storms, the seaward-most dune often limits the landward extent of wave energy; however, if maximum wave run-up exceeds the elevation of the top of the dune, overwash or inundation may occur. The ‘Storm Impact Scale’ presented by Sallenger (2000) classifies barrier beach vulnerability to individual storm events based on the elevation of the frontal dune crest and toe relative to maximum wave run-up. Changes to the dune and beachface can occur over a range of time scales, altering local vulnerability to extreme waves from storms, even as a storm is occurring. As sea level continues to rise, barrier beaches will become increasingly vulnerable to overwash and inundation from a greater number of storms. Our objective is to assess temporal trends in barrier island vulnerability while also exploring island-chain-wide response and recovery from two notably different storm events (Nor’Ida and Hurricane Bonnie) along the undeveloped barrier islands of the Virginia Coast Reserve (VCR). We compare shoreline position and elevations of the frontal dune crest (DHIGH) and dune toe (DLOW) across four lidar data sets collected between 1998-2010. Observed significant wave height and period from the National Data Buoy Center and the Duck, NC Field Research Facility for the time period between 1985 and 2009 are classified to represent one-year, five-year, and ten-year storm events that serve as the basis for comparison of island vulnerability through time to a range of storm severity. Initial results reveal significant spatial and temporal variation in barrier island vulnerability to storms throughout the VCR. Despite the range of variability, all three beach features (i.e., shoreline position, DHIGH and DLOW), have moved landward indicating large-scale, widespread migration, or narrowing, of VCR barrier island landforms over the last 10 years. Potentially evolving long-term trends in island vulnerability appear to be difficult to detect, likely due to the short time window of analysis and the preferential capture of short-term variations as two out of the four lidar data sets were collected immediately following a storm event. Further statistical analysis of changes in frontal dune height (DHIGH) and the distance between the dune toe (DLOW) and shoreline will provide insight into short-term responses to individual storms as well as the potential for future long-term changes in barrier island vulnerability, contributing to a better understanding of barrier island response to rising seas and severe storms.

Electronic Properties of DNA-Based Schottky Barrier Diodes in Response to Alpha Particles.

PubMed

Al-Ta'ii, Hassan Maktuff Jaber; Periasamy, Vengadesh; Amin, Yusoff Mohd

2015-05-21

Detection of nuclear radiation such as alpha particles has become an important field of research in recent history due to nuclear threats and accidents. In this context; deoxyribonucleic acid (DNA) acting as an organic semiconducting material could be utilized in a metal/semiconductor Schottky junction for detecting alpha particles. In this work we demonstrate for the first time the effect of alpha irradiation on an Al/DNA/p-Si/Al Schottky diode by investigating its current-voltage characteristics. The diodes were exposed for different periods (0-20 min) of irradiation. Various diode parameters such as ideality factor, barrier height, series resistance, Richardson constant and saturation current were then determined using conventional, Cheung and Cheung's and Norde methods. Generally, ideality factor or n values were observed to be greater than unity, which indicates the influence of some other current transport mechanism besides thermionic processes. Results indicated ideality factor variation between 9.97 and 9.57 for irradiation times between the ranges 0 to 20 min. Increase in the series resistance with increase in irradiation time was also observed when calculated using conventional and Cheung and Cheung's methods. These responses demonstrate that changes in the electrical characteristics of the metal-semiconductor-metal diode could be further utilized as sensing elements to detect alpha particles.

Associative desorption of hydrogen isotopologues from copper surfaces: Characterization of two reaction mechanisms

NASA Astrophysics Data System (ADS)

Kaufmann, Sven; Shuai, Quan; Auerbach, Daniel J.; Schwarzer, Dirk; Wodtke, Alec M.

2018-05-01

We report quantum-state resolved measurements of angular and velocity distributions of the associative desorption of H2, HD, and D2 from Cu(111) and Cu(211) surfaces. The desorbing molecules have bimodal velocity distributions comprising a "fast" channel and a "slow" channel on both facets. The "fast channel" is promoted by both hydrogen incidence translational and vibrational energy, while the "slow channel" is promoted by vibrational energy but inhibited by translational energy. Using detailed balance, we determine state-specific reaction probabilities for dissociative adsorption and compare these to theoretical calculations. The results for the activation barrier for the "fast channel" on Cu(111) are in agreement with theory within "chemical accuracy" (1 kcal/mole). Results on the Cu(211) facet provide direct information on the effect of increasing step density, which is commonly believed to increase reactivity. Differences in reactivity on the (111) and (211) facets are subtle - quantum state specific reactivity on the (211) surface is characterized by a broader distribution of barrier heights whose average values are higher than for reaction on (111). We fully characterize the "slow channel," which has not been found in theoretical calculations although it makes up a large fraction of the reactivity in these experiments.

Polarization-dependent interfacial coupling modulation of ferroelectric photovoltaic effect in PZT-ZnO heterostructures

NASA Astrophysics Data System (ADS)

Pan, Dan-Feng; Bi, Gui-Feng; Chen, Guang-Yi; Zhang, Hao; Liu, Jun-Ming; Wang, Guang-Hou; Wan, Jian-Guo

2016-03-01

Recently, ferroelectric perovskite oxides have drawn much attention due to potential applications in the field of solar energy conversion. However, the power conversion efficiency of ferroelectric photovoltaic effect currently reported is far below the expectable value. One of the crucial problems lies in the two back-to-back Schottky barriers, which are formed at the ferroelectric-electrode interfaces and blocking most of photo-generated carriers to reach the outside circuit. Herein, we develop a new approach to enhance the ferroelectric photovoltaic effect by introducing the polarization-dependent interfacial coupling effect. Through inserting a semiconductor ZnO layer with spontaneous polarization into the ferroelectric ITO/PZT/Au film, a p-n junction with strong polarization-dependent interfacial coupling effect is formed. The power conversion efficiency of the heterostructure is improved by nearly two orders of magnitude and the polarization modulation ratio is increased about four times. It is demonstrated that the polarization-dependent interfacial coupling effect can give rise to a great change in band structure of the heterostructure, not only producing an aligned internal electric field but also tuning both depletion layer width and potential barrier height at PZT-ZnO interface. This work provides an efficient way in developing highly efficient ferroelectric-based solar cells and novel optoelectronic memory devices.

Humidity influenced capacitance and resistance of an Al/DNA/Al Schottky diode irradiated by alpha particles

PubMed Central

Al-Ta’ii, Hassan Maktuff Jaber; Amin, Yusoff Mohd; Periasamy, Vengadesh

2016-01-01

Deoxyribonucleic acid or DNA based sensors, especially as humidity and alpha particle sensors have become quite popular in recent times due to flexible and highly optimizable nature of this fundamental biomaterial. Application of DNA electronics allow for more sensitive, accurate and effective sensors to be developed and fabricated. In this work, we examined the effect of different humidity conditions on the capacitive and resistive response of Aluminum (Al)/DNA/Al Schottky barrier structure when bombarded by time-dependent dosages of alpha particles. Based on current-voltage profiles, which demonstrated rectifying behaviours, Schottky diode parameters such as ideality factor, barrier height and series resistance was calculated. Results observed generally pointed towards a decrease in the resistance value from the pristine to the radiated structures. It was also demonstrated that under the effect of humidity, the capacitance of the DNA thin film increased from 0.05894 to 92.736 nF, with rising relative humidity level. We also observed the occurrence of the hypersensitivity phenomena after alpha irradiation between 2 to 4 min by observing a drop in the series resistance, crucial in the study of DNA damage and repair mechanisms. These observations may also suggest the exciting possibility of utilizing Al/DNA/Al Schottky diodes as potentially sensitive humidity sensors. PMID:27160654

Polarization-dependent interfacial coupling modulation of ferroelectric photovoltaic effect in PZT-ZnO heterostructures.

PubMed

Pan, Dan-Feng; Bi, Gui-Feng; Chen, Guang-Yi; Zhang, Hao; Liu, Jun-Ming; Wang, Guang-Hou; Wan, Jian-Guo

2016-03-08

Recently, ferroelectric perovskite oxides have drawn much attention due to potential applications in the field of solar energy conversion. However, the power conversion efficiency of ferroelectric photovoltaic effect currently reported is far below the expectable value. One of the crucial problems lies in the two back-to-back Schottky barriers, which are formed at the ferroelectric-electrode interfaces and blocking most of photo-generated carriers to reach the outside circuit. Herein, we develop a new approach to enhance the ferroelectric photovoltaic effect by introducing the polarization-dependent interfacial coupling effect. Through inserting a semiconductor ZnO layer with spontaneous polarization into the ferroelectric ITO/PZT/Au film, a p-n junction with strong polarization-dependent interfacial coupling effect is formed. The power conversion efficiency of the heterostructure is improved by nearly two orders of magnitude and the polarization modulation ratio is increased about four times. It is demonstrated that the polarization-dependent interfacial coupling effect can give rise to a great change in band structure of the heterostructure, not only producing an aligned internal electric field but also tuning both depletion layer width and potential barrier height at PZT-ZnO interface. This work provides an efficient way in developing highly efficient ferroelectric-based solar cells and novel optoelectronic memory devices.

Polarization-dependent interfacial coupling modulation of ferroelectric photovoltaic effect in PZT-ZnO heterostructures

PubMed Central

Pan, Dan-Feng; Bi, Gui-Feng; Chen, Guang-Yi; Zhang, Hao; Liu, Jun-Ming; Wang, Guang-Hou; Wan, Jian-Guo

2016-01-01

Recently, ferroelectric perovskite oxides have drawn much attention due to potential applications in the field of solar energy conversion. However, the power conversion efficiency of ferroelectric photovoltaic effect currently reported is far below the expectable value. One of the crucial problems lies in the two back-to-back Schottky barriers, which are formed at the ferroelectric-electrode interfaces and blocking most of photo-generated carriers to reach the outside circuit. Herein, we develop a new approach to enhance the ferroelectric photovoltaic effect by introducing the polarization-dependent interfacial coupling effect. Through inserting a semiconductor ZnO layer with spontaneous polarization into the ferroelectric ITO/PZT/Au film, a p-n junction with strong polarization-dependent interfacial coupling effect is formed. The power conversion efficiency of the heterostructure is improved by nearly two orders of magnitude and the polarization modulation ratio is increased about four times. It is demonstrated that the polarization-dependent interfacial coupling effect can give rise to a great change in band structure of the heterostructure, not only producing an aligned internal electric field but also tuning both depletion layer width and potential barrier height at PZT-ZnO interface. This work provides an efficient way in developing highly efficient ferroelectric-based solar cells and novel optoelectronic memory devices. PMID:26954833

Schottky barrier and band edge engineering via the interfacial structure and strain for the Pt/TiO2 heterostructure.

PubMed

Ma, Xiangchao; Wu, Xin; Wang, Yucheng; Dai, Ying

2017-07-19

Charge transfer across the Pt/TiO 2 interface, which is mainly determined by the interface Schottky barrier height (SBH), is an important process in the (photo)catalytic and electronic applications of the Pt/TiO 2 composite. Therefore, systematic investigation of the factors that affect the interface SBH is indispensable for understanding and optimizing its performance. In this work, a systematic study of the effects of the interfacial structure and strain on the SBH of the Pt/TiO 2 (001) interface has been carried out based on the first-principles calculations. The results of interface adhesion energy show that two different interfacial structures for the Pt/TiO 2 (001) heterointerface may exist experimentally, namely, O-Pt bonding and Ti-Pt bonding. Moreover, the interfacial structures result in not only different values for the SBH, but also different dependences of the SBH on strain. Detailed investigations show that these versatile modulations of the SBH with the structure and strain are mainly attributed to the strong dependence of the band edges of TiO 2 and the interfacial potential alignments on the strain and structure, suggesting that these results are general and may be applicable to other metal/TiO 2 heterostructures.

Torsional Splitting in the Degenerate Vibrational States of (70)Ge(2)H(6): Rotation-Torsion Analysis of the nu(7) and nu(9) Fundamentals.

PubMed

Lattanzi; di Lauro C; Bürger; Mkadmi

2000-09-01

The rotational and torsional structure of the nu(7) and nu(9) degenerate fundamentals of (70)Ge(2)H(6) has been analyzed under high resolution. The torsional structure of both v(7) = 1 and v(9) = 1 states can be fitted by a simple one-parameter formula. The x,y-Coriolis interaction with the parallel nu(5) fundamental was accounted for in the analysis of nu(7). A strong perturbation of the J structure of the E(3s) torsional component of the KDeltaK = -2 subbranches of nu(9) can be explained by the resonance with an E(3s) excited level of the pure torsional manifold. The perturber is centered at 361.58 cm(-1), very close to the value estimated with a barrier height of 285 cm(-1). This confirms that the fundamental torsional wavenumber is close to 103 cm(-1), in good agreement with the "ab initio" prediction. The torsional splittings of all the infrared active degenerate fundamentals, nu(7), nu(8), and nu(9), follow the trend predicted by theory, and have been fitted by exploratory calculations accounting only for the torsional Coriolis-coupling mechanism of all degenerate vibrational fundamentals in several torsional states. This confirms that torsional Coriolis coupling is the dominant mechanism responsible for the decrease of the torsional splitting in the degenerate vibrational states. A higher value of the barrier had to be used for the nu(9) mode. Copyright 2000 Academic Press.

Implementation of spaceborne lidar-retrieved canopy height in the WRF model

NASA Astrophysics Data System (ADS)

Lee, Junhong; Hong, Jinkyu

2016-06-01

Canopy height is closely related to biomass and aerodynamic properties, which regulate turbulent transfer of energy and mass at the soil-vegetation-atmosphere continuum. However, this key information has been prescribed as a constant value in a fixed plant functional type in atmospheric models. This paper is the first to report impacts of using realistic forest canopy height, retrieved from spaceborne lidar, on regional climate simulation by using the canopy height data in the Weather Research and Forecasting (WRF) model's land surface model. Numerical simulations were conducted over the Amazon Basin during summer season. Over this region, the lidar-retrieved canopy heights were higher than the default values used in the WRF, which are dependent only on plant functional type. By modifying roughness length and zero-plane displacement height, the change of canopy height resulted in changes in surface energy balance by regulating aerodynamic conductances and vertical temperature gradient, thus modifying the lifting condensation level and equivalent potential temperature in the atmospheric boundary layer. Our analysis also showed that the WRF model better reproduced the observed precipitation when lidar-retrieved canopy height was used over the Amazon Basin.

Systems and methods that generate height map models for efficient three dimensional reconstruction from depth information

DOEpatents

Frahm, Jan-Michael; Pollefeys, Marc Andre Leon; Gallup, David Robert

2015-12-08

Methods of generating a three dimensional representation of an object in a reference plane from a depth map including distances from a reference point to pixels in an image of the object taken from a reference point. Weights are assigned to respective voxels in a three dimensional grid along rays extending from the reference point through the pixels in the image based on the distances in the depth map from the reference point to the respective pixels, and a height map including an array of height values in the reference plane is formed based on the assigned weights. An n-layer height map may be constructed by generating a probabilistic occupancy grid for the voxels and forming an n-dimensional height map comprising an array of layer height values in the reference plane based on the probabilistic occupancy grid.

The distribution of free electrons in the inner galaxy from pulsar dispersion measures

NASA Technical Reports Server (NTRS)

Harding, D. S.; Harding, A. K.

1981-01-01

The dispersion measures of a sample of 149 pulsars in the inner Galaxy (absolute value of l 50 deg) were statistically analyzed to deduce the large-scale distribution of free thermal electrons in this region. The dispersion measure distribution of these pulsars shows significant evidence for a decrease in the electron scale height from a local value greater than the pulsar scale height to a value less than the pulsar scale height at galactocentric radii inside of approximately 7 kpc. An increase in the electron density (to a value around .15/cu cm at 4 to 5 kpc) must accompany such a decrease in scale height. There is also evidence for a large-scale warp in the electron distribution below the b + 0 deg plane inside the Solar circle. A model is proposed for the electron distribution which incorporates these features and Monte Carlo generated dispersion measure distributions are presented for parameters which best reproduce the observed pulsar distributions.

Intergenerational influences on the growth of Maya children: The effect of living conditions experienced by mothers and maternal grandmothers during their childhood.

PubMed

Azcorra, Hugo; Dickinson, Federico; Bogin, Barry; Rodríguez, Luis; Varela-Silva, Maria Inês

2015-01-01

To test the hypothesis that living conditions experienced by maternal grandmothers (F1 generation) and mothers (F2 generation) during their childhood are related to height and leg length (LL: height - sitting height) of their 6-to-8 year old children (F3 generation). From September 2011 to June 2012 we obtained height and LL, and calculated z-score values of these measurements for 109 triads (F1 , F2 , F3 ) who are Maya living in Merida, Yucatan, Mexico. Multiple regression models were adjusted to examine the relation of anthropometric and intergenerational socioeconomic parameters of F1 (house index and family size during childhood) and F2 (paternal job loss during childhood) with the z-score values of height and LL of F3 . Children's height and LL were positively associated with maternal height and LL. This association was relatively stronger in LL. Better categories of grand-maternal house index were significantly associated with higher values of height and LL in grandchildren. Grand-maternal family size was positively related with LL, but not with height. Our findings partially support the hypothesis that living conditions experienced by recent maternal ancestors (F1 and F2 ) during their growth period influence the growth of descendants (F3 ). Results suggest that LL is more sensitive to intergenerational influences than is total height and that the transition from a traditional rural lifestyle to urban conditions results in new exposures for risk in human physical growth. © 2015 Wiley Periodicals, Inc.

Estimation of height and body mass index from demi-span in elderly individuals.

PubMed

Weinbrenner, Tanja; Vioque, Jesús; Barber, Xavier; Asensio, Laura

2006-01-01

Obtaining accurate height and, consequently, body mass index (BMI) measurements in elderly subjects can be difficult due to changes in posture and loss of height during ageing. Measurements of other body segments can be used as an alternative to estimate standing height, but population- and age-specific equations are necessary. Our objectives were to validate existing equations, to develop new simple equations to predict height in an elderly Spanish population and to assess the accuracy of the BMI calculated by estimated height from the new equations. We measured height and demi-span in a representative sample of 592 individuals, 271 men and 321 women, 65 years and older (mean +/- SD, 73.8 +/- 6.3 years). We suggested equations to predict height from demi-span by multiple regression analyses and performed an agreement analysis between measured and estimated indices. Height estimated from demi-span correlated significantly (p < 0.001) with measured height (men: r = 0.708, women: r = 0.625). The best prediction equations were as follows: men, height (in cm) = 77.821 + (1.132 x demi-span in cm) + (-0.215 x 5-year age category); women: height (in cm) = 88.854 + (0.899 x demi-span in cm) + (-0.692 x 5-year age category). No significant differences between the mean values of estimated and measured heights were found for men (-0.03 +/- 4.6 cm) or women (-0.02 +/- 4.1 cm). The BMI derived from measured height did not differ significantly from the BMI derived from estimated height either. Predicted height values from equations based on demi-span and age may be acceptable surrogates to derive accurate nutritional indices such as the BMI, particularly in elderly populations, where height may be difficult to measure accurately.

Source of parental reports of child height and weight during phone interviews and influence on obesity prevalence estimates among children aged 3-17 years.

PubMed

Skinner, Asheley Cockrell; Miles, Donna; Perrin, Eliana M; Coyne-Beasley, Tamera; Ford, Carol

2013-01-01

We compared parental reports of children's height and weight when the values were estimated vs. parent-measured to determine how these reports influence the estimated prevalence of childhood obesity. In the 2007 and 2008 North Carolina Child Health Assessment and Monitoring Program surveys, parents reported height and weight for children aged 3-17 years. When parents reported the values were not measured (by doctor, school, or home), they were asked to measure their child and were later called back. We categorized body mass index status using standard CDC definitions, and we used Chi-square tests and the Stuart-Maxwell test of marginal homogeneity to examine reporting differences. About 80% (n=509) of the 638 parents who reported an unmeasured height and/or weight participated in a callback and provided updated measures. Children originally classified as obese were subsequently classified as obese (67%), overweight (13%), and healthy weight (19%). An estimated 28% of younger children (<10 years of age) vs. 6% of older children (aged ≥10 years) were reclassified on callback. Having parents who guessed the height and weight of their children and then reported updated values did not significantly change the overall population estimates of obesity. Our findings demonstrate that using parent-reported height and weight values may be sufficient to provide reasonable estimates of obesity prevalence. Systematically asking the source of height and weight information may help improve how it is applied to research of the prevalence of childhood obesity when gold-standard measurements are not available.

[Normal pressure hydrocephalus: prognostic value of height in patients treated with an identical shunt system].

PubMed

Aguas, Jesús; Rodrigo, Victor; Estupiñan, Francisco; Nogues, Pere; Villalba, Gloria; Villagrasa, Javier; Caral, Luis

2013-01-01

Normal pressure hydrocephalus (NPH) is a clinical entity frequently managed by means of a cerebrospinal fluid shunt. Hydrodynamic hypotheses consider hydrostatic pressure (as well as height) a very important variable for shunt system function. However, we did not find empirical studies supporting the influence of height on clinical response in the literature. Our objective was to study the prognostic value of height, as a variable related to hydrostatic pressure, when an identical shunt system is used. A prospective series of 61 idiopathic NPH cases was analyzed. All cases were shunted by means of a ventricle-peritoneal system with a 100mmH2O opening pressure valve. Anthropometric, clinical, radiological and pressure variables were registered, as well as delay for treatment, improvement and complications. 78.7% of cases improved after shunting. This group of patients was significantly taller (P=.005) than the group without response (median value 165cm versus 152cm). There was also a significant correlation between height and ventricular size decrease after the shunt. In our series opening valve pressure was a constant (100mmHg) and we could consequently focus on the effect of hydrostatic pressure (height). Moreover, we found a positive predictive value for taller patients, probably because we had selected an opening pressure especially suitable for them. Current gravitational valve shunt systems also recommend considering patient height when customising the system. Our study empirically supports this idea. Copyright © 2012 Sociedad Española de Neurocirugía. Published by Elsevier España. All rights reserved.

Wave Overtopping of a Barrier Beach

NASA Astrophysics Data System (ADS)

Thornton, E. B.; Laudier, N.; Macmahan, J. H.

2009-12-01

The rate of wave overtopping of a barrier beach is measured and modeled as a first step in modeling the breaching of a beach impounding an ephemeral river. Unique rate of wave overtopping data are obtained from the measure of the Carmel River, California, lagoon filling during a time when the lagoon is closed-off and there is no river inflow. Volume changes are calculated from measured lagoon height changes owing to wave overtopping by a stage-volume curve, then center differenced and averaged to provide volume rates of change in the lagoon. Wave height and period are obtained from CDIP MOPS directional wave spectra data in 15m fronting the beach. Beach morphology was measured by GPS walking surveys and interpolated for beach slopes and berm heights. Three empirical overtopping models by van der Meer and Janssen (1995), Hedges and Reis (1998) and Pullen et al. (2007) with differing parameterizations on wave height, period and beach slope and calibrated using extensive laboratory data obtained over plane, impermeable beaches are compared with the data. In addition, the run-up model by Stockdon et al. (2006) based on field data is examined. Three wave overtopping storm events are considered when morphology data were available less than 2 weeks prior to the event. The models are tuned to fit the data using a reduction factor to account for beach permeability, berm characteristics, non-normal wave incidence and surface roughness influence. It is concluded that the Stockdon et al. (2006) model underestimates run-up as no overtopping is predicted with this model. The three empirical overtopping models behaved similarly well with regression coefficients ranging 0.72 to 0.86 using a reasonable range of reduction factors 0.66 - 0.81 with an average of 0.74.

Reliability and scientific use of a surgical planning software for anterior cervical discectomy and fusion (ACDF).

PubMed

Barth, Martin; Weiß, Christel; Brenke, Christopher; Schmieder, Kirsten

2017-04-01

Software-based planning of a spinal implant inheres in the promise of precision and superior results. The purpose of the study was to analyze the measurement reliability, prognostic value, and scientific use of a surgical planning software in patients receiving anterior cervical discectomy and fusion (ACDF). Lateral neutral, flexion, and extension radiographs of patients receiving tailored cages as suggested by the planning software were available for analysis. Differences of vertebral wedging angles and segmental height of all cervical segments were determined at different timepoints using intraclass correlation coefficients (ICC). Cervical lordosis (C2/C7), segmental heights, global, and segmental range of motion (ROM) were determined at different timepoints. Clinical and radiological variables were correlated 12 months after surgery. 282 radiographs of 35 patients with a mean age of 53.1 ± 12.0 years were analyzed. Measurement of segmental height was highly accurate with an ICC near to 1, but angle measurements showed low ICC values. Likewise, the ICCs of the prognosticated values were low. Postoperatively, there was a significant decrease of segmental height (p < 0.0001) and loss of C2/C7 ROM (p = 0.036). ROM of unfused segments also significantly decreased (p = 0.016). High NDI was associated with low subsidence rates. The surgical planning software showed high accuracy in the measurement of height differences and lower accuracy values with angle measurements. Both the prognosticated height and angle values were arbitrary. Global ROM, ROM of the fused and intact segments, is restricted after ACDF.

Height and weight errors in aeromedical certification data.

DOT National Transportation Integrated Search

1973-06-01

The Framingham Relative Weight Index (FRWI) of obesity was described in previous reports as a screening aid for detecting susceptibility to coronary heart disease (CHD). FRWI calculation requires measured values of height and weight but the height an...

Superluminal tunneling of a relativistic half-integer spin particle through a potential barrier

NASA Astrophysics Data System (ADS)

Nanni, Luca

2017-11-01

This paper investigates the problem of a relativistic Dirac half-integer spin free particle tunneling through a rectangular quantum-mechanical barrier. If the energy difference between the barrier and the particle is positive, and the barrier width is large enough, there is proof that the tunneling may be superluminal. For first spinor components of particle and antiparticle states, the tunneling is always superluminal regardless the barrier width. Conversely, the second spinor components of particle and antiparticle states may be either subluminal or superluminal depending on the barrier width. These results derive from studying the tunneling time in terms of phase time. For the first spinor components of particle and antiparticle states, it is always negative while for the second spinor components of particle and antiparticle states, it is always positive, whatever the height and width of the barrier. In total, the tunneling time always remains positive for particle states while it becomes negative for antiparticle ones. Furthermore, the phase time tends to zero, increasing the potential barrier both for particle and antiparticle states. This agrees with the interpretation of quantum tunneling that the Heisenberg uncertainty principle provides. This study's results are innovative with respect to those available in the literature. Moreover, they show that the superluminal behaviour of particles occurs in those processes with high-energy confinement.

Understanding the fusion cross section among light nuclei around the Coulomb barrier

NASA Astrophysics Data System (ADS)

Del Zoppo, Antonio; La Cognata, Marco

2017-11-01

In this work we investigate fusion induced by a radioactive 8Li projectile on a 4He gas target, at center-of-mass energies between 0.6 and 5 MeV. The main result is the tendency of the dimensionless fusion cross section to form well visible plateaus alternated to steep rises. This is likely to be the most genuine consequence of the discrete nature of the intervening angular momenta observed so far in fusion reactions right above the Coulomb barrier. A partial-wave analysis, exclusively based on a pure quantal penetration fusion model, identifies a remarkably low-height barrier. Indeed, these plateaus allow enhanced experimental sensitivity to the fusion barrier given that the most barrier-sensitive lowest partial waves are well separated. We expect that the present results for 8Li+4He will promote further investigations of the fusion reaction mechanism between very light ions at energies much below the interaction barrier. For the moment, we believe that understanding the plateau origin in the cross section above the barrier will almost certainly be useful to corroborate the extrapolation to the important astrophysical region below the Coulomb barrier, not only in the case of the 8Li+4He fusion but also for other systems, such as the 12C+12C.

Hybrid matrix method for stable numerical analysis of the propagation of Dirac electrons in gapless bilayer graphene superlattices

NASA Astrophysics Data System (ADS)

Briones-Torres, J. A.; Pernas-Salomón, R.; Pérez-Álvarez, R.; Rodríguez-Vargas, I.

2016-05-01

Gapless bilayer graphene (GBG), like monolayer graphene, is a material system with unique properties, such as anti-Klein tunneling and intrinsic Fano resonances. These properties rely on the gapless parabolic dispersion relation and the chiral nature of bilayer graphene electrons. In addition, propagating and evanescent electron states coexist inherently in this material, giving rise to these exotic properties. In this sense, bilayer graphene is unique, since in most material systems in which Fano resonance phenomena are manifested an external source that provides extended states is required. However, from a numerical standpoint, the presence of evanescent-divergent states in the eigenfunctions linear superposition representing the Dirac spinors, leads to a numerical degradation (the so called Ωd problem) in the practical applications of the standard Coefficient Transfer Matrix (K) method used to study charge transport properties in Bilayer Graphene based multi-barrier systems. We present here a straightforward procedure based in the hybrid compliance-stiffness matrix method (H) that can overcome this numerical degradation. Our results show that in contrast to standard matrix method, the proposed H method is suitable to study the transmission and transport properties of electrons in GBG superlattice since it remains numerically stable regardless the size of the superlattice and the range of values taken by the input parameters: the energy and angle of the incident electrons, the barrier height and the thickness and number of barriers. We show that the matrix determinant can be used as a test of the numerical accuracy in real calculations.

Electromagnetic Saturation of Angstrom-Sized Quantum Barriers at Terahertz Frequencies

NASA Astrophysics Data System (ADS)

Bahk, Young-Mi; Kang, Bong Joo; Kim, Yong Seung; Kim, Joon-Yeon; Kim, Won Tae; Kim, Tae Yun; Kang, Taehee; Rhie, Jiyeah; Han, Sanghoon; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

2015-09-01

Metal-graphene-metal hybrid structures allow angstrom-scale van der Waals gaps, across which electron tunneling occurs. We squeeze terahertz electromagnetic waves through these λ /10 000 000 gaps, accompanied by giant field enhancements. Unprecedented transmission reduction of 97% is achieved with the transient voltage across the gap saturating at 5 V. Electron tunneling facilitated by the transient electric field strongly modifies the gap index, starting a self-limiting process related to the barrier height. Our work enables greater interplay between classical optics and quantum tunneling, and provides optical indices to the van der Waals gaps.

Far-infrared response of spherical quantum dots: Dielectric effects and the generalized Kohn's theorem

NASA Astrophysics Data System (ADS)

Movilla, J. L.; Planelles, J.

2007-05-01

The influence of the dielectric environment on the far-infrared (FIR) absorption spectra of two-electron spherical quantum dots is theoretically studied. Effective mass and envelope function approaches with realistic steplike confining potentials are used. Special attention is paid to absorptions that are induced by the electron-electron interaction. High confining barriers make the FIR absorption coefficients almost independent of the quantum dot dielectric environment. Low barrier heights and strong dielectric mismatches preserve the strong fundamental (Kohn) mode but yield the cancellation of excited absorptions, thus monitoring dielectrically induced phase transitions from volume to surface states.

A New Potential Energy Surface for N+O2: Is There an NOO Minimum?

NASA Technical Reports Server (NTRS)

Walch, Stephen P.

1995-01-01

We report a new calculation of the N+02 potential energy surface using complete active space self-consistent field internally contracted configuration interaction with the Dunning correlation consistent basis sets. The peroxy isomer of N02 is found to be a very shallow minimum separated from NO+O by a barrier of only 0.3 kcal/mol (excluding zero-point effects). The entrance channel barrier height is estimated to be 8.6 kcal/mol for ICCI+Q calculations correlating all but the Ols and N1s electrons with a cc-p VQZ basis set.

Electrical transport properties of nanoplates shaped tungsten oxide embedded poly(vinyl-alcohol) film

NASA Astrophysics Data System (ADS)

Das, Amit Kumar; Chatterjee, Piyali; Meikap, Ajit Kumar

2018-04-01

Tungsten oxide (WO3) nanoplates have been synthesized via hydrothermal method. The average crystallite size of the nanoplates is 28.9 ± 0.5 nm. The direct and indirect band gap of WO3 is observed. The AC conductivity of PVA-WO3 composite film has been observed and carrier transport mechanism follows correlated barrier hopping model. The maximum barrier height of the composite film is 0.1 eV. The electric modulus reflects the non-Debye type behaviour of relaxation time which is simulated by Kohlrausch-Willims-Watts (KWW) function.

Van der Waals heterostructure of phosphorene and graphene: tuning the Schottky barrier and doping by electrostatic gating.

PubMed

Padilha, J E; Fazzio, A; da Silva, Antônio J R

2015-02-13

In this Letter, we study the structural and electronic properties of single-layer and bilayer phosphorene with graphene. We show that both the properties of graphene and phosphorene are preserved in the composed heterostructure. We also show that via the application of a perpendicular electric field, it is possible to tune the position of the band structure of phosphorene with respect to that of graphene. This leads to control of the Schottky barrier height and doping of phosphorene, which are important features in the design of new devices based on van der Waals heterostructures.

Electromagnetic Saturation of Angstrom-Sized Quantum Barriers at Terahertz Frequencies.

PubMed

Bahk, Young-Mi; Kang, Bong Joo; Kim, Yong Seung; Kim, Joon-Yeon; Kim, Won Tae; Kim, Tae Yun; Kang, Taehee; Rhie, Jiyeah; Han, Sanghoon; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

2015-09-18

Metal-graphene-metal hybrid structures allow angstrom-scale van der Waals gaps, across which electron tunneling occurs. We squeeze terahertz electromagnetic waves through these λ/10 000 000 gaps, accompanied by giant field enhancements. Unprecedented transmission reduction of 97% is achieved with the transient voltage across the gap saturating at 5 V. Electron tunneling facilitated by the transient electric field strongly modifies the gap index, starting a self-limiting process related to the barrier height. Our work enables greater interplay between classical optics and quantum tunneling, and provides optical indices to the van der Waals gaps.

Effect of substitution group on dielectric properties of 4H-pyrano [3, 2-c] quinoline derivatives thin films

NASA Astrophysics Data System (ADS)

H, M. Zeyada; F, M. El-Taweel; M, M. El-Nahass; M, M. El-Shabaan

2016-07-01

The AC electrical conductivity and dielectrical properties of 2-amino-6-ethyl-5-oxo-4-(3-phenoxyphenyl)-5,6-dihydro-4H-pyrano[3, 2-c]quinoline-3-carbonitrile (Ph-HPQ) and 2-amino-4-(2-chlorophenyl)-6-ethyl-5-oxo-5,6-dihydro-4H-pyrano [3, 2-c] quinoline-3-carbonitrile (Ch-HPQ) thin films were determined in the frequency range of 0.5 kHz-5 MHz and the temperature range of 290-443 K. The AC electrical conduction of both compounds in thin film form is governed by the correlated barrier hopping (CBH) mechanism. Some parameters such as the barrier height, the maximum barrier height, the density of charges, and the hopping distance were determined as functions of temperature and frequency. The phenoxyphenyl group has a greater influence on those parameters than the chlorophenyl group. The AC activation energies were determined at different frequencies and temperatures. The dielectric behaviors of Ph-HPQ and Ch-HPQ were investigated using the impedance spectroscopy technique. The impedance data are presented in Nyquist diagrams for different temperatures. The Ch-HPQ films have higher impedance than the Ph-HPQ films. The real dielectric constant and dielectric loss show a remarkable dependence on the frequency and temperature. The Ph-HPQ has higher dielectric constants than the Ch-HPQ.

Dual nature of localization in guiding systems with randomly corrugated boundaries: Anderson-type versus entropic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tarasov, Yu.V., E-mail: yutarasov@ire.kharkov.ua; Shostenko, L.D.

A unified theory for the conductance of an infinitely long multimode quantum wire whose finite segment has randomly rough lateral boundaries is developed. It enables one to rigorously take account of all feasible mechanisms of wave scattering, both related to boundary roughness and to contacts between the wire rough section and the perfect leads within the same technical frameworks. The rough part of the conducting wire is shown to act as a mode-specific randomly modulated effective potential barrier whose height is governed essentially by the asperity slope. The mean height of the barrier, which is proportional to the average slopemore » squared, specifies the number of conducting channels. Under relatively small asperity amplitude this number can take on arbitrary small, up to zero, values if the asperities are sufficiently sharp. The consecutive channel cut-off that arises when the asperity sharpness increases can be regarded as a kind of localization, which is not related to the disorder per se but rather is of entropic or (equivalently) geometric origin. The fluctuating part of the effective barrier results in two fundamentally different types of guided wave scattering, viz., inter- and intramode scattering. The intermode scattering is shown to be for the most part very strong except in the cases of (a) extremely smooth asperities, (b) excessively small length of the corrugated segment, and (c) the asperities sharp enough for only one conducting channel to remain in the wire. Under strong intermode scattering, a new set of conducting channels develops in the corrugated waveguide, which have the form of asymptotically decoupled extended modes subject to individual solely intramode random potentials. In view of this fact, two transport regimes only are realizable in randomly corrugated multimode waveguides, specifically, the ballistic and the localized regime, the latter characteristic of one-dimensional random systems. Two kinds of localization are thus shown to coexist in waveguide-like systems with randomly corrugated boundaries, specifically, the entropic localization and the one-dimensional Anderson (disorder-driven) localization. If the particular mode propagates across the rough segment ballistically, the Fabry–Pérot-type oscillations should be observed in the conductance, which are suppressed for the mode transferred in the Anderson-localized regime.« less

Assessing values of air quality and visibility at risk from wildland fires.

Treesearch

Sue A. Ferguson; Steven J. McKay; David E. Nagel; Trent Piepho; Miriam L. Rorig; Casey Anderson; Lara Kellogg

2003-01-01

To assess values of air quality and visibility at risk from wildland fire in the United States, we generated a 40-year database that includes twice daily values of wind, mixing height, and a ventilation index that is the product of windspeed and mixing height. The database provides the first nationally consistent map of surface wind and ventilation index. In addition,...

Biological and Sociocultural Differences in Perceived Barriers to Physical Activity Among Fifth- to Seventh-Grade Urban Girls.

PubMed

Vermeesch, Amber L; Ling, Jiying; Voskuil, Vicki R; Bakhoya, Marion; Wesolek, Stacey M; Bourne, Kelly A; Pfeiffer, Karin A; Robbins, Lorraine B

2015-01-01

Inadequate physical activity (PA) contributes to the high prevalence of overweight and obesity among U.S. adolescent girls. Barriers preventing adolescent girls from meeting PA guidelines have not been thoroughly examined. The threefold purpose of this study was to (a) determine pubertal stage, racial/ethnic, and socioeconomic status (SES) differences in ratings of interference of barriers to PA; (b) examine relationships between perceived barriers and age, body mass index, recreational screen time, sedentary activity, and PA; and (c) identify girls' top-rated perceived barriers to PA. Girls (N = 509) from eight Midwestern U.S. schools participated. Demographic, pubertal stage, perceived barriers, and recreational screen time data were collected via surveys. Height and weight were measured. Accelerometers measured sedentary activity, moderate-to-vigorous PA (MVPA), and light plus MVPA. Girls of low SES reported greater interference of perceived barriers to PA than those who were not of low SES (1.16 vs. 0.97, p = .01). Girls in early/middle puberty had lower perceived barriers than those in late puberty (1.03 vs. 1.24, p < .001). Girls' perceived barriers were negatively related to MVPA (r = -.10, p = .03) and light plus MVPA (r = -.11, p = .02). Girls' top five perceived barriers included lack of skills, hating to sweat, difficulty finding programs, being tired, and having pain. Innovative interventions, particularly focusing on skill development, are needed to assist girls in overcoming their perceived barriers to PA.

On the validity of the Arrhenius equation for electron attachment rate coefficients.

PubMed

Fabrikant, Ilya I; Hotop, Hartmut

2008-03-28

The validity of the Arrhenius equation for dissociative electron attachment rate coefficients is investigated. A general analysis allows us to obtain estimates of the upper temperature bound for the range of validity of the Arrhenius equation in the endothermic case and both lower and upper bounds in the exothermic case with a reaction barrier. The results of the general discussion are illustrated by numerical examples whereby the rate coefficient, as a function of temperature for dissociative electron attachment, is calculated using the resonance R-matrix theory. In the endothermic case, the activation energy in the Arrhenius equation is close to the threshold energy, whereas in the case of exothermic reactions with an intermediate barrier, the activation energy is found to be substantially lower than the barrier height.