Journal articles on the topic 'Ohmic and injection barrier transitions'
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1
Bae, Geun Yeol, Jinsung Kim, Junyoung Kim, Siyoung Lee, and Eunho Lee. "MoTe2 Field-Effect Transistors with Low Contact Resistance through Phase Tuning by Laser Irradiation." Nanomaterials 11, no. 11 (October 22, 2021): 2805. http://dx.doi.org/10.3390/nano11112805.
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Due to their extraordinary electrical and physical properties, two-dimensional (2D) transition metal dichalcogenides (TMDs) are considered promising for use in next-generation electrical devices. However, the application of TMD-based devices is limited because of the Schottky barrier interface resulting from the absence of dangling bonds on the TMDs’ surface. Here, we introduce a facile phase-tuning approach for forming a homogenous interface between semiconducting hexagonal (2H) and semi-metallic monoclinic (1T′) molybdenum ditelluride (MoTe2). The formation of ohmic contacts increases the charge carrier mobility of MoTe2 field-effect transistor devices to 16.1 cm2 V−1s−1 with high reproducibility, while maintaining a high on/off current ratio by efficiently improving charge injection at the interface. The proposed method enables a simple fabrication process, local patterning, and large-area scaling for the creation of high-performance 2D electronic devices.
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Hamui, Leon, Maria Elena Sánchez-Vergara, Ricardo Corona-Sánchez, Omar Jiménez-Sandoval, and Cecilio Álvarez-Toledano. "Innovative Incorporation of Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) as Hole Carrier Transport Layer and as Anode for Organic Solar Cells Performance Improvement." Polymers 12, no. 12 (November 27, 2020): 2808. http://dx.doi.org/10.3390/polym12122808.
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In this work, we present a comparative study of benzoid poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as electrode and as hole carrier transport layer (HTL) in the manufacture of organic photovoltaic devices using Fischer metal-carbene complexes. The performance of the different devices was evaluated for solar cell applications. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the thin films that integrated the devices. A more ordered and crystallized active film microstructure is observed when using benzoid PEDOT:PSS as nucleation layer. The optical gap for both direct and indirect electronic transitions was evaluated from ultraviolet-visible spectroscopy data (UV-vis), as well as the absorption coefficient (α), and the values are in the range of 2.10–2.93 eV. Photovoltaic devices with conventional architecture, using two different chromium carbenes as active layers, were manufactured, and their electrical behavior was studied. The devices were irradiated with different wavelengths between the infrared and ultraviolet regions of the electromagnetic spectrum. Using the PEDOT:PSS film as hole carrier transport layer (HTL) decreases the slope on the ohmic and space charge limited current (SCLC) regions and eliminates the trap-charge limited current (T-CLC) mechanism. Furthermore, a saturation current of ~1.95 × 10−10 A and higher current values ~1.75 × 10−2 A at 4 V, ~4 orders in magnitude larger were observed. The PEDOT:PSS films as HTL in the devices reduced the injection barrier, thus showing a better performance than as anodes in this type of organic solar cells.
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Huang, Yaren, Jonas Buettner, Benedikt Lechner, and Gerhard Wachutka. "The Impact of Non-Ideal Ohmic Contacts on the Performance of High-Voltage SiC MPS Diodes." Materials Science Forum 963 (July 2019): 553–57. http://dx.doi.org/10.4028/www.scientific.net/msf.963.553.
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The wide band gap of SiC semiconductor devices constitutes a serious challenge to build good Ohmic contacts on the surface of the p-type material. This is reflected in the numerical analysis of ”realistic” devices, where we have to cope with serious problems, such as a shifting threshold voltage, reduced forward conductivity, and no noticeable conductivity modulation by minority carrier injection from p+-emitters, in matching measured data with simulation results, as a consequence of the significant impact of non-ideal poor Ohmic contacts. In this work, we used a Schottky contact model together with a barrier tunneling model, instead of common ideal Ohmic contact model, to simulate the non-ideal Ohmic contact on SiC MPS diodes. Based on this approach, the I-V characteristics of real Ohmic contacts can be reproduced in high-fidelity simulations, providing us physical insight of the observed operational behavior.
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Xu, Hongyi, Na Ren, Jiupeng Wu, Zhengyun Zhu, Qing Guo, and Kuang Sheng. "The Impact of Process Conditions on Surge Current Capability of 1.2 kV SiC JBS and MPS Diodes." Materials 14, no. 3 (January 31, 2021): 663. http://dx.doi.org/10.3390/ma14030663.
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This paper demonstrated the impact of process conditions on the surge current capability of 1.2 kV SiC junction barrier Schottky diode (JBS) and merged PiN Schottky diode (MPS). The influence of ohmic contact and defect density produced by implantation was studied in the simulation. The device fabricated with high temperature implantation had less defect density in the implant region compared with room temperature implantation, which contributed to higher hole injection in surge current mode and 20% surge capability improvement. In addition, with lower P+ ohmic contact resistance, the device had higher surge capability. When compared to device fabrication with a single Schottky metal layer in the device active area, adding additional P+ ohmic contact on top of the P+ regions in the device active area resulted in the pn junctions sharing a greater portion of surge current, and improved the devices’ surge capability by ~10%.
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López-Galán, Oscar A., Manuel Ramos, John Nogan, Alejandro Ávila-García, Torben Boll, and Martin Heilmaier. "The electronic states of ITO–MoS2: Experiment and theory." MRS Communications 12, no. 2 (December 16, 2021): 137–44. http://dx.doi.org/10.1557/s43579-021-00126-9.
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AbstractWe report a combination of experimental results with density functional theory (DFT) calculations to understand electronic structure of indium tin oxide and molybdenum disulfide (ITO–MoS2) interface. Our results indicate ITO and MoS2 conform an n-type Schottky barrier of c.a. − 1.0 eV due to orbital interactions; formation of an ohmic contact is caused by semiconducting and metal behavior of ITO as a function of crystal plane orientation. ITO introduces energy levels around the Fermi level in all interface models in the Γ-Μ-Κ-Γ path. The resulted Van der Waals interface and the values of Schottky barrier height enhance electron carrier injection. Graphical abstract
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Pérez, R., Narcis Mestres, Dominique Tournier, Xavier Jordá, Phillippe Godignon, and Miquel Vellvehi. "Temperature Dependence of 4H-SiC JBS and Schottky Diodes after High Temperature Treatment of Contact Metal." Materials Science Forum 483-485 (May 2005): 945–48. http://dx.doi.org/10.4028/www.scientific.net/msf.483-485.945.
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In this work we demonstrate performant characteristics of 1.2KV Schottky, Junction Barrier Schottky (JBS) and implanted PN diodes processed on the same 4H-SiC wafer. A bi-layer Ni/Ti scheme for the contact metallisation submitted to high temperature rapid thermal anneals is proved to form good ohmic contact on p+ implanted areas while maintaining good Schottky characteristics on lightly doped n-type regions. I-V characteristics have been evaluated from room temperature up to 560K. At room temperature, Schottky diodes have slightly better specific onresistance, but when working temperature is increased, the JBS diode exhibits better characteristics due to the temperature dependent activation of bipolar current injection from the p+ grid. From reverse measurements, the JBS diodes showed lower leakage current and higher breakdown voltages in comparison to that of the Schottky diodes in the whole range of temperatures.
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Cha, Jung-Suk, Da-hoon Lee, Kee-Baek Sim, Tae-Ju Lee, Tae-Yeon Seong, and Hiroshi Amano. "Inhomogeneous Barrier Height Characteristics of n-Type AlInP for Red AlGaInP-Based Light-Emitting Diodes." ECS Journal of Solid State Science and Technology 11, no. 3 (March 1, 2022): 035007. http://dx.doi.org/10.1149/2162-8777/ac5d66.
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For micro-light-emitting diode (LED)-based display applications, such as virtual reality and augmented reality, high-performance Ohmic contacts (namely, the improvement of current injection efficiency) is vital to the realization of high-efficiency micro-LEDs. The surface Fermi level pinning characteristics could be comprehended in terms of the relation between work function of metals (ΦM) and Schottky barrier height (SBH, ΦB). In this study, we have investigated the surface Fermi level pinning characteristics of (001) n-AlInP surfaces by employing Schottky diodes with different metals. With an increase in the temperature, ΦB increases linearly and ideality factors (n) decreases. This behavior is related to the barrier height inhomogeneity. Inhomogeneity-model-based ΦB is evaluated to be in the range of 0.86–1.30 eV, which is dependent on the metal work functions and are similar to those measured from capacitance-voltage relation. Further, The S-parameter, the relation between ΦB and ΦM (dΦB/dΦM), is 0.36. This is indicative of the partial pinning of the surface Fermi level at the surface states placed at 0.95 eV below the conduction band. Furthermore, it is also shown that (NH4)2S-passivation results in an increases the mean SBH and the S-parameter (e.g., 0.52).
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Squeo, Benedetta Maria, Wojciech Mróz, Umberto Giovanella, and Mariacecilia Pasini. "Anionic Low Band Gap-Conjugated Polyelectrolytes as Hole-Transporting Layer in Optoelectronics Devices." Chemistry Proceedings 3, no. 1 (November 14, 2020): 18. http://dx.doi.org/10.3390/ecsoc-24-08406.
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In the last years, interfacial engineering has played a critical role in promoting the performance of optoelectronic devices as organic solar cells (OSC) and organic light-emitting diodes (OLEDs) since interfacial layers help to form an ohmic contact between the electrodes and the active layers, which is of great importance for charge collection/injection. Conjugated polyelectrolytes (CPEs), which are conjugated polymers bearing side-chain ionic functionalities such as anionic, cationic, or zwitterionic groups, have emerged as a new class of interfacial materials in thin film-based electronic devices thanks to their ability to reduce the barrier between electrode and active layer. In view of this, we designed and synthesized two novel low bandgap anionic copolymers with different anionic pendant groups and different conjugated backbones to obtain hole-transporting layer (HTL) materials as an alternative to commonly used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate). The functional behavior of these copolymers as anode modifiers is herein preliminarily investigated in an OLED prototype.
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Fatahi, Negin, Arash Boochani, Shahram Solaymani, Elmira Sartipi, and Farzad Ahmadian. "The band offset barrier and optical properties calculation of Co2VGa/GaAs(001) interfaces: A DFT study." International Journal of Modern Physics B 32, no. 01 (January 8, 2018): 1750270. http://dx.doi.org/10.1142/s0217979217502708.
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The structural, electronic, optical properties and band offsets of Co2VGa/GaAs(001) interfaces are discussed within the framework of density functional theory (DFT) using the FP-LAPW method, and the exchange-correlation potential is approximated by GGA. All interface structures are stable in the energy point of view, however the V–Ga/As case is found to be more stable than the others. A remarkable potential difference ([Formula: see text]V) appeared in all the interfaces, so the Co2VGa/GaAs(001) interfaces are good candidates for electron injection. In all the cases, there is no full spin polarization at the Fermi level, but high CBO and [Formula: see text] coefficients make them promising candidates for spin injection in the transport devices. Optical studies confirm the high metallic treatment of these interfaces as the main electron transitions had occurred in the infrared and visible regions. The real parts of the dielectric function in the x-direction indicate the different behaviors of “Co–Co/As and V–Ga/Ga” and “Co–Co/Ga and V–Ga/As” in the infrared area. In addition, the plasmon frequencies had occurred at high UV energies.
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Vermare, L., P. Hennequin, C. Honoré, M. Peret, G. Dif-Pradalier, X. Garbet, J. Gunn, et al. "Formation of the radial electric field profile in the WEST tokamak." Nuclear Fusion 62, no. 2 (December 16, 2021): 026002. http://dx.doi.org/10.1088/1741-4326/ac3c85.
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Abstract Sheared flows are known to reduce turbulent transport by decreasing the correlation length and/or intensity of turbulent structures. The transport barrier that takes place at the edge during improved regimes such as H mode, corresponds to the establishment of a large shear of the radial electric field. In this context, the radial shape of the radial electric field or more exactly of the perpendicular E × B velocity appears as a key element in accessing improved confinement regimes. In this paper, we present the radial profile of the perpendicular velocity measured using Doppler back-scattering system at the edge of the plasma, dominated by the E × B velocity, during the first campaigns of the WEST tokamak. It is found that the radial velocity profile is clearly more sheared in lower single null configuration (with the B × ∇B magnetic drift pointing toward the active X-point) than in upper single null configuration for ohmic and low current plasmas (B = 3.7 T and q 95 = 4.7), consistently with the expectation comparing respectively ‘favourable’ versus ‘unfavourable’ configuration. Interestingly, this tendency is sensitive to the plasma current and to the amount of additional heating power leading to plasma conditions in which the E × B velocity exhibits a deeper well in USN configuration. For example, while the velocity profile exhibits a clear and deep well just inside the separatrix concomitant with the formation of a density pedestal during L–H transitions observed in LSN configuration, deeper E r wells are observed in USN configuration during similar transitions with less pronounced density pedestal.
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Coda, S., A. Merle, O. Sauter, L. Porte, F. Bagnato, J. Boedo, T. Bolzonella, et al. "Enhanced confinement in diverted negative-triangularity L-mode plasmas in TCV." Plasma Physics and Controlled Fusion 64, no. 1 (December 13, 2021): 014004. http://dx.doi.org/10.1088/1361-6587/ac3fec.
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Abstract The favorable confinement properties of negative-triangularity (NT) tokamak configurations were discovered in the TCV tokamak in the late 1990s and were documented over the two following decades, through investigations of predominantly electron-heated plasmas in limited topologies. The most recent experimental campaign in TCV has marked a leap forward, characterized by the development of a variety of diverted NT shapes that are robustly stable with basic Ohmic heating. The application of auxiliary heating, directed now at both electrons and ions (using electron-cyclotron resonance heating as well as neutral-beam injection), has enabled the achievement of record performances for L-mode plasmas, with normalized β values reaching 2.8 transiently (as well as 2 in steady state, but reverting to a limited configuration) and with comparable ion and electron temperatures. The systematic confinement enhancement with NT is confirmed in these experiments. The L-mode existence space is broader than at positive triangularity, with only sporadic transitions to H-mode observed up to 1.4 MW heating power regardless of the magnetic-field-gradient direction relative to the X-point. These experiments are planned to be continued with even higher power following a heating-source upgrade.
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Boikov, K. A., M. S. Kostin, and G. V. Kulikov. "Radiosensory diagnostics of signal integrity in-circuit and peripheral architecture of microprocessor devices." Russian Technological Journal 9, no. 4 (August 26, 2021): 20–27. http://dx.doi.org/10.32362/2500-316x-2021-9-4-20-27.
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For the first time, a passive method for radiosensor diagnostics of the integrity of signals from microprocessor devices was developed and presented. The method is based on the registration of the electrical component of the near field of electromagnetic radiation induced as a result of the clock formation (variability) of the impulse response of a digital circuit caused by the dynamic restructuring of the active configuration of its in-circuit and peripheral architecture. It is shown that real radiation is a superposition of fields of emitters of the active architecture of a microprocessor, each of which has its own impulse and amplitude-frequency characteristics with its own peaks and dips, resonances and excitations. An expression of the free component is presented for the oscillatory nature of the process of energy redistribution between reactive storage devices, which depends on the capacitances of the gate dielectrics of MIS transistors, barrier and diffusion capacities of p-n junctions, inductances and ohmic resistances of circuit elements and the scheme of their architectural connection. An experiment was prepared and carried out on the method of passive radio-wave technical diagnostics of microprocessor devices on a specially developed test sample with a known command execution algorithm. The results of registration of a series of signal radio profiles when starting a sample of a digital device are presented, and a correlation assessment of the reproducibility of the experiment is carried out. It is proved that time interval transitions of free oscillations are formed on the reference signal radio profile. These transitions correspond to the microcontroller’s reference to the periphery according to the algorithm of the command functioning of the sample. The possibility of obtaining detailed information about the nature of the peripheral load and its performance by examining the corresponding sections of the reference signal radio profile is shown. It was found that the spectral-time frames of the software and hardware functioning of the digital device under study are clearly identified on the recorded radio images.
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Park, Sang-Joon, and Tae-Jun Ha. "Improved electric contact of recessed source and drain electrodes for sol–gel-based thin-film transistors consisting of amorphous ZrO2 and IGZO fabricated by microwave-annealing." Applied Physics Letters 120, no. 15 (April 11, 2022): 153301. http://dx.doi.org/10.1063/5.0086833.
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We investigate the effects of recessed source/drain (S/D) electrodes on the device performance of microwave-induced metal-oxide thin-film transistors (oxide-TFTs) by analyzing their contact resistances. High-performance top-gate-bottom-contact oxide-TFTs consisting of sol–gel-based high-k zirconium dioxide dielectric (ZrO2) and indium-gallium-zinc oxide (IGZO) semiconducting films were developed by employing microwave annealing. Vibration energy induced microwave annealing even at a low temperature (∼120 °C) with a short process time (10 min), which is sufficient to form dense metal–oxygen bonding while suppressing oxygen vacancies as defect states, resulted in high-quality sol–gel-based amorphous ZrO2 and IGZO films. The low-voltage operating oxide-TFTs with recessed S/D electrodes exhibited higher field-effect mobility (∼7.0 cm2 V−1 s−1) than those with elevated S/D electrodes (∼0.15 cm2 V−1 s−1). This result is attributed to the conformable deposition of the channel layer on the planar surface of S/D electrodes, leading to the improved interfacial characteristics. Relatively low effective contact resistance (∼79.7 Ω cm), which was extrapolated from a plot of the width-normalized resistance as a function of the channel length using a transmission line method, in oxide-TFTs with recessed S/D electrodes, is compared to that (∼1480.6 Ω cm) of elevated S/D electrodes. This was in good agreement with the Ohmic contact behavior contact where the low charge injection barrier improved charge transport.
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Kranjec, Andrej, Petr Karpov, Yevhenii Vaskivskyi, Jaka Vodeb, Yaroslav Gerasimenko, and Dragan Mihailovic. "Electronic Dislocation Dynamics in Metastable Wigner Crystal States." Symmetry 14, no. 5 (May 1, 2022): 926. http://dx.doi.org/10.3390/sym14050926.
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Metastable states appear in many areas of physics as a result of symmetry-breaking phase transitions. An important challenge is to understand the microscopic mechanisms which lead to the formation of the energy barrier separating a metastable state from the ground state. In this paper, we describe an experimental example of the hidden metastable domain state in 1T-TaS2, created by photoexcitation or carrier injection. The system is an example of a charge density wave superlattice in the Wigner crystal limit displaying discommensurations and domain formation when additional charge is injected either through contacts or by photoexcitation. The domain walls and their crossings in particular display interesting, topologically entangled structures, which have a crucial role in the metastability of the system. We model the properties of experimentally observed thermally activated dynamics of topologically protected defects—dislocations—whose annihilation dynamics can be observed experimentally by scanning tunnelling microscopy as emergent phenomena described by a doped Wigner crystal. The different dynamics of trivial and non-trivial topological defects are quite striking. Trivial defects appear to annihilate quite rapidly at low temperatures on the timescale of the experiments, while non-trivial defects annihilate rarely, if at all.
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DONG, Z. C., X. L. GUO, Y. WAKAYAMA, and J. G. HOU. "MOLECULAR-SCALE ORGANIC ELECTROLUMINESCENCE FROM TUNNEL JUNCTIONS." Surface Review and Letters 13, no. 02n03 (April 2006): 143–47. http://dx.doi.org/10.1142/s0218625x06008207.
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We report the generation and detection of bipolar organic electroluminescence of porphyrin molecules from a nanoscale junction in an ultrahigh vacuum scanning tunneling microscope (STM). Clear molecular fluorescence from porphyrin molecules near metal substrates has been realized through highly localized electrical excitation of molecules in proximity to a sharp tip apex. The molecular origin of the luminescence, arising from the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) radiative transitions of neutral molecules, is clearly established by the observed well-defined vibrationally resolved fluorescence spectra that match perfectly with conventional photoluminescence data from molecular thin films. The molecules fluoresce at low onset voltages for both bias polarities, presenting an example of bipolar organic electroluminescence at the nanoscale. Such bipolar operation suggests a double-barrier model for electron transport, with hot electron injection into unoccupied states of molecules in both polarities. The optical behavior of molecules in the tunnel junction is also found sensitive to the electronic properties of molecules and energy level alignment at the interface. These results offer new information to the optoelectronic behavior of molecules in a nanoscopic environment and may open up new routes to the development of single-molecule science and molecular scale electronics.
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Carpenter, Joseph, Jillian S. Catalanotti, Melissa Notis, Christopher J. Brokus, Timothy P. Moran, Irene Kuo, Hana Akselrod, et al. "1362. Adding Insult to Injury: Association of Stigmatizing Language and Suboptimal Outcomes in People Who Inject Drugs." Open Forum Infectious Diseases 8, Supplement_1 (November 1, 2021): S767—S768. http://dx.doi.org/10.1093/ofid/ofab466.1554.
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Abstract Background The National Academy of Medicine has identified stigma surrounding substance use disorders (SUDs) and infectious diseases (ID) as a key barrier to integration of opioid use disorder (OUD) and ID services. Prior literature on stigmatizing language in OUD clinical care focuses on surveys and theoretical scenarios rather than real-world data. As part of a larger study of patients admitted for infectious complications of injection drug use (CHOICE), we sought to determine how inpatient physicians describe persons with OUD, as well as associations of this language with outcomes along the OUD continuum of care. Methods CHOICE is a retrospective review of adults hospitalized with an infectious complication of OUD and IDU at four academic medical centers. Included patients were hospitalized between 1/1/2018-12/31/2018, had ICD9/10 diagnosis codes consistent with OUD and acute bacterial/fungal infection, and chart review verification of active infection associated with OUD. Data was abstracted regarding demographics, inpatient interventions, transitions of care, and outcomes 1 year after admission. Potentially stigmatizing language was identified based on the discharge summary. “Abuse” and “misuse” were considered potentially stigmatizing; “use disorder” was considered best practice. Associations of language and outcomes were analyzed via logistic generalized estimating equations. Results A total of 287 subjects met inclusion criteria; 119 (42%) were female and the median age was 40 years (IQR: 32 – 52). The most common terms used to describe OUD were “abuse” (190, 66%) and “IVDU” (119, 42%). “Use disorder” was noted in only 72 (25%) charts. In a regression analysis, any mention of “use disorder” was associated with not leaving against medical advice (OR 2.48, 95% CI 1.24 – 4.95), a plan for ongoing OUD treatment (OR 5.17, 95% CI 2.05-13.0), and addiction-specific follow up (OR 2.94, 95% CI 2.34-3.68). Conclusion In this multicenter retrospective study, inpatient physicians commonly referred to patients with OUD using stigmatizing language. When NIH-preferred language was used this was associated with improved outcomes along the OUD continuum of care, possibly reflecting increased awareness of best practices for treating patients with OUD. Disclosures Ellen Eaton, MD , Gilead (Grant/Research Support) Ellen Eaton, MD , Gilead (Individual(s) Involved: Self): Research Grant or Support Greer A. Burkholder, MD, MSPH, Eli Lilly (Grant/Research Support) Sarah Kattakuzhy, MD, Gilead Sciences (Scientific Research Study Investigator, Research Grant or Support) Elana S. Rosenthal, MD, Gilead Sciences (Research Grant or Support)Merck (Research Grant or Support)
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Kanicki, Jerzy. "Metal / Hydrogenated Amorphous Silicon Interfaces." MRS Proceedings 95 (1987). http://dx.doi.org/10.1557/proc-95-399.
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The contact properties between different metals and hydrogenated amorphous silicon, prepared by various deposition techniques in different laboratories, are reviewed. From these studies the appropriate metallizations have been established for the achievement of Schottky diode, quasi-ohmic or ohmic contact to undoped and doped films. The various characteristic parameters describing Schottky barrier interfaces such as ideality factor, current saturation, contact resistance and barrier height are discussed. The dependence of Schottky barrier height upon the metal work function, measuring and annealing temperature, and optical band-gap are also reported. The minority-carrier injection and series resistance effects on the contact properties of a-Si:H diodes are described. All the results are interpreted in terms of a self-consistent model that exhibits an electrode-limited to bulk-limited transition.
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Cai, Xiangbin, Zefei Wu, Xu Han, Yong Chen, Shuigang Xu, Jiangxiazi Lin, Tianyi Han, et al. "Bridging the gap between atomically thin semiconductors and metal leads." Nature Communications 13, no. 1 (April 1, 2022). http://dx.doi.org/10.1038/s41467-022-29449-4.
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AbstractElectrically interfacing atomically thin transition metal dichalcogenide semiconductors (TMDSCs) with metal leads is challenging because of undesired interface barriers, which have drastically constrained the electrical performance of TMDSC devices for exploring their unconventional physical properties and realizing potential electronic applications. Here we demonstrate a strategy to achieve nearly barrier-free electrical contacts with few-layer TMDSCs by engineering interfacial bonding distortion. The carrier-injection efficiency of such electrical junction is substantially increased with robust ohmic behaviors from room to cryogenic temperatures. The performance enhancements of TMDSC field-effect transistors are well reflected by the low contact resistance (down to 90 Ωµm in MoS2, towards the quantum limit), the high field-effect mobility (up to 358,000 cm2V−1s−1 in WSe2), and the prominent transport characteristics at cryogenic temperatures. This method also offers possibilities of the local manipulation of atomic structures and electronic properties for TMDSC device design.
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Sohn, K., H. Lee, and D. A. Hensley. "I-V Characteristics and Interface Properties of Al-Si(P) Contacts by the Krf Excimer Laser Induced Recrystallization." MRS Proceedings 283 (1992). http://dx.doi.org/10.1557/proc-283-733.
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ABSTRACTAl was deposited on the both sides of p-type Si by the sputtering, and the pulsed KrF excimer laser was irradiated on the one side and both sides of Al dot contacts. Due to the thin-high doping recrystallized layer, the transitions from the Schottky diodes to the ohmic contacts via backward diodes were observed in I-V measurement. Good N-shape negative resistances and notches were observed in the diodes, and ohmic contacts. Possible interpretations of the orgin of these phenomena are discussed. And, the simple model of the effective barrier height reduction under the thermionic field emission was developed using WKB approximation, and tunneling theory. By the depth Auger analysis, Al, and Si profiles near Al-Si interface after the laser irradiation were observed.
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Matsuda, Shofu, Chikara Itagaki, Kyoya Tatsuguchi, Masamichi Ito, Hiroto Sasaki, and Minoru Umeda. "Highly efficient hole injection from Au electrode to fullerene-doped triphenylamine derivative layer." Scientific Reports 12, no. 1 (May 4, 2022). http://dx.doi.org/10.1038/s41598-022-10983-6.
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AbstractTriphenylamine derivatives are superior hole-transport materials. For their application to high-functional organic semiconductor devices, efficient hole injection at the electrode/triphenylamine derivative interface is required. Herein, we report the design and evaluation of a Au/fullerene-doped α-phenyl-4′-[(4-methoxyphenyl)phenylamino]stilbene (TPA) buffer layer/TPA/Au layered device. It exhibits rectification conductivity, indicating that hole injection occurs more easily at the Au/fullerene-doped TPA interface than at the Au/TPA interface. The Richardson-Schottky analysis of the device reveals that the hole injection barrier (ΦB) at the Au/fullerene-doped TPA interface decreases to 0.021 eV upon using C70 as a dopant, and ΦB of Au/TPA is as large as 0.37 eV. The reduced ΦB of 0.021 eV satisfies the condition for ohmic contact at room temperature (ΦB$$\le $$ ≤ 0.025 eV). Notably, C70 doping has a higher barrier-reduction effect than C60 doping. Furthermore, a noteworthy hole-injection mechanism, in which the ion–dipole interaction between TPA and fullerenes plays an important role in reducing the barrier height, is considered based on cyclic voltammetry. These results should facilitate the design of an electrode/organic semiconductor interface for realizing low-voltage driven organic devices.
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Wang, Hong, Zhuoyu Ji, Liwei Shang, Yingping Chen, Congyan Lu, Dongmei Li, Yingquan Peng, and Ming Liu. "Low-cost 13.56MHz Rectifier Based on Organic Diode." MRS Proceedings 1402 (2012). http://dx.doi.org/10.1557/opl.2012.145.
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ABSTRACTIn this paper, low-cost rectifier based on an organic diode for use in organic radio frequency identification (RFID) tags is proposed. Pentacene is the electroactive layer, with 7,7,8,8-tetracyanoquinodimethane (TCNQ) modified low-cost copper (Cu) and aluminum (Al) as the Ohmic and Schottky contacts, respectively. Hole injection barrier between Cu and pentacene can be decreased by forming the self-assembled layers of Cu-TCNQ. The diode shows a high rectification ratio of approximately 2×106 at 5V and the organic diode based rectifier circuit generated a dc output voltage of approximately 2V at 13.56MHz, using an input ac signal with zero-to-peak voltage amplitude of 5 V. The results indicate that chemical modification of the low-cost electrodes could be an efficient way toward low-cost high performance organic electronics devices.
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Abkowitz, M., J. S. Facci, and J. Rehm. "Injection Efficiency from Various Metals into Trap Free Molecularly Doped Polymers Evaluated from Combined Analysis of Current-Voltage and Time-of-Flight Drift Mobility Data." MRS Proceedings 488 (1997). http://dx.doi.org/10.1557/proc-488-629.
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AbstractAn experimental procedure which can provide a direct quantitative measure of contact injection efficiency into a trap free transport polymer is described. This technique combines coupled analyses of bias dependent injection current supplied by the contact under test with time-of-flight drift mobility measurements carried out on the same specimen film. This general procedure has been used in a broad range of experiments to evaluate the injection efficiencies from a series of hole injecting contacts of differing work functions into the molecularly doped polymer, TPD/Polycarbonate Two key results are emphasized: (1) Injection efficiency does scale on average with the interfacial barrier, the energy step estimated from substrate workfunction and MDP electrochemical data. In individual cases however, large variations about the norm are clearly identified and can be attributed to variations in the contact surface prior to coating, for example the relative degree of oxidation or, as TOFSIMS reveals, the interdiffusion of metal atoms from adhesive layers which secure the metal coating to a Si wafer substrate. (2) For the case of Au, the injection efficiency of a Au substrate was compared to the behavior of Au vacuum deposited onto the already formed coating under a variety of conditions. The injection efficiency from Au evaporated onto preformed coating initially varies with deposition conditions but relaxes with time under ambient conditions, eventually becoming ohmic. Significant details of this relaxation behavior are described and analyzed in an accompanying paper.
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Gass, Richard G., Howard E. Jackson, P. J. Hughes, and Bernard L. Weiss. "Interdiffusion in Quantum Wells: Mixing Mechanisms and Energy Levels." MRS Proceedings 450 (1996). http://dx.doi.org/10.1557/proc-450-365.
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AbstractCompositional interdiffusion in Al0.3Ga0.7As/GaAs superlattice structures with equal 3.5 nm barrier and well widths induced by Si focused ion beam implantation and subsequent rapid thermal annealing has been modeled. A strong depth dependence of the mixing process is observed at a Si++ energy of 100 keV and at a dose of 1×1014 cm−2; this depth dependence is modeled by considering the second derivative of the vacancy profile. That is the maximum in the vacancy injection generated by the transient vacancy concentration gradient. We have included the dynamics of the spatial vacancy profile in the model and find good agreement with experimental results.Interdiffusion across the well/barrier interfaces modifies the subband structure in AlGaAs/GaAs single quantum well (QW) structures. We have investigated the interrelated changes in both confinement energy of the subband states and the composition dependence of the bandgap energy in the QW, both of which are a strong function of the initial well width. Higher order transitions are found to be more sensitive than the ground state transitions to interdiffusion especially during the early stages of interdiffusion. These calculations model the experimental measurements (photoluminescence and photoreflectance) which are used to characterize interdiffused QW structures.
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McInally, Shane G., Jane Kondev, and Scott C. Dawson. "Length-dependent disassembly maintains four different flagellar lengths in Giardia." eLife 8 (December 19, 2019). http://dx.doi.org/10.7554/elife.48694.
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With eight flagella of four different lengths, the parasitic protist Giardia is an ideal model to evaluate flagellar assembly and length regulation. To determine how four different flagellar lengths are maintained, we used live-cell quantitative imaging and mathematical modeling of conserved components of intraflagellar transport (IFT)-mediated assembly and kinesin-13-mediated disassembly in different flagellar pairs. Each axoneme has a long cytoplasmic region extending from the basal body, and transitions to a canonical membrane-bound flagellum at the ‘flagellar pore’. We determined that each flagellar pore is the site of IFT accumulation and injection, defining a diffusion barrier functionally analogous to the transition zone. IFT-mediated assembly is length-independent, as train size, speed, and injection frequencies are similar for all flagella. We demonstrate that kinesin-13 localization to the flagellar tips is inversely correlated to flagellar length. Therefore, we propose a model where a length-dependent disassembly mechanism controls multiple flagellar lengths within the same cell.
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El-Metwally, Essam Gamal, Mervat Ismail Mohammed, and A. M. Ismail. "Promising naphthol green B dye doped (PVOH-PEG) composite films as a multifunctional material with engineered optical band gap, tunable dielectric properties and nonlinear J–E characteristics." Physica Scripta, April 22, 2022. http://dx.doi.org/10.1088/1402-4896/ac6990.
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Abstract Polymer composite films of polyvinyl alcohol (PVOH) – polyethylene glycol (PEG) /naphthol green B dye (NGB) were prepared using the solution cast technique with different concentrations of NGB (0 - 25 wt. (%)). XRD emphasized the semi-crystalline nature of the base polymer blend (PVOH-PEG) which increased by NGB addition. FTIR spectra of the investigated samples confirmed the formation of hydrogen bonds between the polymer blend hydroxyl groups and the NGB molecules. Optical properties are studied within wavelengths ranged from 245 nm to 1500 nm. Multi-optical energy band gaps (Eg ) were observed in (PVOH-PEG) doped with NGB dye for the allowed indirect and direct transitions and showed a decrease with the addition of NGB dye. Analysis of the refractive index n offered a normal dispersion within the investigated wavelength region. The dependence of the dielectric constant ε', loss ε'' and ac conductivity σac on frequency (100 Hz - 1 MHz) and NGB content were investigated at room temperature (RT). The addition of NGB tends to increase σac of the (PVOH-PEG) blend, that serve in various semiconductor devices. The values of the frequency exponent s and the charge carriers binding energy WM decrease in the presence of NGB dye and are interpreted by the correlated barrier hopping (CBH) model. Electric modulus formalism clarified the presence of a single relaxation peak with a relaxation time depends on the NGB wt. (%). The (current density J - electric field E) characteristics were studied at RT and showed a non-ohmic behavior. The current density J increased with the addition of NGB dye and the dc conduction is discussed in view of Schottky-Richardson and Poole–Frenkel theoretical models.
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Stoleru, Valeria Gabriela, Elias Towe, Chaoying Ni, and Debdas Pal. "Quantum-Dot Molecules for Potential Applications in Terahertz Devices." MRS Proceedings 829 (2004). http://dx.doi.org/10.1557/proc-829-b1.3.
Full textAbstract:
ABSTRACTThe experimental and theoretical results of the electronic and optical properties of quantum dot artificial molecules (AMs), formed by pairs of electronically coupled quantum dots (QDs), are presented here in order to identify the necessary conditions for the development of new types of terahertz (THz) injection lasers based on intraband carrier transitions. We have performed analytical calculations to obtain the spatial strain distribution in vertically aligned (In, Ga)As QDs grown on (001) GaAs substrates by molecular beam epitaxy. Electronic coupling of the dots, mainly governed by the thickness of the separating barrier between the dot layers, is allowed due to the strain field-assisted self-organization of the dots. The calculated strain field reproduces our cross sectional high-resolution transmission electron microscopy observations very well. We further take into account the microscopic effects of the spatial strain distribution on carrier confinement potentials, and compute the electronic structure of the AM. Our calculations of the peak luminescence energies are in good agreement with our experimental results and those of others. The growth of quantum dot molecules represents a major step in tailoring the electronic and optical properties of the nanostructures.