Submillimeter and millimeter optical constants of liquid nitrogen

We present power absorption coefficient measurements of liquid nitrogen in the range 4–28 cm^?1 and measurements of the average value of the refractive index for the range 4–10 cm^?1. The measurements were performed with a polarizing Michelson interferometer. The power absorption coefficient rises quadratically from 0.006±0.002 nepers cm^?1 at 4 cm^?1 to 0.381±0.009 nepers cm^?1 at 28 cm^?1. The average value of the refractive index is 1.20±0.03 between 4 and 10 cm^?1.     

Sb2Te3 and Bi2Te3 Thin Films Grown by Room-Temperature MBE

Sb₂Te₃ and Bi₂Te₃ thin films were grown on SiO₂ and BaF₂ substrates at room temperature using molecular beam epitaxy. Metallic layers with thicknesses of 0.2?nm were alternately deposited at room temperature, and the films were subsequently annealed at 250°C for 2?h. x-Ray diffraction and energy-filtered transmission electron microscopy (TEM) combined with high-accuracy energy-dispersive x-ray spectrometry revealed stoichiometric films, grain sizes of less than 500?nm, and a texture. High-quality in-plane thermoelectric properties were obtained for Sb₂Te₃ films at room temperature, i.e., low charge carrier density (2.6?×?10¹⁹?cm^?3), large thermopower (130???V?K^?1), large charge carrier mobility (402?cm²?V^?1?s^?1), and resulting large power factor (29???W?cm^?1?K^?2). Bi₂Te₃ films also showed low charge carrier density (2.7?×?10¹⁹?cm^?3), moderate thermopower (?153???V?K^?1), but very low charge carrier mobility (80?cm²?V^?1?s^?1), yielding low power factor (8???W?cm^?1?K^?2). The low mobilities were attributed to Bi-rich grain boundary phases identified by analytical energy-filtered TEM.     

The pure rotational spectrum of water vapor—A millimeter,submillimeter, and far infrared analysis

Line positions, strengths, and absolute energies are calculated for the pure rotational spectrum of water in the region between 0 cm^?1 and 877 cm^?1. These calculations are done in the context of a reduced centrifugal distortion Hamiltonian, and are based on microwave measurements of this spectrum to 1 THz, and Far Infrared measurements between 32 cm^?1 and 715 cm^?1.     

Organic Thermoelectric Materials Composed of Conducting Polymers and Metal Nanoparticles

Organic thermoelectric materials consisting of conducting polymers have received much attention recently because of their advantages such as wide availability of carbon, easy syntheses, easy processing, flexible devices, low cost, and low thermal conductivity. Nevertheless, their thermoelectric performance is still not good enough for practical use. To improve their performance, we present herein new kinds of hybrids of organic conducting polymers and metal nanoparticles (NPs). Since hybridization of polyaniline with poly-(N-vinyl-2-pyrrolidone) (PVP)-protected Au NPs decreased the electrical conductivity of polyaniline films from 150?S?cm^?1 to 50?S?cm^?1, we carried out direct hybridization of polyaniline with Au NPs without PVP in this study. Direct hybridization improved the electrical conductivity to as high as 330?S?cm^?1 at 50°C while keeping the Seebeck coefficient at 15???V?m^?1?K^?2. Poly(3,4-ethylenedioxythiophene) (PEDOT) is another promising conducting polymer. Here, we used hybrid films of PEDOT with Au NPs protected by two kinds of ligands, terthiophenethiol and dodecanethiol (DT), revealing that the hybrid of PEDOT with DT-protected Au NPs showed better thermoelectric performance than pristine PEDOT without Au NPs. Addition of DT-protected Au NPs improved the electrical conductivity of the PEDOT films from 104?S?cm^?1 to 241?S?cm^?1 and the thermoelectric figure of merit from 0.62?×?10^?2 to 1.63?×?10^?2 at 50°C.     

Electrical Characteristics of Ti/Al Ohmic Contacts to Molecular Beam Epitaxy-Grown N-polar n-type GaN for Vertical-Structure Light-Emitting Diodes

We investigated the electrical properties of Ti(30?nm)/Al(200?nm) contacts to molecular beam epitaxy-grown N-polar n-GaN with different carrier concentrations. Samples with carrier concentration of 1.2?×?10¹⁸?cm^?3 showed nonohmic behaviors when annealed at 300°C, but ohmic at 500°C and 700°C. All samples with carrier concentration of 2.0?×?10¹⁹?cm^?3 exhibited ohmic behavior. x-Ray photoemission spectroscopy (XPS) results showed that, for samples with carrier concentration of 1.2?×?10¹⁸?cm^?3, the Ga 2p core levels shift to lower or higher binding energy upon annealing at 300°C or above 500°C, respectively. Scanning transmission electron microscopy (STEM) results showed that, for samples with carrier concentration of 1.2?×?10¹⁸?cm^?3, a wurtzite AlN layer (??2?nm thick) formed at the metal/GaN interface when the samples were annealed at 500°C. An interfacial wurtzite AlN layer also formed upon annealing at 700°C, but its thickness was ??4?nm. Based on the XPS and STEM results, the ohmic contact formation and degradation mechanisms are described and discussed.     

Dark Current and Noise Measurements of an InAs/GaSb Superlattice Photodiode Operating in the Midwave Infrared Domain

A midwave infrared pin photodiode based on a type?II InAs/GaSb superlattice (SL) was fabricated, and electrical measurements under dark conditions were performed as a function of temperature. The SL structure exhibits photoluminescence emission at 4.55?μm at 77?K. Deduced from current density–voltage (J–V) measurements, a zero-bias resistance–area product R ₀ A greater than 1?×?10⁶?Ω?cm² at 77?K was measured. Additional noise measurements show no presence of intrinsic 1/f noise above 20?Hz, and the photodiode presents Schottky-limited behavior below ?600?mV. All these results confirm the potential for such SL InAs/GaSb superlattice pin photodiodes operating in the midwave infrared domain.     

Generation of High-Power Sub-THz Waves in Magnetized Turbulent Electron Beam Plasmas

Sub-THz radiation can be generated by conversion of plasma waves into electromagnetic (EM) radiation in a plasma with strong Langmuir (LT) turbulence produced via a two-stream instability of a high current relativistic electron beam (REB). Nonlinear plasmon-plasmon merging results in the generation of photons nearby the 2^nd harmonic of the plasma frequency 2ω _p (“2ω _p -process”). For plasma densities of 10¹⁴???10¹⁵?cm^?3, these frequencies are in the range of sub-THz waves at 370–570 GHz. The specific power density of sub-THz-wave emission from plasmas in the multi-mirror magnetic trap GOL-3 (at BINP) during injection of a 10-μs-REB with a current density of about 1 kA/cm² at plasma densities n _e ?≈?5?10¹⁴?cm^?3, electron temperatures T _e ?≈?1.5 keV and magnetic induction B?≈?4 T was measured to be approx. 1 kW/cm³ in the frequency band around 300 GHz. In the case of a weakly relativistic 100-μs-electron beam (90 keV) with 250 A/cm² the corresponding results are 700 W/cm³ around 90 GHz with an efficiency of 1–2 % at n _e ?≈?3?10¹³?cm^?3 (total power?≈?30 kW). Theoretical investigations show that at a density of n _e ?≈?3?10¹⁵?cm^?3 and a turbulence level of 5 % the generated sub-THz power can reach?≈?1 MW/cm³.     

Investigation of MBE-Growth of Mid-Wave Infrared Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se

Undoped mid-wave infrared Hg_1?xCd_xSe epitaxial layers have been grown to a nominal thickness of 8–14 μm on GaSb (211)B substrates by molecular beam epitaxy (MBE) using constant beam equivalent pressure ratios. The effects of growth temperature from 70°C to 120°C on epilayer quality and its electronic parameters has been examined using x-ray diffraction (XRD) rocking curves, atomic force microscopy, Nomarski optical imaging, photoconductive decay measurements, and variable magnetic field Hall effect analysis. For samples grown at 70°C, the measured values of XRD rocking curve full width at half maximum (FWHM) (116 arcsec), root mean square (RMS) surface roughness (2.7 nm), electron mobility (6.6?×?10⁴ cm² V^?1 s^?1 at 130 K), minority carrier lifetime (～?2 μs at 130 K), and background n-type doping (～?3?×?10¹⁶ cm^?3 at 130 K), indicate device-grade material quality that is significantly superior to that previously published in the open literature. All of these parameters were found to degrade monotonically with increasing growth temperature, although a reasonably wide growth window exists from 70°C to 90°C, within which good quality HgCdSe can be grown via MBE.     

Electrical properties of uncontaminated PbTe films on mica substrates prepared by molecular beam deposition

Uncontaminated PbTe films were prepared by molecular beam deposition under clean conditions in a uhv environment and the film properties were measured in situ. The carrier concentration was found to be determined by source conditions and values between 10¹⁶ cm^?3 (intrinsic level) and n = 5 × 10¹⁸cm^?3 could be obtained in a controllable manner. A low temperature anneal enabled bulk value Hall mobilities (1750 cm² V^?1 sec^?1 at 300 K) to be obtained at room temperature and above which indicated that surface scattering in the films was predominantly specular. The mobility at low temperatures (down to 100 K) was limited by small potential barriers located at the double-positioned grain boundaries which were present in the film. Field effect measurements indicated the potential barriers arose from a continuous distribution of band gap states situated in the grain boundaries. These states had a fairly uniform density (? 10¹²cm^?2 (kT)^?1) but there was some increase towards the conduction band edge. They also limited the field effect mobility (μ_FE) to ?0.5 bulk value, giving μ_FE ? 800cm² (volt sec)^?1 for films with carr concentrations above 5 × 10¹⁷ cm^?3. By exposure to low pressures of oxygen the carrier concentrations in annealed n-type films could be reduced to near intrinsic values with no associated degradation in the electrical properties. This indicated that the films were not compensated with the native p-type defect.     

Evaluation of mobility gaps and density of localized hole states in p-Ge/Ge1−x Six heterostructures in the quantum Hall effect mode

The temperature (0.1 K?T?20 K) and magnetic field (0 T?B?12 T) dependences of the longitudinal (ρ_xx) and Hall (ρ_xy) resistivities have been studied in detail for p-Ge/Ge_1?x Si_x (x=0.07) multilayer heterostructures with hole density p=(2.4–2.6)×10¹¹ cm^?2 and mobility μ=(1.1–1.7)×10⁴ cm² V^?1 s^?1. The energy spectrum parameters of two-dimensional (2D) hole gas in the quantum Hall effect mode have been determined. The mobility gap W=(2–2.5) meV and the background density of localized states g _c =(5–7)×10¹⁰ cm^?2 meV^?1 for the filling factors ν=1 and 2. The results are discussed in terms of long-range impurity potential models for selectively doped 2D systems.     

Hierarchical NiMoS and NiFeS Nanosheets with Ultrahigh Energy Density for Flexible All Solid‐State Supercapacitors

Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free‐standing Ni?Mo?S and Ni?Fe?S nanosheets (NSs) for high‐performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni²⁺ is optimized to attain hierarchical Ni?Mo?S and Ni?Fe?S NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of Ni?Mo?S and Ni?Fe?S NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g^?1 at 1 mA cm^?2), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm^?2, respectively), and superior cycling stabilities. Most importantly, a flexible Ni?Mo?S NS//Ni?Fe?S NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm^?3, excellent energy density of ≈82.13 Wh kg^?1 at 0.561 kW kg^?1, exceptional power density (≈13.103 kW kg^?1 at 61.51 Wh kg^?1) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes.     

Thermoelectric Performance Enhancement of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Composite Films by Addition of Dimethyl Sulfoxide and Urea

Significant enhancement of thermoelectric (TE) performance was observed for free-standing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) composite films obtained from a PEDOT:PSS aqueous solution by simultaneous addition of dimethyl sulfoxide (DMSO) and different concentrations of urea. The electrical conductivity was enhanced from 8.16?S?cm^?1 to over 400?S?cm^?1, and the maximum Seebeck coefficient reached a value of 18.81???V?K^?1 at room temperature. The power factor of the PEDOT:PSS composite films reached 8.81???W?m^?1?K^?2. The highest thermoelectric figure of merit (ZT) in this study was 0.024 at room temperature, which is at least one order of magnitude higher than most polymers and bulk Si. These results indicate that the obtained composite films are a promising thermoelectric material for applications in thermoelectric refrigeration and thermoelectric microgeneration.     

Vibrational and morphological properties of Sn-doped CdS films deposited by ultrasonic spray pyrolysis method

Cd_1?xSn_xS films (x=0.0, 0.1 and 0.2) were prepared by the ultrasonic spray pyrolysis (USP) method on the glass substrate at 300 °C. Effect of Sn doping on the vibrational and morphological properties of CdS films has been investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), FT-IR and Raman spectroscopy. The SEM and AFM measurements showed that the surface morphology of the films was affected by the tin incorporation. The Raman (200–700 cm^?1) and FT-IR (400–4000 cm^?1) spectra of Cd_1?xSn_xS were recorded. The Raman spectrum for Cd_1?xSn_xS films is dominated by an intense band at 300 cm^?1, assigned to the first-order longitudinal optic phonon and the second-order phonon peak 599 cm^?1. The absorption peaks in the FT-IR spectra of Cd_1?xSn_xS located at 540–700 and 1004–1045 cm^?1 can be assigned to the Cd–S and C–O stretching frequencies, respectively. Raman and FT-IR spectra shows decrease in the peak intensity with increasing Sn concentration.     

Hierarchical Ni?Mo?S and Ni?Fe?S Nanosheets with Ultrahigh Energy Density for Flexible All Solid‐State Supercapacitors

Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free‐standing Ni? Mo? S and Ni? Fe? S nanosheets (NSs) for high‐performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni²⁺ is optimized to attain hierarchical Ni? Mo? S and Ni? Fe? S NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of Ni? Mo? S and Ni? Fe? S NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g^?1 at 1 mA cm^?2), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm^?2, respectively), and superior cycling stabilities. Most importantly, a flexible Ni? Mo? S NS//Ni? Fe? S NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm^?3, excellent energy density of ≈82.13 Wh kg^?1 at 0.561 kW kg^?1, exceptional power density (≈13.103 kW kg^?1 at 61.51 Wh kg^?1) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes.     

Chemically Resistant,Shapeable, and Conducting Metal‐Organic Gels and Aerogels Built from Dithiooxamidato Ligand

Metal‐organic gels (MOGs) appear as a blooming alternative to well‐known metal‐organic frameworks (MOFs). Porosity of MOGs has a microstructural origin and not strictly crystalline like in MOFs; therefore, gelation may provide porosity to any metal‐organic system, including those with interesting properties but without a porous crystalline structure. The easy and straightforward shaping of MOGs contrasts with the need of binders for MOFs. In this contribution, a series of MOGs based on the assembly of 1D‐coordination polymer nanofibers of formula [M(DTA)]_n (M^II: Ni, Cu, Pd; DTA: dithiooxamidato) are reported, in which properties such as porosity, chemical inertness, mechanical robustness, and stimuli‐responsive electrical conductivity are brought together. The strength of the M? S bond confers an unusual chemical resistance, withstanding exposure to acids, alkalis, and mild oxidizing/reducing chemicals. Supercritical drying of MOGs provides ultralight metal‐organic aerogels (MOAs) with densities as low as 0.03 g cm^?3 and plastic/brittle behavior depending on the nanofiber aspect ratio. Conductivity measurements reveal a semiconducting behavior (10^?12 to 10^?7 S cm^?1 at 298 K) that can be improved by doping (10^?5 S cm^?1). Moreover, it must be stressed that conductivity of MOAs reversibly increases (up to 10^?5 S cm^?1) under the presence of acetic acid.     

Conductive Nanostructures of MMX Chains

Crystals of [Pt₂(n‐pentylCS₂)₄I] show a transition from semiconductor to metallic with the increase of the temperature (conductivity is 0.3–1.4 S · cm^?1 at room temperature) and a second metallic–metallic transition at 330 K, inferred by electrical conductivity measurements. X‐ray diffraction studies carried out at different temperatures (100, 298, and 350 K) confirm the presence of three different phases. The valence‐ordering of these phases is analyzed using structural, magnetic, and electrical data. Density functional theory calculations allow a further analysis of the band structure derived for each phase. Nanostructures adsorbed on an insulating surface show electrical conductivity. These results suggest that MMX‐polymer‐based nanowires could be suitable for device applications.     

Self‐Doping Cathode Interfacial Material Simultaneously Enabling High Electron Mobility and Powerful Work Function Tunability for High‐Efficiency All‐Solution‐Processed Polymer Light‐Emitting Diodes

A variety of N ‐hydrogenated/N ‐methylated pyridinium salts are elaborately designed and synthesized. Thermogravimetric and X‐ray photoelectron spectra analysis indicate the intensities of the N? H covalent bonds are strengthened step‐by‐step from 3,3′‐(5′‐(3‐(pyridin‐3‐yl)phenyl)‐[1,1′:3′,1″‐terphenyl]‐3,3″‐diyl)dipyridine (Tm)‐HCl to Tm‐HBr and then Tm‐TfOH, which results in gradually improved cathode interfacial modification abilities. The larger dipole moments of N⁺? H containing moieties compared to those of the N⁺? CH₃ endow them with more preferable interfacial modification abilities. Electron paramagnetic resonance signals reveal the existence of radical anions in the solid state of Tm‐TfOH, which enables its self‐doping property and high electron mobility up to 1.67 × 10^?3 cm² V^?1 s^?1. Using the Tm‐TfOH as the cathode interfacial layers (CILs), the phenyl‐substituted poly(para ‐phenylene vinylene)‐based all‐solution‐processed polymer light‐emitting diodes (PLEDs) achieve more preferable device performances than the poly[(9,9‐bis(3′‐(N ,N ‐dimethylamino)propyl)‐2,7‐fluorene)‐alt ‐2,7‐(9,9‐dioctylfluorene)]‐based ones, i.e., high current density of nearly 300 mA cm^?2, very high luminance over 15 000 cd m^?2 at a low bias of 5 V. Remarkably, the thickness of the CILs has little impact on the device performance and high efficiencies are maintained even at thicknesses up to 85 nm, which is barely realized in PLEDs with small‐molecule‐based electron transporting layers.     

Gold‐Cobalt Nanoparticle Alloys Exhibiting Tunable Compositions,Near‐Infrared Emission,and High T2 Relaxivity

We demonstrate the synthesis of discrete, composition‐tunable gold‐cobalt nanoparticle alloys (% Co = 0–100%; diameter = 2–3 nm), in contrast with bulk behavior, which shows immiscibility of Au and Co at room temperature across all composition space. These particles are characterized by transmission electron microscopy and ¹H NMR techniques, as well as inductively coupled plasma mass spectrometry, X‐ray photoelectron spectroscopy, and photoluminescence spectroscopy. In particular, ¹H NMR methods allow the simultaneous evaluation of composition‐tunable magnetic properties as well as molecular characterization of the colloid, including ligand environment and hydrodynamic diameter. These experiments also demonstrate a route to optimize bimodal imaging modalities, where we identify Au_xCo_yNP compositions that exhibit both bright NIR emission (2884 m ^?1cm^?1) as well as some of the highest per‐particle T ₂ relaxivities (12200 mm _NP ^?1s^?1) reported to date for this particle size range.     

A Soft Lithiophilic Graphene Aerogel for Stable Lithium Metal Anode

The lithium metal anode is one of the most promising anodes for next‐generation high‐energy‐density batteries. However, the severe growth of Li dendrites and large volume expansion leads to rapid capacity decay and shortened lifetime, especially in high current density and high capacity. Herein, a soft 3D Au nanoparticles@graphene hybrid aerogel (Au? GA) as a lithiophilic host for lithium metal anode is proposed. The large surface area and interconnected conductive pathways of the Au? GA significantly decrease the local current density of the electrode, enabling uniform Li deposition. Furthermore, the 3D porous structure effectively accommodates the large volume expansion during Li plating/stripping, and the Li_xAu alloy serves as a solid solution buffer layer to completely eliminate the Li nucleation over‐potential. Symmetric cells can stably cycle at 8 mA cm^?2 for 8 mAh cm^?2 and exhibit ultra‐long cycling: 1800 h at 2 mA cm^?2 for 2 mAh cm^?2, and 1200 h at 4 mA cm^?2 for 4 mAh cm^?2, with low over‐potential. Full cells assemble with a Cu@Au? GA? Li anode and LiFePO₄ cathode, can sustain a high rate of 8 C, and retain a high capacity of 59.6 mAh g^?1 after 1100 cycles at 2 C.     

The interface between Hg1−xCdxTe and its native oxide

The results of a study of the electrical properties of the interface between Hg_1?xCd_xTe with x = 0.21 and its native oxide at 77°K are presented. The native oxide is formed by anodic oxidation and results in an interface with reproducible properties. The surface charge, the surface mobility and the effective lifetime are obtained from galvanomagnetic measurements and are related to the semiconductor bulk parameters, the oxide thickness and the annealing conditions. The surface state charge and the metal-semiconductors work function difference are obtained from the shift of the flat band voltage of metal-oxide-semiconductor (MOS) capacitor characteristics. The interface between Hg_1?xCd_xTe and its native anodic oxide is characterized by a density of fast surface states of the order of 5 × 10¹¹cm^?2 (eV^?1) near the middle of the bandgap. The density of states increases towards the band edges to the order of 10¹³cm^?2 (eV^?1). The measured flat band voltage is approximately ?0.5 V for an oxide thickness of 500 Å and for an n-type semiconductor with an electron carrier concentration in the range 1–3 × 10¹⁵cm^?3 at 77°K. The fixed oxide surface state charge is positive for both p-type and n-type semiconductors and is of the order of 6 × 10¹¹ charges per cm^?2. The surface properties, the significance and the reproducibility of the results are evaluated.