Room Temperature In Ambient Atmosphere Research Articles

Cu(In,Ga)Se_2-based solar cells for space applications: proton irradiation and annealing recovery

In this work, we present an experimental study of a Cu(In,Ga)Se_2 (CIGS)-based solar cell (SC), irradiated with protons of energy 80 and 180 keV and with fluences of 10^{12}, 10^{13}, and 10^{14} cm^{-2}, as well as a strategy to recover the induced damage. The possible modifications of the structural, electrical, and optical properties, induced by the proton irradiation, were investigated. Although the irradiation did not promote any major modification in the crystalline structure, it did induce the creation of defects responsible for changes in the electronic structure which caused a partial PL quenching and significant changes in the PL spectral shape, as well as a reduction of the power conversion efficiency and open-circuit voltage of up to 30% as revealed by J–V measurements. The photoluminescence results showed a broadening, redshift and decrease in the signal-to-noise ratio. The recovery of damage induced by irradiation in several SCs was tested through annealing steps performed at different temperatures and time intervals. It was found that the best recovery strategy for the investigated irradiation parameters was carrying out several isothermal annealing at 200 °C for 30 min. This strategy is compatible with the intermittent variation of the temperature in space and allowed to recover a power conversion efficiency comparable to that of the as grown cell. In particular, it must be highlighted that keeping the SC at room temperature in ambient atmosphere and in the dark, did not promote significant recovery in contradiction with some previous reports. This recovery methodology was applied in parallel for non-irradiated SCs and no increase in power conversion efficiency was found, but rather a slight decrease. The dominant radiative recombination channel was, apparently, unchanged with the irradiation and the subsequent recovery process. Nonetheless, changes in the concentration of defects of different types cannot be excluded, which is in line with a significant influence of fluctuating potentials in both as grown and after recovery stages of the solar cell. This work constitutes a first systematic study that simultaneously encompasses the influence of proton irradiation on the optical and electrical properties of CIGS SCs and a damage recovery methodology with a high potential to be explored in space applications. Additionally, it contributes to reinforcing the high potential of CIGS technology in the context of creating constellations of small satellites that are being developed by different entities, particularly private ones.

Stability of Cernox® temperature sensors stored at room temperature over a 29-year period

Many cryogenic applications critically depend upon accurate temperature measurement for success. In certain applications, including aerospace missions, temperature sensor components are procured years in advance of the mission’s launch date in order to accommodate installation and ground-based testing. Once installed there is little opportunity for recalibration, so the stability of the sensor stored at room temperature over extended time periods becomes vitally important. One of the most common cryogenic temperature sensor types used in aerospace applications is the Cernox Resistance Temperature Sensor manufactured by Lake Shore Cryotronics, Inc., and has been commercially available since 1993. For 29 years a set of 35 sensors manufactured from two of the initial production wafers has been stored at room temperature in ambient atmosphere. These sensors have been periodically recalibrated over the 1.4 K to 325 K or 4 K to 325 K temperature range as appropriate to provide an estimate of the long-term stability of these sensors when stored at room temperature. Data for each temperature sensor were analyzed in terms of equivalent temperature shift between each subsequent calibration and its initial calibration in 1992. The data show that the overall 29-year average stability for devices from these two Cernox wafers roughly follows a stability of ±10 mK for temperatures below 10 K and 0.07% of temperature for temperatures above 10 K. Data for an additional nine Cernox devices from an actual JWST production build lot showed they all exhibited stabilities better than ±8 mK for T < 10 K and (ΔT/T) < ±0.075% for T > 10 K.

High speed switching in quantum Dot/Ti-TiOx nonvolatile memory device

We report a Ti-TiOx/CdSe-ZnS core-shell quantum dot based bipolar nonvolatile resistive memory device. The device exhibits an ON/OFF ratio of 100 and is reproducible. The memory device showed good retention characteristics under stress and excellent stability even after 100,000 cycles of switching operation. The switching speed measured was around 15 ns. The devices are solution processed at room temperature in ambient atmosphere. The operating mechanism is discussed based on charge trapping in quantum dots resulting in the Coulomb blockade effect with a ZnS shell layer and metal-oxide layer acting as the barrier to confine the trapped charges. The proposed mechanism is validated by a three terminal device designed exclusively for this purpose.

Laser-Assisted Reduction of Graphene Oxide for Flexible, Large-Area Optoelectronics

This paper reviews recent work on the development and use of a low-temperature, laser-based method for the efficient reduction of graphene oxide (GO) films. The method utilizes a laser beam for the in-situ and nonthermal reduction of solution-processed GO layers onto arbitrary substrates. Compared to other reduction techniques, it is single-step, facile, and can be performed at room temperature in ambient atmosphere without affecting the integrity of the either the graphene lattice or the physical properties of the underling substrate. Using this method, conductive layers of reduced GO with a sheet resistance down to ~700 Ω/sq, are obtained. This is much lower than sheet resistance values reported previously for GO layers reduced by chemical means. As a proof of concept, laser-reduced GO layers were successfully utilized as the transparent anode electrodes in flexible bulk-heterojunction OPVs and as the channel material in field-effect transistors. To the best of our knowledge, this is the only example of an in-situ, postfabrication method for the reduction of GO and its implementation in fully functional opto/electronic devices. The nonthermal nature of the method combined with its simplicity and scalability, makes it very attractive for the manufacturing of future generation large-volume graphene-based opto/electronics.

Abrasive Wear Testing of Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt; Ceramic Composites

Silicon nitride-based nanocomposites with different quantities (0, 1, 2 wt%) of multiwall carbon nanotubes (MWCNT) have been prepared by isostatic pressing. Abrasive tribological tests were carried out at room temperature in ambient atmosphere with various types of abrasives (different material and grain size) and lubricants respectively. Worn surfaces were characterized by surface roughness parameters, surface topography and scanning electron microscope while wear rate was featured by the worn mass. Results indicate that increase in MWCNT-content leads to decrease of abrasive wear resistance which is proven by increase of Ra and Rz roughness parameters and SEM-analyses of the abrasive worn surfaces.

Anti-Stokes bright yellowish emission of NdAlO3 nanocrystals

Infrared laser diode–induced anti-Stokes bright yellowish emission of NdAlO3 nanocrystalline powder was observed at room temperature in ambient atmosphere. The emission intensity was found to be unaltered with lowering temperature and to increase by two orders of magnitude in vacuum. The temperature of bright emission under ambient atmosphere was determined to be 350 °C. It was found that the yellowish emission was accompanied by a giant photocurrent of 0.5 microamperes at relatively low applied voltage. The power dependence of the photocurrent was governed by an avalanche-like mechanism. The origin of the bright emission is discussed in terms of charge transfer luminescence of Nd3+.

A solution processed nonvolatile resistive memory device with Ti/CdSe quantum dot/Ti-TiOx/CdSe quantum dot/indium tin-oxide structure

We report a Ti-TiOx/quantum dot based bipolar nonvolatile resistive memory device. The device has ON/OFF ratio 100 and is reproducible. The memory device showed good retention characteristics under stress and excellent stability even after 100 000 cycles of switching operation. The memory devices are solution processed at room temperature in ambient atmosphere. The operating mechanism is discussed based on charge trapping in quantum dots resulting in Coulomb blockade effect with the metal-oxide layer acting as the barrier to confine the trapped charges. The mechanism is supported by negative differential resistance (NDR) observed exclusively in the ON state.

High performance Sm-Fe-N magnets prepared by compression shearing method

Sm-Fe-N anisotropic magnets were produced from magnetically aligned green compact at room temperature in ambient atmosphere by the compression shearing method. X-ray diffraction studies revealed that the magnets retained their original Sm2Fe17N3 phase structure without any appreciable decomposition of the phase and that the phase had a pronounced crystallographic alignment. The magnetic properties of the Sm-Fe-N anisotropic magnets were dependent on the magnetic alignment of the Sm-Fe-N powder before implementation of the compression shearing method. A Sm-Fe-N anisotropic magnet with the magnetic alignment produced under an applied field of 1.6 MA/m exhibited a maximum energy product of 161 kJ/m3 with a high coercivity of 0.88 MA/m.

Tribology Study of Silicon Nitride-Based Nanocomposites with Carbon Additions

Tribology tests were conducted on silicon nitride-based nanocomposites with various carbon additions to explore the effects of microstructure, the type and quantity of carbon additives and the preparation routes on the behavior. The nanocomposites consisted of Si3N4 and C in the proportions of 1 – 10 wt % carbon nanotube (CNT), or carbon black (CB), or graphite, or graphene. Specimens were produced by hot isostatic pressing. X-ray diffraction and scanning electron microscopy were used to reveal phase composition and microstructure. Unlubricated ball-on-disk tribology tests with silicon nitride counter face were carried out at room temperature in ambient atmosphere. Contact profilometer was used to profile the wear tracks. The friction coefficients of the pure Si3N4 and Si3N4 samples with 3% CNT varied between 0,77-0,81. Addition of 10% graphite and 3% CB to Si3N4 resulted in friction coefficients of 0,83 and 0,72 respectively. Si3N4 samples with 3% graphene showed distinctly lower friction levels of 0,52 and smaller scatter of the measured values. The wear track study revealed that high graphene content in the Si3N4 matrix caused relatively big wear particles and an uneven wear track.

S0305-5-5 マグネシウム合金AZ80押出し材の疲労強度特性に及ぼす応力比の影響([S0305-5]超長寿命)

In order to investigate the effect of stress ratio on high-cycle fatigue properties of an extruded magnesium alloy, axial loading fatigue tests have been performed under three testing conditions of stress ratio, R, of 0, -1 and -1.5 at room temperature in ambient atmosphere using hourglass shaped specimens of AZ80 magnesium alloy extruded (F) and T5-againg treated after extruded (T5). A fatigue limit appeared in the F-specimen only under the testing condition of R=0, while that appeared in the T5-specimen under all stress ratios, because of retardation in crack growth by aging microstructure. From detailed observation of fracture surface, crack initiation mechanism changed from the twin deformation induced in high-stress amplitude level to slip deformation induced in low-stress amplitude level, because of a texture caused by extrusion and the particular deformation characteristics of hep lattice structure in a magnesium alloy.

Blue electroluminescence nanodevice prototype based on vertical ZnO nanowire/polymer film on silicon substrate

We present a polymer-complexing soft template technique to construct the ZnO-nanowire/polymer light emitting device prototype that exhibits blue electrically driven emission with a relatively low-threshold voltage at room temperature in ambient atmosphere, and the ZnO-nanowire-based LED’s emission wavelength is easily tuned by controlling the applied-excitation voltage. The nearly vertically aligned ZnO-nanowires with polymer film were used as emissive layers in the devices. The method uses polymer as binder in the LED device and dispersion medium in the luminescence layer, which stabilizes the quasi-arrays of ZnO nanowires embedding in a thin polymer film on silicon substrate and passivates the surface of ZnO nanocrystals, to prevent the quenching of luminescence. Additionally, the measurements of electrical properties showed that ZnO-nanowire/polymer film could significantly improve the conductivity of the film, which could be attributed to an increase in both Hall mobility and carrier concentration. The results indicated that the novel technique is a low-cost process for ZnO-based UV or blue light emission and reduces the requirement for achieving robust p-doping of ZnO film. It suggests that such ZnO-nanowire/polymer-based LEDs will be suitable for the electro-optical application.

Magnetic properties of Sm–Fe–N thick films produced by compression shearing

Sm–Fe–N powders were deposited onto an aluminum substrate at room temperature in ambient atmosphere by compression shearing. In contrast to other film processing techniques, a thick film was produced at an extremely high production rate of 180μm∕min. The resultant thick film retained the original Sm2Fe17N3 phase structure without any appreciable decomposition of the Sm2Fe17N3 phase. The thick films exhibited magnetic properties matching the original Sm–Fe–N powder.

Influence of austempering temperature on microstructure and fracture toughness of a high-carbon, high-silicon and high-manganese cast steel

Abstract An investigation was carried out to examine the influence of austempering temperature on the microstructure and mechanical properties of a high-carbon (1.00%), high-silicon (3.00%) and high-manganese (2.00%) cast steel. Cylindrical tensile specimens and compact tension specimens were prepared from this cast steel according to ASTM standards and were given four different austempering heat treatments to produce different microstructures. The tensile properties and fracture toughness of these materials were studied at room temperature in ambient atmosphere. Test results indicate that maximum fracture toughness is obtained in this steel when the microstructure contains very high austenitic carbon ( X γ C γ ).

Characterization of carbonate on BaTiO 3 ceramic powders

Surface carbonates on BaTiO 3 (BT) ceramic powders were characterized by diffuse reflectance infrared Fourier transforms (DRIFT) spectroscopy and total carbon analysis (TCA) techniques. Three lots of as-received BT powders were calcined at various temperatures and atmospheres, and aged at room temperature in ambient atmosphere. It was evident from DRIFT spectroscopy and TCA results that all BT powders were different in the amount of carbonates and in the susceptibility to carbonation in air. The carbonates on BT surface decompose after firing at temperatures above 600°C. At 1000°C, the removal of carbonate was shown to be a function of the partial pressure of CO 2 in the calcination atmosphere. When the calcined BT was aged in ambient atmosphere, the carbonation easily reoccurred.

Solid electrodes from refractory powder materials prepared for electroanalytical purposes by a novel method

A novel, simple and inexpensive method for preparation of solid working electrodes from conducting refractory powder materials at room temperature in ambient atmosphere has been developed for electroanalytical purposes. The method is based on the use of a demountable device for hand pressing of the powder mixed with a polymer solution. During the process of pressing, the electric resistance of the electrode is controlled automatically. The electrodes from carbon powder, from titanium nitride and from carbon powder mixed with cobalt(II) phthalocyanine were prepared by this method. Results of voltammetric, stripping voltammetric and chronoamperometric studies showed a number of advantages of the prepared electrodes in comparison with conventional glassy carbon and carbon-paste electrodes.

Proximity Effects between Superconducting and Magnetic Films

Superimposed normal-superconducting films can be used in conjunction with theory to investigate the nature and magnitude of the electron-electron interaction taking place in the normal metal. We report studies in which the normal metals were various types of magnetic materials: the ferromagnets Fe, Ni, and Gd; antiferromagnetic Cr; and the dilute magnetic alloys 1% Fe in Mo and 2.9% Gd in Pb (the last actually being a low-transition-temperature superconductor). The superconducting metal in all cases was pure Pb. Measurements of the transition temperature of the sandwich as a function of Pb film thickness were compared with a combined theory incorporating the de Gennes-Werthamer calculation of the proximity effect in nonmagnetic materials together with the Abrikosov-Gor'kov model of superconductivity in dilute magnetic alloys. Agreement for the alloy systems was satisfactory with no adjustable parameters, while extension of the theory to the concentrated, ordered systems with one parameter adjusted was qualitatively reasonable. Certain aspects of superimposed films in general were also studied: Diffusion of one metal into the other during and after deposition; dependence of the sandwich transition temperature on the order of deposition of the component films; recrystallization at room temperature; and interfacial cell reactions, selectively oxidizing one of the components at room temperature in ambient atmosphere.