Vacuum Level Research Articles

Selection and thermal physical characteristics analysis of in-situ condition preserved coring lunar rock simulant in extreme environment

With the increasing scarcity of Earth’s resources and the development of space science and technology, the exploration, development, and utilization of deep space-specific material resources (minerals, water ice, volatile compounds, etc.) are not only important to supplement the resources and reserves on Earth but also provide a material foundation for establishing extraterrestrial research bases. To achieve large depth in-situ condition-preserved coring (ICP-Coring) in the extreme lunar environment, first, lunar rock simulant was selected (SZU-1), which has a material composition, element distribution, and physical and mechanical properties that are approximately equivalent to those of lunar mare basalt. Second, the influence of the lunar-based in-situ environment on the phase, microstructure, and thermal physical properties (specific heat capacity, thermal conductivity, thermal diffusivity, and thermal expansion coefficient) of SZU-1 was explored and compared with the measured lunar rock data. It was found that in an air atmosphere, low temperature has a more pronounced effect on the relative content of olivine than other temperatures, while in a vacuum atmosphere, the relative contents of olivine and anorthite are significantly affected only at temperatures of approximately −20 and 200 °C. When the vacuum level is less than 100 Pa, the contribution of air conduction can be almost neglected, whereas it becomes dominant above this threshold. Additionally, as the testing temperature increases, the surface of SZU-1 exhibits increased microcracking, fracture opening, and unevenness, while the specific heat capacity, thermal conductivity, and thermal expansion coefficient show nonlinear increases. Conversely, the thermal diffusivity exhibits a nonlinear decreasing trend. The relationship between thermal conductivity, thermal diffusivity, and temperature can be effectively described by an exponential function (R2>0.98). The research results are consistent with previous studies on real lunar rocks. These research findings are expected to be applied in the development of the test and analysis systems of ICP-Coring in a lunar environment and the exploration of the mechanism of machine-rock interaction in the in-situ drilling and coring process.

The Effect of Drying Variables on the Microwave–Vacuum-Drying Characteristics of Mulberries (Morus alba L.): Experiments and Multivariate Models

It is easy to cause increases in temperature and the gasification of water in materials, facilitated via supercharging and the generation of instantaneous strong pressure under the collaborative action of a microwave and a vacuum, thus facilitating the internal cell swelling of materials, changes in fibre structures, and the formation of loose and uniform microstructures. In this experiment, mulberries were dehydrated using microwave–vacuum drying technology. The drying characteristics were disclosed by using crispness as the evaluation index and multiple drying parameters (e.g., products’ surface temperature, microwave power, chamber vacuum level and drying height) as the control variables. The optimised Two-term model can predict the dehydration process of mulberries under multiple drying variables, as determined through the experimental data. The optimal drying variables were determined according to the crispness of the dried mulberries. The optimal puffing quality of mulberries could be gained under a product surface temperature = 50 °C, microwave power = 5.45 W/g, a chamber vacuum level = 0.08 MPa and a drying height = 0 cm. The diffusion coefficient of the available water of the mulberries during the microwave–vacuum drying process ranges from 4.98 × 10−8 to 3.81 × 10−7, and the activation energy for drying is 183.923 KJ/mol.

Toward an increased reliability of chemical bonding assignment in insulating samples by x-ray photoelectron spectroscopy.

X-ray photoelectron spectroscopy (XPS) spectra from solid samples are conventionally referenced to the spectrometer Fermi level (FL). While, in the case of metallic samples, alignment of the sample and the spectrometer FLs can be directly verified from the measured Fermi edge position, thus allowing to assess the surface electrical potential, this is not a workable option for insulators. When applied, it generates a large spread in reported binding energy values that often exceed involved chemical shifts. By depositing insulating amorphous alumina thin films on a variety of conducting substrates with different work functions, we show not only that FL referencing fails but also that the Al2O3 energy levels align instead to the vacuum level, as postulated in the early days of XPS. Based on these model experiments that can be repeated for all sorts of thin-film insulators, a solution to the binding energy reference problem is proposed for reliable assessment of chemical bonding.

Impact of plasma polymerized Iodine-Doped thiophene films for enhanced sensing response towards industrial VOCs

Volatile organic compounds (VOCs) are majorly used in the manufacturing industry and are hazardous to the sustainability of the environment. Polymeric sensors, rather than more traditional metal oxide sensors, are currently taking the lead attention in the greater part of VOC sensing investigations. In polymeric sensors, plasma polymerized thiophene (PPTh) films are being investigated because of their unique properties, wasteless fabrication, and feasibility for commercial mass manufacturing. In the present study, we fabricated PPTh films powered by a 13.6 MHz RF generator with a vacuum level of 10-3 Torr in a home-built plasma system. The gas sensor investigation of PPTh and iodine-doped PPTh samples with various VOCs, such as ethanol, methanol, acetone, benzene, toluene, and dichloromethane, was carried out systematically. The iodine-doped PPTh 10–20 films (48 hr) showed the highest sensitivity for ethanol (∼180) and methanol (∼120) as compared to PPTh for ethanol (∼110) at 1000 ppm gas concentration. A sensitivity degradation study over 60 days revealed the long-term stability of the films in the air. The polar hopping mechanism and decreased charge transport centers after reaction with the hydroxyl group are responsible for resulted sensitivity of iodine-doped PPTh films towards alcohols.

Investigation of the intrinsic outgassing rates for narrow structured vacuum devices under readsorption effect

The narrow structure within the vacuum system usually results in a slow evacuation process. Additionally, the high outgassing rate caused by the large surface-to-volume ratio can prevent the vacuum level from meeting the performance requirements of the device. In this paper, the evacuation of the stainless steel parallel plates is established based on a two-dimensional equation combined with the outgassing theory of the recombination–dissociation-limited model. The relationship between the measured and intrinsic outgassing rates was investigated by varying the gap size, pump-out port size, and temperature. The results show that the internal pressure is nonuniformly distributed during the pump-down process, even reaching a quasiequilibrium state. This indicates that the widely used throughput method can make a difference in measuring outgassing rates. This provides a theoretical basis for testing intrinsic outgassing rates, calculating pressure distribution, and configuring pumps or getters in complex vacuum systems.

ИССЛЕДОВАНИЯ ГАЗОДИНАМИЧЕСКИХ И ГИДРОДИНАМИЧЕСКИХ ПРОЦЕССОВ В ПОЛОСТЯХ И КАНАЛАХ ВАКУУМНЫХ ЗАХВАТНЫХ УСТРОЙСТВ

The article discusses the results of studies of gas-dynamic and hydrodynamic processes in cavities and channels of vacuum gripping devices operating in air, water and mixed media. Transient processes were obtained that occur in the cavities of the gripping devices from the moment the vacuum generator is powered up to the moment of the steady-state vacuum level.

(Invited) Universal Alignment of Surface and Bulk Oxygen Levels in Semiconductors

Lattices of most semiconductors have a large density of intrinsic and extrinsic defects which gives rise to effects such as surface Fermi level (EF) pinning, dopant compensation, asymmetrical p versus n-doping, and device degradation. Oxygen and hydrogen are the two most important impurities in semiconductors because of their ubiquitous presence in growth and device processing environments and consequently their incorporation strongly influences electronic and electrical properties. Therefore, a deeper understanding of the interaction of these species with the semiconductor surface and bulk defects is necessary for enabling the development of devices based on them such as photovoltaic and photocatalytic systems, fuel cells, and many others. Analysis of the reported surface work function values and the substitutional bulk O-defect energies show that the surface Fermi level of position in a broad range of group IV, III-V, II-VI, and I-III-VI2 semiconductors with physisorbed O2 lies universally at approximately -5.1 eV below the vacuum level. Similarly, results show that the energy of the bulk substitutional O-related amphoteric defects incorporated during crystal growth also has a universal energy of ~ -5.0 eV with respect to the vacuum level for most of the investigated semiconductors. It is shown that the process of ‘surface transfer doping’ that involves an adsorbed nanoscale water film on the semiconductor surface is likely responsible for the universal alignment of oxygen levels. Figure 1

Edge-passivated graphene nanoribbons as metal free photocatalyst for efficiently photocatalytic overall water splitting with sunlight

The metal free photocatalysts have more environmentally friendly and low-cost advantages but are challenging to find suitable ones. Using the electronic properties of the edge-passivated graphene nanoribbons (EPGNRs) by manipulating the widths and edges, we demonstrate that 5 EPGNRs consisting of metal free elements, which are screened from 10 graphene nanoribbons passivated by H/N/O/F atoms, can achieve high solar-to-hydrogen efficiency in overall water splitting for hydrogen production. After ensuring the energy and thermodynamic stabilities, we construct 16 possible photocatalytic schemes for each EPGNR. At the same time, the feasible ones are selected by calculating charge density distributions, vacuum levels, and the potential energy of the band edges. 9 eligible schemes for overall water splitting are determined and the solar-to-hydrogen efficiencies are calculated according to the overpotentials and band gaps. The highest value of 34.19% is attributed to the H-GNR-O nanoribbon and a larger 38.71% can be boosted by stain engineering, which reveals that the passivated atoms can substantially manipulate the electronic properties and photocatalytic performance of graphene nanoribbons. The calculated Gibbs free energies confirm that the photocatalytic hydrogen and oxygen generations can be driven by the present EPGNRs. Therefore, the newfound metal free EPGNRs are promising for driving overall water splitting for generating hydrogen in a clean way.

Design vacuum consolidation considering energy requirement

In designing a vacuum consolidation project, it is desirable to quantify the energy required. Explicit close form equations were derived for calculating energy consumptions during a vacuum consolidation in terms of extracting sealed-in air (Wair1), seepage consolidation of soils (Wsoil), draining out the water collected by PVDs (Wwater), and air-leaking rate into a vacuum consolidation system under a given level of vacuum. It is shown that for an ideal vacuum consolidation (no air-leaking), the energy required is higher but comparable with the work done by gravity force of the same magnitude of fill material induced consolidation. The results of the analysis using the design guides in China and/or Japan indicate that only a few percentages of the required effective pump energy are consumed on seepage consolidation and draining out of water collected by PVDs, and the other is for extracting the leaked-in air or possibly just wasted. Therefore, having a good sealing system, and setting a target range of vacuum pressure instead of a single value may increase the energy efficiency. Shortening the duration of a project by reducing the spacing between PVDs can also be a possible option for saving energy. Finally, a conceptual design flowchart was proposed.

Experimental study on liquid-gas phase separation driven by pressure gradient in transport membrane condenser

Flue gas moisture recovery from coal-fired power plants has always been an important topic in the fields of energy and building and gas dehumidification. Moisture and waste heat recovery in a transport membrane condenser (TMC) involves heat transfer, mass transfer and intermolecular interactions. This study, an experiment was designed based on TMC, which revealed the process of vapor condensation on the membrane surface and mass transfer across the membrane, and clarified the driving mechanism of mass transfer. It is found that the main driving force affecting the mass transfer is related to the recovery mechanism and the flowing working fluid. The main driving force influencing mass transfer on the flue gas side is the pressure gradient caused by the vapor pressure difference, whereas on the condensation side, mass transfer is influenced through the heat transfer gradient. Furthermore, high vacuum levels on the permeate side may enhance gas cross-membrane transport, but do not improve mass transfer performance. Compared with a longitudinal spacing of 30 mm, the condensation mass transfer rate of TMC with a longitudinal spacing of 80 mm increased by 107%–174%. The research results have an important role in promoting the realization of resource recovery and energy efficiency.

Optimisation of Vacuum Brazing Conditions for Joining Stainless Steel 321 Sheets by Nickel Based Braze Foil for Regenerative Rocket Nozzle Applications by Taguchi Method

This paper outlines the optimisation of vacuum brazing conditions for joining titanium stabilised Stainless Steel SS321 sheets by Ni-based braze alloy (Ni-Mn-Cr-Co-Si) as brazing filler metal (BFM) for two shelled rocket nozzle applications. This is a specialized brazing technique in which multiple parameters such as temperature, time, argon pressure in the furnace and vacuum level in the channels between the shells are to be precisely controlled in a complex furnace. Brazing temperature, holding time, surface pressure in terms of dead weight and vacuum levels were identified as parameters having significant effect on the bonding strength of a braze joint. Taguchi method was used as a statistical technique for design of experiments to optimise brazing conditions in terms of shear strength. L9(34 ) orthogonal array was designed for conducting the experiments with four parameters at three levels ie temperature (1190oC, 1230oC,1270oC), holding time (10min, 20min, 30min), surface pressure (100kPa, 150kPa, 200kPa) and vacuum level (0.133Pa, 1.33Pa, 13.3Pa). The optimised set of parameters ie temperature: 1230oC, time: 20min, pressure: 100kPa, vac. level: 1.33Pa has been arrived at by Taguchi method via statistical analysis through analysis of means (AVOM) and analysis of variances (ANOVA). Confirmatory test for optimised conditions agreed well with the Taguchi analysis. Also, extensive optical metallography and energy dispersion X-ray analysis across the joint were carried out to study the metallographic morphology across the joint. The fractured surfaces during lap shear tensile testing have also been studied under SEM.

Performance improvement mechanisms of perovskite solar cells by modification of NiO hole-selective contacts with self-assembled-monolayers

This study investigates effects of the modification of NiOx hole-selective contacts (HSCs) with self-assembled monolayers (SAMs), [2-(9H-carbazol-9-yl) ethyl]phosphonic acid (2PACz), on the characteristics of perovskite solar cells, used for perovskite–silicon tandem cells. After the NiOx layers were fabricated by RF sputtering, the 2PACz modification was performed by the spin-coating of a 2PACz solution and subsequent annealing at 100 °C for 10 min. The 2PACz-modified NiOx layer improved the solar cells' open-circuit voltage and short-circuit current density. Photoelectron yield spectroscopy measurements imply that the 2PACz monolayers increase the work function of the NiOx HSCs, thereby enhancing field-effect passivation at the perovskite–HSC interface. Density functional theory calculations and electron spin resonance measurements indicate that an increase in the work function results from a vacuum level shift due to the electric dipole moment of 2PACz molecules and formation of space-charge region at the NiOx–2PACz interface. The performance improvement is explained as a result of enhanced field-effect passivation caused by the vacuum level shift and thus the increase in the work function. These findings, which clarify SAM modification effects of HSCs on solar-cells’ performance, can contribute to the development of highly efficient and reliable perovskite–silicon tandem solar cells.

Pre‐deacidification of hazelnut oil by short‐path distillation: Changes in 3‐chloropropane‐1,2‐diol esters, glycidyl esters, free fatty acids, tocopherols, and diglycerides

AbstractPerforming pre‐deacidification using short‐path distillation at high temperatures and vacuum levels is a general application for fats and oils with high free fatty acids (FFA) to reduce their FFA contents to reasonable levels before steam distillation or neutralization. This study aims to determine the changes in 3‐chloropropane‐1,2‐diol esters (3‐MCPDE), glycidyl esters (GE), and diglyceride (DG) as well as the losses in tocopherols during this process. A bleached hazelnut oil having 12.10% FFA content was distilled using a molecular distillation unit at 200 °C, 220 °C, and 240°C temperatures and 0.25, 0.5, 1, and 2 mbar absolute pressures. The target was to reduce FFA content to less than 2% with minimum tocopherol loss. The results showed that considerable removals in FFA and GE contents were achieved by increasing the temperature and vacuum, while fewer decreases were detected in 3‐MCPDE and DG concentrations. Tocopherols were dramatically decreased by temperature rising, therefore, the lowest temperature (200°C) and absolute pressures (0.25–0.5 mbar) might be suitable for pre‐deacidification of hazelnut oil, where the distilled oil contained 1.78%–1.90% FFA, 243.11–286.76 mg kg–1 tocopherol, 0.50–0.55 mg kg–1 3‐MCPDE, 0.03–0.05 mg kg–1 GE and 4.00–4.22 mg kg–1 DG.Practical Application: Vegetable oils with high free fatty acid (FFA) contents are generally subjected to physical refining to avoid considerable refining loss. However, high temperatures applied to vegetable oils during physical refining result in the formation of 3‐MCPDE&GE, and the loss of some nutrients, such as tocopherols. These adverse effects can be reduced through application of lower temperatures and shorter time during physical refining. This can be applied after the FFA contents of the oils are decreased to reasonable levels (less than 2%) by distillation (pre‐deacidification) before the deodorization. Although this technique has been implemented in many plants, there is almost no information on the effects of applied conditions on 3‐MCPDE and GE and some other minor constituents. This manuscript explains the changes in these compounds during the pre‐deacidification of hazelnut oil by molecular distillation. Suitable distillation conditions were also suggested, which would be very useful for industrial refining plants.

Critical role of electronic states above the vacuum level in photoelectron and secondary electron emission in few-monolayer pentacene films

Critical role of electronic states above the vacuum level in photoelectron and secondary electron emission in few-monolayer pentacene films

In Situ IR Spectroscopy Studies of Atomic Layer-Deposited SnO2 on Formamidinium-Based Lead Halide Perovskite.

Perovskite photovoltaics has achieved conversion efficiencies of 26.0% by optimizing the optoelectronic properties of the absorber and its interfaces with charge transport layers (CTLs). However, commonly adopted organic CTLs can lead to parasitic absorption and device instability. Therefore, metal oxides like atomic layer-deposited (ALD) SnO2 in combination with fullerene-based electron transport layers have been introduced to enhance mechanical and thermal stability. Instead, when ALD SnO2 is directly processed on the absorber, i.e., without the fullerene layer, chemical modifications of the inorganic fraction of the perovskite occur, compromising the device performance. This study focuses on the organic fraction, particularly the formamidinium cation (FA+), in a CsFAPb(I,Br)3 perovskite. By employing in situ infrared spectroscopy, we investigate the impact of ALD processing on the perovskite, such as vacuum level, temperature, and exposure to half and full ALD cycles using tetrakis(dimethylamido)-Sn(IV) (TDMA-Sn) and H2O. We observe that exposing the absorber to vacuum conditions or water half-cycles has a negligible effect on the chemistry of the perovskite. However, prolonged exposure at 100 °C for 90 min results in a loss of 0.7% of the total formamidinium-related vibrational features compared to the pristine perovskite. Supported by density functional theory calculations, we speculate that FA+ deprotonates and that formamidine desorbs from the perovskite surface. Furthermore, the interaction between TDMA-Sn and FA+ induces more decomposition of the perovskite surface compared to vacuum, temperature, or H2O exposure. During the exposure to 10 ALD half-cycles of TDMA-Sn, 4% of the total FA+-related infrared features are lost compared to the pristine perovskite. Additionally, IR spectroscopy suggests the formation and trapping of sym-triazine, i.e., a decomposition product of FA+. These studies enable to decouple the effects occurring during direct ALD processing on the perovskite and highlight the crucial role of the Sn precursor in affecting the perovskite surface chemistry and compromising the device performance.

Socket-residuum coupling integrity affects perception of external stimuli: Effects of altering the transtibial interface using vacuum-assisted suspension.

Relative movement between the socket and residual limb can impair function in prosthesis users. It is plausible that, in addition to its mechanical effect, the integrity of the socket-residuum interface influences the ability of an individual to sense tactile cues through the prosthesis. Vacuum-assisted suspension (VAS) has been shown to reduce relative movement at this interface, providing a means to test this premise. The purpose of this pilot study was to assess the effects of altering socket-residuum interface integrity through the VAS pressure level on the thresholds of perception of an externally applied vibration stimulus. Seven unilateral transtibial prosthesis users participated. Socket-residual limb integrity was altered using the VAS subatmospheric (vacuum) pressure level. Vibration perception tests were conducted at low, mid, and high vacuum levels, targeting 0, 8, and 19 in Hg respectively, and performed in partially loaded and fully loaded conditions. Vibration intensity was increased using a dial until participants delivered a verbal signal indicating it was perceptible, and the nominal intensity was recorded. Intensity thresholds decreased (ie, sensitivity increased) from low to high vacuum settings when fully loaded ( P = 0.008). Differences when partially loaded were nonsignificant and variable across participants. This study provides preliminary evidence that altering the integrity between the socket and residual limb by modifying the vacuum level affects sensation related to the external environment experienced through the prosthesis, although translation of these findings to real-world stimuli remains to be tested.

Steady-state junction current distribution in p-n GaN diodes measured using low-energy electron microscopy (LEEM)

We report on the measurement of the lateral distribution of the junction current of an electrical biased p-n GaN diode by electron emission microscopy using a low-energy electron microscope. The vacuum level at the surface of the diode was lowered by deposition of cesium to achieve negative electron affinity, allowing overflow electrons at the surface of the biased diodes to be emitted and their spatial distribution imaged. The results were compared to the literature, and a good match with analytical solutions by Joyce and Wemple [J. Appl. Phys. 41, 3818 (1970)] was obtained.

Band alignment and crystal stability of Y3Al5−xGaxO12 garnets using density functional theory with hybrid functional

In this study, the dependence of band gap, band alignment, and structural stability of Y3Al5−xGaxO12 garnet (YAGG) solid solutions on Ga content (x) have been investigated using density functional theory (DFT) with PBE0 hybrid functional. The most stable model of YAGG for each x is identified using evolutionary algorithm-based USPEX method. The band alignment was determined by connecting valence band maximum (VBM) and conduction band minimum (CBM) to vacuum level via macroscopic average electrostatic potential of the slab model. Solid solution formation energy as a function of x indicates that YAGG with x = 3.0 (Y3Al2Ga3O12) exhibits remarkable structural stability. At x = 3.0, the analysis of the formation energy contribution shows a dominant contribution from electronic charge redistribution energy while there is no contribution from distortion energy. Bader charge, electron localization function, as well as the projected density of state analysis reveal a strong covalent character of Ga under oxygen tetragonal environment. The calculated PBE0 band gap as a function of x agrees well with the experimental results. Ga admixing significantly lowers the CBM, which exhibits a potential to envelop the shallow electron traps from the forbidden gap. The YAGG band alignment calculated using the proposed vacuum-connecting method is consistent with VRBE results from experiment. The proposed methods used to model site-preferred solid solution and calculate the vacuum-connected band alignment are viable in predicting structural stability and band edge modification via compositional engineering of garnet solid solutions. We expect that this work provides a promising strategy for material design through compositional engineering in obtaining high stability and enhanced performance in garnet compounds.

Experimental Assessment of the Performance of Dual Pneumatic Vitreous Cutters According to Gauge and Cut Rate.

To compare and analyze the performance of dual pneumatic ultra-high-speed vitreous cutters based on their cut rates, vacuum levels, and diameters in terms of flow rate and cutting time. The Constellation Vision System was used to remove egg white for 30 seconds, after which we calculated the flow rate by measuring the change in weight. We then measured the time required to remove 4 mL of egg white. We tested the UltraVit (UV) 7,500 cuts per minute (cpm) probe and the Advanced UltraVit (AUV) 10,000 cpm probe in biased open duty cycle mode, using 23-, 25-, and 27-gauge probes, respectively. In biased open duty cycle, the flow rate tended to decrease as the cut rates increased for all three gauges. At the same cut rates, the flow rate increased as the vacuum level increased (p < 0.05), and as the diameter increased (p < 0.05). Among cutters with the same diameter, the AUV cutter showed higher flow rates than the UV cutter, with increases of 0.267 mL/min (18.5%) at 27 gauge, 0.627 mL/min (20.8%) at 25 gauge, and 1.000 mL/min (20.7%) at 23 gauge (all p < 0.05). The times required to remove 4 mL of egg white took longer with the UV cutter than the AUV cutter for all three gauges (all p < 0.05). The use of a smaller gauge vitreous cutter may reduce the flow rate and increase the time required for vitrectomy, but this can be partially compensated for by increasing the vacuum level as well as using a vitreous cutter with a higher maximum cut rate, improved port size, and improved duty cycle.

High-Sensitivity Quantum-Enhanced Interferometers

High-sensitivity interferometers are one of the basic tools for precision measurement, and their sensitivity is limited by their shot noise limit (SNL), which is determined by vacuum fluctuations of the probe field. The quantum interferometer with novel structures can break the SNL and measure the weak signals, such as the direct observation of gravity wave signal. Combining classical interferometers and the optical parametric amplifier (OPA) can enhance the signal; meanwhile, the quantum noise is kept at the vacuum level, so that the sensitivity of the nonlinear interferometer beyond the SNL can be achieved. By analyzing in detail the influence of system parameters on the precision of quantum metrology, including the intensity of optical fields for phase sensing, the gain factor of OPA, and the losses inside and outside the interferometers, the application conditions of high-sensitivity nonlinear quantum interferometers are obtained. Quantum interferometer-based OPAs provide the direct references for the practical development of quantum precise measurement.