Aluminum Contacts Research Articles

One step synthesis of ZnO nanoparticles from ZDDP and its tribological properties in steel-aluminum contacts

Abstract In order to overcome the poor lubricity of zinc dialkyldithiophosphate (ZDDP) in aluminum contacts, ZnO nanoparticles (ZODDP) modified with dialkyldithiophosphoric acid were prepared through one step process from ZDDP. Compared with ZDDP the sulfur and phosphorus contents of ZODDP decreased by 77.9%～82.8% and 77.3～80.7%. respectively. The tribological properties of ZODDP as the additives of diisooctyl sebacate (DIOS) in steel-aluminum contacts were evaluated on ball-on-disk tribometer. Compared with ZDDP the friction coefficient (cof) and wear rate (wr) of ZODDP decreased by 10.37% and 71.74% respectively. The ZnO nano cores in ZODDP enriched on frictional surface, which avoided the direct contact between friction pairs. The weak chemical interaction between ZnO nano-core and modifier promoted the tribological reaction between modifier and aluminum disks. ZODDP is expected to be a cheap and easily available lubricant additive for aluminium-based materials lubricating.

Room temperature ammonia gas sensor using Meta Toluic acid functionalized graphene oxide

A gas sensor has been fabricated by depositing the thin film of Functionalized Graphene Oxide (GO) using Langmuir Blodget (LB) technique on SiO2/Si wafers. Aluminum (Al) contacts were deposited using thermal evaporation technique for measuring the resistance of fabricated thin film. Three different concentrations (15 mM, 50 mM, 75 mM) of Meta Toluic acid (MTA) have been used for functionalization of GO. X-Ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to characterize the Graphene Oxide (GO) after functionalization. Also, Scanning Electron Microscopy (SEM) was carried out for both GO and functionalized GO to study the surface morphology. Gas sensing behavior of functionalized GO has been investigated using two probe resistance measurement method for different concentration of ammonia gas. Sensor response was studied for ammonia concentration varied from 100 to 2000 ppm. Highest response obtained at 100 ppm concentration was found to be ~12.2% for sample TG75. Higher concentration of MTA (up to a critical value) in GO leads to higher response of ammonia gas. This enhanced gas response has been due to the increased ester formation reaction at the surface of sensing film, which eventually leads to more interaction with NH3 gas molecules. In addition, defects and carbon vacancy in functionalized GO also acts as the trapping sites for gas molecules being sensed. The selectivity of the sensor has been investigated in different environment and sensor was found to be very selective towards ammonia gas. For stability investigation of the fabricated sensor, the sensor response has been recorded for 45 days.

Removal of aluminum from aqueous solution by adsorption on montmorillonite K10, TiO2, and SiO2: kinetics, isotherms, and effect of ions

Montmorillonite K10, TiO2, and SiO2 adsorption capacities for aluminum removal from acidic aqueous solution were studied. The effect of pH, initial aluminum concentration, adsorbent amount, contact time, and ions Ca2+, Mg2+, SO42−, HCO3−, Na+, Cl− were investigated. The experiments showed that tested adsorbents exhibited maximum capacities at pH 4.0. Over the studied adsorbent concentration range of 1.0–5.0 g L−1 the maximum aluminum uptake up to 97.4% was achieved by using 5.0 g L−1 of K10 while the same amount of TiO2 or SiO2 removed 71.9% and 94.6%, respectively. Several isotherm models were examined, and equilibrium data were found matching Freundlich model, whereas K10 data were also reasonably described by Langmuir and Sips isotherm models. The effect of ions on aluminum adsorption by 2.0 g L−1 of K10, TiO2, and SiO2 at pH 4.0 showed that Ca2+ ions presented in the solution lowed the removal efficiency of aluminum by materials tested. The adsorption capacity of K10 was influenced the most—the aluminum removal decreased by more than 50%. For TiO2 and SiO2 the reduction of aluminum removal was less—from 53.7 to 44.5% and from 65.5 to 47.4%, respectively. It was found that aluminum removal by both K10 and SiO2 was also influenced by Mg2+ ions and decreased the efficiency of adsorbents. The presence of HCO3− ions reduced the aluminum removal by TiO2 from 53.7 to 17.5%, while no apparent negative effect of HCO3− ions was observed for K10 and SiO2.

Room temperature ammonia gas sensor using ester functionalization of graphene oxide

A room temperature ammonia gas sensor has been fabricated by depositing the thin film of Functionalized Graphene Oxide (GO) using Langmuir Blodgett (LB) technique on SiO2/Si wafers. Thermal evaporation technique was used for deposition of aluminum (Al) contacts for measuring the resistance of fabricated thin film. Different concentration of Meta Toluic acid (15 mM, 50 mM, 75 mM) has been used for functionalization of GO. X-Ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to characterize the Graphene Oxide (GO) after functionalization. Also, Scanning Electron Microscopy (SEM) was carried out for both GO and functionalized GO. Gas sensing behavior of functionalized GO has been investigated for different concentration of ammonia gas. Sensor response was studied for low concentration (100 ppm) of ammonia gas. Highest response at 100 ppm concentration was found to be ∼12%. Higher concentration of MTA in GO leads to higher response of ammonia gas. This enhanced gas response is attributed to the enhanced ester formation reaction at the surface of sensing film, and more defects and carbon vacancy in functionalized GO, which eventually leads to more interaction with NH3 gas molecules.

Influence of substrate temperature on the deposition of the homostructure SnO2:Sb/SnO2:Er via sol–gel dip-coating

SnO2 thin films doped with Sb5+ and Er3+ were deposited by sol–gel-dip-coating forming the homostructure SnO2:Sb/SnO2:Er, between aluminum contacts. The films were deposited on glass substrates at room temperature and 90 °C. The homostructure showed capacitive behavior as obtained from cyclic voltammetry, and the sample deposited with heated substrate at 90 °C showed a curve similar to a switchable ferroelectric diode, mainly for low scan rates. Heated substrates also lead to device higher transmittance in the near infrared, related to lower electron concentration, but the improvement in the sample quality leads to higher mobility, compensating the lower electron concentration, causing an overall effect of higher conductivity.

In Situ Transmission Electron Microscopy Analysis of Aluminum-Germanium Nanowire Solid-State Reaction.

To fully exploit the potential of semiconducting nanowires for devices, high quality electrical contacts are of paramount importance. This work presents a detailed in situ transmission electron microscopy (TEM) study of a very promising type of NW contact where aluminum metal enters the germanium semiconducting nanowire to form an extremely abrupt and clean axial metal–semiconductor interface. We study this solid-state reaction between the aluminum contact and germanium nanowire in situ in the TEM using two different local heating methods. Following the reaction interface of the intrusion of Al in the Ge nanowire shows that at temperatures between 250 and 330 °C the position of the interface as a function of time is well fitted by a square root function, indicating that the reaction rate is limited by a diffusion process. Combining both chemical analysis and electron diffraction we find that the Ge of the nanowire core is completely exchanged by the entering Al atoms that form a monocrystalline nanowire with the usual face-centered cubic structure of Al, where the nanowire dimensions are inherited from the initial Ge nanowire. Model-based chemical mapping by energy dispersive X-ray spectroscopy (EDX) characterization reveals the three-dimensional chemical cross-section of the transformed nanowire with an Al core, surrounded by a thin pure Ge (∼2 nm), Al2O3 (∼3 nm), and Ge containing Al2O3 (∼1 nm) layer, respectively. The presence of Ge containing shells around the Al core indicates that Ge diffuses back into the metal reservoir by surface diffusion, which was confirmed by the detection of Ge atoms in the Al metal line by EDX analysis. Fitting a diffusion equation to the kinetic data allows the extraction of the diffusion coefficient at two different temperatures, which shows a good agreement with diffusion coefficients from literature for self-diffusion of Al.

Superconducting proximity effect in epitaxial Al-InAs heterostructures

Semiconductor-based Josephson junctions provide a platform for studying the proximity effect due to the possibility of tuning junction properties by gate voltage and large-scale fabrication of complex Josephson circuits. Recently, Josephson junctions using the InAs weak link with epitaxial aluminum contact have improved the product of normal resistance and critical current, IcRN, in addition to fabrication process reliability. Here, we study similar devices with epitaxial contact and find a large supercurrent and substantial product of IcRN in our junctions. However, we find a striking difference when we compare these samples with higher mobility samples in terms of the product of excess current and normal resistance, IexRN. The excess current is negligible in lower mobility devices, while it is substantial and independent of the gate voltage and junction length in high mobility samples. This indicates that even though both sample types have epitaxial contacts, only the high-mobility one has a high transparency interface. In the high mobility short junctions, we observe the values of IcRN/Δ ∼ 2.2 and IexRN/Δ ∼ 1.5 in semiconductor weak links.

In Situ Transmission Electron Microscopy Study of Molybdenum Oxide Contacts for Silicon Solar Cells

In this study, a molybdenum oxide (MoOx) and aluminum (Al) contact structure for crystalline silicon (c‐Si) solar cells is investigated using a combination of transmission line measurements (TLM) and in‐situ transmission electron microscopy (TEM). Cross‐sectional high‐resolution TEM (HRTEM) micrographs reveal a ≈2 nm silicon oxide (SiOx) interlayer at c‐Si/MoOx interface in the as‐deposited state, indicating that formation of SiOx occurs during deposition of MoOx. Moreover, oxygen diffusion takes place from MoOx toward Al resulting in the formation of a ≈2–3 nm aluminum oxide (AlOx) interlayer at the MoOx/Al interface. Overall, it is observed that MoOx/Al contact is relatively stable upon annealing up to 200 °C and still retains ohmic transport with sufficiently low contact resistivity.

Printed silver contacts to CVD diamond detectors

Abstract Novel, printed contacts for single crystal CVD grown diamond particle detectors are reported. Silver contacts with guard-rings were formed by three-dimensional metal printing. The resulting devices exhibit similar properties to the current state-of-the-art diamond detectors employing carbide layer contacts, yet detectors with the printed contacts retain high charge collection efficiency even after exposure to 450 °C (unlike aluminum contact devices for instance). The printed silver contacts do not require high temperature annealing steps as carbide based contacts. The contact printing process is performed within a few minutes in ambient conditions. The novel printed contact method enables contact deposition without expensive vacuum equipment; furthermore, contact patterning can be designed and performed instantaneously, without design and fabrication of expensive photolithography masks and without the need for clean room facilities.

Study of Structural, Optical and Semiconducting Properties of TiO2 Thin Film deposited by RF Magnetron Sputtering

Titanium dioxide (TiO2) thin films were investigated in various fields by growing on different substrates using RF magnetron sputtering technique. Silicon(p-type) and FTO glass were used for deposition and they were kept at room temperature while deposition. The characterization techniques such as X-Ray Diffraction method (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersion X-Ray Spectroscopy (EDS) were carried out to examine the structural properties of the films. The XRD peaks shows that the film is crystalline in nature and the crystallite sizes of different peaks were calculated. EDX and FTIR analysis gives the internal composition and bonding in TiO2 thin film respectively. From the UV-Vis Spectroscopy analysis, it can be shown that in visible range the transmittance of the deposited films is more than 70%. Using tauc plot we got the band gap of the films to be 3.44eV. Schottky barrier diode with aluminium contact have been fabricated and the barrier height(Фb) and the ideality factor(n) of the films were investigated using IV analysis giving a value of 1.6 and 2.4 eV respectively. This shows the semiconducting properties of TiO2 thin film

Ultra-thin atomic layer deposited aluminium oxide tunnel layer passivated hole-selective contacts for silicon solar cells

In this work, we use ultra-thin thickness-controllable spatial atomic layer deposited (ALD) aluminium oxide (AlOx) tunnel layers, which contain high negative fixed charges (Qf), capped by highly boron-doped polysilicon layers to form tunnel layer passivated contacts. The high Qf of the tunnel layers is expected to enhance the carrier selectivity of these passivated hole-extracting contacts. The dependence of the ALD AlOx tunnel layer contact passivation performance on its thickness is investigated. Furthermore, two different thermal charge activation conditions, i.e., fast firing using a belt furnace at 700 and 800 °C are compared. The best measured recombination current density J0 and implied open-circuit voltage iVoc of the developed AlOx/polysilicon passivated contacts with a symmetrical AlOx/SiNx stack passivation are 6.6 fA/cm2 and 723 mV, respectively. Based on the measured J0 and on the measured total contact resistivity of the passivated contact, the practical efficiency limit of a rear-side full area passivated contact solar cell with a conventionally diffused front side is calculated to be as high as 23.2%. Additionally, three rear-side metallization schemes: (1) thermally evaporated full-area silver contacts; (2) screen-printed non-firing-through aluminium contacts and (3) screen-printed firing-through silver-aluminium contacts, are compared. Finally, rear-emitter solar cells, using a rear-side hole-selective AlOx tunnel layer passivated contact, are fabricated, which shows an efficiency of up to 20.5%. While the proposed hole-selective passivated contact scheme appears to be promising based on the simulation prediction, the efficiency of the fabricated cells is largely limited by the non-optimized front-side reflectance and recombination losses as well as the use of non-optimized rear-side metallization schemes.

Detection of high flux synchrotron radiation based on diamond detector for HEPS

High Energy Photon Source (HEPS) with a beam energy of 6 GeV and emittance less than 1.0 nm rad will be constructed in China, which can provide high-brightness hard X-ray in the order of 1022 (phs/s/mm2/mr2/0.1%B.W.). The broadband and high-brightness monochromatic beam flux and white beam flux need new detector other than the ion chambers for measurement in case of saturation under high-flux conditions. The Diamond X-ray detector for the beam position monitoring and high brightness X-ray detection is developing for High Energy Photon Source in China. The diamond detector has advantages over other detector materials: a low atomic number resulting in a low absorption cross-section when used as beam position monitor and a high radiation and wide linear range when used as beam intensity measuring. In this paper, the polycrystalline chemical-vapour-deposition diamond detectors with an aluminium contact have been tested at 1W2B beamline at Beijing Synchrotron Radiation Facility (BSRF). A transmission-mode diamond X-ray detector is designed to simultaneously measure the X-ray flux, beam position in real time.

Lead sulfide colloidal quantum dot photovoltaic cell for energy harvesting from human body thermal radiation

In this paper, we present the development of a solution-processed photovoltaic structure designed to convert human body thermal radiation into electricity. An active layer composed of a layer of isopropylamine-capped lead sulfide (PbS) quantum dots (QDs) covered with a layer of lithium chloride (LiCl) on top is sandwiched between a substrate and an aluminum contact. Experimental measurements reveal that the device was sensitive to infrared radiation with energies lower than the optical bandgap energy of the incorporated nanocrystals (Eg = 1.26 eV), allowing one to harvest thermal radiation from a human body. We used a conceptually different approach to harvest this radiation by intentionally introducing mid-gap states to the lead sulfide quantum dots through passivation with isopropylamine and likely enabling a multi-step photon absorption mechanism.

Development of graphene-based ionizing radiation sensors

Abstract We present the first steps to develop radiation sensors based on the graphene field effect transistor technology. Such a sensor exploits the ambipolar behavior of graphene near its Dirac point and it is not dependent on collecting charges, but it senses ionizing radiation trough the change in conductivity of the graphene layer induced by changes of the electric field. We designed the layout of the sensors with the help of Sentaurs TCAD. We simulated static operations and the dynamic response to radiation and calculated the source–drain current through the graphene layer with a quasi-analytical model. The transistors were produced at the National Enterprise for nanoScience and nanoTechnology by depositing high quality graphene on silicon chips manufactured by the Fondazione Bruno Kessler foundry. To reduce the high contact resistance between graphene and aluminum contacts caused by oxidation of the aluminum surface, we used gold/chromium interfaces. We investigated the sensors behavior by mean of electrical measurements, extracting the graphene properties, such as mobility and doping. We observed modulation of the source–drain current, determined the Dirac point and found the optimal voltage levels to be sensitive to pulsed IR laser light and β -particles.

Response analysis on AlGaN metal–semiconductor–metal photodetectors in a perspective of experiment and theory and the persistent photoconductivity effect

Abstract

Laser Polishing of Cold Work Steel AISI D2 for Dry Metal Forming Tools: Surface Homogenization, Refinement and Preparation for Self-Assembled Monolayers

Liquid lubrication guarantees high precision and surface quality of workpieces in industrial forming processes. In the case of aluminum cold extrusion, wear and cold welding due to direct contact of tool and workpiece are usually prevented by the extensive use of lubricants. Since the use of lubricants is economically and ecologically unfavorable, surface treatments of tools by, e.g. laser polishing and/or coatings are in the focus of current investigations to substitute these lubricants and establish so called “dry metal forming” processes. The material AISI D2, a ledeburitic 12% chromium steel which is known to have a significant amount of chromium carbide precipitations, is widely used in cold extrusion for forming tools. The large fraction of chromium carbide precipitations, however, hinder the formation of a dense self-assembled monolayer (SAM) that is necessary to avoid direct contact of reactive aluminum with surface oxides of the tool. Therefore, a homogeneous distribution of the chemical elements with a smaller fraction or no chromium carbides in the steel matrix, particularly in the tool surface, is aimed for. Using laser polishing, the surface layer is molten by continuous or pulsed laser radiation. Within the melt pool, the elementary distribution is homogenized as a result of thermal convection and diffusion processes, as well as a smoothed surface and a grain refinement are achieved. Consequently, the effects of the surface treatment by laser polishing on the area coverage of self-assembled monolayers are investigated. Thus, a combined surface treatment by laser polishing and functionalization with a dense self-assembled monolayer shall reduce overall adhesive wear. For this investigation, several specimens of conventional manufactured and powder metallurgical molten AISI D2 are laser polished using continuous or pulsed laser radiation or a combination of both. The resulting surfaces are investigated by microscopy and spectroscopic techniques to analyze the surface topography and the elemental distribution near to the surface. These results are compared to those of conventionally hand-polished specimens. Furthermore, the influence of the element homogenization and grain refinement on the area coverage of self-assembled monolayers is explored. First results show that laser polishing of AISI D2 is suitable to achieve a reduction of grain size and a more homogeneous distribution of chromium carbides within the surface layer.

The study of the effects of occupational aluminum exposure on TNFR1 expression and cognitive function

Objective: To analyze the relationship between cognitive function and tumor necrosis factor receptor 1 (TNFR1) expression of occupational exposed workers to aluminum and provide the basis for the diagnosis of cognitive impairment. Methods: 140 cases Shanxi aluminum plant workers were collected in 2016 as the research object, including 70 potroom workers for exposure group, 70 non-electrolytic aluminum plant workers in the control group, respectively. Using mini mental status examination (MMSE), digit span test (DST), fuld object memory examination(FOME) and simple reaction time test(SRTT) evaluate the cognitive function of objects. Using graphite furnace atomic absorption method for the determination of plasma aluminum levels as an indicator of aluminum contact exposure of workers. Using RT-PCR method for detection of tumor necrosis factor receptor 1 (TNFR1) mRNA expression levels. And comparison group differences in cognitive and TNFR1 mRNA expression levels. Results: The plasma aluminum content of exposed group (77.12±27.18) μg/L higher than the control group (55.6±28.69)μg/L (P=0.000); Compared to control group, FOME and MMSE score was significantly increased in the exposed group (P=0.000, P=0.000), SRTT scores significantly higher in the exposed group (P=0.001), DST no significant difference in the control group (P=0.893). Compared to control group, The mRNA expression of TNFR1 was significantly higher in the exposed group(P=0.002); Compared to control group, The protein expression of TNFR1 was significantly higher in the exposed group (P=0.002). By correlation analysis in exposure group, plasma aluminum content was negatively correlated with MMSE and the DST (r=-0.284, r=-0.331, P<0.05) and positively correlated with the SRTT, TNFR1 (mRNA) and TNFR1(protein)(r=0.255, r=0.333, r=0.987, P<0.01), MMSE was negatively related to TNFR1 (mRNA) and TNFR1 (protein) (r=-0.268, r=-0.255, P<0.05); DST was negatively correlated with the SRTT and TNFR1 (protein)(r=-0.267, r=-0.330, P<0.05); SRTT was positively correlated with TNFR1 (protein)(r=0.243, P<0.05); TNFR1 (mRNA) was positively correlated with TNFR1 (protein)(r= 0.340, P<0.01). Conclusion: Cognitive function change of occupational exposed workers to aluminum was related to the increase of TNFR1 expression.

High-resistivity metal-oxide films through an interlayer of graphene grown directly on copper electrodes

Functional oxides are important materials for multiple applications in flexible and transparent electronics. Electrically contacting these oxides to form active channels is often challenging as they suffer significant alteration or instabilities when interfaced with metal electrodes. Here, we demonstrate a new scheme to electrically contact thin films of semiconducting zinc tin oxide (ZnSnO) that employs pre-patterned copper electrodes encapsulated by chemical-vapour-deposited graphene. Measurement of over more than 100 channels with varying geometry and nature of contact shows that the bulk resistivity of the ZnSnO channels with graphene/Cu composite is at least two orders of magnitude larger than the same films deposited directly on aluminium (Al) contacts. Moreover, the ZnSnO channels with Cu/graphene contacts showed nearly ohmic transport, in contrast to space-charge-limited conduction observed for other contacting schemes. Our results outline a new application of graphene in a step towards the development of alternative contacting strategies for oxide electronics.

STM patterned nanowire measurements using photolithographically defined implants in Si(100)

Using photolithographically defined implant wires for electrical connections, we demonstrate measurement of a scanning tunneling microscope (STM) patterned nanoscale electronic device on Si(100). By eliminating onerous alignment and complex lithography techniques, this approach is accessible to researchers in smaller efforts who may not have access to tools like electron beam lithography. Electrical contact to the nanodevices is achieved by implanting patterned, degenerately doped wires in the substrate using photolithography and commercial low energy ion implantation. We bring several isolated, implanted wires to within the STM scanner’s field of view where the STM can detect and smoothly draw contiguous patterns that directly overlap with implant lines for electrical connections. This overlapping provides a two-dimensional (2D) overlap interface with the 2D electron system, in contrast to many state-of-the-art methods that rely on contacting an exposed edge. After the STM pattern is phosphine dosed and overgrown with silicon, photolithography is then used again to align (≈ 160 μm)2 aluminum contact pads onto (≈ 200 μm)2 implanted areas at the ends of the wires. We present detailed results that optimize the spacing of neighboring wires while maintaining electrical isolation after heating to > 1200 °C, a step required for in situ Si surface preparation.

Tribochemical Behavior of Ashless Dialkyl Dithiophosphate Ester as an EP/AW Additive in Mineral Oil for Steel–Aluminum Contact

ABSTRACT Dialkyl dithiophosphate ester (DDPE) used as an extreme pressure/antiwear (EP/AW) additive in mineral base oil (BO) was introduced to a steel–aluminum contact in this study. The tribological performance of DDPE was explored by means of a universal tribotester under different loads and durations. The worn aluminum surface topographies were observed and photographed via laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). Tribochemical interactions between the additive and aluminum surface were investigated using energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The distinction of chemical structure between lubricant untapped and the counterpart retrieved after a 3-h sliding process was detected by Fourier transform infrared spectroscopy (FTIR). The friction coefficient of a BO + DDPE-lubricated friction pair under 300 N shows the lowest value. LSCM and SEM images show that the aluminum surface lubricated with BO + DDPE was well protected under a high loading condition of 300 N, and the 3-h sliding process deteriorated the surface topography. However, DDPE was not able to offer an effective lubricating film under a mild condition of 50 N. EDS results of S and P elements on the worn surface indicate that a tribochemical film was generated under 300 N in the sliding process. XPS results further show that the chemical compounds in the tribochemical film included Al2S3, Al2(SO4)3, AlPO4, and Al2O3. The P-containing compound in the tribofilm acted as a sacrificial layer, whereas the S-containing compounds were more durable. FTIR analyses demonstrate that the phosphorus–sulfur double bond was broken up due to the tribochemical interactions.