Au Source Research Articles

Stability enhancement of PbSe quantum dots via post-synthetic ammonium chloride treatment for a high-performance infrared photodetector

Infrared (IR) emission lead selenide (PbSe) quantum dots (QDs) have gained considerable attention in the last decade due to their potential applications in optoelectronic devices. However, the comprehensive applications of PbSe QDs have not been realized yet due to their high susceptibility to oxidation in air. In this paper, we demonstrate the stability enhancement of PbSe colloidal QDs via a post-synthetic ammonium chloride treatment and its applications in a solution-processed high-performance IR photodetector with a field-effect transistor (FET) configuration by reversely fabricating the PbSe active layer and polymethylmethacrylate (PMMA) dielectric layer. The responsivity and the specific detectivity of the FET-based photodetector Au(source, drain)/PbSe(52 nm)/PMMA(930 nm)/Au(gate) reached 64.17 mA W−1 and 5.08 × 1010 Jones, respectively, under 980 nm laser illumination with an intensity of 0.1 mW cm−2. Therefore, it provides a promising way to make a high-sensitivity near-IR/mid-IR photodetector.

Preparation of high-concentration colloidal solution of silica-coated gold nanoparticles and their application to X-ray imaging

This study proposes a method for preparing high-concentration silica-coated Au (Au/SiO2) nanoparticles in colloidal solution from 1.5 × 10−3 M hydrogen tetrachloroaurate (III) trihydrate as the Au source and 1.0 × 10−2 M sodium citrate as the reducing reagent. The colloidal solution is applied to X-ray computed tomography (CT) imaging of mouse tissue. The Au nanoparticles in the colloidal solution had a diameter of 18.9 nm, and the Au concentration reached 1.5 × 10−3 M. The Au nanoparticles were silica-coated by modifying their surfaces with (3-aminopropyl)trimethoxysilane (APMS), then depositing silica nuclei generated by a sol–gel reaction of tetraethyl orthosilicate (TEOS) in water/ethanol initiated with sodium hydroxide (NaOH) on the surface modified with APMS. A colloidal solution of Au/SiO2 core–shell particles (silica shell thickness = 19.7 nm) was formed in a final as-prepared solution of 2.7 × 10−4 M Au, 2.0 × 10−5 M APMS, 24 M H2O, 1.9 × 10−3 M NaOH, and 4.1 × 10−3 M TEOS. The Au in the as-prepared colloidal solution was further concentrated to 0.27 M by salting-out and centrifugation. The CT value of the concentrated Au/SiO2 colloidal solution was 2.52 × 103 Hounsfield units, double that of a commercial X-ray contrast agent with the same I concentration as the Au concentration. When injected into mouse tissue, the Au/SiO2 colloidal solution demonstrated good imaging capability.

Effects of Au source/drain thickness on electrical characteristics of pentacene thin-film transistors

We investigate the electrical characteristics of top-contact pentacene thin-film transistors (TFTs) fabricated with various thicknesses of the Au source and the drain (S/D) electrodes, i.e., 20, 30, 50, 70, and 105 nm. Pentacene TFTs exhibit enhancements in the drain current and the fieldeffect mobility with increasing thickness of Au S/D electrodes up to 50 nm, after which the TFT performance degrades with increasing Au thickness. A transmission line method is used to analyze the contact resistance between the Au electrode and the pentacene layer in the TFTs, and ultraviolet photoemission spectroscopy measurements are performed to determine the work function of the Au films. The lowest contact resistance, 73 kΩ·cm, is obtained for the 50-nm-thick Au case and is ascribed to the high work function (4.67 eV) of the film. Consequently, the effects of the Au S/D thickness on the performance of top-contact pentacene TFTs can be understood through the behavior of the charge injection at the Au electrode/pentacene interface.

Direct Transfer Printing with Metal Oxide Layers for Fabricating Flexible Nanowire Devices

A direct printing method for fabricating devices by using metal oxide transfer layers instead of conventional transfer media such as polydimethylsiloxane is presented. Metal oxides are not damaged by organic solvents; therefore, electrodes with gaps less than 2 μm can be defined on a metal oxide transfer layer through photolithography. In order to determine a suitable metal oxide for use as transfer layer, the surface energies of various metal oxides are measured, and Au layers deposited on these oxides are transferred onto polyvinylphenol (PVP). To verify the feasibility of our approach, Au source–drain electrodes on transfer layers and Si nanowires (NWs) addressed by the dielectrophoretic (DEP) alignment process are transferred onto rigid and flexible PVP‐coated substrates. Based on transfer test and DEP process, Al2O3 is determined to be the best transfer layer. Finally, Si NWs field effect transistors (FETs) are fabricated on a rigid Si substrate and a flexible polyimide film. As the channel length decreases from 3.442 to 1.767 μm, the mobility of FET on the Si substrate increases from 127.61 ± 37.64 to 181.60 ± 23.73 cm2 V−1 s−1. Furthermore, the flexible Si NWs FETs fabricated through this process show enhanced electrical properties with an increasing number of bending cycles.

Genesis of the Paleoproterozoic NICO iron oxide–cobalt–gold–bismuth deposit, Northwest Territories, Canada: Evidence from isotope geochemistry and fluid inclusions

The NICO deposit is located in the southern portion of the Paleoproterozoic Great Bear magmatic zone, Northwest Territories, Canada. The majority of the mineralization lies within the Bowl Zone, hosted by the Treasure Lake Group (TLG), where heavily altered precursor rocks are interpreted to be carbonate-rich wackes and siltstones. These rocks are crosscut by a set of pre-ore quartz±calcite+amphibole+K-feldspar veins (S1). The Co–Au–Bi (±W–Cu–Mo) mineralization at NICO is contained in stratabound ore lenses within the Bowl Zone, and comprises a prograde assemblage of Co-rich arsenopyrite (arsenopyrite I) and loellingite, cobaltite, pyrite, actinolite, ferrohornblende, biotite and rare scheelite (±molybdenite) along with minor magnetite and amphibole. Retrograde assemblages resulted from re-crystallization of the Co-bearing phases to form arsenopyrite II and III, along with precipitation of marcasite, pyrite, hastingsite, native Bi–Au (±Te) and minor bismuthinite and magnetite. The latest stage of retrograde mineralization comprises chalcopyrite, hastingsite, chlorite, and hematite (±emplectite). Two sets of barren quartz±dolomite+amphibole+K-feldspar+chalcopyrite veins (S2 and S3) post-date the mineralization. The Southern Breccia zone hosts minor U–Cu–Mo mineralization and is interpreted to be the deepest portion of the NICO system. Two molybdenite samples from the Bowl Zone and the Southern Breccia yielded Re–Os ages of 1865±9 and 1877±8Ma, respectively, consistent with the interpreted ca. 1870Ma age of the NICO deposit. This age is also synchronous with the onset of magmatism in the Great Bear magmatic arc (ca. 1875–1850Ma).Ore mineral δ34S values (3.3–6.7‰, sulfides) indicate that crustal sulfur was assimilated by upwelling felsic magmatic melts. The δ18O values of the fluids precipitating magnetite and Co-rich arsenopyrite (6 and 8‰), and from pre- and syn-mineralization magnetite (−0.8 to 1.5‰) support a magmatic-hydrothermal origin of the fluids. Two out of three calcite samples from pre-(S1) and post-ore (S3) veins have also δ13C values consistent with a magmatic origin (−5.5 to −3.6‰). However, one calcite sample from the S3 veins has a value that indicates a reduced sulfur source (−15.6‰). This value is similar to those of the much younger (<1843Ma) giant quartz veins cutting the GBMZ rocks. The quartz δ18O values suggest that S1 (12.7‰) formed at higher temperatures than S2 (13.2–19.14‰) and S3 (9.4–17.1‰), or that in the latter two generations of veins, 18O was enriched during fluid/rock equilibration.Secondary trails of native Bi in S1 vein quartz are associated with liquid–vapor (LV) and liquid–vapor–halite (LVS) inclusions, which indicates that Bi, and possibly Au, were transported in saline to hyper-saline brines (LV-Bi, 2–16wt.% NaCl equiv., 8–22wt.% CaCl2 equiv.; LVS-Bi, >37wt.% NaCl equiv.), with homogenization temperatures of 137–216°C and 192 to >350°C for LV-Bi (ThL+V→L) and LVS-Bi (ThL+S→L), respectively. The presence of calcium-rich fluids might indicate extensive equilibration of those solutions with the host TLG rocks. If a pressure correction is applied to the LV inclusions using a minimum entrapment temperature of 271.4°C (the Bi melting point), a minimum crystallization depth of between approximately 5 and 8km is indicated.Trace element analyses carried out in this study and compiled from Acosta-Góngora et al. (2014) show that the least altered metasedimentary TLG rocks contain up to six times more As (Carbonate unit, 30.5ppm) than the average upper continental crust. Conversely, concentrations of Au (<2ppb), Co (10ppm) and Cu (12ppm) are lower than the crustal values. As such, it is possible that the TLG was a source of As, but is a less likely source of Au, Co and Cu for the NICO deposit; this further supports a magmatic-hydrothermal origin for the metals. Nonetheless, the plurikilometer alteration halo of the NICO system indicates that large amounts of elements could have been leached from the TLG, and potentially some were incorporated to the system. However, detailed studies on structural geology, geochemical modeling, and mass balance calculations need to be carried out to consider if such a scenario is feasible.

Solution-Processed PbSe Colloidal Quantum Dot-Based Near-Infrared Photodetector

A solution-processed near-infrared (NIR) photodetector based on PbSe colloidal quantum dots (CQDs) with a field-effect transistor (FET) configuration was presented. By blending PbSe CQDs into poly(3-hexylthiophene-2, 5-diyl) (P3HT) as active layer, the photosensitive spectrum of P3HT:PbSe nanocomposites extends into the NIR region. The responsivity and the specific detectivity of FET-based photodetector Au(gate)/PMMA (930nm)/P3HT:PbSe(55nm)/Au(source, drain) reached 500 A/W and $5.02 \times 10^{12}$ Jones, respectively, at $V_{\rm DS}=-40$ V and $V_{\rm G}=-40$ V with 40 mW/cm $^{2}$ of 980-nm laser illumination. It gets more stable due to its reverse fabrication using the dielectric layer to cover the active layer from environment air.

The role of metal contacts in the stability of n-type organic field effect transistors

We are presenting a long-time bias stress stability of C60-based n-type organic field effect transistors (OFETs), in bottom gate, top contacts configuration, with aluminium (Al), silver (Ag) and gold (Au) source–drain contacts. The results clearly shows that the bias stress effects in C60-based n-type OFETs is similar to p-type OFETs and it can be reduced by using an appropriate metal for the source–drain contacts. During the bias stress time, the threshold voltage shift and an increase in the contacts resistance have also been measured. On the basis of the stability of the device parameters, it is proposed that the Al source–drain contact-based devices gives better stability as compared to the devices with Ag and Au source–drain contacts. Our results show that the bias stress-induced threshold voltage shift is due to the trapping of charges in the channel region and in the vicinity of the source–drain contacts.

Microorganism-mediated, CTAB-directed aggregation of Au nanostructures around Escherichia coli cells: Towards enhanced Au recovery through coordination of cell-CTAB–ascorbic acid

In this paper, a microorganism-mediated, cetyltrimethylammonium bromide (CTAB)-directed (MCD) aggregation of Au nanostructures around Escherichia coli cells (ECCs) for enhanced Au recovery, from aqueous HAuCl4 is demonstrated for the first time. Owing to the coordination of cell-CTAB–ascorbic acid (AA), one dimensional Au nanostructures grew around the ECCs, inducing the rapid aggregation of Au and the ECCs. The concentrations of CTAB and AA had insignificant effect on the precipitation if the ECC dosage and HAuCl4 concentration were matched. The Au recovery efficiency decreased with increasing CTAB concentration, while a minimum AA concentration was required for higher Au recovery efficiency. The ECC-binding Au ions were reduced to form Au nuclei over the cell surface that provided preferential nucleation sites. Meanwhile, the free ligand-substituted anions in the solution were reduced to Au atoms that served as Au source for growing the Au nanostructures around the ECCs. This work exemplifies a new avenue to enhance the efficiency of recovering Au through the engineering of Au nanostructures.

Stone use and avoidance on Easter Island: Red scoria from the topknot quarry at Puna Pau and other sources

AbstractThe paper presents new observations on the use and avoidance of different red scoria rocks on Easter Island (Rapa Nui), made during fieldwork. It describes the different facies of the rock, their origins, their nature and their context of quarrying and use. From the latter, it is inferred that, for the prehistoric Rapanui, the meaning of red scoria transcended practical utility. A combination of stone context and ethnographic analogy suggests what this meaning or these meanings might be. Stone use on the Island is presented as a model against which the stone use of other prehistoric cultures might be measured.

A Monte Carlo evaluation of dose enhancement by cisplatin and titanocene dichloride chemotherapy drugs in brachytherapy with photon emitting sources

Some chemotherapy drugs contain a high Z element in their structure that can be used for tumour dose enhancement in radiotherapy. In the present study, dose enhancement factors (DEFs) by cisplatin and titanocene dichloride agents in brachytherapy were quantified based on Monte Carlo simulation. Six photon emitting brachytherapy sources were simulated and their dose rate constant and radial dose function were determined and compared with published data. Dose enhancement factor was obtained for 1, 3 and 5 % concentrations of cisplatin and titanocene dichloride chemotherapy agents in a tumour, in soft tissue phantom. The results of the dose rate constant and radial dose function showed good agreement with published data. Our results have shown that depending on the type of chemotherapy agent and brachytherapy source, DEF increases with increasing chemotherapy drug concentration. The maximum in-tumour averaged DEF for cisplatin and titanocene dichloride are 4.13 and 1.48, respectively, reached with 5 % concentrations of the agents, and (125)I source. Dose enhancement factor is considerably higher for both chemotherapy agents with (125)I, (103)Pd and (169)Yb sources, compared to (192)Ir, (198)Au and (60)Co sources. At similar concentrations, dose enhancement for cisplatin is higher compared with titanocene dichloride. Based on the results of this study, combination of brachytherapy and chemotherapy with agents containing a high Z element resulted in higher radiation dose to the tumour. Therefore, concurrent use of chemotherapy and brachytherapy with high atomic number drugs can have the potential benefits of dose enhancement. However, more preclinical evaluations in this area are necessary before clinical application of this method.

Fabrication and Performance of InAlN/GaN-on-Si MOSHEMTs with LaAlO3 Gate Dielectric Using Gate-First CMOS Compatible Process at Low Thermal Budget

Introduction Recently, lattice matched InAlN/AlN/GaN-on-silicon integration approach has attracted increasing attention due to the availability of high-quality GaN epiwafers with high throughput epitaxial growth on large area Si substrates for applications in power and RF devices with low power consumption [1-2]. Meanwhile, the development of gate-first process is useful to realize future self-aligned transistor structures. Conventional fabrication of InAlN/GaN high electron mobility transistors (HEMTs) or metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs) involves gate-last process where high temperature (>800 oC) annealing is required to form Ti/Al/Ni/Au source and drain ohmic contacts [3]. This is a consequence of traditional gate metallization (e.g., Ni/Au) and gate dielectric not being able to survive such a high ohmic annealing temperature. Therefore, the development of good ohmic contacts with a low thermal annealing budget and thermally stable gate dielectric is required to realize the gate-first process integration for InAlN/GaN HEMTs/MOSHEMTs. In the present work, we report the fabrication and characterization of InAlN/GaN MOSHEMTs using a lift-off free, gate-first CMOS compatible process developed at low thermal budget. Experiment The lattice-matched In0.18Al0.82N/AlN/GaN-on-Si (111) HEMT structure used in this experiment is shown schematically in Fig. 1. The MOSHEMT fabrication using a gate-first process started from mesa isolation followed by 20 nm thick LaAlO3 (LAO) deposition using pulsed laser deposition (PLD) with a substrate temperature of 300 oC. Then, W was sputter deposited followed by gate definition using photolithography and dry etching method. Thereafter, Hf/Al/Ta layer was sputter deposited followed by rapid thermal annealing at 600 oC for 60 s in vacuum to form source and drain ohmic contacts. Results and Discussion The contact resistance and contact resistivity of Hf/Al/Ta ohmic contacts, as analyzed from linear transmission line method (LTLM), are found to ~0.60 Ω·mm and 6.7x10-6 Ω·cm2, respectively. At first, the thermal stability and reliability of the LAO gate dielectric upon 600 oC ohmic anneal in vacuum was optimized under several oxygen partial pressures during PLD. Comparison of capacitance-voltage and reverse gate leakage current characteristics of fabricated devices subject to different oxygen partial pressures in the range from 3.1×10-5 Torr to 5×10-3 Torr are shown in Figs. 2(a) and 2(b), respectively. It is found that LAO deposited under an oxygen partial pressure of 2.7×10-4 Torr exhibits the lowest gate leakage and highest accumulation capacitance, predominantly arisen by an increased dielectric permittivity (k~23.2). Finally, the gate-first CMOS compatible MOSHEMTs were fabricated by choosing the above optimized deposition condition for PLD (2.7×10-4 Torr @ 300 oC) of LAO. Devices having gate dimensions of W/L = 2×50/1 μm, gate-to-source distance of Lgs ~ 2 μm, gate-to-drain distance of Lgd ~ 6 μm, were used for DC output and transfer characterizations. The DC output and transfer characteristics are shown in Figs. 3 (a) and (b), respectively. The MOSHEMTs achieve a saturation drain current (Idsat) of 500 mA/mm at zero gate voltage, threshold voltage (Vth) of -12.6 V, maximum extrinsic transconductance (Gmax) of 44 mS/mm and on-resistance (Ron) of ~ 14 Ω/mm. Conclusion In conclusion, a gate-first CMOS compatible process for InAlN/AlN/GaN-on-Si MOSHEMTs fabrication has been developed. A low thermal budget (600 oC) for ohmic annealing is achieved through the use of Hf/Al/Ta source-drain contacts, thus allowing the fabrication of gate-first CMOS compatible MOSHEMTs using LaAlO3 as the gate dielectric as well as for device passivation purpose. The reasonable DC performance demonstrated (Idsat = 500 mA/mm, Gmax = 44 mS/mm, etc.) for a 1 μm gate length shows promising possibility for gate-first process integration of InAlN/GaN-on-Si MOSHEMTs.

Organic ferroelectric gate field-effect transistor memory using high-mobility rubrene thin film

An organic ferroelectric gate field-effect transistor (FET) memory has been fabricated using an organic semiconductor of rubrene thin film with a high mobility and a gate insulating layer of poly(vinylidene fluoride–tetrafluoroethylene) [P(VDF–TeFE)] thin film. A rubrene thin-film sheet was grown by physical vapor transport (PVT), and placed onto a spin-coated P(VDF–TeFE) thin-film layer, and Au source and drain electrodes were formed on this rubrene thin film. A hysteresis loop of the drain current–gate voltage (ID–VG) characteristic has been clearly observed in the ferroelectric gate FET, and is caused by the ferroelectricity. The maximum drain current is 1.5 × 10−6 A, which is about two orders of magnitude larger than that of the P(VDF–TeFE) gate FET using a pentacene thin film. Moreover, the mobility of this organic ferroelectric gate FET using rubrene thin film is 0.71 cm2 V−1 s−1, which is 35 times larger than that of the FET with pentacene thin film.

Light-emitting field-effect transistors combining organic and metal oxide layers with partitioned heterogeneous source and drain electrodes

We fabricated organic light-emitting field-effect transistors (OLEFETs) characterized by partitioned heterogeneous source and drain contacts along with an aluminum-doped zinc oxide (AZO) layer inserted between an organic layer and a gate insulator. We elaborated such contacts so that each contact was made of a metal(s) suitable for injecting either electrons or holes. We fabricated the devices by choosing two of three kinds of metals (Au, Al, and MgAg) and one of three organic semiconductor materials. In the devices with the Au source and MgAg drain contacts, we observed drain currents at both positive and negative drain voltages. Those currents were predominant at negative drain voltages in the devices with Al drain contacts. The most intense current-injected emissions arose from the vicinity of the electron injection contact edges near channels on the AZO layers. Taking into account the energy level consideration of the materials and the effect of the partitioned contacts, we discussed these electrical and emission properties.

Effects of rapid thermal annealing on ohmic contact of AlGaN/GaN HEMTs

Ohmic contacts with Ti/Al/Ti/Au source and drain electrodes on AlGaN/GaN high electron mobility transistors (HEMTs) were fabricated and subjected to rapid thermal annealing (RTA) in flowing N2. The wafer was divided into 5 parts and three of them were annealed for 30 s at 700, 750, and 800 °C, respectively, the others were annealed at 750 °C for 25 and 40 s. Due to the RTA, a change from Schottky contact to Ohmic contact has been obtained between the electrode layer and the AlGaN/GaN heterojunction layer. We have achieved a low specific contact resistance of 7.41 × 10−6 Ω·cm2 and contact resistance of 0.54 Ω·mm measured by transmission line mode (TLM), and good surface morphology and edge acuity are also desirable by annealing at 750 °C for 30 s. The experiments also indicate that the performance of ohmic contact is first improved, then it reaches a peak, finally degrading with annealing temperature or annealing time rising.

Constraints on the timing of the Tennant Event and associated Au–Cu–Bi mineralisation in the Tennant Region, Northern Territory

Detrital zircon dating of the Warramunga Formation that hosts iron-oxide Au–Cu–Bi mineralisation in the Tennant Region indicates that this unit was deposited after ca. 1860Ma. Intrusive felsic porphyries within the Warramunga Formation have U–Pb zircon ages of 1847.5±2.4, 1847.4±2.8, 1846.3±2.9 and 1848.9±2.2Ma, consistent with a single magmatic event at about 1848Ma. Peperitic margins of some of these intrusions indicate that deposition of the Warramunga Formation continued to about the time of porphyry emplacement. The Tennant Creek and Hill of Leaders granites have ages of 1851.1±3.5Ma and 1845.5±2.4Ma respectively, indistinguishable from those of the felsic porphyries, and consistent with previous interpretations that the porphyries are the high-level equivalents of the granitoids of the Tennant Supersuite. Felsic porphyry at the White Devil mine with an age of 1847.4±2.8Ma cross-cuts ironstone that hosts mineralisation, and the S1 foliation, indicating that ironstone formation and deformation occurred soon after deposition of the host succession. Alteration associated with Au–Cu–Bi mineralisation overprints the White Devil porphyry, providing a maximum age for mineralisation. Minimum ages of 1851–1847Ma for mineralisation are provided by previous 40Ar–39Ar age determinations, indicating that mineralisation, deformation and magmatism took place during the ca. 1850–1845Ma Tennant Event, contemporaneous with, or shortly after, the last stages of deposition of the Warramunga Formation. Although there is a close temporal association between mineralisation and felsic intrusive rocks of the Tennant Supersuite, the intrusive rocks are only weakly fractionated, suggesting they were not a significant source of Au and Cu. A felsic volcaniclastic rock from the Rover gold field 90km southwest of Tennant Creek yielded a unimodal zircon age group of 1842.3±4.5Ma, allowing correlation with the younger parts of the Warramunga Formation or the unconformably overlying ca. 1840Ma Ooradidgee Group. Although a detailed correlation remains uncertain, the simplest interpretation is that the Au–Cu–Bi mineralisation at the Rover Field occurred at a broadly similar time to that at Tennant Creek.

X-ray imaging technique using colloid solution of Au/silica core-shell nanoparticles

This work describes X-ray imaging of mouse using a colloid solution of silica-coated Au (Au/SiO2) nanoparticles. A colloid solution of Au nanoparticles with a size of 16.9 nm was prepared using hydrogen tetrachloroaurate (III) trihydrate as Au source and sodium citrate as reducing reagent. Silica coating of the Au nanoparticles was performed by modifying the Au nanoparticle surface with (3-aminopropyl)trimethoxysilane and then by depositing silica nuclei generated through a sol–gel reaction of tetraethyl orthosilicate in water/ethanol initiated with sodium hydroxide on the surface-modified surface, which produced Au/SiO2 particles with a size of 136.4 nm. A computed tomography value of the Au/SiO2 colloid solution with an Au concentration of 0.036 M was as high as 1,184.8 Hounsfield units, which was quite higher than that of a commercial X-ray contrast agent with the same iodine concentration as the Au concentration. Tissues of mouse could be imaged by injecting the Au/SiO2 particle colloid solution into them.

Gated-Controlled Rectification of a Self-Assembled Monolayer-Based Transistor

A vertical gate symmetrical molecular transistor is demonstrated. It includes self-assembled monolayer of ferrocene molecules chemically bonded to be a flat Au source and Au nanoparticles drain electrodes while gated with the central gate electrode. Using this configuration, we show that negative differential resistance, symmetrical behavior, and rectification effects can be tuned by controlling the gate voltage. The I–V curves shift from symmetric to strongly rectifying over a gate voltage range of a few tenths of volts around a threshold value where the junction behaves symmetrically. This is due to charging of the nanoparticle contact, which modifies the spatial profile of the voltage across the junction, a fact that we have included in a simple theoretical model that explains our experimental results quite well. Our device design affords a new way to fine-tune the rectification of molecular devices in a way that does not necessarily involve the Coulomb charging of the wire.

Thin-film transistors fabricated by low-temperature process based on Ga- and Zn-free amorphous oxide semiconductor

We propose the use of indium tungsten oxide (IWO) as a channel material for thin-film transistors (TFTs). In the present study, an IWO film was deposited at room temperature by means of DC magnetron sputtering and then annealed at 100 °C in N2 prior to formation of Au source and drain electrodes. Analysis using X-ray diffraction and transmission electron microscopy revealed that the film remained amorphous even after the post-deposition annealing treatment. TFTs fabricated using a Si substrate as a back-gate electrode showed good performance, with a saturation field-effect mobility of 19.3 cm2 · V−1 · s−1, an on/off current ratio of 8.9 × 109.

A two-stage evolution model for the Amantaytau orogenic-type gold deposit in Uzbekistan

A lithogeochemical, mineral chemical, isotopic, and fluid inclusion study of barren, low-, and high-grade Au-mineralized samples from the shear zone-hosted Amantaytau gold deposit, Uzbekistan, shows that the local host rocks, Late Ordovician–Earlz Silurian carbonacous shales, are likely to have been an important source of Au, As, Ni, and S in the formation of the deposit. Syn-depositional pyrite in these shales contains on average 0.23 ppm Au, 1,083 ppm As, and 861 ppm Ni. The distribution of rare earth elements (REE) indicates a homogeneous source of light REE, whereas the heavy REE distribution reflects most likely primary variations in the sediments. The mineralized zone is marked by a positive Eu anomaly, which supports reducing conditions during the mineralization. A hydrothermal overprint by an aqueous–carbonic fluid is reflected in a high-grade Au-mineralized sample by δ13C values of −13.0 ‰ (V-PDB). The δ34S values in pyrite (−0.13 to +7.30 ‰ CDT) from barren and mineralized samples are consistent with marine sulfate being the principal source of the ore sulfur. Assuming a formation temperature of between 300 and 400 °C for the main stage of mineralization, as indicated by the alteration mineral assemblage, the calculated δ18Ofluid is between 9.5 and 13.4 ‰ V-SMOW, which points at a metamorphic origin of the ore fluid.

2A2-L01 口腔がん小線源治療の被ばく低減ための遠隔線源装填装置 : 線源整列および射出機構(手術支援ロボティクス・メカトロニクス(2))

In oral cancer brachytherapy, doctors are exposed to radiation from ^<198>Au sources. We proposed a remotely loading device to solve this problem. The remotely loading device is composed of a source cartridge, a delivering mechanism, a low-friction tube, and an applicator holder. This paper presents an ^<198>Au sources alignment and delivering mechanisms for the remotely loading source device. Sources aligned in the cartridge are pushed by air pressure and are loaded into an applicator in the holder one by one through the low-friction tube. The doctor can then use the loaded applicator without much exposure dose. Preliminary experiments of alignment and delivery of ^<198>Au sources are shown in this paper.