Enhancing optical characteristics of mediator-assisted wafer-scale MoS2and WS2on h-BN.

Two-dimensional (2D) materials and their heterostructures exhibit intriguing optoelectronic properties; thus, they are good platforms for exploring fundamental research and further facilitating real device applications. The key is to preserve the high quality and intrinsic properties of 2D materials and their heterojunction interface even in production scale during the transfer and assembly process so as to apply in semiconductor manufacturing field. In this study, we successfully adopted a wet transfer existing method to separate mediator-assisted wafer-scale from SiO2/Si growing wafer for the first time with intermediate annealing to fabricate wafer-scale MoS2/h-BN and WS2/h-BN heterostructures on a SiO2/Si wafer. Interestingly, the high-quality wafer-scale 2D material heterostructure optical properties were enhanced and confirmed by Raman and photoluminescence spectroscopy. Our approach can be applied to other 2D materials and expedite mass production for industrial applications.

Factors Associated with Surgical Smoke Self-Protection Behavior of Operating Room Nurses.

Surgical smoke has been proven to be harmful and carcinogenic to humans as well as increasing the risk of acquiring infectious diseases. The operating room nurses' willingness to use protective equipment against surgical smoke was low. The factors associated with personal protective behavior in the operating room against surgical smoke were sparsely explored. The purpose of this study is to determine factors associated with surgical smoke self-protection behavior of the operating room nurses. This was a descriptive correlational study using a convenience sample from a medical center in northern Taiwan. The self-designed questionnaires included personal characteristics and perceived attributes. The data were analyzed by descriptive and linear regression. Attendance at in-service education with regard to surgical smoke, the attitude to surgical smoke, and surgical smoke self-protection barriers were significant factors found in multivariate linear regression after controlling the covariates. The overall model was significant and accounted for 14.2% of variances. In summary, attending in-service education, attitude and barriers in executing self-protective behaviors were significant factors. It is important to promote operating room nurses' health through providing correct surgical smoke knowledge, self-protection strategies to improve attitudes toward surgical smoke, improving the hospital's environment by adding surgical smoke evacuation equipment, and standardizing the operating procedures.

Intense but variable autotrophic activity in a rapidly flushed shallow-water hydrothermal plume (Kueishantao Islet, Taiwan).

Shallow-water hydrothermal plumes concomitantly host both photosynthetic and chemoautotrophic organisms in a single biotope. Yet, rate measurements to quantify the contributions of different autotrophic activity types are scarce. Herein, we measured the light and dark dissolved inorganic carbon (DIC) uptake rates in the plume water of the Kueishantao hydrothermal field using the 13 C-labeling approach. Seventy percent of the plume-water samples had chemoautotrophy as the dominant mode of carbon fixation, with the dark DIC uptake rates (up to 18.6 mg C/m3 /h) within the range of the primary production in productive inner-shelf waters. When considered alongside the geochemical and microbiological observations, the rate data reveal the distribution of different trophic activities in the hydrothermal plume. The autotrophic activity at the initial phase of plume dispersal is low. This is explained by the short response time the chemoautotrophs have to the stimulation from vent-fluid discharge, and the harmful effects of hydrothermal substances on phytoplankton. As plume dispersal and mixing continue, chemoautotrophic activities begin to rise and peak in waters that have low-to-moderate Si(OH)4 content. Toward the plume margin, chemoautotrophy declines to background levels, whereas photosynthesis by phytoplankton regains importance. Our results also provide preliminary indication to the loci of enhanced heterotrophy in the plume. Results of artificial mixing experiments suggest that previously formed plume water is the primary source of microbial inoculum for new plume water. This self-inoculation mechanism, in combination with the intense DIC uptake, helps to sustain a distinct planktonic autotrophic community in this rapidly flushed hydrothermal plume.

Discharge of deeply rooted fluids from submarine mud volcanism in the Taiwan accretionary prism.

Qualitative and quantitative assessments of fluid cycling are essential to address the role and transport of deeply sourced fluids in subduction systems. In this study, sediment cores distributed across a submarine mud volcano (SMV) offshore southwestern Taiwan were investigated to determine the characteristics of fluids generated through the convergence between the Eurasian and Phillippine Sea Plates. The low dissolved chloride concentration combined with the enrichment of 18O, and depletion of 2H of pore fluids suggest the discharge of deep freshwater formed by smectite dehydration at an equilibrium temperature of 100 to 150 °C. The upward fluid velocities, decreasing from 2.0 to 5.0 cm yr-1 at the center to a negligible value at margin sites, varied with the rate and efficiency of anaerobic methanotrophy, demonstrating the impact of fluid migration on biogeochemical processes and carbon cycling. By extrapolating the velocity pattern, the flux of fluids exported from 13 SMVs into seawater amounted up to 1.3-2.5 × 107 kg yr-1, a quantity accounting for 1.1-28.6% of the smectite-bound water originally stored in the incoming sediments. Our results imply that SMVs could act as a conduit to channel the fluids produced from great depth/temperature into seafloor environments in a subduction system of the western Pacific Ocean.

Trophic structure and energy flow in a shallow-water hydrothermal vent: Insights from a stable isotope approach.

Shallow-water hydrothermal vent ecosystems are distinct from the deep-sea counterparts, because they are in receipt of sustenance from both chemosynthetic and photosynthetic production and have a lack of symbiosis. The trophic linkage and energy flow in these ecosystems, however remain elusive, which allows us poor understanding of the whole spectrum of biological components distributed across such environmental gradients. In this study, a thorough isotopic survey was conducted on various biological specimens and suspended particulates collected along four transects across the venting features of a shallow-water hydrothermal field off Kueishan Island, Taiwan. The isotope data combined with a Bayesian-based mixing model indicate that the vent-associated particulate organic matter (vent POM), as primary contribution of chemoautotrophic populations, has a high δ13C value (-18.2 ± 1.1‰) and a low δ15N value (-1.7 ± 0.4‰). Zooplankton and epibenthic crustaceans, as the fundamental consumers, exhibit δ13C and δ15N values ranging from -21.3 to -19.8‰ and +5.1 to +7.5‰, respectively, and can utilize the vent POM for 38-53% of their diets. The vent-obligate crab Xenograpsus testudinatus shows a large variation in δ13C (from -18.8 to -13.9‰) and δ15N values (from 1.1 to 9.8‰), although an omnivorous trophic level (2.5) is identified for it using δ15N values of amino acids, and it can utilize the vent POM for 6-87% of its diet. The consistently low (< 10.0‰) and overlapping δ15N values for most of the analyzed macroinvertebrates suggest extensive ingestion of chemosynthetic production complementing the photosynthetic production, a weak prey-predator relationship and low trophic complexity possibly imposed by the extreme environmental contexts of shallow-water hydrothermal ecosystems.

Steep redox gradient and biogeochemical cycling driven by deeply sourced fluids and gases in a terrestrial mud volcano.

Mud volcanoes provide an accessible channel through which deep subsurface environments can be observed. The manner in which deeply sourced materials shape biogeochemical processes and microbial communities in such geological features remains largely unknown. This study characterized redox transitions, biogeochemical fluxes and microbial communities for samples collected from a methane-rich mud volcano in southwestern Taiwan. Our results indicated that oxygen penetration was confined within the upper 4 mm of fluids/muds and counteracted by the oxidation of pyrite, dissolved sulfide, methane and organic matter at various degrees. Beneath the oxic zone, anaerobic sulfur oxidation, sulfate reduction, anaerobic methanotrophy and methanogenesis were compartmentalized into different depths in the pool periphery, forming a metabolic network that efficiently cycles methane and sulfur. Community members affiliated with various Proteobacteria capable of aerobic oxidation of sulfur, methane and methyl compounds were more abundant in the anoxic zone with diminished sulfate and high methane. These findings suggest either the requirement of alternative electron acceptors or a persistent population that once flourished in the oxic zone. Overall, this study demonstrates the distribution pattern for a suite of oxidative and reductive metabolic reactions along a steep redox gradient imposed by deep fluids in a mud volcano ecosystem.

Microbial Community Composition and Functional Capacity in a Terrestrial Ferruginous, Sulfate-Depleted Mud Volcano.

Terrestrial mud volcanoes (MVs) are an important natural source of methane emission. The role of microbial processes in methane cycling and organic transformation in such environments remains largely unexplored. In this study, we aim to uncover functional potentials and community assemblages across geochemical transitions in a ferruginous, sulfate-depleted MV of eastern Taiwan. Geochemical profiles combined with 16S rRNA gene abundances indicated that anaerobic oxidation of methane (AOM) mediated by ANME-2a group coincided with iron/manganese reduction by Desulfuromonadales at shallow depths deprived of sulfate. The activity of AOM was stimulated either by methane alone or by methane and a range of electron acceptors, such as sulfate, ferrihydrite, and artificial humic acid. Metagenomic analyses revealed that functional genes for AOM and metal reduction were more abundant at shallow intervals. In particular, genes encoding pili expression and electron transport through multi-heme cytochromes were prevalent, suggesting potential intercellular interactions for electron transport involved in AOM. For comparison, genes responsible for methanogenesis and degradation of chitin and plant-derived molecules were more abundant at depth. The gene distribution combined with the enhanced proportions of 16S rRNA genes related to methanogens and heterotrophs, and geochemical characteristics suggest that particulate organic matter was degraded into various organic entities that could further fuel in situ methanogenesis. Finally, genes responsible for aerobic methane oxidation were more abundant in the bubbling pool and near-surface sediments. These methane oxidizers account for the ultimate attenuation of methane discharge into the atmosphere. Overall, our results demonstrated that various community members were compartmentalized into stratified niches along geochemical gradients. These community members form a metabolic network that cascades the carbon transformation from the upstream degradation of recalcitrant organic carbon with fermentative production of labile organic entities and methane to downstream methane oxidation and metal reduction near the surface. Such a metabolic architecture enables effective methane removal under ferruginous, sulfate-depleted conditions in terrestrial MVs.

Humic acids enhance the microbially mediated release of sedimentary ferrous iron.

Iron (Fe) is an essential element for many organisms, but high concentrations of iron can be toxic. The complex relation between iron, arsenic (As), bacteria, and organic matter in sediments and groundwater is still an issue of environmental concern. The present study addresses the effects of humic acids and microorganisms on the mobilization of iron in sediments from an arsenic-affected area, and the microbial diversity was analyzed. The results showed that the addition of 50, 100, and 500 mg/L humic acids enhanced ferrous iron (Fe(II)) release in a time-dependent and dose-dependent fashion under anaerobic conditions. A significant increase in the soluble Fe(II) concentrations occurred in the aqueous phases of the samples during the first 2 weeks, and aqueous Fe(II) reached its maximum concentrations after 8 weeks at the following Fe(II) concentrations: 28.95 ± 1.16 mg/L (original non-sterilized sediments), 32.50 ± 0.71 mg/L (50 mg/L humic acid-amended, non-sterilized sediments), 37.50 ± 1.85 mg/L (100 mg/L humic acid-amended, non-sterilized sediments), and 39.00 ± 0.43 mg/L (500 mg/L humic acid-amended, non-sterilized sediments). These results suggest that humic acids can further enhance the microbially mediated release of sedimentary iron under anaerobic conditions. By contrast, very insignificant amounts of iron release were observed from sterilized sediments (the abiotic controls), even with the supplementation of humic acids under anaerobic incubation. In addition, the As(III) release was increased from 50 ± 10 µg/L (original non-sterilized sediments) to 110 ± 45 µg/L (100 mg/L humic acid-amended, non-sterilized sediments) after 8 weeks of anaerobic incubation. Furthermore, a microbial community analysis indicated that the predominant class was changed from Alphaproteobacteria to Deltaproteobacteria, and clearly increased populations of Geobacter sp., Paludibacter sp., and Methylophaga sp. were found after adding humic acids along with the increased release of iron and arsenic. Our findings provide evidence that humic acids can enhance the microbially mediated release of sedimentary ferrous iron in an arsenic-affected area. It is thus suggested that the control of anthropogenic humic acid use and entry into the environment is important for preventing the subsequent iron contamination in groundwater.

Current Scaling and Dirac Fermion Heating in Multi-Layer Graphene.

We have performed transport measurements on a multi-layer graphene device fabricated by conventional mechanical exfoliation. By using the zero-field resistance of our graphene device as a self-thermometer, we are able to determine the effective Dirac fermion temperature TDF at various driving currents I while keeping the lattice constant fixed. Interesting, it is found that TDF is proportional to Ia where a ~ 1. According to theoretical and experimental studies, the exponent a is given by 2/(2+p) where the charge-phonon scattering rate 1/τph is proportional to TP. Therefore our results yield p ~ 0, suggesting that there is little Dirac fermion-phonon scattering, a great advantage for applications in nanoelectronics.

Temperature-dependent variations in sulfate-reducing communities associated with a terrestrial hydrocarbon seep.

Terrestrial hydrocarbon seeps are an important source of naturally emitted methane over geological time. The exact community compositions responsible for carbon cycling beneath these surface features remain obscure. As sulfate reduction represents an essential process for anoxic organic mineralization, this study collected muddy fluids from a high-temperature hydrocarbon seep in Taiwan and analyzed community structures of sulfate-supplemented sediment slurries incubated anoxically at elevated temperatures. The results obtained demonstrated that sulfate consumption occurred between 40°C and 80°C. Dominant potential sulfate reducers included Desulfovibrio spp., Desulfonatronum spp., Desulforhabdus spp., and Desulfotomaculum spp. at 40°C, Thermodesulfovibrio spp. at 50°C, Thermodesulfovibrio spp. and Thermacetogenium spp. at 60°C, Thermacetogenium spp. and Archaeoglobus spp. at 70°C, and Archaeoglobus spp. at 80°C. None of these potential sulfate reducers exceeded 7% of the community in the untreated sample. Since no exogenous electron donor was provided during incubation, these sulfate reducers appeared to rely on the degradation of organic matter inherited from porewater and sediments. Aqueous chemistry indicated that fluids discharged in the region represented a mixture of saline formation water and low-salinity surface water; therefore, these lines of evidence suggest that deeply-sourced, thermophilic and surface-input, mesophilic sulfate-reducing populations entrapped along the subsurface fluid transport could respond rapidly once the ambient temperature is adjusted to a range close to their individual optima.

Mitogenomic sequences effectively recover relationships within brush-footed butterflies (Lepidoptera: Nymphalidae).

BACKGROUND: Mitogenomic phylogenies have revealed well-supported relationships for many eukaryote groups. In the order Lepidoptera, 113 species mitogenomes had been sequenced (May 14, 2014). However, these data are restricted to ten of the forty-three recognised superfamilies, while it has been challenging to recover large numbers of mitogenomes due to the time and cost required for primer design and sequencing. Nuclear rather than mitochondrial genes have been preferred to reconstruct deep-level lepidopteran phylogenies, without seriously evaluating the potential of entire mitogenomes. Next-generation sequencing methods remove these limitations by providing efficiently massive amounts of sequence data. In the present study, we simultaneously obtained a large number of nymphalid butterfly mitogenomes to evaluate the utility of mitogenomic phylogenies by comparing reconstructions to the now quite well established phylogeny of Nymphalidae. RESULTS: We newly obtained 30 nymphalid mitogenomes via pyrosequencing on the Roche 454 GS Junior system, and combined these sequences with publicly accessible data to provide a 70-taxa dataset covering 37 genes for a 15,495 bp alignment. Polymorphic sites were not homogeneously distributed across the gene. Two gene regions, nad6 and 3' end of nad5, were most variable, whereas the cox1 and 5' ends of rrnL were most conserved. Phylogenetic relationships inferred by two likelihood methods were congruent and strongly supported (>0.95 posterior probability; ML bootstrap >85%), across the majority of nodes for multiple partitioning strategies and substitution models. Bayes factor results showed that the most highly partitioned dataset is the preferred strategy among different partitioning schemes. The most striking phylogenetic findings were that the subfamily Danainae not Libytheinae was sister of the remaining brush-footed butterflies and that, within Limenitidini, the genus Athyma was clearly polyphyletic. None of the single-gene phylogenies recovered the highly supported topologies generated on the basis of the whole mitogenomic data. CONCLUSIONS: Thirty mitogenomes were assembled with 89% completeness from the contigs of pyrosequencing-derived reads. Entire mitogenomes or higher-quality sequences could be obtained by increasing pyrosequencing read coverage or by additional Sanger sequencing. Our mitogenomic phylogenies provide robust nodal support at a range of levels, demonstrating that mitogenomes are both accurate and efficient molecular markers for inferring butterfly phylogeny.

Spatial variations of community structures and methane cycling across a transect of Lei-Gong-Hou mud volcanoes in eastern Taiwan.

This study analyzed cored sediments retrieved from sites distributed across a transect of the Lei-Gong-Hou mud volcanoes in eastern Taiwan to uncover the spatial distributions of biogeochemical processes and community assemblages involved in methane cycling. The profiles of methane concentration and carbon isotopic composition revealed various orders of the predominance of specific methane-related metabolisms along depth. At a site proximal to the bubbling pool, the methanogenic zone was sandwiched by the anaerobic methanotrophic zones. For two sites distributed toward the topographic depression, the methanogenic zone overlaid the anaerobic methanotrophic zone. The predominance of anaerobic methanotrophy at specific depth intervals is supported by the enhanced copy numbers of the ANME-2a 16S rRNA gene and coincides with high dissolved Fe/Mn concentrations and copy numbers of the Desulfuromonas/Pelobacter 16S rRNA gene. Assemblages of 16S rRNA and mcrA genes revealed that methanogenesis was mediated by Methanococcoides and Methanosarcina. pmoA genes and a few 16S rRNA genes related to aerobic methanotrophs were detected in limited numbers of subsurface samples. While dissolved Fe/Mn signifies the presence of anaerobic metabolisms near the surface, the correlations between geochemical characteristics and gene abundances, and the absence of aerobic methanotrophs in top sediments suggest that anaerobic methanotrophy is potentially dependent on iron/manganese reduction and dominates over aerobic methanotrophy for the removal of methane produced in situ or from a deep source. Near-surface methanogenesis contributes to the methane emissions from mud platform. The alternating arrangements of methanogenic and methanotrophic zones at different sites suggest that the interactions between mud deposition, evaporation, oxidation and fluid transport modulate the assemblages of microbial communities and methane cycling in different compartments of terrestrial mud volcanoes.

Experimental evidence for direct insulator-quantum Hall transition in multi-layer graphene.

We have performed magnetotransport measurements on a multi-layer graphene flake. At the crossing magnetic field Bc, an approximately temperature-independent point in the measured longitudinal resistivity ρxx, which is ascribed to the direct insulator-quantum Hall (I-QH) transition, is observed. By analyzing the amplitudes of the magnetoresistivity oscillations, we are able to measure the quantum mobility µq of our device. It is found that at the direct I-QH transition, µqBc ≈ 0.37 which is considerably smaller than 1. In contrast, at Bc, ρxx is close to the Hall resistivity ρxy, i.e., the classical mobility µBc is ≈ 1. Therefore, our results suggest that different mobilities need to be introduced for the direct I-QH transition observed in multi-layered graphene. Combined with existing experimental results obtained in various material systems, our data obtained on graphene suggest that the direct I-QH transition is a universal effect in 2D.

Insulator, semiclassical oscillations and quantum Hall liquids at low magnetic fields.

Magneto-transport measurements are performed on two-dimensional GaAs electron systems to probe the quantum Hall (QH) effect at low magnetic fields. Oscillations following the Shubnikov-de Haas (SdH) formula are observed in the transition from the insulator to QH liquid when the observed almost temperature-independent Hall slope indicates insignificant interaction correction. Our study shows that the existence of SdH oscillations in such a transition can be understood based on the non-interacting model.

Probing temperature-driven flow lines in a gated two-dimensional electron gas with tunable spin-splitting.

We study the temperature flow of conductivities in a gated GaAs two-dimensional electron gas (2DEG) containing self-assembled InAs dots and compare the results with recent theoretical predictions. By changing the gate voltage, we are able to tune the 2DEG density and thus vary disorder and spin-splitting. Data for both the spin-resolved and spin-degenerate phase transitions are presented, the former collapsing to the latter with decreasing gate voltage and/or decreasing spin-splitting. The experimental results support a recent theory, based on modular symmetry, which predicts how the critical Hall conductivity varies with spin-splitting.

Metabolic stratification driven by surface and subsurface interactions in a terrestrial mud volcano.

Terrestrial mud volcanism represents the prominent surface geological feature, where fluids and hydrocarbons are discharged along deeply rooted structures in tectonically active regimes. Terrestrial mud volcanoes (MVs) directly emit the major gas phase, methane, into the atmosphere, making them important sources of greenhouse gases over geological time. Quantification of methane emission would require detailed insights into the capacity and efficiency of microbial metabolisms either consuming or producing methane in the subsurface, and establishment of the linkage between these methane-related metabolisms and other microbial or abiotic processes. Here we conducted geochemical, microbiological and genetic analyses of sediments, gases, and pore and surface fluids to characterize fluid processes, community assemblages, functions and activities in a methane-emitting MV of southwestern Taiwan. Multiple lines of evidence suggest that aerobic/anaerobic methane oxidation, sulfate reduction and methanogenesis are active and compartmentalized into discrete, stratified niches, resembling those in marine settings. Surface evaporation and oxidation of sulfide minerals are required to account for the enhanced levels of sulfate that fuels subsurface sulfate reduction and anaerobic methanotrophy. Methane flux generated by in situ methanogenesis appears to alter the isotopic compositions and abundances of thermogenic methane migrating from deep sources, and to exceed the capacity of microbial consumption. This metabolic stratification is sustained by chemical disequilibria induced by the mixing between upward, anoxic, methane-rich fluids and downward, oxic, sulfate-rich fluids.

Biogeochemical cycling of ferric oxyhydroxide affecting As partition in groundwater aquitard.

High arsenic (As) concentration in groundwater potentially poses a serious threat to the health of local residents in southwestern Taiwan. Although the As release to groundwater is responsible for the reducing bacteria-mediated reductive dissolution of As-rich Fe hydroxides, the influences of FeRB and different organic substrates on As and Fe mobility and transformation were rarely discussed. An experiment that involved As-adsorbed synthetic amorphous Fe(III) hydroxide (HFO) and the inoculation of in situ Fe-reducing bacteria (FeRB) was performed to evaluate the contribution of FeRB to the As mobility and transformation. The batched experiment of As-free HFO showed that the reducing bacteria rapidly induced the reduction of amorphous Fe oxyhydroxide to Fe(II) by reductive dissolution of HFO and formation of Fe-citrate complexation. For aqueous As(V) reduction experiment, arsenate was effectively reduced to As(III) by the facultative anaerobic bacterium in the cultured FeRB. In the experiment of As-containing HFO reduction, the aqueous As(V) acts as an electron acceptor and reduced to As(III) after the reductive dissolution of Fe(III) on HFO. However, the increase in the As(III) concentrations with time for various organic substrates in the As-adsorbed HFO-reducing experiment differ from the rates of As(V) reduction with various organic substrates in the As(V)-reducing experiment. The decrease in sorption sites by coupled reductive dissolution of HFO and the competitive desorption of small molecular organic carbon is apparently the important factor of As mobility. For large molecular organic carbon (i.e., citrate), the significant contribution of citrate on As mobility is the complexation of iron citrate. A working hypothesis model of As biogeochemical cycling is proposed to illustrate the relevant processes in the groundwater aquitard of southwestern Taiwan.

Microbial methane cycling in a terrestrial mud volcano in eastern Taiwan.

Microbial communities responsible for methane cycling in mud volcanoes onshore are poorly characterized. This study analysed bubbling fluids and cored sediments retrieved from a mud volcano in eastern Taiwan. The pore water profiles revealed that methane concentrations generally increased with depth and changed dramatically at different depth intervals at different sites. The methane concentrations were inversely correlated with Fe(2+)/Mn(2+) concentrations and δ(13)C values of methane, marking iron/manganese-methane transition zones in the sediment cores. Archaeal communities were dominated by ANME-2a members and methylotrophic methanogens, whereas bacterial communities consisted primarily of Proteobacteria, Firmicutes and Bacteroidetes. The 16S rRNA gene copy numbers of ANME-2a and Desulfuromonas/Pelobacter populations varied by two to three orders of magnitude along the profile and exhibited a pattern comparable with those of Fe(2+) and δ(13)C values of methane. These lines of evidence suggest a coupling between anaerobic methanotrophy and metal reduction in the metal-methane transition zones under sulfate-deficient conditions, a metabolic scheme contrasting with that observed in marine cold seeps. Anaerobic methanotrophs proliferate by removing methane produced from in situ methanogenesis and originating from the deep source. Methane finally emitted into the atmosphere is quantitatively and isotopically altered by various microbial processes compartmentalized at different depth intervals.

On the direct insulator-quantum Hall transition in two-dimensional electron systems in the vicinity of nanoscaled scatterers.

A direct insulator-quantum Hall (I-QH) transition corresponds to a crossover/transition from the insulating regime to a high Landau level filling factor ν > 2 QH state. Such a transition has been attracting a great deal of both experimental and theoretical interests. In this study, we present three different two-dimensional electron systems (2DESs) which are in the vicinity of nanoscaled scatterers. All these three devices exhibit a direct I-QH transition, and the transport properties under different nanaoscaled scatterers are discussed.

A delta-doped quantum well system with additional modulation doping.

A delta-doped quantum well with additional modulation doping may have potential applications. Utilizing such a hybrid system, it is possible to experimentally realize an extremely high two-dimensional electron gas (2DEG) density without suffering inter-electronic-subband scattering. In this article, the authors report on transport measurements on a delta-doped quantum well system with extra modulation doping. We have observed a 0-10 direct insulator-quantum Hall (I-QH) transition where the numbers 0 and 10 correspond to the insulator and Landau level filling factor ν = 10 QH state, respectively. In situ titled-magnetic field measurements reveal that the observed direct I-QH transition depends on the magnetic component perpendicular to the quantum well, and the electron system within this structure is 2D in nature. Furthermore, transport measurements on the 2DEG of this study show that carrier density, resistance and mobility are approximately temperature (T)-independent over a wide range of T. Such results could be an advantage for applications in T-insensitive devices.