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Mo0.67W0.33Se2 devices show gate-voltage-induced electrical phase transitions.

Various intriguing quantum transport measurements for carbon nanotubes (CNTs) based on their unique electronic band structures have been performed adopting a field-effect transistor (FET), where the contact resistance represents the interaction between the one-dimensional and three-dimensional systems. Recently, van der Waals (vdW) gap tunneling spectroscopy for single-walled CNTs with indium–metal contacts was performed adopting an FET device, providing the direct assignment of the subband location in terms of the current–voltage characteristic. Here, we extend the vdW gap tunneling spectroscopy to multi-walled CNTs, which provides transport spectroscopy in a tunneling regime of ~1 eV, directly reflecting the electronic density of states. This new quantum transport regime may allow the development of novel quantum devices by selective electron (or hole) injection to specific subbands.

We demonstrate a gate-tunable quantum dot (QD) located between two potential barriers defined in a few-layer MoS

The achievement of ultraclean Ohmic van der Waals (vdW) contacts at metal/transition-metal dichalcogenide (TMDC) interfaces would represent a critical step for the development of high-performance electronic and optoelectronic devices based on two-dimensional (2D) semiconductors. Herein, we report the fabrication of ultraclean vdW contacts between indium (In) and molybdenum disulfide (MoS2) and the clarification of the atomistic origins of its Ohmic-like transport properties. Atomically clean In/MoS2 vdW contacts are achieved by evaporating In with a relatively low thermal energy and subsequently cooling the substrate holder down to ~100 K by liquid nitrogen. We reveal that the high-quality In/MoS2 vdW contacts are characterized by a small interfacial charge transfer and the Ohmic-like transport based on the field-emission mechanism over a wide temperature range from 2.4 to 300 K. Accordingly, the contact resistance reaches ~600 Ω μm and ~1000 Ω μm at cryogenic temperatures for the few-layer and monolayer MoS2 cases, respectively. Density functional calculations show that the formation of large in-gap states due to the hybridization between In and MoS2 conduction band edge states is the microscopic origins of the Ohmic charge injection. We suggest that seeking a mechanism to generate strong density of in-gap states while maintaining the pristine contact geometry with marginal interfacial charge transfer could be a general strategy to simultaneously avoid Fermi-level pinning and minimize contact resistance for 2D vdW materials.

In the present study, phase-dependent gas sensitivities of MoS

An inability to precisely control doping has hindered the development of electrically reliable and predictable low-dimensional devices. Here, we demonstrated a modulation of electronic bands of one-dimensional carbon nanotubes (CNTs) over a wide range by using metal electrodes having almost the same work function as the CNT in a dual-gate mode. Gate-response curves obtained from Ti versus In metal-contacted devices showed opposite behaviors in shape and magnitude in an ambipolar state, which was shown to be due to the difference between the pinned positions of their Fermi levels in the band gap of the CNT with different work functions of the metals. By varying the gate-bias voltages of the dual gates, we successfully demonstrated that the electronic band profile of the CNT can be modulated precisely and over a wide range to higher and lower energy levels, resulting in the ability to have it form p-metal, p-type semiconductor, ambipolar, n-type semiconductor, and n-metallic electronic states.

As a consequence of their unique electronic band structures, low-dimensional materials such as one-dimensional (1D) single-wall carbon nanotubes (SWCNTs), 2D graphene and various 2D transition-metal dichalcogenides have exhibited intriguing electrical transport properties when incorporated into field-effect transistors. Meanwhile, the van-der-Waals (vdW) interfaces between top-contacted metals and low-dimensional materials have become a challenging issue for future high-performance electronics. Here, we report a new aspect of vdW interface that offers vdW-gap tunneling spectroscopy by adopting indium (In) as a top-contacted metal on SWCNTs without an artificial insulating tunnel barrier. We show that multiple differential conductance peaks for varying bias voltages correspond to the van Hove singularities existing in the electronic density of states of SWCNTs. Our first-principles calculations reveal that In forms a physisorption interface with a considerable vdW gap, which causes little disruption to the density of states of the SWCNTs near the metal interface and which thus allows vdW-gap tunneling spectroscopy.

Coupling of the electron orbital motion and spin, i.e., spin-orbit coupling (SOC) leads to nontrivial changes in energy-level structures, giving rise to various spectroscopies and applications. The SOC in solids generates energy-band inversion or splitting under zero or weak magnetic fields, which is required for topological phases or Majorana fermions. Here, we examined the interplay between the Zeeman splitting and SOC by performing the transport spectroscopy of Landau levels (LLs) in indium arsenide nanowires under a strong magnetic field. We observed the anomalous Zeeman splitting of LLs, which depends on the quantum number of LLs as well as the electron spin. We considered that this observation was attributed to the interplay between the Zeeman splitting and the SOC. Our findings suggest an approach of generating spin-resolved chiral electron transport in nanowires.

Background:Dementia is a common mental illness associated with aging. Alzheimer’s disease (AD) and Vascular dementia (VaD) are the most common causes of dementia in the elderly. In previous studies, hyperuricemia was suggested to have anti-oxidant effects and possible neuroprotective effects [1,2].Objectives:Hyperuricemia is the most important factor in the pathogenesis of gout. This study aims to investigate association between gout and dementia.Methods:We conducted a nationwide population-based study using the NHIS-NSC database of the Korean populations consisted of 1 million individuals between 2002 and 2013. Gout patients were defined by International Classification of Diseases (ICD)-10 code for gout (M10) and prescriptions for urate lowering therapy including allopurinol, febuxostat and benzbromarone at least 30days. Dementia was also defined by ICD-10 codes for dementia; Alzheimer’s disease (AD; F00), vascular dementia (VaD; F01).Results:Excluded 40 patients with previous diagnosed dementia, total 5,496 gout patients were compared to 27,480 age- and sex-matched control group. The analysis results showed that gout patients had a lower risk of overall dementia [odds ratio (OR): 0.79; 95% confidence interval (CI): 0.63-0.99; p < 0.05] after adjusted for age, sex, household income, comorbidities. The risk of VaD (OR: 0.77; 95% CI: 0.32-1.9; p=0.68) and AD (OR; 0.8; 95% CI: 0.53-1.19; p=0.06) tended to be lower in gout group but these were not significant.Conclusion:Gout patients had a lower risk of dementia. This result tended to exist for both AD and VaD type of dementia.References:[1]Hooper DC, Spitsin S, Kean RB, et al. Uric acid, a natural scavenger of peroxynitrite, in experimental allergic encephalomyelitis and multiple sclerosis. Proc Natl Acad Sci USA. 1998; 95: 675–80.[2]Bowman GL, Shannon J, Frei B, et al. Uric acid as a CNS antioxidant. J Alzheimer’s Dis. 2010; 19: 1331–6.Disclosure of Interests:None declared

We demonstrate a gate-tunable quantum dot (QD) located between two potential barriers defined in a few-layer MoS2. Although both local gates used to tune the potential barriers have disorder-induced QDs, we observe diagonal current stripes in current resonant islands formed by the alignment of the Fermi levels of the electrodes and the energy levels of the disorder-induced QDs, as evidence of the gate-tunable QD. We demonstrate that the charging energy of the designed QD can be tuned in the range of 2–6 meV by changing the local-gate voltages in ∼1 V.

The electrical properties of a single-walled carbon nanotube network were investigated after photoresist treatment with the pristine device. Atomic force microscopy found that the diameters of the single-walled carbon nanotubes were increased after photoresist treatment and that the photoresist could not be completely removed from nanotube surfaces by using a simple cleaning process with an organic solvent. Although the presence of a residual photoresist had no noticeable effects on the Raman spectrum of single-walled carbon nanotubes in our devices, the charge carrier mobilities and the on/off ratios of the single-walled carbon nanotube devices were lowered due to the photoresist treatment, and the gate-hysteresis behavior in the devices that had undergone photoresist treatment was found to be different from that of pristine devices.

The moderate band gap of black phosphorus (BP) in the range of 0.3-2 eV, along a high mobility of a few hundred cm(2) V(-1) s(-1) provides a bridge between the gapless graphene and relatively low-mobility transition metal dichalcogenides. Here, we study the mechanism of electrical and thermoelectric transport in 10-30 nm thick BP devices by measurements of electrical conductance and thermopower (S) with various temperatures (T) and gate-electric fields. The T dependences of S and the sheet conductance (σ□) of the BP devices show behaviors of T(1/3) and exp[-(1/T)(1/3)], respectively, where S reaches ∼0.4 mV/K near room T. This result indicates that two-dimensional (2D) Mott's variable range hopping (VRH) is a dominant mechanism in the thermoelectric and electrical transport in our examined thin BP devices. We consider the origin of the 2D Mott's VRH transport in our BPs as trapped charges at the surface of the underlying SiO2 based on the analysis with observed multiple quantum dots.

We show that graphene device could be controllably doped by the bottom substrate by inserting atomic layer deposition grown ZnO between graphene and SiO 2 substrate. To clarify the effect of bottom ZnO, length of the graphene transistor channel was varied from 20 to 200 μm, while that of ZnO was fixed to 10 μm. Graphene devices supported on ZnO film show marked difference from those supported on SiO 2 substrates; bottom ZnO layer behave as an electron donor. UV illumination experiment on hybrid graphene-ZnO device reveals that the effect of doping from ZnO becomes negligible when the graphene channel length made about four times larger than that of ZnO stripe.

Background:Ankylosing spondylitis (AS) is a chronic inflammatory disease featured with involvement of sacroiliac joint and starts in the second or third decade of life. Female patients with AS are mostly in childbearing ages. There are several studies of pregnancy outcomes but no studies about their offsprings.Objectives:The objective of our study was to invetigate the growth and developement of offsprings from AS mothers.Methods:This is a nationwide population-based case-control study using two South Korean databases that are managed by the National Health Insurance Service (NHIS): (1) the National Health Screening Program for Infants and Children (NHSIC) database, which records screening data of the growth and development of all children; (2) the NHIS database, which covers the entire population and includes comprehensive health claims data. In Korea, the NIH supports patients with 133 rare severe, intractable diseases including AS via a registration system of rare intractable disease (RID). We enrolled subjects born from 2008–2013 who had participated in the NHSIC program at three consecutive times; during 4-6 months (1st), 9-12 months (2nd), either 54-65months or 66-71 months (6th, 7th). The Korean Developmental screening test (K-DST) was used to assess development. By linking maternal and offspring healthcare data through their unique personal identification numbers, we constructed a mother-child database to track the growth of the child. We classified childrens from AS mothers using RID system (ICD code M45.X) and those from non-AS mothers. The primary outcome was to compare the growth and developement of offsprings from AS mothers and those from general popuulation. The secondary outcome was to copare the growth and developement of offsprings from mothers who diagnosed AS before delivery (ante-partum, AS-AP) and those from mothers who diagnosed AS after delivery (postpartum, AS-PP). Low birth weight (LBW) was defined as a birth weight below 2500 g. Growth retardation (GR) was defined as a body wight below 10th percentile according to birth weight reference curves for the south Korean population.Results:A total of 794,544 subjects were identified. Among those cohort subject, there were 369 subjects with AS mother (124 subjects from AS-AP, 245 subjects from AS-PP) while 794,175 subjects with non-AS mother. Offsprings with LBW were comparable between those from AS mother and non-AS mother (OR 1.3, 95% CI 0.74-2.02). At 4-6 months, an OR of GR was comparable between two groups (OR 1.18, 95% CI 0.72-1.92) but increased at 9-12 months (OR 1.62, 95%CI 1.14-2.31) in infants from AS mothers.This difference disappered at 54-71months (OR 0.24,95% CI 0.87-1.74). An OR of development abnormality (i.e. children needed the further evaluation or the follow-up test by K-DST) was also comparable between two groups (OR 0.94, 95% CI 0.71-1.25). Mothers with AS-AP had as about three times as a higher OR for having babies with LBW than mothers with AS-PP (OR 2.8, 95% CI 1.15-6.86). At 4-6 months, an OR of GR was comparable between two groups (OR 0.59, 95% CI 0.19-1.86) but decreased at 9-12 months (OR 0.39, 95%CI 0.16-0.98) in infants from AS-PP.This difference disappered at 54-71months (OR 0.63,95% CI 0.29-1.39). An OR of development abnormality (i.e. children needed the further evaluation or the follow-up test by K-DST) was also comparable between two groups (OR 1.37, 95% CI 0.77-2.43).Conclusion:Growth and development of children from AS mothers were comparable with those from non-AS mothers. Although mothers with AS-AP had significantly higher ORs for having LBW babies than those with AS-PP, their growth and development were comparable between two groups in young childhood.Disclosure of Interests:None declared

In the present study, phase-dependent gas sensitivities of MoS2 chemical sensors were examined. While 1T-phase MoS2 (1T-MoS2) has shown better chemical sensitivity than has 2H-phase MoS2 (2H-MoS2), the instability of the 1T phase has been hindering applications of 1T-MoS2 as chemical sensors. Here, the chemical sensitivity of MoS2 locked in its 1T phase by using a ZnO phase lock was investigated. To develop MoS2 chemical sensors locked in the 1T phase, we synthesized a multi-dimensional nanomaterial by growing ZnO nanorods onto MoS2 nanosheets (ZnO@1T-MoS2). Raman spectroscopy and x-ray photoelectron spectroscopy analyses of such phase-locked 1T-MoS2 subjected to flash light irradiation 100 times confirmed its robustness. ZnO nanomaterials hybridized on MoS2 nanosheets not only froze the MoS2 at its 1T phase, but also increased the active surface area for chemical sensing. The resulting hybridized material showed better response, namely better sensitivity, to NO2 gas exposure at room temperature than did 1T-MoS2 and 2H-MoS2. This result indicated that increased surface area and heterojunction formation between MoS2 and ZnO constitute a more promising route for improving sensitivity than using the 1T phase itself.

Electrical stimulation through direct electrical activation has been widely used to recover the function of neurons, primarily through the extracellular application of thin film electrodes. However, studies using extracellular methods show limited ability to reveal correlations between the cells and the electrical stimulation due to interference from external sources such as membrane capacitance and culture medium. Here, we demonstrate long-term intracellular electrical stimulation of undamaged pheochromocytoma (PC-12) cells by utilizing a vertical nanowire electrode array (VNEA). The VNEA was prepared by synthesizing silicon nanowires on a Si substrate through a vapor-liquid-solid (VLS) mechanism and then fabricating them into electrodes with semiconductor nanodevice processing. PC-12 cells were cultured on the VNEA for 4 days with intracellular electrical stimulation and then a 2-day stabilization period. Periodic scanning via two-photon microscopy confirmed that the electrodes pierced the cells without inducing damage. Electrical stimulation through the VNEA enhances cellular differentiation and neurite outgrowth by about 50% relative to extracellular stimulation under the same conditions. VNEA-mediated stimulation also revealed that cellular differentiation and growth in the cultures were dependent on the potential used to stimulate them. Intracellular stimulation using nanowires could pave the way for controlled cellular differentiation and outgrowth studies in living cells.

The mechanism of charge transfer through nanomaterials such as graphene remains unclear, and the amount of charge that can be transferred from/to graphene without damaging its structural integrity is unknown. In this communication, we show that metallic nanoparticles can be decorated onto graphene surfaces as a result of charge transfer from the supporting substrate to an adjoining solution containing metal ions. Au or Pt nanoparticles were formed with relatively high yield on graphene-coated substrates that can reduce these metal ions, such as Ge, Si, GaAs, Al, and Cu. However, metal ions were not reduced on graphene surfaces coated onto non-reducing substrates such as SiO2 or ZnO. These results confirm that graphene can be doped by exploiting charge transfer from the underlying substrate; thus graphene is not only transparent with respect to visible light, but also with respect to the charge transfer. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Secondary metabolic variation of wild apple (Malus prunifolia) was compared with fruits that contained high flavan-3-ol like grapes (GR), apple (App) and the beverage, black tea (BT). The polyphenol contents in wild apple was higher than in GR and App but less than BT. The identified phenolic acids (gallic, protocatechuic, chlorogenic, p-coumaric and ferulic acids) and flavonoids (quercetin and myricetin) indicate that wild apple was higher than that of App. Among all the samples, BT had highest antioxidant potential in terms of 2,2'-Azinobis (3-thylbenzothiazoline-6-sulfonic acid) diammonium salt (95.36%), metal chelating (45.36%) and phosphomolybdenum activity (95.8 mg/g) because of the high flavan-3-ol content. The gallic acid and epigallocatechin gallate were highly correlated with antioxidant potential and these metabolites levels are higher in wild apple than that of App. Wild apples being a non-commercial natural source, a detailed study of this plant will be helpful for the food additive and preservative industry.

A comparative study was made of the yield, morphological characteristics, biochemical variations and antioxidant activity of Chinese cabbage, grown conventionally, naturally and organically. A significant increase in most amino acids, calcium (63.1 mg/100 g), magnesium (82.4 mg/100 g) and molybdenum (0.12 mg/100 g) was observed with organic cultivation. Conventionally grown Chinese cabbage had higher sugars and organic acid levels than organically grown cabbage, but sucrose level was higher (4.27 g/100 g) in those grown naturally. Though the moisture content of organic and conventional was comparable, the level of crude lipids, ash and carbohydrate content was higher in natural and control grown plants. Under different cultivation methods the total phenolic content was higher with the natural (302 μg/g) followed by organic (283 μg/g) cultivation. Similarly the 1,1-diphenyl-2-picrylhydrazyl and nitrite scavenging potential was highest in natural (70.12, 43.87%) followed by organic (67.28, 42.14%) cultivation. Crop yields were highest with conventional cultivation and slightly increased compared to organic cultivation. Amino acid and phenolic contents were highest with organic cultivation, suggesting that organic cultivation may provide health benefits.

The effect of thermo-cycling treatment on the bond strength and flexural strength of porcelain veneered zirconia was evaluated. After thermo-cycling treatment between 5 degrees C to 55 degrees C, porcelain-zirconia bond strength and zirconia flexural strength was not significantly affected. In the phase analyses using XRD after thermo-cycling treatment, both the experimental group and the control group showed only tetragonal phases. That is, the porcelain-zirconia bond strength and zirconia flexural strength were not affected by low temperature degradation. So low temperature aging treatment did not reduce the flexural strength and the effect of temperature applied to the aging treatment could beignorable.

The plasma parameters in the scrape-off layer (SOL) region and the particle flux at the divertor target are measured by using a fast reciprocating Langmuir probe assembly (FRLPA) and a fixed edge Langmuir probe array (ELPA) in the KSTAR. The e-folding lengths of the plasma density (n e ) and the electron temperature (T e ), λ ne and λ Te , are obtained from the radial profile measurement using the FRLPA at the outboard mid-plane during ohmic and H-mode discharges. Particle fluxes measured by using the ELPA at the divertor target are mapped to the outboard mid-plane, and the fluxes are quite well matched to the radial profile of the particle flux from the FRLPA measurement. Finally, the peak heat flux at the divertor target during edge localized modes (ELMs) can be estimated to be up to 1.0 MWm−2 for the neutral beam power of ~ 2.7 MW by using T e at the separatrix and λ Te from the FRLPA measurements. In this work, the experimental results from the probe measurements in the KSTAR are presented.

The negative charging effect of surface traps on the gate leakage current of AlGaN/GaN high electron mobility transistors (HEMTs) was investigated. The gate leakage current could be decreased by two orders of magnitude by using a photo-electrochemical process to treat of the source and the drain region, but current flowed into the gate even at a negative voltage in a limited region when the measurement was executed with a gate voltage sweep from negative to positive voltage. Also the electrical characteristics of the HEMT were degraded by pulsed operation of the gate. Traps newly generated on the surface were regarded as sources for the current that flowed against the applied voltage, and the number of traps was estimated. Also, a slow transient in the drain current was confirmed based on the results of delayed sweep measurements.

Thick film semiconductor gas sensors based on indium oxide were fabricated on Si substrate. The sensing materials on Si substrate were characterized using optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM), and so on. They were very fine and uniform and we found out that particle sizes were about 20~30 nm through XRD analysis. Gas responses of fabricated sensors were measured in a chamber where gas flow was controlled by mass flow controller (MFC). Their resistance changes were monitored in real time by using data acquisition board and personal computer. Gas response characteristics were examined for formaldehyde (HCHO) gas which was known as the cause of sick building syndrome. Particularly, the sensors showed responses to formaldehyde gas at sub ppm (cf, standard of natural environment in building is about 80 ppb by ministry of environment in Korea), as a function of operating temperatures and gas concentrations. Also, we investigated sensitivity, repetition, selectivity, response speed and reproducibility of the sensors. The lowest detection limit is HCHO 25 ppb and sensitivity at 800 ppb is over 25% at 350 °C operating temperature. The response time (8 s) and recovery time (15 s) to HCHO gas at 200 ppb were very fast compared to other commercial products in flow type measurement condition. Repetition measurement was very good with ±3% in full measurement range. The fabricated metal oxide gas sensor showed good performance to HCHO gas and proved that it could be adaptable to indoor environment in building.

We demonstrated a nonlithographic method for integrating GaAs nanowire (NW) array-based light-emitting diodes (LEDs) on silicon (Si) substrates. A sub-100 nm hole array on a deposited SiO2 layer was patterned on an entire 2 in. Si wafer based on a sacrificed self-assembled InAs NW array. Then, a core–shell n–p junction GaAs NW array was grown on exposed Si windows via the selective-area growth method. The electrical properties of the core–shell n–p junction GaAs NW has been measured and compared to those of the core–shell junction NWs formed via the self-assembled growth method. Room temperature electroluminescence was successfully observed from the fabricated GaAs NW array-based LEDs. The core–shell junction III–V NW array epitaxially grown on a ubiquitous Si platform could be applied to future low-cost optical devices.

Exosomes are enclosed compartments that are released from cells and that can transport biological contents for the purpose of intercellular communications. Research into exosomes is hindered by their rarity. In this article, we introduce a device that uses centrifugal force and a filter with micro-sized pores to generate a large quantity of cell-derived nanovesicles. The device has a simple polycarbonate structure to hold the filter, and operates in a common centrifuge. Nanovesicles are similar in size and membrane structure to exosomes. Nanovesicles contain intracellular RNAs ranging from microRNA to mRNA, intracellular proteins, and plasma membrane proteins. The quantity of nanovesicles produced using the device is 250 times the quantity of naturally secreted exosomes. Also, the quantity of intracellular contents in nanovesicles is twice that in exosomes. Nanovesicles generated from murine embryonic stem cells can transfer RNAs to target cells. Therefore, this novel device and the nanovesicles that it generates are expected to be used in exosome-related research, and can be applied in various applications such as drug delivery and cell-based therapy.

The reversal technique in electrical measurements has been generally used to obtain a genuine value of an interesting physical quantity without unwanted signal offset. In the present work, we developed a novel cryo-switch made of electrical gates on GaAs heterostructure and demonstrate the current-reversal operation for a single-parameter electron pump. In precision measurements, we confirmed that the current values in reversal (i.e., approximately ±12.817 pA) being generated by the electron pump at T = 4.2 K agree well with each other in the deviation and uncertainty levels for various exit gate voltages. We also show that the accuracy level evaluated via the difference between the currents reversed was consistent with the unipolar measurements. Consequently, the measurement uncertainty was improved by a factor of two with the same measurement cycle number because of enhancement of signal-to-noise ratio.

We investigated the electrical transport characteristics of graphene transistors functionalized with a self-assembled monolayer (SAM) of cationic molecules. Contact-opened, channel-opened, and pristine graphene transistors were fabricated, and the changes in their electronic transport properties upon SAM functionalization were investigated. All three types of devices undergo a negative shift in the Dirac charge neutrality point (CNP), with the variation of the contact-opened device larger than that of the channel-opened device. This observation confirms that contact electrodes dope graphene through their work function, and that the work functions of metal electrodes can be modulated through the introduction of cationic SAMs.

Smaller-diameter semiconductor nanowires (NWs) are appropriate for electronic applications due to the lower leakage current and better field effect. However, the mobility of a NW gets smaller with decreasing diameter because surface scattering events of mobile carriers are increased. Therefore, the choice of a proper diameter is a key role for future high-performance transistors based on semiconductor NWs. Here, we control the diameters of catalyst-free InAs NWs grown at various growth temperatures by using metal-organic chemical vapor deposition to be in the range of 30 to 160 nm. The mobility of the fabricated InAs field-effect transistor increases with diameter and decreases with increasing temperature, which indicates that the surface scattering determines the electrical property of NWs.

ZnO nanofibers were synthesized by the electrospinning method. Their electrical transport properties were investigated by fabricating field effect transistors based on single ZnO nanofiber. The electron concentration (n) and the field-effect mobility (@m"e) in the ZnO nanofibers are not so sensitive to the calcination atmosphere; O"2 and N"2. Importantly, n (@m"e) in the ZnO nanofibers is bigger (much smaller) than those in single-crystalline ZnO nanowires. The existence of nanosized gains in the ZnO nanofibers is likely to be responsible for such big differences in n and @m"e. Huge grain boundaries created by nanograins seem to play the role of a source providing electrons and a barrier for electrons to flow as well. To enhance the @m"e, the calcination condition to obtain ZnO nanofibers with larger grains needs to be applied.

To control the gate threshold voltages of nano-devices, we fabricated a GaN nanowire field-effect transistor with a sandwich-type dual-gate structure in which the top- and the bottom-gate electrodes could independently apply a gate voltage bias to the nanowire conducting channel. The fabricated device showed a clear n-type gate response. The gate threshold voltage of the nanowire field-effect transistor could be effectively tuned over a wide range, from −13 V to +1 V, by scanning the topor the bottom-gate voltages between −10 and +10 V, respectively. As the top-gate voltage was varied from −10 V to +10 V, the carrier mobility increased from 16 to 56 cm2/Vs, and the channel conductance increased. The turn-on position of the channel conductance could be tuned precisely by varying the voltage at one of the gates.

We have synthesized four pyrene-derived blue emitting materials using Suzuki cross coupling reactions. All OLED devices using these materials as emitting materials showed efficient blue electroluminescence (EL). Particularly, a device using 1,1'-(9,9-dimethyl-9H-fluorene-2,7-diyl)bis-pyrene (1) showed best EL properties with the luminous efficiency of 4.32 cd/A, the power efficiency of 3.98 lm/W and the external quantum efficiency of 2.48% at 500 cd/m2.

At the heart of ever growing demands for faster signal processing is ultrafast charge transport and control by electromagnetic fields in semiconductors. Intense optical fields have opened fascinating avenues for new phenomena and applications in solids. Because the period of optical fields is on the order of a femtosecond, the current switching and its control by an optical field may pave a way to petahertz optoelectronic devices. Lately, a reversible semimetallization in fused silica on a femtosecond time scale by using a few-cycle strong field (~1 V/Å) is manifested. The strong Wannier-Stark localization and Zener-type tunneling were expected to drive this ultrafast semimetallization. Wider spread of this technology demands better understanding of whether the strong field behavior is universally similar for different dielectrics. Here we employ a carrier-envelope-phase stabilized, few-cycle strong optical field to drive the semimetallization in sapphire, calcium fluoride and quartz and to compare this phenomenon and show its remarkable similarity between them. The similarity in response of these materials, despite the distinguishable differences in their physical properties, suggests the universality of the physical picture explained by the localization of Wannier-Stark states. Our results may blaze a trail to PHz-rate optoelectronics.

The effects of metal contacts and metal overlayers on the electrical properties of carbon nanotubes (CNTs) were studied. We show that the conduction properties of a CNT device can be controllably designed through metal depositions on the sidewall even though the conduction type is not clearly defined by the work function of the contact metal. The conversion from an n-type to a p-type conductor was observed with deposition of an overlayer using a large work function metal (Pd), whereas a p-type to n-type conversion was observed with deposition of an overlayer using a low work function metal (Ti). This behavior was attributed to charge transfer doping or the local bending of nanotube bands beneath the metal overlayer. First-principle calculations revealed that charge transfer doping may be uniquely defined by the work function difference if a metal layer forms a weak contact with the sidewall of a CNT.

In order to examine the influence of multi walled carbon nanotube (MWNT) on physical properties of its biodegradable polymer nanocomposite, biodegradable poly(buthylene succinate) (PBS), which was synthesized from diols and dicarboxylic acids, and MWNT nanocomposites were prepared via a melt-mixing method using a co-rotating intermeshing twin screw extruder. Microstructure of the PBS/MWNT nanocomposites and MWNT were investigated via both scanning electron microscopy and transmission electron microscopy. Their rheological properties were also characterized via rotation and oscillation tests using a rotational rheometer with parallel-plate geometry. It was found that shear viscosity, storage modulus and loss modulus of the nanocomposites examined by a rotational rheometer increased with the MWNT content. Especially their sharp increase for MWNT content of ca. 2.0 wt% was observed, indicating its percolation threshold from the rheological viewpoint which was higher than its electrical percolation threshold (1.0 wt%).

Thin films of SDC for SOFC electrolyte were prepared using electron beam deposition technique. The influence of annealing temperature, substrate temperature and e-beam gun power on the structure and surface morphology of the thin films was examined. It was found that the SDC thin films annealed at 800 degrees C consisted of a single cubic phase and the main crystal structure of the thin films represented those of evaporated electrolyte powders. The crystal orientation of the SDC films increased with substrate temperature and decreased with e-beam gun power. The higher XRD peak intensity was observed for the SDC films deposited on NiO-YSZ substrate compared with those on SiO2 substrate due to the polycrystalline structure of the NiO-YSZ substrate. A good adhesion to the substrate and a columnar structure were observed by the fractured cross-sectional view of the SDC films on NiO-YSZ anode substrate. Electrical conductivity of SDC film with 5 microm thickness was observed to be 2.31 x 10(-3) Sm(-1) at 800 degrees C.

We studied the temperature-dependent electrical transport properties of individual ZnO nanowires with metal contacts. We used temperature dependent gate response curves to obtain the carrier mobility and the carrier concentration of ZnO nanowires as function of temperature; these were estimated from the modified transconductance equation to subtract the unavoidable contact resistance effect. As the temperature was lowered from 300 K, the carrier concentration decreased and the carrier mobility increased until it reached a maximum at 150 K. An increase in the carrier mobility upon cooling occurred due to a decrease in the electron-phonon scattering rate; the scatterings from defects and impurities became dominant at temperatures below 150 K. The intrinsic conduction of the ZnO nanowire itself, neglecting the contact effect, followed the thermal activation process related to zinc interstitials, ZnI , rather than a variable range hopping behavior.

The preS2 antigens of hepatitis B virus (HBV), which causes a serious health problem in the world, have been implicated in hepatocyte cell binding and viral penetration. Therefore, the importance of antibody production against preS2 antigen for early diagnosis of HBV has been well established. In this study, the recombinant HBV preS2 single chain variable fragment (scFv) antibody was successfully expressed in E. coli with the novel cold shock vector (pCold) under the cspA promoter, and its expression level was compared with the pET vector under the T7 promoter. Additionally, a host with an oxidizing cytoplasm, E. coli trxB/gor double mutant, was used to improve the soluble expression. The anti-HBV preS2 scFv using pCold vector was successfully expressed in a soluble and functional form in both wild type and double mutant E. coli, while the scFv using the pET vector was expressed in an insoluble form in spite of using a double mutant providing an oxidizing environment. The induction with 0.05 mM IPTG showed a 2-fold higher functional expression compared to induction with 1 mM IPTG, and the functional expression at the induction temperature (15°C), which is optimal temperature for pCold vector, was improved 2-fold and 3- fold at 4 and 25°C, respectively. The efficacy of anti-HBV preS2 scFv for detecting HBV preS2 antigen was tested and verified by using Ni-decorated single-walled carbon nanotube (SWNT) field effect transistors.

We have employed computer-aided furnace design and process simulation to optimize the conditions under which single-walled carbon nanotubes (SWCNTs) may be grown in high yields on 4 in. wafers for electronic device applications. Hydrokinetic simulations were performed to obtain optimized furnace structures and process conditions in terms of gas flow, temperature, and gas speed. Shower head structures and a flow isolation barrier were installed in an experimental 6 in. furnace, as suggested by the hydrokinetic simulations. To ensure clean surfaces and uniform catalyst islands, catalyst patterns were lifted off using Au films or polydimethylsiloxane. Photolithography was used to fabricate field-effect transistors with SWCNTs grown on 4 in. wafer substrates. The total yield of the nanotube devices increased from 30.5% to 96.4% after optimization.

To elucidate the effect of the work function on the position of the Dirac point, we fabricated graphene devices with asymmetric metal contacts. By measuring the peak position of the resistance for each pair of metal electrodes, we obtained the voltage of the Dirac pointVgDirac(V) from the gate response. We found that the position ofVgDirac(V) in the hybrid devices was significantly influenced by the type of metal electrode. The measured shifts inVgDirac(V) were closely related to the modified work functions of the metal-graphene complexes. Within a certain bias range, the Fermi level of one of the contacts aligned with the electron band and that of the other contact aligned with the hole band.