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The optical, plasmonic, and imaging performance of an infra-red polarized system exceeds that of a conventional infra-red detector due to its high resolution and precision.

The electrical properties of a single facet of an individual ZnO microwire were investigated. Electrode patterns with a Hall bar structure were deposited on the surface of the top facet of the ZnO microwire. Using a suspended and cross-linked poly(methyl methacrylate) ribbon structure, it was possible to define the electrical connections only at the top surface, while avoiding those on the other five sides of the ZnO microwire. Current-voltage characteristics were examined, and Hall measurements were conducted with various magnetic fields. Through our device structure, the electrical properties could be directly probed at specific points on the ZnO surface in a reliable manner. The estimated electrical characteristics demonstrate that the carrier concentration and mobility of the ZnO surface varied along the axial direction of the wire. These results indicate that the charge carrier concentration on the surface of the micro-/nanowire can be sensitively changed according to the synthesis environment. In addition, it is worth noting that the nanoscale local Hall probes, fabricated by our technique, could probe the very slight variation of carrier concentration, which is difficult to detect by a standard transport measurement along the wire.

This review examined whether the physical environment can change the cognitive function of the elderly and categorized the specific environmental types. Four databases, CINAHL, Embase, PubMed, and PsycINFO, were searched for relevant literature published as of December 2020. The framework used was proposed by Arksey and O’Malley, which includes a 5-stage review process. A total of 12 studies were examined. The physical environments with similar characteristics, among all the environmental elements, were grouped together into 4 categories: residential density and road connectivity, limited living space, urban/rural, and care facilities. Residential density and road connectivity, limited living space, and care facilities were found to have a significant effect on the cognitive function of the elderly. However, there was no significant effect on the cognitive function of the elderly when comparing the urban and rural environments. Although studies on environments that affect the cognitive function of the elderly are still ongoing, the ones analyzing specific environments in detail are insufficient. With the increasing importance of the role played by the environment in the cognitive impairment of the elderly, detailed studies on specific environments among the various environmental factors surrounding the elderly, such as this study, should be conducted more actively.

Interlayer coupling in graphene-based van der Waals (vdW) heterostructures plays a key role in determining and modulating their physical properties. Hence, its influence on the optical and electronic properties cannot be overlooked in order to promote various next-generation applications in electronic and opto-electronic devices based on the low-dimensional materials. Herein, the optical and electrical properties of the vertically stacked large area heterostructure of the monolayer graphene transferred onto a monolayer graphene oxide film are investigated. An effective and stable p-doping property of this structure is shown by comparison to that of the graphene device fabricated on a silicon oxide substrate. Through Raman spectroscopy and density functional theory calculations of the charge transport characteristics, it is found that graphene is affected by sustainable p-doping effects induced from underneath graphene oxide even though they have weak interlayer interactions. This finding can facilitate the development of various fascinating graphene-based heterostructures and extend their practical applications in integrated devices with advanced functionalities.

Silicon, a ubiquitous material in modern computing, is an emerging platform for realizing a source of indistinguishable single photons on demand. The integration of recently discovered single-photon emitters in silicon into photonic structures is advantageous to exploit their full potential for integrated photonic quantum technologies. Here, we show the integration of an ensemble of telecom photon emitters in a two-dimensional array of silicon nanopillars. We developed a top-down nanofabrication method, enabling the production of thousands of nanopillars per square millimeter with state-of-the-art photonic-circuit pitch, all the while being free of fabrication-related radiation damage defects. We found a waveguiding effect of the 1278 nm-G center emission along individual pillars accompanied by improved brightness compared to that of bulk silicon. These results unlock clear pathways to monolithically integrating single-photon emitters into a photonic platform at a scale that matches the required pitch of quantum photonic circuits.

Nanoscale electromechanical coupling provides a unique route toward control of mechanical motions and microwave fields in superconducting cavity electromechanical devices. However, conventional devices composed of aluminum have presented severe constraints on their operating conditions due to the low superconducting critical temperature (1.2 K) and magnetic field (0.01 T) of aluminum. To enhance their potential in device applications, we fabricate a superconducting electromechanical device employing niobium and demonstrate a set of cavity electromechanical dynamics, including back-action cooling and amplification, and electromechanically induced reflection at 4.2 K and in strong magnetic fields up to 0.8 T. Niobium-based electromechanical transducers operating at this temperature could potentially be employed to realize compact, nonreciprocal microwave devices in place of conventional isolators and cryogenic amplifiers. Moreover, with their resilience to magnetic fields, niobium devices utilizing the electromechanical back-action effects could be used to study spin-phonon interactions for nanomechanical spin-sensing.

Precise doping-profile engineering in van der Waals heterostructures is a key element to promote optimal device performance in various electrical and optical applications with two-dimensional layered materials. Here, we report tungsten diselenide- (WSe2) based pure vertical diodes with atomically defined p-, i- and n-channel regions. Externally modulated p- and n-doped layers are respectively formed on the bottom and the top facets of WSe2 single crystals by direct evaporations of high and low work-function metals platinum and gadolinium, thus forming atomically sharp p–i–n heterojunctions in the homogeneous WSe2 layers. As the number of layers increases, charge transport through the vertical WSe2 p–i–n heterojunctions is characterized by a series of quantum tunneling events; direct tunneling, Fowler–Nordheim tunneling, and Schottky emission tunneling. With optimally selected WSe2 thickness, our vertical heterojunctions show superb diode characteristics of an unprecedentedly high current density and low turn-on voltages while maintaining good current rectification., Vertical charge transport through homogeneous WSe2 layers can be effectively tuned by the layer number and contacting metals deposited. Here, the authors report WSe2 vertical diodes with superior device performance characteristics based on variable WSe2 thickness and gadolinium and platinum contact metals.

Developing facile techniques to control the formation of combined structures of graphene and metal nanoparticles are key to realizing the various conceptual applications based on plasmonic substrates. Here, we report simultaneous formation of continuously grown graphene sheets by wrapping copper nanoparticles (CuNPs) formed in a state of transition from a pre-evaporated copper film during the annealing process. The morphologies and electrical and optical responses of graphene/CuNPs were characterized by varying the thickness of the copper film. We believe that this technique can be further applied to realize various electronic, optical, and catalytic applications.

Graphene has been considered an ideal material for application in transparent lightweight wearable electronics due to its extraordinary mechanical, optical, and electrical properties originating from its ordered hexagonal carbon atomic lattice in a layer. Precise surface control is critical in maximizing its performance in electronic applications. Graphene grown by chemical vapor deposition is widely used but it produces polymeric residue following wet/chemical transfer process, which strongly affects its intrinsic electrical properties and limits the doping efficiency by adsorption. Here, we introduce a facile dry-cleaning method based on UV irradiation to eliminate the organic residues even after device fabrication. Through surface topography, Raman analysis, and electrical transport measurement characteristics, we confirm that the optimized UV treatment can recover the clean graphene surface and improve graphene-FET performance more effectively than thermal treatment. We propose our UV irradiation method as a systematically controllable and damage-free post process for application in large-area devices.

Spin polarization of electrons through transition metal dichalcogenides (TMDs) from ferromagnetic metals (FMs) is a fascinating phenomenon in condensed matter physics. The spin polarized current makes high- and low-resistance states in FM/TMDs/FM junctions depending on magnetization alignment of FM electrodes. We have manifested vertical spin valve junctions by incorporating MoS2 layers of different thicknesses by an ultraclean fabrication method. The current-voltage (I-V) characteristics show the ohmic contact behavior, indicating that mono-, bi-, and tri-layer MoS2 work as conducting thin film. In contrast, FM/multilayer MoS2/FM junction shows non-linear I-V characteristics and the junction resistance increases as the temperature is lowered, indicating that multilayer MoS2 provides a tunneling barrier between FM electrodes. We have found that the magnetoresistance (MR) ratio increases gradually as the thickness of the MoS2 layer is increased. Our investigation will provide a guide to make an optimal choice in the development of magnetic tunnel junctions with two-dimensional layered TMDs.

Accurate and precise determination of mechanical properties of nanoscale materials is mandatory since device performances of nanoelectromechanical systems (NEMS) are closely related to the flexural properties of the materials. In this study, the intrinsic mechanical properties of highly stressed silicon nitride (SiN) beams of varying lengths are investigated using two different techniques: Dynamic flexural measurement using optical interferometry and quasi-static flexural measurement using atomic force microscopy. The resonance frequencies of the doubly clamped, highly stressed beams are found to be inversely proportional to their length, which is not usually observed from a beam but is expected from a string-like structure. The mass density of the SiN beams can be precisely determined from the dynamic flexural measurements by using the values for internal stress and Young’s modulus determined from the quasi-static measurements. As a result, the mass resolution of the SiN beam resonators was predicted to be a few attograms, which was found to be in excellent agreement with the experimental results. This work suggests that accurate and precise determination of mechanical properties can be achieved through combined flexural measurement techniques, which is a crucial key for designing practical NEMS applications such as biomolecular sensors and gas detectors.

Graphene bubbles are often formed when graphene and other layered two-dimensional materials are vertically stacked as van der Waals heterostructures. Here, we investigate how graphene bubbles and their related disorder impact the quantum transport behavior of graphene in the absence and presence of external magnetic fields. By combining experimental observations and numerical simulations, we find that the disorder induced by the graphene bubbles is mainly from p-type dopants and the charge transport in pristine graphene can be severely influenced by the presence of bubbles via long- and short-range scattering even with a small bubble-coverage of 2% and below. Upon bubble density increase, we observe an overall decrease in carrier mobility, and the appearance of a second Dirac point on the electron carrier side. At high magnetic fields, the disorder from graphene bubbles primarily impacts the quantization of the lowest Landau level, resulting in quantum Hall features associated with a new Dirac cone at high charge carrier density.

We have investigated the performances of barristors with a graphene-tungsten disulfide (WS 2 ) junction by varying the thickness of WS 2 and gate oxide. On-current density ( J ON ) and on- and off-current ratio ( J ON / J OFF ) increases, and sub-threshold swing ( V SS ) decreases with the WS 2 thickness. Also, barristors with thicker WS 2 required less workfunction shift, to switch the barristors. Therefore, unlike the traditional devices, V SS of barristor with gate dielectric 300 nm was smaller than that of 90 nm, when the former is fabricated with thicker WS 2 than the latter. Since materials properties of 2-dimensional semiconductors generally vary with their thickness, the thickness of 2D semiconductors could become a key parameter to engineer the performance of barristors with graphene and the 2D semiconductors.

Assessing atomic defect states and their ramifications on the electronic properties of two-dimensional van der Waals semiconducting transition metal dichalcogenides (SC-TMDs) is the primary task to expedite multi-disciplinary efforts in the promotion of next-generation electrical and optical device applications utilizing these low-dimensional materials. Here, with electron tunneling and optical spectroscopy measurements with density functional theory, we spectroscopically locate the mid-gap states from chalcogen-atom vacancies in four representative monolayer SC-TMDs—WS2, MoS2, WSe2, and MoSe2—, and carefully analyze the similarities and dissimilarities of the atomic defects in four distinctive materials regarding the physical origins of the missing chalcogen atoms and the implications to SC-mTMD properties. In addition, we address both quasiparticle and optical energy gaps of the SC-mTMD films and find out many-body interactions significantly enlarge the quasiparticle energy gaps and excitonic binding energies, when the semiconducting monolayers are encapsulated by non-interacting hexagonal boron nitride layers., Atomic defects impact the electronic properties of atomically thin transition metal dichalcogenides (TMDs). Here, the authors locate the mid-gap states originating from single chalcogen-atom vacancies in four representative semiconducting monolayer films, and analyse their implications for the semiconducting properties of atomically thin TMDs through electron tunneling and optical spectroscopy measurements.

The chemical and mechanical stability of hexagonal boron nitride (h-BN) thin films and their compatibility with other free-standing two-dimensional (2D) crystals to form van der Waals heterostructures make the h-BN-2D tunnel junction an intriguing experimental platform not only for the engineering of specific device functionalities but also for the promotion of quantum measurement capabilities. Here, we exploit the h-BN-graphene tunnel junction to directly probe the electronic structures of single-layer and bilayer graphene in the presence and the absence of external magnetic fields with unprecedented high signal-to-noise ratios. At a zero magnetic field, we identify the tunneling spectra related to the charge neutrality point and the opening of the electric-field-induced bilayer energy gap. In the quantum Hall regime, the quantization of 2D electron gas into Landau levels (LL) is seen as early as 0.2 T, and as many as 30 well-separated LL tunneling conductance oscillations are observed for both electron-...

High mobility single and few-layer graphene sheets are in many ways attractive as nanoelectronic circuit hosts but lack energy gaps, which are essential to the operation of field-effect transistors. One of the methods used to create gaps in the spectrum of graphene systems is to form long period moire patterns by aligning the graphene and hexagonal boron nitride (h-BN) substrate lattices. Here, we use planar tunneling devices with thin h-BN barriers to obtain direct and accurate tunneling spectroscopy measurements of the energy gaps in single- and bi-layer graphene-h-BN superlattice structures at charge neutrality (first Dirac point) and at integer moire band occupancies (second Dirac point, SDP) as a function of external electric and magnetic fields and the interface twist angle. In single-layer graphene we find, in agreement with previous work, that gaps are formed at neutrality and at the hole-doped SDP, but not at the electron-doped SDP. Both primary and secondary gaps can be determined accurately by extrapolating Landau fan patterns to zero magnetic field and are as large as $\simeq$ 17 meV for devices in near perfect alignment. For bilayer graphene, we find that gaps occur only at charge neutrality where they can be modified by an external electric field. Tunneling signatures of in-gap states around neutrality suggest the development of edge modes related to topologically non-trivial valley projected bands due to the combination of an external electric field and moire superlattice patterns., Comment: 6 figures

Spin polarization of electrons through transition metal dichalcogenides (TMDs) from ferromagnetic metals (FMs) is a fascinating phenomenon in condensed matter physics. The spin polarized current makes high- and low-resistance states in FM/TMDs/FM junctions depending on magnetization alignment of FM electrodes. We have manifested vertical spin valve junctions by incorporating MoS2 layers of different thicknesses by an ultraclean fabrication method. The current-voltage (I-V) characteristics show the ohmic contact behavior, indicating that mono-, bi-, and tri-layer MoS2 work as conducting thin film. In contrast, FM/multilayer MoS2/FM junction shows non-linear I-V characteristics and the junction resistance increases as the temperature is lowered, indicating that multilayer MoS2 provides a tunneling barrier between FM electrodes. We have found that the magnetoresistance (MR) ratio increases gradually as the thickness of the MoS2 layer is increased. Our investigation will provide a guide to make an optimal choice in the development of magnetic tunnel junctions with two-dimensional layered TMDs.

Since the successful exfoliation of graphene, various methodologies have been developed to identify the number of layers of exfoliated graphene. The optical contrast, Raman G-peak intensity, and 2D-peak line-shape are currently widely used as the first level of inspection for graphene samples. Although the combination analysis of G- and 2D-peaks is powerful for exfoliated graphene samples, its use is limited in chemical vapor deposition (CVD)-grown graphene because CVD-grown graphene consists of various domains with randomly rotated crystallographic axes between layers, which makes the G- and 2D-peaks analysis difficult for use in number identification. We report herein that the Raman Si-peak intensity can be a universal measure for the number identification of multilayered graphene. We synthesized a few-layered graphene via the CVD method and performed Raman spectroscopy. Moreover, we measured the Si-peak intensities from various individual graphene domains and correlated them with the corresponding layer numbers. We then compared the normalized Si-peak intensity of the CVD-grown multilayer graphene with the exfoliated multilayer graphene as a reference and successfully identified the layer number of the CVD-grown graphene. We believe that this Si-peak analysis can be further applied to various 2-dimensional (2D) materials prepared by both exfoliation and chemical growth.

The optical constants, bandgaps, and band alignments of mono-, bi-, and trilayer WS2 were experimentally measured, and an extraordinarily high dependency on the number of layers was revealed. The refractive indices and extinction coefficients were extracted from the optical-contrast oscillation for various thicknesses of SiO2 on a Si substrate. The bandgaps of the few-layer WS2 were both optically and electrically measured, indicating high exciton-binding energies. The Schottky-barrier heights (SBHs) with Au/Cr contact were also extracted, depending on the number of layers (1-28). From an engineering viewpoint, the bandgap can be modulated from 3.49 to 2.71 eV with additional layers. The SBH can also be reduced from 0.37 eV for a monolayer to 0.17 eV for 28 layers. The technique of engineering materials' properties by modulating the number of layers opens pathways uniquely adaptable to transition-metal dichalcogenides.

Developing substrates that enable both reproducible and highly sensitive Raman detection of trace amounts of molecules in aqueous systems remains a challenge, although these substrates are crucial in biomedicine and environmental sciences. To address this issue, we report spatially uniform plasmonic nanowrinkles formed by intimate contact between plasmonic nanograins on the surface of colloidal crystal monolayers. The Au or Ag nanograin layers coated on hydrogel colloidal crystal monolayers can reversibly wrinkle and unwrinkle according to changes in the water temperature. The reversible switches are directed by surface structural changes in the colloidal crystal monolayers, while the colloids repeat the hydration-dehydration process. The Au and Ag nanowrinkles are obtained upon hydration, thus enabling the highly reproducible detection of Raman probes in water at the nano- and picomolar levels, respectively, throughout the entire substrate area. Additionally, the reversible switching of the nanostructures in the plasmonic nanograin layers causes reversible dynamic changes in the corresponding Raman signals upon varying the water temperature.

Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible, and transparent optoelectronics. In particular, the strong light-matter interaction in graphene has allowed for the development of state-of-the-art photodetectors, optical modulators, and plasmonic devices. In addition, electrically biased graphene on SiO2 substrates can be used as a low-efficiency emitter in the mid-infrared range. However, emission in the visible range has remained elusive. Here we report the observation of bright visible-light emission from electrically biased suspended graphenes. In these devices, heat transport is greatly minimised; thus hot electrons (~ 2800 K) become spatially localised at the centre of graphene layer, resulting in a 1000-fold enhancement in the thermal radiation efficiency. Moreover, strong optical interference between the suspended graphene and substrate can be utilized to tune the emission spectrum. We also demonstrate the scalability of this technique by realizing arrays of chemical-vapour-deposited graphene bright visible-light emitters. These results pave the way towards the realisation of commercially viable large-scale, atomically-thin, flexible and transparent light emitters and displays with low-operation voltage, and graphene-based, on-chip ultrafast optical communications., Comment: 63 page

The mechanical properties of ZnO microwires have been studied using three different methods: quasi-static flexural measurements using atomic force microscopy, static measurements using a nano indenter, and dynamic flexural measurements using optical interferometry. ZnO microwires were synthesized by chemical vapor deposition method, and the crystal structure and quality were examined using x-ray diffraction and photoluminescence spectroscopy. The Young's moduli were estimated using the measurement results from the three methods, and they showed consistent values in the range 67.5–79.4 GPa for microwires with diameters of 1.8 μm ± 100 nm.

Graphene based multi-valued nanoelectromechanical switches are suggested and demonstrated. The device structure having multiple contact sites with different heights under the doubly clamped suspended beam provides multiple contacts to be formed sequentially from the taller electrode to the shorter electrode, which results in multiple logic states. Based on the finite element method simulation, we found that our device characteristics, such as turn-on and threshold voltages, are highly governed by the device design. The proof-of-concept device realized by using a newly developed 3D fabrication method based on the e-beam lithography expresses quaternary logic states successfully with a high stability in repetitive operations.

We investigate the evolution of Au thin films to nanoparticles caused by plasma ion bombardment and report their validity as a catalyst on the growth of carbon nanotubes (CNTs). The Au thin films having 1–50 A thickness ranges were precisely prepared by electron beam deposition. The plasma ion bombardments with the plasma power from 5 to 15 W were performed at 500 °C for 10 min under 1.33 × 102 Pa of Ar to investigate the effects of plasma power on the surface structures. It is interesting that the mean size of Au nanoparticles increased as plasma power gets high in the thinner film cases, which might be the results of sputtering and surface diffusion-related aggregation. On the contrary, the mean particle size of the thicker films decreased at lower plasma power regime due to the sputtering, then, increased again at the highest plasma power, which might be caused by the diffusion-induced aggregation of the films. Finally, to investigate the catalytic ability of the thin film-induced Au nanoparticles, we grew CNTs by a thermal chemical vapor deposition with a methane source. It was found that the Au nanoparticles obtained from the plasma-treated 5 A thick films act as an efficient catalyst for the growth of single-walled CNTs.

We have developed the detection method of the resonance frequency of micro/nano mechanical resonator using optical method. The optical interferometery method enabled us to detect the displacement change of resonators within several nm scale. The micro mechanical resonator was produced by attaching a micro mechanical cantilever to a piezo ceramic. The mass of cantilever was increased by evaporating Au using electron beam evaporator and the mass variation was estimated by detecting the resonance frequency changes.

Resistive random access memory (ReRAM) devices have been extensively investigated resulting in significant enhancement of switching properties. However fluctuations in switching parameters are still critical weak points which cause serious failures during ‘reading’ and ‘writing’ operations of ReRAM devices. It is believed that such fluctuations may be originated by random creation and rupture of conducting filaments inside ReRAM oxides. Here, we introduce defective monolayer graphene between an oxide film and an electrode to induce confined current path distribution inside the oxide film and thus control the creation and rupture of conducting filaments. The ReRAM device with an atomically thin interlayer of defective monolayer graphene reveals much reduced fluctuations in switching parameters compared to a conventional one. Our results demonstrate that defective monolayer graphene paves the way to reliable ReRAM devices operating under confined current path distribution.

A stencil lithography technique has been developed to fabricate organic-material-based electronic devices with sub-micron resolution. Suspended polymethylmethacrylate (PMMA) membranes were used as shadow masks for defining organic channels and top electrodes. Arrays of pentacene field effect transistors (FETs) with various channel lengths from 50 μm down to 500 nm were successfully produced from the same batch using this technique. Electrical transport measurements showed that the electrical contacts of all devices were stable and the normalized contact resistances were much lower than previously studied organic FETs. Scaling effects, originating from the bulk space charge current, were investigated by analyzing the channel-length-dependent mobility and hysteresis behaviors. This novel lithography method provides a reliable means for studying the fundamental transport properties of organic materials at the nanoscale as well as enabling potential applications requiring the fabrication of integrated organic nanoelectronic devices.

With its electrical carrier type as well as carrier densities highly sensitive to light, graphene is potentially an ideal candidate for many optoelectronic applications. Beyond the direct light-graphene interactions, indirect effects arising from induced charge traps underneath the photoactive graphene arising from light-substrate interactions must be better understood and harnessed. Here, we study the local doping effect in graphene using focused-laser irradiation, which governs the trapping and ejecting behavior of the charge trap sites in the gate oxide. The local doping effect in graphene is manifested by large Dirac voltage shifts and/or double Dirac peaks from the electrical measurements and a strong photocurrent response due to the formation of a p-n-p junction in gate-dependent scanning photocurrent microscopy. The technique of focused-laser irradiation on a graphene device suggests a new method to control the charge-carrier type and carrier concentration in graphene in a nonintrusive manner as well as elucidate strong light-substrate interactions in the ultimate performance of graphene devices.

In this paper, we propose an inter-cell interference management scheme using a multi-cell SRN (Shared Relay Node) in order to avoid inter-cell interference and to increase the cell throughput in 3GPP LTE (3rd Generation Partnership Project Long Term Evolution)-Advanced networks. Recently, the CoMP (Coordinated Multi-Point transmission/reception) scheme has received growing attention as a promising scheme for overcoming the inter-cell interference in 3GPP LTE-Advanced networks. In practice, however, when feedback delays and channel estimation errors are considered, the performance of the CoMP scheme may severely degrade. The objective of this paper is to present a new SRN architecture located at the neighboring area of adjacent cells so as to manage the inter-cell interference. The SRN can overhear control signals transmitted by adjacent eNBs (enhanced Node-B) and UEs (User Equipments). Based on the overheard information, the SRN not only performs data retransmission as a usual type II relay but also manages the inter-cell interference. In particular, we suggest a resource allocation scheme and a power control scheme assisted on the SRN for effective interference avoidance, and evaluate their performances through simulations.

The thermal conductivity of suspended single-layer graphene was measured as a function of temperature using Raman scattering spectroscopy on clean samples prepared directly on a prepatterned substrate by mechanical exfoliation without chemical treatments. The temperature at the laser spot was monitored by the frequency of the Raman 2$D$ band of the Raman scattering spectrum, and the thermal conductivity was deduced by analyzing heat diffusion equations assuming that the substrate is a heat sink at ambient temperature. The obtained thermal conductivity values range from $\sim$1800 Wm$^{-1}$K$^{-1}$ near 325 K to $\sim$710 Wm$^{-1}$K$^{-1}$ at 500 K., 4pages, 3 figures

We have investigated single- and bi-layer graphene as source-drain electrodes for n-type MoS2 transistors. Ti-MoS2-graphene heterojunction transistors using both single-layer MoS2 (1M) and 4-layer MoS2 (4M) were fabricated in order to compare graphene electrodes with commonly used Ti electrodes. MoS2-graphene Schottky barrier provided electron injection efficiency up to 130 times higher in the subthreshold regime when compared with MoS2-Ti, which resulted in VDS polarity dependence of device parameters such as threshold voltage (VTH) and subthreshold swing (SS). Comparing single-layer graphene (SG) with bi-layer graphene (BG) in 4M devices, SG electrodes exhibited enhanced device performance with higher on/off ratio and increased field-effect mobility (μFE) due to more sensitive Fermi level shift by gate voltage. Meanwhile, in the strongly accumulated regime, we observed opposing behavior depending on MoS2 thickness for both SG and BG contacts. Differential conductance (σd) of 1M increases with VDS irresp...

A transistor structure composed of an individual single-walled carbon nanotube (SWNT) channel with a graphene electrode was demonstrated. The integrated arrays of transistor devices were prepared by transferring patterned graphene electrode patterns on top of the aligned SWNT along one direction. Both single and multi layer graphene were used for the electrode materials; typical p-type transistor and Schottky diode behavior were observed, respectively. Based on our fabrication method and device performances, several issues are suggested and discussed to improve the device reliability and finally to realize all carbon based future electronic systems.

Analyzes the performance of a simple open loop transmit diversity (TD) scheme proposed by the authors for wideband CDMA systems under Rician multipath fading channels. In particular, the probability density function (pdf) of the output signal-to-noise ratio (SNR) and the uncoded bit error rate (BER) are derived. Numerical results show that the scheme with low complexity outperforms open loop space-time transmit diversity (STTD), and achieves a close performance to ideal closed loop transmit adaptive array (TxAA) in typical Rician multipath fading channels.

We designed and fabricated gravimetric sensors composed of silicon (Si) microbeams surrounded by silicon nitride (SiN) anchors. The oscillation properties of the fabricated devices show that a single oscillation mode originating from quasi-one-dimensional microbeams appears at an applied alternating electric field, which motion is well matched to the theoretical predictions and is much different from the dimensionally mixed oscillation modes in normal non-anchored devices. In addition, in order to elucidate the possibilities of the devices for mass sensing applications, we measured the frequency shift as a function of mass loading in a self-assembled monolayer of 3-aminopropyltrimethoxysilane and Au nanoparticles. The resulting limit of detection was 1.05 × 10−18 g/Hz, which is an extremely high value for micro electromechanical system gravimetric sensors relative to the normal ones.