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Parallelization of pump devices is a direct way to increase the output level of the single-electron pump, which is required for metrological purposes. We fabricated a pair of single-electron pumps in parallel on a chip level and investigated their synchronized electron pumping phenomena. In the investigation, the pumping error was estimated to see whether the error was increased after the parallelization. We found that a proper choice of rf gates must be made in accordance with the direction of the applied magnetic field. In relation with the chirality of the edge state, the rf modulating gates should be chosen not to produce rf-induced heating effects.

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.

The performance of our newly constructed cold-finger cryostat is investigated for the precision measurement of quantum Hall resistance (QHR) and single-electron pump (SEP) current. The cryostat is featured by a vacuum sealed sample chamber that is attached to the 0.3 K-plate inside the inner vacuum can. The nominal base temperature of the sample chamber was 0.4 K. However, the electron temperature estimated with a single-electron transistor was approximately 0.6 K. Precision evaluation of a GaAs QHR device shows that the quantized Hall resistance is equivalent to the nominal value of $h/2e^{2}$ within one part in 108. The Allan deviation data for the SEP current is analyzed to be greater than those obtained from SEP in a wet 3He cryostat at Korean Research Institute of Standards and Science.

We developed a current-reversal operation method for single-parameter electron pumps, based on cryo-gate switches located between the ohmic contacts and quantum dot. The current reversal mode provided an enhanced signal-to-noise ratio, resulting in a reduction of the measurement time to reach the same relative measurement uncertainty, compared to a conventional unipolar current measurement method.

A single-electron pump based on a quantum dot is a promising candidate to realize the quantum current standard based on the new SI definition. In order to develop the quantum current standard, we fabricated two different types of single electron pumps based on GaAs/AlGaAs heterostructures by using KRISS nanofabrication facility. From the measurement results, we successfully observed the quantized current steps from the two differently designed pump devices.

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.

We review recent precision measurements on semiconductor tunable-barrier electron pumps operating in a ratchet mode. Seven studies on five different designs of pumps have reported measurements of the pump current with relative total uncertainties around $10^{-6}$ or less. Combined with theoretical models of electron capture by the pumps, these experimental data exhibits encouraging evidence that the pumps operate according to a universal mechanism, independent of the details of device design. Evidence for robustness of the pump current against changes in the control parameters is at a more preliminary stage, but also encouraging, with two studies reporting robustness of the pump current against three or more parameters in the range of $\sim\!5 \times 10^{-7}$ to $\sim\!2 \times 10^{-6}$. This review highlights the need for an agreed protocol for tuning the electron pump for optimal operation, as well as more rigorous evaluations of the robustness in a wide range of pump designs., Comment: 18 pages, 8 figures

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.

In general, the gears of mixer reducer for concrete mixer truck make use of the differential type planetary gear system to rotate mixer drum smoothly on the initial conditions. The planetary gear system is very important part of mixer reducer for concrete mixer truck because of strength problem. In the present study, calculating the gear specifications and analyzing the gear bending & compressive stresses of the differential planetary gear system for mixer reducer are necessary to analyze gear bending and compressive stresses confidently, for optimal design of the planetary gear system in respect to cost and reliability. As a result, analyzing actual gear bending and compressive stresses of the planetary gear system using Lewes & Hertz equation and verifying the calculated specifications of the planetary gear system, evaluate the results with the data of allowable bending and compressive stress from the Stress-No. of cycles curves of gears.

A single electron pump was incorporated with a quantum Hall resistance and a Josephson voltage for the current evaluation in the framework of Ohm’s law. The pump current of about 60 pA level was amplified by a stable amplifier with a gain of 103 to induce a Hall voltage of about 60 mV level across a 1 MΩ Hall resistance array, which was compared with the Josephson voltage. The gain of the current amplifier was calibrated with a cryogenic current comparator bridge. For two different drive frequencies and repeated thermal cycles, the comparisons demonstrated that the pump current averaged over the first plateau was equal to ef within the combined uncertainty level of 0.3 × 10−6 (k = 1).

Single-parameter single-electron pumps (SEPs) based on a quantum dot have been suggested as promising devices to realize the new definition of the unit of current, the ampere, where quantized current produced from the SEP device is only defined by the elementary charge e and applied external radiofrequency (rf), f, i.e., I = ef. The conventional method to eliminate offset signals in the precision current measurement of pump current has been to measure the current difference between the pump-on and pump-off states. To date, the rf-on and rf-off method has been used to pump between its on and off states. However, this method inevitably induces alternating rf-heating effects and varying temperatures of the device environment, possibly leading to a thermal drift of the offset current. In the current work, we developed a new gate-switching technique that can alternate the pump on and off states while maintaining a constant rf-on state, resulting in a more stable system temperature. Using the gate-switching technique, we achieved a temperature-stabilized environment and performed a precision current measurement with sub-parts per million uncertainty.

We demonstrate the robust operation of a gallium arsenide tunable-barrier single-electron pump operating with 1 part-per-million accuracy at a temperature of $1.3$~K and a pumping frequency of $500$~MHz. The accuracy of current quantisation is investigated as a function of multiple control parameters, and robust plateaus are seen as a function of three control gate voltages and RF drive power. The electron capture is found to be in the decay-cascade, rather than the thermally-broadened regime. The observation of robust plateaus at an elevated temperature which does not require expensive refrigeration is an important step towards validating tunable-barrier pumps as practical current standards., 13 pages, 7 figures (4 in main text and 3 in supplementary info

In order to increase the output current level, we have fabricated a parallelized pump with two gate-tunable quantum-dot pumps based on GaAs/AlGaAs heterostructure. Each pump device is composed of multiple gates forming a quantum dot whose potential shapes and barrier heights are tunable. At optimally potential-tuned condition, we have confirmed that the parallelized pump could be considered as a single pump and its theoretically estimated accuracy stays almost the same as the single one within the theoretical resolution. Thus we produce $I=192\ \mathbf{pA}$ at 0.6 GHz with an expected accuracy as low as 10−6 level.

We characterized KRISS precision measurement system by measuring the Allan deviation of the quantized current generated by GaAsl AIGaAs gate-tunable electron pumps, where the current was amplified by the ultrastable low-nose current amplifier (ULCA) developed by the PTB. The Allan deviation of a phosphor bronze wire generally used at cryogenic temperature showed a white noise level of about 18 fA Hz-1I2. The noise level of the electron pump was improved by a factor 4 with a specific choice of cryogenic cables.

Ultrafast electrically driven nanoscale light sources are critical components in nanophotonics. Compound semiconductor-based light sources for the nanophotonic platforms have been extensively investigated over the past decades. However, monolithic ultrafast light sources with a small footprint remain a challenge. Here, we demonstrate electrically driven ultrafast graphene light emitters that achieve light pulse generation with up to 10 GHz bandwidth across a broad spectral range from the visible to the near-infrared. The fast response results from ultrafast charge-carrier dynamics in graphene and weak electron-acoustic phonon-mediated coupling between the electronic and lattice degrees of freedom. We also find that encapsulating graphene with hexagonal boron nitride (hBN) layers strongly modifies the emission spectrum by changing the local optical density of states, thus providing up to 460% enhancement compared to the gray-body thermal radiation for a broad peak centered at 720 nm. Furthermore, the hBN encapsulation layers permit stable and bright visible thermal radiation with electronic temperatures up to 2000 K under ambient conditions as well as efficient ultrafast electronic cooling via near-field coupling to hybrid polaritonic modes under electrical excitation. These high-speed graphene light emitters provide a promising path for on-chip light sources for optical communications and other optoelectronic applications.

Catalyst-free, very long InAs nanowires (NWs) are grown on a Si (111) substrate by using metal-organic chemical vapor deposition (MOCVD) system and their growth mechanism is studied. The NW height increases very fast in the beginning of the growth because of the mass-transport contribution of the adatoms from the substrate surface to the NW tip. Then, the NWs grow slowly and consistently until their height exceeds 50 μm. The NW diameter is very uniform along the growth axis regardless of the NW height and this clearly differs from that of the NWs grown via the self-catalyzed vapor–liquid–solid method. A transmission line measurement (TLM) is performed on the very long InAs NW to measure the contact resistance between the NW and the metal electrode. The electrical properties of the NW are further examined. The catalyst-free, very long InAs NWs demonstrated here can be used for an interconnection of the nanoelectronic device array by integrating multiple devices on a single NW.

Ultrafast electrically driven light emitter is a critical component in the development of the high bandwidth free-space and on-chip optical communications. Traditional semiconductor based light sources for integration to photonic platform have therefore been heavily studied over the past decades. However, there are still challenges such as absence of monolithic on-chip light sources with high bandwidth density, large-scale integration, low-cost, small foot print, and complementary metal-oxide-semiconductor (CMOS) technology compatibility. Here, we demonstrate the first electrically driven ultrafast graphene light emitter that operate up to 10 GHz bandwidth and broadband range (400 ~ 1600 nm), which are possible due to the strong coupling of charge carriers in graphene and surface optical phonons in hBN allow the ultrafast energy and heat transfer. In addition, incorporation of atomically thin hexagonal boron nitride (hBN) encapsulation layers enable the stable and practical high performance even under the ambient condition. Therefore, electrically driven ultrafast graphene light emitters paves the way towards the realization of ultrahigh bandwidth density photonic integrated circuits and efficient optical communications networks.

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

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.

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.

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.

We summarize the results of precision measurement campaigns on semiconductor tunable-barrier electron pumps undertaken at NPL, over the last 5 years. We have investigated pumps of 3 different designs, fabricated in GaAs and silicon and operated on the 1-electron plateau at frequencies from 230 MHz to 1 GHz. For all measurements we find the pump current equal to e×f within the ≈1 ppm standard uncertainty of the current measurement. This accumulated data strongly suggests that accurate quantized operation of the tunable-barrier pump is a universal property, insensitive to the detailed design of the device. The data includes previously unpublished results.

PURPOSE The insulin-like growth factor II (IGF-II) gene expresses a family of transcripts in embryonic/fetal tissue, and also highly was expressed during hepatocellular carcinogenesis. In this study, we showed that IGF-II mRNA and protein levels are detected in rat embryo, HepG2 human hepatoma cells and Chang liver cells. MATERIALS AND METHODS This study included sections of rat embryos 7~17 days post coitum (d.p.c), HepG2 cells and Chang liver cells. Using immunohistochemistry, Northern blotting and Western blotting, we observed the expression of IGF-II in the rat embryo, HepG2 cells and Chang liver cells. RESULTS We localized IGF-II gene products in sections of rat embryo 7~17 d.p.c by performing immunohistochemistry. The IGF-II was mainly expressed in the proximal endoderm and ectoplacental cone between 7 and 9 d.p.c. At 10 d.p.c. the expression was localized at the heart primodium as well as the proximal endoderm, and at 11 d.p.c. the IGF-II was expressed in the liver and heart. After 12 d.p.c. and 14 d.p.c., the expression was also detected in the brain, muscle and bone, and head mesenchyme, respectively. While the expression of IGF-II protein was not detected in the normal adult liver, intense staining was detected in the heart, liver and choroids plexus at 17 d.p.c. CONCLUSION These results suggest that IGF-II may act as an oncofetal protein during hepatocellular carcinogenesis and embryogenesis.

This paper describes the fabrication and design principles for using transparent graphene interconnects in stretchable arrays of microscale inorganic light emitting diodes (LEDs) on rubber substrates. We demonstrate several appealing properties of graphene for this purpose, including its ability to spontaneously conform to significant surface topography, in a manner that yields effective contacts even to deep, recessed device regions. Mechanics modeling reveals the fundamental aspects of this process, as well as the use of the same layers of graphene for interconnects designed to accommodate strains of 100% or more, in a completely reversible fashion. These attributes are compatible with conventional thin film processing and can yield high-performance devices in transparent layouts. Graphene interconnects possess attractive features for both existing and emerging applications of LEDs in information display, biomedical systems, and other environments.

We use infrared microscopy to image the temperature profile of graphene field-effect transistors functioning at high bias. We find a peak in the temperature profile, i.e. a "hot spot" appears near the drain (anode) electrode of the graphene sheet at high current while operating in the hole-doped regime. The hot spot position shifts on the graphene sheet by tuning the gate voltage into an ambipolar transport regime. This shows a direct demonstration and manipula-tion of Joule heating in graphene transistors. Comparison with a comprehensive electrical-thermal model leads to additional insight into graphene transport and energy dissipation physics.

Understanding the energy transport by charge carriers and phonons in two-dimensional (2D) van der Waals heterostructures is essential for the development of future energy-efficient 2D nanoelectronics. Here, we performed in situ spatially resolved Raman thermometry on an electrically biased graphene channel and its hBN substrate to study the energy dissipation mechanism in graphene/hBN heterostructures. By comparing the temperature profile along the biased graphene channel with that along the hBN substrate, we found that the thermal boundary resistance between the graphene and hBN was in the range of (1–2) 10−7 m2 K W−1 from ~100 °C to the onset of graphene break-down at ~600 °C in air. Consideration of an electro-thermal transport model together with the Raman thermometry conducted in air showed that a doping effect occurred under a strong electric field played a crucial role in the energy dissipation of the graphene/hBN device up to T ~ 600 °C.

One-dimensional crystal growth enables the epitaxial integration of III-V compound semiconductors onto a silicon (Si) substrate despite significant lattice mismatch. Here, we report a short-wavelength infrared (SWIR, 1.4–3 μm) photodetector that employs InAs nanowires (NWs) grown on Si. The wafer-scale epitaxial InAs NWs form on the Si substrate without a metal catalyst or pattern assistance; thus, the growth is free of metal-atom-induced contaminations and is also cost-effective. InAs NW arrays with an average height of 50 μm provide excellent anti-reflective and light trapping properties over a wide wavelength range. The photodetector exhibits a peak detectivity of 1.9 × 108 cm·Hz1/2/W for the SWIR band at 77 K and operates at temperatures as high as 220 K. The SWIR photodetector on the Si platform demonstrated in this study is promising for future low-cost optical sensors and Si photonics.

We have investigated the accuracy dependence of a single-electron pump on the confinement-potential shape of a quantum dot (QD) pump. A uniquely designed QD, which employs multiple gates to control the shape of the QD potential well, is utilized for electron pumping. It has been observed that the accuracy of the pump can be dramatically enhanced by achieving smaller QD size and greater decoupling from the electrodes, which is supported by the so-called decay-cascade model. The accuracy of the pump current is estimated, based on the decay-cascade model, to be close to 0.1 ppm for 80-pA pump current when the confinement-potential shape is optimally tuned. This is the highest reported accuracy, although it is a theoretically estimated value, among QD-based pumps measured at 4.2 K in the absence of an external magnetic field. Our numerical calculations show that the enhancement of the estimated accuracy is mainly due to the increase of the electron addition energy in the QD as well as the increase of the height and thickness of the QD potential barrier.

We report on fabrication and electrical characteristics of high-mobility field-effect transistors (FETs) using ZnO nanorods. For FET fabrications, single-crystal ZnO nanorods were prepared using catalyst-free metalorganic vapor phase epitaxy. Although typical ZnO nanorod FETs exhibited good electrical characteristics, with a transconductance of ∼140nS and a mobility of 75cm2∕Vs, the device characteristics were significantly improved by coating a polyimide thin layer on the nanorod surface, exhibiting a large turn-ON/OFF ratio of 104–105, a high transconductance of 1.9μS, and high electron mobility above 1000cm2∕Vs. The role of the polymer coating in the enhancement of the devices is also discussed.

We use simulations to examine current saturation in sub-micron graphene transistors on SiO2/Si. We find self-heating is partly responsible for current saturation (lower output conductance), but degrades current densities >1 mA/um by up to 15%. Heating effects are reduced if the supporting insulator is thinned, or in shorter channel devices by partial heat sinking at the contacts. The transient behavior of such devices has thermal time constants of ~30-300 ns, dominated by the thickness of the supporting insulator and that of device capping layers (a behavior also expected in ultrathin body SOI transistors). The results shed important physical insight into the high-field and transient behavior of graphene transistors., IEEE Electron Device Letters, DOI: 10.1109/LED.2012.2230393 (2013)

We study graphene nanoribbon (GNR) interconnects obtained from graphene grown by chemical vapor deposition (CVD). We report low- and high-field electrical measurements over a wide temperature range, from 1.7 to 900 K. Room temperature mobilities range from 100 to 500 cm2/V/s, comparable to GNRs from exfoliated graphene, suggesting that bulk defects or grain boundaries play little role in devices smaller than the CVD graphene crystallite size. At high-field, peak current densities are limited by Joule heating, but a small amount of thermal engineering allows us to reach ~2 x 10^9 A/cm2, the highest reported for nanoscale CVD graphene interconnects. At temperatures below ~5 K, short GNRs act as quantum dots with dimensions comparable to their lengths, highlighting the role of metal contacts in limiting transport. Our study illustrates opportunities for CVD-grown GNRs, while revealing variability and contacts as remaining future challenges., Comment: Nano Letters (2012); supplement available online

We use infrared thermal imaging and electrothermal simulations to find that localized Joule heating in graphene field-effect transistors on SiO(2) is primarily governed by device electrostatics. Hot spots become more localized (i.e., sharper) as the underlying oxide thickness is reduced, such that the average and peak device temperatures scale differently, with significant long-term reliability implications. The average temperature is proportional to oxide thickness, but the peak temperature is minimized at an oxide thickness of ∼90 nm due to competing electrostatic and thermal effects. We also find that careful comparison of high-field transport models with thermal imaging can be used to shed light on velocity saturation effects. The results shed light on optimizing heat dissipation and reliability of graphene devices and interconnects.

Recent studies using infrared (IR) imaging of graphene transistors [1,2] have revealed substantial Joule heating under realistic operating conditions for graphene-on-insulator (GOI) devices. Here we use simulations calibrated against experimental data to examine the trends of performance degradation caused by self-heating as a function of insulator (SiO 2 ) thickness. We also examine both unipolar and ambipolar operating conditions, and find that peak channel temperatures are proportional to oxide thickness for the unipolar case (as would be expected), but for ambipolar operation an optimum oxide substrate thickness exists (∼80 nm) which minimizes peak temperature, due to competing electrostatic and thermal effects.

The performance and scaling of graphene-based electronics is limited by the quality of contacts between the graphene and metal electrodes. However, the nature of graphene-metal contacts remains incompletely understood. Here, we use atomic force microscopy to measure the temperature distributions at the contacts of working graphene transistors with a spatial resolution of ~ 10 nm (refs 5-8), allowing us to identify the presence of Joule heating, current crowding and thermoelectric heating and cooling. Comparison with simulation enables extraction of the contact resistivity (150-200 Ω µm²) and transfer length (0.2-0.5 µm) in our devices; these generally limit performance and must be minimized. Our data indicate that thermoelectric effects account for up to one-third of the contact temperature changes, and that current crowding accounts for most of the remainder. Modelling predicts that the role of current crowding will diminish and the role of thermoelectric effects will increase as contacts improve.

Phase change memory (PCM) is a promising candidate for next-generation non-volatile data storage, though its high programming current has been a major concern. By utilizing carbon nanotubes (CNTs) and graphene as interconnects to induce phase change in ultra small regions (∼20 nm) of Ge 2 Sb 2 Te 5 (GST), we are able to build ultra-low power PCM devices. Normal memory operations are demonstrated with exceptionally low current (< 5 µA) and power consumption, nearly two orders of magnitude lower than state-of-the-art. Electrical characterization shows that switching voltages in PCM with both CNT and graphene electrodes are scalable to sub-1 V. Our experiments also pave the way to carbon nanoelectronics with integrated PCM data storage.

We directly image hot spot formation in functioning mono- and bilayer graphene field effect transistors (GFETs) using infrared thermal microscopy. Correlating with an electrical-thermal transport model provides insight into carrier distributions, fields, and GFET power dissipation. The hot spot corresponds to the location of minimum charge density along the GFET; by changing the applied bias this can be shifted between electrodes or held in the middle of the channel in ambipolar transport. Interestingly, the hot spot shape bears the imprint of the density of states in mono- vs. bilayer graphene. More broadly, we find that thermal imaging combined with self-consistent simulation provides a non-invasive approach for more deeply examining transport and energy dissipation in nanoscale devices.

We demonstrate a simple but efficient design for forming tunable single, double and triple quantum dots (QDs) in a sub-μm-long carbon nanotube (CNT) with two major features that distinguish this design from that of traditional CNT QDs: the use of i) Al2Ox tunnelling barriers between the CNT and metal contacts and ii) local side gates for controlling both the height of the potential barrier and the electron-confining potential profile to define multiple QDs. In a serial triple QD, in particular, we find that a stable molecular coupling state exists between two distant outer QDs. This state manifests in anti-crossing charging lines that correspond to electron and hole triple points for the outer QDs. The observed results are also reproduced in calculations based on a capacitive interaction model with reasonable configurations of electrons in the QDs. Our design using artificial tunnel contacts and local side gates provides a simple means of creating multiple QDs in CNTs for future quantum-engineering applications.

We report pseudodielectric function data ⟨e⟩ = ⟨e1⟩ + i⟨e2⟩ from 0.74 to 6.48 eV of oxide-free AlAsSb alloys that are the closest representation to date of the intrinsic bulk dielectric response e of the material. Measurements were performed on 1.3 μm thick films grown on (001) GaAs substrates by molecular beam epitaxy. Data were obtained with the films in situ to avoid oxidation artifacts. Critical-point structures were identified by band-structure calculations done with the linear augmented Slater-type orbital method. Crossings of transitions at the Γ- and X-points and the Γ- and L-points with composition were observed.