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1.
Nano Lett ; 23(1): 319-325, 2023 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-36580275

RESUMO

Logic-in-memory (LIM) has emerged as an energy-efficient computing technology, as it integrates logic and memory operations in a single device architecture. Herein, a concept of ternary LIM is established. First, a p-type 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) transistor is combined with an n-type PhC2H4-benzo[de]isoquinolino[1,8-gh]quinolone diimide (PhC2-BQQDI) transistor to obtain a binary memory inverter, in which a zinc phthalocyanine-cored polystyrene (ZnPc-PS4) layer serves as a floating gate. The contrasting photoresponse of the transistors toward visible and ultraviolet light and the efficient hole-trapping ability of ZnPc-PS4 enable us to achieve an optically controllable memory operation with a high memory window of 18 V. Then, a ternary memory inverter is developed using an anti-ambipolar transistor to achieve a three-level data processing and storage system for more advanced LIM applications. Finally, low-voltage operation of the devices is achieved by employing a high-k dielectric layer, which highlights the potential of the developed LIM units for next-generation low-power electronics.


Assuntos
Eletrônica , Indóis , Poliestirenos , Raios Ultravioleta
2.
Adv Mater ; 34(30): e2201277, 2022 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-35637610

RESUMO

Organic antiambipolar transistors (AATs) have partially overlapped p-n junctions. At room temperature, this p-n junction induces a negative differential transconductance in an AAT. However, the detailed carrier-transport mechanism remains unclear. Herein, an operando photoemission electron microscopy is used to tackle this issue owing to the technique's ability to visualize conductive electrons in real time during transistor operation. Notably, it is observed that when the AAT is on, a depletion layer forms at the lateral p-n junction. The visualized depletion layer shows that both p- and n-type channels have pinch-off states in the gate voltage range when the AAT is in on state. The steep potential gradient at the lateral p-n interface enhances the electron conduction from n-type to p-type semiconductor. Another significant finding is that most electrons are considered to recombine with the accumulated holes in the p-type semiconductor, affording the reduction of photoemission intensity by ≈80%. This technique provides a thorough understanding of carrier transport in AATs, further improving the device performance.

3.
Adv Mater ; 34(15): e2109491, 2022 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-35146811

RESUMO

Electrically reconfigurable organic logic circuits are promising candidates for realizing new computation architectures, such as artificial intelligence and neuromorphic devices. In this study, multiple logic gate operations are attained based on a dual-gate organic antiambipolar transistor (DG-OAAT). The transistor exhibits a Λ-shaped transfer curve, namely, a negative differential transconductance at room temperature. It is important to note that the peak voltage of the drain current is precisely tuned by three input signals: bottom-gate, top-gate, and drain voltages. This distinctive feature enables multiple logic gate operations with "only a single DG-OAAT," which are not obtainable in conventional transistors. Five logic gate operations, which correspond to AND, OR, NAND, NOR, and XOR, are demonstrated by adjusting the bottom-gate and top-gate voltages. Moreover, varying the drain voltage makes it possible to reversibly switch two logic gates, e.g., NAND/NOR and OR/XOR. In addition, the DG-OAATs show a high degree of stability and reliability. The logic gate operations are observed even months later. The hysteresis in the transfer curves is also negligible. Thus, the device concept is promising for realizing multifunctional logic circuits with a simple transistor configuration. Hence, these findings are expected to surpass the current limitations in complementary metal-oxide-semiconductor devices.

4.
Nanoscale ; 13(9): 4978-4984, 2021 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-33634301

RESUMO

We examined the modified electronic structure and single-carrier transport of individual hybrid core-shell metal-semiconductor Au-ZnS quantum dots (QDs) using a scanning tunnelling microscope. Nearly monodisperse ultra-small QDs are achieved by a facile wet chemical route. The exact energy structures are evaluated by scanning tunnelling spectroscopy (STS) measurements at 300 mK for the individual nanoobjects starting from the main building block Au nanocrystals (NCs) to the final Au-ZnS QDs. The study divulges the evolution of the energy structure and the charge transport from the single metallic building block core to the core-shell metal-semiconductor QDs. Furthermore, we successfully determined the contributions related to the quantum-confinement-induced excitonic band structure of the ZnS nano-shell and the charging energy of the system by applying a semi-empirical approach considering a double barrier tunnel junction (DBTJ) arrangement. We detect strong conductance peaks in Au-ZnS QDs due to the overlapping of the energy structure of the Au nano-core and the discrete energy states of the semiconductor ZnS nano-shell. Our findings will help in understanding the electronic properties of metal-semiconductor QDs. The outcomes therefore have the potential to fabricate tailored metal-semiconductor QDs for single-electron devices.

5.
ACS Appl Mater Interfaces ; 13(36): 43030-43038, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34463490

RESUMO

Using a single-device two-dimensional (2D) rhenium disulfide (ReS2) field-effect transistor (FET) with enhanced gas species selectivity by light illumination, we reported a selective and sensitive detection of volatile organic compound (VOC) gases. 2D materials have the advantage of a high surface-area-to-volume ratio for high sensitivity to molecules attached to the surface and tunable carrier concentration through field-effect control from the back-gate of the channel, while keeping the top surface open to the air for chemical sensing. In addition to these advantages, ReS2 has a direct band gap also in multilayer cases, which sets it apart from other transition-metal dichalcogenides (TMDCs). We take advantage of the effective response of ReS2 to light illumination to improve the selectivity and gas-sensing efficiency of a ReS2-FET device. We found that light illumination modulates the drain current response in a ReS2-FET to adsorbed molecules, and the sensing activity differs depending on the gas species used, such as acetone, ethanol, and methanol. Furthermore, wavelength and carrier density rely on certain variations in light-modulated sensing behaviors for each chemical. The device will distinguish the gas concentration in a mixture of VOCs using the differences induced by light illumination, enhancing the selectivity of the sensor device. Our results shed new light on the sensing technologies for realizing a large-scale sensor network in the Internet-of-Things era.

6.
Sci Rep ; 11(1): 18845, 2021 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-34552168

RESUMO

We report on magnetotransport in a high-quality graphene device, which is based on monolayer graphene (Gr) encapsulated by hexagonal boron nitride (hBN) layers, i.e., hBN/Gr/hBN stacks. In the vicinity of the Dirac point, a negative magnetoconductance is observed for high temperatures > ~ 40 K, whereas it becomes positive for low temperatures ≤ ~ 40 K, which implies an interplay of quantum interferences in Dirac materials. The elastic scattering mechanism in hBN/Gr/hBN stacks contrasts with that of conventional graphene on SiO2, and our ultra-clean graphene device shows nonzero magnetoconductance for high temperatures of up to 300 K.

7.
Commun Chem ; 4(1): 29, 2021 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-36697553

RESUMO

Acenes and azaacenes lie at the core of molecular materials' applications due to their important optical and electronic features. A critical aspect is provided by their heteroatom multiplicity, which can strongly affect their properties. Here we report pyrazinacenes containing the dihydro-decaazapentacene and dihydro-octaazatetracene chromophores and compare their properties/functions as a model case at an oxidizing metal substrate. We find a distinguished, oxidation-state-dependent conformational adaptation and self-assembly behaviour and discuss the analogies and differences of planar benzo-substituted decaazapentacene and octaazatetracene forms. Our broad experimental and theoretical study reveals that decaazapentacene is stable against oxidation but unstable against reduction, which is in contrast to pentacene, its C-H only analogue. Decaazapentacenes studied here combine a planar molecular backbone with conformationally flexible substituents. They provide a rich model case to understand the properties of a redox-switchable π-electronic system in solution and at interfaces. Pyrazinacenes represent an unusual class of redox-active chromophores.

8.
Nano Lett ; 20(4): 2551-2557, 2020 Apr 08.
Artigo em Inglês | MEDLINE | ID: mdl-32186384

RESUMO

Graphene/hexagonal boron nitride (hBN) moiré superlattices have attracted interest for use in the study of many-body effects and fractal physics in Dirac fermion systems. Many exotic transport properties have been intensively examined in such superlattices, but previous studies have not focused on single-carrier transport. The investigation of the single-carrier behavior in these superlattices would lead to an understanding of the transition of single-particle/correlated phenomena. Here, we show the single-carrier transport in a high-quality bilayer graphene/hBN superlattice-based quantum dot device. We demonstrate remarkable device controllability in the energy range near the charge neutrality point (CNP) and the hole-side satellite point. Under a perpendicular magnetic field, Coulomb oscillations disappear near the CNP, which could be a signature of the crossover between Coulomb blockade and quantum Hall regimes. Our results pave the way for exploring the relationship of single-electron transport and fractal quantum Hall effects with correlated phenomena in two-dimensional quantum materials.

9.
ACS Appl Mater Interfaces ; 12(7): 8533-8538, 2020 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-32027115

RESUMO

Bubbles at the interface of two-dimensional layered materials in van der Waals heterostructures cause deterioration in the quality of materials, thereby limiting the size and design of devices. In this paper, we report a simple all-dry transfer technique, with which the bubble formation can be avoided. As a key factor in the technique, a contact angle between a picked-up flake on a viscoelastic polymer stamp and another flake on a substrate was introduced by protrusion at the stamp surface. Using this technique, we demonstrated the fabrication of high-quality devices on the basis of graphene/hexagonal boron nitride heterostructures with a large bubble-free region. Additionally, the technique can be used to remove unnecessary flakes on a substrate under an optical microscopic scale. Most importantly, it improves the yield and throughput for the fabrication process of high-quality van der Waals heterostructure-based devices.

10.
ACS Appl Mater Interfaces ; 11(50): 47635-47641, 2019 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-31769645

RESUMO

An innovative novel interface has been designed and developed to be used as a potential active layer in chemically sensitive field-effect transistor (Chem-FET) sensor devices for the specific sensing of Cs+. In this study, the synthesis of a specific Cs+ probe based on calix[4]arene benzocrown ether, its photophysical properties, and its grafting onto a single lipid monolayer (SLM) recently used as an efficient ultrathin organic dielectric in Chem-FETs are reported simultaneously. On the basis of both optical and NMR titration experiments, the probe has shown high selectivity and specificity for Cs+ compared to interfering cations, even if an admixture is used. Additionally, Attenuated Total Reflectance Fourier Transform Infra Red (ATR-FTIR) spectroscopy was successfully used to characterize and prove the efficient grafting of the probe onto a SLM and the formation of the innovative novel sensing layer.

11.
ACS Appl Mater Interfaces ; 11(40): 36871-36879, 2019 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-31525896

RESUMO

Phase-transition field-effect transistors (FETs) are a class of steep-slope devices that show abrupt on/off switching owing to the metal-insulator transition (MIT) induced in the contacting materials. An important avenue to develop phase-transition FETs is to understand the charge injection mechanism at the junction of the contacting MIT materials and semiconductor channels. Here, toward the realization of high-performance phase-transition FETs, we investigate the contact properties of heterojunctions between semiconducting transition-metal dichalcogenides (TMDCs) and vanadium dioxide (VO2) that undergoes a MIT at a critical temperature (Tc) of approximately 340 K. We fabricated transistors based on molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) in contact with the VO2 source/drain electrodes. The VO2-contacted MoS2 transistor exhibited n-type transport both below and above Tc. Across the MIT, the on-current was observed to increase only by a factor of 5, in contrast to the order-of-magnitude change in the resistance of the VO2 electrodes, suggesting the existence of high contact resistance. The Arrhenius analyses of the gate-dependent drain current confirmed the formation of the interfacial barrier at the VO2/MoS2 contacts, irrespective of the phase state of VO2. The VO2-contacted WSe2 transistor showed ambipolar transport, indicating that the Fermi level lies near the mid gap of WSe2. These observations provide insights into the contact properties of phase-transition FETs based on VO2 and TMDCs and suggest the need for contact engineering for high-performance operations.

12.
ACS Omega ; 4(5): 8669-8673, 2019 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-31459956

RESUMO

Highly oriented, multilayer molecular films of picene and dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) molecules with the long axis parallel to the substrate (parallel configuration, hereafter) were fabricated on their characteristic bulklike monolayer. These molecules form a dense monolayer with a bulklike molecular arrangement on metal surfaces such as Au(111), which allows further stacking of parallel molecules. Indeed, upon adsorption of picene and DNTT on these dense monolayers, growth of straight islands of multilayer without the dendritic layer was observed. Particularly, in the case of picene, one-dimensional islands with lengths over 100 µm were formed and aligned in 3-fold symmetric directions of the substrate, which was not observed in the case of DNTT. X-ray diffraction measurements revealed the presence of [201̅] and [211̅] planes and the absence of the [001] diffractions, indicating that the one-dimensional islands of picene indeed consist of parallel molecules. The formation of huge crystalline islands in the case of picene, in contrast to the case of DNTT, is likely induced by the stronger intermolecular force, as suggested from the calculation of the vibrational energy.

13.
Sci Rep ; 9(1): 3031, 2019 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-30816251

RESUMO

We report on the observation of quantum transport and interference in a graphene device that is attached with a pair of split gates to form an electrostatically-defined quantum point contact (QPC). In the low magnetic field regime, the resistance exhibited Fabry-Pérot (FP) resonances due to np'n(pn'p) cavities formed by the top gate. In the quantum Hall (QH) regime with a high magnetic field, the edge states governed the phenomena, presenting a unique condition where the edge channels of electrons and holes along a p-n junction acted as a solid-state analogue of a monochromatic light beam. We observed a crossover from the FP to QH regimes in ballistic graphene QPC under a magnetic field with varying temperatures. In particular, the collapse of the QH effect was elucidated as the magnetic field was decreased. Our high-mobility graphene device enabled observation of such quantum coherence effects up to several tens of kelvins. The presented device could serve as one of the key elements in future electronic quantum optic devices.

14.
Nano Lett ; 18(7): 4355-4359, 2018 07 11.
Artigo em Inglês | MEDLINE | ID: mdl-29961329

RESUMO

Multivalued logic circuits, which can handle more information than conventional binary logic circuits, have attracted much attention as a promising way to improve the data-processing capabilities of integrated circuits. In this study, we developed a ternary inverter based on organic field-effect transistors (OFET) as a potential component of high-performance and flexible integrated circuits. Key elements are anti-ambipolar and n-type OFETs connected in series. First, we demonstrate an organic ternary inverter that exhibits three distinct logic states. Second, the operating voltage was greatly reduced by taking advantage of an Al2O3 gate dielectric. Finally, the operating voltage was finely tuned by the designing of the device geometry. These results are achievable owing to the flexible controllability of the device configuration, suggesting that the organic ternary inverter plays an important role with regard to high-performance organic integrated circuits.

15.
ACS Appl Mater Interfaces ; 10(3): 2762-2767, 2018 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-29277988

RESUMO

The main purpose of this study is to establish a guideline for controlling the device properties of organic antiambipolar transistors. Our key strategy is to use interface engineering to promote carrier injection at channel/electrode interfaces and carrier accumulation at a channel/dielectric interface. The effective use of carrier injection interlayers and an insulator layer with a high dielectric constant (high-k) enabled the fine tuning of device parameters and, in particular, the onset (Von) and offset (Voff) voltages. A well-matched combination of the interlayers and a high-k dielectric layer achieved a low peak voltage (0.25 V) and a narrow on-state bias range (2.2 V), indicating that organic antiambipolar transistors have high potential as negative differential resistance devices for multivalued logic circuits.

16.
Nanoscale ; 9(31): 11297-11302, 2017 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-28761943

RESUMO

Quantum molecular devices have a potential for the construction of new data processing architectures that cannot be achieved using current complementary metal-oxide-semiconductor (CMOS) technology. The relevant basic quantum transport properties have been examined by specific methods such as scanning probe and break-junction techniques. However, these methodologies are not compatible with current CMOS applications, and the development of practical molecular devices remains a persistent challenge. Here, we demonstrate a new vertical resonant tunneling transistor for large-scale integration. The transistor channel is comprised of a MOS structure with C60 molecules as quantum dots, and the structure behaves like a double tunnel junction. Notably, the transistors enabled the observation of stepwise drain currents, which originated from resonant tunneling via the discrete molecular orbitals. Applying side-gate voltages produced depletion layers in Si substrates, to achieve effective modulation of the drain currents and obvious peak shifts in the differential conductance curves. Our device configuration thus provides a promising means of integrating molecular functions into future CMOS applications.

17.
Nano Lett ; 16(12): 7474-7480, 2016 12 14.
Artigo em Inglês | MEDLINE | ID: mdl-27960497

RESUMO

Optical switching organic field-effect transistors (OFETs) provide a new direction for optoelectronics based on photochromic molecules. However, the patterning of OFETs is difficult because conventional fabrication processes, including lithography and ion etching, inevitably cause severe damage to organic molecules. Here, we demonstrate laser patterning of one-dimensional (1D) channels on an OFET with a photochromic diarylethene (DAE) layer. The main findings are (i) a number of 1D channels can be repeatedly written and erased in the DAE layer by scanning focused ultraviolet and visible light laser beams alternately between the source and drain electrodes, (ii) the conductivity (or resistivity) of the 1D channel can be controlled by the illumination conditions, such as the laser power density and the scan speed, and (iii) it is possible to draw an analogue adder circuit by optically writing 1D channels so that a portion of the channels overlaps and to perform optical summing operations by local laser illumination of the respective channels. These findings will open new possibilities for realizing various optically reconfigurable, low-dimensional organic transistor circuits, which are not possible with conventional thin film OFETs.

18.
ACS Nano ; 10(9): 9000-8, 2016 09 27.
Artigo em Inglês | MEDLINE | ID: mdl-27548516

RESUMO

Contributing to the need for new graphene nanoribbon (GNR) structures that can be synthesized with atomic precision, we have designed a reactant that renders chiral (3,1)-GNRs after a multistep reaction including Ullmann coupling and cyclodehydrogenation. The nanoribbon synthesis has been successfully proven on different coinage metals, and the formation process, together with the fingerprints associated with each reaction step, has been studied by combining scanning tunneling microscopy, core-level spectroscopy, and density functional calculations. In addition to the GNR's chiral edge structure, the substantial GNR lengths achieved and the low processing temperature required to complete the reaction grant this reactant extremely interesting properties for potential applications.

19.
Nat Commun ; 7: 10609, 2016 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-26881966

RESUMO

Future one-dimensional electronics require single-crystalline semiconductor free-standing nanorods grown with uniform electrical properties. However, this is currently unrealistic as each crystallographic plane of a nanorod grows at unique incorporation rates of environmental dopants, which forms axial and lateral growth sectors with different carrier concentrations. Here we propose a series of techniques that micro-sample a free-standing nanorod of interest, fabricate its arbitrary cross-sections by controlling focused ion beam incidence orientation, and visualize its internal carrier concentration map. ZnO nanorods are grown by selective area homoepitaxy in precursor aqueous solution, each of which has a (0001):+c top-plane and six {1-100}:m side-planes. Near-band-edge cathodoluminescence nanospectroscopy evaluates carrier concentration map within a nanorod at high spatial resolution (60 nm) and high sensitivity. It also visualizes +c and m growth sectors at arbitrary nanorod cross-section and history of local transient growth events within each growth sector. Our technique paves the way for well-defined bottom-up nanoelectronics.

20.
ACS Nano ; 9(3): 2989-3001, 2015 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-25689728

RESUMO

Modern field-effect transistors or laser diodes take advantages of band-edge structures engineered by large uniaxial strain εzz, available up to an elasticity limit at a rate of band-gap deformation potential azz (= dEg/dεzz). However, contrary to aP values under hydrostatic pressure, there is no quantitative consensus on azz values under uniaxial tensile, compressive, and bending stress. This makes band-edge engineering inefficient. Here we propose SEM-cathodoluminescence nanospectroscopy under in situ nanomanipulation (Nanoprobe-CL). An apex of a c-axis-oriented free-standing ZnO nanorod (NR) is deflected by point-loading of bending stress, where local uniaxial strain (εcc = r/R) and its gradient across a NR (dεcc/dr = R(-1)) are controlled by a NR local curvature (R(-1)). The NR elasticity limit is evaluated sequentially (εcc = 0.04) from SEM observation of a NR bending deformation cycle. An electron beam is focused on several spots crossing a bent NR, and at each spot the local Eg is evaluated from near-band-edge CL emission energy. Uniaxial acc (= dEg/dεcc) is evaluated at regulated surface depth, and the impact of R(-1) on observed acc is investigated. The acc converges with -1.7 eV to the R(-1) = 0 limit, whereas it quenches with increasing R(-1), which is attributed to free-exciton drift under transversal band-gap gradient. Surface-sensitive CL measurements suggest that a discrepancy from bulk acc = -4 eV may originate from strain relaxation at the side surface under uniaxial stress. The nanoprobe-CL technique reveals an Eg(εij) response to specific strain tensor εij (i, j = x, y, z) and strain-gradient effects on a minority carrier population, enabling simulations and strain-dependent measurements of nanodevices with various structures.

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