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2.
Nature ; 573(7775): 507-518, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31554977

RESUMO

The development of silicon semiconductor technology has produced breakthroughs in electronics-from the microprocessor in the late 1960s to early 1970s, to automation, computers and smartphones-by downscaling the physical size of devices and wires to the nanometre regime. Now, graphene and related two-dimensional (2D) materials offer prospects of unprecedented advances in device performance at the atomic limit, and a synergistic combination of 2D materials with silicon chips promises a heterogeneous platform to deliver massively enhanced potential based on silicon technology. Integration is achieved via three-dimensional monolithic construction of multifunctional high-rise 2D silicon chips, enabling enhanced performance by exploiting the vertical direction and the functional diversification of the silicon platform for applications in opto-electronics and sensing. Here we review the opportunities, progress and challenges of integrating atomically thin materials with silicon-based nanosystems, and also consider the prospects for computational and non-computational applications.

3.
Sci Rep ; 9(1): 6147, 2019 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-30992498

RESUMO

A pressing challenge in engineering devices with topological insulators (TIs) is that electron transport is dominated by the bulk conductance, and so dissipationless surface states account for only a small fraction of the conductance. Enhancing the surface-to-volume ratio is a common method to enhance the relative contribution of such states. In thin films with reduced thickness, the confinement results in symmetry-breaking and is critical for the experimental observation of topologically protected surface states. We employ micro-Raman and tip-enhanced Raman spectroscopy to examine three different mechanisms of symmetry breaking in Bi2Te3 TI thin films: surface plasmon generation, charge transfer, and application of a periodic strain potential. These mechanisms are facilitated by semiconducting and insulating substrates that modify the electronic and mechanical conditions at the sample surface and alter the long-range interactions between Bi2Te3 and the substrate. We confirm the symmetry breaking in Bi2Te3 via the emergence of the Raman-forbidden [Formula: see text] mode. Our results suggest that topological surface states can exist at the Bi2Te3/substrate interface, which is in a good agreement with previous theoretical results predicting the tunability of the vertical location of helical surface states in TI/substrate heterostructures.

4.
Nano Lett ; 19(3): 1976-1981, 2019 03 13.
Artigo em Inglês | MEDLINE | ID: mdl-30779591

RESUMO

The vertical stacking of van der Waals (vdW) materials introduces a new degree of freedom to the research of two-dimensional (2D) systems. The interlayer coupling strongly influences the band structure of the heterostructures, resulting in novel properties that can be utilized for electronic and optoelectronic applications. Based on microwave microscopy studies, we report quantitative electrical imaging on gated molybdenum disulfide (MoS2)/tungsten diselenide (WSe2) heterostructure devices, which exhibit an intriguing antiambipolar effect in their transfer characteristics. Interestingly, in the region with significant source-drain current, electrons in the n-type MoS2 and holes in the p-type WSe2 segments are nearly balanced, whereas the heterostructure area is depleted of mobile charges. The spatial evolution of local conductance can be ascribed to the lateral band bending and formation of depletion regions along the line of MoS2-heterostructure-WSe2. Our work vividly demonstrates the microscopic origin of novel transport behaviors, which is important for the vibrant field of vdW heterojunction research.

5.
Adv Mater ; 31(15): e1806790, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30773734

RESUMO

2D materials have attracted much interest over the past decade in nanoelectronics. However, it was believed that the atomically thin layered materials are not able to show memristive effect in vertically stacked structure, until the recent discovery of monolayer transition metal dichalcogenide (TMD) atomristors, overcoming the scaling limit to sub-nanometer. Herein, the nonvolatile resistance switching (NVRS) phenomenon in monolayer hexagonal boron nitride (h-BN), a typical 2D insulator, is reported. The h-BN atomristors are studied using different electrodes and structures, featuring forming-free switching in both unipolar and bipolar operations, with large on/off ratio (up to 107 ). Moreover, fast switching speed (<15 ns) is demonstrated via pulse operation. Compared with monolayer TMDs, the one-atom-thin h-BN sheet reduces the vertical scaling to ≈0.33 nm, representing a record thickness for memory materials. Simulation results based on ab-initio method reveal that substitution of metal ions into h-BN vacancies during electrical switching is a likely mechanism. The existence of NVRS in monolayer h-BN indicates fruitful interactions between defects, metal ions and interfaces, and can advance emerging applications on ultrathin flexible memory, printed electronics, neuromorphic computing, and radio frequency switches.

6.
Nanotechnology ; 30(23): 235602, 2019 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-30780133

RESUMO

Monolayer graphene is commonly grown on Cu substrates due to the self-limiting nature of graphene synthesis by chemical vapor deposition (CVD). Consequently, the growth of multilayer graphene by CVD has proven to be relatively difficult. This study demonstrates that the number of layers in graphene synthesized on a copper substrate can be precisely set by controlling the partial pressure of hydrogen gas used in the CVD process. This study also shows that a pressure threshold exists for a distinct transition from monolayer to multilayer graphene growth. This threshold is shown to be the boundary where the graphene growth process on Cu by CVD is no longer a self-limiting process. In addition, the multilayer graphene synthesized through the pressure control method forms in the Volmer-Weber mode with an AB stacking structure.

7.
ACS Nano ; 12(12): 12512-12522, 2018 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-30507160

RESUMO

Few-layer black phosphorus (BP) with an in-plane puckered crystalline structure has attracted intense interest for strain engineering due to both its significant anisotropy in mechanical and electrical properties and its high intrinsic strain limit. Here, we investigated the phonon response of few layer BP under uniaxial tensile strain (∼7%) with in situ polarized Raman spectroscopy. Together with the first-principles density functional theory (DFT) analysis, the anisotropic Poisson's ratio in few-layer BP was verified as one of the primary factors that caused the large discrepancy in the trend of reported Raman frequency shift for strained BP, armchair (AC) direction in particular. By carefully including and excluding the anisotropic Poisson's ratio in the DFT emulations, we rebuilt both trends reported for Raman mode shifts. Furthermore, the angle-resolved Raman spectroscopy was conducted in situ under tensile strain for systematic investigation of the in-plane anisotropy of BP phonon response. The experimentally observed thickness and crystallographic orientation dependence is elaborated using DFT theory as having a strong correlation between the strain-perturbated electronic-band structure and the phonon vibration modes. This study provides insight, both experimentally and theoretically, for the complex electron-phonon interaction behavior in strained BP, which enables diverse possibilities for the strain engineering of electrical and optical properties in BP and similar two-dimensional nanomaterials.

8.
ACS Appl Mater Interfaces ; 10(44): 38280-38286, 2018 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-30360043

RESUMO

Over the past decades, organic field-effect transistor (OFET) gas sensors have maintained a rapid development. However, the majority of OFET gas sensors show insufficient detection capability towards oxidizing gases such as nitrogen oxide, compared with the inorganic counterpart. In this paper, a new strategy of OFET nitrogen dioxide (NO2) gas sensor, consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(9-vinylcarbazole) (PVK) blend, is reported. Depending on the gate voltage, this sensor can operate in two modes at room temperature. Of the two modes exposed to NO2 for 5 min, when the gate voltage is 0 V, the highest NO2 responsivity of this OFET is >20 000% for 30 ppm (≈700% for 600 ppb) with the 1:1 P3HT/PVK blend, it is ≈40 times greater than that with the pure P3HT. The limit of detection of ≈300 ppb is achieved, and there is still room for improvement. While in the condition of -40 V, the response increases by 15 times than that with the pure P3HT. This is the first attempt to improve the OFET sensing performance using PVK, which usually functions as a hole-transport layer in the light- emitting device. The enhancement of sensing performance is attributed to the aggregation-controlling and hole-transporting/electron-blocking effect of PVK. This work demonstrates that the hole-transport material can be applied to improve the NO2 sensor with simple solution process, which expands the material choice of OFET gas sensors.

9.
ACS Nano ; 12(10): 10383-10392, 2018 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-30226980

RESUMO

Optical manipulation of colloidal nanoparticles and molecules is significant in numerous fields. Opto-thermoelectric nanotweezers exploiting multiple coupling among light, heat, and electric fields enables the low-power optical trapping of nanoparticles on a plasmonic substrate. However, the management of light-to-heat conversion for the versatile and precise manipulation of nanoparticles is still elusive. Herein, we explore the opto-thermoelectric trapping at plasmonic antennas that serve as optothermal nanoradiators to achieve the low-power (∼0.08 mW/µm2) and deterministic manipulation of nanoparticles. Specifically, precise optical manipulation of nanoparticles is achieved via optical control of the subwavelength thermal hot spots. We employ a femtosecond laser beam to further improve the heat localization and the precise trapping of single ∼30 nm semiconductor quantum dots at the antennas where the plasmon-exciton coupling can be tuned. With its low-power, precise, and versatile particle control, the opto-thermoelectric manipulation can have applications in photonics, life sciences, and colloidal sciences.

10.
Chem Soc Rev ; 47(16): 6370-6387, 2018 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-30065980

RESUMO

Silicene, the ultimate scaling of a silicon atomic sheet in a buckled honeycomb lattice, represents a monoelemental class of two-dimensional (2D) materials similar to graphene but with unique potential for a host of exotic electronic properties. Nonetheless, there is a lack of experimental studies largely due to the interplay between material degradation and process portability issues. This review highlights the state-of-the-art experimental progress and future opportunities in the synthesis, characterization, stabilization, processing and experimental device examples of monolayer silicene and its derivatives. The electrostatic characteristics of the Ag-removal silicene field-effect transistor exhibit ambipolar charge transport, corroborating with theoretical predictions on Dirac fermions and Dirac cone in the band structure. The electronic structure of silicene is expected to be sensitive to substrate interaction, surface chemistry, and spin-orbit coupling, holding great promise for a variety of novel applications, such as topological bits, quantum sensing, and energy devices. Moreover, the unique allotropic affinity of silicene with single-crystalline bulk silicon suggests a more direct path for the integration with or revolution to ubiquitous semiconductor technology. Both the materials and process aspects of silicene research also provide transferable knowledge to other Xenes like stanene, germanene, phosphorene, and so forth.

11.
Nat Commun ; 9(1): 2524, 2018 06 28.
Artigo em Inglês | MEDLINE | ID: mdl-29955064

RESUMO

Recently, non-volatile resistance switching or memristor (equivalently, atomristor in atomic layers) effect was discovered in transitional metal dichalcogenides (TMD) vertical devices. Owing to the monolayer-thin transport and high crystalline quality, ON-state resistances below 10 Ω are achievable, making MoS2 atomristors suitable as energy-efficient radio-frequency (RF) switches. MoS2 RF switches afford zero-hold voltage, hence, zero-static power dissipation, overcoming the limitation of transistor and mechanical switches. Furthermore, MoS2 switches are fully electronic and can be integrated on arbitrary substrates unlike phase-change RF switches. High-frequency results reveal that a key figure of merit, the cutoff frequency (fc), is about 10 THz for sub-µm2 switches with favorable scaling that can afford fc above 100 THz for nanoscale devices, exceeding the performance of contemporary switches that suffer from an area-invariant scaling. These results indicate a new electronic application of TMDs as non-volatile switches for communication platforms, including mobile systems, low-power internet-of-things, and THz beam steering.

12.
Adv Mater ; : e1704749, 2018 May 11.
Artigo em Inglês | MEDLINE | ID: mdl-29749007

RESUMO

From a fundamental science perspective, black phosphorus (BP) is a canonical example of a material that possesses fascinating surface and electronic properties. It has extraordinary in-plane anisotropic electrical, optical, and vibrational states, as well as a tunable band gap. However, instability of the surface due to chemical degradation in ambient conditions remains a major impediment to its prospective applications. Early studies were limited by the degradation of black phosphorous surfaces in air. Recently, several robust strategies have been developed to mitigate these issues, and these novel developments can potentially allow researchers to exploit the extraordinary properties of this material and devices made out of it. Here, the fundamental chemistry of BP degradation and the tremendous progress made to address this issue are extensively reviewed. Device performances of encapsulated BP are also compared with nonencapsulated BP. In addition, BP possesses sensitive anisotropic photophysical surface properties such as excitons, surface plasmons/phonons, and topologically protected and Dirac semi-metallic surface states. Ambient degradation as well as any passivation method used to protect the surface could affect the intrinsic surface properties of BP. These properties and the extent of their modifications by both the degradation and passivation are reviewed.

13.
ACS Appl Mater Interfaces ; 10(13): 11101-11107, 2018 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-29528211

RESUMO

Scanning thermal microscopy measurements reveal a significant thermal benefit of including a high thermal conductivity hexagonal boron nitride (h-BN) heat-spreading layer between graphene and either a SiO2/Si substrate or a 100 µm thick Corning flexible Willow glass (WG) substrate. At the same power density, an 80 nm thick h-BN layer on the silicon substrate can yield a factor of 2.2 reduction of the hot spot temperature, whereas a 35 nm thick h-BN layer on the WG substrate is sufficient to obtain a factor of 4.1 reduction. The larger effect of the h-BN heat spreader on WG than on SiO2/Si is attributed to a smaller effective heat transfer coefficient per unit area for three-dimensional heat conduction into the thick, low-thermal conductivity WG substrate than for one-dimensional heat conduction through the thin oxide layer on silicon. Consequently, the h-BN lateral heat-spreading length is much larger on WG than on SiO2/Si, resulting in a larger degree of temperature reduction.

14.
Nat Nanotechnol ; 13(1): 92, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-29317780
15.
Nano Lett ; 18(1): 434-441, 2018 01 10.
Artigo em Inglês | MEDLINE | ID: mdl-29236504

RESUMO

Recently, two-dimensional (2D) atomic sheets have inspired new ideas in nanoscience including topologically protected charge transport,1,2 spatially separated excitons,3 and strongly anisotropic heat transport.4 Here, we report the intriguing observation of stable nonvolatile resistance switching (NVRS) in single-layer atomic sheets sandwiched between metal electrodes. NVRS is observed in the prototypical semiconducting (MX2, M = Mo, W; and X = S, Se) transitional metal dichalcogenides (TMDs),5 which alludes to the universality of this phenomenon in TMD monolayers and offers forming-free switching. This observation of NVRS phenomenon, widely attributed to ionic diffusion, filament, and interfacial redox in bulk oxides and electrolytes,6-9 inspires new studies on defects, ion transport, and energetics at the sharp interfaces between atomically thin sheets and conducting electrodes. Our findings overturn the contemporary thinking that nonvolatile switching is not scalable to subnanometre owing to leakage currents.10 Emerging device concepts in nonvolatile flexible memory fabrics, and brain-inspired (neuromorphic) computing could benefit substantially from the wide 2D materials design space. A new major application, zero-static power radio frequency (RF) switching, is demonstrated with a monolayer switch operating to 50 GHz.

16.
ACS Omega ; 3(10): 13828-13836, 2018 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-31458081

RESUMO

Nowadays, photocatalysis has gained tremendous interest owing to the fact that it can overcome water crisis as well as the environmental issues by utilizing a major source of solar energy. The nanohybrid structures of Gd3+- and Sn4+-doped bismuth ferrite (Bi1-x Gd x Fe1-y Sn y ; BGFSO) with two-dimensional (2D) MXene sheets are synthesized by the coprecipitation method. The 2D sheets have a large surface area, incorporation of which into Bi1-x Gd x Fe1-y Sn y (BGFSO) nanoparticles provides a path for electrons to flow, which results in large recombination time and thus enhances dye degradation. The Bi0.90Gd0.10Fe0.80Sn0.20O3/MXene (BGFO-20Sn/MXene) nanohybrid shows 100% degradation of Congo dye from the catalytic solution in 120 min, which is highly efficient for industrial application.

17.
Nanoscale ; 9(37): 13947-13955, 2017 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-28782790

RESUMO

Resonance energy transfer (RET) from plasmonic metal nanoparticles (NPs) to two-dimensional (2D) materials enhances the performance of 2D optoelectronic devices and sensors. Herein, single-NP scattering spectroscopy is employed to investigate plasmon-trion and plasmon-exciton RET from single Au nanotriangles (AuNTs) to monolayer MoS2, at room temperature. The large quantum confinement and reduced dielectric screening in monolayer MoS2 facilitates efficient RET between single plasmonic metal NPs and the monolayer. Because of the large exciton binding energy of monolayer MoS2, charged excitons (i.e., trions) are observed at room temperature, which enable us to study the plasmon-trion interactions under ambient conditions. Tuning of plasmon-trion and plasmon-exciton RET is further achieved by controlling the dielectric constant of the medium surrounding the AuNT-MoS2 hybrids. Our observation of switchable plasmon-trion and plasmon-exciton RET inspires new applications of the hybrids of 2D materials and metal nanoparticles.

18.
ACS Nano ; 11(8): 7634-7641, 2017 08 22.
Artigo em Inglês | MEDLINE | ID: mdl-28719739

RESUMO

Tattoo-like epidermal sensors are an emerging class of truly wearable electronics, owing to their thinness and softness. While most of them are based on thin metal films, a silicon membrane, or nanoparticle-based printable inks, we report sub-micrometer thick, multimodal electronic tattoo sensors that are made of graphene. The graphene electronic tattoo (GET) is designed as filamentary serpentines and fabricated by a cost- and time-effective "wet transfer, dry patterning" method. It has a total thickness of 463 ± 30 nm, an optical transparency of ∼85%, and a stretchability of more than 40%. The GET can be directly laminated on human skin just like a temporary tattoo and can fully conform to the microscopic morphology of the surface of skin via just van der Waals forces. The open-mesh structure of the GET makes it breathable and its stiffness negligible. A bare GET is able to stay attached to skin for several hours without fracture or delamination. With liquid bandage coverage, a GET may stay functional on the skin for up to several days. As a dry electrode, GET-skin interface impedance is on par with medically used silver/silver-chloride (Ag/AgCl) gel electrodes, while offering superior comfort, mobility, and reliability. GET has been successfully applied to measure electrocardiogram (ECG), electromyogram (EMG), electroencephalogram (EEG), skin temperature, and skin hydration.

19.
Nat Nanotechnol ; 12(4): 287-288, 2017 04 06.
Artigo em Inglês | MEDLINE | ID: mdl-28383038
20.
Sci Rep ; 7(1): 1202, 2017 04 26.
Artigo em Inglês | MEDLINE | ID: mdl-28446781

RESUMO

This paper reports a 100% inkjet printed transistor with a short channel of approximately 1 µm with an operating speed up to 18.21 GHz. Printed electronics are a burgeoning area in electronics development, but are often stymied by the large minimum feature size. To combat this, techniques were developed to allow for the printings of much shorter transistor channels. The small gap size is achieved through the use of silver inks with different chemical properties to prevent mixing. The combination of the short channel and semiconducting carbon nanotubes (CNT) allows for an exceptional experimentally measured on/off ratio of 106. This all inkjet printed transistor allows for the fabrication of devices using roll-to-roll methodologies with no additional overhead compared to current state of the art production methods.

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