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1.
Nat Commun ; 11(1): 1205, 2020 03 05.
Artigo em Inglês | MEDLINE | ID: mdl-32139679

RESUMO

Since its invention in the 1960s, one of the most significant evolutions of metal-oxide-semiconductor field effect transistors (MOS-FETs) would be the three dimensionalized version that makes the semiconducting channel vertically wrapped by conformal gate electrodes, also recognized as FinFET. During the past decades, the width of fin (W[Formula: see text]) in FinFETs has shrunk from about 150 nm to a few nanometers. However, W[Formula: see text] seems to have been levelling off in recent years, owing to the limitation of lithography precision. Here, we show that by adapting a template-growth method, different types of mono-layered two-dimensional crystals are isolated in a vertical manner. Based on this, FinFETs with one atomic layer fin are obtained, with on/off ratios reaching [Formula: see text]. Our findings push the FinFET to the sub 1 nm fin-width limit, and may shed light on the next generation nanoelectronics for higher integration and lower power consumption.

2.
Adv Mater ; : e1907288, 2020 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-31977113

RESUMO

In a modern electronics system, charge-coupled devices and data storage devices are the two most indispensable components. Although there has been rapid and independent progress in their development during the last three decades, a cofunctionality of both sensing and memory at single-unit level is yet premature for flexible electronics. For wearable electronics that work in ultralow power conditions and involve strains, conventional sensing-and-memory systems suffer from low sensitivity and are not able to directly transform sensed information into sufficient memory. Here, a new transformative device is demonstrated, which is called "sen-memory", that exhibits the dual functionality of sensing and memory in a monolithic integrated circuit. The active channel of the device is formed by a carbon nanotube thin film and the floating gate is formed by a controllably oxidized aluminum nanoparticle array for electrical- and optical-programming. The device exhibits a high on-off current ratio of ≈106 , a long-term retention of ≈108 s, and durable flexibility at a bending strain of 0.4%. It is shown that the device senses a photogenerated pattern in seconds at zero bias and memorizes an image for a couple of years.

3.
Nat Commun ; 10(1): 2809, 2019 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-31243279

RESUMO

Large-area high-quality AB-stacked bilayer graphene films are highly desired for the applications in electronics, photonics and spintronics. However, the existing growth methods can only produce discontinuous bilayer graphene with variable stacking orders because of the non-uniform surface and strong potential field of the solid substrates used. Here we report the growth of wafer-scale continuous uniform AB-stacked bilayer graphene films on a liquid Pt3Si/solid Pt substrate by chemical vapor deposition. The films show quality, mechanical and electrical properties comparable to the mechanically exfoliated samples. Growth mechanism studies show that the second layer is grown underneath the first layer by precipitation of carbon atoms from the solid Pt, and the small energy requirements for the movements of graphene nucleus on the liquid Pt3Si enables the interlayer epitaxy to form energy-favorable AB stacking. This interlayer epitaxy also allows the growth of ABA-stacked trilayer graphene and is applicable to other liquid/solid substrates.

4.
Nat Commun ; 10(1): 2302, 2019 05 24.
Artigo em Inglês | MEDLINE | ID: mdl-31127105

RESUMO

Anisotropy in crystals arises from different lattice periodicity along different crystallographic directions, and is usually more pronounced in two dimensional (2D) materials. Indeed, in the emerging 2D materials, electrical anisotropy has been one of the recent research focuses. However, key understandings of the in-plane anisotropic resistance in low-symmetry 2D materials, as well as demonstrations of model devices taking advantage of it, have proven difficult. Here, we show that, in few-layered semiconducting GaTe, electrical conductivity anisotropy between x and y directions of the 2D crystal can be gate tuned from several fold to over 103. This effect is further demonstrated to yield an anisotropic non-volatile memory behavior in ultra-thin GaTe, when equipped with an architecture of van der Waals floating gate. Our findings of gate-tunable giant anisotropic resistance effect pave the way for potential applications in nanoelectronics such as multifunctional directional memories in the 2D limit.

5.
ACS Appl Mater Interfaces ; 11(19): 17629-17636, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-31026138

RESUMO

It is essentially important to synthesize uniform graphene films with a controlled number of layers because their properties strongly depend on the number of layers. Although chemical vapor deposition (CVD) on Cu has been widely used to synthesize large-area graphene films, the growth on solid and liquid Cu (L-Cu) suffers from poor thickness uniformity with a great number of adlayers and difficulty in forming continuous films even after a long growth time of hours, respectively. Here, we found that nonuniform graphene films initially grown on solid Cu (S-Cu) foil can rapidly transform into continuously uniform monolayer graphene film on L-Cu within 3 min. Moreover, the films obtained show larger grain size, higher quality, better optical and electrical properties, and better performance in organic light-emitting diode applications than the original films grown on S-Cu foil. By using carbon isotope labeling, we revealed that the multilayer-to-monolayer transition of graphene on L-Cu experiences etching-"self-aligning"-coalescence processes. This two-step CVD method not only opens up a new way for the rapid growth of uniform monolayer graphene films but also provides helpful information for the controlled growth of uniform monolayers of other 2D materials such as monolayer h-BN.

6.
ACS Appl Mater Interfaces ; 11(12): 11699-11705, 2019 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-30839190

RESUMO

Carbon nanotube (CNT) thin-film transistors are expected to be promising for use in flexible electronics including flexible and transparent integrated circuits and in wearable chemical and physical sensors and for driving the circuits of flexible display panels. However, current devices based on CNT channels suffer from poor performance uniformity and low manufacturing yield; therefore, they are still far from being practical. This is usually caused by nonuniform deposition of the semiconducting CNTs and the rough surface of flexible substrates. Here, we report CNT thin-film transistors (TFTs) driving a flexible 64 × 64 pixel active matrix light-emitting diode display (AMOLED) by improving the formation of uniform CNT films and developing a new pretreatment technique for flexible substrates. The achieved AMOLED has uniform brightness and a high yield of 99.93% in its 4096 pixels. More than 8000 TFTs with high-purity semiconducting CNTs as the channel material show an average on-off current ratio of ∼107 and a carrier mobility of 16 cm2 V-1 s-1. The standard deviations of the on-state current and the carrier mobility are 4.1 and 6.5%, respectively. Our result shows that the panel driven by high-purity semiconducting CNTs is a promising strategy for the development of next-generation flexible, large-area displays.

7.
Sci Adv ; 4(5): eaap9264, 2018 05.
Artigo em Inglês | MEDLINE | ID: mdl-29736413

RESUMO

Single-wall carbon nanotubes (SWCNTs) are ideal for fabricating transparent conductive films because of their small diameter, good optical and electrical properties, and excellent flexibility. However, a high intertube Schottky junction resistance, together with the existence of aggregated bundles of SWCNTs, leads to a degraded optoelectronic performance of the films. We report a network of isolated SWCNTs prepared by an injection floating catalyst chemical vapor deposition method, in which crossed SWCNTs are welded together by graphitic carbon. Pristine SWCNT films show a record low sheet resistance of 41 ohm □-1 at 90% transmittance for 550-nm light. After HNO3 treatment, the sheet resistance further decreases to 25 ohm □-1. Organic light-emitting diodes using this SWCNT film as anodes demonstrate a low turn-on voltage of 2.5 V, a high current efficiency of 75 cd A-1, and excellent flexibility. Investigation of isolated SWCNT-based field-effect transistors shows that the carbon-welded joints convert the Schottky contacts between metallic and semiconducting SWCNTs into near-ohmic ones, which significantly improves the conductivity of the transparent SWCNT network. Our work provides a new avenue of assembling individual SWCNTs into macroscopic thin films, which demonstrate great potential for use as transparent electrodes in various flexible electronics.

8.
Nat Commun ; 8(1): 970, 2017 10 17.
Artigo em Inglês | MEDLINE | ID: mdl-29042545

RESUMO

Atomically thin two-dimensional semiconducting materials integrated into van der Waals heterostructures have enabled architectures that hold great promise for next generation nanoelectronics. However, challenges still remain to enable their applications as compliant materials for integration in logic devices. Here, we devise a reverted stacking technique to intercalate a wrinkle-free boron nitride tunnel layer between MoS2 channel and source drain electrodes. Vertical tunnelling of electrons therefore makes it possible to suppress the Schottky barriers and Fermi level pinning, leading to homogeneous gate-control of the channel chemical potential across the bandgap edges. The observed features of ambipolar pn to np diode, which can be reversibly gate tuned, paves the way for future logic applications and high performance switches based on atomically thin semiconducting channel.Van der Waals heterostructures of atomically thin materials hold promise for nanoelectronics. Here, the authors demonstrate a reverted stacking fabrication method for heterostructures and devise a vertical tunnel-contacted MoS2 transistor, enabling gate tunable rectification and reversible pn to np diode behaviour.

9.
Adv Mater ; 29(29)2017 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-28585225

RESUMO

The ultrafast growth of high-quality uniform monolayer WSe2 is reported with a growth rate of ≈26 µm s-1 by chemical vapor deposition on reusable Au substrate, which is ≈2-3 orders of magnitude faster than those of most 2D transition metal dichalcogenides grown on nonmetal substrates. Such ultrafast growth allows for the fabrication of millimeter-size single-crystal WSe2 domains in ≈30 s and large-area continuous films in ≈60 s. Importantly, the ultrafast grown WSe2 shows excellent crystal quality and extraordinary electrical performance comparable to those of the mechanically exfoliated samples, with a high mobility up to ≈143 cm2 V-1 s-1 and ON/OFF ratio up to 9 × 106 at room temperature. Density functional theory calculations reveal that the ultrafast growth of WSe2 is due to the small energy barriers and exothermic characteristic for the diffusion and attachment of W and Se on the edges of WSe2 on Au substrate.

10.
Adv Mater ; 29(16)2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-28240393

RESUMO

Monolayer circular graphene platelets with a grain structure gradient in the radial direction are synthesized by chemical vapor deposition on immiscible W-Cu substrates. Because of the different interactions and growth behaviors of graphene on Cu and tungsten carbide, such substrates cause the formation of grain size and orientation gradients through the competition between Cu and tungsten carbide in graphene growth.

12.
Nat Commun ; 7: 11160, 2016 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-27025784

RESUMO

The growth of high-quality semiconducting single-wall carbon nanotubes with a narrow band-gap distribution is crucial for the fabrication of high-performance electronic devices. However, the single-wall carbon nanotubes grown from traditional metal catalysts usually have diversified structures and properties. Here we design and prepare an acorn-like, partially carbon-coated cobalt nanoparticle catalyst with a uniform size and structure by the thermal reduction of a [Co(CN)6](3-) precursor adsorbed on a self-assembled block copolymer nanodomain. The inner cobalt nanoparticle functions as active catalytic phase for carbon nanotube growth, whereas the outer carbon layer prevents the aggregation of cobalt nanoparticles and ensures a perpendicular growth mode. The grown single-wall carbon nanotubes have a very narrow diameter distribution centred at 1.7 nm and a high semiconducting content of >95%. These semiconducting single-wall carbon nanotubes have a very small band-gap difference of ∼0.08 eV and show excellent thin-film transistor performance.

13.
J Obstet Gynaecol Res ; 41(8): 1214-22, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-25913643

RESUMO

AIM: The aim of this study was to identify the incidence and risk factors of bacterial vaginosis among pregnant women. MATERIAL AND METHODS: Prospective data from a cohort of 668 pregnant women were used to identify potential risk factors for bacterial vaginosis during pregnancy by Cox proportional hazards regression. RESULTS: A total of 204 incident cases of bacterial vaginosis were diagnosed in 274.8 woman-years of follow-up. The bacterial vaginosis incidence rate was 0.74 per 1 woman-year and median prevalence during follow-up was 15.6%. In the adjusted model, changing underwear nearly everyday, miscarriage history, urinary tract infection during follow-up, husbands' education level, and concurrent trichomoniasis and candidiasis remained significantly associated with bacterial vaginosis (adjusted hazard ratio and 95% confidence interval were 1.87 [1.26-2.77]; 2.96 [1.96-4.47]; 2.41 [1.05-5.49]; 0.50 [0.32-0.77]; 1.82 [1.02-3.25]; 1.88 [1.30-2.70], respectively). CONCLUSION: Bacterial vaginosis during pregnancy can be affected by many factors, and some are indirectly acting factors. Further prospective studies that include a larger sample size and more information on the development of bacterial vaginosis are needed.


Assuntos
Complicações Infecciosas na Gravidez/epidemiologia , Vaginose Bacteriana/epidemiologia , Adulto , China/epidemiologia , Feminino , Humanos , Incidência , Gravidez , Modelos de Riscos Proporcionais , Estudos Prospectivos , Fatores de Risco , Vaginose Bacteriana/etiologia
14.
J Hazard Mater ; 119(1-3): 245-9, 2005 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-15752872

RESUMO

Heavy metals are one of the important factors that affect the final disposal of sewage sludge. In this paper, the metal mobility and bioavailability of heavy metals in sewage sludge were studied by using Community Bureau of Reference (BCR) sequential extraction procedure to get more information for the reasonable disposal of sludge. Sewage sludge was collected from five municipal wastewater treatment plants and three industrial wastewater treatment plants. The sludge was examined for and the total concentrations and different chemical fractions of Cd, Cr, Pb, Cu, Ni and Zn. The total metal concentrations of heavy metals in sludge varied greatly. The contents of Zn and Cu were the highest, followed by then Cr, Ni and Pb and the content of Cd was the least. There was no significant difference in total metal concentration between municipal and industrial wastewater treatment plants. Fractions extracted by the BCR sequential procedure were acid soluble/exchangeable, reducible and oxidizable fraction. Sludge pH was found to have profound effect on the chemical fractions of heavy metals. Acidic sludges (Xiamen and Jinlin Petrochemical Group Co., wastewater treatment plant) had higher proportion of the acid soluble/exchangeable fractions than in neutral sludge. In neutral sludges, Pb and Cr were principally distributed in between the oxidizable fraction and the residual fraction; Cu was in the oxidizable fraction; Cd mainly in the residual fraction in municipal wastewater treatment plants and had high percentage of acid soluble/exchangeable and reducible fractions in industrial wastewater treatment plants; Ni and Zn had higher percentage in the acid soluble/exchangeable and the oxidizable fraction.


Assuntos
Resíduos Industriais , Metais Pesados/análise , Esgotos/química , Eliminação de Resíduos Líquidos/métodos , Monitoramento Ambiental , Oxirredução
15.
Artigo em Chinês | MEDLINE | ID: mdl-14673508

RESUMO

A novel coronavirus (SARS-coronavirus, SARS-CoV) was discovered as the pathogen of the severe acute respiratory syndrome (SARS). According to studies with other coronaviruses, the membrane protein (M protein) is the main structural protein and the recombinant M protein may be useful as an antigen for detecting antibodies against coronavirus and for preparing vaccine. In this work, the M protein of SARS-CoV was expressed in E. coli as fusion protein with maltose binding protein at N-terminus and MxeGyrA intein CBD at C-terminus. The recombinant protein was identified by Western blot and mass spectrometry. The soluble parts of the cell crude extract were then partially purified by MBP affinity chromatography. The purified protein will be used for the studies on M protein's structure and the development of diagnostic method of SARS.


Assuntos
Vírus da SARS/genética , Proteínas da Matriz Viral/genética , Sequência de Aminoácidos , Western Blotting , Proteínas de Transporte/genética , Proteínas de Transporte/isolamento & purificação , Proteínas de Transporte/metabolismo , Regulação Viral da Expressão Gênica , Proteínas Ligantes de Maltose , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/isolamento & purificação , Proteínas Recombinantes de Fusão/metabolismo , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Vírus da SARS/metabolismo , Análise de Sequência de Proteína , Proteínas da Matriz Viral/química , Proteínas da Matriz Viral/metabolismo
16.
Artigo em Inglês | MEDLINE | ID: mdl-12796820

RESUMO

Penicillin G Acylas (PGA) of Providencia rettgeri (ATCC 25599) was evolved using a modified DNA family shuffling method. The identity of pga genes from Escherichia coli, Kluyvera citrophila and Providencia rettgeri ranges from 62.5% to 96.9%. The pga genes from above three species were recombined and shuffled to create interspecies pga gene fusion libraries. By substituting assembled chimaeras for corresponding region of pETPPGA, different recombinants were constructed and expressed in E. coli JM109(DE3). Mutants with obvious beta-lactam synthetic activity were selected from the plates and the ratios of synthesis to hydrolysis (S/H) were determined subsequently. It was shown that the primary structures of selected positives exhibited significant diversity among each library. The best mutant possessed 40% higher synthetic activity than the wild type enzyme of PrPGA. It was further proved in this study that the domain of alpha subunit contributed much more to improve the specific activity of synthesis. Results showed a recombinant PGA with higher synthetic activity was acquired by the method of DNA shuffling.


Assuntos
Embaralhamento de DNA/métodos , Escherichia coli/enzimologia , Kluyvera/enzimologia , Penicilina Amidase/genética , Providencia/enzimologia , DNA Bacteriano/genética , Ativação Enzimática , Escherichia coli/genética , Escherichia coli/metabolismo , Regulação Enzimológica da Expressão Gênica , Kluyvera/genética , Penicilina Amidase/metabolismo , Plasmídeos/genética , Mutação Puntual , Providencia/genética , Proteínas Recombinantes de Fusão/genética , Recombinação Genética , Homologia de Sequência
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