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1.
Nanotechnology ; 30(2): 02LT01, 2019 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-30411716

RESUMO

Negative transconductance (NTC) refers to the phenomenon of the N-shape transfer characteristic appearing with a current peak and valley. It has been extensively studied in the past few decades due to its applications in logic and memory devices. Here, we observe unique antibipolar transfer characteristics and NTC behavior in multi-layer 2,6-diphenyl anthracene organic thin-film transistors grown on h-BN, which is due to the vertical potential barrier between the charge accumulation region near the substrate and the neutral bulk region under the contacts. The applied extrinsic electric field could effectively modulate the barrier height, resulting in a competition for charge carrier transport between lateral and vertical directions. Based on the NTC and antibipolar properties, a frequency doubler has been fabricated on a single transistor, which provides a new building block for organic logic circuits.

2.
Nano Lett ; 19(1): 331-337, 2019 01 09.
Artigo em Inglês | MEDLINE | ID: mdl-30511871

RESUMO

Two-dimensional layered materials (2DLMs) are of considerable interest for high-performance electronic devices for their unique electronic properties and atomically thin geometry. However, the atomically thin geometry makes their electronic properties highly susceptible to the environment changes. In particular, some 2DLMs (e.g., black phosphorus (BP) and SnSe2) are unstable and could rapidly degrade over time when exposed to ambient conditions. Therefore, the development of proper passivation schemes that can preserve the intrinsic properties and enhance their lifetime represents a key challenge for these atomically thin electronic materials. Herein we introduce a simple, nondisruptive, and scalable van der Waals passivation approach by using organic thin films to simultaneously improve the performance and air stability of BP field-effect transistors (FETs). We show that dioctylbenzothienobenzothiophene (C8-BTBT) thin films can be readily deposited on BP via van der Waals epitaxy approach to protect BP against oxidation in ambient conditions over 20 d. Importantly, the noncovalent van der Waals interface between C8-BTBT and BP effectively preserves the intrinsic properties of BP, allowing us to demonstrate high-performance BP FETs with a record-high current density of 920 µA/um, hole drift velocity over 1 × 107 cm/s, and on/off ratio of 1 × 104 to ∼1 × 107 at room temperature. This approach is generally applicable to other unstable two-dimensional materials, defining a unique pathway to modulate their electronic properties and realize high-performance devices through hybrid heterojunctions.

3.
Sci Adv ; 3(9): e1701186, 2017 09.
Artigo em Inglês | MEDLINE | ID: mdl-28913429

RESUMO

Organic thin-film transistors (OTFTs) with high mobility and low contact resistance have been actively pursued as building blocks for low-cost organic electronics. In conventional solution-processed or vacuum-deposited OTFTs, due to interfacial defects and traps, the organic film has to reach a certain thickness for efficient charge transport. Using an ultimate monolayer of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) molecules as an OTFT channel, we demonstrate remarkable electrical characteristics, including intrinsic hole mobility over 30 cm2/Vs, Ohmic contact with 100 Ω · cm resistance, and band-like transport down to 150 K. Compared to conventional OTFTs, the main advantage of a monolayer channel is the direct, nondisruptive contact between the charge transport layer and metal leads, a feature that is vital for achieving low contact resistance and current saturation voltage. On the other hand, bilayer and thicker C8-BTBT OTFTs exhibit strong Schottky contact and much higher contact resistance but can be improved by inserting a doped graphene buffer layer. Our results suggest that highly crystalline molecular monolayers are promising form factors to build high-performance OTFTs and investigate device physics. They also allow us to precisely model how the molecular packing changes the transport and contact properties.

4.
Nano Lett ; 16(6): 3754-9, 2016 06 08.
Artigo em Inglês | MEDLINE | ID: mdl-27183049

RESUMO

Precise assembly of semiconductor heterojunctions is the key to realize many optoelectronic devices. By exploiting the strong and tunable van der Waals (vdW) forces between graphene and organic small molecules, we demonstrate layer-by-layer epitaxy of ultrathin organic semiconductors and heterostructures with unprecedented precision with well-defined number of layers and self-limited characteristics. We further demonstrate organic p-n heterojunctions with molecularly flat interface, which exhibit excellent rectifying behavior and photovoltaic responses. The self-limited organic molecular beam epitaxy (SLOMBE) is generically applicable for many layered small-molecule semiconductors and may lead to advanced organic optoelectronic devices beyond bulk heterojunctions.

5.
Phys Rev Lett ; 116(1): 016602, 2016 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-26799035

RESUMO

One of the basic assumptions in organic field-effect transistors, the most fundamental device unit in organic electronics, is that charge transport occurs two dimensionally in the first few molecular layers near the dielectric interface. Although the mobility of bulk organic semiconductors has increased dramatically, direct probing of intrinsic charge transport in the two-dimensional limit has not been possible due to excessive disorders and traps in ultrathin organic thin films. Here, highly ordered single-crystalline mono- to tetralayer pentacene crystals are realized by van der Waals (vdW) epitaxy on hexagonal BN. We find that the charge transport is dominated by hopping in the first conductive layer, but transforms to bandlike in subsequent layers. Such an abrupt phase transition is attributed to strong modulation of the molecular packing by interfacial vdW interactions, as corroborated by quantitative structural characterization and density functional theory calculations. The structural modulation becomes negligible beyond the second conductive layer, leading to a mobility saturation thickness of only ∼3 nm. Highly ordered organic ultrathin films provide a platform for new physics and device structures (such as heterostructures and quantum wells) that are not possible in conventional bulk crystals.

6.
Nat Commun ; 5: 5162, 2014 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-25330787

RESUMO

Two-dimensional atomic crystals are extensively studied in recent years due to their exciting physics and device applications. However, a molecular counterpart, with scalable processability and competitive device performance, is still challenging. Here, we demonstrate that high-quality few-layer dioctylbenzothienobenzothiophene molecular crystals can be grown on graphene or boron nitride substrate via van der Waals epitaxy, with precisely controlled thickness down to monolayer, large-area single crystal, low process temperature and patterning capability. The crystalline layers are atomically smooth and effectively decoupled from the substrate due to weak van der Waals interactions, affording a pristine interface for high-performance organic transistors. As a result, monolayer dioctylbenzothienobenzothiophene molecular crystal field-effect transistors on boron nitride show record-high carrier mobility up to 10 cm(2) V(-1) s(-1) and aggressively scaled saturation voltage ~1 V. Our work unveils an exciting new class of two-dimensional molecular materials for electronic and optoelectronic applications.

7.
ACS Nano ; 8(6): 5738-45, 2014 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-24836121

RESUMO

We report on a strong photoluminescence (PL) enhancement of monolayer MoS2 through defect engineering and oxygen bonding. Micro-PL and Raman images clearly reveal that the PL enhancement occurs at cracks/defects formed during high-temperature annealing. The PL enhancement at crack/defect sites could be as high as thousands of times after considering the laser spot size. The main reasons of such huge PL enhancement include the following: (1) the oxygen chemical adsorption induced heavy p doping and the conversion from trion to exciton; (2) the suppression of nonradiative recombination of excitons at defect sites, which was verified by low-temperature PL measurements. First-principle calculations reveal a strong binding energy of ∼2.395 eV for an oxygen molecule adsorbed on a S vacancy of MoS2. The chemically adsorbed oxygen also provides a much more effective charge transfer (0.997 electrons per O2) compared to physically adsorbed oxygen on an ideal MoS2 surface. We also demonstrate that the defect engineering and oxygen bonding could be easily realized by mild oxygen plasma irradiation. X-ray photoelectron spectroscopy further confirms the formation of Mo-O bonding. Our results provide a new route for modulating the optical properties of two-dimensional semiconductors. The strong and stable PL from defects sites of MoS2 may have promising applications in optoelectronic devices.

8.
Adv Mater ; 26(20): 3275-81, 2014 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-24677272

RESUMO

Memristive devices based on vertical heterostructures of graphene and TiOx show a significant power reduction that is up to ∼10(3) times smaller than that of conventional structures. This power reduction arises as a result of a tunneling barrier at the interface. The barrier is tunable, opening up the possibility of engineering several key memory characteristics.

9.
Chin Med J (Engl) ; 124(11): 1695-9, 2011 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-21740780

RESUMO

BACKGROUND: Pancreatic cancer is one of the most lethal human cancers with a very low survival rate of 5 years. Conventional cancer treatments including surgery, radiation, chemotherapy or combinations of these show little effect on this disease. Several proteins have been proved critical to the development and the progression of pancreatic cancer. The aim of this study was to investigate the effect of resveratrol on apoptosis in pancreatic cancer cells. METHODS: Several pancreatic cancer cell lines were screened by resveratrol, and its toxicity was tested by normal pancreatic cells. Western blotting was then performed to analyze the molecular mechanism of resveratrol induced apoptosis of pancreatic cancer cell lines. RESULTS: In the screened pancreatic cancer cell lines, capan-2 and colo357 showed high sensitivity to resveratrol induced apoptosis. Resveratrol exhibited insignificant toxicity to normal pancreatic cells. In resveratrol sensitive cells, capan-2 and colo357, the activation of caspase-3 was detected and showed significant caspase-3 activation upon resveratrol treatment; p53 and p21 were also detected up-regulated upon resveratrol treatment. CONCLUSION: Resveratrol provides a promising anti-tumor strategy to fight against pancreatic cancer.


Assuntos
Apoptose/efeitos dos fármacos , Estilbenos/farmacologia , Western Blotting , Caspase 3/metabolismo , Sobrevivência Celular/efeitos dos fármacos , Humanos , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Neoplasias Pancreáticas/metabolismo , Resveratrol , Células Tumorais Cultivadas
10.
Xi Bao Yu Fen Zi Mian Yi Xue Za Zhi ; 25(12): 1136-9, 2009 Dec.
Artigo em Chinês | MEDLINE | ID: mdl-19961801

RESUMO

AIM: To prepare specific monoclonal antibody against human S100A4 protein and establish a reliable method to detect S100A4 protein in tumor specimens. METHODS: A standard hybridoma method was used to generate monoclonoal antibodies against recombinant human S100A4. ELISA, Western blot and immunohistochemistry were used to validate this antibody and the antibody is used to examine specimens of human breast and colon cancers. RESULTS: One hybridoma cell line which secreted monoclonal antibody specifically against recombinant human S100A4 protein was obtained and named as D101. The monoclonal antibody is shown to be more specific for S100A4 protein than the polyclonal antibody, at least in Western blot. The monoclonal antibody is suitable for detecting the expression of S100A4 in specimens from human tissues and gave results consistent with those of a commercially available polyclonal antibody in a small group of breast and colorectal carcinomas. CONCLUSION: The monoclonal antibody is specific for S100A4 and can be produced on a large scale; therefore it will be more reproducible for future clinical applications.


Assuntos
Anticorpos Monoclonais , Hibridomas , Anticorpos Monoclonais/imunologia , Especificidade de Anticorpos , Ensaio de Imunoadsorção Enzimática , Humanos , Imuno-Histoquímica
11.
Chin Med J (Engl) ; 120(15): 1348-52, 2007 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-17711742

RESUMO

BACKGROUND: Pancreatic cancer is one of the most common tumors and has a 5-year survival for all stages of less than 5%. Most patients with pancreatic cancer are diagnosed at an advanced stage and therefore are not candidates for surgical resection. In recent years, investigation into alternative treatment strategies for this aggressive disease has led to advances in the field of gene therapy for pancreatic cancer. E. coli purine nucleoside phosphorylase/6-methylpurine deoxyribose (ePNP/MePdR) is a suicide gene/prodrug system where PNP enzyme cleaves nontoxic MePdR into cytotoxic membrane-permeable compounds 6-methylpurine (MeP) with high bystander activity. hTERT is expressed in cell lines and tissues for telomerase activity. In this study we examined the efficacy of ePNP under the control of hTERT promoter sequences and assessed the selective killing effects of the ePNP/prodrug MePdR system on pancreatic tumors. METHODS: Recombinant pET-PNP was established. The protein of E. coli PNPase was expressed and an antibody to E. coli PNPase was prepared. Transcriptional activities of hTERT promoter sequences were analyzed using a luciferase reporter gene. A recombinant phTERT-ePNP vector was constructed. The ePNP/MePdR system affects SW1990 human pancreatic cancer cell lines in vitro. RESULTS: The hTERT promoter had high transcriptional activity and conferred specificity on cancer cell lines. The antibody to E. coli PNPase was demonstrated to be specific for the ePNP protein. The MePdR treatment induced a high in vitro cytotoxicity on the sole hTERT-ePNP-producing cell lines and affected SW1990 cells in a dose-dependent manner. CONCLUSIONS: The hTERT promoter control of the ePNP/MePdR system can provide a beneficial anti-tumor treatment in pancreatic cancer cell lines including a good bystander killing effect.


Assuntos
Escherichia coli/enzimologia , Terapia Genética , Neoplasias Pancreáticas/terapia , Regiões Promotoras Genéticas , Nucleosídeos de Purina/uso terapêutico , Purina-Núcleosídeo Fosforilase/genética , Telomerase/genética , Linhagem Celular Tumoral , Humanos
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