Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 11 de 11
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Rev Sci Instrum ; 89(11): 114903, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30501276

RESUMO

The higher critical electric field of ß-gallium oxide (Ga2O3) gives promise to the development of next generation power electronic devices with improved size, weight, power, and efficiency over current state-of-the-art wide bandgap devices based on 4H-silicon carbide (SiC) and gallium nitride (GaN). However, it is expected that Ga2O3 devices will encounter serious thermal issues due to the poor thermal conductivity of the material. In this work, self-heating in Ga2O3 Schottky barrier diodes under different regimes of the diode operation was investigated using diverse optical thermography techniques including thermoreflectance thermal imaging, micro-Raman thermography, and infrared thermal microscopy. 3D coupled electro-thermal modeling was used to validate experimental results and to understand the mechanism of heat generation for the diode structures. Measured top-side and cross-sectional temperature fields suggest that device and circuit engineers should account for the concentrated heat generation that occurs near the anode/Ga2O3 interface and/or the lightly doped drift layer under both forward and high voltage reverse bias conditions. Results of this study suggest that electro-thermal co-design techniques and top-side thermal management solutions are necessary to exploit the full potential of the Ga2O3 material system.

2.
ACS Appl Mater Interfaces ; 6(19): 16755-62, 2014 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-25197772

RESUMO

Hexagonal boron nitride (h-BN) atomic layers are synthesized on polycrystalline copper foils via a novel chemical vapor deposition (CVD) process that maintains a vapor-phase copper overpressure during growth. Compared to h-BN films grown without a copper overpressure, this process results in a >10× reduction of 3-dimensional BN fullerene-like surface features, a reduction of carbon and oxygen contamination of 65% and 62%, respectively, an increase in h-BN grain size of >2×, and an 89% increase in electrical breakdown strength.

3.
ACS Nano ; 6(6): 5234-41, 2012 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-22545808

RESUMO

Hexagonal boron nitride (h-BN) is a promising dielectric material for graphene-based electronic devices. Here we investigate the potential of h-BN gate dielectrics, grown by chemical vapor deposition (CVD), for integration with quasi-freestanding epitaxial graphene (QFEG). We discuss the large scale growth of h-BN on copper foil via a catalytic thermal CVD process and the subsequent transfer of h-BN to a 75 mm QFEG wafer. X-ray photoelectron spectroscopy (XPS) measurements confirm the absence of h-BN/graphitic domains and indicate that the film is chemically stable throughout the transfer process, while Raman spectroscopy indicates a 42% relaxation of compressive stress following removal of the copper substrate and subsequent transfer of h-BN to QFEG. Despite stress-induced wrinkling observed in the films, Hall effect measurements show little degradation (<10%) in carrier mobility for h-BN coated QFEG. Temperature dependent Hall measurements indicate little contribution from remote surface optical phonon scattering and suggest that, compared to HfO(2) based dielectrics, h-BN can be an excellent material for preserving electrical transport properties. Graphene transistors utilizing h-BN gates exhibit peak intrinsic cutoff frequencies >30 GHz (2.4× that of HfO(2)-based devices).


Assuntos
Compostos de Boro/química , Grafite/química , Nanopartículas/química , Nanopartículas/ultraestrutura , Cristalização/métodos , Módulo de Elasticidade , Substâncias Macromoleculares/química , Campos Magnéticos , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Propriedades de Superfície
4.
ACS Nano ; 5(10): 8062-9, 2011 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-21905713

RESUMO

We present a novel method for the direct metal-free growth of graphene on sapphire that yields high quality films comparable to that of graphene grown on SiC by sublimation. Graphene is synthesized on sapphire via the simple decomposition of methane at 1425-1600 °C. Film quality was found to be a strong function of growth temperature. The thickness, structure, interface characteristics, and electrical transport properties were characterized in order to understand the utility of this material for electronic devices. Graphene synthesized on sapphire is found to be strain relieved, with no evidence of an interfacial buffer layer. There is a strong correlation between the graphene structural quality and carrier mobility. Room temperature Hall effect mobility values were as high as 3000 cm(2)/(V s), while measurements at 2 K reached values of 10,500 cm(2)/(V s). These films also display evidence of the quantum Hall effect. Field effect transistors fabricated from this material had a typical current density of 200 mA/mm and transconductance of 40 mS/mm indicating that material performance may be comparable to graphene on SiC.

5.
Nano Lett ; 11(9): 3601-7, 2011 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-21805989

RESUMO

We explore the effect of high-κ dielectric seed layer and overlayer on carrier transport in epitaxial graphene. We introduce a novel seeding technique for depositing dielectrics by atomic layer deposition that utilizes direct deposition of high-κ seed layers and can lead to an increase in Hall mobility up to 70% from as-grown. Additionally, high-κ seeded dielectrics are shown to produce superior transistor performance relative to low-κ seeded dielectrics and the presence of heterogeneous seed/overlayer structures is found to be detrimental to transistor performance, reducing effective mobility by 30-40%. The direct deposition of high-purity oxide seed represents the first robust method for the deposition of uniform atomic layer deposited dielectrics on epitaxial graphene that improves carrier transport.

6.
Nano Lett ; 11(9): 3875-80, 2011 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-21805993

RESUMO

We directly demonstrate the importance of buffer elimination at the graphene/SiC(0001) interface for high frequency applications. Upon successful buffer elimination, carrier mobility increases from an average of 800 cm(2)/(V s) to >2000 cm(2)/(V s). Additionally, graphene transistor current saturation increases from 750 to >1300 mA/mm, and transconductance improves from 175 mS/mm to >400 mS. Finally, we report a 10× improvement in the extrinsic current gain response of graphene transistors with optimal extrinsic current-gain cutoff frequencies of 24 GHz.

7.
Eur J Pharmacol ; 578(1): 65-75, 2008 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-17900559

RESUMO

Previously, we found pulmonary gas trapping to be a rapid, simple and objective measure of methacholine-induced airway obstruction in naïve mice. In this study we extended that finding by using methacholine-induced pulmonary gas trapping to differentiate airway responses of ovalbumin-sensitized, ovalbumin-exposed (Positive Control) and ovalbumin-sensitized, sodium chloride-exposed (Negative Control) mice. Additionally, pulmonary gas trapping and enhanced pause were compared following methacholine exposure in sensitized and nonsensitized mice. Finally, we examined by nose-only inhalation the ability of the glucocorticosteroid budesonide and the peroxisome proliferator-activated receptor-gamma agonist ciglitazone to modify methacholine-induced airway responses in ovalbumin-sensitized mice. Positive Controls exhibited a 7.8-fold increase in sensitivity and a 2.4-fold enhancement in the maximal airway obstruction to methacholine versus Negative Controls. Following methacholine, individual Positive and Negative Control mouse enhanced pause values overlapped in 9 of 9 studies, whereas individual Positive and Negative Control mouse excised lung gas volume values overlapped in only 1 of 9 studies, and log[excised lung gas volume] correlated (P=0.023) with in vivo log[enhanced pause] in nonsensitized mice. Finally, budesonide (100.0 or 1000.0 microg/kg) reduced methacholine-mediated airway responses and eosinophils and neutrophils, whereas ciglitazone (1000.0 microg/kg) had no effect on methacholine-induced pulmonary gas trapping, but reduced eosinophils. In conclusion, pulmonary gas trapping is a more reproducible measure of methacholine-mediated airway responses in ovalbumin-sensitized mice than enhanced pause. Also, excised lung gas volume changes can be used to monitor drug interventions like budesonide. Finally, this study highlights the importance of running a positive comparator when examining novel treatments like ciglitazone.


Assuntos
Asma/tratamento farmacológico , Broncodilatadores/farmacologia , Budesonida/farmacologia , Tiazolidinedionas/farmacologia , Administração por Inalação , Obstrução das Vias Respiratórias/induzido quimicamente , Obstrução das Vias Respiratórias/tratamento farmacológico , Animais , Antiasmáticos/administração & dosagem , Antiasmáticos/farmacologia , Hiper-Reatividade Brônquica/induzido quimicamente , Hiper-Reatividade Brônquica/tratamento farmacológico , Broncodilatadores/administração & dosagem , Budesonida/administração & dosagem , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Eosinófilos/efeitos dos fármacos , Eosinófilos/metabolismo , Masculino , Cloreto de Metacolina/toxicidade , Camundongos , Camundongos Endogâmicos BALB C , Neutrófilos/efeitos dos fármacos , Neutrófilos/metabolismo , Ovalbumina , PPAR gama/agonistas , Tiazolidinedionas/administração & dosagem
8.
Artigo em Inglês | MEDLINE | ID: mdl-19126494

RESUMO

Large-size and high-quality ReCa(4)O(BO(3))(3) (ReCOB, Re = rare earth) single crystals were grown by the Czochralski pulling method. In this work, the electrical properties were investigated at room temperature and elevated temperature for YCa(4)O(BO(3))(3) (YCOB). The dielectric permittivity, piezoelectric strain coefficient, and electromechanical coupling were found to be on the order of 11, 6.5 pC/N, and 12.5%, respectively, with a high piezoelectric voltage coefficient around 0.067 Vm/N. The electrical resistivity of YCOB was found to be 2 x 10(8) Ohm.m at 800 degrees C, with Q values of 4,500 at 950 degrees C. The frequency/temperature coefficient of YCOB was found to be -75 to -85ppm/K in the temperature range of 30 to 950 degrees C, depending on the crystal orientations. Together with their temperature-independent properties, ReCOB crystals are promising candidates for sensing applications at elevated temperatures.


Assuntos
Eletroquímica/instrumentação , Eletroquímica/métodos , Temperatura Alta , Ítrio/química , Boratos/química , Compostos de Cálcio/química , Cristalização , Impedância Elétrica , Metais Terras Raras/química , Compostos de Oxigênio/química , Transdutores
9.
Bioorg Med Chem Lett ; 17(24): 6910-3, 2007 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-17976987

RESUMO

Several P4 domain derivatives of the general d-phenylglycinamide-based scaffold (2) were synthesized and evaluated for their ability to bind to the serine protease factor Xa. Some of the more potent compounds were evaluated for their anticoagulant effects in vitro. A select subset containing various P1 indole constructs was further evaluated for their pharmacokinetic properties after oral administration to rats.


Assuntos
Antitrombina III/síntese química , Antitrombina III/farmacologia , Glicina/análogos & derivados , Anticoagulantes/síntese química , Anticoagulantes/química , Anticoagulantes/farmacologia , Antitrombina III/química , Cristalografia por Raios X , Fator Xa/química , Fator Xa/metabolismo , Glicina/síntese química , Glicina/química , Glicina/farmacologia , Humanos , Modelos Moleculares , Estrutura Molecular , Ligação Proteica , Relação Estrutura-Atividade
10.
Eur J Pharmacol ; 563(1-3): 213-5, 2007 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-17374534

RESUMO

In asthmatic mice, dexamethasone (30.0 mg/kg) was administered orally once daily on Days 24-27. One hour after dexamethasone on Day 25-27, the mice were exposed to ovalbumin aerosols. Twenty-eight days after the initial ovalbumin immunization, we found that dexamethasone reduced methacholine-induced pulmonary gas trapping and inhibited bronchoalveolar lavage eosinophils and neutrophils. However, five days after the last dose of dexamethasone and last ovalbumin aerosol exposure in other asthmatic mice, the airway obstructive response to methacholine was exacerbated in dexamethasone-treated mice compared to vehicle-treated mice on Day 32. Further, eosinophils, but not neutrophils, were still inhibited after cessation of dexamethasone. Thus, discontinuing dexamethasone worsened methacholine-induced pulmonary gas trapping of asthmatic mice in the absence of eosinophilic airway inflammation.


Assuntos
Resistência das Vias Respiratórias/efeitos dos fármacos , Antiasmáticos/farmacologia , Anti-Inflamatórios/farmacologia , Asma/tratamento farmacológico , Hiper-Reatividade Brônquica/fisiopatologia , Broncoconstritores/farmacologia , Dexametasona/farmacologia , Cloreto de Metacolina/farmacologia , Administração Oral , Animais , Antiasmáticos/administração & dosagem , Antiasmáticos/uso terapêutico , Anti-Inflamatórios/administração & dosagem , Anti-Inflamatórios/uso terapêutico , Asma/induzido quimicamente , Asma/fisiopatologia , Hiper-Reatividade Brônquica/prevenção & controle , Líquido da Lavagem Broncoalveolar/citologia , Dexametasona/administração & dosagem , Dexametasona/uso terapêutico , Modelos Animais de Doenças , Esquema de Medicação , Eosinófilos/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Neutrófilos/efeitos dos fármacos , Ovalbumina , Eosinofilia Pulmonar/fisiopatologia , Eosinofilia Pulmonar/prevenção & controle , Recidiva
11.
J Med Chem ; 48(3): 893-6, 2005 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-15689175

RESUMO

A vinyl azide cyclization method was used to synthesize three different carbocyclic[g]indole scaffolds as inhibitors of human nonpancreatic secretory phospholipase A2. Each scaffold demonstrated potent enzyme activity in a chromogenic assay system, with select examples also demonstrating potent activity in a secondary DOC/PC assay. Compound 11, representative of the cyclopent[g]indole series, gave an IC50 of 10 nM for the inhibition of hnps-PLA2 in the chromogenic assay.


Assuntos
Acetatos/síntese química , Ciclopentanos/síntese química , Indóis/síntese química , Fosfolipases A/antagonistas & inibidores , Acetatos/química , Ciclopentanos/química , Humanos , Indóis/química , Fosfolipases A/química , Fosfolipases A2 , Relação Estrutura-Atividade
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA