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1.
Nature ; 579(7798): 219-223, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-32132712

RESUMO

Ultrathin two-dimensional (2D) semiconducting layered materials offer great potential for extending Moore's law of the number of transistors in an integrated circuit1. One key challenge with 2D semiconductors is to avoid the formation of charge scattering and trap sites from adjacent dielectrics. An insulating van der Waals layer of hexagonal boron nitride (hBN) provides an excellent interface dielectric, efficiently reducing charge scattering2,3. Recent studies have shown the growth of single-crystal hBN films on molten gold surfaces4 or bulk copper foils5. However, the use of molten gold is not favoured by industry, owing to its high cost, cross-contamination and potential issues of process control and scalability. Copper foils might be suitable for roll-to-roll processes, but are unlikely to be compatible with advanced microelectronic fabrication on wafers. Thus, a reliable way of growing single-crystal hBN films directly on wafers would contribute to the broad adoption of 2D layered materials in industry. Previous attempts to grow hBN monolayers on Cu (111) metals have failed to achieve mono-orientation, resulting in unwanted grain boundaries when the layers merge into films6,7. Growing single-crystal hBN on such high-symmetry surface planes as Cu (111)5,8 is widely believed to be impossible, even in theory. Nonetheless, here we report the successful epitaxial growth of single-crystal hBN monolayers on a Cu (111) thin film across a two-inch c-plane sapphire wafer. This surprising result is corroborated by our first-principles calculations, suggesting that the epitaxial growth is enhanced by lateral docking of hBN to Cu (111) steps, ensuring the mono-orientation of hBN monolayers. The obtained single-crystal hBN, incorporated as an interface layer between molybdenum disulfide and hafnium dioxide in a bottom-gate configuration, enhanced the electrical performance of transistors. This reliable approach to producing wafer-scale single-crystal hBN paves the way to future 2D electronics.

2.
Psychiatry Res ; 284: 112680, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-31806402

RESUMO

This study is to identify the performance of children with and without ADHD in open-ended and closed-ended creativity assessments, and investigate the moderating effect of medicated and unmedicated Children. The study subjects included third to sixth graders: 43 children with ADHD and 43 typically developing children. The participants with ADHD were those who were identified by local Committees of Identification, Placement and Consultation for Children with Special Needs or those who were diagnosed by medical institutions. Children with ADHD were further divided into medicated (22 participants) and unmedicated groups (21 participants) based on their current medication treatment. This study employed the New Tests of Creative Thinking to gauge the participants' open-ended creativity, while Remote Associates Test and the Insight Test were used to assess the participants' closed-ended creativity. Although previous evidence for creativity in children with ADHD have been mixed, this study includes medication as moderation variable and suggests that the performance of unmedicated children with ADHD in the open-ended creativity assessments was better than medicated children with ADHD and typically developing children. The study results can further explore the creativity characteristics of children with ADHD.

3.
Adv Mater ; 31(18): e1900861, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30907033

RESUMO

2D transition metal dichalcogenide (TMD) layered materials are promising for future electronic and optoelectronic applications. The realization of large-area electronics and circuits strongly relies on wafer-scale, selective growth of quality 2D TMDs. Here, a scalable method, namely, metal-guided selective growth (MGSG), is reported. The success of control over the transition-metal-precursor vapor pressure, the first concurrent growth of two dissimilar monolayer TMDs, is demonstrated in conjunction with lateral or vertical TMD heterojunctions at precisely desired locations over the entire wafer in a single chemical vapor deposition (VCD) process. Owing to the location selectivity, MGSG allows the growth of p- and n-type TMDs with spatial homogeneity and uniform electrical performance for circuit applications. As a demonstration, the first bottom-up complementary metal-oxide-semiconductor inverter based on p-type WSe2 and n-type MoSe2 is achieved, which exhibits a high and reproducible voltage gain of 23 with little dependence on position.

4.
ACS Nano ; 11(12): 12817-12823, 2017 12 26.
Artigo em Inglês | MEDLINE | ID: mdl-29182852

RESUMO

Two-dimensional (2D) materials are drawing growing attention for next-generation electronics and optoelectronics owing to its atomic thickness and unique physical properties. One of the challenges posed by 2D materials is the large source/drain (S/D) series resistance due to their thinness, which may be resolved by thickening the source and drain regions. Recently explored lateral graphene-MoS21-3 and graphene-WS21,4 heterostructures shed light on resolving the mentioned issues owing to their superior ohmic contact behaviors. However, recently reported field-effect transistors (FETs) based on graphene-TMD heterostructures have only shown n-type characteristics. The lack of p-type transistor limits their applications in complementary metal-oxide semiconductor electronics. In this work, we demonstrate p-type FETs based on graphene-WSe2 lateral heterojunctions grown with the scalable CVD technique. Few-layer WSe2 is overlapped with the multilayer graphene (MLG) at MLG-WSe2 junctions such that the contact resistance is reduced. Importantly, the few-layer WSe2 only forms at the junction region while the channel is still maintained as a WSe2 monolayer for transistor operation. Furthermore, by imposing doping to graphene S/D, 2 orders of magnitude enhancement in Ion/Ioff ratio to ∼108 and the unipolar p-type characteristics are obtained regardless of the work function of the metal in ambient air condition. The MLG is proposed to serve as a 2D version of emerging raised source/drain approach in electronics.

5.
ACS Appl Mater Interfaces ; 9(10): 9110-9117, 2017 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-28222259

RESUMO

We study the band discontinuity at the GaN/single-layer (SL) WSe2 heterointerface. The GaN thin layer is epitaxially grown by molecular beam epitaxy on chemically vapor deposited SL-WSe2/c-sapphire. We confirm that the WSe2 was formed as an SL from structural and optical analyses using atomic force microscopy, scanning transmission electron microscopy, micro-Raman, absorbance, and microphotoluminescence spectra. The determination of band offset parameters at the GaN/SL-WSe2 heterojunction is obtained by high-resolution X-ray photoelectron spectroscopy, electron affinities, and the electronic bandgap values of SL-WSe2 and GaN. The valence band and conduction band offset values are determined to be 2.25 ± 0.15 and 0.80 ± 0.15 eV, respectively, with type II band alignment. The band alignment parameters determined here provide a route toward the integration of group III nitride semiconducting materials with transition metal dichalcogenides (TMDs) for designing and modeling of their heterojunction-based electronic and optoelectronic devices.

6.
ACS Appl Mater Interfaces ; 8(49): 33673-33680, 2016 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-27960387

RESUMO

A well-dispersed PtCu alloy nanoparticles (NPs) on three-dimensional nitrogen-doped graphene (PtCu/3D N-G) electrocatalyst has been successfully synthesized by a conventional hydrothermal method combined with a high-efficiency microwave-assisted polyol process. The morphology, composition, and structures are well-characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammograms illustrate that the as-prepared PtCu/3D N-G electrocatalyst possesses the larger electrochemical active surface area, lower onset potential, higher current density, and better tolerance to CO poisoning than PtCu NPs on reduced graphene oxide and XC-72 carbon black in acid solution. In addition, long-time chronoamperometry reveals that the PtCu/3D N-G catalyst exhibits excellent stability even longer than 60 min toward acid methanol electrooxidation. The remarkably enhanced performance is related to the combined effects of uniformly interconnected three-dimensional porous graphene networks, nitrogen doping, modified Pt alloy NPs, and strong binding force between Pt alloy NPs and 3D N-G structures.

7.
Small ; 12(40): 5530-5537, 2016 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-27578319

RESUMO

The remote hydrogen plasma is able to create abundant S-vacancies on amorphous molybdenum sulfide (a-MoSx ) as active sites for hydrogen evolution. The results demonstrate that the plasma-treated a-MoSx exhibits superior performance and higher stability than Pt in a proton exchange membrane based electrolyzers measurement as a proof-of-concept of industrial application.

8.
ACS Appl Mater Interfaces ; 6(20): 17679-85, 2014 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-25266066

RESUMO

Molybdenum sulfide has recently attracted much attention because of its low cost and excellent catalytical effects in the application of hydrogen evolution reaction (HER). To improve the HER efficiency, many researchers have extensively explored various avenues such as material modification, forming hybrid structures or modifying geometric morphology. In this work, we reported a significant enhancement in the electrocatalytic activity of the MoSx via growing on Tetracyanoquinodimethane (TCNQ) treated carbon cloth, where the MoSx was synthesized by thermolysis from the ammonium tetrathiomolybdate ((NH4)2MoS4) precursor at 170 °C. The pyridinic N- and graphitic N-like species on the surface of carbon cloth arising from the TCNQ treatment facilitate the formation of Mo(5+) and S2(2-) species in the MoSx, especially with S2(2-) serving as an active site for HER. In addition, the smaller particle size of the MoSx grown on TCNQ-treated carbon cloth reveals a high ratio of edge sites relative to basal plane sites, indicating the richer effective reaction sites and superior electrocatalytic characteristics. Hence, we reported a high hydrogen evolution rate for MoSx on TCNQ-treated carbon cloth of 6408 mL g(-1) cm(-2) h(-1) (286 mmol g(-1) cm(-2) h(-1)) at an overpotential of V = 0.2 V. This study provides the fundamental concepts useful in the design and preparation of transition metal dichalcogenide catalysts, beneficial in the development in clean energy.

9.
J Chin Med Assoc ; 75(4): 171-5, 2012 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-22541146

RESUMO

BACKGROUND: To investigate flow in the ductus venosus at 11-13 + 6 weeks of gestation in women with normal pregnancies in the Taiwanese population. METHODS: Two hundred and fifty-two normal singleton pregnancies with gestational ages ranging from 11 to 13 + 6 weeks were examined in this study. The pulsatility index for veins (PIV), resistance index (RI), peak velocity during ventricular systole (S-wave), and peak velocity during ventricular diastole (D-wave) were recorded from the ductus venosus. RESULTS: We analyzed 252 participants who all fulfilled the inclusion and exclusion criteria of our study. The mean maternal age was 31 (range 19-45 years), with a corresponding gestational age of 12 + 4 weeks (range 11-13 + 6). No significant change was found in the vascular indices as gestational age increased for the S-wave (S-wave = 1.4214 (GA) + 17.448, r = 0.09, P = 0.154), PIV (PIV = -0.0358 (GA) + 1.4143, r = -0.05, P = 0.378) and RI (RI = -0.035 (GA) + 1.1478, r = -0.064, P = 0.468). In contrast, the D-wave behaved differently from the other variables. There was a significant increase (r = 0.155, P = 0.013) in the D-wave with gestational age (D-wave = 1.4896 (GA) - 7.1547). CONCLUSION: D-wave velocity in the ductus venosus increased with gestational age. S-wave peak velocity showed an increasing trend and PIV showed a decreasing trend with gestational age, but they did not reach statistical significance.


Assuntos
Coração Fetal/fisiologia , Feto/irrigação sanguínea , Ultrassonografia Doppler em Cores , Ultrassonografia Pré-Natal , Velocidade do Fluxo Sanguíneo , Feminino , Humanos , Gravidez , Primeiro Trimestre da Gravidez , Segundo Trimestre da Gravidez , Fluxo Pulsátil
10.
J Am Acad Nurse Pract ; 24(3): 160-5, 2012 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-22404794

RESUMO

PURPOSE: To discuss a case of scrub typhus complicated with acute respiratory distress syndrome (ARDS) in a 67-year-old female. An overview of the prevalence and pathogenesis of the disorder, clinical diagnosis, and treatment are presented. DATA SOURCES: Case report, diagnostic evidence, and scientific literature. CONCLUSIONS: If not properly treated, scrub typhus can cause serious complications, such as ARDS and septicemia. When left untreated, the mortality rate for scrub typhus will be increased. When there is a cause to believe that scrub typhus is present, doxycycline treatment leads to rapid symptom improvement. IMPLICATIONS FOR PRACTICE: People might not be aware of the possibility of scrub typhus because it had been a more common disease in the past. Nurse practitioners (NPs) should take a detail history and be aware of common clinical manifestations to promote the early recognition and appropriate treatment of scrub typhus, which would prevent severe complications and reduce mortality. A resurgence of the disease could occur at any time among military troops serving in endemic regions.


Assuntos
Síndrome do Desconforto Respiratório do Adulto/etiologia , Tifo por Ácaros/complicações , Idoso , Antibacterianos/uso terapêutico , Feminino , Humanos , Síndrome do Desconforto Respiratório do Adulto/tratamento farmacológico , Síndrome do Desconforto Respiratório do Adulto/patologia , Tifo por Ácaros/tratamento farmacológico , Tifo por Ácaros/patologia
11.
Am J Obstet Gynecol ; 202(2): 174.e1-7, 2010 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-19931041

RESUMO

OBJECTIVE: On the basis of outcome data from concurrent chemoradiotherapy (CCRT) for locally advanced cervical squamous cell carcinoma, the authors developed a nomogram for predicting survival outcome. STUDY DESIGN: Two hundred fifty-one eligible patients with International Federation of Gynecology and Obstetrics stage IIB-IVA squamous cell carcinoma of the uterine cervix who underwent CCRT were included for the construction of the nomogram. Predictor variables included age, serum squamous cell carcinoma antigen, tumor size, parametrium invasion, hydronephrosis, bladder/rectum invasion, and lymph node metastases. Internal validation of the nomogram was performed. RESULTS: A nomogram for predicting the 5 year overall survival for these patients was constructed on the basis of a Cox regression model from 7 parameters. The concordance index was 0.69. CONCLUSION: This nomogram is a predictive tool, upon external validation, that can be used to counsel patients in predicting outcomes. The discriminatory ability of the nomogram indicates that this population should not be considered homogeneous with respect to risk of death.


Assuntos
Neoplasias do Colo do Útero/mortalidade , Adulto , Antígenos de Neoplasias/sangue , Terapia Combinada , Feminino , Humanos , Imagem por Ressonância Magnética , Pessoa de Meia-Idade , Estadiamento de Neoplasias , Prognóstico , Modelos de Riscos Proporcionais , Serpinas/sangue , Tomografia Computadorizada por Raios X , Neoplasias do Colo do Útero/patologia , Neoplasias do Colo do Útero/terapia
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