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ACS Nano ; 13(3): 3341-3352, 2019 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-30758945


A defect-controlled approach for the nucleation and epitaxial growth of WSe2 on hBN is demonstrated. The WSe2 domains exhibit a preferred orientation of over 95%, leading to a reduced density of inversion domain boundaries (IDBs) upon coalescence. First-principles calculations and experimental studies as a function of growth conditions and substrate pretreatment confirm that WSe2 nucleation density and orientation are controlled by the hBN surface defect density rather than thermodynamic factors. Detailed transmission electron microscopy analysis provides support for the role of single-atom vacancies on the hBN surface that trap W atoms and break surface symmetry leading to a reduced formation energy for one orientation of WSe2 domains. Through careful control of nucleation and extended lateral growth time, fully coalesced WSe2 monolayer films on hBN were achieved. Low-temperature photoluminescence (PL) measurements and transport measurements of back-gated field-effect transistor devices fabricated on WSe2/hBN films show improved optical and electrical properties compared to films grown on sapphire under similar conditions. Our results reveal an important nucleation mechanism for the epitaxial growth of van der Waals heterostructures and demonstrate hBN as a superior substrate for single-crystal transition-metal dichalcogenide (TMD) films, resulting in a reduced density of IDBs and improved properties. The results motivate further efforts focused on the development of single crystal hBN substrates and epilayers for synthesis of wafer-scale single crystal TMD films.

Biosens Bioelectron ; 74: 207-13, 2015 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-26143460


In the present study, we manifest that traditionally used gold nanoparticles when supported on molybdenum disulfide nanoribbons matrix (MoS2 NRs-Au NPs) show synergistically enhanced intrinsic peroxidase like catalytic activity and can catalyze the oxidation of 3,3',5,5' tetramethyl benzidine by H2O2 to produce a highly sensitive blue shade product depending on level of free cholesterol, when tested on complex system of human serum. Further the system attests appreciable kinetics, owing to Km value as low as 0.015 mM and better loading capacity (Vmax=6.7×10(-6) M s(-1)). Additionally, the proposed system is stable for weeks with ability to perform appreciably in wide pH (3-6) and temperature range (25-60 °C). Utilizing this potential, the present work proposes a cholesterol detection color wheel which is used along with cost effective cholesterol detection strips fabricated out of proposed MoS2 NRs-Au NPs system for quick and reliable detection of free cholesterol using unaided eye.

Colesterol/sangue , Dissulfetos/química , Ouro/química , Nanopartículas Metálicas/química , Molibdênio/química , Benzidinas/química , Técnicas Biossensoriais , Catálise , Colorimetria , Humanos , Peróxido de Hidrogênio/química , Limite de Detecção , Nanopartículas Metálicas/ultraestrutura , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Oxirredução