Tianjin Key Laboratory of Film Electronic & Communication Devices, School of Electrical and Electronic Engineering, Tianjin University of Technology, Tianjin 300384, China
Abstract:In this paper, Co3O4、MoO3 and Se powders were used as precursors in in-situ co-growth chemical vapor deposition method. Cobalt-doped MoSe2 nanosheets were grown on SiO2 substrate at 710 ℃. The influence of hydrogen content on its growth and regulation mechanism was discussed. Surface morphology analysis showed that the introduction of hydrogen promoted the formation of oxy-selenium metal compounds required for nucleation and the CoMoSe compound molecules required for lateral growth. AFM(atomic force microscope) results show that hydrogen is beneficial to the growth of single-layer two-dimensional cobalt-doped MoSe2. With the increase of the amount of Co3O4 precursor, the Raman and PL(photoluminescence) spectra of the sample showed red shift and blue shift, respectively, and the bandgap was modulated from 1.52 eV to 1.57 eV. The XPS(X-ray photoelectron spectroscopy) results analysis showed that the elemental composition ratio of Co was 4.4%. The magneto and electric properties of the samples were analyzed by SQUID-VSM(superconducting quantum interference device) and semiconductor parameter analyzer for electrical testing. The results show that MoSe2 changes from diamagnetic to soft magnetic after Co incorporation; the threshold voltage of back gate FETs is shifted by 5 V from pure MoSe2, and the off-state current is lower. This research provides a basis for the research and application development of ultra-thin two-dimensional materials. Keywords:two-dimensional materials/ MoSe2/ Colbat-doping/ chemistry phase deposition(CVD)
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3.1.氢气流量对掺Co MoSe2薄膜生长的影响
如图2(a)—(h)所示为氢气流量从4 sccm逐渐增加到11 sccm原位共生长得到的掺Co MoSe2样品的光学显微镜图像. 随氢气流量增加样品尺寸增加, 5 sccm时样品最大达到20 μm, 氢气流量为6 sccm及以上时由于二次成核密度增加, 横向生长受到抑制. 图 2 不同氢气流量下生长掺Co MoSe2样品OM图 Figure2. OM of Co-doped MoSe2 under different H2 flow rates.
图3为不同氢气流量(4, 5, 9, 10 sccm)下样品原子力形貌图, AFM断面扫描获得样品厚度如图3(e)—(h), 厚度结果表明图3(a)—(c)中样品为单层, 图3(d)中样品为双层; 选择合适的氢气流量不仅可促进样品横向生长同时实现单层可控生长. 图 3 不同氢气流量下样品形貌情况 (a)?(d)为二维形貌图; (e)?(h)为沿红色虚线的高度测量结果 Figure3. Topographic measurements under different H2 flow rates: (a)?(d) Topography; (e)?(h) profile line along the red dash line.