Transition metal dichalcogenides such as MoS2 and WS2 are low-dimensional semiconductor materials. MoS2 and WS2 nanotubes and flakes were grown by a chemical transport reaction under a temperature gradient. I2 was used as a transport agent for previously synthesized MoS2 and WS2, respectively. These multilayered nanotubes are indirect bandgap semiconductors with a bandgap depending on their diameter. WS2 flakes were prepared by the sulfurization of thin WOx flakes. To increase the field enhancement of such low-dimensional structures by a higher aspect ratio, two approaches were examined: (a) the MoS2 and WS2 nanotubes were attached individually by a focused ion beam with Pt on dry etched n-type Si pillars and (b) the WS2 flakes were grown directly on the surface of the (n-type and p-type) Si pillars. Integral field emission measurements were performed in a diode configuration with a 50 μm mica spacer in a vacuum chamber at pressures of about 10−9 mbar. At a voltage of 900 V (18 MV/m), the integral emission current from the nanotubes is up to 11 μA for the lateral mounted MoS2 and about 1.3 μA (1.0 μA) for the upright mounted WS2 (MoS2). The onset voltage for a current of 1 nA is about 550 V for MoS2 and 500 V for WS2, respectively. The voltage conversion factor is in the range of 6 × 104–8 × 104 cm−1 for the nanotubes. The mounted MoS2 flakes show a field emission current of about 6 μA at 18 MV/m in contrast to the directly grown WS2 flakes, which show a pronounced saturation regime and, therefore, a lower emission current of about 0.5 μA is reached at 1500 V (25 MV/m). The WS2 flakes show a two times higher (1 × 105 cm−1) voltage conversion factor in comparison to the MoS2 flakes (5 × 104 cm−1). The extracted characteristics of the current-limiting part show a difference in the behavior of the extracted current-limiting characteristics between the lateral (linear) and upright mounted (exponential) nanotubes and the MoS2 flakes. In contrast, the WS2 flakes show charge carrier depletion effects.

中文翻译：

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纳米管和过渡金属二硫属化物薄片的场发射

过渡金属二硫属化物如 MoS2 和 WS2 是低维半导体材料。MoS2 和 WS2 纳米管和薄片在温度梯度下通过化学传输反应生长。I2 分别用作先前合成的 MoS2 和 WS2 的转运剂。这些多层纳米管是间接带隙半导体，带隙取决于它们的直径。WS2 薄片是通过薄 WOx 薄片的硫化制备的。为了通过更高的纵横比增加这种低维结构的场增强，研究了两种方法：（a）通过聚焦离子束将 MoS2 和 WS2 纳米管分别附着在干蚀刻 n 型硅柱上和（ b) WS2 薄片直接生长在（n 型和 p 型）Si 柱的表面上。积分场发射测量是在二极管配置中进行的，在大约 10-9 毫巴的压力下，在真空室中使用 50 μm 云母垫片。在 900 V (18 MV/m) 的电压下，纳米管的积分发射电流对于横向安装的 MoS2 高达 11 μA，对于直立安装的 WS2 (MoS2) 约为 1.3 μA (1.0 μA)。对于 MoS2 和 WS2，1 nA 电流的起始电压分别约为 550 V 和 500 V。纳米管的电压转换系数在 6 × 104–8 × 104 cm-1 范围内。与直接生长的 WS2 薄片相比，安装的 MoS2 薄片在 18 MV/m 下显示出约 6 μA 的场发射电流，后者显示出明显的饱和状态，因此，在 1500 V 时达到约 0.5 μA 的较低发射电流(25 MV/m)。与 MoS2 薄片 (5 × 104 cm-1) 相比，WS2 薄片显示出高两倍 (1 × 105 cm-1) 的电压转换因子。限流部分的提取特性显示了横向（线性）和直立安装（指数）纳米管与二硫化钼薄片之间提取的限流特性的行为差异。相比之下，WS2 薄片显示出电荷载流子耗尽效应。