Growth Mechanisms and Electronic Properties of Vertically Aligned MoS2

Abstract

Thin films of layered semiconductors emerge as highly promising materials for energy harvesting and storage, optoelectronics and catalysis. Their natural propensity to grow as oriented crystals and films is one of their distinct properties under recent focal interest. Specifically, the reaction of transition metal films with chalcogen vapor can result in films of vertically aligned (VA) layers, while metal-oxides react with chalcogens in vapor phase to produce horizontally aligned crystals and films. The growth mechanisms of vertically oriented films are not yet fully understood, as well as their dependence on the initial metal film thickness and growth conditions. Moreover, the resulting electronic properties and the role of defects and disorder had not yet been studied, despite their critical influence on catalytic and device performance. In this work, we study the details of oriented growth of MoS2 with complementary theoretical and experimental approaches. We present a general theoretical model of diffusion-reaction growth that can be applied to a large variety of layered materials synthesized by solid-vapor reaction. Moreover, we inspect the relation of electronic properties to the structure of vertically aligned MoS2 and shed light on the density and character of defects in this material. Our measurements on Si-MoS2 p-n hetero-junction devices point to the existence of polarizable defects that impact applications of vertical transition-metal dichalcogenide materials.

Vertically-oriented MoS2 nanosheets for nonlinear optical devices

“…These results are consistent with theoretical models of the diffusion-reaction growth proposed for the synthesis of vertically-oriented MoS 2 . 29 From the HR-TEM cross-section lamella analysis (Fig. S4 †) we also found an orientation-disordered region extending from the surface to the first 20 nanometers, where both vertical and horizontal MoS 2 nanosheets are present.…”

“…22 Specifically, thicker and more uniform Mo-metal seed layers lead to a higher fraction of v-MoS 2 layers. Additionally, theoretical models have been also constructed aiming to describe the synthesis of vertically-oriented MoS 2 based on the solid-vapor reaction, [21][22][23][24] though most of these predictions remain to be verified.…”

Tuning the orientation of few-layer MoS2 films using one-zone sulfurization

“…However, the effect of the heating rate is by far less explored. Stern et al 38 prepared MoS 2 from 70 nm thick Mo layer using two different heating rates (20 C min À1 and 5 C min À1 ). They observed a gradual transition from the disordered crystalline MoS 2 to vertically oriented morphology.…”

Catalytic Hydrogen Evolution Reaction Enhancement on Vertically Aligned MoS2 by Synergistic Addition of Silver and Palladium

“…Similar structures have been used in the past for Nb‐doping of MoS 2 using CVD . After preparation in the electron beam deposition system, samples were sulfurized as described in the materials and methods section . The VA‐MoS 2 and Ag/VA‐MoS 2 samples were both additionally modified by Pd galvanic replacement using a 10 μM PdCl 2 electrolyte bath.…”