2D Layered Transition Metal Dichalcogenide Semiconductors via Non-Aqueous Electrodeposition

过渡金属二卤化物(TMDCs)是式为ME2的无机材料(M=金属；E=硫化物=硫、硒或碲)。它们形成与二碘化镉相关的二维层状六方结构，其中层内的金属-硫族键非常强，而层间的金属-硫族键要弱得多(范德华相互作用)--即石墨的无机类似物。它们形成了一类极其重要的功能半导体，通过改变金属或硫化物的类型，可以调节半导体的带隙，使它们在广泛的应用中发挥作用。由于它们的结构和半导体特性，这些材料被广泛认为有可能给下一代电子产品带来革命性的变化，例如，允许大规模制造2D纳米晶体管，导致更强大和更快的设备。控制它们的维度以产生高度各向异性的ME2的单独层，导致了许多显著的性质，包括强烈的自旋分裂。因此，硫化钼/硒(MoE2)等材料的2D薄膜在各种应用中是非常有前途的候选材料。在技术上最重要的应用之一是在下一代2D晶体管中。它们缺乏“悬挂”键和结构稳定性，使其成为后硅CMOS(互补金属氧化物半导体)晶体管的主要候选者，特别是在低功率电子产品中。直到2012年，才报道了第一个完全基于2D TMDDC的场效应晶体管(FET)-使用从晶体中剥离单个层获得的钼或二硫化钨，结合氮化硼栅电介质和石墨烯电极。在可伸缩和可控制的样品制备方面的进展，以制备大量原子薄且均匀的TMDC层是需要的关键突破。我们的提案以一种独特的方式解决了这些问题。我们的愿景是率先开发一种通用平台，用于从定制的单分子化合物中非水电沉积高质量的2D层状TMDC薄膜，这些化合物可以作为金属和硫化物的来源。我们的首要任务是展示电沉积MoE_2，WE_2和具有磁性的NbE_2薄膜，很好地控制沉积薄膜中存在的M：E比和它们的形貌。我们将对它们的功能特性(电和磁)进行基准测试。由于远离导电电极表面的逐个原子生长是电沉积的固有特征，但不是其他替代(蒸气)沉积方法的典型，我们将寻求通过以下方式来利用这一独特的机会：(I)使用特殊设计的凹线电极，直接从电极的导电表面到2D层的边缘(M-E键最强)产生电接触，(Ii)将2D TMDC直接电沉积到制造的后栅晶体管结构中，以创建演示器件；这种方法将消除几个昂贵和不方便的处理步骤，例如剥离以形成单独的TMDC层，转移和电接触到TMDC的van der Waals层的顶部，以及更推测的是，(Iii)通过在实验期间改变前驱物源，基于顺序沉积p型和n型TMDC半导体，直接沉积p-n-p型结。通过这种方式，我们将确定电沉积作为生产包含这些重要材料的下一代设备的替代低成本处理方法的可行性。这是一个高风险/高收益的项目，有可能产生重大影响，在中短期内为学术研究人员提供许多机会，从长远来看，可能会产生非常重大的商业影响。

Transition metal dichalcogenides (TMDCs) are inorganic materials of formula ME2 (M = metal; E = chalcogen = sulfur, selenium or tellurium). They form 2-dimensional layered hexagonal structures related to that of cadmium diiodide, in which the metal-chalcogen bonding within the layers is very strong, whilst that between the layers is much weaker (van der Waals interactions) - i.e. inorganic analogues of graphite. They form a class of extremely important functional semiconductors, and by changing the metal or chalcogen type, the semiconductor band gap can be tuned, making them useful for a wide range of applications. As a result of both their structures and their semiconducting properties, these materials are widely considered to have the potential to revolutionalise next generation electronics, e.g. allowing the mass manufacture of 2D nanotransistors, leading to more powerful and faster devices. Controlling their dimensionality to produce individual layers of highly anisotropic ME2, leads to a number of remarkable properties, including strong spin splitting. Hence 2D thin films of materials such as molybdenum sulfide/selenide (MoE2) are highly promising candidates in a variety of applications. Amongst the most technologically important application is in next generation 2D transistors. Their lack of 'dangling' bonds and structural stability make them the primary candidate for post-Si CMOS (Complementary Metal-Oxide-Semiconductor) transistors, particularly in low power electronics. Only as recently as 2012, the first field effect transistors (FETs) based solely upon 2D TMDCs were reported - using molybdenum or tungsten disulfide obtained by exfoliation of individual layers from crystals, combined with boron nitride gate dielectric and graphene electrodes. Advances in scalable and controllable sample preparation to make large amounts of atomically thin and uniform TMDC layers is the key breakthrough required. Our proposal addresses these issues in a unique way. Our vision is to pioneer the development of a versatile platform for the non-aqueous electrodeposition of high quality 2D layered TMDC thin films from custom-made single molecular compounds that can act as the source of both the metal and the chalcogen. Our priorities are to demonstrate electrodeposition of MoE2, WE2 and the magnetically interesting NbE2 films with good control of the M:E ratio present in the deposited films and their morphology. We will benchmark their functional properties (electrical and magnetic). Since atom-by-atom growth away from a conducting electrode surface is an intrinsic feature of electrodeposition, but is not typical of other alternative (vapour) deposition methods, we will seek to exploit this unique opportunity by: (i) using specially designed recessed-line electrodes to create an electrical contact directly from the conducting surface of the electrode to the edge of the 2D layer (where the M-E bonding is strongest),(ii) electrodepositing the 2D TMDC directly into a fabricated back-gate transistor structure to create a demonstrator device; this approach would eliminate several expensive and inconvenient processing steps, such as exfoliation to form individual TMDC layers, transfer and electrical contacting onto the top of the van der Waals layer of the TMDC, and, more speculatively,(iii) directly depositing a p-n-p type junction based on sequentially depositing p-type and n-type TMDC semiconductors, by changing the precursor source during the experiment. In this way we will establish the viability of electrodeposition as an alternative low-cost processing method for the production of next generation devices incorporating these important materials. This is a high-risk/high-gain project that has the potential to have significant impact, opening up many opportunities for academic researchers in the short-medium term, and which could have very significant commercial impact in the longer term.