Semiconducting two-dimensional (2D) materials, particularly extremely thin molybdenum disulfide (MoS) films, are attracting considerable attention from academia and industry owing to their distinctive optical and electrical properties. Here, we present the direct growth of a MoS monolayer with unprecedented spatial and structural uniformity across an entire 8 inch SiO/Si wafer. The influences of growth pressure, ambient gases (Ar, H), and S/Mo molar flow ratio on the MoS layered growth were explored by considering the domain size, nucleation sites, morphology, and impurity incorporation. Monolayer MoS-based field effect transistors achieve an electron mobility of 0.47 cm V s and on/off current ratio of 5.4 × 10. This work demonstrates the potential for reliable wafer-scale production of 2D MoS for practical applications in next-generation electronic and optical devices.

more attention due to their low resistance and relatively high ductility. One of the main methods used previously to fabricate transparent and stretchable conductors with metal nanomaterials is to create buckling confi gurations of metal nanowires on stretchable polymers, which can be classifi ed as in-plane or out-of-plane buckling (wavy) confi gurations. [ 25,26 ] For example, Ho et al. reported the fabrication of transparent and stretchable conductors based on buckled Ag nanowire fi lms with in-plane or out-of-plane buckling confi gurations. [ 25 ] In a similar approach, it was also demonstrated that the prestrain mode (e.g., uniaxial or biaxial prestrain), extent of prestrain ( ε pre ), and adhesion between metal nanowires and a stretchable substrate are important factors that affect the stretchability of such conductors. [ 26 ] Another approach is to obtain fl exibility or stretchability by making nanowire-based networks or one-body mesh structures. [23][24][25][26][27][28][30][31][32][33][34][35] Most studies concerning one-body mesh structures have reported their applications for fl exible conductors, rather than stretchable ones, with only a few exceptions. [ 30,34 ] For example, Jang et al. reported stretchable conductors made from one-body Pt nanomesh. [ 30 ] Although their Pt nanomesh maintained its conductive properties at as much as 16% strain, its stretchability does not seem to be high enough for it to be used in true wearable electronic devices. This limited stretchability is probably due to the rigid nature of its tightly connected one-body confi guration. On the other hand, networks of metallic nanowires are rather promising for future use as transparent and stretchable electrodes. [25][26][27][28] In these cases, the sheet resistance of percolated networks of metallic nanowires is critically governed by the aspect ratio, areal density, and size dispersity of nanowires. [ 36 ] Recently, extremely long metal nanofi bers generated via electrospinning techniques have been in the limelight as an alternative to metal nanowires, due to their extremely high aspect ratios as well as the simple and cost-effective fabrication process used to produce them. [37][38][39] In particular, metal nanofi ber networks in the form of nanotroughs [ 37,38 ] and metal/polymer core-shell structures [ 39 ] generated using electrospinning techniques have low strain sensitivities under tensile strains up to 70% due to the high aspect ratio of the nanofi bers and the network structures into which they are arranged. However, combining the above-mentioned buckled and network confi gurations with metallized electrospun nanofi bers has not been investigated for the fabrication of transparent and stretchable conductors.Herein, a novel strategy for obtaining transparent and stretchable conductors is presented, one that employs these two main approaches simultaneously. To the best of our knowledge, this proposed confi guration of a buckled long nanofi ber In the past decade, the fi eld of stretchable electronics has gained importa...

Batch growth of high-mobility (μFE > 10 cm2V–1s–1) molybdenum disulfide (MoS2) films can be achieved by means of the chemical vapor deposition (CVD) method at high temperatures (>500 °C) on rigid substrates. Although high-temperature growth guarantees film quality, time- and cost-consuming transfer processes are required to fabricate flexible devices. In contrast, low-temperature approaches (<250 °C) for direct growth on polymer substrates have thus far achieved film growth with limited spatial homogeneity and electrical performance (μFE is unreported). The growth of a high-mobility MoS2 film directly on a polymer substrate remains challenging. In this study, a novel low-temperature (250 °C) process to successfully overcome this challenge by kinetics-controlled metal–organic CVD (MOCVD) is proposed. Low-temperature MOCVD was achieved by maintaining the flux of an alkali-metal catalyst constant during the process; furthermore, MoS2 was directly synthesized on a polyimide (PI) substrate. The as-grown film exhibits a 4 in. wafer-scale uniformity, field-effect mobility of 10 cm2V–1s–1, and on/off ratio of 105, which are comparable with those of high-temperature-grown MoS2. The directly fabricated flexible MoS2 field-effect transistors demonstrate excellent stability of electrical properties following a 1000 cycle bending test with a 1 mm radius.

Phase transition and coexistence of 2H (trigonal prismatic structure) and 1T′ (distorted octahedral structure) phases occur easily in molybdenum ditelluride (MoTe 2 ) when compared with other 2D MX 2 type (M = Mo, W and X = S, Se) transition metal dichalcogenides (TMDs) because of small discrepancies in the cohesive energy. [1][2][3][4] Phase-engineered 2D TMDs, particularly MoTe 2 films including 2H, 1T′, and 1T phases, are very attractive candidates for numerous electronic applications, such as ambipolar field-effect transistors (FETs), environmental sensors, superconductors, spintronics, and valley optoelectronics. [5][6][7][8] Atomically thin-layer 2H MoTe 2 possesses a narrow bandgap energy of 1 eV in comparison to the bandgap energy (1.89 eV) of monolayer MoS 2 and is a potential candidate for various optoelectronic device applications, such as solar cells and photodetectors. [3,8,9] From the electronic device application point of view, the 2H and the 1T phases, i.e., semiconducting and semimetal MoTe 2 are applicable as a 2D materials beyond molybdenum disulfide such as molybdenum ditelluride (MoTe 2 ) have attracted increasing attention because of their distinctive properties, such as phase-engineered, relatively narrow direct bandgap of 1.0-1.1 eV and superior carrier transport. However, a wafer-scale synthesis process is required for achieving practical applications in next-generation electronic devices using MoTe 2 thin films. Herein, the direct growth of atomically thin 1T′, 1T′-2H mixed, and 2H phases MoTe 2 films on a 4 in. SiO 2 /Si wafer with high spatial uniformity (≈96%) via metal-organic vapor phase deposition is reported. Furthermore, the wafer-scale phase engineering of few-layer MoTe 2 film is investigated by controlling the H 2 molar flow rate. While the use of a low H 2 molar flow rate results in 1T′ and 1T′-2H mixed phase MoTe 2 films, 2H phase MoTe 2 films are obtained at a high H 2 molar flow rate. Field-effect transistors fabricated with the prepared 2H and 1T′ phases MoTe 2 channels reveal p-type semiconductor and semimetal properties, respectively. This