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.

A two-dimensional molybdenum disulfide (MoS2)-based gas sensor was decorated with Pt nanoparticles (NPs) for high sensitivity and low limit of detection (LOD) for specific gases (NH3 and H2S). The two-dimensional MoS2 film was grown at 400°C using metal organic gas vapour deposition. To fabricate the MoS2 gas sensor, an interdigitated Au/Ti electrode was deposited using the electron beam (e-beam) evaporation method with a stencil mask. The MoS2 gas sensor without metal decoration sensitively detects NH3 and H2S gas down to 2.5 and 30 ppm, respectively, at room temperature (RT). However, for improved detection of NH3 and H2S gas, we investigated the functionalization strategy using metal decoration. Pt NP decoration modulated the electronic properties of MoS2, significantly improving the sensitivity of NH3 and H2S gas by 5.58× and 4.25×, respectively, compared with the undecorated MoS2 gas sensor under concentrations of 70 ppm. Furthermore, the Pt NP-decorated MoS2 sensor had lower LODs for NH3 and H2S gas of 130 ppb and 5 ppm, respectively, at RT.

In the era of hyperconnected contemporary society, hardware and information security become more dependent on advanced cryptographic primitives. A physically unclonable function (PUF), originally implemented by an algorithmic means as software-based security, is considered as an immediate security solution. Nanomaterial-based PUFs have recently received considerable attention but have often limitations on unclonability and scalability for practical applications. Here, we report that heteronanostructures of vertically orientated molybdenum disulfide (MoS 2 ) nanoflakes and titanium dioxide (TiO 2 ) aggregates can be used for a versatile PUF. The band alignment of heteronanostructured MoS 2 /TiO 2 results in photogenerated electron transfer and turns off the bright state of emitters, offering an entropy source. After von Neumann debiasing, extracted cryptographic keys show a large encoding capacity and reliable PUF performance, including randomness, uniqueness, reproducibility, low false rates, and long-term stability. The unique hybridization of the most common semiconductor nanomaterials could not only offer inherent asymmetry not to be cloned for a PUF but also guarantee scalable nanomanufacturing strategies to augment cryptosystems.

Inverse‐vulcanized polymeric sulfur has received considerable attention for application in waste‐based infrared (IR) polarizers with high polarization sensitivities, owing to its high transmittance in the IR region and thermal processability. However, there have been few reports on highly sensitive polymeric sulfur‐based polarizers by replication of pre‐simulated dimensions to achieve a high transmission of the transverse magnetic field (TTM) and extinction ratio (ER). Herein, a 400‐nanometer‐pitch mid‐wavelength infrared bilayer linear polarizer with self‐aligned metal gratings is introduced on polymeric sulfur gratings integrated with a spacer layer (SM‐polarizer). The dimensions of the SM‐polarizer can be closely replicated using pre‐simulated dimensions via a systematic investigation of thermal nanoimprinting conditions. Spacer thickness is tailored from 40 to 5100 nm by adjusting the concentration of polymeric sulfur solution during spin‐coating. A tailored spacer thickness can maximize TTM in the broadband MWIR region by satisfying Fabry–Pérot resonance. The SM‐polarizer yields TTM of 0.65, 0.59, and 0.43 and ER of 3.12 × 103, 5.19 × 103, and 5.81 × 103 at 4 µm for spacer thicknesses of 90, 338, and 572 nm, respectively. This demonstration of a highly sensitive and cost‐effective SM‐polarizer opens up exciting avenues for infrared polarimetric imaging and for applications in polarization manipulation.

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Gas sensors applied in real-time detection of toxic gas leakage, air pollution, and respiration patterns require a reliable test platform to evaluate their characteristics, such as sensitivity and detection limits. However, securing reliable characteristics of a gas sensor is difficult, owing to the structural difference between the gas sensor measurement platform and the difference in measurement methods. This study investigates the effect of measurement conditions and system configurations on the sensitivity of two-dimensional (2D) material-based gas sensors. Herein, we developed a testbed to evaluate the response characteristics of MoS2-based gas sensors under a NO2 gas flow, which allows variations in their system configurations. Additionally, we demonstrated that the distance between the gas inlet and the sensor and gas inlet orientation influences the sensor performance. As the distance to the 2D gas sensor surface decreased from 4 to 2 mm, the sensitivity of the sensor improved to 9.20%. Furthermore, when the gas inlet orientation was perpendicular to the gas sensor surface, the sensitivity of the sensor was the maximum (4.29%). To attain the optimum operating conditions of the MoS2-based gas sensor, the effects of measurement conditions, such as gas concentration and temperature, on the sensitivity of the gas sensor were investigated.

Vertically aligned two-dimensional (2D) molybdenum disulfide nanoflowers (MoS2 NFs) have drawn considerable attention as a novel functional material with potential for next-generation applications owing to their inherently distinctive structure and extraordinary properties. We report a simple metal organic chemical vapor deposition (MOCVD) method that can grow high crystal quality, large-scale and highly homogeneous MoS2 NFs through precisely controlling the partial pressure ratio of H2S reaction gas, P SR, to Mo(CO)6 precursor, P MoP, at a substrate temperature of 250 °C. We investigate microscopically and spectroscopically that the S/Mo ratio, optical properties and orientation of the grown MoS2 NFs can be controlled by adjusting the partial pressure ratio, P SR/P MoP. It is also shown that the low temperature MOCVD (LT-MOCVD) growth method can regulate the petal size of MoS2 NFs through the growth time, thereby controlling photoluminescence intensity. More importantly, the MoS2 NFs/GaAs heterojunction flexible solar cell exhibiting a power conversion efficiency of ∼1.3% under air mass 1.5 G illumination demonstrates the utility of the LT-MOCVD method that enables the direct growth of MoS2 NFs on the flexible devices. Our work can pave the way for practical, easy-to-fabricate 2D materials integrated flexible devices in optical and photonic applications.

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