UCLA

The 2D materials have drawn great interests since they have been exploited. Although they have excellent properties, the mass production has been a great challenge. To overcome this, a solution proceeded approach was introduced in 2018. The MoS2 ink is prepared by intercalating ammonia salt into the raw material and exfoliated the bulk materials into small thin flakes and get a suspension solution. This MoS2 ink can be easily spin-coated on to hydrophilic surface and form a uniform large-scaled semiconducting thin film with high performance. The thin films are made of flakes overlapped with each other by van der Waals force, so we call them van der Waals thin film (VDWTF). And my projects are main about the applications of the VDWTF. The first application is using the thin film as conventional transistors. And we manage to build an integrated pressure sensor array, by combining solution-processed two-dimensional (2D) MoS2 van der Waals (vdW) thin film transistor (TFT) active matrix and conductive micropyramidal pressure-sensitive rubber (PSR) electrodes made of polydimethylsiloxane/carbon nanotube composites, to achieve spatially revolved pressure mapping with excellent contrast and low power consumption. We demonstrate a 10 by 10 active matrix by using the 2D MoS2 vdW-TFTs with high on-off ratio, minimal hysteresis, and excellent device-to-device uniformity. The combination of the vdW-TFT active matrix with the highly uniform micropyramidal PSR electrodes creates an integrated pressure sensing array for spatially resolved pressure mapping. This study demonstrates that the solution-processed 2D vdW-TFTs offer a solution for active-matrix control of pressure sensor arrays, and could be extended for other active matrix arrays of electronic. Because the thin film MoS2 has a high light transmission rate, our thin film can applied for optoelectronic devices as transparent transistor. Here we merge our thin film transparent phototransistors (TPTs) with liquid crystal (LC) modulators to create an optoelectronic neuron array that allows self-amplitude modulation of spatially incoherent light, achieving a large nonlinear contrast over a broad spectrum at orders-of-magnitude lower intensity than most optical nonlinear materials. For a proof-of-concept demonstration, we fabricated 10,000 optoelectronic neurons, each serving as a nonlinear filter, and experimentally demonstrated an intelligent imaging system that uses their nonlinear response to significantly reduce input glares while retaining the weaker-intensity objects within the field of view of a cellphone camera. This nonlinear glare-reduction capability is important for various imaging applications, including autonomous driving, machine vision, and security cameras. Beyond imaging and sensing, this optoelectronic neuron array, with its nonlinear self-amplitude modulation for processing incoherent broadband light, might also find applications in optical computing, where nonlinear activation functions that can work under ambient light conditions are highly sought. In the next chapter, we demonstrate the application of the VDWTF as flexible electronics. The films feature a sliding and rotation degree of freedom among the staggered nanosheets to ensure mechanical stretchability and malleability, as well as a percolating network of nanochannels to endow permeability and breathability. With an excellent mechanical match to soft biological tissues, the freestanding films can naturally adapt to local surface topographies and seamlessly merge with living organisms with highly conformal interfaces, rendering living organisms with electronic functions, including leaf-gate and skin-gate transistors. On-skin transistors allow high-fidelity monitoring and local amplification of skin potentials and electrophysiological signals.