Ming Liang Jin

High-Resolution p-Type Metal Oxide Semiconductor Nanowire Array as an Ultrasensitive Sensor for Volatile Organic Compounds

The development of high-performance volatile organic compound (VOC) sensor based on a p-type metal oxide semiconductor (MOS) is one of the important topics in gas sensor research because of its unique sensing characteristics, namely, rapid recovery kinetics, low temperature dependence, high humidity or thermal stability, and high potential for p-n junction applications. Despite intensive efforts made in this area, the applications of such sensors are hindered because of drawbacks related to the low sensitivity and slow response or long recovery time of p-type MOSs. In this study, the VOC sensing performance of a p-type MOS was significantly enhanced by forming a patterned p-type polycrystalline MOS with an ultrathin, high-aspect-ratio (∼25) structure (∼14 nm thickness) composed of ultrasmall grains (∼5 nm size). A high-resolution polycrystalline p-type MOS nanowire array with a grain size of ∼5 nm was fabricated by secondary sputtering via Ar(+) bombardment. Various p-type nanowire arrays of CuO, NiO, and Cr2O3 were easily fabricated by simply changing the sputtering material. The VOC sensor thus fabricated exhibited higher sensitivity (ΔR/Ra = 30 at 1 ppm hexane using NiO channels), as well as faster response or shorter recovery time (∼30 s) than that of previously reported p-type MOS sensors. This result is attributed to the high resolution and small grain size of p-type MOSs, which lead to overlap of fully charged zones; as a result, electrical properties are predominantly determined by surface states. Our new approach may be used as a route for producing high-resolution MOSs with particle sizes of ∼5 nm within a highly ordered, tall nanowire array structure.

Highly Efficient Top‐Illuminated Flexible Polymer Solar Cells with a Nanopatterned 3D Microresonant Cavity

Top-illuminated flexible polymer solar cells with 3D micoresonant cavity provide not only powerful light-trapping but also electrical enhancement, resulting in significant enhancement of power efficiency (26.4%). Capping layer (CL) enhanced the transmittance of the transparent electrodes, increasing electric field intensity in the photoactive layer by forming microresonant cavity, and the nano-pattern on the rear electrodes caused significant enhancement to the Jsc by improving light absorption and charge collection.

An Ultrasensitive, Visco‐Poroelastic Artificial Mechanotransducer Skin Inspired by Piezo2 Protein in Mammalian Merkel Cells

An artificial ionic mechanotransducer skin with an unprecedented sensitivity over a wide spectrum of pressure by fabricating visco-poroelastic nanochannels and microstructured features, directly mimicking the physiological tactile sensing mechanism of Piezo2 protein is demonstrated. This capability enables voice identification, health monitoring, daily pressure measurements, and even measurements of a heavy weight beyond capabilities of human skin.

Ultraclean transfer of CVD-grown graphene and its application to flexible organic photovoltaic cells

We demonstrate a PMMA reverse transfer method, where a PMMA/graphene bilayer was reversely transferred onto target substrates, to better control both contamination and crack formation relative to conventional approaches. Based on this novel transfer process, the graphene sheet resistance was greatly reduced by about 50% at the same transmittance, exhibiting ∼200% higher efficiency when applied in a solar cell as the anode.

Surface plasmon assisted high performance top-illuminated polymer solar cells with nanostructured Ag rear electrodes

Highly efficient plasmonic Ag rear electrodes in top-illuminated PSCs employing MoO3/Ag (13 nm)/MoO3 stacks as top transparent electrodes were successfully demonstrated, resulting in the significant enhancement of solar cell performance with a PCE of up to 7.18%. The hemispherical Ag nanostructured arrays effectively concentrate incident light within the photoactive layer in addition to contributing to extended stability with a robust structure.

High-performance of PEDOT/PSS free organic solar cells on an air-plasma-treated ITO substrate.

In this work, we demonstrate the high-performance of a PEDOT:PSS free organic photovoltaic cell (OPVC) using an air-plasma modified ITO surface, followed by controlled solvent evaporation and annealing of the P3HT:PCBM photoactive layer. Ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and conductive atomic force microscopy (c-AFM) results show that the work function of ITO was increased to as high as that of PEDOT:PSS (5.2 eV) after air-plasma treatment, along with significantly enhanced electrical homogeneity. From the dynamic secondary ion mass spectroscopy (DSIMS) results, we confirm that the thermodynamic stability of the slow-dried active layer is attributed to the uniform vertical compositional distribution on the air plasma treated ITO surface, even after thermal annealing at 150 °C for 10 min. The resulting device has an open-circuit voltage of 0.65 V, a fill factor of 63%, and a power conversion efficiency of 3.38%, providing a high performance PEDOT:PSS free OPVC device.

Nanoporous SiCOH/CxHy dual phase films with an ultralow dielectric constant and a high Young's modulus

We used plasma-enhanced chemical vapor deposition (PECVD) of allyltrimethylsilane (ATMS), consisting of an allyl group along with three methyl groups attached to silicon, to form a low dielectric constant (low-k) and high modulus SiCOH matrix. We found that the dielectric constant and mechanical properties of the low-k material are strongly affected by the selection of the precursor, processing conditions such as the deposition temperature and post-treatment, the introduction of a second labile phase, and the chemical structure and composition of the films. After porogen (pore generator) treatment with cyclohexene oxide (CHO), the resulting material exhibited a low dielectric constant with excellent mechanical and thermal properties, having k ∼ 2.4 and a Youngs modulus of 8.4 GPa. FT-IR and XPS results show that this is caused by the desorption of the labile phase (CxHy), the formation of Si–O cage-like structures, and changes in the chemical composition of films after thermal treatment. SiO2, SiO3, and SiO4 impart greater modulus and hardness to the films by increasing the stable component of Si–O in the SiCOH matrix.

Highly robust SiCOH/mesoporous SiO2 ultralow dielectric films with heterostructures

We report here a new dual-coating method for the deposition of SiCOH (elementally descriptive but not representing the stoichiometry) ATMS (allyltrimethylsilane) low-k films on mesoporous SiO2 (SBA-15)/PEG (polyethylene glycol) composite films to improve the dielectric constant and mechanical properties of SiCOH/SBA-15 dual forms. The deposition was achieved via a two-step process: (i) pre-treatment, where SBA-15 was mixed with a dispersion of PEG in DI water, and SBA-15/PEG composite films were formed by spin-coating; and (ii) post-treatment, involving the deposition of SiCOH films on SBA-15s functionalized with PEGs and post-thermal annealing. In comparison with SiCOH-only films, SiCOH/SBA-15 dual forms exhibited a 20% reduction in the dielectric constant without a significant loss of mechanical properties after post-thermal annealing. SEM, TEM, XRD, BET, FT-IR, EP, and XPS results show that the enhanced electrical properties can be attributed to mesoporous SiO2 and additional porosity gained through the removal of PEG and CxHy (thermally labile phases in SiCOH films) after post-thermal annealing. In the SiCOH/SBA-15 dual forms, the SBA-15 layer is expected to function as a soft layer which acts as a buffer layer to prevent the rapid decay of the modulus and hardness.

Comparison of blend morphologies of the nano-patterned photoactive films via two different techniques: thermal-assisted and solvent-assisted soft-nanoimprint lithography

In this work, we investigate the blend morphology of nano-patterned P3HT:PCBM mixture films formed by different patterning processes and their effect on the performance of organic photovoltaic cells (OPVCs). Patterns were prepared by thermal and solvent-assisted soft nanolithography using flexible poly(dimethylsiloxane) (PDMS) molds in order to give different patterning conditions. The vertical and lateral phase separation of the blend mixture and the crystallinity and orientation of the polymer chain were examined by various characterization methods, including atomic force microscopy (AFM), transmission electron microscopy (TEM), dynamic secondary ion mass spectroscopy (DSIMS) and grazing incident X-ray diffraction (GIXRD). We found that blend morphologies are greatly affected by the patterning conditions which include the modulus and mobility of each component and the interaction between the polymer blend and the mold surface during the patterning procedure. The device prepared by thermal-assisted soft nanoimprint lithography (SNL) showed the highest performance due to the uniform vertical compositional distribution and enhanced vertical conformation and high crystallinity of the polymer chain.

10 nm scale nanopatterning on flexible substrates by a secondary sputtering phenomenon and their applications in high performance, flexible and transparent conducting films

We present a simple nanopatterning method for flexible substrates with high resolution (approx. 15 nm) that uses the secondary sputtering phenomenon (SSP) and no solvents at room temperature, and characterize flexible and transparent conducting films that have performances comparable to that of ITO films yet higher mechanical stability.