Jian-Zhang Chen

Rapid Atmospheric Pressure Plasma Jet Processed Reduced Graphene Oxide Counter Electrodes for Dye-Sensitized Solar Cells

In this work, we present the use of reduced graphene oxide (rGO) as the counter electrode materials in dye-sensitized solar cells (DSSCs). rGO was first deposited on a fluorine-doped tin oxide glass substrate by screen-printing, followed by post-treatment to remove excessive organic additives. We investigated the effect of atmospheric pressure plasma jet (APPJ) treatment on the DSSC performance. A power conversion efficiency of 5.19% was reached when DSSCs with an rGO counter electrode were treated by APPJs in the ambient air for a few seconds. For comparison, it requires a conventional calcination process at 400 °C for 15 min to obtain comparable efficiency. Scanning electron micrographs show that the APPJ treatment modifies the rGO structure, which may reduce its conductivity in part but simultaneously greatly enhances its catalytic activity. Combined with the rapid removal of organic additives by the highly reactive APPJ, DSSCs with APPJ-treated rGO counter electrode show comparable efficiencies to furnace-calcined rGO counter electrodes with greatly reduced process time. This ultrashort process time renders an estimated energy consumption per unit area of 1.1 kJ/cm(2), which is only one-third of that consumed in a conventional furnace calcination process. This new methodology thus saves energy, cost, and time, which is greatly beneficial to future mass production.

Enhanced thermoelectric power in dual-gated bilayer graphene.

The thermoelectric power of a material, typically governed by its band structure and carrier density, can be varied by chemical doping that is often restricted by solubility of the dopant. Materials showing large thermoelectric power are useful for many industrial applications, such as the heat-to-electricity conversion and the thermoelectric cooling device. Here we show a full electric-field tuning of thermoelectric power in a dual-gated bilayer graphene device resulting from the opening of a band gap by applying a perpendicular electric field on bilayer graphene. We uncover a large enhancement in thermoelectric power at a low temperature, which may open up a new possibility in low temperature thermoelectric application using graphene-based device.

Reliability of Active-Matrix Organic Light-Emitting-Diode Arrays With Amorphous Silicon Thin-Film Transistor Backplanes on Clear Plastic

We have fabricated active-matrix organic light emitting diode (AMOLED) test arrays on an optically clear high-temperature flexible plastic substrate at process temperatures as high as 285 degC using amorphous silicon thin-film transistors (a-Si TFTs). The substrate transparency allows for the operation of AMOLED pixels as bottom-emission devices, and the improved stability of the a-Si TFTs processed at higher temperatures significantly improves the reliability of the light emission over time.

Atmospheric pressure plasma jet annealed ZnO films for MgZnO/ZnO heterojunctions

Rf-sputtered ZnO films, annealed by atmospheric pressure plasma jet (APPJ), are characterized and used for MgZnO/ZnO heterostructures. The highly reactive N2 plasma generated by APPJ allows much shorter treatment time compared with conventional thermal anneals. The APPJ treatment can increase the crystallinity of ZnO films and release the compressive residue stresses, verified by XRD and UV‐Vis transmission measurements. In our previous studies, we demonstrate that thermal anneal is the critical step for the formation of two-dimensional electron gases in defective rf-sputtered MgZnO/ZnO heterostructures. This paper reports the experimental results that APPJ treatments can be used for the same purpose with a much shorter processing time. A thirty-second APPJ anneal on ZnO can be used to replace 400 ◦ C×30min furnace-anneal to promote the formation of 2DEGs in MgZnO/ZnO heterostructure. The ultra-short processing time is attributed to the synergy of plasma reactivity and temperature of APPJ. (Some figures may appear in colour only in the online journal)

Interfacial microstructures of rf-sputtered TiNi shape memory alloy thin films on (100) silicon

Abstract Interfacial microstructures of TiNi thin films rf sputtered on to Si(100) and post-annealed at 400–700°C for 30mins have been investigated using analytical and high-resolution transmission electron microscopy. For annealing temperatures below 600°C, a very thin amorphous (Si, O)-rich layer is observed at the interface. Ni atoms are the primary diffusing species and NiSi2 forms triangularly and epitaxially towards the Si substrate. TiNi films initially crystallize after 30 min at 500°C. Si and Ti atoms begin to migrate in specimens annealed at 600°C for 30min. At this temperature, a near-Ti4Ni4Si7 phase in triangular NiSi2 and a near-TiNiSi phase in the TiNi film are simultaneously nucleated and grown at the interface. For the specimens annealed at 700°C for 30 min, two layers of Ti4Ni4Si7 and TiNiSi form at the interface with the sequence TiNi/TiNiSi/Ti4Ni4Si7/Si. Triangular NiSi2 islands are now embedded in the Ti4Ni4Si7 layer. A mechanism of interfacial microstructure evolution is proposed to explain the temperature effect on the interfacial reaction layers between the TiNi film and the Si(100).

Silver halide fiber-based evanescent-wave liquid droplet sensing with room temperature mid-infrared quantum cascade lasers.

Quantum cascade lasers and unclad silver halide fibers were used to assemble mid-infrared fiber-optics evanescent-wave sensors suitable to measure the chemical composition of liquid droplets. The laser wavelengths were chosen to be in the regions which offer the largest absorption contrast between constituents inside the mixture droplets. A pseudo-Beer-Lambert law fits well with the experimental data. Using a 300microm diameter fiber with a 25 mm immersion length, the signal to noise ratios correspond to 1 vol.% for alpha-tocophenol in squalane and 2 vol.% for acetone in aqueous solution for laser wavenumbers of 1208 cm-1 and 1363 cm-1, respectively.

Electrical properties of modulation-doped rf-sputtered polycrystalline MgZnO/ZnO heterostructures

Modulation doping effect is studied in large-area rf-sputtered polycrystalline MgZnO/ZnO heterostructures. Both polarization effect at the MgZnO/ZnO interface and carrier transferring from the modulation doping layer contribute to the improvement of electrical conductivity of the heterostructure. Modulation doping provides greater enhancement in electrical properties when Mg content in the barrier layer is lower. Temperature-independent carrier concentration is observed in low-temperature Hall measurement, indicating the existence of two-dimensional electron gas in the modulation-doped polycrystalline MgZnO/ZnO structure. The slight drop in mobility at low temperatures is caused mainly by the roughness scattering and impurity scattering. (Some figures may appear in colour only in the online journal)

A study of mixing in thermocapillary flows on micropatterned surfaces

The recent introduction of actuation mechanisms for microfluidic transport based on free surface flows raises a number of interesting questions involving efficient mixing configurations, especially in systems with small aspect ratios. This work investigates the characteristics of convective and diffusive mixing in continuous–mode streaming of thermocapillary microflows on chemically micropatterned surfaces. Mixing times and mixing lengths relevant to chemical microreactors or gas sensors are investigated for various geometries and parameter ranges. Scaling arguments and full numerical solutions are presented to extract optimal operating conditions. Confocal fluorescence microscopy measurements of the interfacial diffusive broadening in adjacent flowing streams confirm numerical predictions. Three important mixing regimes, based on analogues of purely diffusive dynamics, Rhines–Young shear–augmented diffusion and Taylor–Aris dispersion are identified and investigated for use in free surface flows with large surface–to–volume ratios.

Atmospheric-pressure-plasma-jet processed nanoporous TiO2 photoanodes and Pt counter-electrodes for dye-sensitized solar cells

We demonstrate the rapid fabrication of dye-sensitized solar cells (DSSCs) with both TiO2 photoanodes and Pt counter-electrodes processed using atmospheric pressure plasma jets (APPJs). The rapid conversion of PtCl62− to Pt for the counter-electrode of DSSCs is achieved using a 1 min 360 °C air-quenched N2 APPJ. The APPJ-processed Pt counter-electrode is then used together with an APPJ-calcined nanoporous TiO2 photoanode to make DSSCs that exhibit comparable efficiencies to those of cells fabricated using conventional furnace-calcination processes. APPJs can reduce the calcination durations from 30 min to 4 min for the nanoporous TiO2 photoanode and from 15 min to 1 min for the Pt counter electrode. The ultra-short processes of DSSCs are benefited from the synergistic effects of the energetic nitrogen molecules and the heat of APPJs.

Ultrafast synthesis of continuous Au thin films from chloroauric acid solution using an atmospheric pressure plasma jet

Au can be easily formed by thermal calcination via the reduction of chloroauric acid. However, a conventional hot-plate or furnace calcination procedure often results in a piecewise and island-like film. In this study, the rapid synthesis of continuous Au thin films from spin-coated chloroauric acid precursor films is demonstrated by using an atmospheric pressure plasma jet (APPJ). The sheet resistance decreases from 2.175 to 0.997 Ω sq−1 as the APPJ processing time increases from 7 to 60 s. This ultrafast synthesis of continuous Au thin films is made possible by the synergistic effect of the highly energetic/reactive nitrogen species and the heat generated by APPJs.