Zuqin Liu

Multilevel memory based on molecular devices

Multilevel molecular memory devices were proposed and demonstrated for nonvolatile data storage up to three bits (eight levels) per cell, in contrast to the standard one-bit-per-cell (two levels) technology. In the demonstration, charges were precisely placed at up to eight discrete levels in redox active molecules self-assembled on single-crystal semiconducting nanowire field-effect transistors. Gate voltage pulses and current sensing were used for writing and reading operations, respectively. Charge storage stability was tested up to retention of 600 h, as compared to the longest retention of a few hours previously reported for one-bit-per-cell molecular memories.

Highly simplified phosphorescent organic light emitting diode with >20% external quantum efficiency at >10,000 cd/m2

A simplified trilayer green phosphorescent organic light emitting diode with high efficiency and an ultralow efficiency roll-off has been demonstrated. In particular, the external quantum efficiency drops <1% from 100 to 5,000 cd/m2 and remains as high as ∼21.9% at 10,000 cd/m2. The power efficiency is also significantly improved, reaching 78.0 lm/W at 100 cd/m2, 50.5 lm/W at 5,000 cd/m2, and 42.8 lm/W at 10,000 cd/m2. The working mechanism of this simple device structure with an unprecedented high efficiency is also discussed.

Synthesis, Electronic Properties, and Applications of Indium Oxide Nanowires

Abstract: Single‐crystalline indium oxide nanowires were synthesized using a laser ablation method and characterized using various techniques. Precise control over the nanowire diameter down to 10 nm was achieved by using monodisperse gold clusters as the catalytic nanoparticles. In addition, field effect transistors with on/off ratios as high as 104 were fabricated based on these nanowires. Detailed electronic measurements confirmed that our nanowires were n‐type semiconductors with thermal emission as the dominating transport mechanism, as revealed by temperature‐dependent measurements. Furthermore, we studied the chemical sensing properties of our In2O3 nanowire transistors at room temperature. Upon exposure to a small amount of NO2 or NH3, the nanowire transistors showed a decrease in conductance of up to five or six orders of magnitude, in addition to substantial shifts in the threshold gate voltage. Our devices exhibit significantly improved chemical sensing performance compared to existing solid‐state sensors in many aspects, such as the sensitivity, the selectivity, the response time and the lowest detectable concentrations. We have also demonstrated the use of UV light as a “gas cleanser” for In2O3 nanowire chemical sensors, leading to a recovery time as short as 80 seconds.

Pushing the limit of metal-oxide nanowire chemical sensing: selective detection of NO2 down to ppb levels

We demonstrate detection of NO2 down to ppb levels using transistors based on both single and multiple In2O3 nanowires operating at room temperature. This represents orders-of-magnitude improvement over previously reported metal oxide film or nanowire/nanobelt sensors. A comparison between the single and multiple nanowire sensors reveals that the latter have numerous advantages in terms of great reliability, high sensitivity and simplicity in fabrication. Furthermore, selective detection of NO2 can be readily achieved with multiple-nanowire sensors even with other common chemicals such as NH3, O2, CO and H2 around.

Laser ablation synthesis of oxide nanowires and their properties

We report an efficient and reliable laser-ablation approach for large-scale synthesis of SnO/sub 2/ and ZnO nanowires. The nanowire growth followed the vapor-liquid-solid model. Precise control over the nanowire diameters has been achieved by using monodispersed gold clusters as the catalyst. Detailed material analysis such as transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to confirm the crystal structure of the nanowires. In addition, field effect transistors have been constructed based on individual SnO/sub 2/ nanowires, and excellent n-type transistor characteristics were observed. These nanowire transistors were further demonstrated to work as sensitive UV detectors.