Chun-Hsiung Wang

p-Si nanowires/SiO2/n-ZnO heterojunction photodiodes

Influence of a SiO2 ultrathin film on n-ZnO/p-silicon nanowires photodiodes has been investigated. With a SiO2 thin layer, the diode characteristics can be significantly improved, which exhibits high responsivity under a reverse bias. Based on the electron conversion efficiency measurement, we show that the ultrathin SiO2 layer with positive fixed charges not only acts as a hole blocking layer but also helps the photogenerated electrons to tunnel through the barrier. In addition, the SiO2 layer can effectively passivate the defects generated by wet etching process. It is expected that our approach can be extended to many other nanoscale heterojunction devices.

Mechanically tunable surface plasmon resonance based on gold nanoparticles and elastic membrane polydimethylsiloxane composite

Surface plasmon in nanoscaled materials has recently attracted a great deal of attention due to its possibility in a wide range of application. From a practical standpoint, it is desirable for the devices having a tunability of surface plasmon frequency. To achieve this goal, in this study, a composite consisting of two-dimensional gold nanoparticles array embedded in elastic polydimethylsiloxane (PDMS) membrane has been synthesized. Because the elastic PDMS membrane has a high malleability, with an external stress, it is very easy to regulate the interparticle distance in the gold nanoparticle array. The change in the distance between each nanoparticle will alter the surface plasmon interaction, and hence surface plasmon frequency can be manipulated. It is found that when the interparticle distance increases, the enhanced surface plasma mutual coupling will cause the blueshift of surface plasmon resonance frequency. The observed result satisfies the forecast based on electromagnetic theory.

Cardiac tamponade in an infant : a rare complication of central venous catheterisation

A 2994g infant suffered cardiac tamponade from an infusion of total parenteral nutrition through an indwelling central venous catheter. The infant survived as a result of early diagnosis and aggressive therapeutic intervention. Cardiac tamponade secondary to central venous catheterisation is rare, but potentially lethal. Possible mechanisms are direct puncture by the catheter tip, or osmotic injury from the use of hypertonic solutions. To avoid this complication, the catheter tip should be prevented from entering the right atrium and its position should be checked periodically by chest X ray. Cardiac tamponade should be considered in any patient with a central venous catheter whose clinical condition deteriorates suddenly. Diagnostic or therapeutic pericardiocentesis should be employed as the first measure and time should not be wasted on other diagnostic procedures.

Tunable coupling between exciton and surface plasmon in liquid crystal devices consisting of Au nanoparticles and CdSe quantum dots

We report controllable coupling between exciton and localized surface plasmon in a liquid crystal device consisting of gold nanoparticles and CdSe quantum dots. Through an external electric voltage, the emission wavelength of quantum dots can be manipulated. The underlying mechanism is based on the fact that by changing the dielectric index of liquid crystal with an external bias, the surface plasmon frequency of metal nanoparticles can be adjusted. It is therefore possible to control the energy difference between exciton and surface plasmon resonance, and hence to change their coupling strength. Our strategy may open up a possible route for the development of smart optoelectronic devices with tunable emission color.

Ultraviolet electroluminescence from hybrid inorganic/organic ZnO/GaN/poly(3-hexylthiophene) dual heterojunctions.

Based on hybrid inorganic/organic n-ZnO nanorods/p-GaN thin film/poly(3-hexylthiophene)(P3HT) dual heterojunctions, the light emitting diode (LED) emits ultraviolet (UV) radiation (370 nm - 400 nm) and the whole visible light (400 nm -700 nm) at the low injection current density. Meanwhile, under the high injection current density, the UV radiation overwhelmingly dominates the room-temperature electroluminescence spectra, exponentially increases with the injection current density and possesses a narrow full width at half maximum less than 16 nm. Comparing electroluminescence with photoluminescence spectra, an enormously enhanced transition probability of the UV luminescence in the electroluminescence spectra was found. The P3HT layer plays an essential role in helping the UV emission from p-GaN material because of its hole-conductive characteristic as well as the band alignment with respect to p-GaN. With our new finding, the result shown here may pave a new route for the development of high brightness LEDs derived from hybrid inorganic/organic heterojuctions.

Highly sensitive MOS photodetector with wide band responsivity assisted by nanoporous anodic aluminum oxide membrane

A new approach for developing highly sensitive MOS photodetector based on the assistance of anodic aluminum oxide (AAO) membrane is proposed, fabricated, and characterized. It enables the photodetector with the tunability of not only the intensity but also the range of the response. Under a forward bias, the response of the MOS photodetector with AAO membrane covers the visible as well as infrared spectrum; however, under a reverse bias, the near-infrared light around Si band edge dominates the photoresponse. Unlike general MOS photodetectors which only work under a reverse bias, our MOS photodetectors can work even under a forward bias, and the responsivity at the optical communication wavelength of 850nm can reach up to 0.24 A/W with an external quantum efficiency (EQE) of 35%. Moreover, the response shows a large enhancement factor of 10 times at 1050 nm under a reverse bias of 0.5V comparing with the device without AAO membrane. The underlying mechanism for the novel properties of the newly designed device has been proposed.

Magnetically tunable surface plasmon resonance based on a composite consisting of noble metal nanoparticles and a ferromagnetic thin film

We demonstrate magnetically tunable surface plasmon resonance based on a composite consisting of noble metal nanoparticles and ferromagnetic thin film. We found that both the frequency and linewidth of the localized surface plasmon resonance can be manipulated by applying an external magnetic field. The underlying mechanism is attributed to the variation of the dielectric constant in the ferromagnetic thin film resulting from the change of magnetization. Our result shown here paves an alternative route for manipulation of the characteristics of the surface plasmon resonance, which may serve as a new design concept for the development of magneto-optical devices.