Cih-Su Wang

Biologically inspired flexible quasi-single-mode random laser: An integration of Pieris canidia butterfly wing and semiconductors

Quasi-periodic structures of natural biomaterial membranes have great potentials to serve as resonance cavities to generate ecological friendly optoelectronic devices with low cost. To achieve the first attempt for the illustration of the underlying principle, the Pieris canidia butterfly wing was embedded with ZnO nanoparticles. Quite interestingly, it is found that the bio-inspired quasi-single-mode random laser can be achieved by the assistance of the skeleton of the membrane, in which ZnO nanoparticles act as emitting gain media. Such unique characteristics can be interpreted well by the Fabry-Perot resonance existing in the window-like quasi-periodic structure of butterfly wing. Due to the inherently promising flexibility of butterfly wing membrane, the laser action can still be maintained during the bending process. Our demonstrated approach not only indicates that the natural biological structures can provide effective scattering feedbacks but also pave a new avenue towards designing bio-controlled photonic devices.

Surface plasmon enhanced energy transfer between type I CdSe/ZnS and type II CdSe/ZnTe quantum dots

Fluorescence resonant energy transfer (FRET) has been investigated between donor-acceptor pairs of type I CdSe/ZnS and type II CdSe/ZnTe quantum dots (QDs). An Au nanoparticles assisted FRET enhancement was clearly demonstrated. It is found that the efficiency of the energy transfer depends on the excitation wavelength and is largest when in resonance with the Au surface plasmon mode. With the large tunability of the emission intensity in near infrared region, our finding paves an excellent route for creating highly efficient optoelectronic devices and bioimaging labels derived from type II QDs.

Photoluminescence properties of CdTe∕CdSe core-shell type-II quantum dots

We report investigations on the optical properties of type-II CdTe∕CdSe core-shell quantum dots. By varying the core size, we provide an elegant way to verify that the detected emission signal indeed arises from type-II band alignment. The photoluminescence (PL) peak energy increases with a third root of the excitation power. Both of the PL peak energy and linewidth exhibit unique temperature dependence. All these observations can be rationalized by the band bending effect resulting from the spatially separated photoexcited carriers in a type-II band alignment.

Multiple deep-seated cavernomas in the third ventricle, hypothalamus and thalamus.

Summary¶Background. Cavernomas are rarely located in the third ventricle, hypothalamus, or thalamus. In this report, we present our experience managing a patient with three cavernomas, one each in the floor of the third ventricle, hypothalamus, and left thalamus. Case presentation. This 62-year-old woman had had an unsteady gait and weakness of both legs for six months. Magnetic resonance imaging (MRI) revealed multiple intracranial tumours in the third ventricle, hypothalamus, and left thalamus. The third ventricle tumour was found to be a cavernoma by intra-operative endoscopic examination and then was excised via a transcortical, transventricular approach. Pathology revealed a cavernoma. The other two tumours were assumed to be cavernomas because of their MRI features. Three days after surgery, the patient developed right hemiparesis and disturbance of consciousness. Computed tomography revealed a left thalamic haemorrhage. After conservative treatment, her conscious level gradually recovered and she could walk with support seven months after surgery. Interpretation. Our experience with this rare case of multiple, deep-seated cavernomas suggests that management of such patients requires specific consideration of the clinical manifestations, location, size, and previous bleeding history.

Tunable emission based on the composite of Au nanoparticles and CdSe quantum dots deposited on elastomeric film

A simple approach to investigate the dependence of emission on the separation distance between metal nanoparticles and semiconductor quantum dots is demonstrated. Without varying the mixed concentrations, a tunable emission is achieved based on the deposition of the composite of Au nanoparticles and CdSe quantum dots on elastomeric film. By utilizing the inherent nature of the elasticity of the elastomeric film, it is found that depending on the separation distance, the emission intensity can be quenched or enhanced. The underlying mechanism can be explained quite well by the interplay between the local field excitation due to surface plasmons and electrons transfer to metal nanoparticles.

Surface-Plasmon-Enhanced Ultraviolet Random Lasing from ZnO Nanowires Assisted by Pt Nanoparticles

We report a surface-plasmon-enhanced random laser emission from highly disordered ZnO nanowires with the assistance of Pt nanoparticles. The underlying mechanism of the enhanced lasing efficiency can be attributed to the energy transfer from Pt nanoparticles to ZnO nanowires due to the strong local field induced by the surface plasmon resonance of Pt nanoparticles. Furthermore, the Pt nanoparticles can serve as an excellent scattering medium, which enormously increases the multiple scattering probability experienced by the random cavity modes. Our strategy provided here is very useful for creating highly efficient optoelectronic devices.

Tunable energy transfer efficiency based on the composite of mixed CdSe quantum dots and elastomeric film

We demonstrate a facile and general approach to investigate the dependence of energy transfer on the separation distance between proximal mixed-size quantum dots. Without varying the mixed concentrations, the tunable energy transfer efficiency is achieved based on the composite of mixed quantum dots and elastomeric film by utilizing the inherent nature of the flexibility of elastomeric film. To demonstrate our working principle, the composite of mixed-size CdSe quantum dots and poly-dimethylsiloxane has been studied. The results clearly show that the energy transfer process between proximal quantum dots follows the Forster resonance energy transfer, in which the dependence of the transfer efficiency E as a function of the donor-acceptor distance R obeys E=1∕[1+(R∕R0)6].

Stretchable Random Lasers with Tunable Coherent Loops.

Stretchability represents a key feature for the emerging world of realistic applications in areas, including wearable gadgets, health monitors, and robotic skins. Many optical and electronic technologies that can respond to large strain deformations have been developed. Laser plays a very important role in our daily life since it was discovered, which is highly desirable for the development of stretchable devices. Herein, stretchable random lasers with tunable coherent loops are designed, fabricated, and demonstrated. To illustrate our working principle, the stretchable random laser is made possible by transferring unique ZnO nanobrushes on top of polydimethylsiloxane (PDMS) elastomer substrate. Apart from the traditional gain material of ZnO nanorods, ZnO nanobrushes were used as optical gain materials so they can serve as scattering centers and provide the Fabry-Perot cavity to enhance laser action. The stretchable PDMS substrate gives the degree of freedom to mechanically tune the coherent loops of the random laser action by changing the density of ZnO nanobrushes. It is found that the number of laser modes increases with increasing external strain applied on the PDMS substrate due to the enhanced possibility for the formation of coherent loops. The device can be stretched by up to 30% strain and subjected to more than 100 cycles without loss in laser action. The result shows a major advance for the further development of man-made smart stretchable devices.

Optical properties of InGaN quantum dots grown by SiNx nanomasks

InGaN quantum dots (QDs) deposited on SiNx nanomasks have been investigated by atomic force microscopy, photoluminescence (PL), and photoluminescence excitation (PLE) measurements. It was found that the size of QDs can be well controlled by SiNx nanomasks, enabling the manipulation of quantum confinement effect. The PL spectra of InGaN QDs contain several fine structures, and the main peaks can be attributed to families of QDs with different sizes. The emission arising from InGaN QDs and GaN buffer layer can be clearly distinguished based on PLE measurement, which can be used to improve the interpretation in the previous reports. Our study indicates that the quantum confined Stark effect due to piezoelectric field plays a very important role in the optical properties of InGaN QDs, which is very useful for the application of optoelectronic devices.

Optical detection of deoxyribonucleic acid hybridization with InGaN/GaN multiple quantum wells

Based on the high surface sensitivity of piezoelectric polarization of strained nitride semiconductors, surface functionalized nitride light emitting devices (LEDs) provide an excellent opportunity for the development of biological sensors. To demonstrate our working principle, a probe chip based on In0.22Ga0.78N∕GaN multiple quantum wells has been constructed and exposed to target DNA solutions, matched and/or mismatched, with different concentrations. The pronounced changes of photoluminescence spectra as well as Raman scattering A1(LO) spectra in matched target DNA clearly illustrate the feasibility of our proposed mechanism. The results shown here open up a new possibility for the application of nitride LEDs in biosensor engineering.