Li-Hua Jin

Electrically Driven Quantum Dot/Wire/Well Hybrid Light‐Emitting Diodes

Electrically driven quantum dot, wire, and well hybrid light-emitting diodes are demonstrated by using nanometer-sized pyramid structures of GaN. InGaN quantum dots, wires, and wells are formed at the tops, edges, and sidewalls of pyramids, respectively. The hybrid light-emitting diodes containing low-dimensional quantum structures are good candidates for broad-band highly efficient visible lighting sources.

Quantum dot‐based protein micro‐ and nanoarrays for detection of prostate cancer biomarkers

In this article, we demonstrate the fabrication and detection of cancer protein biochips consisting of micro‐ and nanoarrays whereby pegylated quantum dots (QDs) conjugated to antibodies (Abs) of prostate specific antigens (PSA) were used for the detection of clinical biomarkers such as PSA. BSA which acts as an efficient blocking layer in microarrays, tends to show an interaction with QDs. In view of this fact, we investigated two series of samples which were fabricated in the presence and absence of BSA blocking layer. Variation in the incubation time required for the antigen–antibody interaction to take place, different proteins as controls and the effect of bare QDs on these microarrays, were the three main parameters which were studied in these two series. Samples fabricated in the absence of BSA blocking layer exhibited an extremely high specificity in the detection of cancer proteins and were also marked by negligible nonspecific binding effects of QDs, in stark contrast to the samples fabricated using BSA as a blocking layer. Fabrication of nanoarrays of QD‐conjugated PSA Abs having a spot size of nearly 900 nm has also been demonstrated. Thus, we show the potential offered by QDs in in vitro analysis of cancer biomarker imaging.

Optical transition dynamics in ZnO/ZnMgO multiple quantum well structures with different well widths grown on ZnO substrates

We report the optical properties of ZnO/ZnMgO multiple quantum well (MQW) structures with different well widths grown on ZnO substrates by molecular beam epitaxy. Photoluminescence (PL) spectra show MQW emissions at 3.387 and 3.369 eV for the ZnO/ZnMgO MQW samples with well widths of 2 and 5 nm, respectively, due to the quantum confinement effect. Time-resolved PL results show an efficient photogenerated carrier transfer from the barrier to the MQWs, which leads to an increased intensity ratio of the well to barrier emissions for the ZnO/ZnMgO MQW sample with the wider well width.

Enhanced detection sensitivity of pegylated CdSe/ZnS quantum dots-based prostate cancer biomarkers by surface plasmon-coupled emission

We demonstrate the fabrication and detection of quantum dots (QDs)-based prostate specific antigens (PSAs) cancer protein biochips by using enhanced surface plasmon-coupled emission measurements (SPCE). The PSAs are immobilized on a SiO(2)-protected thin gold substrate and pegylated QDs which conjugated with antibodies of PSA are used as fluorescent probes. Due to the excellent brightness of the QDs and the high directionality of emission, as well as the high light collection efficiency of SPCE, the limit of detection (LOD) is down to 10 fg/mL (equal to 0.3 fM) for the PSA chips by using QDs-based cancer protein. We expect that this QDs-based SPCE measurement system with the low LOD supplies a great potential for detecting various cancer biomarkers that are present in only low concentrations within the human body.

Size-dependent radiative decay processes in graphene quantum dots

Radiative decay processes have been studied in graphene quantum dots (GQDs) by varying their size. The photoluminescence (PL) decay traces are well fitted to a biexponential function with lifetimes of τ1 and τ2, indicating their fast and slow components, respectively. The τ1 is almost constant, irrespective of the average GQD size (da) for two excitation wavelengths of 305 and 356 nm. In contrast, the τ2 decreases as da increases for da ≤ ∼17 nm, but da > ∼17 nm, it increases with increasing da for both the excitation wavelengths, similar to the size-dependent behaviors of the time-integrated PL peak energy. We propose that the τ1 and τ2 originate from size-independent fast band-to-band transition and size-dependent slow transition resulting from the edge-state variation at the periphery of GQDs, respectively.

Quenching dynamics in CdSe/ZnS core/shell quantum dots-gold nanoparticle conjugates in aqueous solution

We investigated carrier dynamics of luminescence quenching in CdSe/ZnS core/shell quantum dots (QDs) in the absence and presence of gold nanoparticles (Au NPs) in aqueous solution. We emphasized that the observed quenching phenomenon in the QDs-Au NP composites can be a result of the interplay of the Forster resonance energy transfer and surface plasmon enhancement process of Au NPs on QDs. Different QDs with emission wavelengths varying from 545 to 619 nm were used to investigate the quenching dynamics. The recovery dynamics of the quenching was also confirmed by the addition of sodium chloride in the QDs-Au NP composites.

Silica encapsulation of toluene soluble quantum dots with high photostability.

We report the silica encapsulation of toluene soluble single quantum dots (QDs) with various silica layer thicknesses. The photoluminescence of silica-encapsulated QD showed a blue shift as the silica layer increased. Although the measured decay lifetime and the quantum yields of the silica-encapsulated QDs decreased as the SiO2 layer increased, the silica-encapsulated QDs showed good photostability for certain silica layer thicknesses. Furthermore, photoblinking, the characteristic optical property of single QD, did not change after silica encapsulation. Silica encapsulation of toluene soluble QDs offers great potential for advanced optical applications.

Tunable Catalytic Alloying Eliminates Stacking Faults in Compound Semiconductor Nanowires

Planar defects in compound (III-V and II-VI) semiconductor nanowires (NWs), such as twin and stacking faults, are universally formed during the catalytic NW growth, and they detrimentally act as static disorders against coherent electron transport and light emissions. Here we report a simple synthetic route for planar-defect free II-VI NWs by tunable alloying, i.e. Cd(1-x)Zn(x)Te NWs (0 ≤ x ≤ 1). It is discovered that the eutectic alloying of Cd and Zn in Au catalysts immediately alleviates interfacial instability during the catalytic growth by the surface energy minimization and forms homogeneous zinc blende crystals as opposed to unwanted zinc blende/wurtzite mixtures. As a direct consequence of the tunable alloying, we demonstrated that intrinsic energy band gap modulation in Cd(1-x)Zn(x)Te NWs can exploit the tunable spectral and temporal responses in light detection and emission in the full visible range.

Bio-information scanning technology using an optical pick-up head.

We have developed a low cost and a highly compact bio-chip detection technology by modifying a commercially available optical pick-up head for CD/DVD. The highly parallel and miniaturized hybridization assays are addressed by the fluorescence emitted by the DNA-chip using the optical pick-up head. The gap between the objective lens and the bio-chip is regulated by the focus servo during the detection of the fluorescence signal. High-resolution and high-speed scanning is effectively realized by this simple scanning system instead of utilizing high-precision mechanism. Regardless of achievement of effective detection mechanism, the technique of fluorescence detection can prove to be disadvantageous because of the low stability of the dyes with low S/N ratio and an expensive setup such as a PMT detector is always required for fluorescence detection. We propose, for the first time, a novel scanning scheme based on metal nanoparticles in combination with a bio-chip substrate having a phase change recording layer. We found that the phase change process is highly affected by the existence of the densely condensed metal nanoparticles on the phase change layer during the writing process of the pick-up head.

Active packing method for blue light-emitting diodes with photosensitive polymerization: formation of self-focusing encapsulates.

A novel light-emitting diode (LED) packaging method, named the active packaging (AP) method, is presented in this paper. In this method, during the LED packaging process, the light emitted from a GaN LED chip itself is employed to package the LED encapsulant, thereby eliminating the need to utilize a mold. Current injection into a bare LED chip, triggers a photosensitive epoxy to polymerize, leading to the formation of mushroom lamp cap on the LED chip. The emission properties of LEDs fabricated by this method, including their emission beam profiles and light outputs, were characterized. The results showed that a self-focusing effect happened with the addition of an epoxy on the chip. The simulation demonstrated that the geometry the encapsulant controlled the beam pattern of emission. Further, the self-focusing effect was believed to be caused by the combination of the threshold energy of epoxy polymerization, the beam pattern and the power output of the LED chip.