Jianyou Li

Self-assembled deoxyguanosine based molecular electronic device on GaN substrates

Nanoscale hybrid molecular organic photodetectors based on self-assembled guanosine molecules conjugated to wide-bandgap GaN semiconductors has been realized in the ultraviolet wavelength regime. Metal-semiconductor-metal based photodetector is fabricated using ordering of modified guanosine based semiconductor nanowires which exhibit I-V characteristics with high current response and higher rectification ratio compared to Si based hybrid photodetectors. Photocurrent response of a two-terminal device shows the typical characteristics of a semiconductor photodiode with a cutoff wavelength at ∼325nm. The I-V characteristics have been elucidated using the induced polarization properties of self-assembled guanosine semiconductor.

Enhanced Luminescence Efficiency from Hydrogel Microbead Encapsulated Quantum Dots

In this paper, a novel quantum dot (QD) based nanomaterial system is presented for efficient FRET analysis. The quantum dots have been embedded in hydrogel microspheres based on poly(N-isopropylacrylamide) (PNIPAM) a thermoresponsive polymer that undergoes a volume phase transition across the low critical solution (LCST). The optical properties of the quantum dots entrapped within the gel microspheres has been modified due to change in refractive index, volume density of the surrounding hydrogel medium. The QDs encapsulated in the PNIPAM microspheres showed 100–200 % enhancement in the PL efficiency as the microgels shrank at the temperature above the LCST temperature of the gel.

Carrier Dynamics in UV InGaN Multiple Quantum Well Inverted Hexagonal Pits

The emission and recombination characteristics of UV or blue light emission from InGaN/GaN quantum well (QW) structures influenced by V-shaped pits have been investigated by near-field and time-resolved photoluminescence measurements. Localization of charge carriers due to the potential barriers caused by the V-shaped pit formation is observed to be modified by thermal excitation. Temperature dependence of recombination dynamics shows evidence of a more complex potential barrier produced by the inverted hexagonal pits embedded within the multiple QWs. The emission from the narrow V-shaped pit QWs shows anomalous temperature dependence behavior that is significantly different from the emission from c-plane QWs. The carrier recombination process in c-plane QWs is significantly longer ~ 5 ns compared to the ~ 1.5 ns in V-shaped pit QWs at low temperatures due to the larger piezoelectric fields in wider wells. At room temperature, the recombination lifetimes are comparable due to increased carrier separation and delocalization within the V-shaped pit QWs.

Intrinsic Polarization of Self-Assembled Guanosine Supramolecules in GaN-Based Metal–Semiconductor–Metal Nano-Structures

The transport properties of self-assembled guanosine supramolecules (SAGS) confined within nanoscale metal electrodes on transparent GaN semiconductor substrates have been studied. The modified guanosine molecules have been used as self-assembled nanowires to realize nanoscale UV-Visible photodetectors with self-assembly length ranging from 30 to 450 nm. The ribbon-like guanosine supramolecules exhibit semiconductor properties and have polarization along its axis due to the strong intrinsic dipole moment of guanosine molecules. The charge transport through the SAGS wire with nanoscale metal-semiconductor-metal structure on passivated Ga-terminated GaN surface can be explained by Schottky type conductivity and near-surface-states. The intrinsic polarization in SAGS nano-wires changes the band-offset at the metal-semiconductor interface similar to semiconductor photodiodes.

CdTe quantum dot in tunable hydrogel nanocrystals

Optical emission from CdTe quantum dots (QDs) embedded in poly-N-isopropylacrylamide hydrogel nanocrystallites can be enhanced over 100% using thermal and electrical stimulus. Relative distance amongst QDs was modified tuning the hydrogel facilitating resonant energy transfer.

Self-Assembled Guanosine-Based Nanoscale Molecular Photonic Devices

The semiconductor industry has seen a remarkable miniaturization trend, driven by innovations in nanofabrication and nanoscale characterization [1]. Semiconductor technology can currently manufacture devices with feature size less than 100 nm. A modern microprocessor can have more than 500 million transistors. Electronic integrated circuits are inherently single-channel connected device arrays within a two-dimensional printed circuit board [2]. By further shrinking transistor size, one approaches the technical, physical, and economical limits, which will be reached within a few years [3]. At the same time, the insulating layer is also getting thinner leading to an enhancement in the current leakage and resulting in short circuit [4]. Manufacture cost increases drastically with further size reduction. As this trend is likely to yield faster and compact electronic and photonic devices, the size of microelectronic circuit components will soon need to reach the scale of atoms or molecules [1]. Those limitations and application requirements inspired extensive research aimed at developing new materials, device concepts, and fabrication approaches that may enable the integrated devices to overcome the limitations of the conventional microelectronic technology. This will require a conceptual design of new device structures beyond CMOS technology which may require alternative materials to overcome these limits. Hybrid organic–inorganic system is one of the alternative solutions.

Polarization effect of self-assembled guanosine crystal on the transport properties of metal-semiconductor-metal structure

Guanosine molecules have strong dipole moment and can self-assemble in confined space to ribbon-like structure with polarization along its axis. Single molecule current-voltage and photocurrent measurements show that the polarization depends on the ribbon length and affect electric characterization of the MSM structure.

Characterization and light emission properties of osmium silicides synthesized by low energy ion implantation

Low energy (55 KeV) Osmium ( Os − ) negative ion beam was used to implant (5×10 16 atoms/cm 2 ) into p-type-Si (100). The implantation was performed with the ion source of a National Electrostatic Corp. 3 MV Tandem accelerator. The implanted sample was subsequently annealed at 650 °C in a gas mixture that was 4% H 2 + 96% Ar. Rutherford Backscattering spectrometry (RBS) analysis with 1.5 MeV Alpha particles was used to monitor the precipitate formation. Photoluminescence (PL) measurements were also performed to study possible applications of silicides in light emission. Cross-sectional Scanning Electron Microscopy (X-SEM) was performed for topographic image of the implanted region. RBS along with PL measurements indicate that the presence of osmium silicide (Os 2 Si 3 ) phase for light emission in the implanted region of the sample.

Resonant energy transfer due to exciton-exciton interaction in the strong coupling regime in Hybrid InGaN Quantum Wells

Resonant coupling of excitons in strongly confined hybrid perovskite conjugated to InGaN quantum wells is observed. Temperature and time-resolved-photoluminescence (PL) reveal 10 times enhancement of recombination lifetime in strong-coupling regime due to resonant energy transfer.

Self-assembled oligonucleotide semiconductor conjugated to GaN nanostructures for biophotonic applications

We investigate the optical properties of a new class of wide-bandgap semiconductor based biomaterial system. We have synthesized a guanosine derivative with a strong dipole moment, which self-assemble in ∼ 50 –100 nm confined pits to form a ribbon like semiconductor structure (SAGC). SAGC were successfully self-assembled on GaN/AlN QD matrix and the luminescence from GaN QDs can be resonantly transferred to the SAGC molecules resulting in a significant enhancement in emission from the guanine molecules. We also propose the design of ultraviolet-visible photonic bandgap structures based on hybrid SAGC-GaN photonic crystal.