Ziyao Wang

Multilayered graphene used as anode of organic light emitting devices

In this report, we find multilayered graphene, which has good transparency, conductivity and suitable work function, can be used as the anode for the organic light emitting device. Our device structure is Al/glass/multilayered graphene/V2O5/NPB/CBP:(ppy)2Ir(acac)/Bphen/Bphen:Cs2CO3/Sm/Au. The maximum luminance efficiency and maximum power efficiency reach 0.75 cd/A and 0.38 lm/W, respectively. We believe that by optimizing the hole density and uniforming the thickness of the multilayered graphene anode, the device efficiency can be remarkably increased in the future.

Field emission from AlN nanoneedle arrays

AlN nanoneedles with an average tip dimension of ∼15nm were synthesized via a simple vapor deposition method. The AlN nanoneedles exhibit excellent field-emission properties with a low turn-on field of 3.1V∕μm and a high current density of 4.7mA∕cm2 at the field of 9.9V∕μm. The field enhancement factor for a single nanoneedle is estimated to be as high as 30 000 due to its small tip radius. These features make the AlN nanoneedles a competitive candidate for field-emission-based displays.

Field-emission properties of TiO2 nanowire arrays

Aligned TiO2 nanowire arrays were fabricated onto Si wafers by a simple thermal deposition (PVD) method. Scanning electron microscopy and high-resolution transmission electron microscopy observations confirm that the as-prepared TiO2 nanowires are single-crystalline and of high purity. Field emission measurements showed that the TiO2 nanowire arrays could provide stable, high-current electron emission at a low voltage. The emission current monitored over a period of 24 h fluctuated gently but did not show degradation. The cathode-luminescence (CL) images captured by a CCD camera were very bright and their CL intensity was homogeneous. This remarkable performance reveals that TiO2 nanowire arrays are well suited for commercial use in electron devices, particularly flat panel displays.

Synthesis and field emission properties of TiSi2 nanowires

TiSi2 is a high-melting compound with excellent conductivity ∼severalμΩcm. TiSi2 nanowires were fabricated in large scale by a simple vapor phase deposition method. The as-synthesized TiSi2 nanowires were investigated using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman scattering. Field emission property of TiSi2 nanowires was studied and an emission current density of 5mA∕cm2 was obtained and no obvious degradation was observed in a life stability experiment period for over ∼40h. The cathodoluminescence images were very bright and homogenous. The remarkable performance reveals that the TiSi2 nanowires can serve as a good candidate for commercial application in vacuum microelectronic devices, particularly flat panel displays.

Interface structure and phase of epitaxial SrTiO3 (110) thin films grown directly on silicon

The interface structure and phase between SrTiO3 (110) on Si (100) have been investigated using high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. The SrTiO3∕Si interface was found to be epitaxially crystallized without any amorphous oxide layer. The formation of Sr silicate at the interface was suggested by considering the fact of the core-level spectra of the Si 2p, O 1s, and Sr 3d. Our results suggest that the presence of a coincident site lattice at the interface between Si and a Sr silicate and/or SrTiO3 may help to stabilize SrTiO3 in the epitaxial orientation reported in the work.

Improved Performance of Spherical BaWO4 : Tb3 + Phosphors for Field-Emission Displays

Spherical BaWO 4 :Tb 3+ phosphors were prepared by the polyol method and postannealed at 900°C. A variety of properties were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Fourier transform IR spectra, low-voltage cathodoluminescence, photoluminescence spectra, and lifetime. The as-prepared phosphors were well-crystallized under relatively low synthesis temperature (160°C) and composed of spherical particles with an average size of 100 nm. After postannealing treatment, crystallinity of the phosphors is significantly improved and average particle size is increased to around 220 nm. Under low-voltage (≤4.5 kV) excitation of electron beam, bright green cathodoluminescence was observed, which is attributed to the characteristic emissions from Tb 3+ ( 5 D 3 - 7 F J and 5 D 4 - 7 F J transitions). The luminance was significantly improved from 141 to 4866 cd/m 2 after postannealing, which is mostly attributed to the improvement of crystallinity.

Effect of buffer gas ratios on the relationship between cell temperature and frequency shifts of the coherent population trapping resonance

We studied the relationship between pressure ratio of the buffer gases (argon and neon) and the rate of coherent population trapping resonance frequency shift with cell temperature in Rb85. We found that when the total pressure of the buffer gases varies within the range of 5–15kPa, the frequency shift rate varies along a bell shaped curve. Every curve crossed the horizontal axis at two points that are roughly symmetrical with respect to the midpoint at 1:1. This allows us to minimize the rate of frequency shift by adjusting the pressure ratio of the buffer gases to these two points.

Enhancement of Alq3 fluorescence by nanotextured silver films deposited on porous alumina substrates

Enhanced photoluminescence was found in tris-8-hydroxyquinoline aluminum deposited onto nanotextured silver films with porous alumina substrates. The surface-enhanced Raman signals and shortened lifetimes suggested the presence of enhanced local electromagnetic field due to the plasmon resonance of nanotextured silver films. The photoluminescence enhancement was attributed to the increase in absorption and quantum yield. The authors analyzed the increase in quantum yield and found that the highest quantum yield was enhanced by 2.3 times compared with the samples based on flat Ag film with the same thickness. The enhancement of quantum yield has potential applications in electro-optic devices.

Highly efficient phosphorescent organic light-emitting diode with a nanometer-thick Ni silicide / polycrystalline p-Si composite anode

A phosphorescent organic light-emitting diode (PhOLED) with a nanometer-thick (approximately 10 nm) Ni silicide/ polycrystalline p-Si composite anode is reported. The structure of the PhOLED is Al mirror/ glass substrate / Si isolation layer / Ni silicide / polycrystalline p-Si/ V(2)O(5)/ NPB/ CBP: (ppy)(2)Ir(acac)/ Bphen/ Bphen: Cs(2)CO(3)/ Sm/ Au/ BCP. In the composite anode, the Ni-induced polycrystalline p-Si layer injects holes into the V(2)O(5)/ NPB, and the Ni silicide layer reduces the sheet resistance of the composite anode and thus the series resistance of the PhOLED. By adopting various measures for specially optimizing the thickness of the Ni layer, which induces Si crystallization and forms a Ni silicide layer of appropriate thickness, the highest external quantum efficiency and power conversion efficiency have been raised to 26% and 11%, respectively.

Enhancement on top emission of organic light-emitting diode via scattering surface plasmons by nano-aggregated outcoupling layer

A stable self nano-aggregated bathocuproine film was fabricated and introduced atop of conventional organic light emitting diode for enhancing top emission leading to 2.7 times enhancement on top emission due to scattering surface plasmon energy.