ABSTRACT
It is the first time that cadmium sulfide (CdS) nanorods have been fabricated on silicon (Si) pyramid surface by the hydrothermal reaction method. In our work, the Si pyramid morphology is able to increase the adhesion between the CdS seed layer and Si wafer. Hence, it is critical for CdS nanorods to grow successfully. During the fabrication process, the glutathione is used as the complexing agent for the formation of the CdS nanorods. By continuously adjusting the experimental conditions, the thickness of the CdS seed layer, the concentration of the glutathione, and the temperature and time of the hydrothermal reaction, the optimal condition for CdS nanorods growth on Si pyramid surface is 80 nm seed layer, 0.2-0.3 mmol glutathione, 200 °C, and 1.5 h. The Cd and S elements have a ratio of 1:1.03 from the energy-dispersive spectroscopy test, which is in agreement with the stoichiometric composition of CdS. The CdS nanorods have a bandwidth of 2.22 eV through the optical absorption spectra. The photosensitivity response test results reveal these CdS nanorods on the Si pyramid structure have an obvious photosensitive effect. From the analysis, the CdS nanorods can grow on any morphological Si surface if the adhesion between the CdS seed layer and the Si surface is strong enough.
ABSTRACT
W18O49 nanowires were synthesized by thermal evaporation, and the effects of X-ray irradiation on their crystalline structure, chemical composition, and field emission properties were systematically investigated. High-energy X-ray irradiation created nanoprotrusions on the surface of W18O49 nanowires and introduced crystalline slipping in the lattice. X-ray photoelectron spectroscopy results showed that the content of lattice oxygen increased and nitrogen was incorporated into the W18O49 nanowires after X-ray irradiation. Nevertheless, a stable and high current emission still could be obtained from the W18O49 nanowires after X-ray irradiation, with a slight increase in the threshold field from 6.4 to 7.9 MV m-1. The mechanism of the change in crystalline structure, chemical composition, and field emission performance of W18O49 nanowires induced by X-ray irradiation is discussed.
ABSTRACT
A new prism-array lens for high-energy X-ray focusing has been constructed using an array of different prisms obtained from different parabolic structures by removal of passive parts of material leading to a multiple of 2π phase variation. Under the thin-lens approximation the phase changes caused by this lens for a plane wave are exactly the same as those caused by a parabolic lens without any additional corrections when they have the same focal length, which will provide good focusing; at the same time, the total transmission and effective aperture of this lens are both larger than those of a compound kinoform lens with the same focal length, geometrical aperture and feature size. This geometry can have a large aperture that is not limited by the feature size of the lens. Prototype nickel lenses with an aperture of 1.77â mm and focal length of 3â m were fabricated by LIGA technology, and were tested using CCD camera and knife-edge scan method at the X-ray Imaging and Biomedical Application Beamline BL13W1 at Shanghai Synchrotron Radiation Facility, and provided a focal width of 7.7â µm and a photon flux gain of 14 at an X-ray energy of 50â keV.
ABSTRACT
The focusing performance of polymethyl methacrylate compound long kinoform lenses with 70 µm aperture and 19.5 mm focal length was characterized with 8 keV x rays using the knife-edge scan method at the 4W1A transmission x-ray microscope beamline of Beijing Synchrotron Radiation Facility. The experiment result shows a best FWHM focus size of 440 nm with 31% diffraction efficiency.
ABSTRACT
A simple fabrication technology for both nanoscrews and nanoholes by Cesium Chloride (CsCI) self-assembly lithography and dry etching on silicon substrates is demonstrated. The porous Al template ranging from 400 nm to 2 µm average diameter is formed by lift-off the CsCl nanoislands in DI water as the ICP etching masks for nanoholes. Nanoscrews and nanoholes of desired height/depth from 1.2 to 4 µm are obtained by this method. The reflectance of nanoscrew and nanohole structures can achieve below 5% from wavelength of 400 to 1000 nm which is much lower than that of pyramid but the performance of pyramid solar cells is the best. Results show that the performance of nanoscrew and nanohole solar cells is strongly affected by some other factors such as surface passivation and electrode-contact property. Therefore, not only the antireflection advantage but also the surface passivation and improving the electrode-contact property should be considered together to improve nanostructure solar cells photovoltaic performance.
ABSTRACT
InGaN flip-chip light-emitting diodes on bulk GaN substrate (FS-FCLEDs) with hemisphere-cones-hybrid surface were fabricated using both dry etching with CsCl nanoislands as mask and chemical wet etching. Compared with the corresponding flat LEDs, the light output power of FS-FCLEDs with combined nanostructures shows an enhancement factor of 1.9 at 350mA injection current. Finite-difference time-domain (FDTD) simulation results show that such enhancement of the output power is mainly attributed to the reduction of the total internal reflection and increase of the light scattering probability in the hemisphere-cones-hybrid surface, which is due to a combination effect of light diffraction at the nanocones edges, and light interference within the hemisphere and nanocones.
Subject(s)
Gallium/chemistry , Lighting/instrumentation , Semiconductors , Equipment Design , Equipment Failure AnalysisABSTRACT
InGaN-based light emitting diodes (LEDs) with a top nano-roughened p-GaN surface are fabricated using self-assembled CsCl nano-islands as etch masks. Following formation of hemispherical GaN nano-island arrays, electroluminescence (EL) spectra of roughened LEDs display an obvious redshift due to partial compression release in quantum wells through Inductively Coupled Plasma (ICP) etching. At a 350-mA current, the enhancement of light output power of LEDs subjected to ICP treatment with durations of 50, 150 and 250 sec compared with conventional LED have been determined to be 9.2, 70.6, and 42.3%, respectively. Additionally, the extraction enhancement factor can be further improved by increasing the size of CsCl nano-island. The economic and rapid method puts forward great potential for high performance lighting devices.
