Yen-Chih Lee

Effect of boron doping on the electron-field-emission properties of nanodiamond films

The electron-field-emission (EFE) behavior of the nanodiamond films was observed to be pronouncedly superior to that of the diamond films with micrometer- or submicrometer-sized grains, which is ascribed to the presence of abundant grains boundaries with sp2 bonds. Incorporation of boron species into the nanodiamond films further improves the EFE properties for the films. The best EFE properties achieved are turn-on field E0=18V∕μm with EFE capacity J=0.7mA∕cm2 at around 30V∕μm applied field. However, boron doping into the nanodiamond films does not result in consistent boron-content dependence of the EFE properties for the films as those in conventional micrometer-sized diamonds. The complication is explained by the fact that the small size of the diamond grains (∼20nm) may not be able to accommodate the boron species into the lattices to effectively act as acceptor dopants. Moreover, the formation of aggregates of the nanosized diamond grains may alter the local field enhancement factor, which further c...

Fabrication of an ultra-nanocrystalline diamond-coated silicon wire array with enhanced field-emission performance

Large-area ultra-nanocrystalline diamond-coated silicon nanowire (UNCD/SiNW) field-emitter arrays were prepared by the deposition of ultra-nanocrystalline diamond (UNCD) on the tips of arrays of silicon nanowires (SiNWs) with uniform diameters. The electron field-emission (EFE) behavior of UNCD/SiNW arrays as well as that of the SiNW arrays has been observed. The SiNWs exhibit good electron field-emission properties with turn-on fields (E0) of about 7.6 V µm−1, which is superior to the EFE properties of planar-silicon materials. The turn-on fields are related to the diameter of the SiNWs. Coating the SiNWs with a UNCD film further improves their EFE properties. The threshold field for attaining Je = 0.1 mA cm−2 EFE current density is 16.0 V µm−1 for bare SiNWs and 10.2 V µm−1 for UNCD/SiNWs. The improvement in EFE properties due to the UNCD coating is presumably due to the lower work function of field emission of the UNCD materials, compared to that of the silicon materials.

On the enhancement of field emission performance of ultrananocrystalline diamond coated nanoemitters

Ultrananocrystalline diamond (UNCD) nanoemitters were synthesized by a microwave plasma enhanced chemical vapor deposition process using silicon nanowires (SiNWs) as the template. Preseeding markedly enhances the nucleation of diamond on the SiNW templates, resulting in UNCD grains of smaller size and uniform distribution, which leads to significantly improved electron field emission (EFE) properties. The EFE for UNCD nanoemitters can be turned on at (E0)UNCD-NE=4.4V∕μm, achieving large EFE current density, (Je)UNCD-NE=13.9mA∕cm2 at an applied field of 12V∕μm, which is comparable with that of carbon nanotubes, but with much better processing reliability.

Current image tunneling spectroscopy of boron-doped nanodiamonds

The electron field emission properties of the nanodiamond films were examined using scanning tunneling microscopic (STM) technique. Current image tunneling spectroscopic measurements reveal the direct dependence of electron tunneling/field emission behavior of the films on the proportion of grain boundaries present. Local tunneling current-voltage (It–V) measurements show that incorporation of boron species insignificantly alters the occupied state, but markedly modifies the empty state of the diamond films, viz. it induces the presence of impurity states for the films heavily doped with borons, resulting in smaller emission energy gap for the samples. Such a characteristic improves both the local electron field emission behavior of the diamond films measured by STM and the average electron field emission properties measured by conventional parallel plate setup. These results infer clearly that the presence of impurity states due to boron doping is a prime factor improving the field emission properties fo...

Effect of High-Q Ba4Ti13O30 Materials on The Dielectric Properties of (Bax,Sr1−x)Tio3 Films For Microwave Communication

Nano-sized BaTiO3, SrTiO3 and TiO2 powders have been used to synthesize (Ba x ,Sr1−x )TiO3 materials via mixed oxide process. Then (Ba x ,Sr1−x )TiO3 (BST) (x = 0.5 and 0.6) with addition of high-Q (quality factor) Ba4Ti13O30 (BT) materials were screen printed on Al2O3 substrates. The prepared thick films of BST/BT with three layered and five layered composite materials were sintered at 1275°C (4 h). The microwave dielectric properties of the bulk ceramics and the thick films were measured by resonant cavity method at higher microwave frequencies (9.5 GHz). The three layered thick films have dielectric constant of 13.4 for x = 0.5 and 15.5 for x = 0.6. The five layered thick films possess dielectric constant of 12.7 for x = 0. 5 and 15.8 for x = 0.6. The frequency × quality factor (f × Q) increases markedly with a larger magnitude of 1600 for the three layered thick films than the five layered ones. The results imply that the BST/BT composite thick films have potential application in tunable microwave devices.

Low Loss Tunable Thick Films Based on (Ba,Sr)TiO3 and Ba4Ti13O30 Materials

Modification on microwave dielectric properties of (Ba0.6Sr0.4)TiO3 (BST) materials due to the incorporation of Ba4Ti13O30 (B4T13) materials was investigated. The dielectric constant of the BST materials was lowered from KBST = 600 to KCOMP = 100, whereas the quality factor of the materials was increased markedly from (Q ×} f)BST = 80 to (Q ×} f)COMP = 2,000, due to the addition of B4T13 materials. Evanescent microwave probe (EMP) measurements indicate that the thick films prepared from the mixture contain two phases. The low-K and high-Q particulates, which are presumably B4T13 phase, are distributed uniformly among the high-K and low-Q matrix, resulting in a tunable materials with improved microwave dielectric properties.

Electron field emission property of boron doping nano-crystalline diamond

The effects of boron doping on the nucleation behavior and the characteristics of nano-crystalline diamond (NCD) films were investigated. NCD films were prepared by microwave plasma enhanced chemical vapor deposition and were grown on mirror-polished p-type Si(100) substrate by bias enhanced growth technique. The morphologies and bonding structures of the films were characterized by field emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray diffraction. The increase in proportion of sp/sup 2/-bonded grain boundaries in finer grain NCD films is assumed to be the main modifying factor in the electron field emission of the film.

Microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 prepared by inverse-microemulsion process

Abstract Microwave dielectric properties of Ba(Zn1/3Nb2/3)O3, BZN, materials have been improved by using inverse-microemulsion process for preparing the BZN powders. The as-prepared powders, which are amorphous clusters about 100 nm in size, can be converted directly into pure perovskite phase without forming intermediate or secondary phase. BZN materials with high enough density (94% T.D.) can be obtained by sintering the materials at 1400°C for 24 h. Thus prepared BZN samples exhibit very good microwave dielectric properties, Qxf=15500 GHz.