Zhongchun Wang

Optical properties of anatase TiO2 thin films prepared by aqueous sol-gel process at low temperature

TiO2 thin films were spin-coated on Si (100) substrates via an aqueous sol–gel route using Ti(OBun)4 and H2O2 as starting materials, and were annealed in air at different temperatures up to 550 °C for 1 h. X-Ray diffractometry indicates that crystallization into anatase started at 350 °C. The 350 °C-annealed films were further characterized by Auger electron spectroscopy, X-ray photoelectron spectroscopy, and variable angle spectroscopic ellipsometry. The results show that homogeneous, carbon-free TiO2 films with high refractive index (n=2.3 at 550 nm) were successfully obtained under an annealing temperature as low as 350 °C. The indirect and direct optical absorption bandgaps of the anatase film are estimated as 3.23 and 3.80 eV, respectively.

Nanocrystalline diamond from carbon nanotubes

Structural phase transformation from multiwalled carbon nanotubes to nanocrystalline diamond by hydrogen plasma post-treatment was carried out. Ultrahigh equivalent diamond nucleation density above 1011 nuclei/cm2 was easily obtained. The diamond formation and growth mechanism was proposed to be the consequence of the formation of sp3 bonded amorphous carbon clusters. The hydrogen chemisorption on curved graphite network and the energy deposited on the carbon nanotubes by continuous impingement of activated molecular or atomic hydrogen are responsible for the formation of amorphous carbon matrix. Diamond nucleates and grows in the way similar to that of diamond chemical vapor deposition processes on amorphous carbon films.

Electrical properties of SrTiO3 thin films on Si deposited by magnetron sputtering at low temperature

Deposition of SrTiO3 (STO) thin films by radio-frequency magnetron sputtering in an ultrahigh vacuum system at a low substrate temperature (∼200 °C) was performed in order to produce high-quality STO/p-Si (100) interfaces and STO insulator layers with dielectric constants of high magnitude. The STO films were identified as polycrystalline by x-ray diffraction, and were approximated with a layered structure according to the best fitting results of raw data from both Rutherford backscattering spectroscopy and variable angle spectroscopic ellipsometry. Room-temperature current–voltage and capacitance–voltage (C–V) measurements on Al/STO/p-Si diodes clearly revealed metal–insulator–semiconductor behavior, and the STO/p-Si interface state densities were of the order of 1011 eV−1 cm−2. The dielectric constant of the STO film was 65, and the dielectric loss factor varied between 0.05 and 0.55 for a frequency range of 1 kHz–10 MHz. For a 387 nm thick STO film, the dielectric breakdown field was 0.31 MV cm−1, and ...

Effect of high-energy Si+ ion irradiation on the crystallization behavior of amorphous strontium titanate films

Abstract Amorphous strontium titanate (STO) films deposited on Si substrates by magnetron sputtering at room temperature were irradiated with 2 MeV Si ions at doses of 5×10 16 –1.5×10 17 Si + /cm 2 and post-annealed at 450 °C in vacuum. The compositional and structural changes of STO films after the ion irradiation were examined by Rutherford backscattering spectrometry, scanning electron microscopy and X-ray diffraction measurements. The Sr:Ti:O ratio of the as-deposited films was found to be approximately 0.8:1:3. Ion irradiation did not affect the amount of Sr and Ti significantly and the films remained amorphous. After annealing, however, the formation of STO crystals was observed and Sr and O were slightly lost from the films. As compared to the un-irradiated STO films, the ion-irradiated ones showed significantly enhanced crystallization behaviors upon vacuum annealing.

Electrical characterisation of SrTiO3/Si interfaces

Deposition of SrTiO3 (STO) thin films by ultra-high vacuum rf magnetron sputtering was performed in order to produce high-quality STO/p-Si (1 0 0) interfaces and STO insulator layers with high diel ...

Properties of Al-SrTiO/sub 3/-ITO capacitors for microelectronic device applications

Growth of SrTiO/sub 3/ (STO) thin films on indium tin oxide (ITO) substrates took place by RF magnetron sputtering under various deposition conditions. Subsequent Al metallization created metal-insulator-metal (MIM) capacitors. The properties of such capacitors were investigated by means of structural and electrical measurements, revealing the films transparency, the dielectric constant, the switching time characteristics, and the trapped charges density. Dielectric constant values as high as 120 were obtained for low frequencies of around 2 kHz, the switching time was found to be 3.2 /spl mu/s and the trapped charges were found equal to 2.9 nCcm/sup -2/. The results showed that the films were suitable for use in electronic devices where high capacitance is required and for potential applications in optical devices.

DIAMOND NANORODS FROM CARBON NANOTUBES BY HYDROGEN PLASMA TREATMENT

Single crystalline diamond nanorods with diameters of 4–8 nm and with lengths up to 200 nm have been synthesized by hydrogen plasma post-treatment of multiwalled carbon nanotubes. The diamond nanorods were identified to have a core-sheath structure with inner core being diamond crystal and outer shell being amorphous carbon. A growth mechanism for the diamond nanorods was proposed.