Shichang Zou

Infrared analysis of the irradiation effects in aromatic polyimide films

A Fourier transform infrared (FTIR) spectroscopic investigation of the ion-beam-induced chemical and structural modification in polyimide (PI) films is presented. Our experimental considerations provide a foundation for a quantitative evaluation of the infrared (IR) results for this thermally stable polymer on the deterioration of chemical bonding with irradiation fluence. It is found that chemical structure in PI is subjected to a severe alteration within the dose range from 1 × 1014 to 1 × 1015 B+/cm2. The radical structure modification is completed only as irradiation reaches 1 × 1016 B+/cm2, at which point one may find that there exists a resemblance in profile shape between the IR spectrum of the high-dose irradiated PI film and the one-phonon states density (DOS) of amorphous graphite. This suggests that a structure similar to amorphous graphitic carbon films will be formed in the ion-beam-modified PI film when dose comes to a certain threshold. This “graphitization” process under ion bombardment is also supported by the experimental results from ultraviolet (UV)-visible spectroscopic study.

FORMATION OF COVALENT SOLID CNX COMPOUNDS BY HIGH-DOSE NITROGEN IMPLANTATION INTO CARBON THIN-FILMS

Our preliminary studies show that covalent solid CNx compounds can be synthesized by high dose nitrogen implantation into carbon thin films. 100 keV N+ ions at a dosage of 1.2×1018 cm−2 were implanted at different temperatures. The samples were evaluated by x‐ray photoelectron spectroscopy (XPS), x‐ray diffraction analysis, and Fourier transform infrared absorption spectroscopy (FTIR). N(1s) core level line XPS analyses show the existence of two different N(1s) bonding states, corresponding to the nitrogen of the C–N covalent bonding state and free state nitrogen, respectively. More importantly, it can be clearly seen that the content of C–N covalent bonding state in the samples is increased with increasing of the implanting temperature of samples. When implantation was performed at 500u2009°C, C(1s) XPS studies show the existence of three different C(1s) bonding states, corresponding to graphite, i‐carbon, and the carbon of C–N covalent bonding state, respectively, and FTIR analyses indicate that there is an...

Optical transition properties of β‐FeSi2 film

Optical transition of properties of β‐FeSi2 film have been investigated by optical transmittance absorption measurement, spectroscopic ellipsometry and reflectivity. Optical transmittance absorption measurement ranging from 0.5 to 1.1 eV revealed the direct transition at E0=0.84 eV, while absorption curve obtained from the spectroscopic measurement in the range of 1.5–4.5 eV implied additional transition at E’=1.05 eV, it is suggested that such additional transition originates from spin–orbit splitting at Γ (center of Brillouin’s zone). Reflectivity goes to the maximum value near Eg, indicating that the joint density of states in the transition at Eg is very high. Another peak which is related with the transition at E’ was also observed in the reflectivity spectra.

STRUCTURAL PROPERTIES OF CARBON NITRIDE FILMS PREPARED BY HIGH DOSE NITROGEN IMPLANTATION INTO CARBON THIN FILMS

Carbon nitride films were successfully prepared by ion beam synthesis method. 100 keV N+ ions at a dosage of 1.2×1018 cm−2 were implanted into carbon thin films at different temperatures. The samples were evaluated by x‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, cross‐sectional transmission electron microscopy (XTEM), Rutherford backscattering spectroscopy (RBS), x‐ray diffraction analysis (XRD), and Vickers microhardness measurement. XPS results show that most of the implanted nitrogen atoms are free state. Most of the carbon atoms have C–C bonding and a little of them form a C–N bond. It also can be clearly seen that the content of the C–N covalent bonding state in the samples is increased by raising the implanting temperature of the samples. Raman spectrum indicates that there is a Raman band near 2300 cm−1 corresponding to carbon‐nitrogen stretching. XTEM and RBS studies show that there is a buried layer of carbon nitride. XRD and TEM analyses reveal that the buried carbon nitride is pr...

Reactive deposition epitaxial growth of β‐FeSi2 film on Si(111): In situ observation by reflective high energy electron diffraction

Reactive deposition epitaxial growth of β‐FeSi2 film on Si(111) has been studied by in situ observation of reflective high energy electron diffraction combined with ex situ Auger electron spectroscopy depth profile analysis. The direct phase formed at the top surface after iron coverage has been determined to be mixture Fe3Si and Fe5Si3, FeSi, and β‐FeSi2, respectively, according to the results of different deposit temperature. Diffraction patterns as well as the depth profile for the Fe/Si ratio have been discussed.

FORMATION OF BURIED CARBON NITRIDE BY HIGH-DOSE NITROGEN IMPLANTATION INTO CARBON THIN-FILM

Abstract Buried carbon nitride was obtained by using 100 keV N + implantation into carbon thin film with a dose of 1.2 × 10 18 cm −2 at 500°C. N(1s) core level line X-ray photoelectron spectroscopy (XPS) analyses show the existence of two different N(1s) bonding states, corresponding to the nitrogen in a Cue5f8N covalent bonding state and free state nitrogen, respectively. C(1s) XPS studies indicate the existence of three different C(1s) bonding states, corresponding to graphite, i-carbon and carbon with a Cue5f8N covalent bonding state, respectively. Fourier transformation infrared absorption spectroscopy (FTIR) measurements point out that there is an absorption band near 2200 cm −1 assigned to the Cue5fcN covalent bonding. Cross-sectional transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry (RBS) measurements show that there is a buried carbon nitride layer. X-ray diffraction (XRD) shows the buried carbon nitride is amorphous. Vickers microhardness evaluation indicates the sample has a higher hardness than that of carbon thin film. The Implantation of Reactive Ions into Silicon (IRIS) computer program has been used to simulate the formation of the buried β-C 3 N 4 layer as N + ions are implanted into carbon. We find good agreement between experimental measurements and IRIS simulation.

Preparation of thin films by filtered arc deposition and ion assisted arc deposition

Abstract The present work focuses on Filtered Arc Deposition (FAD) and Ion Assisted Arc Deposition (IAAD) techniques. The properties of TiN, a-diamond and a-C:N films prepared by FAD and IAAD have been investigated in respect to surface morphologies, field emission behavior and optical properties.

Tetrahedral amorphous-carbon thin films for silicon-on-insulator application

The application of a silicon-on-insulator substrate in a high-power integrated circuit is limited by the self-heating effect, caused by the poor thermal conductivity of the buried SiO2. We introduce tetrahedral amorphous-carbon thin films, formed by the filtered arc deposition method, as an alteration. We investigated the surface morphology, microstructure, and electrical properties of these films. The films deposited under a substrate bias of −200 V displayed outstanding surface topography (low surface roughness with the Rrms value under 0.5 nm) and excellent electrical property (breakdown field of 4.7 MV/cm). The film has a high content of sp3 bonds of carbon (87%) and low content of oxygen (<2%).

A study of oxygen ion implantation into ferroelectric Pb(Zr,Ti)O3 films

Abstract Oxygen ions with 40 keV energy and doses of 1 × 1012 to 5 × 1014 / cm2 were implanted into ferroelectric Pb(Zr,Ti)O3 (PZT) thin films. X-ray diffraction patterns show that no obvious difference appears in the crystalline structure of PZT films before and after implantation; however, measurement of electrical properties shows that both remanent polarization and dielectric constant of the film decrease with increase of the implanted ion dose. The PZT film will completely become a linear dielectric if the implanted ion dose increases to 5 × 1014 / cm2. A possible mechanism for the loss of remanent polarization after ion implantation is proposed.

Photoluminescence properties of thermal SiO2 films implanted by silicon and nitrogen ions

Intense UV–visible photoluminescence (PL) was observed at room temperature from thermal SiO2 films implanted by Si and N ions. There were two PL bands at ∼330 and ∼660 nm shown in the as-implanted sample, while another band at ∼430 nm was observed apart from the other two bands. No shifts were observed in the PL spectra with increasing annealing temperature. The annealing temperature dependences of N distribution, PL intensity and electron spin resonance (ESR) signals were also measured. It is found that the PL is related to the N in the films. The PL is suggested to originate from complex of Si, N and O.