Yushi Suzuki

Structural and electrical properties and current–voltage characteristics of nitrogen-doped diamond-like carbon films on Si substrates by plasma-enhanced chemical vapor deposition

We have deposited nitrogen-doped diamond-like carbon (N-DLC) films by plasma-enhanced chemical vapor deposition using CH4, N2, and Ar, and investigated the effects of N doping on the structure and the electrical, mechanical, and optical properties of the N-DLC films. We fabricated undoped DLC/p-type Si and N-DLC/p-type Si heterojunctions and examined the current–voltage characteristics of the heterojunctions. When the N2 flow ratio was increased from 0 to 3.64%, the resistivity markedly decreased from the order of 105 Ωcm to that of 10−2 Ωcm and the internal stress also decreased. The resistivity gradually increased with increasing N2 flow ratio from 3.64 to 13.6%, and then it decreased at a N2 flow ratio of 13.6%. These behaviors can be explained in terms of the clustering of sp2 carbons and the formation of sp3C–N, sp2C=N, sp1C≡N, and C–H n bonds. The rectification ratio of the heterojunction using the N-DLC film prepared at 3.64% was 35.8 at ±0.5 V.

Photoluminescence of the Dehydrated Ag-type Zeolite A Packed under Air

The photoluminescence (PL) and extended X-ray absorption fine structure (EXAFS) measurements have been carried out for the dehydrated fully Ag + exchanged zeolite A powders packed with controlled amounts of the adsorbed H 2 O molecules. The powders are designated as “air-packed 12Ag-A” and have been prepared by packing the dehydrated 12Ag-A in the glass cell under air at different temperatures between 120 and 30 °C in the cooling process after the dehydration at 500 °C for 24 h under air. The PL spectra obtained by radiation of 400 nm light have main peaks around 2.15 eV and subpeaks around 2.70 eV. The PL spectra were fitted by four Gaussians. The peak around 2.15 eV consists of the band I ∼1.94 eV and band II ∼2.10 eV, while the subpeak around 2.70 eV of the band III ∼2.50 eV and band IV ∼2.80 eV. The temperature variations of the integral intensities for the bands II and IV show maxima between 50 and 80 °C where the interaction between the zeolite framework and the adsorbed H 2 O molecules is found to ...

In-situ XAFS study of Ag clusters in Ag-type zeolite-A

We studied the relation between structure of the Ag clusters produced in Ag-type zeolite-A and properties of photo luminescence (PL) by use of in-situ X-ray absorption fine structure (XAFS). Ag clusters are generated in the cavity of Ag-type zeolite-A which is cooled to room temperature after heated at 500°C for 24 hours under vacuum or atmosphere. We investigated the change of the Ag clusters in the zeolite cavity when various gases are introduced: oxygen, nitrogen, water vapor, and their mixture. The Ag clusters were breakdown when H2O gas was introduced and the fact of the breakdown of the cluster is necessary for appearing the strong PL band. It was suggested that the structural change in the zeolite induced by the formation and breakdown of the Ag clusters is key point of the PL mechanism.

XAFS and IR Studies on Luminescent Silver Zeolites

In this chapter, studies of structures and optical properties of Ag-zeolite A by means of X-ray absorption fine structure (XAFS) and infrared (IR) spectra are presented. XAFS is a powerful tool to study the local structure of Ag nanoclusters in the zeolite cavity and IR spectra are quite sensitive to the change in zeolite lattice affected by the production of Ag clusters. First, we focus on the creation of Ag clusters in zeolite A by heat treatment under atmosphere and vacuum. Second, we discuss the mechanism of photolumines‐ cence for Ag-zeolite composite. It is widely believed that the emitting point is Ag clusters in the Ag zeolite; on the other hand, our recent result is contradicted that Ag clusters are broken down in the strongly emitting species.

IR and XAFS studies of photoluminescent Ag-type zeolite-A

We examined the relation between the zeolite framework, Ag clusters, and properties of photoluminescence (PL) using in-situ infrared spectroscopy (IR) and X-ray absorption fine structure (XAFS). The Ag clusters are generated in the cavity of Ag-type zeolite-A that is cooled to room temperature after heating at 500°C for 24 hour under vacuum or in atmosphere. The Ag clusters in the zeolite cavity break down when air is introduced. According to the formation and breakdown of the Ag cluster, the infrared spectrum of the zeolite framework changed slightly. Then, this change was compensated by irradiation of the excitation light. Results suggest that the structural change in the zeolite induced by the formation and breakdown of the Ag clusters is a key point of the PL mechanism.