VHF Plasma CVD Synthesis of Photochromic ZnO Nanoparticle
- PDF / 311,500 Bytes
- 5 Pages / 432 x 648 pts Page_size
- 44 Downloads / 193 Views
MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.80
VHF Plasma CVD Synthesis of Photochromic ZnO Nanoparticle Hiroshi Kajiyama1, Shin Kuboyama2, Atsushi Otomo3, Hiroki Uyama1, Toshihiro Matsuura1, Shuhei Inoue3, Yukihiko Matsumura3, Keiji Takata4, Kentaro Tomita2, Kiichiro Uchino2 1
Tokushima Bunri University, Sanuki, 769-2193, Japan
2
Kyushu University, Kasuga, 816-8580, Japan
3
Hiroshima University, Higashi-hiroshima, 739-8524, Japan
4
Kansai University, Suita, 564-8680, Japan
Abstract
Photochromic (PC) ZnO nanoparticles are synthesized for the first time by using a VHF plasma enhanced CVD apparatus. The prepared ZnO film changes from transparent to PC state under UV irradiation; on being subjected to heat treatment, it changes back to transparent state. There is a threshold temperature for attaining the PC phase. The DebyeWaller factor of Zn atoms is specifically large for the PC ZnO. The ZnO nanoparticles contain carbon as impurity. The effects of C-O bonds on the ZnO crystal structure and density of states (DOS) are simulated based on density-functional theory. The results reveal that the crystal structure is slightly distorted and a sufficient DOS for PC light absorption is formed in the band gap.
INTRODUCTION Zinc oxide (ZnO) is a ϩ-Ϭ compound semiconductor with a wide band gap of 3.3 eV. It is of much interest for optical applications, such as, green phosphor [1], photocatalyst [2], sunscreen ingredient [3] and transparent electrode [4]. If ZnO could store electricity, a photovoltaic battery could be constructed by forming a junction of ptype and n-type ZnO. Therefore, the photochromic (PC) transition of ZnO is gaining
1573
Downloaded from https://www.cambridge.org/core. The Librarian-Seeley Historical Library, on 05 Dec 2019 at 01:02:13, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2019.80
interest. So far, ZnO has been fabricated using dc-magnetron sputtering [5] and reactive plasma deposition [6]. However, ZnO thus obtained has high purity and is not a PC material. The purpose of this study is to synthesize ZnO nanoparticles by chemical vapor deposition of an organometallic compound by using a VHF (80 MHz) plasma enhanced CVD apparatus. In this procedure, the purity of ZnO is reduced as carbon and other species are likely incorporated during crystal growth. It is confirmed that the as-grown ZnO nanoparticles transform to a PC state under UV irradiation and are bleached by heat treatment. It is observed that the Debye-Waller factor of Zn atoms is specifically large for PC ZnO. The relation between ZnO crystal structure and PC state is discussed.
EXPERIMENTAL DETAILS The schematic of the VHF plasma enhanced CVD apparatus used in this study is shown in figure 1. The excitation frequency and electric power were 80 MHz and 150 W, respectively. ZnO film was synthesized from diethylzinc (Zn(C 2H5)2) and oxygen using 80 MHz plasma [7]. Argon was used as the carrier gas. A glass substrate was used wit
Data Loading...
