FULL PAPER DOI: 10.1002/ejic.201001071 Vertically Well-Aligned In 2 O 3 Cone-Like Nanowire Arrays Grown on Indium Substrates Wenyan Yin, [a] Matt Doty, [b] Chaoying Ni, [b] Changwen Hu,* [a] Minhua Cao,* [a] and Bingqing Wei* [c] Keywords: Indium / Nanostructures / Chemical vapor deposition / Arrays / Luminescence Single-crystalline, cone-like In 2 O 3 nanowire (NW) arrays were directly synthesized on the surface of indium grains without any catalyst by using a simple chemical vapor depo- sition (CVD) method. The indium grains served both as the indium source, which reacted with different oxygen sources, and the substrate for the growth of the cone-like In 2 O 3 NW arrays. The controllable synthesis of the cone-like In 2 O 3 NW 1. Introduction One-dimensional (1D) semiconductor nanowires (NWs) have become the focus of intensive investigations over the past decade for a variety of applications such as optoelec- tronic devices and sensors. [1–3] So far, light-emitting di- odes, [4] lasers, [5] photodetectors, [6] and field-effect transis- tors [7,8] have been made from these semiconductor NWs. Among them, vertically oriented 1D NWs are the basic building blocks for constructing such devices and are par- ticularly interesting. Different 1D NW arrays can be formed through self-assembly of these basic NW building blocks. Compared with randomly distributed NWs reported in ear- lier studies, vertically oriented semiconductor NW arrays with controllable diameter and length are likely more suit- able for many applications, such as solar cells, active ele- ments for 3D electronics. [9–11] In view of the increasing interest in 1D NW arrays, it is of great importance to design and synthesize them in order to study their potential tech- nological applications. At the same time, understanding the growth mechanisms and key growth processes is of critical importance and remains a challenge for control and optimi- zation of the synthesis and properties of NW arrays. [a] Key Laboratory of Cluster Science, Ministry of Education of China, Department of Chemistry, Beijing Institute of Technology, Beijing 100081, P. R. China E-mail: caomh@bit.edu.cn cwhu@bit.edu.cn [b] Department of Materials Science and Engineering, University of Delaware, Newark, DE 19716, USA [c] Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA E-mail: weib@udel.edu © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2011, 1570–1576 1570 arrays with variable densities, sizes, and morphologies were achieved by adjusting the oxygen sources. A possible mecha- nism was proposed for the formation of the cone-like In 2 O 3 NW arrays. The photoluminescence spectrum of the low- density, cone-like In 2 O 3 NW arrays shows emission in a wide range, from the visible (yellow light) into the near infrared region. Indium oxide (In 2 O 3 ), a well-known n-type semiconduc- tor oxide with a wide band gap of about 3.6eV, has been frequently used in the microelectronic field in gas detectors, window heaters, solar cells, memory devices, and flat-panel display materials. [12–14] Almost all of the reported In 2 O 3 nanomaterials, particularly In 2 O 3 NWs, [15–18] have been prepared by well-developed methods such as chemical vapor deposition (CVD), [15,16] pulsed laser deposition (PLD), [17] alumina or mesoporous silica template method, [18] and so on. However, to the best of our knowl- edge, current methods reported for the synthesis of oriented 1D In 2 O 3 NW arrays generally suffer from some drawbacks, such as costly substrates, catalysts, metalorganic precursors, and inexpungible templates. [18–22] Therefore, there is a need to synthesize controllable In 2 O 3 NW arrays through other facile, economical, effective approaches on simple sub- strates without catalysts, rigorous vacuum conditions, and complicated templates. In the study reported in this paper, cone-like In 2 O 3 NW arrays were grown in situ on the surface of indium grains at 900°C by a simple CVD route. Here, the indium grains served themselves as both the indium source, which reacted with different oxygen sources, and as the substrate for the growth of cone-like NW arrays. Cone-like In 2 O 3 NW arrays with controllable densities, sizes, and morphologies were achieved by adjusting the oxygen sources. The mixture of gallium oxide and graphite powder or industrial purity ar- gon with a trace amount of oxygen (2 ppm) acted as the different oxygen sources. The low-density, well-aligned, cone-like In 2 O 3 NW arrays were obtained when the mixture of gallium oxide and graphite powder acted as the oxygen source. When the industrial purity argon acted as a carrier gas and oxygen source, high-density cone-like In 2 O 3 NW arrays were obtained, in which the cones have a nanometer-