Size-Controllable Growth of Single Crystal In(OH) 3 and In 2 O 3 Nanocubes Qun Tang, † Wenjia Zhou, † Wu Zhang, † Shaomin Ou, † Ke Jiang, ‡ Weichao Yu, † and Yitai Qian* ,†,‡ Department of Chemistry and Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China Received March 8, 2004 ABSTRACT: Single crystal In(OH) 3 nanocubes were synthesized by a designed novel hydrothermal treatment, and the size can be simply moderated by varying the hydrothermal temperature. By calcining the In(OH) 3 nanocubes in air at 400 °C, single crystal In 2 O 3 nanocubes were also prepared with the size slightly shrinking. Room temperature photoluminescence showed a broad photoluminescence emission spectrum in the blue-green region with its maximum intensity centered at 450 nm, which was mainly attributed to the effect of the oxygen deficiencies. Introduction Inorganic nanoparticles with well-defined shapes are of special interest to understand basic size-dependent, scaling laws and may be useful in a wide range of applications. Fields that would greatly benefit from advances in the synthesis of well-defined nanostructures include photonics, nanoelectronics, information storage, catalysis, and biosensors. Recently, a breakthrough was made in the synthesis of nanocubes. Monodispersed noble metal and Cu 2 O nanocubes were prepared by controlled oxidation-reduction reactions in surfactant solution and epitaxial electrodeposition on InP (001). 1 Li et al. reported the fabrication of single crystal CaF 2 nanocubes through a simple surfactant-free precipita- tion and hydrothermal procedure. 2 Indium oxide and the closely related indium tin oxide are two important TCOs that are useful in wide ap- plications such as electrooptic modulators, low emissiv- ity windows, solar cells, flat panel displays, and elec- trochromic windows in dissipating static electricity from the windows on xerographic copiers. 3 As In 2 O 3 holds a wide gad gap (In 2 O 3 direct gap of 3.55-3.75 eV) close to GaN, its nanostructure might hold possible applica- tions in nanoscale optoelectronic devices. Furthermore, the possibility of using the nanostructure of In 2 O 3 for UV lasers, detectors, and as gas sensors for ozone and nitrogen dioxide is appealing. 4 Inorganic particles al- ways showed unique size- and shape-dependent proper- ties. For instance, the gas-sensing ability of In 2 O 3 has been showed to increase significantly by decreasing its particle size. 4 It is imaginable that size and shape controllable growth of In 2 O 3 nanoparticles might pave the way to further elevate its performance. Recently, a In 2 O 3 nanoparticle with a square or rhombohedral shape was subsequently produced. 5 In this communica- tion, we designed an oxidation hydrothermal route to In(OH) 3 nanocubes in the absence of surfactant. In 2 O 3 nanocubes were subsequently obtained by calcination of In(OH) 3 nanocubes. As a wide band gap transparent semiconductor, the photoluminescence (PL) of In 2 O 3 nanocubes was investigated in detail. Experimental Section The detailed experimental procedure is as follows: 35 mL of 4 M NaOH solution was fully mixed with 6 mL of 30% H2O2 in a 50 mL autoclave; subsequently, 2.0 g of metal indium particle was immersed into the solution, and then, the auto- clave was sealed and put into an oven at 200 °C for 24 h. The white power was then collected from the solution, rinsed with deionized water, and dried in air at 40 °C. The as-prepared white powders were calcined in a boat crucible at a temper- ature of 400 °C and maintained for 2 h in air. The calcination temperature was determined by the DTA/TG (not shown here). Results and Discussion The phase purity of the as-prepared hydrothermal and calcined products was evidenced with a Rigaku X-ray diffractometer with Cu KR radiation (λ ) 0.15418 nm). All of the reflection of the X-ray diffraction (XRD) pattern of the hydrothermal product in Figure 1a could be readily indexed to a pure body centered cubic phase [space group: Im 3 (204)] of In(OH) 3 with a lattice con- * To whom correspondence should be addressed. Tel: 86-551- 3603204. Fax: 86-551-3607402. † Department of Chemistry. ‡ Structure Research Laboratory. Figure 1. XRD pattern of the obtained In(OH)3 (a) and In2O3 (b) nanocubes. CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 1 147 - 150 10.1021/cg049914d CCC: $30.25 © 2005 American Chemical Society Published on Web 08/19/2004