The photophysics of titanium dioxide (TiO 2 ) sensitized by dyes, [1,2] polymers, [3,4] and semiconductors [5,6] has been widely studied with an aim of solar energy conversion by the photovoltaic effect. These potential sensitizers have to have a suitable band gap, to absorb sunlight efficiently, and a proper conduction band edge, to transfer light-excited electrons to TiO 2 rapidly. Dye-sensitized TiO 2 photovoltaic solar cells (the socalled Grätzel-type solar cell), which exhibit an energy conversion efficiency of around 10 %, were successfully pioneered by Grätzel and co-workers. [1,2,7] However, dyes are relatively expensive, [8] and organic compounds have shorter lifetimes and are less stable than inorganic materials, for example, when used as semiconductors. Among these semiconductors, quantum-dotsensitized TiO 2 nanoparticles (sensitized by InP, PbS, CdS, Ag 2 S) have been well-examined [5,6] and showed the evidence of electron transfer from the quantum dots into the TiO 2 . Indium nitride is another candidate for this type of semiconductor-sensitized TiO 2 system. Based on a model calculation, the conversion efficiency of InN/Si tandem films could reach as much as 32 % at AM = 1.5, [9] where AM, air mass, is a large body of air with similar temperature and moisture properties throughout. Therefore, nanocrystalline TiO 2 films with an extremely large surface-to-volume ratio of InN/TiO 2 tandem films may be considered as potential candidates for photovoltaic applications.InN, a well-characterized III-V semiconductor with a stable wurtzite crystal structure, [10] has been used for visible optoelectronics and high-efficiency solar cell applications. [11][12][13] This chemically stable and robust InN has a useful range of band gaps, 0.7-2.1 eV, [14][15][16][17][18] which result from the crystallinity [16] and quantum confinement effects.[18] The magnitude of the band gap can be adjusted to match the conduction band edges of InN and TiO 2 by doping with Ga, for example, to form an In x Ga 1Àx N alloy, [19,20] or by doping TiO 2 with nitrogen to form TiO 2Àx N x . [21,22] The growth of InN films has been performed on silicon substrates, [23] sapphire, GaN, and GaAs. [24][25][26] Various methods have been used including organometallic chemical vapor deposition (OMCVD), [27][28][29] laser-assisted OMCVD, [23] magnetron sputtering, [30,31] molecular beam epitaxy (MBE), [14,16] and halogen-transport vapor-phase epitaxy.[32] In conventional OMCVD deposition on standard substrates, trimethyl indium (TMIn) has been used as the most efficient indium precursor, [15,18,23] and hydrazoic acid (HN 3 ) is the most efficient nitride precursor. [18,23] The objective of this Communication is to demonstrate the deposition of high-quality InN films onto TiO 2 nanoparticles using TMIn and HN 3 by low-pressure OMCVD for the first time. The deposited InN films were analyzed by X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV/Vis spectroscopy. Figure 1 shows two XRD patterns ...