Complete composition tunability of InGaN nanowires using a combinatorial approach. Nat Mater 6:951

Department of Chemistry, University of California, Berkeley, CA 94720, USA.
Nature Material (Impact Factor: 36.5). 01/2008; 6(12):951-6. DOI: 10.1038/nmat2037
Source: PubMed


The III nitrides have been intensely studied in recent years because of their huge potential for everything from high-efficiency solid-state lighting and photovoltaics to high-power and temperature electronics. In particular, the InGaN ternary alloy is of interest for solid-state lighting and photovoltaics because of the ability to tune the direct bandgap of this material from the near-ultraviolet to the near-infrared region. In an effort to synthesize InGaN nitride, researchers have tried many growth techniques. Nonetheless, there remains considerable difficulty in making high-quality InGaN films and/or freestanding nanowires with tunability across the entire range of compositions. Here we report for the first time the growth of single-crystalline In(x)Ga(1-x)N nanowires across the entire compositional range from x=0 to 1; the nanowires were synthesized by low-temperature halide chemical vapour deposition and were shown to have tunable emission from the near-ultraviolet to the near-infrared region. We propose that the exceptional composition tunability is due to the low process temperature and the ability of the nanowire morphology to accommodate strain-relaxed growth, which suppresses the tendency toward phase separation that plagues the thin-film community.

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    • "The methods to fabricate 1D TiO 2 nanostructures include colloidal synthesis [19] [20], electrodeposition [21], organometallic chemical vapor deposition (OMCVD) [22] [23], chemical vapor deposition (CVD) [24] [25], oblique-angle deposition (OAD) [11], hydrothermal processes [26] [27]. Besides, one unique method for the fabrication and tailoring of nanostructured materials is via ion beam modification [28]. "
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    ABSTRACT: In this work, well-ordered nanorods were fabricated on the surface of TiO2 thin films deposited on Ti sheets by an ion irradiation method using nitrogen ion irradiation with the energy of 65 keV to a fluence of 1 × 1017 ions/cm2. These TiO2 nanorods are about 120 nm in length and 20–40 nm in diameter. After post-irradiation annealing at 500 °C in O2, the nanorod array photoelectrode displays largely enhanced performance for photoelectrochemical (PEC) water splitting compared to that of the un-irradiated TiO2 thin films with a planar structure. The influences of the irradiated ion energy on the morphology and photocurrent density of the nanorods were investigated. The 65 keV N+ irradiated TiO2 thin films shows a higher photocurrent density than those of the 45 and 85 keV N+ irradiated TiO2 thin films. We also discussed the influence of annealing conditions on the PEC performance of TiO2 nanorods, and it was found that the nanorods annealed at 600 °C in vacuum produce a much higher photocurrent density of 0.6 mA/cm2 at 0.8 V (vs. a saturated calomel electrode), which is about 7 times higher than that of the nanorods annealed in oxygen. This work proposes that ion irradiation combination with thermal annealing in vacuum could be an effective approach for developing nanostructured materials for water splitting.
    International Journal of Hydrogen Energy 04/2015; 40(15). DOI:10.1016/j.ijhydene.2015.02.087 · 3.31 Impact Factor
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    • "High vacuum chemical vapour deposition (HV-CVD) provides several interesting features involving addressable combinatorial experiments for fast optimization of thin films [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12], controlled growth of nanowires in a vapour–liquid–solid (VLS) process [13] [14] [15], and selective area growth exploiting laser [16] [17] [18], ion [19], or electron [20] beam assisted depositions. "
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    ABSTRACT: Chemical vapour deposition (CVD) processes depend on the availability of suitable precursors. Precursors that deliver a stable vapour pressure are favourable in classical CVD processes, as they ensure process reproducibility. In high vacuum CVD (HV-CVD) process vapour pressure stability of the precursor is of particular importance, since no carrier gas assisted transport can be used. The dimeric Nb2(OEt)10 does not fulfil this requirement since it partially dissociates upon heating. Dimethylamino functionalization of an ethoxy ligand of Nb(OEt)5 acts as an octahedral field completing entity and leads to Nb(OEt)4(dmae). We show that Nb(OEt)4(dmae) evaporates as monomeric molecule and ensures a stable vapour pressure and, consequently, stable flow. A set of HV-CVD experiments were conducted using this precursor by projecting a graded molecular beam of the precursor onto the substrate at deposition temperatures from 320 °C to 650 °C. Film growth rates ranging from 8 nm · h- 1 to values larger than 400 nm · h- 1 can be obtained in this system illustrating the high level of control available over the film growth process. Classical CVD limiting conditions along with the recently reported adsorption-reaction limited conditions are observed and the chemical composition, microstructural and optical properties of the films are related to the corresponding growth regime. Nb(OEt)4(dmae) provides a large process window of deposition temperatures and precursor fluxes over which carbon-free and polycrystalline niobium oxide films with growth rates proportional to precursor flux are obtained. This feature makes Nb(OEt)4(dmae) an attractive precursor for combinatorial CVD of niobium containing complex oxide films that are finding an increasing interest in photonics and photoelectrochemical water splitting applications. The adsorption-reaction limited conditions provide extremely small growth rates comparable to an atomic layer deposition (ALD) process indicating that HV-CVD has the potential to be an alternative to ALD for growth of ultrathin films on low aspect ratio substrates.
    Thin Solid Films 11/2014; 571. DOI:10.1016/j.tsf.2014.09.073 · 1.76 Impact Factor
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    • "Significant efforts have been focused on developing better photocatalysts to increase the solar absorption efficiency and broaden the range of solar spectrum captured [1] [2]. Nanostructured semiconductors [4] (e.g., GaP, InGaN and GaN:ZnO) and metal oxides (e.g., TiO 2 , NaTaO 3 , WO 3 , SrTiO 3 ), which offers large surface area for both co-catalyst loading and chemical reactions and tunability in their electronic structures [5], are being extensively studied for their improved photocatalytic performance [2]. In addition to the band gap engineering in these semiconductors, it is equally important to understand the kinetics of the water splitting reaction. "
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    ABSTRACT: A novel Ag-alumina hybrid surface-enhanced Raman spectroscopy (SERS) platform has been designed for the spectroscopic detection of surface reactions in the steady state. Single crystalline and faceted silver (Ag) nanoparticles with strong light scattering were prepared in large quantity, which enables their reproducible self-assembly into large scale monolayers of Raman sensor arrays by the Langmuir-Blodgett technique. The close packed sensor film contains high density of sub-nm gaps between sharp edges of Ag nanoparticles, which created large local electromagnetic fields that serve as “hot spots” for SERS enhancement. The SERS substrate was then coated with a thin layer of alumina by atomic layer deposition to prevent charge transfer between Ag and the reaction system. The photocatalytic water splitting reaction on a monolayer of anatase TiO2 nanoplates decorated with Pt co-catalyst nanoparticles was employed as a model reaction system. Reaction intermediates of water photo-oxidation were observed at the TiO2/solution interface under UV irradiation. The surface-enhanced Raman vibrations corresponding to peroxo, hydroperoxo and hydroxo surface intermediate species were observed on the TiO2 surface, suggesting that the photo-oxidation of water on these anatase TiO2 nanosheets may be initiated by a nucleophilic attack mechanism.
    Nano Research 12/2013; 7(1):132-143. DOI:10.1007/s12274-013-0380-0 · 7.01 Impact Factor
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