Article

Composition-Tuned ConSi Nanowires: Location-Selective Simultaneous Growth along Temperature Gradient

Department of Chemistry, KAIST, Daejeon 305-701, Korea.
ACS Nano (Impact Factor: 12.88). 05/2009; 3(5):1145-50. DOI: 10.1021/nn900191g
Source: PubMed

ABSTRACT We report the simultaneous and selective synthesis of single-crystalline Co(n)Si NWs (n = 1-3) and their corresponding crystal structures--simple cubic (CoSi), orthorhombic (Co(2)Si), and face-centered cubic (Co(3)Si)--following a composition change. Co(n)Si NWs were synthesized by placing the sapphire substrates along a temperature gradient. The synthetic process is a successful demonstration of tuning the chemical composition in Co(n)Si NWs. The synthesis and detailed crystal structure of single-crystalline Co(2)Si and Co(3)Si are reported for the first time including the bulk and the nanostructure phases. The electrical and magnetic properties of Co(2)Si NWs are investigated and compared with those of CoSi NWs.

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Available from: Sunghun Lee, Aug 15, 2014
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    • "For example, Kim et al. reported the synthesis of high-quality single-crystalline NiSi NWs using CVD at the low temperature of ∼400 • C, which exhibited typical metallic behaviors and promising field-emission properties [12]. In the report of Seo et al., high density free-standing single-crystalline cobalt silicide NWs with tunable compositions were grown by placing the sapphire substrates along a temperature gradient during the CVD process, and these exhibited controllable electric and magnetic properties according to the crystal structure of the NWs [13]. Another widely adopted method to fabricate silicide NWs is the solid-state reaction method, in which transition metal films are reacted with silicon NWs for silicidation [14], [15]. "
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    ABSTRACT: We report for the first time synthesis of high-density arrays of vertically well-aligned cobalt monosilicide (CoSi) nanowires (NWs) in a large area via a solid-state reaction. The vertical arrays of 1-μm-long Si NWs were first grown on a p-type (1 0 0) Si substrate by the aqueous electroless etching (AEE) method, and a 40-nm-thick Co layer was conformally deposited using a thermal atomic layer deposition system as revealed by SEM and transmission electron microscope analyses. The rapid thermal annealing process was carried out at various temperatures ranging from 700 to 1000 °C; the X-ray diffraction analysis confirmed that the polycrystalline CoSi NW arrays were formed at temperatures above 900 °C. The required high driving force for this silicide formation can be attributed to the significant amounts of oxygen-related contaminants at the defect sites of the highly rough surfaces of AEE-grown Si NWs. To demonstrate practical applications, field emitters and Schottky diodes were fabricated using the vertically aligned CoSi NW arrays. The field emission measurements showed a turn-on field of 10.9 V/μm and a field enhancement factor of 328, indicating the feasibility of vertically aligned CoSi NW arrays as promising field emitters. For the Schottky diodes, the measured Schottky barrier height was 0.52 eV and the estimated ideality factor obtained from the I-V characteristic curves was 2.28.
    IEEE Transactions on Nanotechnology 09/2013; 12(5):704-711. DOI:10.1109/TNANO.2013.2268578 · 1.62 Impact Factor
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    • "Cobalt silicide nanowires have many relatively good characteristics, including low resistivity, good thermal stability, appropriate work function, and compatibility with current processing of Si devices. There are three main methods for synthesizing CoSi NWs, including reactions of CoCl2 with silicon substrates by chemical vapor deposition (CVD) processes [26-28], cobalt silicide nanocables grown on Co films [29], and CVD with single-source precursors [30]. In this work, we synthesized cobalt silicide nanowires through CVD processes and changed and studied the effects of several critical processing parameters. "
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    ABSTRACT: In this work, cobalt silicide nanowires were synthesized by chemical vapor deposition processes on Si (100) substrates with anhydrous cobalt chloride (CoCl2) as precursors. Processing parameters, including the temperature of Si (100) substrates, the gas flow rate, and the pressure of reactions were varied and studied; additionally, the physical properties of the cobalt silicide nanowires were measured. It was found that single-crystal CoSi nanowires were grown at 850[degree sign]C ~ 880[degree sign]C and at a lower gas flow rate, while single-crystal Co2Si nanowires were grown at 880[degree sign]C ~ 900[degree sign]C. The crystal structure and growth direction were identified, and the growth mechanism was proposed as well. This study with field emission measurements demonstrates that CoSi nanowires are attractive choices for future applications in field emitters.
    Nanoscale Research Letters 07/2013; 8(1):308. DOI:10.1186/1556-276X-8-308 · 2.52 Impact Factor
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    • "For example, Kim et al. reported the synthesis of high-quality single-crystalline NiSi NWs using CVD at the low temperature of ∼400 • C, which exhibited typical metallic behaviors and promising field-emission properties [12]. In the report of Seo et al., high density free-standing single-crystalline cobalt silicide NWs with tunable compositions were grown by placing the sapphire substrates along a temperature gradient during the CVD process, and these exhibited controllable electric and magnetic properties according to the crystal structure of the NWs [13]. Another widely adopted method to fabricate silicide NWs is the solid-state reaction method, in which transition metal films are reacted with silicon NWs for silicidation [14], [15]. "
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    ABSTRACT: A facile method to selectively grow vertically-aligned silicon nanowires (SiNWs) which can inherit the doping concentration from its mother wafer, with controllable length, is demonstrated using the combination of photolithography and aqueous electroless etching. The use of SU-8-2002, a chemically and mechanically robust photoresist (PR) material, provided a high selectivity for the etching reaction on the exposed surface of 1-μm-thick n+ doped p-type (1 0 0) Si substrate, resulting in the fabrication of ∼30-μm-long vertically-aligned SiNW photodiode arrays on the desired locations, while the areas covered with SU-8-2002 remained unreacted. Optical and field emission scanning electron microscope analyses confirmed that SiNWs were selectively grown while retaining the shape of the PR patterns. The electrical and optical measurements of the fabricated p–n+ junction SiNW photodiodes were compared to those of reference planar p–n+ junction Si photodiodes: the current density of the p–n+ junction SiNW photodiodes was approximately 3 times greater than that of the planar counterpart at the forward bias of 5 V, which can be attributed to the high density of defect states on the rough surfaces of the synthesized SiNWs, leading to the increased recombination efficiencies for the injected carriers. In addition, the photoresponse of the p–n+ SiNW photodiode arrays was 3.4 times higher than that of the planar device at −3.5 V due to the increase in the light scattering.
    Applied Surface Science 06/2013; 274:79–84. DOI:10.1016/j.apsusc.2013.02.099 · 2.54 Impact Factor
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