Growth of single-crystalline cobalt silicide nanowires and their field emission property
© Lu et al.; licensee Springer. 2013
Received: 21 May 2013
Accepted: 27 June 2013
Published: 3 July 2013
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°C ~ 880°C and at a lower gas flow rate, while single-crystal Co2Si nanowires were grown at 880°C ~ 900°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.
KeywordsCVD Cobalt silicide Nanowires Single crystalline Field emission
Possessing low resistivity and excellent compatibility with conventional silicon device processing, transition metal silicide nanowires have been widely studied [1–5]. Compared with silicon nanowires (NWs), fabricating free-standing silicide NWs is more complicated since metal silicides have lots of phases. In terms of methods, the synthesis of free-standing silicide NWs can be divided into four classifications, which are silicidation of silicon nanowires [6–11], delivery of silicon to metal films [12–16], reactions between transition metal sources and silicon substrates [17–22], and simultaneous metal and silicon delivery [23–25]. 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 , and CVD with single-source precursors . In this work, we synthesized cobalt silicide nanowires through CVD processes and changed and studied the effects of several critical processing parameters. Additionally, we conducted scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses for identifying the structure and composition of the resultant products and investigating their growth mechanisms. Also, the electrical properties of the nanosilicides were measured and discussed for potential applications.
In our study, we synthesized cobalt silicide nanowires by CVD processes using single-crystal Si (100) wafers of native oxide as substrates, anhydrous cobalt chloride powders (97%) as precursors, and Ar gas (99.99%) with H2 gas (15%) as carrier gases. The metal sources were put in the upstream zone where the temperature was 610°C, while the silicon (100) substrates were put in the downstream zone, the temperature range of which was 750°C ~ 900°C. To understand the factors that influence the growth of cobalt silicide nanowires, we conducted experiments with different substrate temperatures, vapor pressures, and gas flow rates. SEM was utilized for the morphology of the nanowires, and TEM analysis was conducted for structure identification and atomic resolution imaging of the nanowires.
Results and discussion
In this study, using a CVD method, we have synthesized cobalt silicide nanowires of two different phases, which are CoSi NWs and Co2Si NWs, respectively. Effects of some processing parameters, including the temperature, gas flow rate, and pressure, were investigated; for example, the number of CoSi nanowires shows a decreasing trend with the increasing gas flow rate. Also, the growth mechanism has been proposed. Electrical measurements demonstrate that the CoSi nanowires are potential field-emitting materials.
KCL acknowledges the support from the National Science Council through grant 100-2628-E-006-025-MY2.
- Zhang SL, Ostling M: Metal silicides in CMOS technology: past, present, and future trends. Crit Rev Solid State Mat Sci 2003, 28: 1–129. 10.1080/10408430390802431View ArticleGoogle Scholar
- Chen LJ: Silicide Technology for Integrated Circuits. London: The Institution of Electrical Engineers; 2004.View ArticleGoogle Scholar
- Zhang SL, Smith U: Self-aligned silicides for ohmic contacts in complementary metal–oxide–semiconductor technology. Vac J Sci Technol A 2004, 22: 1361–1370. 10.1116/1.1688364View ArticleGoogle Scholar
- Maszara WP: Fully silicided metal gates for high-performance CMOS technology: a review. J Electrochem Soc 2005, 152: G550-G555. 10.1149/1.1924307View ArticleGoogle Scholar
- Schmitt AL, Higgins JM, Szczech JR, Jin S: Synthesis and applications of metal silicide nanowires. J Mater Chem 2010, 20: 223–235. 10.1039/b910968dView ArticleGoogle Scholar
- Yamamoto K, Kohno H, Takeda S, Ichikawa S: Fabrication of iron silicide nanowires from nanowire templates. Appl Phys Lett 2006, 89: 083107. 10.1063/1.2338018View ArticleGoogle Scholar
- Lu KC, Wu WW, Wu HW, Tanner CM, Chang JP, Chen LJ, Tu KN: In-situ control of atomic-scale Si layer with huge strain in the nano-heterostructure NiSi/Si/NiSi through point contact reaction. Nano Lett 2007, 7: 2389–2394. 10.1021/nl071046uView ArticleGoogle Scholar
- Wu WW, Lu KC, Wang CW, Hsieh HY, Chen SY, Chou YC, Yu SY, Chen LJ, Tu KN: Growth of multiple metal/semiconductor nanoheterostructures through point and line contact reactions. Nano Lett 2010, 10: 3984–3989. 10.1021/nl101842wView ArticleGoogle Scholar
- Lu KC, Wu WW, Ouyang H, Lin YC, Huang Y, Wang CW, Wu ZW, Huang CW, Chen LJ, Tu KN: The influence of surface oxide on the growth of metal/semiconductor nanowires. Nano Lett 2011, 11: 2753–2758. 10.1021/nl201037mView ArticleGoogle Scholar
- Hsu SC, Hsin CL, Yu SY, Huang CW, Wang CW, Lu CM, Lu KC, Wu WW: Single-crystalline Ge nanowires and Cu3Ge/Ge nano-heterostructures. Cryst Eng Comm 2012, 14: 4570–4574. 10.1039/c2ce25316jView ArticleGoogle Scholar
- Wu WW, Lu KC, Chen KN, Yeh PH, Wang CW, Lin YC, Huang Y: Controlled large strain of Ni silicide/Si/Ni silicide nanowire heterostructures and their electron transport properties. Appl Phys Lett 2010, 97: 203110. 10.1063/1.3515421View ArticleGoogle Scholar
- Kim J, Lee ES, Han CS, Kang Y, Kim D, Anderson WA: Observation of Ni silicide formation and field emission properties of Ni silicide nanowires. Microelectron Eng 2008, 85: 1709–1712. 10.1016/j.mee.2008.04.034View ArticleGoogle Scholar
- Kim J, Anderson WA: Spontaneous nickel monosilicide nanowire formation by metal induced growth. Thin Solid Films 2005, 483: 60–65. 10.1016/j.tsf.2004.12.025View ArticleGoogle Scholar
- Kim CJ, Kang K, Woo YS, Ryu KG, Moon H, Kim JM, Zang DS, Jo MH: Spontaneous chemical vapor growth of NiSi nanowires and their metallic properties. Adv Mater 2007, 19: 3637–3642. 10.1002/adma.200700609View ArticleGoogle Scholar
- Kim J, Shin DH, Lee ES, Han CS, Park YC: Electrical characteristics of single and doubly connected Ni silicide nanowire grown by plasma-enhanced chemical vapor deposition. Appl Phys Lett 2007, 90: 253103. 10.1063/1.2749430View ArticleGoogle Scholar
- Yan XQ, Yuan HJ, Wang JX, Liu DF, Zhou ZP, Gao Y, Song L, Liu LF, Zhou WY, Wang G, Xie SS: Synthesis and characterization of a large amount of branched Ni2Si nanowires. Appl Phys A 2004, 79: 1853–1856.View ArticleGoogle Scholar
- Kang K, Kim SK, Kim CJ, Jo MH: The role of NiOx overlayers on spontaneous growth of NiSix nanowires from Ni seed layers. Nano Lett 2008, 8: 431–436. 10.1021/nl072326cView ArticleGoogle Scholar
- Chueh YL, Chou LJ, Cheng SL, Chen LJ, Tsai CJ, Hsu CM, Kung SC: Synthesis and characterization of metallic TaSi2 nanowires. Appl Phys Lett 2005, 87: 223113. 10.1063/1.2132523View ArticleGoogle Scholar
- Chueh YL, Ko MT, Chou LJ, Chen LJ, Wu CS, Chen CD: TaSi2 nanowires: a potential field emitter and interconnect. Nano Lett 2006, 6: 1637–1644. 10.1021/nl060614nView ArticleGoogle Scholar
- Xiang B, Wang QX, Wang Z, Zhang XZ, Liu LQ, Xu J, Yu DP: Synthesis and field emission properties of TiSi2 nanowires. Appl Phys Lett 2005, 86: 243103. 10.1063/1.1948515View ArticleGoogle Scholar
- Ouyang L, Thrall ES, Deshmukh MM, Park H: Vapor phase synthesis and characterization of ϵ-FeSi nanowires. Adv Mater 2006, 18: 1437–1440. 10.1002/adma.200502721View ArticleGoogle Scholar
- Varadwaj KSK, Seo K, In J, Mohanty P, Park J, Kim B: Phase-controlled growth of metastable Fe5Si3 nanowires by a vapor transport method. J Am Chem Soc 2007, 129: 8594–8599. 10.1021/ja071439vView ArticleGoogle Scholar
- Szczech JR, Schmitt AL, Bierman MJ, Jin S: Single-crystal semiconducting chromium disilicide nanowires synthesized via chemical vapor transport. Chem Mater 2007, 19: 3238–3243. 10.1021/cm0707307View ArticleGoogle Scholar
- Song Y, Schmitt AL, Jin S: Ultralong single-crystal metallic Ni2Si nanowires with low resistivity. Nano Lett 2007, 7: 965–969. 10.1021/nl0630687View ArticleGoogle Scholar
- Schmitt AL, Bierman MJ, Schmeisser D, Himpsel FJ, Jin S: Synthesis and properties of single-crystal FeSi nanowires. Nano Lett 2006, 6: 1617–1621. 10.1021/nl060550gView ArticleGoogle Scholar
- Seo K, Lee S, Yoon H, In J, Varadwaj KSK, Jo Y, Jung MH, Kim J, Kim B: Composition-tuned Co(n)Si nanowires: location-selective simultaneous growth along temperature gradient. ACS Nano 2009, 3: 1145–1150. 10.1021/nn900191gView ArticleGoogle Scholar
- Liang YH, Yu SY, Hsin CL, Huang CW, Wu WW: Growth of single-crystalline cobalt silicide nanowires with excellent physical properties. J Appl Phys 2011, 110: 074302. 10.1063/1.3643007View ArticleGoogle Scholar
- Tsai CI, Yeh PH, Wang CY, Wu HW, Chen US, Lu MY, Wu WW, Chen LJ, Wang ZL: Cobalt silicide nanostructures: synthesis, electron transport, and field emission properties. Cryst Growth Des 2009, 9: 4514–4518. 10.1021/cg900531xView ArticleGoogle Scholar
- Hsin CL, Yu SY, Wu WW: Cobalt silicide nanocables grown on Co films: synthesis and physical properties. Nanotechnology 2010, 21: 485602. 10.1088/0957-4484/21/48/485602View ArticleGoogle Scholar
- Schmitt AL, Lei Z, Schmeiβer D, Himpsel FJ, Jin S: Metallic single-crystal CoSi nanowires via chemical vapor deposition of single-source precursor. J Phys Chem B 2006, 110: 18142–18146. 10.1021/jp064646aView ArticleGoogle Scholar
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