Silicon nanowires prepared by electron beam evaporation in ultrahigh vacuum
© Xu et al.; licensee Springer. 2012
Received: 10 February 2012
Accepted: 6 May 2012
Published: 6 May 2012
One-dimensional silicon nanowires (SiNWs) were prepared by electron beam evaporation in ultrahigh vacuum (UHV). The SiNWs can be grown through either vapor–liquid-solid (VLS) or oxide-assisted growth (OAG) mechanism. In VLS growth, SiNWs can be formed on Si surface, not on SiO2 surfaces. Moreover, low deposition rate is helpful for producing lateral SiNWs by VLS. But in OAG process, SiNWs can be grown on SiO2 surfaces, not on Si surfaces. This work reveals the methods of producing large-scale SiNWs in UHV.
KeywordsSilicon nanowires Preparation Vapor–liquid-solid Oxide-assisted growth Ultrahigh vacuum
One-dimensional (1D) nanomaterials have stimulated great interest due to their importance in basic academic research and potential technology applications [1, 2]. It is widely accepted that 1D nanomaterials not only play vital roles as interconnects and functional units for nanodevices, but also provide opportunities to investigate the dependence of electrical, thermal, and mechanical properties on the dimensionality and size reduction [2–4]. Among all 1D nanomaterials, silicon nanowires (SiNWs) are particularly attractive [5–9] because of the center role of silicon (Si) in semiconductor industry. Moreover, a wealth of traditional knowledge about Si material is helpful for understanding the relationships between its properties and nanostructures. In addition, the mature Si-based technology can be exploited to fabricate future nanodevices.
Many methods have been developed to prepare 1D SiNWs [5–16]. However, most SiNWs were produced in air atmosphere or low vacuum conditions [5–12]. Synthesis of SiNWs in ultrahigh vacuum (UHV) is helpful for obtaining highly pure products, as well as better evaluating their properties and understanding the related mechanisms. Therefore, the growth of SiNWs in UHV has attracted considerable attention recently [13–16]. Schubert et al. reported the preparation of vertical Si nanowhiskers in UHV by molecular beam epitaxy through vapor–liquid-solid (VLS) growth . Similarly, Irrera et al. prepared vertical SiNWs in UHV by electron beam evaporation (EBE) through VLS [14, 15]. Differently, Xu et al. introduced a new method to synthesize SiNWs in UHV by EBE through oxide-assisted growth (OAG) mechanism .
In this work, we demonstrated the feasibility of producing lateral SiNWs in UHV by EBE through both VLS and OAG mechanisms. The critical factors for 1D nanowire formations were also discussed.
Si(111) wafers sized 1 × 1 cm2 were chosen as the deposition substrates. Before being used, the Si substrates were ultrasonically cleaned in methanol for 15min followed by a dip in a diluted hydrofluoric acid (HF) solution for removing organic contaminations and surface oxides. The SiO2/Si(111) substrates were prepared by deposition of SiO2 films on Si(111) wafers using a plasma-enhanced chemical vapor deposition system (Orion II, Trion Technology, Clearwater, FL, USA) under the conditions of 13.56MHz, 600W, 0.6Torr, 300°C, and a N2O/SiH4 flux ratio of 100/150sccm. These SiO2/Si(111) substrates were ultrasonically cleaned with successive rinses of acetone and methanol. After having been dried by N2 gas, the cleaned substrates were transferred immediately to a UHV EBE system (Balzers ULS 400, Balzers Ltd., Liechtenstein, Switzerland) for depositions at constant rate of 0.02nm/s. The base pressure was 2 × 10−10mbar, and the process pressure was maintained at 1 × 10−7mbar or below during the depositions.
The as-deposited materials were characterized exsitu by tapping mode atomic force microscopy (AFM, Nanoscope III, Veeco Instruments, Inc., Plainview, NY, USA) and scanning electron microscopy (SEM, FEI XL30S-FEG, FEI Company, NE Dawson Creek Drive, Hillsboro, OR, USA), respectively.
Results and discussion
If a 100-nm-thick SiO2/Si(111) was used as the substrate, the case is different after the same Au and Si depositions. Figure 1c reveals that only 0D nanoparticles, but no any 1D nanowires, were formed on the SiO2 surface. The large particles in Figure 1c are Au, while the small ones are Si. Figure 1a and c suggest that molten Au-Si alloys are formed on the Si surface, and thus 1D SiNWs growth by VLS is induced (Figure 1a) [5–7,10-13]. But on the SiO2 surface, the interactions of Au-O and Si-O between the substrate and arriving species prevent the coalescence of Au and Si. Therefore, no Au-Si alloys can be created on the SiO2 surface, and thus no wires are yielded through VLS (Figure 1c). Although Pecora et al. similarly deduced the negative effects of SiO2 layer on the growth of SiNWs , they ignored the interactions between the substrate and arriving species. We believe that such interactions are critical in physical vapor deposition processes.
Large-scale SiNWs were successfully prepared by EBE in UHV through both VLS and OAG mechanisms. In VLS growth, Au-Si alloys created on the HF-treated Si substrates catalytically induce the growth of 1D SiNWs at 700°C. However, the Au-O and Si-O interactions inhibit the formation of Au-Si alloys, and thus no SiNWs can be grown through VLS on the SiO2 surfaces. In OAG process, the strong interactions of Si-Si between the Si substrates and deposited Si species prevent the formation of 1D SiNWs. In contrast, SiO2 surfaces provide suitable interactions so that SiNWs can be grown at 700°C through OAG on such substrates. This work reveals the methods to produce 1D SiNWs by EBE in UHV.
Atomic force microscopy
Electron beam evaporation
Scanning electron microscopy
We would like to thank Professor Zhongfan Liu and Professor Huizhong Huang in Peking University, Proessor Zhanpin Li in Beijing Electron Spectroscopy Center of Tsinghua University for their assistance. This work is supported by the National Natural Science Foundation of China (NSFC 61071032).
- Baughman RH, Zakhidov AA, de Heer WA: Carbon nanotubes—the route toward applications. Science 2002, 297: 787. 10.1126/science.1060928View Article
- Xia Y, Yang P, Sun Y, Wu Y, Mayers B, Gates B, Yin Y, Kim F, Yan H: One-dimensional nanostructures: synthesis, characterization, and applications. Adv Mater 2003, 15: 353. 10.1002/adma.200390087View Article
- Ruda HE, Polanyi JC, Yang SY, Wu ZH, Philipose U, Xu T, Yang S, Kavanagh KL, Liu JQ, Yang L, Wang Y, Robbie K, Yang J, Cooke DG, Budz AJ, Haugen HK: Developing 1D nanostructure arrays for future nanophotonics. Nanoscale Res Lett 2006, 1: 99. 10.1007/s11671-006-9016-6View Article
- Chiu H-Y, Deshpande VV, Postma HWCh, Lau CN, Mikó C, Forró L, Bockrath M: Ballistic photon thermal transport in multiwalled carbon nanotubes. Phys Rev Lett 2005, 95: 226101.View Article
- Morales AM, Lieber CM: A laser ablation method for the synthesis of crystalline semiconductor nanowires. Science 1998, 279: 208. 10.1126/science.279.5348.208View Article
- Holmes JD, Johnston KP, Doty RC, Korgel BA: Control of thickness and orientation of solution-grown silicon nanowires. Science 2000, 287: 1471. 10.1126/science.287.5457.1471View Article
- Cui Y, Lauhon LJ, Gudlksen MS, Wang JF, Lieber CM: Diameter-controlled synthesis of single-crystal silicon nanowires. Appl Phys Lett 2001, 78: 2214. 10.1063/1.1363692View Article
- Lauhon LJ, Gudlksen MS, Wang D, Lieber CM: Epitaxial core-shell and core-multishell nanowire heterostructures. Nature 2002, 420: 57. 10.1038/nature01141View Article
- Ma DDD, Lee CS, Au FCK, Tong SY, Lee ST: Small-diameter silicon nanowire surfaces. Science 1874, 2003: 299.
- Ozaki N, Ohno Y, Takeda S: Silicon nanowhiskers grown on a hydrogen-terminated silicon (111) surface. Appl Phys Lett 1998, 73: 3700. 10.1063/1.122868View Article
- Zeng XB, Xu YY, Zhang SB, Hu ZH, Diao HW, Wang YQ, Kong GL, Liao XB: Silicon nanowires grown on a pre-annealed Si substrate. J Cryst Growth 2003, 347: 13.View Article
- Roussel M, Chen W, Talbot E, Lardé R, Cadel E, Gourbilleau F, Grandidier B, Stiévenard D, Pareige P: Atomic scale investigation of silicon nanowires and nanoclusters. Nanoscale Res Lett 2011, 6: 271. 10.1186/1556-276X-6-271View Article
- Schubert L, Werner P, Zakharov ND, Gerth G, Kolb FM, Long L, Gosele U, Tan TY: Silicon nanowhiskers grown on <111 > Si substrates by molecular-beam epitaxy. Appl Phys Lett 2004, 84: 4968. 10.1063/1.1762701View Article
- Irrera A, Pecora EF, Priolo F: Control of growth mechanisms and orientation in epitaxial Si nanowires grown by electronbeam evaporation. Nanotechnology 2009, 20: 135601. 10.1088/0957-4484/20/13/135601View Article
- Artoni P, Pecora EF, Irrera A, Priolo F: Kinetics of Si and Ge nanowires growth through electronbeam evaporation. Nanoscale Res Lett 2011, 6: 162. 10.1186/1556-276X-6-162View Article
- Xu XD, Wang YC, Liu ZF, Zhao RG: A new route to large-scale synthesis of silicon nanowires in ultrahigh vacuum. Adv Funct Mater 2007, 17: 1729. 10.1002/adfm.200600658View Article
- Yu L, Alet P-J, Picardi G, Cabarrocas PR: An in-plane solid-liquild-solid growth mode for self-avoiding lateral silicon nnaowires. Phys Rew Lett 2009, 102: 125501.View Article
- Pecora EF, Irrera A, Priolo F: Influence of O contamination and Au cluster properties on the structural features of Si nanowires. Thin Solid Films 2010, 518: 2562. 10.1016/j.tsf.2009.08.019View Article
- Wahlström E, Lopez N, Schaub R, Thostrup P, Rønnau A, Africh C, Lægsgaard E, Nørskov JK, Besenbacher F: Bonding of gold nanoclusters to oxygen vacancies on rutile TiO2(110). Phys Rev Lett 2003, 90: 026101.View Article
- Parker SC, Campbell CT: Reactivity and sintering kinetics of Au/TiO2(110) model catalysts particle size effects. Topics Cata 2007, 44: 3. 10.1007/s11244-007-0274-zView Article
- Taga Y: Review of plasma thin-film technology in automobile industry. Surf Coat Technol 1999, 112: 339. 10.1016/S0257-8972(98)00760-9View Article
- Kwon J-Y, Yoon T-S, Kim K-B, Min S-H: Comparison of the agglomeration behavior of Au and Cu films sputter deposited on silicon dioxide. J Appl Phys 2003, 93: 3270. 10.1063/1.1556178View Article
- Ruffino F, Canino A, Grimaldi MG, Giannazzo F, Roccaforte F, Raineri V: Kinetic mechanism of the thermal-induced self-organization of Au/Si nanodroplets on Si(100): size and roughness evolution. J Appl Phys 2008, 104: 024310. 10.1063/1.2955784View Article
- Ruffino F, Grimaldi MG, Giannazzo F, Roccaforte F, Raineri V: Atomic force microscopy study of the kinetic roughening in nanostructured gold films on SiO2. Nanoscale Res Lett 2009, 4: 262. 10.1007/s11671-008-9235-0View Article
- Xu XD, Wang YC, Liu ZF: Large-scale fabrication of uniform gold nanoparticles in ultrahigh vacuum. J Cryst Growth 2005, 285: 372. 10.1016/j.jcrysgro.2005.08.048View Article
- Cotton FA, Wilkinson G, Gaus PL: Basic inorganic chemistry. Wiley, New York; 1995.
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