Influence of thin<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">SiO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>interlayers on chemical reaction and microstructure at the Ni/Si(111) interface

Liehr, M.; Lefakis, H.; LeGoues, F. K.; Rubloff, Gary W.

doi:10.1103/physrevb.33.5517

Cited by 31 publications

(19 citation statements)

References 20 publications

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“…Indeed, previous studies of metals on ultra-thin silicon oxides have shown that pinholes or defects in the oxide significantly enhances the diffusion process. [40,41,42,43] By determining the critical oxide thickness that prevents silicide formation for iron catalyst, we can extrapolate to determine the critical thickness for cobalt and nickel which are the other common singlewalled nanotube catalysts. For cobalt, the bulk diffusion parameters are…”

Section: Resultsmentioning

confidence: 99%

Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO₂ Diffusion Barriers

Simmons

Nichols

Marcus

et al. 2006

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The ability to integrate carbon nanotubes, especially single-walled carbon nanotubes, seamlessly onto silicon would expand the range of applications considerably. Though direct integration using chemical vapor deposition is the simplest method, the growth of single-walled carbon nanotubes on bare silicon and on ultra-thin oxides is greatly inhibited due to the formation of a non-catalytic silicide. Using x-ray photoelectron spectroscopy, we show that silicide formation occurs on ultra-thin oxides due to thermally activated metal diffusion through the oxide. Silicides affect the growth of single-walled nanotubes more than multi-walled nanotubes due to the increased kinetics at the higher single-walled nanotube growth temperature. We demonstrate that nickel and iron catalysts, when deposited on clean silicon or ultra-thin silicon dioxide layers, begin to form silicides at relatively low temperatures, and that by 900 o C, all of the catalyst has been incorporated into the silicide, rendering it inactive for subsequent single-walled nanotube growth.We further show that a 4 nm silicon dioxide layer is the minimum diffusion barrier thickness which allows for efficient single-walled nanotube growth.

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Section: Resultsmentioning

confidence: 99%

Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO₂ Diffusion Barriers

Simmons

Nichols

Marcus

et al. 2006

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“…As a rule of thumb, Huettig and Tamman temperatures are semiempirically defined as 0.3 and 0.5 times the melting point in K, respectively, to indicate the temperature at which atoms become mobile at defects (269°C for Fe) or in the bulk (631°C for Fe). 31 This neglects substrate interactions 20,32 and the fact that for small particles mobility occurs at much lower temperatures.…”

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confidence: 99%

“…The SiO 2 layer can prevent uncontrolled silicide formation 20 and serves as gate dielectric for FET fabrication. High-purity Fe, Co, and Ni catalyst films and Al layers are deposited by thermal evaporation.…”

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confidence: 99%

Catalytic Chemical Vapor Deposition of Single-Wall Carbon Nanotubes at Low Temperatures

et al. 2006

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We report surface-bound growth of single-wall carbon nanotubes (SWNTs) at temperatures as low as 350°C by catalytic chemical vapor deposition from undiluted C 2 H 2 . NH 3 or H 2 exposure critically facilitates the nanostructuring and activation of sub-nanometer Fe and Al/Fe/Al multilayer catalyst films prior to growth, enabling the SWNT nucleation at lower temperatures. We suggest that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.Carbon nanotubes (CNTs) have been a driving force for current advances in nanotechnology, both on an applied and on a fundamental level. Single-wall carbon nanotubes have shown the highest Young's modulus and highest axial thermal conductivity of any solid. Moreover, SWNTs have the highest current carrying capacity of any conductor, which makes them an attractive electronic, sensing, or heat sinking material for nano-electromechanical systems (NEMS) and future (hybrid) integrated circuitry. 1,2Defect-free SWNT synthesis is generally thought to require high temperatures (T). 3 This belief arises from the success of high-T deposition processes. Arc-discharge, laser ablation, and high-pressure CO conversion with inherent (local) temperatures in the order of 1000-4000°C have been optimized mainly for bulk CNT production. 3 For device fabrication, these techniques heavily rely on purification from other carbon allotropes and an indirect postgrowth assembly via stable suspensions. In comparison, catalytic chemical vapor deposition (CVD) allows selective, aligned CNT growth directly onto a substrate and thus presently is the only economically viable process for integrating CNTs into a device. 1,[4][5][6] This approach, however, exposes the substrate to the CNT growth temperature and atmosphere, which creates a need for less aggressive, low T processing conditions. Present back-end CMOS technology allows a maximum temperature of 400-450°C, the limit being set by the mechanical integrity of low dielectric constant intermetal dielectrics. 7 Thermal CVD of SWNTs has been reported at 550°C in furnace 8 and cold wall systems. 9 In situ environmental transmission electron microscopy (TEM) experiments show SWNT nucleation at 480°C. 10 Random-network FETs have been fabricated with SWNTs grown at 450°C by remote plasma-enhanced (PE) CVD.11 However, the high temperatures of bulk production techniques still dominate growth model considerations with the assumption that the catalyst cluster has to be liquefied and that the catalyst bulk is ratecontrolling.12,13 These considerations are also transferred to surface-bound CVD. 14 CNT growth below 500°C is not thought to be possible based on calculations of size-corrected melting points 14 and carbon saturation. 15In this Letter, we report SWNT growth at temperatures below 450°C by thermal CVD at cold wall conditions and demonstrate field effects in as-integrated SWNT FETs. We use evaporated thin catalyst films, which allow accurate patterning by standard lithography techniques and thus compa...

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“…Their TEM results, however, indicate straining at the Si/SiO 2 interface that may be caused by silicide formation after Ni diffusion through the native oxide film during rapid thermal annealing. Liehr and co-workers [16] report that, in the presence of SiO 2 diffusion barriers, solid-state reactions between Ni and Si at or above 900°C are limited by Ni diffusion through pinholes in the oxide film. At such high temperatures, the activation energy for Ni diffusion is further lowered by complementary decomposition of SiO 2 , which generates defect-rich areas and, hence, preferential diffusion pathways.…”

Section: Introductionmentioning

confidence: 99%

Structural changes during the reaction of Ni thin films with (100) silicon substrates

et al. 2012

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Ultrathin films of nickel deposited onto (1 0 0) Si substrates were found to form kinetically constrained multilayered interface structures characterized by structural and compositional gradients. The presence of a native SiO 2 on the substrate surface in tandem with thickness-dependent intrinsic stress of the metal film limits the solid-state reaction between Ni and Si. A roughly 6.5 nm thick Ni film on top of the native oxide was observed regardless of the initial nominal film thickness of either 5 or 15 nm. The thickness of the silicide layer that formed by Ni diffusion into the Si substrate, however, scales with the nominal film thickness. Cross-sectional in situ annealing experiments in the transmission electron microscope elucidate the kinetics of interface transformation towards thermodynamic equilibrium. Two competing mechanisms are active during thermal annealing: thermally activated diffusion of Ni through the native oxide layer and subsequent transformation of the observed compositional gradient into a thick reaction layer of NiSi 2 with an epitaxial orientation relationship to the Si substrate; and, secondly, metal film dispersion and subsequent formation of faceted Ni islands on top of the native oxide layer.

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Influence of thinSiO2interlayers on chemical reaction and microstructure at the Ni/Si(111) interface

Cited by 31 publications

References 20 publications

Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO₂ Diffusion Barriers

Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO₂ Diffusion Barriers

Catalytic Chemical Vapor Deposition of Single-Wall Carbon Nanotubes at Low Temperatures

Structural changes during the reaction of Ni thin films with (100) silicon substrates

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Influence of thinSiO2interlayers on chemical reaction and microstructure at the Ni/Si(111) interface

Cited by 31 publications

References 20 publications

Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO2 Diffusion Barriers

Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO2 Diffusion Barriers

Catalytic Chemical Vapor Deposition of Single-Wall Carbon Nanotubes at Low Temperatures

Structural changes during the reaction of Ni thin films with (100) silicon substrates

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Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO₂ Diffusion Barriers

Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO₂ Diffusion Barriers