The experimental setup and resulting localized 1D nanostructure synthesis onto a suspended MEMS bridge. (a) A room temperature reaction chamber where the vapor phase reactant and pressure are controlled globally while the temperature is controlled locally by the remote heating of the MEMS bridge. (b) Silicon nanowire synthesis localized to a long region at the center of the MEMS bridge. [(c) and (d)] Close up views of the localized growth regions illustrating temperature-dependent growth rates (scale bars are ). (e) A MEMS silicon microbridge with two symmetric silicon nanowire growth regions and (f) the corresponding temperature distribution between the room temperature ends of the MEMS bridge. The growth regions illustrate the location of the ideal temperature environment required for the reaction to take place. Other noted regions exhibit local temperatures that are too high or too low for the reaction to take place.
(a) Localized CNT growth at appropriately heated regions of a silicon microbridge. (b) Scanning electron microscopy (SEM) images after the synthesis illustrate the dependence of the CNT growth as a function of local temperature (c). (d) The increase in the mass was detected through a natural frequency shift in the microbridge using an AFM. Adapted with permission from E. Sunden, T. Wright, J. Lee, W. King, and S. Graham, Appl. Phys. Lett. 88, 033107 (2006). Copyright 2006, American Institute of Physics. (Ref. 35).
Localized hotplate setup developed by Haque et al. Embedded tungsten heaters enable the localized growth of CNTs on chips with CMOS circuitry. (a) Schematic cross section of integrated hotplate-CMOS unit and (b) optical image of hotplate and CMOS areas. Adapted with permission from M. S. Haque, K. B. K. Teo, N. L. Rupensinge, S. Z. Ali, I. Haneef, S. Maeng, J. Park, F. Udrea, and W. Milne, Nanotechnology 19, 025607, 2008. Copyright 2008, IOP Publishing Ltd. Ref. 41.
The direct and site-specific integration of silicon nanowires among multiple MEMS structures. The central MEMS structure, the growth structure, is resistively heated facilitating localized nanowire synthesis. The secondary structures remain at room temperature. A local electric-field placed between the growth and secondary structures assists in guiding the synthesis and self-assembly to yield an organized nanowire array between the MEMS structures.
Example of vertically aligned CNT synthesis through laser-assisted CVD by Park et al. CNTs were synthesized in arrays with diameters, held together by van der Waals forces. Adapted with permission from J. B. Park, S. H. Jeong, M. S. Jeong, S. C. Lim, I. H. Lee, and Y. H. Lee, Nanotechnology 20, 185604, 2009. Copyright 2009, IOP Publishing Ltd. Ref. 51.
Experimental setup for CNT synthesis. (a) Schematic overview of the CNT synthesis chamber, chip holder, and induction heating coil. (b) Thermal profile of inductively heated silicon chip. (c) Estimated temperature profile for a one-minute test. Synthesis has been demonstrated for (d) CNTs, (e) zinc oxide nanowires, and (f) titanium dioxide nanoswords.
Synthesis of nanoswords locally on MEMS structures by induction heating. The large, alternating magnetic field of the coil induces Joule heating in the MEMS ring, enabling localized synthesis of nanostructures in a matter of minutes.
The in situ analysis of Raman spectra has been demonstrated to provide information about the growth of localized synthesis processes using the setup shown in (a) from Dittmer et al. Their results in (b) for different growth times (c) show that for various excitation wavelengths, the G/D ratio changes with time at constant growth temperature, indicating a greater percentage of larger diameter CNTs or an amorphous layer of carbon. Reprinted from Chem. Phys. Lett. 457, S. Dittmer, N. Olofsson, J. E. Weis, O. A. Nerushev, A. V. Gromov, and E. E. B. Campbell, In situ Raman studies of single-walled carbon nanotubes grown by local catalyst heating, 206–210, Copyright 2008, with permission from Elsevier. Ref. 38.
Design and properties of a microscale heater with high temperature uniformity. (a) SEM image of cantilevered heater with design schematic as the inset. Intrinsic silicon, lightly doped silicon, and heavily doped silicon regions are shown. (b) Simulated (left) and experimental (right) temperature distribution and (c) simulated power dissipation at a power input of 20 mW. Reprinted from Sensors and Actuators A, Vol. 152, N. L. Privorotskaya and W. P. King, Silicon Microcantilever Hotplates with High Temperature Uniformity, 160–167, Copyright 2009, with permission from Elsevier. Ref. 78.
A technique presented by Kawano et al. enables real-time feedback of localized CNT synthesis process. (a) The experimental set up for real-time monitoring where the voltage on the secondary structure is monitored as a functions time. (b) Localized synthesis of CNTs among the growth and secondary MEMS structures. (c) A close up view of the region between the top section of the growth structure and the opposing section of the secondary structure. A change in voltage was recorded with each CNT contact formed to the secondary structure.
The setup demonstrated by Hart et al. may provide valuable, real-time information about the dynamics and kinetics during nanostructure synthesis. By using a locally heated silicon substrate, the growth chip may be quickly heated and the quartz chamber may be monitored by a CCD camera to monitor the growth of the nanostructures, as shown in [(a)–(h)]. A. J. Hart, L. van Laake, and A. H. Slocum: Desktop growth of carbon-nanotube monoliths with in situ optical imaging. Small 2007. 3. 772–777. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. Ref. 67.
(a) Schematic of a multiprobe array for neural recording. Typical probe diameters exceed , which is too large for the probing of neurons. Conversely, using insulated CNTs, the probe diameter may be reduced significantly. [(b)–(e)] Demonstration of a packaged MEMS-based CNT probe of Kawano et al. (f) transmission electron microscopy (TEM) inspection of the probe verifies the 50 nm thick C-type paralyene layer surrounding the 10 nm diameter CNT.
Locally synthesized CNTs and process parameters. (SCCM denotes standard cubic centimeter per minute at STP.)
Locally synthesized 1D nanostructures and process parameters.
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