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Suspended heated silicon platform for rapid thermal control of surface reactions with application to carbon nanotube synthesis
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View: Figures


Image of FIG. 1.
FIG. 1.

Design of heated platform and steel electrodes. (a) Schematic representation of “indirect heating” mode. Catalyst may be deposited directly onto the suspended platform (“direct heating”), or a second substrate may be placed on top of the heated substrate. (indirect heating). (b) Detail showing clamping of heated platform (front view, to scale).

Image of FIG. 2.
FIG. 2.

(Color online) Rate of temperature change vs temperature for a lumped model of a suspended heater element. (a) Constant current operation, where all equilibrium points are stable. (b) Constant voltage operation, where some equilibrium points are stable, and where no equilibrium points exist for .

Image of FIG. 3.
FIG. 3.

(Color online) Thermal model. (a) The thermal model describes two domains having different temperature-dependent material properties. Symmetry is translated to a boundary condition of no heat flux in the center of the heater. The connection between a steel electrode and the heater is modeled as a constant thermal contact resistance. (b) Definition of an element on which an integral form of the energy-conservation equation is applied.

Image of FIG. 4.
FIG. 4.

(Color online) Time constants and heat flow rates as function of temperature for a suspended heater element.

Image of FIG. 5.
FIG. 5.

(Color online) Model validation for a suspended element. Measured current values were used as input for the numerical model. Measured and simulated (dashed graphs) values of voltage drop over the heater and temperature at three locations are shown. Temperature is measured using K-type thermocouples at the center of the heater (top graph), from the end (middle graph), and from the end (bottom graph).

Image of FIG. 6.
FIG. 6.

(Color online) Zoom in at Fig. 5 showing good correspondence, even for highly dynamic input (simulation is dashed line).

Image of FIG. 7.
FIG. 7.

Simulated steady-state temperature profiles for given input current values. A uniform temperature extends over an increasingly large area of the heater with increasing current.

Image of FIG. 8.
FIG. 8.

(Color online) Prototype “platform-in-tube” reactor apparatus, where suspended heated platform is mounted on stainless steel contact electrodes and sealed inside horizontal quartz tube. Inset shows oblique view of platform at , with VA-CNT microstructures growing from lithographically patterned catalyst film.

Image of FIG. 9.
FIG. 9.

(Color online) Elastokinematically constrained furnace tube end caps using lip seals: (a) Cross-section drawing showing Viton seals recessed in grooved aluminum and (b) cap seal for o.d. quartz tube, with one lip seal.

Image of FIG. 10.
FIG. 10.

(Color online) CNT films grown from catalyst-coated silicon substrates rested on the resistively heated platform: (a) Tangled SWCNT film, grown from catalyst film in ; (b) thick VA-CNT film, grown from film in ; (c) alignment of CNTs within film shown in (b); (d) thick VA-CNT film, grown as in (b) with pretreatment by flowing gas through heated delivery pipe; and (e) optical image of film on silicon substrate, placed next to two stacked United States pennies (each thick).

Image of FIG. 11.
FIG. 11.

(Color online) Optical imaging of VA-CNT film growth on the suspended heated platform, with platform at : (a) Side view showing initial configuration, where “cap” substrate is placed on top of growth substrate to moderate gas flow and to serve as an optical reference and (b) snapshot after of reaction, where the film thickness exceeds .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Suspended heated silicon platform for rapid thermal control of surface reactions with application to carbon nanotube synthesis