Insitu Observation of the Formation Dynamics of Nanohelices
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0924-Z06-06
Insitu Observation of the Formation Dynamics of Nanohelices Terence Yeoh1, Maribeth Mason1, Zack Feinberg1, Martin Leung1, Mehmet Tasci2, Victor Elarde2, and James J Coleman2 1 Microelectronics Technology Department, The Aerospace Corporation, 2350 E. El Segundo Blvd, El Segundo, CA, 90245 2 Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 208 N Wright Street, Urbana, Illinois, 61801
ABSTRACT Strained InGaAs/GaAs bridges were released by a focused ion beam in order to observe the relaxation dynamics of the structure. Releasing the bridges resulted in the formation of chiral nanotubes with diameter of 920 nm and length 8.5 microns. The total time required for nanoscroll formation took > 20 minutes. From observing the scrolling action through time, it was found that the strain relief process differed from traditional wet etched nanoscrolls due to the simultaneous relief of strain from the released structures. INTRODUCTION In recent years, nanoscroll formation has been a subject of interest for nano electro mechanical systems.[1-3] These strained materials, when released, scroll and fold in specific patterns and shapes depending on the underlying, prebuilt strain. The resulting structures have the potential to create induction coils for microwave antennas, optical modulators, negative index of refraction metamaterials, and, if designed properly, a method for creating ultrathin transmission electron microscopy sample films for embedded nanomaterial tomography and holography. Little is known of the actual process of scrolling and nanoscroll formation. In this paper we observed the kinetics of formation by releasing a strained In0.20Ga0.80As/GaAs film using a focused ion beam (FIB) and observed the dynamics of scroll formation by scanning electron microscopy. EXPERIMENTAL DETAILS The samples in this work were grown in an atmospheric pressure metalorganic chemical vapor deposition reactor with a vertical rotating susceptor at 760 Torr with TMIn, TMGa and AsH3 sources on (001) (±0.5°) oriented GaAs substrates. A GaAs buffer layer of 100 nm was grown at 800 ° C before a 2 µm sacrificial etch layer of
Al0.60Ga0.40As was grown. After this the substrate was cooled to 625 °C before depositing 72 Å film of In0.20Ga0.80As. This thickness corresponds to less than one half the critical thickness for dislocation formation of a strained quantum well. In this case, the critical thickness for dislocation formation, or 2HC, for In0.20Ga0.80As on GaAs is approximately 16.6 nm. The InGaAs strained layer was then capped with a film of 72 Å of GaAs. In order to create bridges of strained InGaAs/GaAs, trenches were etched on either side of the bridge to expose the sacrificial etch layer. 100 nm of SiO2 was deposited by plasma enhanced chemical vapor deposition (PECVD) and then patterned by photolithograpy. A reactive ion etch using CF4 at 35 mTorr for 5 minutes was used in order to remove the unpatterned oxide. After the photoresist was removed using acetone, an inductively coupled plasma RIE et
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