SEMICONDUCTOR NANOWIRE MANIPULATION USING IPTOELECTRONIC TWEEZERS Arsh Jamshidi, Peter J. Pauzauskie, Aaron T. Ohta, Pei-Yu Chiou, Peidong Yang and Ming C, Wu University of Caligormia, Berkeley,USA IEEE MEMS2007 報告人 : 蘇聖欽

Outline  Motivation  Theoretical Background  Optical Tweezers  Optoelectronic tweezers Theory  Optoelectronic tweezers Force  Device Structure  Experimental Results  Experimental Setup  Manipulation of Silicon Nanowires  Speed and Trapping Radius Measurements  Nanowires Assembly  Conclusion

Motivation  The ability of optical tweezers to perform parallel assembly is hampered by their high optical power density (107w/cm2) and small area (approximately 1 um*1 um).  Dielectrophoresis can trap nanowires,but he trapping sites are fixed the electrode pattern.  OET is capable of manipulating a large number of microparticles or cells over a large area.

Outline  Motivation  Theoretical Background  Optical Tweezers  Optoelectronic tweezers Theory  Optoelectronic tweezers Force  Device Structure  Experimental Results  Experimental Setup  Manipulation of Silicon Nanowires  Speed and Trapping Radius Measurements  Nanowire Assembly  Conclusion

Optical Tweezers  Mie regime( 米氏定理 ) :  適用的粒子大小 diameter of particle >> 。  動量守恆原理 。  Rayleigh regime( 雷利定理 ) :  適用的粒子大小 diameter of particle << 。  電磁波理論，變動的電場使粒子極化，產生引力。 electric field particle

Optoelectronic tweezers Theory  They use AC voltage producing electric field. Arsh Jamshidi,2007 OET Mechanical Optical Tweezers Dielectrophoresis Optical Electrical Electric field OET device

Optoelectronic tweezers Force  Optoelectronic tweezers force under an AC bias is given by:  Drag force: η:viscous V:nanowires velocity Re(K):depolarization factor l:nanowirws length r:nanowires radius Arsh Jamshidi,2007

Device Structure  OET device apparatus :  a top indium-tin–oxide (ITO) electrode  a 1–um-thick layer of photoconductive material (amorphous silicon)  An applied AC bias of 20 Vpp at 50kHz Arsh Jamshidi, um ITO Liquid 1um amorphous silicon 20Vpp

Outline  Motivation  Theoretical Background  Optical Tweezers  Optoelectronic tweezers Theory  Optoelectronic tweezers Force  Device Structure  Experimental Results  Experimental Setup  Manipulation of Silicon Nanowires  Speed and Trapping Radius Measurements  Nanowire Assembly  Conclusion

Experimental Setup 4mW HeNe Laser Attenuator 40x OET Device mirror Motorizesed stage 20x CCD Camera Equipment : - A 632nm HeNe laser -A 40X objective lens -Solution of DI water and KCl -Olympus BX51M microscopy using a CCD camera

Manipulation of Silicon Nanowires  The long-axis of the nanowires (CdS) aligned with the electric field in the liquid layer.  Si nanowires experienced an attractive force towards the illuminated area after turning on the laser. Arsh Jamshidi,2007 r:100nm l:1-5um

Speed and Trapping Radius Measurements  Si nanowires with 390Ω-cm magnitudes comparable to the experimental results.  Figure shows the measured maximum speed of the nanowires versus the applied AC voltage. Arsh Jamshidi,2007 Max speed: 135um/s Max radius: 120um

Separation of two nanowires  Nanowires within a trapping radius can still be trapped individually by controlling the scanning speed of the laser spot. Arsh Jamshidi,2007 r:100nm l:1-5um

Nanowire Assembly  A spherical lens is used to create a line laser pattern for movement of Si nanowires in arrays of 2 or 3. Arsh Jamshidi,2007

Conclusion  The flexibility of the optoelectronic tweezers device, low required optical power intensity (optical tweezers power 10 7 w/cm 2, OET power 100w/cm 2 ).  Large working area makes OET a very attractive tool for the manipulation for nanowires (arrays of 2 or 3).  A maximum velocity of 135um/s and a trapping radius of 122um are achieved using this method.

Reference [1] Arsh Jamshidi, Peter J. Pauzauskie, Aaron T. Ohta, Pei- Yu Chiou, Peidong Yang and Ming C, Wu, “SEMICONDUCTOR NANOWIRE MANIPULATION USING IPTOELECTRONIC TWEEZERS ”, IEEE MEMS,pp (2007). [2]Aaron T. Ohta, Pei Yu Chiou, and Min C. Wu, ”Dynamic DMD-Driven Optoelectronic Tweezers for Microscopic Particle Manipulation”, University of California,Los Angeles(2004).

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