Direct deposition of continuous metal nanostructures by thermal dip-pen nanolithographyDip-Pen NanolithographySlide 3Thermal DPNExperimentsSlide 6TestingConclusionsDirect deposition of continuous metal nanostructures by thermal dip-pen nanolithographyApplied Physics Letter, January 2006B.A. Nelson and W.P. King, Georgia TechA.R. Laracuente, P.E. Sheehan, and L.J. Whitman, Naval Research LabDip-Pen Nanolithography•Scanning probe-based lithography technique using probe tip like a pen•Tip is dipped in chemical “ink” and transfers nanoparticles, biomolecules, etc. to substrate through contact “writing”•Resolution: 15 nm or betterDip-Pen Nanolithography•Conventional DPN requires inks that are mobile at ambient conditions•Deposition rate controlled by changing ambient conditions (temperature, humidity) or heating/cooling substrate; dynamic control difficult•Unable to ‘turn-off’ deposition, causing contamination and smearing•Metrology not possible without unintended deposition or prior cleaning of probe tip•Emphasis on organics and biomolecules, not conductive metalsThermal DPN•Heating element integrated into cantilever•Allows use of “inks” that are solid in ambient conditions•Deposition easily turned on/off by modulating heating element•Surface imaging possible without smearing/contaminationExperiments•Silicon AFM cantilever with embedded microscale heater•Estimated ~20 nm radius of curvature•Thermal time constant of 1 - 10 µs•Temperature sensitive resistance (2 - 7 kΩ for 25 - 550 °C) used for calibration•Indium as deposition metal (melting point = 156.6 °C)•Loading: Indium substrate scanned with 500 nN contact force at 6 µm/s with tip temperature of ~1030 °CExperiments•Continuous lines deposited by reheating cantilever while contacting substrate•Dimensions depend on tip loading, temperature, speed, and repetitions•Successful deposition for:•250 - 800 °C•0.01 - 18 µm/s•32 - 128 raster scans•Borosilicate glass, quartz, silicon substrates•50 - 300 nm thick, 3 - 12 nm high•Imaging with cooled, coated tip had no effect on deposited linesTesting•Gold electrodes with 500 nm gap fabricated using EBL on 100 nm thick silicon oxide film on silicon substrate•Indium-coated tip used to image electrodes before deposition•Indium deposition at 425 °C, 4 µm/s•Resulting line 5 nm tall, 100 - 200 nm wide•Auger electron nanoprobe spectra shows structure is indium oxide•I-V measurements show deposition is continuous and ohmic (R = 2.5 x 104 Ω-cm)Conclusions•Traditional DPN capabilities expanded by tDPN•tDPN adds dynamic control of deposition, ability to scan with loaded tip, use of solid metal “inks”•Technique could be used to perform in situ inspection and repair of nanoelectronics•Parallel deposition/metrology possible with cantilever
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