Supporting Information
Contact Transport of Focused Ion Beam-Deposited Pt to Si Nanowires: From
Measurement To Understanding
J. J. Ke, K. T. Tsai, Y. A. Dai, and J. H. He*
1
Institute of Photonics and Optoelectronics, and Department of Electrical Engineering,
National Taiwan University, Taipei, 10617 Taiwan
1
The galvanic wet etching was adopted to fabricate single crystalline Si nanowires
(NWs) at room temperature in HF/AgNO3 solution.1 A single-crystal n-type Si wafer
was rinsed with acetone and hydrofluoric acid. Due to intrinsic etching mechanism of Si
in HF/AgNO3 solution, the high-quality Si NW arrays can be produced on the n-type Si
wafer by simply immersing the wafer into HF/AgNO3 solution for an appropriate
etching time. To construct the I-V testing structures, we first made photolithographically
prepared Cr/Au (5/60 nm) patterns on an insulating substrate which consists of a Si
wafer capped with a 600-nm-thick SiO2 layer deposited by plasma-enhanced chemical
vapor deposition. The Si NWs were separated from the parent wafers by sonication in a
transfer solvent (e.g., ethanol) and transferred to patterned substrates via micropipette.
Ga ion beam-induced deposition in an FEI Dual-Beam NOVA 600 FIB instrument is
employed with a trimethylcyclopentadienyl-platinum (CH3)3Pt(CpCH3) injector to
selectively deposit Pt metal to connect the Si NWs with the Cr/Au pads. The Ga ion
beams were accelerated to 30 kV, injecting perpendicular to the Si NWs, and the income
flux was set at 50 pA during the deposition. The dimensions of Pt deposition areas are
300 nm in width and 300 nm in height.
To study the morphologic of FIB-Pt/Si NW interfaces, structural analysis in
near-contacts region has been carried out using a JEOL JEM 2100F scanning
transmission electron microscopy, which provides conventional transmission electron
microscopy (TEM) imaging, selected-area electron diffraction, and high resolution
bright field image. The TEM sample was prepared by slicing the contact region using
FIB. The I-V curves of two-probe and four-probe measurement was performed using
Keithley 4200 parameter analyzer in the LakeShore TTP4 cryogenic probe station at
5×10-6 torr. In order to examine the electrical transport which governs the current flow
at the contacts of the FIB-Pt to Si NWs, the temperature-dependent measurements were
2
utilized at the temperature range from 100 K to 400 K.
3