Laser Assisted Field Induced Oxide Nanopatterning (27096)
A system to effect field induced oxidation (FIO) nanopatterning of hydrogen passivated silicon surfaces with an atomic force microscope (AFM) controlled by laser irradiation.
ADVANTAGES: Local oxidation on H:Si(111) surfaces can be fully suppressed or activated by toggling a laser luminating a lightly doped silicon AFM cantilever. Laser assisted FIO provides an alternative and flexible means for controlling oxide nanopatterning.
SUMMARY: Since the initial report of field induced oxidation (FIO) of silicon surfaces with a scanning tunneling microscope in 1990, numerous methods of silicon surface modification via scanning probe microscopy have been reported. The FIO process is generally thought to be limited by electrochemical reactions in the water meniscus that are initiated by charge injection from the probe into the meniscus. Thus schemes for influencing the charge injection rate may be exploited for control of FIO nanopatterning. This invention utilizes this principle by controlling FIO nanopatterning under a constant bias by toggling the on/off state of a visible laser that is focused on the AFM cantilever.
Patterning was performed on hydrogen passivated silicon surfaces, H:Si(111), employing a lightly doped n-type silicon AFM probe. The probe holder was electrically isolated from the AFM and connected to a variable gain current preamplifier to monitor current flow during both pattern formation on H:Si(111) and bias sweeps applied to the silicon probe while in contact with thermally deposited gold-on-silicon substrates. A diode laser (0.2 mW, 670 nm) served as the cantilever deflection laser. Contact mode AFM was performed in ambient conditions (35-45% relative humidity, 22-24ºC) at a setpoint force of 10-30 nN, and patterns were created with a 10 V sample bias. A protocol to eliminate spurious light, maintain stable tip-sample contact force, and pattern with and without bias was developed. Under these conditions patterning only occurs when the laser is on consistent with the laser influencing the free carrier concentration in the doped silicon probe.
Laser assisted FIO oxide nanopatterns were generated by toggling the laser with a rate of 8 Hz while scanning a 4 m² region with a fast 1 Hz rate and 10 V sample bias. The resulting oxide nanopattern reflects the laser toggle rate, as patterning only occurs when the laser is on (Figure 1). Laser assisted FIO provides a novel and effective strategy for controlling oxide nanopatterning on hydrogen passivated silicon surfaces.
Mark Hersam and Liam Pingree
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