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Optical manipulation of work function contrasts on metal thin films

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Science Advances  02 Mar 2018:
Vol. 4, no. 3, eaao6050
DOI: 10.1126/sciadv.aao6050
  • Fig. 1 Photocurrents and photovoltages under partial illumination.

    (A) Schematic showing a semiconductor coated with metal partially illuminated on the surface with the remaining area blocked from light. (B) Photocurrent generated in 15-nm Au/n-Si under partial illumination, with the electrons flowing from the bright zone to the dark zone. (C) Photovoltage generated under partial illumination in 15-nm Au/n-Si. (D) Effect of metal film thickness on the photocurrent.

  • Fig. 2 Effect of illumination on surface potential.

    (A and B) Surface potential maps of 15-nm Au/n-Si before (A) and after (B) illumination. (C) Surface potential map showing instantaneous photoresponse when two light ON/OFF cycles were triggered, which resulted in a surface potential map with distinct bright and dark bands corresponding to the cycles of light ON and OFF. (D) WF shift determined from the surface potential histograms corresponding to the bright and dark scans. The peak of the histogram being the average WF, the peak-to-peak distance gives the average WF shift.

  • Fig. 3 Effect of film thickness.

    (A to C) KPFM (CPD) plots for Au films of thickness 15 nm (A), 60 nm (B), and 300 nm (C) on Si. (D) Effect of film thickness on the WF shift.

  • Fig. 4 KPFM on different metallic thin films.

    (A to C) CPD plots for Au (A), W (B), and Pt (C) films under different illumination intensities. Each CPD map has five step-like features (first to fifth), with the first step being the highest surface potential shift (left most) under 18 mW/cm2 illumination intensity and the second to fifth steps being the shifts obtained, respectively, at light intensities of 7, 1, 0.2, and 0.04 mW/cm2. (D) Effect of light intensity on the WF shift.

  • Fig. 5 Band structures of a metal-semiconductor junction forming a Schottky junction.

    (A to C) Without illumination (A), with illumination (B), and under selective illumination (C) showing flow of electrons from the bright zone (the region of low WF) to the dark zone (the region of high WF). (D) Possibility of continuous tuning of WF by choosing a specific metal and a specific light intensity. The dark ellipses present the experimental WF data under light intensities from 0.04 to 18 mW/cm2, and the dashed ellipses present a projection of WF under higher light intensities of 50 and 100 mW/cm2. A projection of data had to be made to estimate the WF shift at 100 mW/cm2 because the light intensity on the sample surface could not be increased beyond 18 mW/cm2 in the KPFM setup owing to instrumentation constraints. The projections are made using the linear interpolation/extrapolation program in Origin Pro 8.0 (OriginLab).

  • Fig. 6 A proof-of-concept photodetector.

    (A) A photodetector setup showing the dependence of the photocurrent on the position of the light source. The actual chamber used is black and opaque to light, and the schematic shows a transparent chamber for illustrative purposes. (B) Photocurrent observed on opening a specific slot (x axis) with all the other slots closed.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/3/eaao6050/DC1

    fig. S1. IV characteristics and photobehavior in different metal/n-Si systems.

    fig. S2. KPFM surface potential map of a plain n-type Si, which shows no significant WF shift under two cycles of dark and illumination cycles.

    fig. S3. Effect of metal film thickness (Au sputtered on glass) on transmittance of light at a wavelength of 600 nm.

    fig. S4. Metal thickness effect in case of back illumination.

    fig. S5. Light and dark IV characteristics.

    fig. S6. Temperature profile of Au/n-Si under dark and illumination conditions.

    fig. S7. Effect of the relative position of the sample with respect to the illumination zone.

    table S1. WF modification in Au, Pt, and W by various chemical methods.

    movie S1. Surface photocurrents under partial illumination of metal/n-Si.

    movie S2. Sensitivity of photoresponse to the relative position of the sample.

    References (2735)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. IV characteristics and photobehavior in different metal/n-Si systems.
    • fig. S2. KPFM surface potential map of a plain n-type Si, which shows no significant WF shift under two cycles of dark and illumination cycles.
    • fig. S3. Effect of metal film thickness (Au sputtered on glass) on transmittance of light at a wavelength of 600 nm.
    • fig. S4. Metal thickness effect in case of back illumination.
    • fig. S5. Light and dark IV characteristics.
    • fig. S6. Temperature profile of Au/n-Si under dark and illumination conditions.
    • fig. S7. Effect of the relative position of the sample with respect to the illumination zone.
    • table S1. WF modification in Au, Pt, and W by various chemical methods.
    • Legends for movies S1 and S2
    • References (27–35)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Surface photocurrents under partial illumination of metal/n-Si.
    • movie S2 (.mp4 format). Sensitivity of photoresponse to the relative position of the sample.

    Files in this Data Supplement:

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