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Nonlinear femtosecond laser induced scanning tunneling microscopy
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1. G. Binnig, H. Rohrer, Ch. Gerber, and E. Weibel, Phys. Rev. Lett. 49, 57 (1982).
2. R. J. Hamers and D. G. Cahill, Appl. Phys. Lett. 57, 2031 (1990).
3. V. Gerstner, A. Knoll, W. Pfeiffer, A. Thon, and G. Gerber, J. Appl. Phys. 88, 4851 (2000).
4. S. Grafström, J. Appl. Phys. 91, 1717 (2002).
5. R. J. Hamers and D. G. Cahill, J. Vac. Sci. Technol. B 9, 514 (1991).
6. M. J. Feldstein, P. Vöhringer, W. Wang, and N. F. Scherer, J. Phys. Chem. 100, 4739 (1996).
7. O. Takeuchi, M. Aoyama, R. Oshima, Y. Okada, H. Oigawa, N. Sano, H. Shigekawa, R. Morita, and M. Yamashita, Appl. Phys. Lett. 85, 3268 (2004).
8. S. Yoshida, Y. Terada, R. Oshima, O. Takeuchi, and H. Shigekawa, Nanoscale 4, 757 (2012).
9. A. Dolocan, D. P. Acharya, P. Zahl, P. Sutter, and N. Camillone III, J. Phys. Chem. C 115, 10033 (2011).
10. S. W. Wu and W. Ho, Phys. Rev. B 82, 085444 (2010).
11. J. Lee, S. M. Perdue, D. Whitmore, and V. A. Apkarian, J. Chem. Phys. 133, 104706 (2010).
12. A. Sanchez, C. F. Davis, K. C. Liu, and A. Javan, J. Appl. Phys. 49, 5270 (1978).
13. N. M. Miskovsky, P. H. Cutler, A. Mayer, B. L. Weiss, B. Willis, T. E. Sullivan, and P. B. Lerner, J. Nanotechnol. 2012, 512379.
14. P. K. Tien and J. P. Gordon, Phys. Rev. 129, 647 (1963).
15. M. Buttiker and R. Landauer, Phys. Scr. 32, 429 (1985).
16. A. Thon, M. Merschdorf, W. Pfeifer, T. Klamroth, P. Saalfrank, and D. Diesing, Appl. Phys. A 78, 189 (2004).
17. S. W. Wu, N. Ogawa, and W. Ho, Science 312, 1362 (2006).
18. J. G. Simmons, J. Appl. Phys. 34, 1793 (1963).
19. R. H. Fowler and L. Nordheim, Proc. R. Soc. A 119, 173 (1928).
20. M. Heiblum, S. Wang, J. Whinnery, and T. K. Gustafson, IEEE J. Quantum Electron. 14, 159 (1978).
21. J. P. Litz, J. P. Camden, and D. J. Masiello, J. Phys. Chem. Lett. 2, 1695 (2011).
22. K. J. Savage, M. M. Hawkeye, R. Esteban, A. G. Borisov, J. Aizpurua, and J. J. Baumberg, Nature (London) 491, 574 (2012).
23. J. F. Jia, K. Inoue, H. Hasegawa, W. S. Yang, and T. Sakurai, Phys. Rev. B 58, 1193 (1998).
24. J. Freund, J. Halbritter, and J. K. H. Horber, Microsc. Res. Tech. 44, 327 (1999).
25. H. Petek and S. Ogawa, Prog. Surf. Sci. 56, 239 (1997).
26. C. Guillon, P. Langot, N. D. Fatti, and F. Vallee, Proc. SPIE 5352, 65 (2004).
27. C. Sammet, M. Völcker, W. Krieger, and H. Walther, J. Appl. Phys. 78, 6477 (1995).
28. W. Li and L. E. Reichl, Phys. Rev. B 60, 15732 (1999).
29. I. Urdaneta, A. Keller, O. Atabek, and V. Mujica, J. Chem. Phys. 127, 154110 (2007).
30. M. J. Hagmann, A. Efimov, A. J. Taylor, and D. A. Yarotski, Appl. Phys. Lett. 99, 011112 (2011).
31. M. J. Hagmann, S. Pandey, A. Nahata, A. J. Taylor, and D. A. Yarotski, Appl. Phys. Lett. 101, 231102 (2012).
32. L. V. Keldysh, Sov. Phys. JETP 20, 1307 (1965).
33. M. Grifoni and P. Hänggi, Phys. Rep. 304, 229 (1998).
34.COMSOL Multiphysics Modeling Software, version 4.2.
35. P. B. Johnson and R. W. Christy, Phys. Rev. B 6, 4370 (1972).
36. J. H. Weaver, Phys. Rev. B 12, 1293 (1975).
37. H. Kawano, Prog. Surf. Sci. 83, 1 (2008).
38. J. Simmons, J. Appl. Phys. 35, 2472 (1964).
39. D. M. Volkov, Z. Phys. 94, 250 (1935).
40. R. Esteban, A. G. Borisov, P. Nordlander, and J. Aizpurua, Nat. Commun. 3, 825 (2012).
41. S. L. Kleinman, R. R. Frontiera, A.-I. Henry, J. A. Deringer, and R. P. Van Duyne, Phys. Chem. Chem. Phys. 15, 21 (2013).
View: Figures


Image of FIG. 1.

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FIG. 1.

Experimental setup for optically induced electron tunneling. LPC: laser power controller, PC: prism compensator, PD: photodiode, RF: radiofrequency driver, AOM: acousto-optic modulator, τ d : temporal delay between the 0th and 1st order outputs of AOM. The fast-axis of the half-wave plate HWP2 is set to α = −22.5° with respect to the initially p-polarized undiffracted output (shown in red arrows, diffracted output is in green). Mflip: flip mounted mirror for He:Ne laser-tip alignment. Insets: (1) focused ion beam milled W tip. A schematic representation of the focused cross-polarized fields (red/green arrows) delivered by HWP2 to the STM junction overlaid on the Au topography. The lower panel illustrates the action of the composite wave plate in generating 0/π-phase change for field polarizations parallel/orthogonal to the fast axes (double headed black arrows) of each of the two plates.

Image of FIG. 2.

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FIG. 2.

Calculated spatial intensity variation of the synthesized phase modulated vector field (Eq. (2) of text) at the focus of a 1.25 NA microscope objective. The total ( ) and z-component |E Z |2 intensities are simulated at t = 0 and t = π/ω B, respectively. To maintain a normalized intensity gray scale multiplicative factors were used on (b)–(d) with respect to the peak intensity of (a).

Image of FIG. 3.

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FIG. 3.

Laser-tip alignment: A co-propagating He-Ne laser is used for precise alignment of the tip. The tip is z-modulated while rastering over the laser focus, and the modulated backscattered light is detected with a lock-in amplifier and photodiode. The tip is parked at the center of the image for the rest of the measurements.

Image of FIG. 4.

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FIG. 4.

The tunneling current at the beat frequency, J ω , shows exponential nonlinearity on electric field E L /irradiation intensity. The measurement is carried out in the tunneling regime, under constant DC current mode, J DC = 0.5 nA, and at a bias of V B = −2 V. The curve is the functional fit to Eq. (3) of the text, with fit parameters: J 0 = 3.58 pA, a = 3.22 nA × Å2/V2, b = 2.18 μA × Å2/V2, and ϕ = 0.52 V/Å.

Image of FIG. 5.

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FIG. 5.

Cross-correlation of the cross-polarized pulse trains as a function of time delay (τ). (a) Cross-modulated current at the tunnel junction (J ω ) shows the optical carrier frequency as indicated by the Fourier transform (red). (b) Norm of J ω and photodiode signal (red circles) simultaneously detected by mixing on a linear polarizer. The junction is under constant current feedback (J DC = 0.5 nA, V B = −2 V), irradiated at a laser peak power of 4 × 1014 W/m2 (average power 0.6 mW). The detected current of 40 pA at τ = 0 corresponds to 3 electrons per pulse.

Image of FIG. 6.

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FIG. 6.

Constant fluence cross-correlation current, J ω at 100 fs (gray) and 200 fs pulsewidth (blue), respectively, and their Gaussian fits (in red). The modulated current tracks intensity. The junction is in the tunneling regime, J DC = 0.5 nA and V B = −2.0 V.

Image of FIG. 7.

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FIG. 7.

The photocurrent decays exponentially with tip-sample distance with a laser field dependent decay length. (a) The logarithmic photocurrent normalized to its value at contact (z0) at the applied laser field at the junction E L = 0.050 V/Å (blue), 0.055 V/Å (green), 0.065 V/Å (purple). The fits to J ω(E L , z) = J ω(z 0) exp [−2κ(E L )(zz 0)] are shown by the solid lines. The dependence of the tunneling range on applied field is shown in the inset: κ = 3.7 nm−1 (blue), 0.73 nm−1 (green), 0.14 nm−1 (purple). (b) Comparative plot between DC tunneling current and laser induced tunneling current. κ = 12.25 nm−1 for J DC at V B = −0.5 V.

Image of FIG. 8.

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FIG. 8.

Laser induced STM imaging of plasmons on a cluster of gold nanospheres. Simultaneously recorded (a) topography, J DC and (b) laser induced current, J ω . The selected areas of interest highlight hot spots: (1) inter-sphere plasmon for which line-profiles are provided in (c). X and Z indicate the horizontal cut and topographic height, respectively. (2) and (3) highlight local plasmonic hot spots in complex cavities, the magnifications of which are shown in (d) and (e).

Image of FIG. 9.

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FIG. 9.

Topography of the Au substrate at −0.2 V (a) and −3.5 V bias (c); and simultaneously acquired laser induced images at an applied laser intensity of 0.6 mW in (b) and (d). (e) Plot of laser induced current J ω measured at the areas marked by triangle and circle as a function of DC bias and schematic diagrams illustrating the sense of net laser induced current in the junctions. Shaded areas indicate the range spanned by multiple recording points.

Image of FIG. 10.

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FIG. 10.

Comparison between laser induced STM (J ω ) and local workfunction (dI/dZ) on a corrugated gold substrate: topography, J ω , and dI/dZ map scanning the same area. The DC current set point is 0.5 nA, the DC bias is −1 V, and the laser power at the junction P = 0.5 mW.

Image of FIG. 11.

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FIG. 11.

Model of the tunnel junction used in simulations: (a) flat gold surface, (b) an asperity modeled by a 2 nm half sphere, (c) local fields expressed as enhancement profiles, β(z) = E L (z)/E 0 as a function of gap z. The dashed line is the form ac/d (used in Eq. (11) of the text) to highlight that the enhancement is inversely proportional to the gap distance d. Note the negative enhancement due to field penetration, which is largest on the gold asperity, and for short gaps. The optical field penetrates the electrodes and leads to the collective electron displacement that accounts for the field enhancement.

Image of FIG. 12.

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FIG. 12.

Tunneling barrier for zero bias: (a) in the absence of the laser field; (b) snapshots of the dynamic barrier for E 0 = 0.02 V/Å and d = 1 nm gap showing the asymmetry on the tunneling directions (inset shows the plot without breaking the axis); (c) snapshots of the dynamic barrier for E 0 = 0.06 V/Å and d = 10 nm gap.

Image of FIG. 13.

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FIG. 13.

Calculated bias dependent transmission probability T(V B ) using Eq. (9) of text: on flat surface (blue), and on half sphere (red) for two typical applied optical fields, solid E 0 = 0.02 V/Å and dashed E 0 = 0.01 V/Å. The asymmetry of the junction is evident in the shift of the zero-crossing. On the asperity, the transmission remains positive up to −2 V, therefore the net current is reversed. The change in asymmetry as a function of applied field demonstrates the competition between the asymmetry of the field free junction and the plasmon enhanced field induced transmission.


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We demonstrate ultrafast laser driven nonlinear scanning tunneling microscopy (STM), under ambient conditions. The design is an adaptation of the recently introduced cross-polarized double beat method, whereby z-polarized phase modulated fields are tightly focused at a tunneling junction consisting of a sharp tungsten tip and an optically transparent gold film as substrate. We demonstrate the prerequisites for ultrafast time-resolved STM through an operative mechanism of nonlinear laser field-driven tunneling. The spatial resolution of the nonlinear laser driven STM is determined by the local field intensity. Resolution of 0.3 nm–10 nm is demonstrated for the intensity dependent, exponential tunneling range. The demonstration is carried out on a junction consisting of tungsten tip and gold substrate. Nano-structured gold is used for imaging purposes, to highlight junction plasmon controlled tunneling in the conductivity limit.


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Scitation: Nonlinear femtosecond laser induced scanning tunneling microscopy