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Title: Soft X-Ray Second Harmonic Generation as an Interfacial Probe

Abstract

Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (~284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from the first atomic layer at the open surface. Here, this technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.

Authors:
 [1];  [1];  [2];  [3];  [4];  [4];  [5];  [5];  [1];  [1];  [1];  [4];  [4];  [4];  [4];  [6];  [4];  [4];  [4];  [4] more »;  [4];  [4];  [4];  [7];  [3];  [8];  [9];  [10];  [2];  [2];  [11];  [4];  [3];  [1];  [12] « less
  1. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  4. Elettra-Sincrotrone Trieste S.C.p.A., Trieste (Italy)
  5. National Research Council of Italy, Padova (Italy); Univ. of Padova, Padova (Italy)
  6. Elettra-Sincrotrone Trieste S.C.p.A., Trieste (Italy); Univ. of Nova Gorica, Nova Gorica (Slovenia)
  7. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  8. Center for High Pressure Science & Technology Advanced Research, Shanghai (China)
  9. Elettra-Sincrotrone Trieste S.C.p.A., Trieste (Italy); Elettra Lab., Trieste (Italy)
  10. National Research Council of Italy, Padova (Italy)
  11. Elettra-Sincrotrone Trieste S.C.p.A., Trieste (Italy); C.R. Frascati, Frascati (Rome) (Italy)
  12. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1418311
Grant/Contract Number:
AC02-05CH11231; AC02-76SF00515; AC36-08GO28308; SC0004993; W911NF-13-1-0483; W911NF-17-1-0163; DGE 1106400; AC36-08-GO28308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 120; Journal Issue: 2; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Citation Formats

Lam, R. K., Raj, S. L., Pascal, T. A., Pemmaraju, C. D., Foglia, L., Simoncig, A., Fabris, N., Miotti, P., Hull, C. J., Rizzuto, A. M., Smith, J. W., Mincigrucci, R., Masciovecchio, C., Gessini, A., Allaria, E., De Ninno, G., Diviacco, B., Roussel, E., Spampinati, S., Penco, G., Di Mitri, S., Trovo, M., Danailov, M., Christensen, S. T., Sokaras, D., Weng, T. -C., Coreno, M., Poletto, L., Drisdell, W. S., Prendergast, D., Giannessi, L., Principi, E., Nordlund, D., Saykally, R. J., and Schwartz, C. P. Soft X-Ray Second Harmonic Generation as an Interfacial Probe. United States: N. p., 2018. Web. doi:10.1103/PhysRevLett.120.023901.
Lam, R. K., Raj, S. L., Pascal, T. A., Pemmaraju, C. D., Foglia, L., Simoncig, A., Fabris, N., Miotti, P., Hull, C. J., Rizzuto, A. M., Smith, J. W., Mincigrucci, R., Masciovecchio, C., Gessini, A., Allaria, E., De Ninno, G., Diviacco, B., Roussel, E., Spampinati, S., Penco, G., Di Mitri, S., Trovo, M., Danailov, M., Christensen, S. T., Sokaras, D., Weng, T. -C., Coreno, M., Poletto, L., Drisdell, W. S., Prendergast, D., Giannessi, L., Principi, E., Nordlund, D., Saykally, R. J., & Schwartz, C. P. Soft X-Ray Second Harmonic Generation as an Interfacial Probe. United States. doi:10.1103/PhysRevLett.120.023901.
Lam, R. K., Raj, S. L., Pascal, T. A., Pemmaraju, C. D., Foglia, L., Simoncig, A., Fabris, N., Miotti, P., Hull, C. J., Rizzuto, A. M., Smith, J. W., Mincigrucci, R., Masciovecchio, C., Gessini, A., Allaria, E., De Ninno, G., Diviacco, B., Roussel, E., Spampinati, S., Penco, G., Di Mitri, S., Trovo, M., Danailov, M., Christensen, S. T., Sokaras, D., Weng, T. -C., Coreno, M., Poletto, L., Drisdell, W. S., Prendergast, D., Giannessi, L., Principi, E., Nordlund, D., Saykally, R. J., and Schwartz, C. P. 2018. "Soft X-Ray Second Harmonic Generation as an Interfacial Probe". United States. doi:10.1103/PhysRevLett.120.023901.
@article{osti_1418311,
title = {Soft X-Ray Second Harmonic Generation as an Interfacial Probe},
author = {Lam, R. K. and Raj, S. L. and Pascal, T. A. and Pemmaraju, C. D. and Foglia, L. and Simoncig, A. and Fabris, N. and Miotti, P. and Hull, C. J. and Rizzuto, A. M. and Smith, J. W. and Mincigrucci, R. and Masciovecchio, C. and Gessini, A. and Allaria, E. and De Ninno, G. and Diviacco, B. and Roussel, E. and Spampinati, S. and Penco, G. and Di Mitri, S. and Trovo, M. and Danailov, M. and Christensen, S. T. and Sokaras, D. and Weng, T. -C. and Coreno, M. and Poletto, L. and Drisdell, W. S. and Prendergast, D. and Giannessi, L. and Principi, E. and Nordlund, D. and Saykally, R. J. and Schwartz, C. P.},
abstractNote = {Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (~284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from the first atomic layer at the open surface. Here, this technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.},
doi = {10.1103/PhysRevLett.120.023901},
journal = {Physical Review Letters},
number = 2,
volume = 120,
place = {United States},
year = 2018,
month = 1
}

Journal Article:
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  • Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (~284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from themore » first atomic layer at the open surface. Here, this technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.« less
  • Titanium dioxide (TiO{sub 2}) is a wide band-gap semiconductor having two common crystal forms: rutile and anatase. Due to its high physical and chemical stability, it is extensively studied as a photocatalyst for photolysis of water, and for oxidative photomineralization of organic pollutants in wastewater, aimed at harvesting solar energy. The authors report the first direct observation of an interfacial charge-transfer complex using second-harmonic spectroscopy. The second-harmonic spectrum of catechol adsorbed on 0.4 micron-sized TiO{sub 2} (anatase) colloidal particles in aqueous suspension reveals a charge-transfer band centered at 2.72 eV (456 nm). In addition, the adsorption isotherm of catechol onmore » the colloidal TiO{sub 2} suspension was obtained and gave an excellent fit to the Langmuir adsorption model. From this, the authors infer the free energy of the adsorption to be {Delta}G{degree} = {minus}6.8 kcal/mol.« less
  • Understanding and rationally controlling the properties of nanomaterial surfaces is a rapidly expanding field of research due to the dramatic role they play on the optical and electronic properties vital to light harvesting, emitting and detection technologies. This information is essential to the continued development of synthetic approaches designed to tailor interfaces for optimal nanomaterial based device performance. In this work, closely spaced electronic excited states in model CdSe quantum dots (QDs) are resolved using second harmonic generation (SHG) spectroscopy, and the corresponding contributions from surface species to these states are assessed. Two distinct spectral features are observed in themore » SHG spectra, which are not readily identified in linear absorption and photoluminescence excitation spectra. These features include a weak band at 395 6 nm, which coincides with transitions to the 2S1/2 1Se state, and a much more pronounced band at 423 4 nm arising from electronic transitions to the 1P3/2 1Pe state. Chemical modification of the QD surfaces through oxidation resulted in disappearance of the SHG band corresponding to the 1P3/2 1Pe state, indicating prominent surface contributions. Signatures of deep trap states localized on the surfaces of the QDs are also observed. We further find that the SHG signal intensities depend strongly on the electronic states being probed and their relative surface contributions, thereby offering additional insight into the surface specificity of SHG signals from QDs.« less
  • We have constructed an instrument for observing the second harmonic generation (SHG) in the soft x-ray region. The two beams are focused on the GaAs thin film, and the scattered beam corresponding to the SHG signal is detected by a photomultiplier tube (PMT). For detecting the small signal of the SHG, we have developed a novel modulation technique with a piezo actuator and a digital lock-in amplifier. The result of the experiment is almost consistent with the assumption that the SHG has been detected in our experiment.