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We demonstrate heterodyne detected transient vibrational sum frequency generation (VSFG) spectroscopy and use it to probe transient electric fields caused by interfacial charge transfer at organic semiconductor and metal interfaces. The static and transient VSFG spectra are composed of both non-resonant and molecular resonant responses. To further disentangle both contributions, we apply phase rotation to make the imaginary part of the spectra be purely molecular responses and the real part of the spectra be dominated by non-resonant signals. By separating non-resonant and molecular signals, we can track their responses to the transient electric-fields at interfaces independently. This technique combined with the phase sensitivity gained by heterodyne detection allows us to successfully identify three types of photoinduced dynamics at organic semiconductor/metal interfaces: coherent artifacts, optical excitations that do not lead to charge transfer, and direct charge transfers. The ability to separately follow the influence of built-in electric fields to interfacial molecules, regardless of strong nonresonant signals, will enable tracking of ultrafast charge dynamics with molecular specificities on molecular optoelectronics, photovoltaics, and solar materials.
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Charge Transfer and Built-in Electric Fields Between a Crystalline Oxide and Silicon
We report charge transfer and built-in electric fields across the epitaxial SrNbxTi1−xO3−δ=Sið001Þ interface. Electrical transport measurements indicate the formation of a hole gas in the Si and the presence of built-in fields. Hard x-ray photoelectron measurements reveal pronounced asymmetries in core-level spectra that arise from these built-in fields. Theoretical analysis of core-level spectra enables built-in fields and the resulting band bending to be spatially mapped across the heterojunction. The demonstration of tunable charge transfer, built-in fields, and the spatial mapping of the latter, lays the groundwork for the development of electrically coupled, functional heterojunctions.
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- Award ID(s):
- 1508530
- PAR ID:
- 10123733
- Date Published:
- Journal Name:
- Physical review letters
- Volume:
- 123
- ISSN:
- 1079-7114
- Page Range / eLocation ID:
- 026805
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/doi.org/10.1103/PhysRevLett.123.026805
