Mr. Andrey Krayev Profile

Andrey Krayev

at HORIBA Scientific

SPIE Involvement:

Conference Program Committee | Author

Proceedings Article | 5 October 2023 Presentation

Andrey Krayev, Ziyang Gan, Antony George, Andrey Turchanin

Proceedings Volume PC12651, PC126510B (2023) https://doi.org/10.1117/12.2676029

KEYWORDS: Monolayers, Crystals, Raman spectroscopy, Silicon, Semiconducting wafers, Raman scattering, Microscopy, Imperfections, Gold, Gallium nitride

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Proceedings Article | 5 October 2023 Presentation

Importance of multi-color TERS imaging for the nanoscale characterization of 2D semiconductors and heterostructures thereof

Andrey Krayev

Proceedings Volume PC12654, PC1265403 (2023) https://doi.org/10.1117/12.2676052

KEYWORDS: Semiconductors, Heterojunctions, Silver, Raman spectroscopy, Transition metals, Spectroscopy, Scanning probe microscopy, Raman scattering, Plasmons, Plasmonics

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Tip enhanced Raman Scattering (TERS) imaging is gaining more and more popularity for the nanoscale spectroscopic characterization of novel 2D semiconductors and their vertical and lateral heterostructures. Gap mode TERS imaging when a thin sample is sandwiched between the TERS active SPM probe and plasmonic substrate like silver or gold, is the most popular and advantageous option due to strong enhancement of optical electric field in the tip-substrate cavity. Despite multiple examples of successful application of the gap-mode TERS imaging of nanoscale heterogeneities in 2D semiconductors such as transition metal dichalcogenides (TMD), the exact physics of complex interaction between the plasmons in the tip-substrate junction and excitons in TMDs remains poorly understood. One of the possible approaches towards probing complex resonant phenomena occurring in gap-mode TERS experimental conditions is performing TERS imaging with varied excitation wavelength [1]. I’ll demonstrate that the TERS spectra of WS2-WSe2 vertical heterostructures obtained with 785 nm, 632.8 nm, 671 nm and 593.8 nm excitation may differ significantly, the intensity of characteristic Raman bands of WSe2 at around 250-260 cm-1 being extremely low in case of 632.8 nm excitation but rising as we move to shorter or longer excitation wavelengths. I’ll discuss the advantages of concurrent two-color excitation TERS imaging as well as interesting counterintuitive variations of the intensity of TERS bands of the monolayer WS2 as the function of the excitation wavelength. Finally, I’ll demonstrate that the ratio of the intensity of the in-plane E2g and the out-of-plane A1g modes in the above- and below- the-band-gap non resonant TERS spectra of bilayer WS2 on silver inverses as we move from 532 nm to 785 nm excitation. Références [1] Andrey Krayev, Peng Chen, Humberto Terrones, Xidong Duan, Zhengwei Zhang, and Xiangfeng Duan The Journal of Physical Chemistry C 2022, 126, 11, 5218-522 DOI: 10.1021/acs.jpcc.1c10469

Proceedings Article | 3 October 2022 Presentation

Recent advances in TERS/TEPL characterization of lateral and vertical heterostructures of TMDCs

Andrey Krayev

Proceedings Volume PC12200, PC1220008 (2022) https://doi.org/10.1117/12.2636756

KEYWORDS: Heterojunctions

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Proceedings Article | 9 September 2019 Presentation

Unexpected discoveries in TERS imaging of 2D materials on metals (Conference Presentation)

Andrey Krayev

Proceedings Volume 11085, 110850V (2019) https://doi.org/10.1117/12.2530717

KEYWORDS: Raman spectroscopy, Metals, Gold, Chromium, Confocal microscopy, Microscopy, Spatial resolution, Plasmonics, Silver, Graphene

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Raman microscopy proved to be an extremely useful technique for characterization of 2D materials such as graphene, transition metal dichalcogenides (TMDs), black phosphorous, etc. Unfortunately, natural spatial resolution of confocal Raman microscopy, which is limited by the wavelength of the laser used (400-800 nm), is not sufficient for mapping heterogeneities and defects in these materials with characteristic dimensions of few – to few tens of nanometers. Tip Enhanced Raman Spectroscopy (TERS) provides dramatically improved spatial resolution of Raman maps, down to few nanometers, and in addition provides dramatic enhancement of the Raman signal. Since TERS is a relatively new technique, peculiarities of the near-field Raman response of many 2D materials still remain to be discovered and explained. Interesting unexpected effect was observed in the course of TERS characterization of WSe2 and MoSe2 exfoliated to gold and chromium. It is well known that TERS produces the strongest enhancement in so-called gap mode, when a thin sample is sandwiched between a plasmonic tip and a plasmonic substrate, usually silver or gold. To our surprise, TERS spectra of both WSe2 and MoSe2 crystals exfoliated to chromium showed very similar intensities of characteristic Raman bands compared to samples exfoliated to gold, although the background spectra obtained from the bare metal areas were much weaker for chromium compared to gold. Calculations of the optical field intensity of a TERS probe over gold and chromium surface confirmed that we indeed observed a gap mode TERS response on non-plasmonic chromium substrate. This important observation expands the choice of substrates suitable for high quality TERS characterization of 2D materials. Another interesting phenomenon discovered in the course of TERS imaging of WSe2 and MoSe2 deposited on metallic substrates was the appearance of new Raman peak in WSe2 deposited on silver at 295-297 cm-1 and an intense peak in TERS spectra of MoSe2 at 335cm-1, which is either absent or much less pronounced in conventional confocal Raman spectra of this material. We’ll discuss possible nature of these unexpected peaks.

Proceedings Article | 17 September 2018 Presentation

On the nature of increased TERS/TEPL signal in wrinkles of 2D materials (Conference Presentation)

Andrey Krayev

Proceedings Volume 10726, 1072609 (2018) https://doi.org/10.1117/12.2320659

KEYWORDS: Graphene, Excitons, Raman spectroscopy, Luminescence, Confocal microscopy, Carbon, Gold, Transition metals, Optical spectroscopy, Microscopy

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Proceedings Article | 17 September 2018 Presentation

Phys-Chem nm-scale characterization of 2D materials: technique is there-use it! (Conference Presentation)

Andrey Krayev

Proceedings Volume 10725, 107250M (2018) https://doi.org/10.1117/12.2323105

KEYWORDS: Raman spectroscopy, Semiconductors, Luminescence, Transition metals, Optoelectronics, Spectroscopes, Spatial resolution, Scanning transmission electron microscopy, Chemical species, Spectroscopy

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Proceedings Article | 15 September 2016 Presentation + Paper

TERS at work: 2D materials, from graphene to 2D semiconductors

Andrey Krayev, Sergey Bashkirov, Vasily Gavrilyuk, Vladimir Zhizhimontov, Marc Chaigneau, Maruda Shanmugasundaram, A. Edward Robinson

Proceedings Volume 9925, 99250A (2016) https://doi.org/10.1117/12.2237678

KEYWORDS: Graphene, Semiconductors, Oxides, Raman spectroscopy, Spatial resolution, Diamond, Gold, Optical lithography, Confocal microscopy, Luminescence

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