Pump-probe scanning near field optical microscopy: Sub-wavelength resolution chemical imaging and ultrafast local dynamics

Karki, Khadga Jung; Namboodiri, M.N.; Khan, Tahir Zeb; Materny, Arnulf

doi:10.1063/1.3701724

Cited by 32 publications

(44 citation statements)

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“…This equation is particularly useful in experiments where the focus spot size of the pump beam is much bigger than the probe, like we are using here. When the probe focus is comparable to the pump, the bleach signal samples nano-particles that are excited with different intensities and the signals due to single and multi-excitons get averaged19. In this case a more generalized approach may be useful9.…”

Section: Resultsmentioning

confidence: 99%

Multiple exciton generation in nano-crystals revisited: Consistent calculation of the yield based on pump-probe spectroscopy

Karki

Zheng

et al. 2013

Sci Rep

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Multiple exciton generation (MEG) is a process in which more than one exciton is generated upon the absorption of a high energy photon, typically higher than two times the band gap, in semiconductor nanocrystals. It can be observed experimentally using time resolved spectroscopy such as the transient absorption measurements. Quantification of the MEG yield is usually done by assuming that the bi-exciton signal is twice the signal from a single exciton. Herein we show that this assumption is not always justified and may lead to significant errors in the estimated MEG yields. We develop a methodology to determine proper scaling factors to the signals from the transient absorption experiments. Using the methodology we find modest MEG yields in lead chalcogenide nanocrystals including the nanorods.

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Section: Resultsmentioning

confidence: 99%

Multiple exciton generation in nano-crystals revisited: Consistent calculation of the yield based on pump-probe spectroscopy

Karki

Zheng

et al. 2013

Sci Rep

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“…However, for a rigorous calculation of the MEG yield we need to evaluate the proper scaling factor that relates the populations to the signal's amplitude. When the experiments are performed under the condition of uniform illumination of the probed sample's volume by the pump pulse [107], the scaling factors can also be computed from the pump-probe measurements themselves, following the procedure outlined by Karki et al [104] Figure 9(a) shows the pump-probe signal of PbSe nanorods at short temporal delay (S(t 0 )), before 15 ps (blue points), and long temporal delay (S(t l )), after 800 ps (red points), when the sample is excited with femtosecond pulses. The band-gap of the nanorods is about 1 eV, and the energy of the excitation photons is about 1.6 eV.…”

Section: Multiple Exciton Generation (Meg)mentioning

confidence: 99%

Ultrafast photoinduced dynamics in quantum dot-based systems for light harvesting

et al. 2015

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KEYWORDScolloidal quantum dots, electron transfer, energy transfer, core shell quantum dots, quantum dot solar cell ABSTRACT Colloidal semiconductor nanocrystals, referred to as quantum dots, offer simple low-temperature solution-based methods for constructing optoelectronic devices such as light emitting diodes and solar cells. We review recent progress in the understanding of photoinduced processes in key components of a certain type of quantum dot solar cells where the dots sensitize a suitable metal oxide, such as ZnO or TiO 2 , for electron injection, and NiO for hole injection. The electron and hole injection dynamics are discussed in detail as a function of the quantum dot size and core-shell structure, the linker molecule type, and the morphology of the accepting metal oxide. Hole trapping is identified as a major factor limiting the performance of quantum dot-based devices. We review possible strategies for improvement that use core-shell structures and directed excitation energy transfer between quantum dots. Finally, the generation and injection of multiple excitons are revisited. We show that the assumption of a linear relationship between the intensity of transient absorption signal and the number of excitons does not generally hold, and this observation can partially explain highly disparate results for the efficiency of generating multiple excitons. A consistent calculation procedure for studies of multiple exciton generation is provided. Finally, we offer a brief personal outlook on the topic.

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“…A major drawback of this technique is that it does not deliver information about the orientation of polymer chains inside crystallites and the local degree of order. [24,25] Additional information, e.g., about the angle between transition dipole moment and polymer backbone, can be extracted by Raman spectroscopy, which can be combined with SNOM. [19][20][21] These techniques allow spatially averaged insights into the overall orientation of polymer chains and the overall degree of order in the sample.…”

mentioning

confidence: 99%

“…Therefore, AFM investigations are often combined with scattering techniques such as grazing-incidence X-ray scattering (GIXS), [12][13][14][15][16] resonant soft-X-ray scattering (R-SoXS), [12,13,17] or small-angle neutron scattering (SANS), [18] or with polarization-dependent absorption techniques such as near-edge X-ray absorption fine structure (NEXAFS). [24,25] Additional information, e.g., about the angle between transition dipole moment and polymer backbone, can be extracted by Raman spectroscopy, which can be combined with SNOM. Other techniques to characterize semicrystalline films of organic semiconductors comprise polarized optical microscopy.…”

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confidence: 99%

Imaging Nanoscale Morphology of Semiconducting Polymer Films with Photoemission Electron Microscopy

et al. 2017

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Photoemission electron microscopy in combination with polarized laser light is presented as a tool permitting direct imaging of polymer-chain orientation and local degree of order in semicrystalline samples of semiconducting polymers, a promising class of materials for future electronics. The key advantages of this imaging tool are its nondestructive and fast measurements, straightforward data analysis, the low complexity of sample preparation, and the possibility of performing measurements on a broad variety of technologically relevant substrates. The high spatial resolution of the microscope provides insights into the nanoscale morphology, which is relevant for the material's performance in electronic devices.

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Pump-probe scanning near field optical microscopy: Sub-wavelength resolution chemical imaging and ultrafast local dynamics

Cited by 32 publications

References 10 publications

Multiple exciton generation in nano-crystals revisited: Consistent calculation of the yield based on pump-probe spectroscopy

Multiple exciton generation in nano-crystals revisited: Consistent calculation of the yield based on pump-probe spectroscopy

Ultrafast photoinduced dynamics in quantum dot-based systems for light harvesting

Imaging Nanoscale Morphology of Semiconducting Polymer Films with Photoemission Electron Microscopy

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