Near-Field Spectroscopy of the Quantum Constituents of a Luminescent System

Hess, Harald F.; Betzig, Eric; Harris, T. D.; Pfeiffer, L. N.; West, K. W.

doi:10.1126/science.264.5166.1740

Cited by 527 publications

(257 citation statements)

References 31 publications

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“…The past decades have witnessed the development of several successful attempts in this regard, such as scanning near-field optical microscopy (SNOM) [1][2][3][4][5], single-molecule spectroscopy [6][7][8][9][10] and the combination of the two [11][12][13][14]. These efforts have however suffered from the mismatch between light and nanoscale matter, which leads to a small throughput between the input and output signals.…”

Section: Introductionmentioning

confidence: 99%

Light scattering under nanofocusing: Towards coherent nanoscopies

Mohammadi

Agio

2012

Optics Communications

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We investigate light scattering under nanofocusing in the context of coherent spectroscopy. We discuss the different mechanisms that may enhance the signal in extinction and how these depend on nanofocusing as well as on the probed system. We find that nanofocusing may improve the detection sensitivity by orders of magnitude under realistic conditions, enabling scanning implementations of coherent spectroscopy at the nanoscale.

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Section: Introductionmentioning

confidence: 99%

Light scattering under nanofocusing: Towards coherent nanoscopies

Mohammadi

Agio

2012

Optics Communications

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“…Inhomogeneities in size and shape within ensemble samples result in spectral broadening that is many orders of magnitude larger than single QD spectra. 9,15 Though the mechanisms are thought to be quite different, the study of single QDs has revealed phenomena common to other single chromophore systems such as blinking 4 and spectral diffusion. [9][10][11][12] It has also revealed new characteristics specific to QDs such as ultranarrow transition line widths, 9,15 giant Overhauser shifts, 16 multicarrier effects, 17,18 and fluctuating local electric fields.…”

mentioning

confidence: 99%

Influence of Spectral Diffusion on the Line Shapes of Single CdSe Nanocrystallite Quantum Dots

1999

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We study the emission line shapes of single CdSe nanocrystallite quantum dots. Single dot line shapes are found to result from rapid spectral shifting of the emission spectrum rather than the intrinsic physics of the quantum dot. A strong dependence of single dot line widths on excitation intensity, wavelength, temperature, and integration time is found and is correlated with the number of times that the quantum dot is excited during the acquisition of a single spectrum. The observed results are consistent with thermally assisted spectral diffusion, activated by the release of excess excitation energy.Recent advances in the detection of single molecules have been responsible for a level of understanding in condensed phase systems that was not previously possible. Of particular interest are incoherent dynamic effects, which can be completely hidden when averaged over an ensemble. In recent years, single chromophore spectroscopy has allowed the direct observation of single enzyme reactions, 1 single energy transfer events, 2 and single molecule rotational dynamics. 3 In addition, new and unexpected physical phenomena have been observed, which appear to be common to many single chromophore systems, such as fluorescence blinking 4-6 and spectral shifting (spectral diffusion). [7][8][9][10][11][12] One field that has greatly benefited from single chromophore spectroscopy is the study of semiconductor quantum dots (QDs). QDs are of great interest due to their unique size dependent optical properties, 13 which can easily be tuned during fabrication. 14 Unfortunately, the characteristics that make QDs interesting also make them inherently difficult to study. Inhomogeneities in size and shape within ensemble samples result in spectral broadening that is many orders of magnitude larger than single QD spectra. 9,15 Though the mechanisms are thought to be quite different, the study of single QDs has revealed phenomena common to other single chromophore systems such as blinking 4 and spectral diffusion. [9][10][11][12] It has also revealed new characteristics specific to QDs such as ultranarrow transition line widths, 9,15 giant Overhauser shifts, 16 multicarrier effects, 17,18 and fluctuating local electric fields. 12 One area of particular interest which can, in principle, be addressed on the single QD level, is the nature of the homogeneous line shape. While theory predicts that QDs should have atomic-like spectral transitions due to long excited-state lifetimes and weak coupling to acoustic phonons, 19 previous ensemble experiments have suggested that line widths in both excitation [20][21][22] and emission 23-25 are quite broad (for example, "homogeneous" line widths extracted from fluorescence line narrowing experiments in CdSe nanocrystallite QDs are reported to be ∼5 meV 26 ). It was expected that single QD spectroscopy would uncover the true "homogeneous" line width. However, while single dot line widths are typically found to be significantly narrower than what is seen in ensemble experiments, many single dot exp...

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“…Near field microscopy and spectroscopy provide direct information on the spatial and energy distribution of light emitting nanometric centers [1][2][3][4][5] of semiconductor quantum structures. Moreover near field spectroscopy offers unique attributes in addition to high spatial resolution which might be explored in future experiments.…”

mentioning

confidence: 99%

Is the spatially averaged spectrum equal to the global spectrum?

Pistone¹,

Stefano²,

Savasta³

et al. 2003

phys. stat. sol. (c)

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Near-field optical spectroscopy and microscopy give access to excitations that cannot be revealed in the far zone. In order to investigate these remarkable differences, we present a theoretical analysis of the local optical properties of semiconductor quantum wells including the effects of disorder arising from interface fluctuations. The far-field absorption spectrum is compared with spatially averaged absorption spectra calculated at different spatial resolutions. We find that summing up local optical spectra does not reproduce the global spectrum in contrast to findings at diffraction-limited resolutions.Near field microscopy and spectroscopy provide direct information on the spatial and energy distribution of light emitting nanometric centers [1-5] of semiconductor quantum structures. Moreover near field spectroscopy offers unique attributes in addition to high spatial resolution which might be explored in future experiments. For instance, the presence of optical fields with high lateral spatial frequencies able to excite surface states with high k-vectors not accessible by far-field optical excitations allows the possibility to confine the optical excitation to a very small volume below the diffraction limit. As a consequence optical spectra of homogeneous surface systems can display remarkable differences in the near and far zones [6,7]. These spectral changes are caused by the loss of evanescent modes (corresponding to modes with high lateral spatial frequencies) in the far zone. They have been analyzed theoretically in ideal disorder-free surface systems where in-plane k-vectors are good quantum numbers.Here we analyze, in a realistic surface system affected by disorder effects, these additional opportunities of near-field spectroscopy. To what extent these spectral changes are detectable in real systems affected by disorder and imperfections? Are spatially averaged near-field spectra equal to far-field spectra? In order to isolate spectral changes due to excitation of states not accessible by far-field optical probes, we compare far-field absorption spectra with spatially averaged absorption spectra [8]. These averaged spectra are composed summing up local spectra obtained centering the confined illuminating beams on a fine mesh of points on the quantum well plane and they are calculated at different spatial resolutions. Our analysis is performed on quantum wells (QWs). Interface fluctuations in QWs result in an effective 2D (two-dimensional) spatially correlated random potential that tends to localize the center of mass (COM) motion of excitons [9,10] and produces an inhomogeneous Gaussian-like absorption line [11,12]. Inhomogeneities and disorder effects give rise to surface quantum states, eventually localized, with mixed in-plane k-vectors (the in-plane k-vector is no more a good quantum number).

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Near-Field Spectroscopy of the Quantum Constituents of a Luminescent System

Cited by 527 publications

References 31 publications

Light scattering under nanofocusing: Towards coherent nanoscopies

Light scattering under nanofocusing: Towards coherent nanoscopies

Influence of Spectral Diffusion on the Line Shapes of Single CdSe Nanocrystallite Quantum Dots

Is the spatially averaged spectrum equal to the global spectrum?

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