Intersublevel Spectroscopy on Single InAs-Quantum Dots by Terahertz Near-Field Microscopy
TL;DR: Using scattering-type near-field infrared microscopy in combination with a free-electron laser, intersublevel transitions in buried single InAs quantum dots are investigated and signals from bound-to-bound transitions of single electrons in a probe volume of the order of (100 nm)(3).
Abstract: Using scattering-type near-field infrared microscopy in combination with a free-electron laser, intersublevel transitions in buried single InAs quantum dots are investigated. The experiments are performed at room temperature on doped self-assembled quantum dots capped with a 70 nm GaAs layer. Clear near-field contrast of single dots is observed when the photon energy of the incident beam matches intersublevel transition energies, namely the p-d and s-d transition of conduction band electrons confined in the dots. The observed room-temperature line width of 5–8 meV of these resonances in the mid-infrared range is significantly below the inhomogeneously broadened spectral lines of quantum dot ensembles. The experiment highlights the strength of near-field microspectroscopy by demonstrating signals from bound-to-bound transitions of single electrons in a probe volume of the order of (100 nm)3.
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TL;DR: In this paper, the authors demonstrate ultrabroadband time-resolved terahertz spectroscopy on a single InAs nanowire with 10nm spatial resolution and sub-100 fs time resolution.
Abstract: The authors demonstrate ultrabroadband time-resolved THz spectroscopy on a single InAs nanowire with 10 nm spatial resolution and sub-100 fs time resolution. Phase-locked ultrashort pulses in the rich terahertz spectral range1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18 have provided key insights into phenomena as diverse as quantum confinement7, first-order phase transitions8,12, high-temperature superconductivity11 and carrier transport in nanomaterials1,6,13,14,15. Ultrabroadband electro-optic sampling of few-cycle field transients1 can even reveal novel dynamics that occur faster than a single oscillation cycle of light4,8,10. However, conventional terahertz spectroscopy is intrinsically restricted to ensemble measurements by the diffraction limit. As a result, it measures dielectric functions averaged over the size, structure, orientation and density of nanoparticles, nanocrystals or nanodomains. Here, we extend ultrabroadband time-resolved terahertz spectroscopy to the sub-nanoparticle scale (10 nm) by combining sub-cycle, field-resolved detection (10 fs) with scattering-type near-field scanning optical microscopy (s-NSOM)16,17,18,19,20,21,22,23,24,25,26. We trace the time-dependent dielectric function at the surface of a single photoexcited InAs nanowire in all three spatial dimensions and reveal the ultrafast (<50 fs) formation of a local carrier depletion layer.
222 citations
TL;DR: This work focuses on the pioneering efforts to study the nanoscale electrodynamic properties of plasmonic metamaterials, strongly correlated quantum materials, and polaritonic systems at room or cryogenic temperatures.
Abstract: Infrared and optical spectroscopy represents one of the most informative methods in advanced materials research. As an important branch of modern optical techniques that has blossomed in the past decade, scattering-type scanning near-field optical microscopy (s-SNOM) promises deterministic characterization of optical properties over a broad spectral range at the nanoscale. It allows ultrabroadband optical (0.5-3000 µm) nanoimaging, and nanospectroscopy with fine spatial (<10 nm), spectral (<1 cm-1 ), and temporal (<10 fs) resolution. The history of s-SNOM is briefly introduced and recent advances which broaden the horizons of this technique in novel material research are summarized. In particular, this includes the pioneering efforts to study the nanoscale electrodynamic properties of plasmonic metamaterials, strongly correlated quantum materials, and polaritonic systems at room or cryogenic temperatures. Technical details, theoretical modeling, and new experimental methods are also discussed extensively, aiming to identify clear technology trends and unsolved challenges in this exciting field of research.
193 citations
Dissertation•
01 Jan 2015
TL;DR: In this article, the femtosecond dynamics of low-energy elementary excitations, e.g. phonons, plasmons and excitons, at the surface of solid-state systems were observed using a nanometer-sized metal tip of the atomic force microscope.
Abstract: This thesis has introduced a novel microscope which combines the outstanding properties of ultrafast multi-terahertz spectroscopy and scattering-type scanning near-field optical microscopy to observe the femtosecond dynamics of low-energy elementary excitations, e.g. phonons, plasmons and excitons, at the surface of solid-state systems. Ultrabroadband phase-locked mid-infrared light pulses are focused onto a nanometer-sized metal tip of the atomic force microscope. When approached to a sample surface, the tip acts as a local optical probe, confining the light pulses at its apex. Detection of the scattered radiation reveals information about the optical properties of the sample with a spatial resolution of 10nm, ultimately limited by the tip radius of curvature. Electro-optic sampling, one of the most notable techniques of terahertz spectroscopy, is employed to detect the scattered oscillating electric near field directly in the time domain with a temporal resolution of 10fs. Together with pump-probe experiments this technique enables the observation of the dynamics of low-energy elementary excitations on sub-cycle timescales, faster than a single oscillation cycle of the multi-terahertz probe pulses. The combination of ultrafast multi-terahertz spectroscopy and near-field microscopy culminates in a unique microscope that achieves an unprecedented combined temporal (10fs) and spatial (10nm) resolution in the mid-infrared wavelength region.%%%%In dieser Dissertation wird ein neuartiges Mikroskop beschrieben, welches die herausragenden Eigenschaften der ultraschnellen multi-Terahertz Spektroskopie und der Nahfeldmikroskopie verbindet. Damit ist es zum ersten Mal moglich die Femtosekunden-Dynamik von niederenergetischen Elementaranregungen, wie zum Beispiel Phononen, Plasmonen oder Exzitonen, direkt an der Oberflache von Festkorpern zu untersuchen. Ultrabreitbandige, phasen-stabile, mittelinfrarote Lichtimpulse werden dazu auf die Spitze eines Rasterkraftmikroskops fokussiert. Angenahert an die Oberflache einer Probe, fungiert diese Spitze als Nanometer grose Sonde, die das Licht an ihrem Ende bundelt. Die Detektion des gestreuten Lichts ermoglicht es dann Informationen uber die lokalen optischen Eigenschaften der Probe direkt unterhalb der Spitze zu erhalten. Die raumliche Auflosung betragt hierbei 10 Nanometer und ist grundsatzlich nur durch den Radius der Spitze limitiert. In diesem Experiment wird das gestreute elektrische Nahfeld direkt mit Hilfe eines Elektro-optischen Detektors gemessen. Diese Methode gewahrleistet eine ultimative Zeitauflosung von 10fs und erlaubt in Kombination mit Anrege-Abtast Experimenten eine direkte Beobachtung der Dynamik von niederenergetischen Elementaranregungen auf einer Sub-Zyklen Zeitskala, schneller als ein einzelner Oszillationszyklus des multi-Terahertz Abtastimpulses. Die Kombination von ultraschneller multi-Terahertz Spektroskopie mit der Nahfeldmikroskopie gipfelt in einem einzigartigen Mikroskop mit einer bisher nicht dagewesenen kombinierten zeitlichen (10fs) und raumlichen…
190 citations
TL;DR: This work quantitatively measures local dielectric constants and infrared absorption of samples with 2 orders of magnitude improved spatial resolution compared to far-field measurements and obtains local infrared absorption spectra with unprecedented accuracy in peak position and shape, which is the key to quantitative chemometrics on the nanometer scale.
Abstract: Scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared nanospectroscopy (nano-FTIR) are emerging tools for nanoscale chemical material identification. Here, we push s-SNOM and nano-FTIR one important step further by enabling them to quantitatively measure local dielectric constants and infrared absorption. Our technique is based on an analytical model, which allows for a simple inversion of the near-field scattering problem. It yields the dielectric permittivity and absorption of samples with 2 orders of magnitude improved spatial resolution compared to far-field measurements and is applicable to a large class of samples including polymers and biological matter. We verify the capabilities by determining the local dielectric permittivity of a PMMA film from nano-FTIR measurements, which is in excellent agreement with far-field ellipsometric data. We further obtain local infrared absorption spectra with unprecedented accuracy in peak position and shape, which is the key to quantitative chemometrics on the nanometer scale.
159 citations
TL;DR: Spectroscopic analysis of infrared-resonant antenna probes for tip-enhanced optical microscopy corroborates their functionality as resonant antennas and verifies the broad tunability, and experimentally demonstrates high-performance mid-infrared nanoimaging of molecular absorption.
Abstract: We report the development of infrared-resonant antenna probes for tip-enhanced optical microscopy. We employ focused-ion-beam machining to fabricate high-aspect ratio gold cones, which replace the standard tip of a commercial Si-based atomic force microscopy cantilever. Calculations show large field enhancements at the tip apex due to geometrical antenna resonances in the cones, which can be precisely tuned throughout a broad spectral range from visible to terahertz frequencies by adjusting the cone length. Spectroscopic analysis of these probes by electron energy loss spectroscopy, Fourier transform infrared spectroscopy, and Fourier transform infrared near-field spectroscopy corroborates their functionality as resonant antennas and verifies the broad tunability. By employing the novel probes in a scattering-type near-field microscope and imaging a single tobacco mosaic virus (TMV), we experimentally demonstrate high-performance mid-infrared nanoimaging of molecular absorption. Our probes offer excellent...
124 citations
References
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TL;DR: In this paper, a new type of semiconductor laser is studied, in which injected carriers in the active region are quantum mechanically confined in two or three dimensions (2D or 3D), and the effects of such confinements on the lasing characteristics are analyzed.
Abstract: A new type of semiconductor laser is studied, in which injected carriers in the active region are quantum mechanically confined in two or three dimensions (2D or 3D). Effects of such confinements on the lasing characteristics are analyzed. Most important, the threshold current of such laser is predicted to be far less temperature sensitive than that of conventional lasers, reflecting the reduced dimensionality of electronic state. In the case of 3D‐QW laser, the temperature dependence is virtually eliminated. An experiment on 2D quantum well lasers is performed by placing a conventional laser in a strong magnetic field (30 T) and has demonstrated the predicted increase of T0 value from 144 to 313 °C.
3,069 citations
TL;DR: In this paper, the authors provide numerical and graphical information about many physical and electronic properties of GaAs that are useful to those engaged in experimental research and development on this material, including properties of the material itself, and the host of effects associated with the presence of specific impurities and defects is excluded from coverage.
Abstract: This review provides numerical and graphical information about many (but by no means all) of the physical and electronic properties of GaAs that are useful to those engaged in experimental research and development on this material. The emphasis is on properties of GaAs itself, and the host of effects associated with the presence of specific impurities and defects is excluded from coverage. The geometry of the sphalerite lattice and of the first Brillouin zone of reciprocal space are used to pave the way for material concerning elastic moduli, speeds of sound, and phonon dispersion curves. A section on thermal properties includes material on the phase diagram and liquidus curve, thermal expansion coefficient as a function of temperature, specific heat and equivalent Debye temperature behavior, and thermal conduction. The discussion of optical properties focusses on dispersion of the dielectric constant from low frequencies [κ0(300)=12.85] through the reststrahlen range to the intrinsic edge, and on the ass...
2,115 citations
TL;DR: In this paper, a scheme that realizes controlled interactions between two distant quantum dot spins is proposed, where the effective long-range interaction is mediated by the vacuum field of a high finesse microcavity.
Abstract: The electronic spin degrees of freedom in semiconductors typically have decoherence times that are several orders of magnitude longer than other relevant time scales. A solid-state quantum computer based on localized electron spins as qubits is therefore of potential interest. Here, a scheme that realizes controlled interactions between two distant quantum dot spins is proposed. The effective long-range interaction is mediated by the vacuum field of a high finesse microcavity. By using conduction-band-hole Raman transitions induced by classical laser fields and the cavity-mode, parallel controlled-not operations, and arbitrary single qubit rotations can be realized.
1,702 citations
TL;DR: In this paper, the strain distribution in and around pyramidal InAs/GaAs quantum dots (QD's) on a thin wetting layer fabricated recently with molecular-beam epitaxy, is simulated numerically.
Abstract: The strain distribution in and around pyramidal InAs/GaAs quantum dots (QD's) on a thin wetting layer fabricated recently with molecular-beam epitaxy, is simulated numerically. For comparison analytical solutions for the strain distribution in and around a pseudomorphic slab, cylinder, and sphere are given for isotropic materials, representing a guideline for the understanding of strain distribution in two-, one-, and zero-dimensional pseudomorphic nanostructures. For the pyramidal dots we find that the hydrostatic strain is mostly confined in the QD; in contrast part of the anisotropic strain is transferred from the QD into the barrier. The optical-phonon energies in the QD are estimated and agree perfectly with recent experimental findings. From the variation of the strain tensor the local band-gap modification is calculated. Piezoelectric effects are additionally taken into account. The three-dimensional effective-mass single-particle Schr\"odinger equation is solved for electrons and holes using the realistic confinement potentials. Since the QD's are in the strong confinement regime, the Coulomb interaction can be treated as a perturbation. The thus obtained electronic structure agrees with luminescence data. Additionally AlAs barriers are considered.
1,056 citations
TL;DR: In this article, the authors demonstrate the use of the apertureless approach to scan near field optical microscopy to obtain contrast in vibrational absorption on a scale of about 100 nanometres, about one-hundredth of a wavelength.
Abstract: Identification of chemical compounds by vibrational spectroscopy at infrared wavelengths requires macroscopic samples: the spatial resolution is diffraction-limited to a scale of about half the wavelength, or about five micrometres. The scanning near-field optical microscope1,2, however, can reveal sub-wavelength detail because it uses near-field probing rather than beam focusing. Here we demonstrate the use of the aperture-less approach to scanning near-field optical microscopy3,4,5,6 to obtain contrast in vibrational absorption on a scale of about 100 nanometres, about one-hundredth of a wavelength. We record infrared scattering from the tip of an atomic force microscope scanned over a composite polymer film. At the boundary between different polymers we observe contrast changes owing to changes in vibrational absorption. The contrast is strongly enhanced in the near field of the probe tip, which we interpret as evidence of surface-enhanced infrared absorption7. When extended to multi-wavelength operation, this approach should enable imaging of chemical composition at nanometre resolution.
864 citations