Haut PDF Single photon emission from graphene quantum dots at room temperature

Single photon emission from graphene quantum dots at room temperature

Single photon emission from graphene quantum dots at room temperature

Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany In the field of condensed matter, graphene plays a central role as an emerging material for nanoe- lectronics. Nevertheless, graphene is a semimetal, which constitutes a severe limitation for some fu- ture applications. Therefore, a lot of efforts are being made to develop semiconductor materials whose structure is compatible with the graphene lattice. In this perspective, little pieces of gra- phene represent a promising alternative [1, 2]. In particular, their electronic, optical and spin properties can be in principle controlled by de- signing their size, shape and edges [3–6]. As an example, graphene nanoribbons with zigzag edges have localized spin polarized states [7, 8]. Like- wise, singlet-triplet energy splitting can be chosen by designing the structure of graphene quantum dots [9]. Moreover, bottom-up molecular synthe- sis put these potentialities at our fingertips [3, 5]. Here, we report on a single emitter study that di- rectly addresses the intrinsic properties of a single graphene quantum dot. In particular, we show that graphene quantum dots emit single photons at room temperature with a high purity, a high brightness and a good photostability. These re- sults pave the way to the development of new quantum systems based on these nanoscale pieces of graphene.
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Single photon emission from graphene quantum dots at room temperature

Single photon emission from graphene quantum dots at room temperature

Jean-Sébastien Lauret 1 Graphene being a zero-gap material, considerable efforts have been made to develop semiconductors whose structure is compatible with its hexagonal lattice. Size reduction is a promising way to achieve this objective. The reduction of both dimensions of graphene leads to graphene quantum dots. Here, we report on a single-emitter study that directly addresses the intrinsic emission properties of graphene quantum dots. In particular, we show that they are ef ficient and stable single-photon emitters at room temperature and that their emission wavelength can be modi fied through the functionalization of their edges. Finally, the inves- tigation of the intersystem crossing shows that the short triplet lifetime and the low crossing yield are in agreement with the high brightness of these quantum emitters. These results represent a step-forward in performing chemistry engineering for the design of quantum emitters.
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Fast exciton spin relaxation in single quantum dots

Fast exciton spin relaxation in single quantum dots

γ X and γ Y . The fact that both bright states are equally populated is a central assumption of our model and it requires a non-resonant excitation of the QD to avoid any polarization memory of the excitation laser, as de- tailed below. If the system dynamics is only driven by radiative recombination [Fig. 1(a)], the steady-state PL intensity of both bright exciton states in the weak excita- tion regime is exactly the same whatever the difference in oscillator strengths. This result may be surprising at first sight but simply stems from a quantum efficiency equal to unity for both |Xi and |Y i states: every single exciton which is photo-generated on a bright state will give rise to the emission of a single photon. While the steady-
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Storage and retrieval of THZ-bandwidth single photons using a room-temperature diamond quantum memory

Storage and retrieval of THZ-bandwidth single photons using a room-temperature diamond quantum memory

The high carrier frequency of the optical phonon (40 THz [18] ) and a large detuning from the conduction band (∼950 THz) are the key features allowing storage of THz-bandwidth photons. These features also provide an intrinsically low noise floor: the large detuning from optical resonance eliminates fluorescence noise, and the high energy of the optical phonon results in low thermal phonon population at room temperature. Four-wave mixing noise, which is a pervasive problem in many Λ-level systems [17,23] , is suppressed in diamond due to the large splitting and the high optical dispersion [20] . Following excitation, the optical phonons decay into a pair of acoustic phonons with a characteristic time scale of 3.5 ps [24] , which sets the storage lifetime of the memory. The advantage of the rapid acoustic decay is that it returns the crystal lattice to the ground state, resetting the memory such that it is ready to store the next photon. This subnanosecond reset time permits GHz repetition rates in the diamond phonon system.
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Single-molecule light emission at room temperature on a wide-band-gap semiconductor

Single-molecule light emission at room temperature on a wide-band-gap semiconductor

29, rue J. Marvig, B.P. 94347, 31055 Toulouse, France (Received 24 March 2014; revised manuscript received 29 August 2014; published 17 September 2014) Room-temperature light emission from single chemisorbed perylene based molecules adsorbed on silicon carbide (SiC) is probed by scanning tunneling microscopy (STM). A new approach to STM-induced luminescence of a single molecule is explored using a wide-band-gap semiconductor to decouple electronically the molecule from the surface. After molecular adsorption, the lowest unoccupied molecular orbital and the highest occupied molecular orbital (HOMO) both lie within the bulk band gap and below the Fermi level of the substrate. The maximum photon energy of the light emission from the molecule shows a fixed shift of 1.5 eV relative to the maximum energy of the tunnel electrons. This is consistent with the photons being generated by inelastic electron tunneling between the HOMO and the unoccupied electronic states of the STM tip.
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Multiplexed single-photon source based on multiple quantum dots embedded within a single nanowire

Multiplexed single-photon source based on multiple quantum dots embedded within a single nanowire

Experimental Setup. PL measurements were made in a closed-cycle helium cryostat operating at 4 K. The nanowire quantum dots were pumped along the axis of the photonic nanowire waveguide through a 100× objective. Continuous- wave excitation was provided by a HeNe laser (λ = 633 nm). For pulsed excitation, a diode laser at λ = 670 nm with a pulse width of 100 ps and a repetition rate of 40 MHz (80 MHz) was used for correlation (photoluminescence) measurements. The dot emission was collected through the same microscope objective and for spectral measurements was dispersed using a grating spectrometer and detected with a liquid-nitrogen- cooled CCD. The second-order correlation measurements were made using a fiber-based HBT arrangement. The emission from the nanowire was fiber-coupled and sent to a fi ber-based tunable filter (bandwidth ∼0.1 nm, tuning range λ = 950 ± 30 nm) for spectral filtering of individual quantum dot emission lines. The filtered emission was sent to two fiber- coupled APDs (timing jitters ∼200 ps) via a 50:50 fiber beamsplitter.
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Deconstructing the room-temperature emission spectra of nanocrystals using Photon-Correlation Fourier Spectroscopy

Deconstructing the room-temperature emission spectra of nanocrystals using Photon-Correlation Fourier Spectroscopy

Figure 6-1: The S-PCFS setup combines confocal microscopy setup used in FCS with the interferometer and correlation setup of PCFS. 6.1 S-PCFS Theory: Combining FCS with PCFS When the emission from FCS is passed through an interferometer, we can take ad- vantage of one of the unique properties of PCFS: the measurement of the energy dif- ferences between photons rather than their absolute energies. In the solution-phase version of PCFS, or S-PCFS, the energy differences between pairs of photons emit- ted by the same particle reflect the single-nanocrystal spectral profile. In contrast, photon pairs emitted from different particles depend on the peak emission energies of each particle and therefore reflect the inhomogeneously-broadened ensemble spec- trum. Because the detection of photons originating from the same NC is statistically enhanced at timescales shorter than the particle dwell time in the focal volume, the single-particle contribution can be disentangled from the ensemble while maintaining ensemble-level statistics. 166 Thus, the spectral correlation function for the average
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Monitoring stimulated emission at the single-photon level in one-dimensional atoms

Monitoring stimulated emission at the single-photon level in one-dimensional atoms

DOI: 10.1103/PhysRevA.85.023811 PACS number(s): 42.50.Ct, 42.50.Gy I. INTRODUCTION Exploration of the light-matter interaction at the single- photon level is a goal of quantum optics that has been successfully achieved so far with emitters in high-quality- factor microwave [ 1 ] or optical cavities [ 2 ]. High atom-field couplings are obtained at the price of keeping the photons trapped in the mode, which may limit their exploitation for all practical purposes. Alternative strategies have thus emerged, based on the coupling of the emitter to a one-dimensional (1D) electromagnetic environment. A pioneering realization of such a “1D atom” consisted in an atom coupled to a leaky directional cavity [ 3 ]. Nowadays, 1D atoms can be implemented in a wide range of physical systems, from quantum dots (QDs) embedded in photonic wires [ 4 ], in photonic crystals [ 5 ], or in plasmonic waveguides [ 6 ], to superconducting qubits in circuit QED [ 7 , 8 ], and to atoms [ 9 ] and molecules in tightly focused beams [ 10 ]. When probed with a resonant field, the natural directionality of 1D atoms allows a high mode matching to be reached between the incoming and the scattered light, manifested by the destructive interference of the two fields [ 5 , 8 , 10 , 11 ]. Equivalently, perfect mode matching allows saturation of the emitter with a single photon [ 11 ], so that 1D atoms have been identified as promising single-photon transistors [ 6 ] and two-photon gates [ 12 ].
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Room-temperature InAs/InP Quantum Dots laser operation based on heterogeneous “2.5 D” Photonic Crystal

Room-temperature InAs/InP Quantum Dots laser operation based on heterogeneous “2.5 D” Photonic Crystal

A radically different behavior can be observed for specific structures where the detuning between the resonant mode and the optical gain is similar, and provided that the quality of the photonic crystal is higher. In particular, Figure 4(b) shows the L-L and Q-L curves obtained on a second structure, where the resonant mode stands at 1490nm. The spontaneous emission background is also plotted on the L-L curve in Fig. 4(b). One could first note that this background saturates for a pumping power over 250µW, with a very low emitted power. If we now consider the peak at 1490nm, two main regimes can be observed. In a first regime, under 1mW, there is a sub-linear increase of the experimental Q-factor together with a roughly linear increase of the emitted power. The linewidth decrease may be attributed to the saturation of the absorption of the QDs, and laser emission cannot be asserted for the corresponding pumping power range. In the second regime, above 1mW we observe a linear increase on both the L-L and Q-L curves. In particular, the experimental Q-factor is linearly increased until the maximum resolution of the spectrometer is reached (Q ≈9000, as indicated in Fig. 4(b)). As a consequence, the spectral linewidth is inversely proportional to the number of photons in the resonant mode. Therefore, and on the basis of classical laser analysis, we can conclude that laser emission occurs in this second regime. One could note that very similar trends were observed on Q-L curves in very recent papers, on laser structures combining photonic crystal cavities and a single layer of QDs at low temperature [4], or photonic crystal cavities and a multi-layer of QDs at room temperature [6].
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Biexciton binding of Dirac fermions confined in colloidal graphene quantum dots

Biexciton binding of Dirac fermions confined in colloidal graphene quantum dots

Measurement of biexciton emission in C168 is extremely challenging on account of the low photoluminescence quantum yield of C168 single excitons (∼0.002) and rapid rate (3 ps −1 ) of biexciton Auger recombination. 31 Moreover, rapid carrier cooling allows for measurement of photoluminescence only from the lowest-energy single- and biexciton states. Therefore, we study biexcitons by transient absorption (TA) measure- ments in which the single-to-biexciton transition does not require a long-lived biexciton for its observation and in which one can access higher-energy biexcitons. TA measurements on C168 were performed as described previously. 31 C168 was prepared following the synthesis of Yan and Li. 11 Prior characterization has established the high structural and size uniformity of the synthetic product. 11 C168 was dissolved in anhydrous toluene, and loaded in a nitrogen atmosphere in a 1 mm path length fused-silica cuvette sealed with Teflon valves. GQD solutions were prepared to optical densities of ∼0.2 at 3.1 eV. C168 in toluene was excited at 3.1 eV and probed with ∼130 fs temporal resolution using a broadband continuum (for Figure 1. Extrapolated singlet exciton (X) and biexciton (XX) states,
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Synthesis and properties of graphene quantum dots and nanomeshes

Synthesis and properties of graphene quantum dots and nanomeshes

Figure 2.22: Schematic representation of the experimental setup for the measurement of the g (2) function In our case, the correlation function plotted in Figure 2.23a exhibits a g (2) (  ) = 0.05. This result is in strong contrast with the results of such experiments performed on “top-down” GQDs made from graphene oxide where no antibunching was observed. 17 In this study, the absence of antibunching was interpreted as a consequence of the extrinsic nature of the states at the origin of the luminescence: multidefect sites emitting in an uncorrelated manner. In our case, we have performed measurements on more than 30 specimens of GQD 3, all of them leading to g (2) (0) < 0.1. Moreover, the weak value observed for the g (2) (0) is an indication of the good purity of single photon emission associated with the single graphene quantum dots. This result strongly suggests that GQDs synthesized via the “bottom-up” approach constitute interesting alternatives to other single emitters, such as defects in WSe2, 18–22 in h-BN 23–25 or to carbon nanotubes. 26 Indeed, the emission wavelength of GQDs can be tuned thank to their size and/or functionalities. In addition, water soluble GQDs could find important applications in biology as stable, bright and non-toxic dyes. These results have been summarized in a paper deposited on ArXiv 27 and have been accepted for publication in Nature Communications. 28
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Single spin control and readout in silicon coupled quantum dots

Single spin control and readout in silicon coupled quantum dots

swept. The drain bias is 5mV. We can see regular oscillations of the conductance, so under each gate we can accumulate a single dot and have coulomb blockade. As expected, the first visible peak appears not so after the room-temperature threshold. Oscillations for gate two are quite regular, with a period of 36mV and a first peak at 486mV. On the contrary, gate one shows an isolated peak at 420mV. The lower voltage of first peak is in accordance with the room temperature threshold voltages, which are shifted in the same way. We attribute this lone resonance to a transport enhanced by a single dopant in the access barriers. In figure 2.14a the stability diagram, so the plot of current as function of both gates. It has been acquired at T=15mK, a side gate bias of -250mV and 10mV of bias. We can clearly see conduction spots triangle shaped. In the region for Vg1>500mV these triangles are regularly spaced, with a large amount of co-tunnelling between them. As stated before, we attribute these to coulomb peaks of two dots in series, with a large (>10) number of electron inside. The co-tunnelling is compatible with the gate geometry that doesn’t cover fully the nanowire, thus reducing the barriers height at high dots filling. At Vg1 ≈ 430mV we can see a “band” of triangles; as stated before, we attribute the same double dot system, but their transport signature is visible due to a dopant assisting the tunnelling. These triangles are attributed the very firsts electrons tunnelling in the system. Measurement at large drain bias (not shown) suggest that is case, since no current is spotted below this region. A definitive answer is however impossible, given the lack of a charge detector/ In figure 2.14b we measured the first visible triangle (highlighted in blue in figure 2.14a) with a small bias of 2.5mV and the side gate voltage tuned to -280mV for optimal results. From now, all the measurements reported are done under these bias conditions, unless differently stated. The lever arm matrix, defined as the matrix that link the variation of the applied potential to the variation of dot’s chemical potential
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Photon correlations on a room temperature semi-conductor single photon emitter.

Photon correlations on a room temperature semi-conductor single photon emitter.

The strength of condensed matter systems is their tunability. Engineering on solid state system provide the possibility to change the properties of the emitter at will. The colour of photons emitted by nanocrystals is determined by their size and can cover wavelength ranging from infrared to UV[6]. This is also true for semi conductor quantum dots, and the wide range covered by the possible emission energies is made accessible by the variety of semi-conductor materials which can compose the quantum dot. Even if such considerations are often overlooked, the nanometric size of these structures are also bringing important processes dominating their physics: carriers-phonon coupling, exchange interaction between conned carriers spins or cou- pling between carriers and magnetic spins eventually inserted in or outside the quantum dot. However, the control of the size and of the semi-conductor composition is limited by the growth conditions imposed by the conventionnal Stranski-Krastanov (SK) method. The quantum dots are self-assembled by release of elastic energy accumulated by lattice mismatch between the semi- conductor host matrix and the quantum dot semi-conductor. Thus, control of the quantum dot dimensions is dicult. Alternative techniques enabling growth of quantum dots embedded in nanowires are suppressing these limitations, allowing a large choice of the composing materials, and oering, in principle, the possibility to tune the quantum dots dimensions: they are putting scalability of semiconductor heterostructures at a higher level.
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Biexciton Quantum Yield of Single Semiconductor Nanocrystals from Photon Statistics

Biexciton Quantum Yield of Single Semiconductor Nanocrystals from Photon Statistics

in this work. The quantitative connection explored here between g (2) and the biexciton quantum yield has important implications for the routine use of g (2) data in PL microscopy. A g (2) (τ) measurement essentially reports on the probability distribution of the time-separation (τ) between pairs of photons emitted by a source. When g (2) (τ) shows a dip at τ = 0, the source is said to be “antibunched”, considered the signature of a quantum emitter. 1 In fact, even under weak excitation, strong anti-bunching from a single emitter requires an efficient mechanism to suppress multiphoton emission or block its detection, 1 such as the impossibility of two-photon absorption in atoms, 13 spectral separation of exciton and multiexciton lines in epitaxial quantum dots, 14 or BX emission quenching by the Auger mechanism in NCs. Therefore, strong antibunching is a sufficient condition for establishing that a single emitter has been isolated, but it is commonly and incorrectly assumed that it is also a necessary condition. If the possibility of a 0-time low-power residual feature due to BX emission is not contemplated, fluorophores that show appreciable signal at τ = 0 will be judged as not being properly isolated single emitters. Such selection bias against emitters with appreciable η bx affected our earlier work on the photon statistics of single CdSe-based
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Single- and two-photon imaging of human micrometastases and disseminated tumour cells with conjugates of nanobodies and quantum dots

Single- and two-photon imaging of human micrometastases and disseminated tumour cells with conjugates of nanobodies and quantum dots

Samples of 30 µg of total protein extracts reduced by 50 mM of sample reducing agent (RSA, Novex), were separated by SDS-PAGE (NuPAGE Novex TRIS acetate 3–8% gel, Invitrogen) and transferred to nitrocellulose membranes (Amersham Biosciences). The membranes were blocked with 5% bovine serum albumin (BSA, Sigma-Aldrich) in 0.05% TBS-T (Tris-buffered saline supplemented with Tween-20) for 1 h at room temperature (RT), probed for 2 h with either an anti-HER2 rabbit polyclonal antibody (pAb-HER2, Neu (C-18):sc-284, Santa Cruz Biotechnology, dilution of 1:200) or a an anti-CEA rabbit monoclonal antibody (mAb-CEA, EPCEAR7 ab133633, Abcam, dilution of 1:1000), each diluted in blocking solution. Mouse monoclonal anti-β-actin anti- body was used as protein loading control (mAb-β-actin, Abcam 8226, dilution of 1:1000). Blots were incubated with a horseradish peroxidase (HRP)-conjugated anti-rabbit antibody (1:8000, GE Healthcare Life Sciences) and developed using chemiluminescent HRP substrate (Millipore Immobilon system). Signals were detected by using a Bio-Rad Chem-Doc luminescence detection system.
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Bright Room-Temperature Single-Photon Emission from Defects in Gallium Nitride

Bright Room-Temperature Single-Photon Emission from Defects in Gallium Nitride

By fixing the thickness of the cubic inclusion to 5 bilayers and setting the localization potential of the hole so that the latter yields a ZPL wavelength of 680 nm for the point defect in pure wurtzite GaN, our simulation gives rise to the spectral spreading between 600 nm and 705 nm (see Figure 4c) if point defects are distributed uniformly between -4 nm to 4 nm with respect to the middle of the cubic inclusion. The calculated binding energy, i.e., the Coulomb-coupling in the corresponding exciton depends on the actual location of the point defects and goes up to 35 meV. The relative signal intensities are weighted according to the thermal stability of the excitons at room temperature for each defect location that lead to the final ZPL distribution of the emitters in Figure 4c. The modeling results are in good agreement with the experimental data, both in terms of ZPL energies and ZPL distribution. More information about the modelling is given in the supporting information.
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Frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory

Frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory

bandwidth d ¼ 4.1 nm full-width at half-maximum (FWHM)) and a strong write pulse (800, 5 nm FWHM) are in Raman resonance with the optical phonon band (frequency 40 THz). The large detuning of both fields from the conduction band (detuning DE950 THz) allows for the storage of high-bandwidth photons, while the memory exhibits a quantum-level noise floor even at room temperature 6 . The input signal photon is stored in the memory by Raman absorption with the write pulse, creating an optical phonon. After a delay t, the read pulse annihilates the phonon and creates a modified output photon. By tuning the wavelength and bandwidth of the read pulse, we convert the wavelength of the input signal photon over a range of 17 nm as well as performing bandwidth compression to 2.2 nm and expansion to 7.6 nm (FWHM). The diamond memory is ideally suited to this task, offering low-noise frequency manipulation of THz-bandwidth quantum signals at a range of visible and near- infrared wavelengths in a robust room-temperature device 35 .
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Synthesis and single-photon emission properties of graphene quantum dots

Synthesis and single-photon emission properties of graphene quantum dots

3 Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS, Université Pierre et Marie Curie, Université Paris Diderot, PSL, Sorbonne Paris Cité, Sorbonne Université, 24, rue Lhomond, 75005 Paris, FRANCE 4 Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, GERMANY The outstanding electronic, optical and mechanical properties of graphene strongly inspire the scientific community at both the fundamental and applicative levels. However, along this way several key scientific issues have to be addressed and one of the main challenges of the field is the control and modification of graphene electronic properties, and notably the controlled opening of a sizable bandgap. For the last decade, a great attention has been paid to the size reduction of graphene using conventional top-down approaches (lithography and etching, thermal treatments and oxidation of bulk materials) to fabricate graphene quantum dots (GQDs)[1] or graphene nanoribbons (GNRs).[2] However, top-down approaches do not permit to manipulate the structure of the material at the atomic scale. In particular, they do not allow a sufficient control of the morphology and oxidation state of the edges, which drastically impact the properties. In order to truly control, with the required level of precision, the morphology and the composition of the materials and of its edges, the bottom-up approach is the relevant way to proceed[3][4].
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Microscopic theory of the optical properties of colloidal graphene quantum dots

Microscopic theory of the optical properties of colloidal graphene quantum dots

Here we present a microscopic theory of the optical properties of colloidal graphene quantum dots based on a combination of the tight-binding TB description of the pz single-electron sta[r]

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Theory of biexcitons and biexciton-exciton cascade in graphene quantum dots

Theory of biexcitons and biexciton-exciton cascade in graphene quantum dots

X + XX. Here, E XX and E GS are, respectively, the XX and GS energies. The labeling of the horizontal axis is as follows. The label vMcM corresponds to a CI subspace constructed from the first M valence and conduction states. The rest of the labels denote the choice of the cutoff parameter C for the case in which all GS + X configurations on 15 valence and 23 conduction states are taken into account while restricting the number of XX’s as described above. Since all classes of excitations, GS, X, and XX, converge at different rates, we track the convergence of the eigenvalues instead of excitation energies from the ground state. One can extrapolate converged
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