QArray: a GPU-accelerated constant capacitance model simulator for large
quantum dot arrays
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Semiconductor quantum dot arrays are a leading architecture for the development of quantum technologies. Over the years, the constant capacitance model has served as a fundamental framework for simulating, understanding, and navigating the charge stability diagrams of small quantum dot arrays. However, while the size of the arrays keeps growing, solving the constant capacitance model becomes computationally prohibitive. This paper presents an open-source software package able to compute a $100 \times 100$ pixels charge stability diagram of a 16-dot array in less than a second. Smaller arrays can be simulated in milliseconds - faster than they could be measured experimentally, enabling the creation of diverse datasets for training machine learning models and the creation of digital twins that can interface with quantum dot devices in real-time. Our software package implements its core functionalities in the systems programming language Rust and the high-performance numerical computing library JAX. The Rust implementation benefits from advanced optimisations and parallelisation, enabling the users to take full advantage of multi-core processors. The JAX implementation allows for GPU acceleration.Keywords:
Constant (computer programming)
Single dot spectroscopy is performed on two-color CdSe/ZnS/CdSe core/barrier/shell nanostructures. Unlike quantum dots cores, these systems have two phases with which to emit and ultimately examine for blinking analysis. These particles are brighter than conventional quantum dots and also show the photoluminescence (PL) intensity and energy fluctuations characteristic of quantum dots. Single dot spectral diffusion analysis yields no measureable energy shift correlation between the core and the shell on the 200 ms time scale. In contrast, the single dot PL from the CdSe shell has narrower linewidths than the CdSe core, indicating differences in its spectral diffusion on shorter timescales.
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We report here the fluorescence energy transfer between two types of inorganic semiconductor nanocrystals: one is doped (d-dots) with optically active transition metal ion and other one is the undoped quantum dots (q-dots). While the two types of undoped quantum dots do not show significant energy transfer, the doped quantum dots under similar conditions show efficient energy transfer to the undoped one. The difference in the lifetime makes the doped quantum dots as donor for quantum dots. Exploring Cu-doped and Mn-doped d-dots as donor with the suitable size of CdSe q-dots as acceptor, we report here a detailed study of d-dot to q-dot energy transfer and investigate the possible mechanism.
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Electro-absorption modulator
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It is synthesized that the CdS and CdSe quantum dots with the different sizes in the organic phase. The CdS and CdSe quantum dots were assembled into multi-layer composite nanostructures using LB technology. We also investigate the fluorescence resonance energy transfer (FRET) of the quantum dots system and the multi-layer nanostructures. The results reveal that the fluorescence intensity of CdS quantum dots comparatively weaken seriously with the complete volatilization of solvents in CdS and CdSe quantum dots hybrid solution. This results in the enhancing of the FRET rate as minishing the intervals of quantum dots. In multi-layer composite nanostructures, the fluorescence intensity of CdSe quantum dots layer en- hances with increasing the layer number of CdS quantum dots. This shows the increase of FRET rate with adding donor layers.
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Tne photoluminescence of CdSe quantum dots with different diameter were studied in toluene and on silicon substrate. Single CdSe quantum dot was prepared through a simple method, which was conformed by AFM images.
Cadmium selenide
Characterization
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Coulomb blockade
Differential capacitance
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The growth of multilayer GaSb(quantum dots)/GaAs and their luminescence property have been studied.The results show that the number of layer seems no obvious effect on the density of quantum dots.However,increasing the number of layer leads to the size of quantum dots becoming larger.Furthermore,the quantum dots accumulate as the number of QD layers reaches to a certain degree and some holes are formed in the location of the quantum dot accumulated,as the thickness of quantum dots increases there will be some holes just on the locations the quantum dots gathered.The results suggest that relatedness effect exists between each quantum layer and the GaAs covering layer can not grow well at the location of the accumulated GaSb quantum dots.As a result,the GaSb quantum dots become accumulate easier and evaporate easier in the following GaSb quantum dots grown,which will lead to the forming of the hole.The PL spectra of GaSb(quantum dots)/GaAs shows a broad photoluminescence peak of quantum dots,due to the broad distribution of the size of the quantum dots.
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Quantum dots (QDs)-based solar cells have received great attention as a cost-effective and highly efficient alternative to conventional solar cells. In addition, QDs are considered to have potential for opening a new way to utilize hot photogenerated carriers or for generating multiple charge carriers with a single photon. This thesis describes the formation of multilayer quantum dots assembly based on layer-by-layer technique and their application for quantum dot-sensitized solar cells (QDSSCs). Two different layer-by-layer (LBL) assembly methods were applied for multilayer assembly, one is based on electrostatic interaction and the other is based on metal ligand coordination.
For the electrostatic LBL assembly of quantum dots, strong polyelectrolyte quantum dots were used as assembly building units. The strong polyelectrolyte quantum dots surfaces with sulfonates or quaternary ammoniums can endow quantum dots with excellent colloidal stability independent of the pH and ionic strength and can be exploited to achieve stable and flexible electrostatic LBL assembly. To maximize the absorption of incident light and the generation of excitons by CdSe QDs within a fixed thickness of TiO2 film, a multilayer of CdSe QDs was prepared on the mesoporous TiO2 film by electrostatic LBL assembly and the experimental conditions of QD deposition were optimized by controlling the concentration of salt and repeating the LBL deposition a few times. A double-layer assembly of QDs using the electrostatic interaction is exploited for the study of Forster resonance energy transfer (FRET) in QDSSCs. Donor (overcoated CdSe/CdS/ZnS QDs) and acceptor QDs (bare CdSe QDs) are prepared with oppositely charged surface ligands. They showed energy transfer with FRET efficiency of 76% from the photoluminescence decay lifetime of donor QDs which dramatically decreased in films with acceptor QD layer. The double-layer of QDs based on energy transfer improved light harvesting by funneling photons energy from the donor QD layer to the acceptor QD layer through non-radiative transfers of the excited state energy in QDSSCs.
For the metal-ligand coordination-induced layer-by-layer assembly of quantum dots, metal chalcogenide complexes ligand modified quantum dots were used as assembly building units. Before applying metal-ligand coordination-induced assembly in QDSSCs, it was needed to replace mesoporous TiO2 to aligned 1D nanostructures since small pore size of mesoporous TiO2 make infiltration of colloidal quantum dots into mesopore structure difficult and ineffective and are easily blocked while depositing QDs. In addition, the vertically aligned 1D nanostructures, ZnO nanowires, suggested to improve electron transport by avoiding the particle-to-particle hopping or percolation through a random polycrystalline network usually happened in the mesoporous TiO2 network. The overcoating shell, TiO2, could also improve overall of photovoltaic properties reducing the recombination processes by the formation of an energy barrier at the core oxide surface or…
Layer by layer
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Lattice (music)
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Many processes of interest in quantum dots involve charge or energy transfer from one dot to another. Energy transfer in films of quantum dots as well as between linked quantum dots has been demonstrated by luminescence shift, and the ultrafast time-dependence of energy transfer processes has been resolved. Bandgap variation among dots (energy disorder) and dot separation are known to play an important role in how energy diffuses. Thus, it would be very useful if energy transfer could be visualized directly on a dot-by-dot basis among small clusters or within films of quantum dots. To that effect, we report single molecule optical absorption detected by scanning tunneling microscopy (SMA-STM) to image energy pooling from donor into acceptor dots on a dot-by-dot basis. We show that we can manipulate groups of quantum dots by pruning away the dominant acceptor dot, and switching the energy transfer path to a different acceptor dot. Our experimental data agrees well with a simple Monte Carlo lattice model of energy transfer, similar to models in the literature, in which excitation energy is transferred preferentially from dots with a larger bandgap to dots with a smaller bandgap.
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