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14 pages, 2297 KiB

Open AccessEditor’s ChoiceArticle

Sub-Bandgap Sensitization of Perovskite Semiconductors via Colloidal Quantum Dots Incorporation

by G. Ribeiro, G. Ferreira, U. D. Menda, M. Alexandre, M. J. Brites, M. A. Barreiros, S. Jana, H. Águas, R. Martins, P. A. Fernandes, P. Salomé and M. J. Mendes

Nanomaterials 2023, 13(17), 2447; https://doi.org/10.3390/nano13172447 - 29 Aug 2023

Viewed by 1367

Abstract

By taking advantage of the outstanding intrinsic optoelectronic properties of perovskite-based photovoltaic materials, together with the strong near-infrared (NIR) absorption and electronic confinement in PbS quantum dots (QDs), sub-bandgap photocurrent generation is possible, opening the way for solar cell efficiencies surpassing the classical [...] Read more.

By taking advantage of the outstanding intrinsic optoelectronic properties of perovskite-based photovoltaic materials, together with the strong near-infrared (NIR) absorption and electronic confinement in PbS quantum dots (QDs), sub-bandgap photocurrent generation is possible, opening the way for solar cell efficiencies surpassing the classical limits. The present study shows an effective methodology for the inclusion of high densities of colloidal PbS QDs in a MAPbI₃ (methylammonium lead iodide) perovskite matrix as a means to enhance the spectral window of photon absorption of the perovskite host film and allow photocurrent production below its bandgap. The QDs were introduced in the perovskite matrix in different sizes and concentrations to study the formation of quantum-confined levels within the host bandgap and the potential formation of a delocalized intermediate mini-band (IB). Pronounced sub-bandgap (in NIR) absorption was optically confirmed with the introduction of QDs in the perovskite. The consequent photocurrent generation was demonstrated via photoconductivity measurements, which indicated IB establishment in the films. Despite verifying the reduced crystallinity of the MAPbI₃ matrix with a higher concentration and size of the embedded QDs, the nanostructured films showed pronounced enhancement (above 10-fold) in NIR absorption and consequent photocurrent generation at photon energies below the perovskite bandgap. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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24 pages, 11377 KiB

Open AccessArticle

Reversible Quantum-Dot Cellular Automata-Based Arithmetic Logic Unit

by Mohammed Alharbi, Gerard Edwards and Richard Stocker

Nanomaterials 2023, 13(17), 2445; https://doi.org/10.3390/nano13172445 - 29 Aug 2023

Cited by 6 | Viewed by 1778

Abstract

Quantum-dot cellular automata (QCA) are a promising nanoscale computing technology that exploits the quantum mechanical tunneling of electrons between quantum dots in a cell and electrostatic interaction between dots in neighboring cells. QCA can achieve higher speed, lower power, and smaller areas than [...] Read more.

Quantum-dot cellular automata (QCA) are a promising nanoscale computing technology that exploits the quantum mechanical tunneling of electrons between quantum dots in a cell and electrostatic interaction between dots in neighboring cells. QCA can achieve higher speed, lower power, and smaller areas than conventional, complementary metal-oxide semiconductor (CMOS) technology. Developing QCA circuits in a logically and physically reversible manner can provide exceptional reductions in energy dissipation. The main challenge is to maintain reversibility down to the physical level. A crucial component of a computer’s central processing unit (CPU) is the arithmetic logic unit (ALU), which executes multiple logical and arithmetic functions on the data processed by the CPU. Current QCA ALU designs are either irreversible or logically reversible; however, they lack physical reversibility, a crucial requirement to increase energy efficiency. This paper shows a new multilayer design for a QCA ALU that can carry out 16 different operations and is both logically and physically reversible. The design is based on reversible majority gates, which are the key building blocks. We use QCADesigner-E software to simulate and evaluate energy dissipation. The proposed logically and physically reversible QCA ALU offers an improvement of 88.8% in energy efficiency. Compared to the next most efficient 16-operation QCA ALU, this ALU uses 51% fewer QCA cells and 47% less area. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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11 pages, 6055 KiB

Open AccessArticle

Colloidal Quantum Dot Nanolithography: Direct Patterning via Electron Beam Lithography

by Taewoo Ko, Samir Kumar, Sanghoon Shin, Dongmin Seo and Sungkyu Seo

Nanomaterials 2023, 13(14), 2111; https://doi.org/10.3390/nano13142111 - 20 Jul 2023

Viewed by 1615

Abstract

Micro/nano patterns based on quantum dots (QDs) are of great interest for applications ranging from electronics to photonics to sensing devices for biomedical purposes. Several patterning methods have been developed, but all lack the precision and reproducibility required to fabricate precise, complex patterns [...] Read more.

Micro/nano patterns based on quantum dots (QDs) are of great interest for applications ranging from electronics to photonics to sensing devices for biomedical purposes. Several patterning methods have been developed, but all lack the precision and reproducibility required to fabricate precise, complex patterns of less than one micrometer in size, or require specialized crosslinking ligands, limiting their application. In this study, we present a novel approach to directly pattern QD nanopatterns by electron beam lithography using commercially available colloidal QDs without additional modifications. We have successfully generated reliable dot and line QD patterns with dimensions as small as 140 nm. In addition, we have shown that using a 10 nm SiO₂ spacer layer on a 50 nm Au layer substrate can double the fluorescence intensity compared to QDs on the Au layer without SiO₂. This method takes advantage of traditional nanolithography without the need for a resist layer. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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10 pages, 2263 KiB

Open AccessArticle

Quantum-Dot-Induced Modification of Surface Functionalization for Active Applications of Whispering Gallery Mode Resonators

by Inga Brice, Vyacheslav V. Kim, Armands Ostrovskis, Arvids Sedulis, Toms Salgals, Sandis Spolitis, Vjaceslavs Bobrovs, Janis Alnis and Rashid A. Ganeev

Nanomaterials 2023, 13(13), 1997; https://doi.org/10.3390/nano13131997 - 3 Jul 2023

Viewed by 1094

Abstract

Quantum dots can modify the properties of the whispering gallery mode resonators (WGMRs) used in various potential applications. A deposition of a suitable nanomaterial for the surface functionalization of WGMRs allows for the achievement of high quality (Q) factors. Here, we show that [...] Read more.

Quantum dots can modify the properties of the whispering gallery mode resonators (WGMRs) used in various potential applications. A deposition of a suitable nanomaterial for the surface functionalization of WGMRs allows for the achievement of high quality (Q) factors. Here, we show that the WGMR surface can be functionalized using quantum dots. We demonstrate that WGMRs covered with thin layers of HgS and PbS quantum dots are suitable for third-harmonic generation due to the high Q factor of the developed microresonators, thus significantly lowering the pumping power required for nonlinear optical interactions. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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9 pages, 2784 KiB

Open AccessArticle

Annealing-Modulated Surface Reconstruction for Self-Assembly of High-Density Uniform InAs/GaAs Quantum Dots on Large Wafers Substrate

by Xiangjun Shang, Xiangbin Su, Hanqing Liu, Huiming Hao, Shulun Li, Deyan Dai, Mifeng Li, Ying Yu, Yu Zhang, Guowei Wang, Yingqiang Xu, Haiqiao Ni and Zhichuan Niu

Nanomaterials 2023, 13(13), 1959; https://doi.org/10.3390/nano13131959 - 28 Jun 2023

Viewed by 1009

Abstract

In this work, we developed pre-grown annealing to form β2 reconstruction sites among β or α (2 × 4) reconstruction phase to promote nucleation for high-density, size/wafer-uniform, photoluminescence (PL)-optimal InAs quantum dot (QD) growth on a large GaAs wafer. Using this, the QD [...] Read more.

In this work, we developed pre-grown annealing to form β2 reconstruction sites among β or α (2 × 4) reconstruction phase to promote nucleation for high-density, size/wafer-uniform, photoluminescence (PL)-optimal InAs quantum dot (QD) growth on a large GaAs wafer. Using this, the QD density reached 580 (860) μm⁻² at a room-temperature (T) spectral FWHM of 34 (41) meV at the wafer center (and surrounding) (high-rate low-T growth). The smallest FWHM reached 23.6 (24.9) meV at a density of 190 (260) μm⁻² (low-rate high-T). The mediate rate formed uniform QDs in the traditional β phase, at a density of 320 (400) μm⁻² and a spectral FWHM of 28 (34) meV, while size-diverse QDs formed in β2 at a spectral FWHM of 92 (68) meV and a density of 370 (440) μm⁻². From atomic-force-microscope QD height distribution and T-dependent PL spectroscopy, it is found that compared to the dense QDs grown in β phase (mediate rate, 320 μm⁻²) with the most large dots (240 μm⁻²), the dense QDs grown in β2 phase (580 μm⁻²) show many small dots with inter-dot coupling in favor of unsaturated filling and high injection to large dots for PL. The controllable annealing (T, duration) forms β2 or β2-mixed α or β phase in favor of a wafer-uniform dot island and the faster T change enables optimal T for QD growth. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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13 pages, 2137 KiB

Open AccessArticle

Model of a GaAs Quantum Dot in a Direct Band Gap AlGaAs Wurtzite Nanowire

by Daniele Barettin, Igor V. Shtrom, Rodion R. Reznik and George E. Cirlin

Nanomaterials 2023, 13(11), 1737; https://doi.org/10.3390/nano13111737 - 25 May 2023

Viewed by 1489

Abstract

We present a study with a numerical model based on

\vec{k} \cdot \vec{p}

, including electromechanical fields, to evaluate the electromechanical and optoelectronic properties of single GaAs quantum dots embedded in direct band gap AlGaAs nanowires. The geometry and the dimensions [...] Read more.

We present a study with a numerical model based on

\vec{k} \cdot \vec{p}

, including electromechanical fields, to evaluate the electromechanical and optoelectronic properties of single GaAs quantum dots embedded in direct band gap AlGaAs nanowires. The geometry and the dimensions of the quantum dots, in particular the thickness, are obtained from experimental data measured by our group. We also present a comparison between the experimental and numerically calculated spectra to support the validity of our model. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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15 pages, 895 KiB

Open AccessArticle

Parabolic–Gaussian Double Quantum Wells under a Nonresonant Intense Laser Field

by Esin Kasapoglu, Melike Behiye Yücel and Carlos A. Duque

Nanomaterials 2023, 13(8), 1360; https://doi.org/10.3390/nano13081360 - 14 Apr 2023

Cited by 3 | Viewed by 1504

Abstract

In this paper, we investigate the electronic and optical properties of an electron in both symmetric and asymmetric double quantum wells that consist of a harmonic potential with an internal Gaussian barrier under a nonresonant intense laser field. The electronic structure was obtained [...] Read more.

In this paper, we investigate the electronic and optical properties of an electron in both symmetric and asymmetric double quantum wells that consist of a harmonic potential with an internal Gaussian barrier under a nonresonant intense laser field. The electronic structure was obtained by using the two-dimensional diagonalization method. To calculate the linear and nonlinear absorption, and refractive index coefficients, a combination of the standard density matrix formalism and the perturbation expansion method was used. The obtained results show that the electronic and thereby optical properties of the considered parabolic–Gaussian double quantum wells could be adjusted to obtain a suitable response to specific aims with parameter alterations such as well and barrier width, well depth, barrier height, and interwell coupling, in addition to the applied nonresonant intense laser field. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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10 pages, 1375 KiB

Open AccessArticle

Core and Shell Contributions to the Phonon Spectra of CdTe/CdS Quantum Dots

by Volodymyr Dzhagan, Nazar Mazur, Olga Kapush, Oleksandr Selyshchev, Anatolii Karnaukhov, Oleg A. Yeshchenko, Mykola I. Danylenko, Volodymyr Yukhymchuk and Dietrich R. T. Zahn

Nanomaterials 2023, 13(5), 921; https://doi.org/10.3390/nano13050921 - 1 Mar 2023

Cited by 1 | Viewed by 1869

Abstract

The parameters of the shell and interface in semiconductor core/shell nanocrystals (NCs) are determinant for their optical properties and charge transfer but are challenging to be studied. Raman spectroscopy was shown earlier to be a suitable informative probe of the core/shell structure. Here, [...] Read more.

The parameters of the shell and interface in semiconductor core/shell nanocrystals (NCs) are determinant for their optical properties and charge transfer but are challenging to be studied. Raman spectroscopy was shown earlier to be a suitable informative probe of the core/shell structure. Here, we report the results of a spectroscopic study of CdTe NCs synthesized by a facile route in water, using thioglycolic acid (TGA) as a stabilizer. Both core-level X-ray photoelectron (XPS) and vibrational (Raman and infrared) spectra show that using thiol during the synthesis results in the formation of a CdS shell around the CdTe core NCs. Even though the spectral positions of the optical absorption and photoluminescence bands of such NCs are determined by the CdTe core, the far-infrared absorption and resonant Raman scattering spectra are dominated by the vibrations related with the shell. The physical mechanism of the observed effect is discussed and opposed to the results reported before for thiol-free CdTe Ns as well as CdSe/CdS and CdSe/ZnS core/shell NC systems, where the core phonons were clearly detected under similar experimental conditions. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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20 pages, 3622 KiB

Open AccessArticle

Structural Properties and Energy Spectrum of Novel GaSb/AlP Self-Assembled Quantum Dots

by Demid S. Abramkin, Mikhail O. Petrushkov, Dmitrii B. Bogomolov, Eugeny A. Emelyanov, Mikhail Yu. Yesin, Andrey V. Vasev, Alexey A. Bloshkin, Eugeny S. Koptev, Mikhail A. Putyato, Victor V. Atuchin and Valery V. Preobrazhenskii

Nanomaterials 2023, 13(5), 910; https://doi.org/10.3390/nano13050910 - 28 Feb 2023

Cited by 6 | Viewed by 1745

Abstract

In this work, the formation, structural properties, and energy spectrum of novel self-assembled GaSb/AlP quantum dots (SAQDs) were studied by experimental methods. The growth conditions for the SAQDs’ formation by molecular beam epitaxy on both matched GaP and artificial GaP/Si substrates were determined. [...] Read more.

In this work, the formation, structural properties, and energy spectrum of novel self-assembled GaSb/AlP quantum dots (SAQDs) were studied by experimental methods. The growth conditions for the SAQDs’ formation by molecular beam epitaxy on both matched GaP and artificial GaP/Si substrates were determined. An almost complete plastic relaxation of the elastic strain in SAQDs was reached. The strain relaxation in the SAQDs on the GaP/Si substrates does not lead to a reduction in the SAQDs luminescence efficiency, while the introduction of dislocations into SAQDs on the GaP substrates induced a strong quenching of SAQDs luminescence. Probably, this difference is caused by the introduction of Lomer 90°-dislocations without uncompensated atomic bonds in GaP/Si-based SAQDs, while threading 60°-dislocations are introduced into GaP-based SAQDs. It was shown that GaP/Si-based SAQDs have an energy spectrum of type II with an indirect bandgap and the ground electronic state belonging to the X-valley of the AlP conduction band. The hole localization energy in these SAQDs was estimated equal to 1.65–1.70 eV. This fact allows us to predict the charge storage time in the SAQDs to be as long as >>10 years, and it makes GaSb/AlP SAQDs promising objects for creating universal memory cells. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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Review

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40 pages, 9793 KiB

Open AccessEditor’s ChoiceReview

Direct Optical Patterning of Quantum Dots: One Strategy, Different Chemical Processes

by Francesco Antolini

Nanomaterials 2023, 13(13), 2008; https://doi.org/10.3390/nano13132008 - 5 Jul 2023

Viewed by 1763

Abstract

Patterning, stability, and dispersion of the semiconductor quantum dots (scQDs) are three issues strictly interconnected for successful device manufacturing. Recently, several authors adopted direct optical patterning (DOP) as a step forward in photolithography to position the scQDs in a selected area. However, the [...] Read more.

Patterning, stability, and dispersion of the semiconductor quantum dots (scQDs) are three issues strictly interconnected for successful device manufacturing. Recently, several authors adopted direct optical patterning (DOP) as a step forward in photolithography to position the scQDs in a selected area. However, the chemistry behind the stability, dispersion, and patterning has to be carefully integrated to obtain a functional commercial device. This review describes different chemical strategies suitable to stabilize the scQDs both at a single level and as an ensemble. Special attention is paid to those strategies compatible with direct optical patterning (DOP). With the same purpose, the scQDs’ dispersion in a matrix was described in terms of the scQD surface ligands’ interactions with the matrix itself. The chemical processes behind the DOP are illustrated and discussed for five different approaches, all together considering stability, dispersion, and the patterning itself of the scQDs. Full article

(This article belongs to the Special Issue Study on Quantum Dot and Quantum Dot-Based Device)

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