Silicon Quantum Dots Research Articles

RETRACTED: Nanoscale silicon porous materials for efficient hydrogen storage application

The increasing energy demand and the worldwide energy crisis must be met in large part via the sustainable growth of hydrogen energy, since this economy is relied upon to provide clean and carbon-free energy carriers. It is anticipated that the growing demand for light and heavy fuel cell cars would stimulate the development of onboard solid-state hydrogen technology. The research here concentrates on the importance of various permeable substances such as polymers in general, metallic substances, and complex metal hydrides, even if Si nanostructures (SiNSs) have become known as the obvious contender for solid-state hydrogen storage systems. SiNSs have gained prominence as a leading candidate for solid-state hydrogen storage systems. Renowned for their high storage capacity, SiNSs, including silicon nanowires and quantum dots, exhibit promising potential in addressing challenges associated with traditional hydrogen storage methods, positioning them as a key player in advancing clean and efficient energy storage technologies. SiNSs play a crucial role in advancing solid-state hydrogen storage technology. SiNSs, including silicon nanowires and quantum dots, exhibit high storage capacity. Despite challenges like surface oxidation, SiNS holds promise for efficient hydrogen storage, contributing to the development of sustainable energy solutions and mitigating the environmental impact associated with conventional automotive technologies. We focus on the processes that result in permeable silicon, nanowires made of porous silicon, and Si quantum dots. This investigation elucidates the characteristics and patterns of hydrogen's aid, the value of hydrogen power in automobiles for reducing global warming occurrences, and the potential of using SiNSs for hydrogen storage in tandem with other forms of transition and alkali earth materials to meet these difficulties. It demonstrates how catalysts are critical to fixing the current reversibility and desorption problems with hydrogen energy storage. As a result of the analysis, energy suppliers and Si-based fuel cells may be better able to tailor their services to individual customers' needs, which might boost the growth of the hydrogen energy industry.

Bright silicon quantum dot synthesis and LED design: insights into size–ligand–property relationships from slow- and fast-band engineering

Abstract Multicolor, bright silicon quantum dots (SiQDs)—SiQDs with photoluminescence in a range of colors and quantum yields (PLQYs) of >90%—are promising heavy-metal-free light sources for full-color displays, lighting, and biomedical imaging. Colloidal SiQDs can be used to manufacture devices via printing and roll-to-roll processing. Furthermore, the in vivo use of biodegradable SiQDs and Si nanomaterials, for imaging cancer cells and as drug delivery systems, has been demonstrated. However, a large body of research demonstrates that the photoluminescence (PL) wavelength and PLQY of colloidal SiQDs are dependent not only on the SiQD particle size but also on the methods and/or procedures and chemical reagents used to synthesize them. This is because SiQDs are quite sensitive to both the intrinsic properties of Si and external factors. These intrinsic and external factors can be respectively linked to different PL mechanisms: the quantum confinement effect, which produces a slow-decaying “S”-band PL signal, and surface ligand effects, corresponding to fast-decaying “F”-band PL. This review focuses on mechanistic insights into the relationships linking the structures, ligands, and optical properties of SiQDs. Synthesis methods and the application performance of bright multicolor colloidal SiQDs, based on excellent state-of-the-art experimental and theoretical studies, are also reviewed.

Not all silicon quantum dots are equal: photostability of silicon quantum dots with and without a thick amorphous shell.

Luminescent colloidal silicon quantum dots (SiQDs) are sustainable alternatives to metal-based QDs for various optical applications. While the materials are reliant on their photoluminescence efficiency, the relationship between the structure and photostability of SiQDs is yet to be well studied. An amorphous silicon (a-Si) shell was recently discovered in SiQDs prepared by thermally-processed silicon oxides. As a-Si is known as a source of defects upon UV irradiation, the disordered shell could potentially have an adverse effect on the optical properties of nanoparticles. Herein, the photostability of ∼5 nm diameter SiQDs with an amorphous shell was compared with that of over-etched SiQDs of equivalent dimensions that bore an a-Si shell of negligible thickness. An UV-induced degradation study was conducted by subjecting toluene solutions of SiQDs to 365 nm light-emitting diodes (LEDs) under an inert atmosphere for predetermined times up to 72 hours. The structure, composition, and optical responses of the exposed SiQDs were evaluated.

Towards Atomic Scale Quantum Dots in Silicon: An Ultra-Efficient and Robust Subtractor Using Proposed P-Shaped Pattern

Towards Atomic Scale Quantum Dots in Silicon: An Ultra-Efficient and Robust Subtractor Using Proposed P-Shaped Pattern

Why do Si quantum dots with stronger fast emission have lower external photoluminescence quantum yield?

We explain the observed correlation of increased fast emission of quantum dots with lower photoluminescence quantum yield as selective lifetime-based quenching, or in other words, preferential switching off of quantum dots with slow emission.

Polyhedral oligomeric silsesquioxane (POSS)-silicon/carbon quantum dots nanocomposites for cell imaging.

Silicon quantum dots (SiQDs) and carbon quantum dots (CQDs) are renowned for their outstanding applications in fluorescence imaging and biosensing. However, their small size poses significant challenges in terms of preparation, collection, and purification. Polyhedral oligomeric silsesquioxanes (POSS), an organic-inorganic nanohybrid with a cage-like structure, has recently attracted considerable attention due to its excellent biocompatibility. In this research, we utilize the encapsulating properties of POSS to improve the optical property of SiQDs/CQDs through an in situ synthesis strategy, resulting in the production of blue-emitting POSS-SiQDs, green-emitting POSS-G-CNDs, and red-emitting POSS-R-CNDs. By examining their structural and optical characteristics, it is found that these hybrid materials exhibit excellent luminescent properties, biocompatibility and cell membrane permeability. This facilitates multicolor intracellular imaging and underscores their successful application in biological imaging. Our study presents a novel approach to synthesize POSS-QDs composite nanomaterials with new perspectives in biological imaging and medical diagnostics.

Alleviating the volume expansion of silicon anodes by constructing a high-strength ordered multidimensional encapsulation structure.

The application of silicon-based nanomaterials in fast-charging scenarios is hindered by volume expansion during lithiation and side reactions induced by surface effects. Constructing a robust encapsulation structure with high mechanical strength and conductivity is pivotal for optimizing the electrochemical performance of nanostructured silicon anodes. Herein, we propose a multifaceted hierarchical encapsulation structure featuring excellent mechanical strength and high conductivity by sequentially incorporating SiO x , hard carbon, and closed-pore carbon layers around silicon quantum dots, thereby enabling stable cycling at high current densities. In this structure, the ultra-thin SiO x layer strengthens the Si-C interface, while the outermost carbon matrix with closed pores functions both as a conductive network and a barrier against electrolyte intrusion. Notably, the synthesized material exhibits a specific capacity of 1506 mA h g-1 with 90.17% retention after 300 cycles at 1.0 A g-1. After 500 cycles at 5.0 A g-1, it retains 640.4 mA h g-1, over 70% of its initial capacity.

Observation of anodic electrochemiluminescence from silicon quantum dots for the detection of hydrogen peroxide.

Silicon quantum dots (QDs) with stable positively charged intermediates are prepared using chemical etching to generate strong anodic electrochemiluminescence (ECL) under a positive potential. Their surfaces could be passivated in the presence of strong oxidants, leading to enhanced ECL and offering the ability to carry out analysis for hydrogen peroxide.

Silicon nanocrystal hybrid photocatalysts as models to understand solar fuels producing assemblies

A rhenium metal complex tethered to a silicon quantum dot allows exploration of the effects of catalyst anchoring and Re–Si energetic alignment on photocatalytic CO2 reduction activity.

Cost-Effective Ultrabright Silicon Quantum Dots and Highly Efficient LEDs from Low-Carbon Hydrogen Silsesquioxane Polymers.

Cost-effective methods of synthesizing bright colloidal silicon quantum dots (SiQDs) for use as heavy-metal-free QDs, which have applications as light sources in biomedicine and displays, are required. We report simple protocols for synthesizing ultrabright colloidal SiQDs and fabricating SiQD LEDs based on hydrogen silsesquioxane (HSQ) polymer synthesis. Red photoluminescence with a quantum yield (PLQY) of 60-80% and LEDs with an external quantum efficiency (EQE) of >10% were obtained at 1/3600th of the cost of existing methods. This was achieved by using HSiCl3 and a low-polarity solvent to prepare the HSQ polymer and by optimizing the LED hole-injection layer thickness. A stochastic analysis of 31 SiQD syntheses revealed that SiQDs with the highest PLQYs were obtained from a hard, low-carbon HSQ polymer precursor containing many Si-H groups and cage structures. Notably, simple FTIR measurements predicted whether a HSQ polymer would yield high-PLQY SiQDs and high-EQE LEDs. These straightforward, cost-effective protocols should lead to advances in SiQD synthesis and LED fabrication methods.

Combination of gold nanoclusters and silicon quantum dots for ratiometric fluorometry: One system, two mechanisms

A ratiometric fluorometry based on silicon quantum dots (SiQDs) and gold nanoclusters (AuNCs) is constructed for detecting activity of butyrylcholinesterase (BChE) in human serum. By using thiobutyrylcholine iodide (BTCh) as the substrate of BChE-catalyzed hydrolysis reaction, variation of fluorescence emission from AuNCs is employed as an indicator of BChE activity since one of the hydrolysis products, thiocholine (TCh), would influence the aggregation state of AuNCs and consequently led to the change of fluorescence quantum efficiency of AuNCs. It is interesting that there are two mechanisms working for the fluorescence emission of aggregated AuNCs: aggregation-induced emission enhancement (AIEE) and aggregation-caused quenching (ACQ) with the presence of TCh at very low and higher concentration levels, respectively. Although both of these mechanisms can be utilized for sensing BChE, their opposite influence on the fluorescence emission of aggregated AuNCs should be worthy of attention, especially in the process of developing fluorescence methods for detecting trace targets by using AuNCs. In order to eliminate the fluctuation of fluorophotometer, SiQDs is chosen as the fluorophore to develop by ratiometric fluorescence methods in this work. Additionally, obvious aggregation of AuNCs induces significant decrease of inner filter effect (IFE) on the fluorescence emitted from SiQDs, while mild aggregation of AuNCs demonstrates little IFE. The linear ranges for detecting activity of BChE are 0.004 – 0.05 U/L and 0.5 – 20 U/L by ratiometric fluorometry based on the AIEE and ACQ, respectively. The very different responses originated from AIEE and ACQ of AuNCs would respectively make their own contributions to the determination of BChE activities at very low or high levels, which facilitate the developments of enhanced or quenched fluorescence methods. However, the detection of BChE activities at medium levels might suffer from the combination of AIEE and ACQ with ambiguous fractions. Therefore, it must be careful during the processes of developing and applying fluorescence methods based on the AIEE and ACQ of AuNCs, as well as the process of evaluating their analytical performance.

(Invited) Silicon Quantum Dot Single-Electron Pumps for the Closure of the Quantum Metrology Triangle

Si quantum dot (QD) devices fabricated by MOSFET technology are promising for future and ultimate quantum electronics such as quantum electrical standards and quantum computers. We have developed Si tunable-barrier QD devices with a quasi-gate-all-around (GAA) nanowire [1], which are designed to be used as basic elements such as single-electron (SE) transfer devices and qubits; the precise manipulation of charges and their states are realized in the QDs. The device is especially suitable for high-speed tunable-barrier SE pumps driven at GHz frequencies [2,3] which can generate an electric current via a single QD precisely equal to the elementary charge times the driving frequency and thereby are promising for quantum current standards [4].To achieve a high accuracy using tunable-barrier SE pumps [5-7], proper designs of device structures are required to secure robust charge quantization. The potential shape of the QD and the entrance tunnel barrier [8] are critical parameters to dictate the pump accuracy because they determine the charging energy and energy filtering effect during SE capture into the QD. Furthermore, deep understanding of electron dynamics such as mechanism crossover of the dynamical charge quantization process [9] and quantum nonadiabatic excitation [10]/electron-phonon relaxation inside the QD are important to get optimal accuracy and extend the frequency breakdown of SE pumps. We have recently developed a device simulator of Si GAA-nanowire SE pumps [11], which is a useful tool to find optimal design and control parameters in all the above-mentioned respects.One of the long-desired targets of SE pumps is to close the quantum metrology triangle (QMT) [12] by checking the consistency among three quantum electrical standards: the SE current standard, the quantum Hall resistance standard, and Josephson voltage standard (JVS). The Japanese QMT project [13] has aimed to conduct the QMT experiment with sub-ppm uncertainty in a single dilution refrigerator by placing all the quantum electric standards inside it. Our key approaches are to use quantum Hall array resistance (QHAR) [14] and parallelized Si SE pumps, which provide higher resistance and current respectively, making the generated voltage more easily compared to JVS. In the project we have succeeded in developing a current-reversal technique with electromechanical relays to cancel out the drift and low frequency noise from various sources in the measurement setup, and applying it to high accuracy measurement of current delivered by a Si SE pump [15]. We have also recently performed a comparison measurement of two Si SE pump operated in parallel and thereby have confirmed a sub-ppm level accuracy [16]. All these progresses will lead to a more precise closure of QMT at deep sub-ppm level in the new future. Si MOSFET technology continues to expand its versatility into quantum electronics technology. This work was supported by JSPS KAKENHI Grant Number JP18H05258. A. Fujiwara et al., Appl. Phys. Lett. 84, 1323 (2004); Appl. Phys. Lett. 88 053121 (2006).A. Fujiwara et al., Appl. Phys. Lett. 92, 042102 (2008)G. Yamahata et al., Appl. Phys. Lett. 106, 023112 (2015).N.-H. Kaneko et al., Meas. Sci. Technology 27 032001 (2016).B. Kaestner and V. Kashcheyevs, Rep. Prog. Phys. 78, 103901 (2015).G. Yamahata et al., Appl. Phys. Lett. 109, 013101 (2016).S. P. Giblin et al., Metrologia 56, 044004 (2019).N. Johnson et al., Appl. Phys. Lett. 115, 162103 (2019).G. Yamahata et al., Phys. Rev. B 103, 245306 (2021).G. Yamahata et al., Nat. Nanotechnol. 14, 1019 (2019).A. Fujiwara et al., in the Conference on Precision Electromagnetic Measurements (CPEM 2022).F. Piquemal and G. Genevès, Metrologia 37, 207 (2000).https://www.jsps.go.jp/file/storage/grants/j-grantsinaid/12_kiban/ichiran_30/e-data/h_30_eng_18h05258.pdf; http://www.brl.ntt.co.jp/people/afuji/kakenS/ (only in Japanese).T. Oe et al., IEEE Trans. Instrum. Meas. 66, 1475 (2017).S. Nakamura et al., IEEE Trans. Instrum. Meas, under review.S. Nakamura et al., in preparation.

Quantum Logic gate from Silicon quantum dots

Quantum Logic gate from Silicon quantum dots

Fabrication of silicon quantum dots-methyl viologen nanohybrids: Turn-On-Off-On fluorescence nanoprobe for the detection of d-penicillamine

This study provides a straightforward, one-step hydrothermal approach for synthesizing water-soluble silicon quantum dots (SiQDs). The surface of the synthesized SiQDs is modified by the carboxylic acid functional group (A:SiQDs) after succinic anhydride treatment. The modified A:SiQDs, which emitted blue light fluorescence, showed high stability against photobleaching, thermal stability, and good water solubility. The A:SiQDs are conjugated with methyl viologen (MV2+) to develop a nanohybrid for specific D-Penicillamine (D-PA) detection with an LOD of 8 nM. The suggested sensor was effectively used to analyze D-PA in commercial pharmaceutical formulations using the conventional addition method, and it produced results with good accuracy and precision that were nearly equal to those measured.

Bifunctional Silicon Quantum Dots for Antibacterial Application and Highly Sensitive Detection of Tetracycline

Bifunctional Silicon Quantum Dots for Antibacterial Application and Highly Sensitive Detection of Tetracycline

Target-Driven Annular DNA Walker Coupled with Electrochemiluminescent Silicon Quantum Dots for APE1 Bioanalysis.

Functional DNA walkers with substantial nanostructures have been extensively investigated; however, their stability still faces challenges when exposed to diverse nuclease in clinical biological samples, resulting in the unreliability of actual assessment. This work proposed a target-driven annular DNA walker with enhanced stability enabling the sensitive and reliable response to different concentrations of apurinic/apyrimidinic endonuclease 1 (APE1), by preparing silicon quantum dots (SiQDs) as electrochemiluminescence (ECL) emitters. Specifically, the SiQDs showed significant strong and stable ECL signals by purifying the microenvironment of SiQDs through the dialysis removal of the gel-like layers surrounding the SiQDs. The relative standard deviation (RSD) of their ECL signal had been improved 16.59 times under consecutive scanning compared to that of SiQDs without dialysis, demonstrating a significant improvement in ECL stability. Subsequently, in the presence of APE1, the designed annular DNA walker was activated to move along the numerous quenching probes within the continuous cross-based DNA orbits, which were immobilized to the SiQD-modified electrode, providing ECL readout signals. The linear range of this ECL biosensor was 1.0 × 10-13 U·μL-1 to 1.0 × 10-7 U·μL-1, and the limit of detection (LOD) was as low as 1.766 × 10-14 U·μL-1. This work provides a novel structure of a DNA walker with nuclease resistance for clinical sample detection and designs a new strategy for synthesizing SiQDs with favorable ECL performance, tremendously expanding the ECL application of SiQDs.

Hybrid Systems Based on Porous Silicon Photonic Crystals, Liquid Crystals, and Quantum Dots

Hybrid Systems Based on Porous Silicon Photonic Crystals, Liquid Crystals, and Quantum Dots

Simulation study on quantum dot formation of double-qubit-Si-MOS device

Silicon quantum dots (QDs) are essential physical carriers of quantum bits (qubits) in quantum computing. However, their extremely small size renders them highly sensitive to both the fabrication process and surrounding environment. Accuracy and stability must be carefully considered. In this study, we propose a double gate QD device model based on silicon metal-oxide-semiconductor (Si-MOS) for the generation of spin qubits. Using a Technology Computer Aided Design (TCAD) simulation, we investigated the impact of device dimensions, including oxide layer thickness, channel length, and spacer length, on the QD structure. Additionally, we examined the effects of the temperature and interface trap concentration on QD formation. An equivalent circuit model was employed to assess the charging energy (Ec) of QDs. Our results demonstrate that by appropriately adjusting these parameters, it is possible to achieve a QD structure with a wide level spacing and small size capable of accommodating as few as four electrons. Furthermore, we calculated an Ec of 33 meV for the QDs.

Improved optoelectrical properties for organic solar cells by introducing silicon quantum dots via eco-friendly and simple process

In this study, we synthesized eco-friendly silicon quantum dots (SiQDs) with absorption ≤400 nm and light emission of 440 nm and 500–550 nm. SiQDs were introduced into ZnO (sol-gel), an electron transport layer (ETL) of organic solar cells (OSCs) with an inverted structure.The introduction of SiQDs led to a smoother and more uniform surface morphology of the ETL. SiQDs improved the carrier mobility of the device, and increased carrier transport by reducing carrier recombination and interfacial resistance. Furthermore, SiQDs were found to convert ultraviolet (UV) light to visible light via light conversion effect. They contributed to improved JSC and FF in OSCs, and improved the power conversion efficiency (PCE) from 14.48 % to 15.31 % for the PM6:BTP-eC9 device (JSC: 24.42 mA cm−2 to 24.87 mA cm−2, FF: 73.05 %–75.23 %) and from 15.43 % to 16.3 % for the PM6:L8-BO device (JSC: 23.37 mA cm−2 to 24.57 mA cm−2, FF: 75.95 %–76.77 %).SiQD-doped ZnO, with eco-friendly synthesized SiQDs, not only improved the efficiency with the ETL of OSCs, but also demonstrated good stability.

Multi-signal aptasensor for thrombin detection based on catalytically active gold nanoparticles and fluorescent silicon quantum dots.

A multi-signal aptasensor for thrombin determination isproposed based on catalytically active gold nanoparticles (AuNPs) and fluorescent silicon quantum dots (SiQDs). Yellow 4-Nitrophenol (4-NP) could be converted to colorless 4-Aminophenol (4-AP) by catalytically active aptamer-modified AuNPs (S1-AuNPs). The SiQDs emitted strong blue fluorescence at 455nm at the excitation wavelength of 367nm. When thrombin was absent, S1-AuNPs could catalytically reduce yellow 4-NP to colorless 4-AP. When thrombin was added, the aptamer could be transformed into a G-quadruplex structure, which masked the surface-active catalytic sites of AuNPs and restrained the reduction of 4-NP. Thus, the fluorescence of SiQDs was greatly quenched by 4-NP through the inner filter effect (IFE), and the solution color remained yellow. As the concentration of thrombin increased, the catalytic activity of S1-AuNPs decreased. The concentration of 4-NP that was converted to 4-AP declined and the unconverted 4-NP increased. In this process, the absorption peak of 4-NP at 400nm increased while the fluorescence emission of SiQDs at 455nm decreased. The linear ranges of the fluorometric and colorimetric aptasensor were 0.5-30nM and 0.3-30nM, respectively. The limits of detection (LOD) for the two modes were 0.15nM and 0.13nM. Furthermore, a portable sensing platform was constructed by combining the smartphone-based device with the software ImageJ for the determination of thrombin. With the advantages of cost-effectiveness, simplicity of operation and broad applicability, this aptasensor provided a new perspective for on-site determinationof thrombin in the clinical field.