SiC Quantum Dots Research Articles

Electronic Properties of Si and C Substitutional Defects and Porosity in C‐Rich and Si‐Rich Hydrogenated Roundish SiC Quantum Dots: An Ab‐Initio Study

AbstractIn this study, SiC quantum dots (SiC‐QD's) are studied, and some roundish SiC‐QD's with the incorporation of defects by removing a carbon or silicon atom are considered. Fourteen configurations are modeled in which the position of the silicon or carbon defect for each configuration is changed, considering that due to the chemical composition, it allows more Si atoms or more C atoms on the QD surface. All calculations are performed using the Density Functional Theory (DFT) methodology. The electronic exchange correlation is treated using the Generalized Gradient Approximation (GGA) with the Revised Perdew–Burke–Ernzerhof (RPBE) functional. The electronic energy levels of each configuration are calculated as well as the partial density of states to know the origin of the energy gap in each quantum dot. The final step is to analyze the energy formation to determine chemical stability.

Determination of quantum size effect of colloidal SiC quantum dots by cyclic voltammetry

Determination of quantum size effect of colloidal SiC quantum dots by cyclic voltammetry

A theoretical study of the electronic properties of hydrogenated spherical‐like SiC quantum dots with C‐rich and Si‐rich compositions

AbstractQuantum dots have many potential applications in opto‐electronics, energy storage, catalysis, and medical diagnostics, silicon carbide quantum dots could be very attractive for many biological and technological applications due to their chemical inertness and biocompatibility, however, there are seldom theoretical studies that could boost the development of these applications. In this work, the electronic properties of hydrogenated spherical‐like SiC quantum dots with C‐rich and Si‐rich compositions are investigated using density functional theory calculations. The quantum dots are modeled by removing atoms outside a sphere from an otherwise perfect SiC crystal, the surface dangling bonds are passivated with H atoms. Our results exhibit that the electronic properties of the SiC‐QD are strongly influenced by their composition and diameter size. The energy gap is always higher than that of the crystalline SiC, making these SiC QD's suitable for applications at harsh temperatures. The density of states and the energy levels show that the Si‐rich quantum dots had a higher density of states near the conduction band minimum, which indicates better conductivity. These results could be used to tune the electronicproperties of SiC quantum dots for optoelectronic applications.

Design and mechanism insight on SiC quantum dots sensitized inverse opal TiO2 with superior photocatalytic activities under sunlight

Design and mechanism insight on SiC quantum dots sensitized inverse opal TiO2 with superior photocatalytic activities under sunlight

Native surface oxidation yields SiC-SiO2 core-shell quantum dots with improved quantum efficiency.

Silicon carbide is an important wide-bandgap semiconductor with wide applications in harsh environments and its applications rely on a reliable surface, with dry or wet oxidation to form an insulating layer at temperatures ranging from 850 to 1250 °C. Here, we report that the SiC quantum dots (QDs) with dimensions lying in the strong quantum confinement regime can be naturally oxidized at a much lower temperature of 220 °C to form core/shell and heteroepitaxial SiC/SiO2 QDs with well crystallized silica nanoshells. The surface silica layer enhances the radiative transition rate of the core SiC QD by offering an ideal carrier potential barrier and diminishes the nonradiative transition rate by reducing the surface dangling bonds, and, as a result, the quantum yield is highly improved. The SiC/SiO2 QDs are very stable in air, and they have better biocompatibility for cell-labeling than the bare SiC QDs. These results pave the way for constructing SiC-based nanoscale electronic and photonic devices.

Correction to “Core and Surface Electronic States and Phonon Modes in SiC Quantum Dots Studied by Optical Spectroscopy and Hybrid TDDFT”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to “Core and Surface Electronic States and Phonon Modes in SiC Quantum Dots Studied by Optical Spectroscopy and Hybrid TDDFT”Yuanyuan LiYuanyuan LiMore by Yuanyuan Li, Xiaoyu LiuXiaoyu LiuMore by Xiaoyu Liu, Tianyuan LiangTianyuan LiangMore by Tianyuan Liang, and Jiyang Fan*Jiyang FanMore by Jiyang Fanhttp://orcid.org/0000-0003-1894-036XCite this: J. Phys. Chem. C 2021, 125, 17, 9590Publication Date (Web):April 26, 2021Publication History Published online26 April 2021Published inissue 6 May 2021https://doi.org/10.1021/acs.jpcc.1c03357Copyright © 2021 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views311Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (426 KB) Get e-Alerts Get e-Alerts

Core and Surface Electronic States and Phonon Modes in SiC Quantum Dots Studied by Optical Spectroscopy and Hybrid TDDFT

The surface of the SiC quantum dot (QD) is a complex two-dimensional system that comprises fruitful surface reconstruction and passivation which affect its chemistry and photophysics. Here, we repo...

Fabrication and Study Properties of ZnO/SiC Quantum Dots

In this research, heterojunction was developed by using SiC quantum dots. High-quality n-ZnO film on commercial p-SiC quantum dots has been prepared based on utilizing pulse laser deposition technique and spin coating under the pressure of 10−5 mbar, deposited at room temperature on a substrate of glass at various values of the thickness (113.3 and 160) nm, respectively. Then, annealed for two hours at 450 °C. ZnO/SiC QDs were described by the estimation of XRD and FE-SEM. XRD estimation uncovered that the SiC QDs prepared by spin coating with dye were hexagonal structure. The pulse laser deposition PLD method used to make ready ZnO thin film was hexagonal wurtzite with high-quality polycrystalline. UV-Visible spectrophotometer utilized in the range of (200-800) nm to determine spectral absorbance, transmittance, and energy gap of heterojunction. The optical properties results showed that the transmittance was (98 and 87)% for ZnO film and SiC, respectively. The pure ZnO thin film allowed a direct energy gap (Eg) that was 3.8 eV, while SiC QDs were 2.65 eV direct energy gap.

Engineering silicon-carbide quantum dots for third generation photovoltaic cells.

Interested in the recent development of the building up of photovoltaic devices using graphene-like quantum dots as a novel electron acceptor; we study in this work the optoelectronic properties of edge-functionalized SiC quantum dots using the first principles density functional. For an accurate quantitative estimation of key parameters, a many-body perturbation theory within GW approximation is also performmed. We examine the ability to tailor the electronic gap and optical absorption of the new class of QDs through hydroxylation and carboxylation of seam atoms, in order to improve their photovoltaic efficiency. The HOMO-LUMO energy gap was significantly altered in terms of the type, the concentration and the position of functional groups. The spatial charge separation and charge transfer characterizing our systems seem very prominent to use as dye-sensitized solar cells. Furthermore, the optical band gap of all our compounds is in the NIR-visible energy window, and exhibits a magnitude smaller than that calculated in the pristine case, which enhances the photovoltaic efficiency. Likewise, absorption curves, exciton binding energy and singlet-triplet energy splitting have been broadly modified by functionalization confirming the great luminescent yield of SiCQDs. Depending on the size, SiC quantum dots absorb light from the visible to the near-infrared region of the solar spectrum, making them suitable for third generation solar cells.

SiC-functionalized fluorescent aptasensor for determination of Proteus mirabilis.

Aptamer-modified SiC quantum dots (DNA-SiC QDs) as fluorescent aptasensor are described for thedetermination of Proteus mirabilis. The SiC QDs were synthesized through one-pot hydrothermal method with particle sizes of about 14nm. The amino-modified aptamers against P. mirabilis were conjugated to the surfaces of SiC QDs for bacteria recognition. The aptamer with anaffinity for target protein can bound to P. mirabilis and this causes a decrease in the fluorescence intensity of DNA-SiC QDs. P. mirabilis levels were tested by the aptasensor within 35min with fluorescence excitation/emission maxima at 320/420nm. The linear range is from 103 to 108CFUmL-1 and the limit of detection is 526CFUmL-1 (S/N= 3). The aptasensor was used for determination of P. mirabilis in pure milk samples and obtained good accuracy (87.6-104.5%) and recovery rates (85-110.2%)were obtained. The detection in simulated forensic identification samples (pure milk, milk powder, blood, and urine) obtained gavesatisfactory coincidence rates with the method of bacterial isolation and identification as standard. These results demonstrate that the fluorescent aptasensor is a potential tool for identification of P. mirabilis in forensic food poisoning cases. Graphical abstract Determination of P. mirabilis is based on SiC QDs fluorescence aptasensor. The SiC QDs with plentiful carboxyl groups on the surface can be synthesized via one-pot hydrothermal route. After activated by EDC/NHS, the SiC QDs can bind to aptamer to form fluorescence aptasensors. When the target P. mirabilis exists, the fluorescence of aptasensor will be quenched and the determination of the P. mirabilis based on the fluorescence change can be analyzed.

SiC quantum dot formation in SiO2 layer using double hot-Si+/C+-ion implantation technique

We experimentally studied the material structure and photoluminescence (PL) properties of SiC quantum-dots (QD) in SiO2 layer (Si+/C+–OX) fabricated by double hot-Si+/C+ ion implantation into SiO2 and the post N2 annealing, comparing with those of SiC-dots by single hot-C+ ion implanted oxide (C+–OX) and crystal-Si layers (C+–Si). X-ray photoemission spectroscopy for Si+/C+–OX confirmed Si–C bonds even in SiO2, which is the direct verification of SiC formation in SiO2. Moreover, transmission electron microscope analyzes showed that 2 nm diameter SiC-dots with a clear lattice spots were successfully formed in Si+/C+–OX. After N2 annealing, we demonstrated strong PL emission from Si+/C+–OX, and the PL intensity IPL of Si+/C+–OX is approximately 2.6 and 12 times larger than those of C+–Si and C+–OX, respectively. The stronger IPL of Si+/C+–OX is possibly attributable to QD-induced PL-efficiency enhancement in Si+/C+–OX. Moreover, PL photon energy at the peak IPL of Si+/C+–OX rapidly increases to approximately 2.4 eV after N2 annealing.

One-step fabrication of photoluminescent SiC quantum dots through a radiation technique

The fabrication of PL SiC-QDs by using ionic liquid-based microemulsions combined with electron beam radiation.

Reversible/Irreversible Photobleaching of Fluorescent Surface Defects of SiC Quantum Dots: Mechanism and Sensing of Solar UV Irradiation

AbstractKnowledge about photobleaching properties of the fluorescent surface defects of the semiconductor quantum dots (QDs) is crucial for their applications. Here, the photobleaching properties of the fluorescent surface defects of the colloidal 3C‐SiC QDs are reported. The combined experimental and theoretical study reveals that the observed violet fluorescence at around 392 nm stems from the carboxylic acid group‐related surface defects. When the SiC QDs are exposed to the UV irradiation, the 392 nm fluorescent surface defects show both reversible and irreversible photobleaching, whereas the 438 nm fluorescent surface defects show only irreversible photobleaching. The photochemical mechanisms dominating these phenomena are explored. The photobleaching property of the SiC QDs is utilized to detect the solar UV irradiation with high accuracy. The photobleaching of the SiC QDs is highly sensitive to the hydrogen or metal ion concentration in the colloid solution. These findings deepen the understanding of the properties of the fluorescent surface defects of the SiC QDs and pave the way for their applications in sensing.

Quasi‐White Light‐Emitting Devices Based on SiC Quantum Dots

White electroluminescence based on quantum dots (QDs) is usually realized by incorporating different types of QDs or QDs plus rare earth ion phosphors into a single device. Herein, we report quasi‐white electroluminescence in pure silicon carbide QDs‐based light‐emitting devices (LEDs). The carrier transport and recombination mechanisms are investigated through analyzing the current density versus bias curves and spatial distribution of energy levels. The carrier transport mechanism is dominated by quantum tunneling at low bias and direct injection at high bias, respectively. The quasi‐white electroluminescence arises from recombination of the injected electrons and holes in the SiC QDs in the devices.

Molecular-Level Insight into How Hydroxyl Groups Boost Catalytic Activity in CO2 Hydrogenation into Methanol

Summary Exploring how hydrophilicity regulates catalytic properties at the molecular level remains a grand challenge, although it has great potential to offer guidelines for developing highly efficient catalysts and deepen the mechanistic understanding of heterogeneous catalysis. Here, we provide molecular-level insight into the influence of surface hydroxyl groups on hydrophilic SiC quantum dots (QDs) on CO 2 hydrogenation. In CO 2 hydrogenation into methanol, SiC QDs exhibited higher catalytic activity and lower activation energy than commercial SiC. Mechanistic studies revealed that the surface hydroxyl species on SiC QDs was directly involved in CO 2 hydrogenation through the addition of H atoms in hydroxyl groups into CO 2 to form HCOO* as the intermediate. The unique reaction path decreased the energy barrier for the formation of HCOO*, facilitating the activation of CO 2 . Our understanding of surface hydrophilicity directly instructs the development of efficient catalysts toward CO 2 hydrogenation.

Photoluminescent two-dimensional SiC quantum dots for cellular imaging and transport

Two-dimensional (2D) ultrathin SiC has received intense attention due to its broad band gap and resistance to large mechanical deformation and external chemical corrosion. However, the synthesis and application of ultrasmall 2D SiC quantum dots (QDs) has not been explored. Herein, we synthesize a type of monolayered 2D SiC QDs with advanced photoluminescence (PL) properties via a facile hydrothermal route. Their average size and thickness can be easily adjusted by altering the reaction time. The ultrasmall 2D SiC QDs exhibit a long fluorescence lifetime of 2.59 μs due to efficient quantum confinement. The applications of SiC QDs are demonstrated through labeling A549, HeLa, and NHDF cells and delivering agents for intracellular low-abundant microRNA (miRNA) detection. This advance in preparing photoluminescent SiC QDs is of great significance for broadening their potential in biomedical and optical applications.

Self-Trapped Exciton and Large Stokes Shift in Pristine and Carbon-Coated Silicon Carbide Quantum Dots

SiC quantum dots have potential applications in the fields of optoelectronics, biological imaging, etc. However, the theoretical studies of their optical spectra have been limited to the energy gap calculations, and the microscopic mechanism of the photoluminescence process has not been clearly understood. Here, we study the optical absorption and emission spectra for pristine and carbon-coated SiC quantum dots via time-dependent density functional tight-binding method. The results show that optical absorption spectra of pristine SiC quantum dots are generally governed by the quantum confinement effect, which however will break down for the carbon-coated SiC quantum dots. Large Stokes shift in the optical emission spectra for all quantum dots is found, which is attributed to the self-trapped exciton accompanying with stretched chemical bond. The location of self-trapped exciton and the type of stretched bond will be affected by the coated carbon shell, which can be utilized to tune the optical emission properties.

Quantum confinement effect in 6H-SiC quantum dots observed via plasmon–exciton coupling-induced defect-luminescence quenching

The quantum confinement effect is one of the crucial physical effects that discriminate a quantum material from its bulk material. It remains a mystery why the 6H-SiC quantum dots (QDs) do not exhibit an obvious quantum confinement effect. We study the photoluminescence of the coupled colloidal system of SiC QDs and Ag nanoparticles. The experimental result in conjunction with the theoretical calculation reveals that there is strong coupling between the localized electron-hole pair in the SiC QD and the localized surface plasmon in the Ag nanoparticle. It results in resonance energy transfer between them and resultant quenching of the blue surface-defect luminescence of the SiC QDs, leading to uncovering of a hidden near-UV emission band. This study shows that this emission band originates from the interband transition of the 6H-SiC QDs and it exhibits a remarkable quantum confinement effect.

Group‐IV semiconductors at the nanoscale

The European Materials Research Society's (E-MRS) spring conference was held in Lille from May 2 to May 6, 2016. The conference attracted some 3000 participants and the scientific program was divided into ∼35 parallel symposia, grouped into 5 main themes. Symposium O: Group IV semiconductors at the nanoscale – towards applications in photonics, electronics and life sciences received 106 abstracts. The symposium program was laid out on 7 half-days including 16 invited presentations, 34 contributed talks and 48 posters in one poster session. The opening, invited talk was given by Dr. Leigh Canham on nanostructured silicon for medical use. His discovery of the luminescent properties of nanoscale silicon in 1990 makes him a true legendary in the field. While this first session was devoted to nanostructures for bio applications, other sessions were focused on nanowires, biosensing, silicon and germanium nanocrystals, two-dimensional layers, nanoscale memories, carbon and SiC quantum dots, and finally, theory. The symposium was well attended with sometimes up to ∼100 attendees, but typically attracting some 30–50 people in the audience. The symposium had three sponsors. The proceedings of the symposium contains 13 papers out of 18 submitted. We had decided to select physica status solidi (a) as the journal for publishing these proceedings instead of the less strict physica status solidi (c). That demanded somewhat higher quality from the submitted papers and a reviewing process involving two referees on every paper. Jan Linnros Tom Gregorkiewicz Minoru Fujii Mark Reed

Microstructure evolution and energy band alignment at the interface of a Si-rich amorphous silicon carbide/c-Si heterostructure

The microstructure evolution of Si-rich amorphous a-SiC:H films obtained under different annealing conditions was investigated by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The influence of its microstructure on the energy band alignment at a Si-rich a-SiC:H/n-type c-Si hetero-interface was analyzed by ultraviolet visible transmission spectroscopy and ultraviolet photoelectron spectroscopy. The results revealed that the as-deposited Si-rich a-SiC:H film was mainly in an amorphous state. After annealing, Si and SiC quantum dots (QDs) formed, and the crystallinity of the QDs and the proportion of SiC QDs increased with increasing the annealing time at the same annealing temperature. It is found that the energy band alignment at the hetero-interface was influenced by the crystallinity of the films, the sizes of the QDs, and the relative proportion of Si to SiC QDs in a-SiC:H films. Moreover, the contact potential at the hetero-interface decreased with the improved crystallinity of the QDs in a-SiC:H film. The determination of energy band alignment at the Si-rich a-SiC:H/c-Si hetero-interface is beneficial to understanding the carrier transport behavior and designing hetero-structure devices.