We demonstrate the self-formation of hexagonal nanotemplates on GaAs (111)B substrates patterned with arrays of inverted tetrahedral pyramids during metal-organic vapor phase epitaxy and its role in producing high-symmetry, site-controlled quantum dots (QDs). By combining atomic force microscopy measurements on progressively thicker GaAs epitaxial layers with kinetic Monte Carlo growth simulations, we demonstrate self-maintained symmetry elevation of the QD formation sites from three-fold to six-fold symmetry. This symmetry elevation stems from adatom fluxes directed towards the high-curvature sites of the template, resulting in the formation of a fully three-dimensional hexagonal template after the deposition of relatively thin GaAs layers. We identified the growth conditions for consistently achieving a hexagonal pyramid bottom, which are useful for producing high-symmetry QDs for efficient generation of entangled photons.
This perspective provides an overview of the techniques that have been developed for the conjugation of DNA to colloidal quantum dots (QDs), or semiconductor nanocrystals. Methods described include: ligand exchange at the QD surface, covalent conjugation of DNA to the QD surface ligands, and one-step DNA functionalization on core QDs or during core/shell QD synthesis in aqueous solution, with an emphasis on the most recent progress in our lab. We will also discuss emerging trends in DNA-functionalized QDs for potential applications. 相似文献
We investigated the temperature-dependent resonance energy transfer (ET) from CdSe–ZnS core–shell quantum dots (QDs) to monolayer MoS2. QDs/MoS2 structures were fabricated using a spin-coating method. Photoluminescence (PL) spectra and decay curves of the QDs/MoS2 structures were measured in the temperature range of 80?400 K. The results indicate that the PL intensity of the QDs decreased approximately 81% with increasing temperature, whereas that of the MoS2 increased up to a maximum of 78% at 300 K because of the combined effect of thermal quenching and the ET in the QDs/MoS2 structures. The ET efficiency and ET rate also exhibited similar variation trends, both increased with increasing temperature from 80 to 260 K and then decreased until 400 K, resulting in a maximum ET efficiency of 22% and an ET rate of 1.17 ns–1 at ~260 K. These results are attributed to the varied distribution of the localized excitons and free excitons in the QDs/MoS2 structures with increasing temperature.
The luminescence of semiconductor quantum dots (QDs) can be adjusted using the piezotronic effect. An external mechanical force applied on the QD generates a piezoelectric potential, which alters the luminescence of the QD. A small mechanical force may induce a significant change on the emission spectrum. In the case of InN QDs, it is demonstrated that the unforced emission wavelength is more than doubled by a force of 1 μN. The strategy of using the piezotronic effect to tune the color of the emission leads to promising noncontact forcemeasurement applications in biological and medical sensors and force-sensitive displays. Several piezoelectric semiconductor materials have been investigated in terms of the tunability of the emission wavelength in the presence of an external applied force. It is found that CdS and CdSe demonstrate much higher tunability δλ/δF, which makes them suitable for micro/nano-newton force measurement applications.
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.
The development of photocatalysts that can effectively harvest visible light is essential for advances in high-efficiency solar-driven hydrogen generation. Herein, we synthesized water soluble CuInS2 (CIS) and Cu-In-Zn-S (CIZS) quantum dots (QDs) by using one-pot aqueous method. The CIZS QDs are well passivated by glutathione ligands and are highly stable in aqueous conditions. We subsequently applied these QDs as a light harvesting material for photocatalytic hydrogen generation. Unlike most small band gap materials that show extremely low efficiency, these new QDs display remarkable energy conversion efficiency in the visible and near-infrared regions. The external quantum efficiency at 650 nm is ～1.5%, which, to the best of our knowledge, is the highest value achieved until now in the near-infrared region.
In recent years, significant attention has been paid to perovskite materials. In particular, lead triiodide-based perovskites have exhibited superb optoelectronic properties. Enhancing the stability of these materials is an essential step towards large-scale applications. In this study, by simply adding trioctylphosphine (TOP) as part of the post-synthesis treatment, we significantly enhance the stability of CsPbI3 quantum dots (QDs) in the solution phase, which otherwise decay rapidly in hours. For CsPbI3 QDs treated with TOP, the absorption and photoluminescence emission properties are unchanged over the course of weeks, and the quantum yield remains almost constant at 30% even after 1 month. The morphologies of both treated and untreated QDs are initially cubic; however, the treated QDs largely maintain their initial size and shape, while the untreated ones lose size uniformity, which is a sign of degradation. Infrared spectroscopy and X-ray photoelectron spectroscopy confirm the presence of P in the TOP-treated QDs. We insights that help to resolve the intrinsic instability issue of triiodide perovskite materials and devices.
Carbon quantum dots (CQDs) have emerged as potential alternatives to classical metal-based semiconductor quantum dots (QDs) due to the abundance of their precursors, their ease of synthesis, high biocompatibility, low cost, and particularly their strong photoresponsiveness, tunability, and stability. Light is a versatile, tunable stimulus that can provide spatiotemporal control. Its interaction with CQDs elicits interesting responses such as wavelength-dependent optical emissions, charge/electron transfer, and heat generation, processes that are suitable for a range of photomediated bioapplications. The carbogenic core and surface characteristics of CQDs can be tuned through versatile engineering strategies to endow specific optical and physicochemical properties, while conjugation with specific moieties can enable the design of targeted probes. Fundamental approaches to tune the responses of CQDs to photo-interactions and the design of bionanoprobes are presented, which enable biomedical applications involving diagnostics and therapeutics. These strategies represent comprehensive platforms for engineering multifunctional probes for nanomedicine, and the design of QD probes with a range of metal-free and emerging 2D materials.
All-inorganic cesium lead halide perovskite quantum dots (QDs) have been a promising candidate for optoelectronic devices in recent years, such as light-emitting diodes, photodetectors and solar cells, owing to their superb optoelectronic properties. Still, the stability issue of nanocrystals is a bottleneck for their practical application. Herein, we report a facile method for the synthesis of a series of phosphine ligand modified CsPbBr3 QDs with high PL intensity. By introducing organic phosphine ligands, the tolerance of CsPbBr3 QDs to ethanol, water and UV light was dramatically improved. Moreover, the phosphine ligand modified QD films deposited on the glass subtracts exhibit superior PL intensity and optical stability to those of pristine QD based films.
Semiconductor quantum dots (QDs) have shown great promise as fluorescent probes for molecular, cellular and in vivo imaging. However, the fluorescence of traditional polymer-encapsulated QDs is often quenched by proton-induced etching in
acidic environments. This is a major problem for applications of QDs in the gastrointestinal tract because the gastric (stomach)
environment is strongly acidic (pH 1–2). Here we report the use of proton-resistant surface coatings to stabilize QD fluorescence
under acidic conditions. Using both hyperbranched polyethylenimine (PEI) and its polyethylene glycol derivative (PEG-grafted
PEI), we show that the fluorescence of core shell CdSe /CdS/ ZnS QDs is effectively protected from quenching in simulated
gastric fluids. In comparison, amphiphilic lipid or polymer coatings provide no protection under similarly acidic conditions.
The proton-resistant QDs are found to cause moderate membrane damage to cultured epithelial cells, but PEGylation (PEG grafting)
can be used to reduce cellular toxicity and to improve nanoparticle stability.
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We investigate the spin wave (SW) modes in high-aspect-ratio single-crystal ferromagnetic nanowires (FMNWs) using an all-optical time-resolved magnetooptical Kerr effect (TR-MOKE) microscope. The precessional magnetization dynamics in such FMNWs unveil the presence of uniform and quantized SW modes that can be tuned by varying the bias magnetic field (H). The frequencies of the modes are observed to decrease systematically with a decreasing magnetic field, and the number of modes in the spectrum is reduced from four to three for H < 0.7 kOe. To understand these results, we perform micromagnetic simulations that reveal the presence of edge, standing wave, and uniform SW modes in the nanowires (NWs). Our simulations clearly show how the standing wave and uniform SW modes coalesce to form a single mode with uniform precession over the entire NW for H < 0.7 kOe, reproducing the experimentally observed reduction in modes. Our study elucidates the possibility of manipulating the SW modes in magnetic nanostructures, which is useful for applications in magnonic and spintronic devices.
Gold nanostructures are among the noble metal nanomaterials being intensely studied due to their good biocompatibility, tunable localized surface plasmon resonance (SPR), and ease of modification. These properties give gold nanostructures many potential chemical and biomedical applications. Herein, we demonstrate the critical role of oxygen activation during the decomposition of hydrogen peroxide (H2O2) in the presence of photoexcited gold nanorods (AuNRs) by using electron spin resonance (ESR) techniques. Upon SPR excitation, O2 is activated first, and the resulting reactive intermediates further activate H2O2 to produce ?OH. The reactive intermediates exhibit singlet oxygen-like (1O2-like) reactivity, indicated by 1O2-specific oxidation reaction, quenching behaviors, and the lack of the typical 1O2 ESR signal. In addition, by using the antioxidant sodium ascorbate (NaA) as an example, we show that hydroxyl radicals from H2O2 activation can induce much stronger NaA oxidation than that in the absence of H2O2. These results may have significant biomedical implications. For example, as oxidative stress levels are known to influence tumorigenesis and cancer progression, the ability to control redox status inside tumor microenvironments using noble metal nanostructures may provide new strategies for regulating the metabolism of reactive oxygen species and new approaches for cancer treatment.
Contactless monitoring with photoelectron microspectroscopy of the surface potential along individual nanostructures, created by the X-ray nanoprobe, opens exciting possibilities to examine quantitatively size- and surface-chemistry-effects on the electrical transport of semiconductor nanowires (NWs). Implementing this novel approach-which combines surface chemical microanalysis with conductivity measurements-we explored the dependence of the electrical properties of undoped GaAs NWs on the NW width, temperature and surface chemistry. By following the evolution of the Ga 3d and As 3d core level spectra, we measured the position-dependent surface potential along the GaAs NWs as a function of NW diameter, decreasing from 120 to ?20 nm, and correlated the observed decrease of the conductivity with the monotonic reduction in the NW diameter from 120 to ~20 nm. Exposure of the GaAs NWs to oxygen ambient leads to a decrease in their conductivity by up to a factor of 10, attributed to the significant decrease in the carrier density associated with the formation of an oxide shell. Open image in new window相似文献
Recent theoretical studies revealed that two-dimensional (2D) antimonene has attractive characteristics, such as superior photothermal conductivity, absorption over a wide range, high mobility, and good spintronic properties. Herein, we report a reliable liquid phase exfoliation (LPE) route for the preparation of high-quality high-stability atomically thin (AT) antimonene via high ultrasonic power. The AT antimonene delivers a high specific capacity of up to 860 mA·h·g–1, with high rate capability and good cycling stability as an anode of a sodium ion battery (SIB). The good conductivity and 2D structure endow AT antimonene with more active sites for sodium storage, a facilitated pathway for electron transfer and mass transport, and the capability to reduce the volume expansion during the discharge–charge process.
Nanosized metal (Pt or Pd)-decorated TiO2 nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO2 NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO2 under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO2 NFs were found to exhibit enhanced performance compared to Pt-decorated TiO2 NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO2 NFs exhibited higher selectivity for methanol, typically producing ～90 ppmg?1·h?1 methanol. The CO2 photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations.
The extinction coefficient of semiconductor nanocrystals is a key parameter for understanding both the quantum confinement and applications of the nanocrystals. The existing extinction coefficients of CdE (E = Se, S) nanocrystals were found to have an unacceptable deviation for the zinc-blende CdE quantum dots (QDs). The analysis reveals that, in addition to the interference of impurities, the commonly applied extinction coefficient per CdE nanocrystal is sensitive to the size, shape, and density of the surface ligands of nanocrystals. The extinction coefficient per CdE unit does not depend on accurate information of the size, shape, and number of surface ligands of the nanocrystals. A new three-step purification scheme was developed to investigate three classes of possible impurities for accurate determination of the extinction coefficient per CdE unit, including CdE clusters not considered previously. Given that the sole ligands of zinc-blende CdE nanocrystals are cadmium fatty acid salts (CdFa2), a universal formula for the nanocrystals can be written as (CdE)n(CdFa2)m. The n:m ratio was accurately determined for purified nanocrystals. The resulting extinction coefficients per unit for both CdSe and CdS QDs were found to decrease exponentially as the size of the QDs increases, with the corresponding bulk value as the large-size limit.
The development of high-resolution nanosized photoacoustic contrast agents is an exciting yet challenging technological advance. Herein, antibody (breast cancer-associated antigen 1 (Brcaa1) monoclonal antibody)- and peptide (RGD)-functionalized gold nanoprisms (AuNprs) were used as a combinatorial methodology for in situ photoacoustic imaging, angiography, and localized hyperthermia using orthotopic and subcutaneous murine gastric carcinoma models. RGD-conjugated PEGylated AuNprs are available for tumor angiography, and Brcaa1 monoclonal antibody-conjugated PEGylated AuNprs are used for targeting and for in situ imaging of gastric carcinoma in orthotopic tumor models. In situ photoacoustic imaging allowed for anatomical and functional imaging at the tumor site. In vivo tumor angiography imaging showed enhancement of the photoacoustic signal in a time-dependent manner. Furthermore, photoacoustic imaging demonstrated that tumor vessels were clearly damaged after localized hyperthermia. This is the first proof-of-concept using two AuNprs probes as highly sensitive contrasts and therapeutic agents for in situ tumor detection and inhibition. These smart antibody/peptide AuNprs can be used as an efficient nanotheranostic platform for in vivo tumor detection with high sensitivity, as well as for tumor targeting therapy, which, with a single-dose injection, results in tumor size reduction and increases mice survival after localized hyperthermia treatment.
Superconducting spin valves based on the superconductor/ferromagnet (S/F) proximity effect are considered to be a key element in the emerging field of superconducting spintronics. Here, we demonstrate the crucial role of the morphology of the superconducting layer in the operation of a multilayer S/F1/F2 spin valve. We study two types of superconducting spin valve heterostructures, with rough and with smooth superconducting layers, using transmission electron microscopy in combination with transport and magnetic characterization. We find that the quality of the S/F interface is not critical for the S/F proximity effect, as regards the suppression of the critical temperature of the S layer. However, it appears to be of paramount importance in the performance of the S/F1/F2 spin valve. As the morphology of the S layer changes from the form of overlapping islands to a smooth case, the magnitude of the conventional superconducting spin valve effect significantly increases. We attribute this dramatic effect to a homogenization of the Green function of the superconducting condensate over the S/F interface in the S/F1/F2 valve with a smooth surface of the S layer.
Nanoparticle quantum dots (QDs) are ideal materials for multiplexed biomarker detection, localization, and quantification.
Both direct and indirect methods are available for QD-based immunohistofluorescence (QD-IHF) staining; the direct method,
however, has been considered laborious and costly. In this study, we optimized and compared the indirect QD-IHF single staining
procedure using QD-secondary antibody conjugates and QD-streptavidin conjugates. Problems associated with sequential multiplex
staining were identified quantitatively. A method using a QD cocktail solution was developed allowing simultaneous staining
with three antibodies against E-cadherin, epidermal growth factor receptor and β-catenin in formalin-fixed and paraffin-embedded
(FFPE) tissues. The expression of each biomarker was quantified by using the cocktail and the sequential methods. Comparison
of the two methods demonstrated that the cocktail method provided more consistent and stable QD signals for each multiplexed
biomarker than the sequential method, and provides a convenient tool for multiplexing biomarkers in both research and clinical
applications.
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Identification of atomic disorders and their subsequent control has proven to be a key issue in predicting, understanding, and enhancing the properties of newly emerging topological insulator materials. Here, we demonstrate direct evidence of the cation antisites in single-crystal SnBi2Te4 nanoplates grown by chemical vapor deposition, through a combination of sub-ångström-resolution imaging, quantitative image simulations, and density functional theory calculations. The results of these combined techniques revealed a recognizable amount of cation antisites between Bi and Sn, and energetic calculations revealed that such cation antisites have a low formation energy. The impact of the cation antisites was also investigated by electronic structure calculations together with transport measurement. The topological surface properties of the nanoplates were further probed by angle-dependent magnetotransport, and from the results, we observed a two-dimensional weak antilocalization effect associated with surface carriers. Our approach provides a pathway to identify the antisite defects in ternary chalcogenides and the application potential of SnBi2Te4 nanostructures in next-generation electronic and spintronic devices.
