Quantum Dots Hybrid Structures Research Articles

Tuning the SERS Capabilities of ZnO Nanowire Arrays Functionalized with Au Quantum Dots for Highly Sensitive Detection of Methylene Blue

AbstractThe development of a surface enhanced Raman scattering (SERS) substrate capable of sensing the target analyte at low concentration has always been demanding. In this prospective, ZnO−Au quantum dots (QDs) hybrid structure with tunable surface properties and high chemical stability is considered a promising material for SERS applications. Here, a novel ZnO@Au QDs hybrid structures with various amounts of Au QDs (ZnO−Aux QDs, where x=0.2, 0.4, 0.6 and 1.0) was synthesized by employing solvothermal along with electrodeposition approach. The optimized substrate, ZnO@Au QDs (0.6) exhibits excellent SERS sensitivity for the detection of MB up to 1 nM with a good reproducibility. The chemical and compositional analysis show that the surface defects are formed due to the interface interactions which not only promote charge transfer between ZnO nanowires and Au QDs complex but also enhanced the Raman scattering of target analyte. The developed substrate demonstrates excellent SERS uniformity which makes them reliable choice for the detection of multi‐analyte for practical applications.

Improved Al2O3 RRAM performance based on SiO2/MoS2 quantum dots hybrid structure

Resistive random access memory (RRAM) has attracted considerable attention due to its fast access speed and high storage density. Two different reset modes (progressive reset and abrupt reset) of RRAM have been observed previously, the former showing good uniformity but small switching window, while the latter having large switching window but poor stability and high power consumption. To overcome these limitations, an approach was proposed to control the formation and fracture of conductive filaments with interface engineering, specifically by adding a SiO2 limiting layer and MoS2 quantum dots (QDs). Modified with a SiO2/MoS2 QD hybrid structure, the Al2O3-based RRAM transforms from progressive reset mode to abrupt reset mode. The insertion not only expands the switching window by more than 100 times with excellent readability but also dramatically reduces the power consumption (<5 μW), accompanied by extremely high uniformity and reliability, which demonstrates significant potential for nonvolatile memory application. Meanwhile, the design viewpoint of combining functional layers with quantum dots provides an excellent strategy for enhancing RRAM performance in the future.

Bactericidal Activity of Multilayered Hybrid Structures Comprising Titania Nanoparticles and CdSe Quantum Dots under Visible Light.

Titania nanoparticle/CdSe quantum dot hybrid structures are a promising bactericidal coating that exhibits a pronounced effect against light-sensitive bacteria. Here, we report the results of a comprehensive study of the photophysical properties and bactericidal functionality of these hybrid structures on various bacterial strains. We found that our structures provide the efficient generation of superoxide anions under the action of visible light due to electron transfer from QDs to titania nanoparticles with ~60% efficiency. We also tested the antibacterial activity of hybrid structures on five strains of bacteria. The formed structures combined with visible light irradiation effectively inhibit the growth of Escherichia coli, Bacillus subtilis, and Mycobacterium smegmatis bacteria, the last of which is a photosensitive causative agent model of tuberculosis.

Enhancement of photodetection by PbSe quantum dots on atomic-layered GeS devices

Hybrid structures of quantum dots (QDs) on two-dimensional materials have aroused great interest because of their high absorbance properties and tunable wavelength detection ranges. In this work, 1.44 times the photoresponse bandwidth of PbSe QDs on atomic-layered GeS hybrid structure devices is achieved compared with pure GeS devices due to the transfer of photogenerated carriers between the PbSe QDs and the GeS film. A doubling of the peak photoresponsivity is obtained at a wavelength of 635 nm, and the detectivity of the hybrid devices increases by 39.5 and 27.4 times under 808 and 980 nm illumination, respectively. Additionally, tripling of the carrier mobility is measured in the hybrid devices (165.2 cm2 V−1 s−1) compared with that of pure atomic-layered GeS devices (54.2 cm2 V−1 s−1). The concentration of PbSe QDs on the GeS films is optimized for the highest photoresponsivity and carrier mobility of the hybrid devices. The results indicate that a hybrid structure of QDs on atomic-layered materials is a promising way to enhance photodetection.

Fano–Andreev and Fano–Majorana Correspondence in Quantum Dot Hybrid Structures

Fano–Andreev and Fano–Majorana Correspondence in Quantum Dot Hybrid Structures

Graphene/PbS quantum dot hybrid structure for application in near-infrared photodetectors

A graphene-PbS quantum dot (QD) composite for application in high-performance near-infrared (NIR) photodetectors (PDs) is proposed in this study. A single-layer graphene flake and oleic acid-capped PbS QD composite is fabricated through the conventional sonication process, in hexane solution. Field emission scanning electron microscopy images of the graphene-PbS QD composite dispersed on a glass substrate confirm that the composite contains both aggregated graphene flakes and single-layer graphene with wrinkles; Transmission electron microscopy images reveal close packing with uniform size. The increased absorbance and quenched photoluminescence intensity of the graphene-PbS QD composite supports enhanced photoinduced charge transfer between graphene and the PbS QDs. Moreover, the specific Raman mode of the PbS QDs, embedded in the spectrum, is enhanced by combination with graphene, which can be interpreted by SERS as relevant to the photoinduced charge transfer between the Pbs QDs and graphene. For device application, a PD structure comprised by graphene-PbS QDs is fabricated. The photocurrent of the PD is measured using a conventional probe station with a 980-nm NIR laser diode. In the fabricated PD comprising graphene-PbS QDs, five-times higher photocurrent, 22% faster rise time, and 47% faster decay time are observed, compared to that comprising PbS QDs alone. This establishes the potential of the graphene-PbS QD composite for application in ultrathin, flexible, high-performance NIR PDs.

Fabrication of hybrid graphene/CdS quantum dots film with the flexible photo-detecting performance

Abstract In this work, a flexible photodetector has been fabricated based on graphene/CdS quantum dots hybrid structures. Large area graphene film has been synthesized by chemical vapor deposited technique. After transferring it onto polyethylene terephthalate (PET) substrate, the sandwiched film of PET/graphene/PET showed high transparency. Also, using a chemical bath deposition method, a hybrid film of graphene/CdS quantum dots was successfully fabricated on the PET substrate. The in-situ growth method provides an ideal condition for CdS quantum dots crystallization, resulting in the excellent interface between the graphene and CdS quantum dots. In particular, the charge transfer and photoconductive model was analyzed by investigating the film's light history effect. The fabricated photodetector presented a high performance in visible band photodetection, creating a new opportunity for the development of the flexible, large area, and cost-effective photodetector.

Fano‐Andreev and Fano‐Majorana Correspondence in Quantum Dot Hybrid Structures

AbstractA correspondence on the single‐electron transport properties between systems of different nature, a topological quantum system and a (conventional) non‐topological one, is demonstrated. Specifically, the equivalence between the Fano resonances obtained in T‐shaped double quantum dot system coupled to a superconducting lead (QD–QD–S) and a topological superconductor ring nanowire (QD–MBSs) is presented. The non‐zero value of the Fano (anti)resonance in the conductance of the QD‐MBSs systems is shown as a consequence of a complex Fano factor , which is equivalent to the complex Fano factor of the QD–QD–S. The complex nature of is understood as a sign of a phase introduced by the superconducting lead in the QD–QD–S. It is because of this phase that the correspondence between the QD–QD–S and the QD–MBSs is possible. It is believed that these results can help to reveal the importance of the Fano interference process toward the understanding of the role of the superconductor lead in the QD–QD–S system as well as giving a clear signature of the presence of MBS's in the topological system.

Fano‐Majorana Effect and Bound States in the Continuum on a Crossbar‐Shaped Quantum Dot Hybrid Structure

AbstractTransport properties are investigated through a crossbar‐shaped structure formed by a quantum dot (QD) coupled to two normal leads and embedded between two 1D topological superconductors (TSCs). Each TSC hosts Majorana‐bound states (MBSs) at its ends, which can interact between them with an effective coupling strength. A signature of bound states in continuum (BIC) is found in the MBSs spectral function. By allowing finite inter MBSs coupling, BICs splitting is observed and shows projection in transmission for asymmetric coupling case as quasi‐BICs. As a consequence, it is also shown that the Fano effect, arising from interference phenomena between MBSs hybridization trough QD, is observed with a half‐integer amplitude modulation. It is believed that the findings can help to better understand the properties of MBSs and their interplay with QDs.

Optoelectronic properties of graphene quantum dots with molybdenum disulfide

ABSTRACTThe presence of a direct optical bandgap in the transition metal dichalcogenide (TMD) layers leads to promising applications in optoelectronic devices such as phototransistors and photodetectors. These devices are commonly fabricated using few-layer and monolayer MoS2 sheets obtained using mechanical exfoliation or chemical vapor deposition techniques. The hybrid structure of quantum dots (QDs) and 2D materials has been investigated to provide outstanding properties for various applications. Herein we report the fabrication of a hybrid QDs/MoS2 photodetector consisting of graphene quantum dots (GQDs) and multilayer MoS2 sheets. The hybrid GQDs and MoS2 films are characterized by atomic force microscopy (AFM); additionally, the I-V characteristics are measured by two-point probe station.

Red/green/blue selective phototransistors with a hybrid structure of quantum-dots and an oxide semiconductor

Color-selective phototransistors have been developed using a hybrid film of quantum-dots (QDs) and an oxide semiconductor. The zinc oxide (ZnO) phototransistor with QDs with a 2.96 eV band gap showed a photocurrent when illuminated by 450 nm light. The device with QDs with a 2.28 eV band gap started to show a photocurrent under 520 nm light, and the device with QDs with a 1.95 eV band gap showed a photocurrent under light with a wavelength of 635 nm. The photocurrent with low-energy photons, such as visible light, originated when small band-gap QDs absorbed and converted visible light into photoelectrons, and the transparent wide band-gap ZnO supplied a conductive channel in the conduction band to allow the photocurrent to flow through the device. Based on those results, we developed a color-selective phototransistor that can separate red, green, and blue light using a hybrid structure of ZnO and multilayer QDs. The device showed photoresponsivity values of 0.032, 0.053, and 0.26 mA/W to red, green, and blue light, respectively, which are different enough to distinguish the color of the visible light. Therefore, we fabricated and characterized a photogating inverter to convert the color of visible light into an electrical voltage signal. Our results show that the hybrid film of ZnO and QDs could be a feasible way to develop a highly transparent, full-color image sensor.

Plasmon-gating photoluminescence in graphene/GeSi quantum dots hybrid structures

Plasmon-gating photoluminescence in graphene/GeSi quantum dots hybrid structures

Plasmon-gating photoluminescence in graphene/GeSi quantum dots hybrid structures.

The ability to control light-matter interaction is central to several potential applications in lasing, sensing, and communication. Graphene plasmons provide a way of strongly enhancing the interaction and realizing ultrathin optoelectronic devices. Here, we find that photoluminescence (PL) intensities of the graphene/GeSi quantum dots hybrid structures are saturated and quenched under positive and negative voltages at the excitation of 325 nm, respectively. A mechanism called plasmon-gating effect is proposed to reveal the PL dependence of the hybrid structures on the external electric field. On the contrary, the PL intensities at the excitation of 405 and 795 nm of the hybrid structures are quenched due to the charge transfer by tuning the Fermi level of graphene or the blocking of the excitons recombination by excitons separation effect. The results also provide an evidence for the charge transfer mechanism. The plasmon gating effect on the PL provides a new way to control the optical properties of graphene/QD hybrid structures.

High-sensitive electrochemical sensor of Sudan I based on template-directed self-assembly of graphene-ZnSe quantum dots hybrid structure

In this work, a very sensitive electrochemical sensor for Sudan I was established based on nanohybrids of graphene-ZnSe quantum dots. Positively charged cetyltrimethyl-ammonium bromide (CTAB) functionalized graphene was used as a template-directed building block to self-assemble negatively charged ZnSe quantum dots (QDs). The hybrids of ZnSe-CTAB-graphene exhibited strong enrichment effect on Sudan I and gave superior electrocatalytic activity towards the oxidation of Sudan I. Applying differential pulse voltammetry (DPV), the peak current of Sudan I is proportional to its concentration in the range from 0.004 to 2.0μM and 2.0 to 15.0μM. This report is the first on applying graphene-ZnSe hybrids for electrochemical sensing.

Enhanced field emission of graphene–ZnO quantum dots hybrid structure

The cathode of graphene was prepared by the electrophoretic deposition (EPD) and ZnO quantum dots (QDs) were grown on the surface of graphene sheets by solution method to improve the field emission (FE) properties. The graphene/ZnO QDs hybrid emitters exhibited efficient field emission with lower turn-on field of 0.9V/μm, lower threshold field of 2.6V/μm, higher field enhancement factor of 3923 and more stable emission current stability than pristine graphene. The improved field emission performance was attributed to ZnO QDs, which introduce more defects, increase the number of emitting sites and decrease the work function. This investigation proposed that graphene/ZnO QDs composites are promising field cathodes in FE applications.

Effect of graphene on photoluminescence properties of graphene/GeSi quantum dot hybrid structures

Graphene has been discovered to have two effects on the photoluminescence (PL) properties of graphene/GeSi quantum dot (QD) hybrid structures, which were formed by covering monolayer graphene sheet on the multilayer ordered GeSi QDs sample surfaces. At the excitation of 488 nm laser line, the hybrid structure had a reduced PL intensity, while at the excitation of 325 nm, it had an enhanced PL intensity. The attenuation in PL intensity can be attributed to the transferring of electrons from the conducting band of GeSi QDs to the graphene sheet. The electron transfer mechanism was confirmed by the time resolved PL measurements. For the PL enhancement, a mechanism called surface-plasmon-polariton (SPP) enhanced absorption mechanism is proposed, in which the excitation of SPP in the graphene is suggested. Due to the resonant excitation of SPP by incident light, the absorption of incident light is much enhanced at the surface region, thus leading to more exciton generation and a PL enhancement in the region. The results may be helpful to provide us a way to improve optical properties of low dimensional surface structures.

Metal enhanced fluorescence on nanoporous gold leaf-based assay platform for virus detection

In the present study, a rapid, sensitive and quantitative detection of influenza A virus targeting hemagglutinin (HA) was developed using hybrid structure of quantum dots (QDs) and nanoporous gold leaf (NPGL). NPGL film was prepared by dealloying bimetallic film where its surface morphology and roughness were fairly controlled. Anti-influenza A virus HA antibody (ab66189) was bound with NPGL and amine (–NH2) terminated QDs. These biofunctionalized NPGL and QDs formed a complex with the influenza virus A/Beijing/262/95 (H1N1) and the photoluminescence (PL) intensities of QDs were linearly correlated with the concentrations of the virus up to 1ng/mL while no PL was observed in the absence of the virus, or in bovine serum albumin (BSA, 1µg/mL) alone. In addition, it was demonstrated that this assay detected successfully influenza virus A/Yokohama/110/2009 (H3N2) that is isolated from a clinical sample, at a concentration of ca. 50 plaque forming units (PFU)/mL. This detection limit is 2-order more sensitive than a commercially available rapid influenza diagnostic test. From these results, the proposed assay may offer a new strategy to monitor influenza virus for public health.

Strong passivation effects on the properties of an InAs surface quantum dot hybrid structure

We report on an InAs quantum dot (QD) hybrid structure with a top surface QD layer coupled to two buried QD layers that is highly sensitive to surface passivation. After 180 min of passivation, the photoluminescence (PL) peak of the surface QDs shifts from 1545 to 1275 nm while its intensity decreases by one order of magnitude. Time-resolved PL reveals a significant decrease of carrier tunneling between the QD layers because of the surface state modification by chemical treatment. A simple model with rate equations is used to explain the observed optical performance. Our results show that the optical performance of this hybrid structure is very sensitive to the surface environment, making it a potential candidate for sensing applications.

ChemInform Abstract: Optical Molecular Sensing with Semiconductor Quantum Dots (QDs)

AbstractReview: 183 refs.