Metal-semiconductor Nanostructures Research Articles

All-optical generation of static electric field in a single metal-semiconductor nanoantenna

Electric field is a powerful instrument in nanoscale engineering, providing wide functionalities for control in various optical and solid-state nanodevices. The development of a single optically resonant nanostructure operating with a charge-induced electrical field is challenging, but it could be extremely useful for novel nanophotonic horizons. Here, we show a resonant metal-semiconductor nanostructure with a static electric field created at the interface between its components by charge carriers generated via femtosecond laser irradiation. We study this field experimentally, probing it by second-harmonic generation signal, which, in our system, is time-dependent and has a non-quadratic signal/excitation power dependence. The developed numerical models reveal the influence of the optically induced static electric field on the second harmonic generation signal. We also show how metal work function and silicon surface defect density for different charge carrier concentrations affect the formation of this field. We estimate the value of optically-generated static electric field in this nanoantenna to achieve ≈108V/m. These findings pave the way for the creation of nanoantenna-based optical memory, programmable logic and neuromorphic devices.

Plasmonic Nanocrystal Assembly-Semiconductor Hybrids for Boosting Visible to Near-Infrared Photocatalysis.

Plasmonic metal-semiconductor hybrid photocatalysts have received much attention because of their wide light harvesting range and efficient charge carrier generation capability originating from plasmon energy transfer. Here, we introduce a plasmonic metal-semiconductor hybrid nanostructure consisting of a Au core-satellite assembly and crystalline TiO2. The formation of Au@TiO2-Au core-satellite assemblies using TiO2 as a spacer and the subsequent growth of outer TiO2 shells on the core-satellite assemblies, followed by calcination, successfully generated Au core-satellite assembly@TiO2 nanostructures. Exquisite control over the growth of the TiO2 interlayer enabled the regulation of the gap distance between the core and satellite Au nanocrystals within the same hybrid morphology. Due to the structural controllability of the present approach, the gap-distance-dependent plasmonic and photocatalytic properties of the hybrid nanostructures could be explored. The nanostructures possessing the most closely arranged Au nanocrystals showed high photocatalytic activity under visible to near-infrared light irradiation, which can be attributed to strong plasmon coupling between the core and satellite Au nanocrystals that can expedite the formation of intense plasmon energy and its transfer to TiO2.

The influence of the size of a one-faced metallic head in Janus nanoparticles as a co-catalyst on the photocatalytic efficiency of hydrogen evolution under vis light irradiation

Janus nanoparticles (NPs) consisting of MoOxSy nanospheres and silver (Ag) head, successfully developed by a simple, controlled method were in the first time they were applied as a co-catalysts in photocatalytic hydrogen generation reaction under vis light irradiation (λ > 420 nm). The MoOxSy-Ag as a co-catalysts were deposited on the obtained ZnIn2S4 microspheres (ZIS) using physical absorption method. The influence of the size of a one-faced metallic head (Ag) in JNPs as a co-catalyst on the photocatalytic efficiency of hydrogen evolution has been investigated. Sample 2.5-Ag-MoOxSy@ZIS with the co-catalyst with the smallest head in the range of about 61–71 nm was characterized by 34 times higher photocatalytic hydrogen generation activity compared to pure ZIS. JNPs as a co-catalyst are characterized as asymmetric structure and precisely adjusted interface and thus, they influence on a very good electron mobility in hybrid metal-semiconductor nanostructures. JNPs can be a new alternativity to metal co-catalysts used in a photocatalytic hydrogen production reaction.

Tuning Geometric Chirality in Metallic and Hybrid Nanostructures by Controlled Nanoscale Crystal Symmetry Breaking.

Understanding and controlling chirality in inorganic crystalline materials at the nanoscale is crucial in elucidating fundamental chirality-dependent physical and chemical processes as well as advancing new technological prospects, but significant challenges remain due to the lack of material control. Here, we have developed a facile and general bottom-up synthetic strategy for achieving chiral plasmonic Au nanostructures, including nanocubes and nanorods with fine chirality control. The underlying chiral mechanism enabled by the chiral boundary morphology is substantiated by theoretical modeling and finite element method (FEM) simulation. Because of the robustness of induced handedness and their small size, these as-synthesized chiral nanostructures can be further employed as building blocks toward the formation of complex chiral nanostructures. We have demonstrated a new class of chiral hybrid metal-semiconductor nanostructures that can allow integration of chirality with other properties and functionalities. All of these together have paved the way to engineer nanoscale inorganic chirality and thus study various emerging chirality-entangled effects with practical technological applications.

Engineering of plasmonic metal-semiconductor yolk-shell nanostructures for multi-intensified photodynamic- and immuno- therapy against drug resistant bacteria

Photodynamic therapy (PDT) as well as immunotherapy are effective therapies to combat the systemic infection. Nevertheless, the development of the treatments are restrained by the lack of efficient photosensitizers (PS) and the genetic diversity of the bacteria. Here, we report Ag doped Au-CdS1−ySey yolk-shell nanostructures (AYSs) which exhibit excellent near-infrared (NIR) light induced PDT and immunotherapy performance. The tailored plasmonic Au nanorods (NRs) are able to gather the NIR light, offering the basis for PDT. Moreover, high yield of reactive oxygen species (ROS) is achieved through the following creativity: i) enhanced light trapping ability by the microcavity, ii) smooth injection process of hot electrons (HEs) by the suitable band gap alignment, iii) inhibiting the combination of electric charges by the doped Ag with appropriate concentration. Therefore, the AYSs exhibit more 30 times of ROS production as well as lower 64 times of MIC than the conventional core-shell nanostructures. Notably, repeated enhanced antibacterial PDT are carried out to obtain versatile antigens from various dead bacteria to awaken the immune cells adequately and boost immune response with the help of Selenium (Se) which is distributed in the shell. As a result, the systemic drug resistant bacterial infection is cured successfully.

Optimal Geometry for Plasmonic Hot-Carrier Extraction in Metal-Semiconductor Nanocrystals.

Plasmon-induced energy and charge transfer from metal nanostructures hold great potential for harvesting solar energy. Presently, the efficiencies of charge-carrier extraction are still low due to the competitive ultrafast mechanisms of plasmon relaxation. Using single-particle electron energy loss spectroscopy, we correlate the geometrical and compositional details of individual nanostructures to their carrier extraction efficiencies. By removing ensemble effects, we are able to show a direct structure-function relationship that permits the rational design of the most efficient metal-semiconductor nanostructures for energy harvesting applications. In particular, by developing a hybrid system comprising Au nanorods with epitaxially grown CdSe tips, we are able to control and enhance charge extraction. We show that optimal structures can have efficiencies as high as 45%. The quality of the Au-CdSe interface and the dimensions of the Au rod and CdSe tip are shown to be critical for achieving these high efficiencies of chemical interface damping.

A comparative study of photocatalytic activity of Na+-Ag+ ion-exchanged glass-ceramics with metallic Ag, semiconductor AgBr, and hybrid Ag-AgBr nanoparticles.

Photocatalytic glass-ceramics doped with metallic Ag, semiconductor AgBr, and hybrid metal-semiconductor Ag-AgBr nanostructures were synthesized via low-temperature Na+-Ag+ ion exchange. The spectral features of the nanostructures in the silicate glass matrix as well as their photocatalytic performance were studied in detail. Glass-ceramics containing hybrid metal-semiconductor nanostructures were shown to possess one order of magnitude higher photocatalytic activity compared to their counterparts with metallic and semiconductor nanostructures. Hybrid metal-semiconductor nanostructures allow enhancement of the net density of photogenerated hot electrons.

Фотокаталитическое разложение растворов метилового оранжевого на поверхности нанопористых слоев меди, серебра и их йодидов

The efficiency of photocatalytic decomposition of methyl orange solutions on the surface of nanoporous layers of copper, silver and their iodides has been studied. It is shows that nanoporous layers on metal substrates have two absorption bands: they absorb radiation in the UV and Vis spectral range. The process of decomposition of methyl orange molecules on the surface of metal-semiconductor nanostructures Cu-CuI and Ag-AgI occurs under the action of UV and Vis irradiation. While transparency of the methyl orange solution increases.

Dual-functional copper (Cu0/Cu2+)-modified SrTiO3-δ nanosheets with enhanced photothermal catalytic performance for CO2 reduction and H2 evolution

In recent years, metal–semiconductor heterojunctions have been intensively researched in the field of photocatalysis due to the effective spatial separation of photo-induced electron-hole pairs. Here, the dual-functional copper (Cu0/Cu2+)-modified SrTiO3-δ nanosheets (Cu/STCO) are successfully synthesized by a two-step route. First, Cu2+-doped SrTiO3-δ (STCO) nanosheets are synthesized by a hydrothermal method and then Cu0 nanoparticles (NPs) are in situ formed from the STCO under H2 atmosphere at 500 °C. The optimized ratio 6 %-Cu/STCO photocatalyst exhibits the best photothermal catalytic performance for CO2 reduction reaction (CO2RR) and H2 evolution performance. The detailed characterization demonstrate that the Cu2+ dopant extend the light absorption range and the in situ generated Cu0 NPs effectively improve the separation ability of photogenerated charge carriers by forming the Schottky contact with STCO. The excited localized surface plasmon resonance (LSPR) effect of metallic Cu0 in Cu/STCO shows a considerable catalysis performance even under 600 nm monochromatic light irradiation. The density functional theory (DFT) calculations suggest that the Cu/STCO diminishes the barrier of the rate-determining steps of the CO2RR and H2 evolution thus perform the outstanding catalysis ability in two filed. This work presents the synergistic effect of Cu0 and Cu2+ on enhancing the photothermal catalytic performance for CO2RR and H2 evolution and offers a novel strategy to synthesize the metal–semiconductor nanostructures for efficient harnessing of solar energy into fuel.

Length-Dependent Photocatalytic Activity of Hybrid Ag-CdS Nanorods

Hybrid metal–semiconductor nanostructures are promising photocatalysts for a wide span of reactions. Determining the relationship of their geometry with catalytic efficiency is critical for optimization of the catalysts. In this work, Ag-CdS nanorods with five different lengths (from 25.0 to 106.5 nm) have been synthesized using a seed-mediated growth method. High-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) studies confirmed that the formation of a metal tip and semiconductor body part and they absorb strongly and broadly in the UV and visible wavelength range. The nanorods have been employed as photocatalysts for methyl orange degradation and their catalytic efficiency exhibited length-dependence. Specifically, the highest efficiency was observed in the rods of intermediate length (72.1 nm). Time-dependent photoluminescence decay revealed that the Ag-CdS rods with high catalytic efficiency have a higher probability to go through charge-separation-recombination pathway than the rods with low catalytic efficiency. Understanding the physical process in these hybrid structures provides insight into fine-tuning their geometry to improve the charge transfer efficiency from the metal to the semiconductor domain. Thus, better hybrid nanomaterials can be designed and fabricated for photocatalytic and other applications.

Novel insight into charge transfer regulation based on carrier density-dependent Ag/ITO composite films

Cosputtering technology was utilized to prepare a Ag and indium tin oxide (ITO) composite on a flat polystyrene (PS) microsphere array. The carrier density estimated by Hall effect testing of different Sn concentrations in the cosputtered films can be tuned from 1018 to 1020 cm−3. The bandgap calculated based on ultraviolet photoelectron spectroscopy can be adjusted within the range of 3.95–4.02 eV. We explored the possible mechanism of charge transfer (CT) by varying the bandgap and explained the causes of the surface-enhanced Raman scattering (SERS). Surprisingly, a synchronous change in the CT process with the carrier density was discovered. This observation suggests that the CT process can be precisely regulated by changes in the composition of the metal-semiconductor nanostructures. Our study provides a reference for the application of Ag/ITO films as alternative near-infrared plasmonic materials.

Inorganic Chiral Hybrid Nanostructures for Tailored Chiroptics and Chirality-Dependent Photocatalysis.

Inorganic chiral hybrid nanostructures that embed chirality within distinct material compositions can create novel chiral properties and functionalities absent from achiral nanostructures; however, they remain largely unexplored. We report, for the first time, a class of chiral plasmonic metal-semiconductor core-shell nanostructures that employ structurally chiral nanoparticles as chirality inducing templates to grow functional shell materials, which allowed us to independently control material parameters such as core geometry and shell thickness, as well as handedness of the system. We experimentally and theoretically achieved enhanced and tunable chiroptical activity of the heterostructures as a result of the core-shell strong coupling effect. As a proof-of-concept demonstration, we demonstrate that the chiral hybrid nanostructures can drive chirality-dependent photocatalytic hydrogen generation under circularly polarized light. This study enables rational design and functionalization of chiral hybrid nanomaterials towards enhanced chiral light-matter interactions and chiral device applications.

Switching effects in plasmon circuits based on thin metal films and nanostructures with increased photoconductivity

The features of optical control of surface plasmon-polariton propagation in plasmon circuits based on thin metal waveguides and semiconductor nanostructures are considered. A model of a plasmon resonator with additional elements based on semiconducting materials exhibiting strong photoconductivity is proposed. By means of numerical simulation, the possibility of switching the surface plasmon-polariton flux in the plasmon circuit by switching on/off the external optical pumping field, which changes the contribution of light-induced conduction of control elements, is shown. Keywords: surface plasmon-polaritons, metal plasmon waveguide, photoconductivity, plasmon resonator.

One-pot synthesis of yolk-shell Cu/Cu2O nanospheres with tunable morphologies for assisting photocatalytic hydrogen evolution

We report a facile, one-pot synthesis of spherical Cu/Cu 2 O yolk-shell nanocrystals (Cu/Cu 2 O YSNSs) with tunable morphologies and explored their applications for assisting photocatalytic hydrogen evolution. The success of current synthesis relies on the reduction of Cu(NO 3 ) 2 by ascorbic acid in the presence of octadecyl trimethylammonium chloride (OTAC) and hexamethylenetetramine (HMTA). It is found that the variation of OTAC concentration would lead to the formation of Cu/Cu 2 O YSNSs with tunable morphologies. The as-prepared Cu/Cu 2 O YSNSs are further anchored by TiO 2 nanoparticles (Degussa P25) to construct Cu/Cu 2 O/TiO 2 nanocomposites for applications in photocatalytic H 2 evolution under simulated sunlight irritation. The resulting metal-semiconductor nanostructures have remarkable photocatalytic activity in H 2 evolution from water-methanol mixtures, with the product rate being almost 97 times greater than that of the pure P25 catalysts. Such improvement should be attributed to the unique hollow structure and the presence of multi-valent copperish species. The current study describes a feasible one-pot strategy to synthesize copperish oxide nanocrystals with tunable yolk-shell morphologies and validates their promising use in as co-catalyst for photocatalytic hydrogen evolution to illustrate the advantage from both the structure and composition. Yolk-shell Cu/Cu 2 O nanospheres with tunable morphologies are prepared in high purity via a one-pot method. By anchoring with TiO 2 nanoparticles (P25), they exhibit excellent photocatalytic activity (~97 times greater than P25 in hydrogen production rate) and long-term durability towards photocatalytic hydrogen evolution, illustrating the structural and morphological advantages.

In-situ Synthesis rGO/NiO Nanorod Nanocomposites Via One-Step Hydrothermal Method and Investigating Physical Properties of Nanocomposites

In-situ nanocomposites of reduced graphene oxide (rGO) and niken oxide (NiO) nanowire were prepared by direct introducing homemade graphene oxide (GO) into precursor solution of NiO with different weight contents of GO (0.0, 0.5, and 1.0 wt.%) before carrying out the one-step hydrothermal process. Homemade GO was synthesized from graphene nanoflakes via Hummer method. Crystal structure and crystallinity of nanocomposites were analyzed using X-ray diffraction method. Scanning electron microscopy was used to study the morphology of nanocomposites. The absorbability of nanocomposites was evaluated through the absorption experiment with two organic dyes: methyl orange and congo red. The results show that compositing with GO does not affect the crystal structure of NiO but it causes the break of NiO nanorod into shorter nanorods, the increase of microstrain in NiO nanorods, and the increase of the absorption efficiency of nanocomposite with both methyl orange and congo red. The results are contribution to the study on hybrid/nanocomposite materials of carbon-based materials and metal oxide semiconductor nanostructures.

Fabrication of antireflective silver-capped tin oxide nano-obelisk arrays as high sensitive SERS substrate

Hybrid noble metal-semiconductor oxide nanostructures often provide unique and synergetic functionalities that are highly desirable in various practical applications. However, the fabrication of such systems with desired functionalities using cost-effective techniques is still a great challenge. In this work, we report a facile route for the preparation of novel Ag/SnO2 nano-obelisk arrayed thin films on silicon substrates by spray pyrolysis and thermal evaporation techniques. The prepared samples exhibited broadband antireflectance in both UV and visible regions attributed to the refractive index gradient and scattering provided by the nano-obelisk arrays. The localised surface plasmon resonance of silver nanocaps further enhanced the light absorption contributing to the antireflective property of the hybrid system. Ag/SnO2 nano-obelisk arrayed thin film exhibited excellent SERS performance with an enhancement factor of 1.13 × 108 with a limit of detection value of 10−12 M for the trace detection of R6G dye. In addition, Ag/SnO2 nano-obelisk arrayed thin film based SERS substrate exhibited good homogeneity across the measured spots and outstanding stability which are essential for quantitative field analysis. The results indicate that the Ag/SnO2 nano-obelisk arrayed thin films are efficient SERS substrates with the merits of having the ease of production, high sensitivity and stability for various practical sensing applications.

Catalytic activity of Au@Cu2O core-shell nanostructure for the organic pollutant remediation

Core-shell metal-semiconductor nanostructures have established worldwide interest due to their magnificent chemical, optical and electrical behavior as compared to their monometallic analogous. Wet chemically synthesized gold-copper oxide (Au@Cu2O) core-shell nanostructures were studied for catalytic activity for the degradation of dyes such as crystal violet (CV) and congo red (CR) and the reduction of organic pollutant, 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) and compared with Au nanoparticles (Au NPs). The Au@Cu2O nanostructures show ten times higher reduction rate for 4-NP than that of monometallic Au NPs. The adsorption followed by degradation of CV, and CR dyes in aqueous solution has been investigated with Au NPs and Au@Cu2O core-shell nanostructures. Kinetics study has been performed using Au NPs and Au@Cu2O core-shell nanostructure for the 4-NP reduction, CV and CR degradation. The synergistic effect in Au@Cu2O core-shell nanostructure facilitates catalytic activity compared to the monometallic Au NPs.

A sandwich-structured surface plasmon ultraviolet photodetector based on ZnO thin film

In this article, novel sandwich-structured surface plasmon ultraviolet (UV) photodetectors based on ZnO thin films with engineered rear metal electrode were fabricated by radio-frequency magnetron sputtering. An exhaustive study about the impact of a dissimilar metallic layer (Au and Pt) on the structural, optical, and electrical properties of the device was carried out. The carrier collection property of the sandwich structure devices has the advantages of horizontal and vertical joint collection. In theory, adding a new metal semiconductor layer introduces a contact area and increases the resistance. An ultra-low dark noise current of less than 2.0 × 10–7 A and a responsivity exceeding 1.6 A/W were achieved with the prepared ZnO-based UV-PDs in the rear metallic electrode mode. The devices based on the ZnO/Pt/ZnO and MgZnO/Pt/MgZnO sandwich structures show high responsivity and fast response. This study provides a depletion layer width method for the fabrication of high-response UV photodetectors for surface plasmon-based materials by integrating metal semiconductor nanostructures. A homogeneous two-layer UV photodetector is constructed, which changes the traditional single-layer device structure and overcomes drawbacks of the single device structure.

Metal-semiconductor heterostructures for surface-enhanced Raman scattering: synergistic contribution of plasmons and charge transfer.

After 45 years of its first observation, surface-enhanced Raman spectroscopy (SERS) has become an ultrasensitive tool applied in chemical analysis, materials science, and biomedical research. SERS-active nanomaterials, such as noble metals, transition metals, and semiconductors, have undergone extensive development. The hybridization of semiconductors with plasmonic metal nanomaterials is highly effective in boosting light harvesting and conversion, which enables the rapid growth of metal-semiconductor hybrid nanostructures in SERS-based research fields. With the combination of the unique photoelectric properties and giant SERS signals attributed to the synergistic contribution of plasmons and change transfer (CT), metal-semiconductor heterostructures allow diverse and novel applications of SERS in CT investigations for the rational design of photovoltaic devices and ultrasensitive chemical or biological sensing. In this review, we specifically discuss SERS-active metal-semiconductor heterostructures including their building blocks, enhancement mechanisms, and applications. Moreover, we highlight the current challenges and opportunities for future research in this field based on our recent studies and other related research.

Photo-enhanced electrocatalytic hydrogen evolution reaction coupled semiconductor with plasma in neutral solution.

A gold-ruthenium/zinc oxide nanorod composite was synthesized. The electrochemical catalytic efficiency of the noble metal-semiconductor nanostructure increased by nearly 30% under the irradiation of an external light source. It provides an efficient way of thinking for the design of electrocatalysts with a photoresponse.