Layer Of Ag Nanoparticles Research Articles

Surface plasmon resonance bilayer graphene /Al2O3/GaAs Schottky junction near-infrared photodetector

In this paper, a bilayer graphene (BLG)/GaAs Schottky junction near-infrared (NIR) photodetector is investigated. The dark current is suppressed by inserting an Al2O3 passivation layer between the BLG and GaAs to prevent electron tunneling. In addition, a layer of Ag nanoparticles (NPs) is spin-coated on the surface of the BLG, which utilizes the plasma effect of the Ag NPs to enhance the local electric field, and promote the excitation and transport of the carriers in the BLG, thereby increasing photocurrent of the device. The combination of interface passivation and plasma effect has greatly improved the performance of BLG/GaAs Schottky junction NIR photodetector. Under the 808 nm incident light, the responsivity of the photodetector is 120 mA/W, which is 20 times higher than the traditional graphene/GaAs photodetector, the detection rate of the device can reach to 3.43 × 1011cm Hz1/2W−1 with the fast response/recovery time of 8.16 μs/98.43 μs. This high-performance BLG/GaAs Schottky junction can be widely used for the photo detection and solar cells fields.

The finite-difference time-domain (FDTD) guided preparation of Ag nanostructures on Ti substrate for sensitive SERS detection of small molecules

Surface-enhanced Raman Scattering (SERS) has become a powerful analytical technique for highly sensitive detection of target molecules. Its performance, however, is heavily dependent on the substrates. Relatively low sensitivity for small molecules and poor reproducibility in quantitative analysis are often encountered in most of nanoparticle modified SERS substrate. The present work starts by theoretical investigation of the electromagnetic field enhancement by nanomaterials of coinage metals with different sizes. The finite-difference time-domain (FDTD) simulation results revealed that the Ag NPs with the size around 100 nm exhibit the strongest SERS effect and the ‘Ag-Ag’ gaps have shown higher electromagnetic field enhancement than that of the ‘Ag-Ti’ gap. Subsequently, a multilayered Ag nanoparticles SERS substrate (or other coinage metals) was prepared by a two-step electroless deposition of Ag on Ti substrate. This was achieved by in situ reduction of Ag precursor to subsequently form a Ag nanoflake (Ag NF) layer and a Ag nanoparticle (Ag NPs) layer on the Ti base (Ti/AgNFs/AgNPs). The as-prepared SERS substrate showed a substantially enhanced SERS effect for small molecule detection and detection limit as low as 1.0 × 10-17 M for picric acid (PA), 1.0 × 10-14 M for p-nitrotoluene (PNT) and 1.0 × 10-6 M for uric acid (UA) were obtained respectively. The facile method developed in this work should be widely applicable for in-situ preparation of other SERs substrates.

Toward white light emission from plasmonic-luminescent hybrid nanostructures

Abstract We study the light emission of plasmonic-luminescent hybrid nanostructures consisting of Ag nanoparticles (NPs) embedded in europium oxide (EuOX). The Ag NPs present a bidimensional organization in the nanostructures and they optically behave as oblate spheroids. The photoluminescence (PL) spectral response of the nanostructures evolves from a narrow red emission characteristic of Eu3+ ions in absence of Ag NPs to a broad blue-green emission band associated with Eu2+ ions when the layer of Ag NPs is present. This behavior is not related to a change in the Eu2+/Eu3+ ratio, which is verified by compositional analysis. Instead, a detailed investigation of the PL emission of the nanostructures suggests that the coupling of the Ag NPs to the Eu2+ ions present in the EuOX layer, which manifests itself in an efficient sensitization of these ions, enhances their broad visible emission. In particular, the longitudinal mode of the Ag NPs surface plasmon is considered to be responsible for the efficient energy transfer for the non-normal incidence excitation PL configuration used. Finally, the use of a capping amorphous Al2O3 layer allows improving the robustness of hybrid nanostructures and further enhances their PL emission. These findings provide a new path to actively control the selective excitation of Eu2+ and Eu3+ ions via a controlled coupling with the surface plasmon resonance modes of the Ag NPs and points to these nanostructures as promising building blocks for the development of integrable white light sources.

Enhanced photoluminescence of CdS quantum dots thin films on Cu and Ag nanoparticles

Fluorescent nanoparticles (NPs) exhibit unique optical properties which are utilized to prepare highly sensitive sensors. This paper illustrates the enhancement of luminescence emission of CdS quantum dots (QDs) from self-assembled metallic NPs of Cu and Ag. Metallic NPs, especially of Cu, Ag and Au exhibit unique and tunable plasmonic properties which are further manipulated by varying their size and shape. In the present study, plasmonic NPs were fabricated on glass substrate heated at 400 °C for the conversion of metallic layers into homogeneous NPs so as to create plasmonic response from these uniform NPs. The bimetallic layers of Ag and Cu NPs form a composite material having higher thermal conductivity, higher chemical stability and lower value of thermal expansion than monometallic layer of NPs. The photo-luminescence enhancement of CdS QDs thin films deposited on Cu and Ag NPs would find applications as light emitters and sensing devices. The attachment of CdS QDs on these bimetallic layers was confirmed by studying their optical properties. The morphology of the three prepared samples was analysed by scanning electron microscopy, which confirms the homogeneous deposition of spherical Cu and Ag NPs having size ranging from 20 to 55 nm (approximately). The above obtained outcomes illustrate the localized surface plasmon resonance characteristic of metal NPs which can be applied further for chemical and biological sensing

Introducing an Electrochemical Sensor Based on Two Layers of Ag Nanoparticles Decorated Graphene for Rapid Determination of Methadone in Human Blood Serum

Introducing an Electrochemical Sensor Based on Two Layers of Ag Nanoparticles Decorated Graphene for Rapid Determination of Methadone in Human Blood Serum

Synthesis of Silver Nanoparticles by Plasma-Assisted Hot-Filament Evaporation for Enhancing in Luminescence Properties of Organic Light Emitting Diode

In this work, silver (Ag) nanoparticles were synthesized using plasma-assisted hot-filament evaporation, both with and without plasma deposition environments. This technique was used for the deposition of the nanoparticles in high-density, with controlling the size and interparticle separation. The size and interparticle separation acted as the primary factors of the variation of the localized surface plasmon resonance characteristics of the nanoparticles. The Ag nanoparticles reflected an additional layer in a typical organic light-emitting diode (OLED). The OLED with the Ag nanoparticles layer resulted in a low operating voltage, with a high luminance that reached 62.9 % under the hydrogen plasma environment, as compared to the reference device (OLED without the Ag nanoparticles layer). The effects of the Ag nanoparticles synthesis layer, both with and without plasma deposition on the OLED luminance, were also discussed.

Achieving High Power Density and Long‐Term Stable Flexible Triboelectric Nanogenerators through Surface Functionalization of High Work‐Function Electrode with Cationic Thiol‐Based Self‐Assembled Monolayer

AbstractIn this study, a reliable strategy is demonstrated to improve performance and stability of a triboelectric nanogenerator (TENG) by using cationic (11‐mercaptoundecyl)‐N,N,N‐trimethylammonium bromide (MUTAB) self‐assembled monolayer (SAM) as the surface modification layer for high work‐function (WF) Ag electrode. The thiol head group of MUTAB can form covalent bond to Ag surface, while the positively charged ammonium group can induce favorable surface dipole moment to lower the WF of Ag layer, enabling efficient charge transfer from Ag electrode to polydimethylsiloxane (PDMS) dielectric layer. This strategy is highly compatible with large‐area flexible TENG based on solution‐processed Ag nanoparticle layer, affording open‐circuit voltage (Voc) of 1008 V, short‐circuit current (Isc) of 124.9 µA, and power density of 39.4 W m−2. To the best of our knowledge, such remarkable power density represents the highest value ever reported for SAM‐modified TENG. Taking advantage of high output characteristics of flexible TENG, 328 light‐emitting diodes can be lit up instantaneously. More encouragingly, the resulting TENG also possesses good stability, maintaining ≈96% of its original Voc after 300 000 cycles of continuous testing. The present findings highlight the importance of surface modification with SAM for efficient and long‐term stable TENG, which can advance the development of intelligent self‐powered systems.

Synthesis of Ag NPs layer and its application as SERS substrate in the determination of p-phenylenediamine

An Ag nanoparticles (NPs) layer was synthesized on Ag sheet by alloying/electrochemical dealloying method: X-ray diffraction confirmed that the new Ag phase appeared after removing Ga from Ag-Ga alloy, and scanning electron microscopy examination showed that the prepared Ag layer had a NPS structure. The fine microstructure of silver resulted in significant SERS enhancement effect, while the NPs layer was used as the SERS substrate: when the prepared NPs layer was used as a SERS substrate to detect p-phenylenediamine (PPD), it exhibited a strong SERS peak at 1590 cm−1. The result revealed that the intensity of SERS peaks was linear to the logarithm of PPD concentration in the range from 10−16 mol L−1 to 10−12 mol L−1 and the detection limit was 1.0 × 10−17 mol L−1.

Nanoparticles enhanced laser ablation propulsion (NE-LAP) of Cu: A response surface regression approach

The nanoparticles (NPs) present on the surface of the sample interact with the electromagnetic field of the incident laser pulse and provide better ablation efficiency. The large surface area of NPs and the mechanism of surface plasmon resonance (SPR) positively affect the Laser Matter Interaction. In this work, we report for the first time to the best of our knowledge the use of silver (Ag) NPs for the enhancement of Laser Ablation Propulsion (LAP) parameters of the metallic targets. An Nd:YAG laser (Quantel Brilliant) having pulse duration 5 ns operating at 1064 nm was used to ablate the copper samples with and without Ag NPs coatings. The Ag Nanoparticles layer was deposited using a spin coating technique. The spatial distribution of the deposited nanoparticles layer on the copper substrate was confirmed using the Atomic Force Microscopy (AFM). The LAP parameters, namely the momentum coupling coefficient Cm, the exhaust velocity VE, the specific impulse Isp and the ablation efficiency ηAB, were calculated. We have also studied the effects of various parameters like laser fluenece, coating of nanoparticles, as well as the interaction effect (fluence × coating) on the ablation efficiency using the Response Surface Regression approach. The analysis has revealed that the Ag nanoparticles coating over the surface of the propellant significantly enhances the LAP parameters. This opens a new avenue for the application of nanoparticles in the field of laser propulsion.

Facile synthesis of nanogels modified Fe3O4@Ag NPs for the efficient adsorption of bovine & human serum albumin.

This article describes the preparation of Fe3O4 nanoparticles and its decoration with a layer of tiny Ag nanoparticles at room temperature. Later on, the synthesized Fe3O4@Ag heterostructures were protected with Silica and finally modified with Poly(N-isopropyl acrylamide) (PNIPA) nanogels through post-synthesis method to get multifunctional (superparamagnetic, plasmonic and thermosensitive) nanocomposite. The structural characteristics of Fe3O4@Ag@SiO2-PNIPA nanogels composite were investigated by instrumental techniques such as Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD) and Vibrating Sample Magnetometer (VSM). The average particles diameter was calculated from XRD data through Scherer formula and it was found as 14nm. The Fe3O4@Ag@SiO2-PNIPA polymeric composites were assessed for the adsorption of Bovine Serum Albumin (BSA) and Human Serum Albumin (HSA) proteins from aqueous media. The adsorption data of BSA and HSA were best explained by Langmuir isotherm model with maximum adsorption capacities of 322 and 166 (mg/g) respectively showing mono-layer adsorption. The kinetics data for both the proteins were fairly interpreted by pseudo-second-order model. Thermodynamics studies revealed that the adsorption phenomena of BSA and HSA on the surface of Fe3O4@Ag@SiO2-PNIPA nanogels composite are spontaneous and exothermic.

Efficiency enhancement in blue phosphorescent organic light emitting diode with silver nanoparticles prepared by plasma-assisted hot-filament evaporation as an external light-extraction layer

The uniform growth of silver (Ag) nanoparticles in large areas is important for improving the flat panel devices, mainly organic light emitting diodes (OLED). In this work, two dimensional (2D) arrays of Ag nanoparticles were grown on glass surface substrates via plasma-assisted hot-filament evaporation technique at different plasma environments: no plasma, plasma cleaning (PC), plasma deposition (PD) and PC&PD, which were utilized as an external light-extraction layer for blue phosphorescent OLED device. The surface morphology of the Ag nanoparticles revealed the formation of spherical-like shapes of uniform size which ranged from 7 to 14 nm at different plasma conditions. X-ray diffraction showed that the nanoparticles were mainly single crystals and their crystallinity was significantly enhanced by employing plasma process in PC&PD. The localized surface plasmon resonance peaks of Ag nanoparticles were located at around 380–430 nm which suggests a dependency on diameter and interparticle spacing. The variation of refractive index of Ag nanoparticles 2D array in the visible wavelength from 1.9 to 2.4 plays a key role in high performance OLED. The light-extraction of the OLED device with Ag nanoparticles at PC&PD condition appeared to increase by 82.5% the luminance efficiency compared to that of a reference device without the Ag nanoparticle layer. The effects of the plasma environment on the morphological, structural and optical properties of Ag nanoparticles layer are discussed in the following sections by taking into consideration the effects of glass modification by these Ag nanoparticles on OLED performance.

CNTs/ZnO and CNTs/ZnO/Ag multilayers spray coated on cellulose fiber for use as an efficient humidity sensor

The exceptional high surface area and wide band gap ranges of semiconductor metal oxide nanostructures owe unique chemical, optical and physical properties that have grabbed their utilization for humidity sensing applications. In this framework, cost-effective sensors have been fabricated using a simple spray coating technique. Initially, the sonication was carried out for all the conductive inks such as carbon nanotubes (CNTs), zinc oxide (ZnO) and silver (Ag) nanoparticles (NPs) for 15 min in each case and then sprayed over conducting cellulose polymer substrate. Surface study demonstrated conducting networks of CNTs and cellulose polymer, and layers of ZnO and Ag NPs, as well. The analysis of elemental composition confirmed the required stoichiometric contents. Sensing measurement of CNTs/ZnO/Ag sample showed smaller resistance and enhanced current as compared to CNTs/ZnO sample. Hence, the device showed an efficient activity to sense humidity.

Z-scheme heterostructure BiOCl-Ag-AgBr with enhanced sunlight-driven photocatalytic activity in simultaneous removal of Cr6+ and phenol contaminants

In this study, we constructed a Z-scheme photocatalyst BiOCl-Ag-AgBr for the first time, with the aim of simultaneously removing the heavy metal Cr6+ ions and organic pollutant phenol in waste water. It was found that Ag nanoparticles (NPs) were selectively deposited on the {001} facets of BiOCl nanosheets in the process of photoreduction, and the outer layer of Ag NPs was further transformed into AgBr in the presence of Fe3+ and Br−. Compared with BiOCl and BiOCl-Ag, the ternary structure BiOCl-Ag-AgBr displays obviously higher photocatalytic activity for both Cr6+ reduction and phenol degradation. There exists a synergetic effect between Cr6+ ions and phenol for enhancing the photocatalytic activity of photocatalysts, i.e., the presence of Cr6+ ions can promote the degradation of phenol, while the existence of phenol also accelerates the reduction of Cr6+. The radical trapping experiments confirmed that BiOCl-Ag-AgBr is a Z-scheme semiconductor and all of e−, O2−, OH, and h+ take part in the reactions of Cr6+ reduction and phenol degradation. The superior photocatalytic activity of BiOCl-Ag-AgBr should be ascribed to both its excellent sunlight response and the effective separation efficiency of photogenerated charge carriers with high redox ability.

Patterning Ag nanoparticles by selective wetting for fine size Cu-Ag-Cu bonding

Metal nanoparticles (NPs) are promising bonding materials to replace Sn alloys in fine size Cu-Cu bonding. However, the method of rapidly patterning NPs on solder joints with sizes less than 30 µm is one of the main barriers that impede the practical applications of NPs in Cu-Cu bonding, especially in mass production. In this paper, a novel method of patterning Ag NPs on Cu pads by selective wetting was introduced. Cu pads with diameters down to 5 µm were coated with Ag NPs successfully. When sizes of Cu pads were larger than 10 μm, high density could be achieved and the ratio of diameters to pitches of Cu pads could reach 2/3. Furthermore, the thickness and the coverage of the Ag NPs layer could be raised by repeating coating. In the bonding test, the shear strength increased significantly with the increase of the bonding temperature and the bonding time. It could reach 22.92 MPa after sintering for 5 min at 250 °C under a bonding pressure of 20 MPa in N2. With the aforementioned advantages, patterning NPs by selective wetting will be one of the potential methods for applying NPs to Cu pads in Cu-NPs-Cu bonding.

Effect of Plasmonic Ag Nanoparticles on the Performance of Inverted Perovskite Solar Cells

Recently, perovskite solar cells (PSCs) have attracted phenomenal research interest due to their potential as the next‐generation photovoltaics. Despite rapid development in this field, further increasing their power conversion efficiency (PCE) remains a critical issue for the commercialization of PSCs. Herein, the application of Ag nanoparticle (NP) layers via vapor‐phase deposition onto perovskite active layers is investigated. The formation of unique, crescent‐shaped Ag NPs is confirmed by scanning electron microscopy (SEM), which shows that the NPs self‐assemble along the grain boundaries of perovskite, leading to their unique shape. The PCE for devices incorporating an optimized size of Ag NPs of 79 ± 6 nm increase from 11.63% to 13.46% with an improvement factor of 15.74%. The increase in PCE is can be attributed to an increase in short‐circuit current density (Jsc) that is assigned to an increase in optical path length and absorption. NPs exhibit the ability to increase the optical path length of photons in the device due to the near‐field and far‐field enhancement (plasmonic scattering) and consequently may act to improve the photon‐to‐electron conversion efficiency (ΔIPCE) and PCE of PSCs. Moreover, ultraviolet photoelectron spectroscopy reveals a decrease in hole injection barrier (ϕh), which also contributes to enhanced performance.

Graphene oxide-highly anisotropic noble metal hybrid systems for intensified surface enhanced Raman scattering and direct capture and sensitive discrimination in PCBs monitoring

Graphene oxide (GO)-anisotropic noble metal hybrid systems were developed as highly sensitive and reproducible surface enhanced Raman scattering (SERS) platform, in which ultrathin GO was embedded between two metallic layers of flower-like Ag nanoparticles (AgNFs) and gold nanostars (AuNSts). Due to multi-dimensional plasmonic coupling effect, the well-designed AgNFs-GO-AuNSts sandwich structures possessed ultrahigh sensitivity with the detection limit of R6G as low as 1.0 × 10−13 M and high enhancement factor of 2.59 × 107. Additionally, the GO interlayer could function as protective shell to suppress the oxidation of bottom silver layer and efficiently position the target analytes within hot spots. These features endow the substrate with high stability and excellent reproducibility (Signal variations < 7%). Particularly, the GO sandwiched substrate can be explored for the direct capture and sensitive detection of polychlorinated biphenyls (PCBs) without any organic modifier as molecule harvester. This minimum detected concentration was estimated as low as 3.4 × 10-6 M. The detection method based on GO mediated sandwich substrate avoids complicated surface modification manipulations and improves the substrate cleanness. Moreover, the resultant sandwich substrates can be used to recognize fingerprint peaks of different PCBs in their complex mixture, revealing great potential applications in SERS-based simultaneous detection of multiple pollutants with low affinity.

Cubic Silver Nanoparticles Fixed on TiO2 Nanotubes as Simple and Efficient Substrates for Surface Enhanced Raman Scattering.

In this work we show that ordered freestanding titanium oxide nanotubes (TiO2 NT) may be used as substrates for the simple and efficient immobilization of anisotropic plasmonic nanoparticles. This is important because anisotropic plasmonic nanostructures usually give greater spectral enhancement than spherical nanoparticles. The size of the pores in a layer of titanium oxide nanotubes can be easily fitted to the size of many silver plasmonic nanoparticles highly active in SERS (surface-enhanced Raman scattering) spectroscopy (for example, silver nanocubes with an edge length of ca. 45 nm), and hence, the plasmonic nanoparticles deposited can be strongly anchored in such a titanium oxide substrate. The tubular morphology of the TiO2 substrate used allows a specific arrangement of the silver plasmonic nanoparticles that may create many so-called SERS hot spots. The SERS activity of a layer of cubic Ag nanoparticles (AgCNPs) deposited on a tubular TiO2 substrate (AgCNPs@TiO2 NT) is about eight times higher than that of the standard electrochemically nanostructured surface of a silver electrode (produced by oxidation reduction cycling). Furthermore, a super hydrophilic character of the TiO2 nanotubes surface allows for a uniform distribution of AgCNPs, which are deposited from an aqueous suspension. The new AgCNPs@TiO2 NT hybrid layer ensures a good reproducibility of SERS measurements and exhibits a higher temporal stability of the achievable total SERS enhancement factor—one that is far better than standard SERS silver substrates. To characterize the morphology and chemical composition of such evidently improved SERS platforms thus received, we applied microscopic techniques (SEM, and scanning transmission electron microscopy (STEM)) and surface analytical techniques (Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS)).

Optimizing the spacing of Ag nanoparticle layers to enhance the performance of ZnO/Ag/ZnO/Ag/ZnO multilayer-structured UV photodetectors

In this study, the ZnO/Ag/ZnO/Ag/ZnO (ZAZAZ) multilayer-structured UV photodetectors (PDs) were fabricated and investigated with an emphasis on the effects of the spacing between the two Ag nanoparticle (NP) layers. The results indicated that embedding two Ag NP layers can significiantly improved UV PD responsivity. Owing to optimazation of the spacing between the two layers, responsivity of multilayer- structured PDs was enhanced from 11.69 to 24.32 A/W. Also, the absorption band-edges and photoresponse cutoff wavelength of ZAZAZ multilayer-structured PDs showed a significant redshift in comparition with the bare ZnO photodetector. This was ascribed to near-field effects of surface plasmons. This novel research described a creative method for increaing the performance of ZnO PDs.

Optical and Structural Properties of Ag and c-Si Nanostructures Formed During the Metal-Assisted Chemical Etching of Silicon

This study consisting of two parts is concerned with the features of the three-stage process of the metal-assisted chemical etching (MACE) of silicon. This process is used to fabricate silicon nanostructures. In the first part of this work, a layer of self-assembled Ag nanoparticles chemically deposited from a solution on the surface of single-crystal silicon (c-Si) (MACE stage 1) was studied, and the second part includes of investigation of Si nanostructures formed in stages 2 and 3. By means of spectroscopic ellipsometry (in the range of wavelengths λ = 250–900 nm), the pseudodielectric functions of the nanostructures were determined and compared for all the three stages of the MACE process. In addition, for the Si nanostructures, the parameters of layers (the thickness and void fraction) were calculated in the context of the multilayer optical model, with the use of Bruggeman’s effective-medium approximation and fitting procedures.

Multifunctional Fe3O4@mTiO2@noble metal composite NPs as ultrasensitive SERS substrates for trace detection

Multifunctional materials have become the development trend of current material preparation. We reported a typical layer-by-layer method for the fabrication of multifunctional Fe3O4@mTiO2@noble metal triplex core-shell composite nanoparticle (NP), which is composed of a magnetic Fe3O4 particle as the core, a mesoporous TiO2 interlayer and a layer of Ag nanoparticles or Au nanorods as the shell. The obtained Fe3O4@mTiO2@noble metal composite NPs have shown excellent surface enhanced Raman scattering (SERS) sensitivity. Raman results present that the limit of detection (LOD) for crystal violet (CV), p-aminothiophnol (p-ATP) and p-mercaptobenzoic acid (p-MBA) of the Fe3O4@mTiO2@noble metal composite NPs substrates are as low as 1.0 × 10−9 M, 1.0 × 10−12 M and 1.0 × 10−9 M, respectively. In addition, the composite NPs also show high reproducibility and stability across the entire area with relative standard deviations (RSD) less than 15.00%. These highly sensitivity with good reproducibility can be attributed to the presence of plentiful “hot spots” produced by magnetic aggregation and target molecules enrichment by mesoporous TiO2 adsorption for practical application. Fe3O4@mTiO2@Ag composite NPs were used for thiram detection and the detection limit can reach to 5.0 × 10−8 M (about 0.012 ppm), which is lower than the maximal residue limit of 7 ppm in fruit prescribed by the U.S. Environmental Protection Agency. These multifunctional composite NPs provide easy separation, enrichment and trace detection of the analyte, exhibiting a great prospect as a potential SERS sensor in complex environments.