Monolayer Of Ag Nanoparticles Research Articles

Uniform monolayer of branched silver nanoplates-assembled nanoparticles for sensitive and reproducible SERS detection of harmful molecules

Surface-enhanced Raman scattering (SERS) technique can offer the fingerprint information of trace substances, and thus has wide potential applications in many fields. There is still a requirement to develop new and effective methods to construct high-performance SERS substrates. Here, a facile electrodeposition method is presented for fabricating large-scale uniform films assembled by branched silver (Ag) nanoplates. The morphology and structure of such film are highly uniform over a large area, which can ensure good spectral uniformity and reproducibility. There are dense sub-10 nm gaps between neighboring Ag nanoplates and between neighboring branches, forming plenty of hot spots. Therefore, the Ag nanoparticle monolayer exhibits high SERS activity along with excellent spectral repeatability. It is found that the limits of detection (LODs) towards rhodamine 6G and 4-aminothiophenol can reach 0.387 pM and 49.0 pM, respectively, showing high sensitivity of the designed SERS substrate. The enhancement factor of the prepared roughened Ag nanoparticle monolayer is computed to be as large as 2.37 × 108. Then, the highly roughened nanoparticle monolayer is used to detect cationic dye and fungicide (methylene blue, MB) and a synthetic cytokinin (6-benzylaminopurine, 6-BAP), and the corresponding LODs are determined down to 1.1 nM and 28.8 pM, respectively. Such LODs are much lower than the tolerance for MB and 6-BAP residues established by some authoritative regulations. Sensitive monitoring of 6-BAP residue on vegetables and fruits can also be achieved using such SERS substrate, indicating its promising application in environment monitoring and food safety supervision.

Hierarchical membrane integration of shear stress-resistant nanoparticles and biomimetic micropatterns for ultrahigh and durable biofouling resistance

• Anti-biofouling pattern and biocidal nanoparticles were hierarchically integrated onto membranes. • Langmuir-Schaefer technique and nonsolvent-induced phase separation were rationally combined. • Silver nanoparticle integration is highly resistant to hydrodynamic shear stress (30 cm/s). • The resultant membrane enhanced biofouling resistance by 100% compared to the pristine counterpart. Herein, we report a rational strategy for fabricating dual-functional microfiltration (MF) membranes hierarchically integrated with micropatterns and Ag nanoparticles (NPs) for ultrahigh and durable fouling resistance. To harness hydrodynamic force and chemical oxidation for an enhanced anti-biofouling ability, a monolayer of Ag NPs was transferred onto negative patterns of polyurethane acrylate molds via the Langmuir-Schaefer technique. Then, they were integrated onto the biomimetic micropattern of porous polyacrylonitrile (PAN) membranes through nonsolvent-induced phase separation. Without the use of chemical linkers, our method achieved a stable and partial embedment of Ag NPs onto the porous PAN network and exhibited a negligible loss of Ag NPs even after exposure to high shear stress. Compared with the same micropatterned MF membranes without Ag NPs and the bare MF membranes, the resultant MF membrane significantly suppressed the decrease in water flux for the microbial solution by over 40% and 100%, respectively, owing to the dual anti-bacterial activities of the biocidal property of Ag NPs and the hydrodynamic repulsion of the micropatterns. Our hierarchical fabrication method can be applied to various biocidal NPs for ultrahigh biofouling-resistant porous membranes.

Conductive nanosheets produced by UV irradiation of a Ag nanoparticle monolayer at the air-water interface.

In a previous study, we demonstrated that conductive Au nanosheets can be prepared by UV irradiation of an Au nanoparticle monolayer spreading on water. In this study, we applied this UV irradiation technique to inexpensive Ag nanoparticles (NPs) to expand their versatility. UV irradiation of Ag NPs on water resulted in the formation of large Ag NPs and was ineffective for preparing conductive Ag films. The solubilization of additives in the water phase, however, resulted in the conversion of the large Ag NPs into a nanosheet, and the solubilization method was highly effective for preparing transparent conductive Ag films with an optical transmittance of above 70%.

Ultrafast Saturable Absorbers: Fused Silica with Embedded 2D‐Like Ag Nanoparticle Monolayer: Tunable Saturable Absorbers by Interparticle Spacing Manipulation (Laser Photonics Rev. 14(2)/2020)

Ultrafast Saturable Absorbers: Fused Silica with Embedded 2D‐Like Ag Nanoparticle Monolayer: Tunable Saturable Absorbers by Interparticle Spacing Manipulation (Laser Photonics Rev. 14(2)/2020)

Fused Silica with Embedded 2D‐Like Ag Nanoparticle Monolayer: Tunable Saturable Absorbers by Interparticle Spacing Manipulation

AbstractSaturable absorbers are key elements for generation of ultrafast laser pulses. The commercially available semiconductor saturable absorber mirrors are wavelength sensitive and with complex fabrication process and high cost. Fused silica is one of the basic materials for various optical applications. Plasmonic nanoparticles can be used to efficiently modulate the optical properties of dielectric materials owing to the enhanced field effects based on localized surface plasmonic resonance. Ion implantation is a direct technique to synthesize plasmonic nanoparticles inside dielectric materials, which can simultaneously tailor the optical nonlinearity of substrates significantly. In this work, Ag ion implantation into fused silica with tunable interparticle spacing is used to generate broadband optical nonlinearities and to endow silica with ultrafast saturable absorption property. This ion implantation forms a 2D‐like Ag nanoparticle monolayer buried inside fused silica wafer. The fused silica with embedded 2D‐like Ag nanoparticle monolayer is further applied as a new saturable absorber to generate ultrafast laser pulses with pulse duration of 27 ps and repetition rate of 6.5 GHz through the passive mode‐locking process. This work opens up a new route to develop low‐cost, highly stable saturable absorbers, and offers the possibility to build novel silica‐based photonic systems through nanoparticle spacing manipulation.

A versatile β-cyclodextrin functionalized silver nanoparticle monolayer for capture of methyl orange from complex wastewater

The toxic organic dye contaminants in wastewater are extremely harmful to the ecosystem. Surface enhanced Raman scattering (SERS) is a technique with high sensitivity and chemical specificity which fulfills the requirements for monitoring dye contaminants in wastewater. However, as one of the common dye contaminants, methyl orange (MO) has very weak affinity to metallic surfaces and is difficult to be detected by SERS at low concentrations. Therefore, a new type of SERS substrate with Ag nanoparticle monolayer functionalized by mono-6-deoxy-6-thio-β-cyclodextrin (β-CD-SH) was prepared to efficiently capture and detect MO in wastewater with a limit of detection of 5 × 10−7 mol/L. The hydrophobic cavity of β-CD is responsible for the efficient trap and enrichment of MO on the Ag NPs surface, achieving a strong SERS signal of MO at low concentrations and at different pH values. This study provides new insight into designing a well-performed adsorbent for the capture and detection of organic contaminants.

How to make microscale pores on a self-assembled Ag nanoparticle monolayer

In this short communication, we report a procedure for the fabrication of microscale pores on a rigid self-assembled Ag nanoparticle monolayer with nanothickness. Here, condensed water droplets on a hydrophobic substrate are used as a pore formation template for Langmuir-Schaefer film deposition. The optical properties of the Ag nanoparticle monolayer were influenced by the porous structure, e.g., the localized surface plasmon resonance (LSPR) peak was weakened and broadened for the porous monolayer compared with the homogeneous monolayer, even though the number of particles on the substrate should be the same between them. The pores obtained by this method were robust and could be used as a mask for metal deposition or local fluorescence imaging. This environmentally friendly technique can provide a micropatterned surface with a minimal cytotoxicity, which has high potential for LSPR mediated biosensing and bioimaging applications.

Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM) Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF) state to low resistance (ON) state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

Quantitative determination of melamine in milk using Ag nanoparticle monolayer film as SERS substrate

A Raman method employing silver nanoparticle (Ag NP) monolayer film as Surface-enhanced Raman Scattering (SERS) substrate was presented to rapidly detect melamine in milk. The Ag NPs with 80nm diameter were modified by polyvinylpyrrolidone to improve their uniformity and chemical stability. The treatment procedure of liquid milk required only addition of acetic acid and centrifugation, and required time is less than 15min. The Ag NP monolayer film significantly enhanced Raman signal from melamine and allowed experimentally reproducible determination of the melamine concentration. A good linear relationship (R2=0.994) between the concentration and Raman peak intensity of melamine at 681cm−1 was obtained for melamine concentrations between 0.10mgL−1 and 5.00mgL−1. This implies that this method can detect melamine concentrations below 1.0mgL−1, the concentration currently considered unsafe.

Preparation of Mono-Layered Ag Nanoparticles for Charge-Trap Sites of Memory Thin-Film Transistors Using In-Ga-Zn-O Channel

We propose a methodology for the formation of silver (Ag) nanoparticle monolayer as charge trapping layer of nonvolatile memory thin-film transistor using an indium-gallium-zinc oxide semiconductor channel layer. Atomic-layer-deposited Al2O3-amine treatment Ag configuration were employed as tunneling/charge-trap layers, respectively. The memory devices showed wide memory window of 8.0 V, when the gate voltage was swept from −20 to 20 V. The high on/off current ratios of 5.81 × 105 and 1.29 × 103 could be obtained for the memory device, when the program pulse duration was reduced to 1 μs and 5 ns, respectively. The Ag nanoparticle monolayer could be prepared by using the amine-functionalized Al2O3 layer. The areal density of Ag nanoparticle was controlled by modulating the Ag ratio in polystyrene (PS) mixture and optimized at Ag:PS ratio of 5:5.

Submicron patterns obtained by thermal-induced reconstruction of self-assembled monolayer of Ag nanoparticles and their application in SERS

Abstract The layer-by-layer (LbL) self-assembly technique was employed for the deposition of poly(diallyldimethylammonium chloride) (PDDA) and triangular Ag nanoplates on glass substrates. A thermal-induced reconstruction of these polyelectrolyte-linked nanoparticle (NP) films was presented. Before the reconstruction, triangular Ag nanoplates were distributed uniformly on the surface with an average interval of 50 ± 15 nm. After the reconstruction, the triangular Ag nanoplates accumulated into discrete stacks with an average interval of 90 ± 25 nm. The temperature-dependent experiments were done and the optimal temperature for the formation of the reconstructed patterns was 120 °C. The possible mechanism of the NP movement and stacking was analyzed. Under the experimental conditions, a hydrophobic environment was formed because of the vacuum and heating. As a result the polyelectrolyte-linked Ag NPs preferred to congregate due to the lowered surface energy. Finally the submicron patterns were formed. The ultraviolet–visible (UV–vis) absorption and surface-enhanced Raman scattering (SERS) properties of the films before and after the reconstruction was investigated. The reconstructed films with submicron patterns had better SERS enhancement ability, which was 1300 times to the original films. The reconstruction method of the monolayer films showed great potential in the surface design and related applications.

Plasmon-Related Modification of Spectral Kinetic Properties of Copper Phthalocyanine Thin Films in the Presence of Silver Nanoparticles*

We have studied the relaxation dynamics for hot electrons in hybrid layered nanocomposites based on island o lms of silver and copper phthalocyanine. Using femtosecond kinetic spectroscopy, we have shown that the fast component of the bleaching relaxation kinetics in the spectral region corresponding to the absorption bands of copper phthalocyanine correlates with the recovery kinetics for surface plasmon resonance absorption of the silver nanoparticles. This suggests that the fast relaxing bleaching recorded in the absorption bands of copper phthalocyanine and its dynamics are not due to a change in the populations of the energy states of copper phthalocyanine but rather to a change in the state of the plasmon nanoparticles, as a result of their excitation by femtosecond pulses and subsequent relaxation. Introduction. The ultrafast optical response of semiconductor thin o lms and nanostructures is one of the important properties explaining why these materials are in demand and promising for designing hardware components for nanophotonics and optoelectronics. Until recently, the effect of plasmon nanoparticles on the properties of semiconductor thin-o lm components were analyzed mainly with a view toward the possibility of changing their spectrally selective characteristics, in particular in order to increase the efo ciency of active elements in solar batteries. It has been established that doping functional semiconductor layers with plasmon nanoparticles can substantially change their absorption and conductivity because of the near-o eld effects arising in such systems and also as a result of additional possibilities for energy and charge carrier transfer in such structures (1, 2). At the same time, we know (3, 4) that the surface plasmon resonance (SPR) absorption band is substantially transformed when the nanoparticles are excited by ultrashort laser pulses, acting on the electronic subsystem of metallic nanoparticles. It is logical to assume that the change in state of the nanoparticles should be re? ected in fast dynamics of the near-o eld distribution pattern and consequently in fast dynamics of surface-enhanced effects, in particular the effect of modio cation of the absorption spectrum of copper phthalocyanine (CuPc) in the presence of Ag nanoparticles. This may prove to be useful in development of new types of dynamic devices: modulators, switches. The aim of this work was to study the characteristic features of the appearance of fast charge carrier relaxation processes in non-steady state absorption spectra of layered hybrid nanocomposites based on island o lms of silver and CuPc when the Ag nanoparticles are excited by femtosecond laser pulses in the SPR absorption region. Sample Preparation Procedure. The experimental samples were prepared by successive thermal vaporization under vacuum of Ag and CuPc materials on glass and quartz substrates at room temperature. The residual gas pressure was 2·10 -3 Pa. The thicknesses of the deposited layers were monitored with a quartz sensor. The spectral characteristics of the experimental samples were recorded on a Cary 500 spectrophotometer. Three groups of samples were prepared: 1) planar Ag nanostructures (close packed monolayers); 2) CuPc thin o lms; 3) two-layer Ag/CuPc nanostructures (a close packed monolayer of Ag nanoparticles, covered with a CuPc o lm). Steady-State Absorption Spectra. In the absorption spectrum of an Ag monolayer with metal surface density

Self-assembly Ag nanoparticle monolayer film as SERS Substrate for pesticide detection

A self-assembled protocol is introduced to provide effective platforms for the fabrication of ordered Ag nanosized monolayer film. The assembled Ag nanosized monolayer film was characterized using scanning electronic microscopy and surface-enhanced Raman scattering (SERS). The results show that the assembled SERS substrate own excellent Raman enhancement and reproducibility. The synthesized SERS-active substrate was further used to detect methyl-parathion, and the limitation of detection can reach 10−7M.

Plasmonic backscattering enhanced inverted photovoltaics

A plasmonic nanoparticle incorporated inverted organic photovoltaic structure was demonstrated where a monolayer of Ag nanoparticles acted as a wavelength selective reflector. Enhanced light harvesting via plasmonic backscattering into the photovoltaic absorber was observed, resulting in a two-fold improvement in the photocurrent and increased open-circuit voltage. Further, utilizing an optical spacer, the plasmonic backscattering was spectrally controlled, thereby modulating the external quantum efficiency and the photocurrent. Unlike a regular thin-film metallic back reflector, excellent off-resonance optical transmission in excess of 80% was observed from the Ag nanoparticles, making this structure highly suitable for semi-transparent and multi-junction photovoltaic applications.

Plasmon-enhanced optical absorption and photocurrent in organic bulk heterojunction photovoltaic devices using self-assembled layer of silver nanoparticles

Improved optical absorption and photocurrent for polythiophene–fullerene bulk heterojunction photovoltaic devices is demonstrated using a unique self-assembled monolayer of Ag nanoparticles formed from a colloidal solution. With the presence of suitable nanoparticle organic capping groups that inhibit its propensity to agglomerate, the particle-to-particle spacing can be tailored. Transmission electron microscopy reveals the self-assembled Ag nanospheres are highly uniform with an average diameter of ∼4 nm and controllable particle-to-particle spacing. The localized surface plasmon resonance peak is ∼465 nm with a narrow full width at half maximum (95 nm). In the spectral range of 350–650 nm, where the organic bulk heterojunction photoactive film absorbs, an enhanced optical absorption is observed due to the increased electric field in the photoactive layer by excited localized surface plasmons within the Ag nanospheres. Under the short-circuit condition, the induced photo-current efficiency (IPCE) measurement demonstrates that the maximum IPCE increased to ∼51.6% at 500 nm for the experimental devices with the self-assembled layer of Ag nanoparticles, while the IPCE of the reference devices without the plasmon-active Ag nanoparticles is ∼45.7% at 480 nm. For the experimental devices under air mass 1.5 global filtered illuminations with incident intensity of 100 mW/cm 2, the increased short-circuit current density is observed due to the enhancement of the photogeneration of excitons near the plasmon resonance of the Ag nanoparticles.

Langmuir–Blodgett Ag nanoparticle monolayer patterned by pulsed laser-induced selective desorption

The control of nanoparticle distribution on a solid substrate is an important and challenging issue in the development of novel nanostructured devices. Here we present a simple optical method for obtaining regular geometric nanoparticle arrangements. Monolayered Ag-nanoparticle films were deposited on glass substrates by the Langmuir–Blodgett (LB) technique. The nanoparticles could be quickly desorbed from the substrate without causing a surface damage, when exposed to pulsed Nd:YAG laser with an energy density over a threshold value. This made it possible to obtain well-aligned patterned arrays simply by a spatial modulation of the pulse energy density. The effects of pulse duration, exposure time, and particle size on this laser-induced selective desorption process are discussed.

Interfacial Rheology of an Ultrathin Nanocrystalline Film Formed at the Liquid/Liquid Interface

We report the interfacial properties of monolayers of Ag nanoparticles 10-50 nm in diameter formed at the toluene-water interface under steady as well as oscillatory shear. Strain amplitude sweep measurements carried out on the film reveal a shear thickening peak in the loss moduli (G") at large amplitudes followed by a power law decay of the storage (G') and loss moduli with exponents in the ratio 2:1. In the frequency sweep measurements at low frequencies, the storage modulus remains nearly independent of the angular frequency, whereas G" reveals a power law dependence with a negative slope, a behavior reminiscent of soft glassy systems. Under steady shear, a finite yield stress is observed in the limit of shear rate .gamma going to zero. However, for .gamma > 1 s-1, the shear stress increases gradually. In addition, a significant deviation from the Cox-Merz rule confirms that the monolayer of Ag nanoparticles at the toluene-water interface forms a soft two-dimensional colloidal glass.

An approach for fabricating self-assembled monolayer of Ag nanoparticles on gold as the SERS-active substrate

In this paper, an approach for fabricating an active surface-enhanced Raman scattering (SERS) substrate is adopted. This approach is based on the assembling of silver nanoparticles film on gold substrate. Rhodamine 6G (R6G) and p-aminothiophenol ( p-ATP) were used as probe molecules for SERS experiments, showing that this new active substrate has sensitivity to SERS response. Tapping-mode atomic force microscopy (AFM) was also used to investigate the surface morphology following the fabricating process of the active SERS substrate, which showed that large quantities of silver nanoparticles were uniformly coated on the substrate.

A convenient phase transfer route for Ag nanoparticles

Generally, phase transfer of metal nanoparticles between aqueous phase and organic phase need two reagents at last. One is stabilizer of nanoparticles , the other is phase-transfer agent (Chem. Lett. 21 (1992) 1527; J. Colloid Interface Sci. 161 (1993) 471; J. Phys. Chem B 101 (1997) 9876; Chem. Commun. (1997) 537; Langmuir 14 (1998) 602; J. Phys. Chem B 103 (1999) 7238; Chem. Mater. 13 (2001) 4692; Langmuir 17 (2001) 733; Langmuir 16 (2000) 9775; Langmuir 18 (2002) 3364; J. Am. Chem. Soc. 123 (2001) 11148). In this paper, Ag nanoparticle prepared by tannic acid reduction of AgNO 3 in aqueous medium were transferred to chloroform solution via a remarkably simple one-step route under the effect of phase-transfer inducer dimethyldioctadecylammonium chloride (DDAC), where no special stabilizer was required. Monolayer of Ag nanoparticles is obtained on carbon film by self-assembly using chloroform organosol. The effect of the inducer DDAC concentration is checked, and it was found that 5×10 −3 mol dm −3 of DDAC was the optimum concentration for phase transfer of Ag nanoparticles. The organosol, Ag nanoparticle self-assembled monolayer and phase transfer were characterized by UV-vis spectra, TEM , ED and TF-IR.

A convenient phase transfer route for Ag nanoparticles

Generally, phase transfer of metal nanoparticles between aqueous phase and organic phase need two reagents at last. One is stabilizer of nanoparticles, the other is phase-transfer agent (Chem. Lett. 21 (1992) 1527; J. Colloid Interface Sci. 161 (1993) 471; J. Phys. Chem B 101 (1997) 9876; Chem. Commun. (1997) 537; Langmuir 14 (1998) 602; J. Phys. Chem B 103 (1999) 7238; Chem. Mater. 13 (2001) 4692; Langmuir 17 (2001) 733; Langmuir 16 (2000) 9775; Langmuir 18 (2002) 3364; J. Am. Chem. Soc. 123 (2001) 11148). In this paper, Ag nanoparticle prepared by tannic acid reduction of AgNO 3 in aqueous medium were transferred to chloroform solution via a remarkably simple one-step route under the effect of phase-transfer inducer dimethyldioctadecylammonium chloride (DDAC), where no special stabilizer was required. Monolayer of Ag nanoparticles is obtained on carbon film by self-assembly using chloroform organosol. The effect of the inducer DDAC concentration is checked, and it was found that 5×10 −3 mol dm −3 of DDAC was the optimum concentration for phase transfer of Ag nanoparticles. The organosol, Ag nanoparticle self-assembled monolayer and phase transfer were characterized by UV-vis spectra, TEM, ED and TF-IR.