Ultraviolet-visible and surface-enhanced Raman scattering spectroscopy studies on self-assembled films of ruthenium phthalocyanine on organic monolayer-modified silver substrates

A self-assembled film of ruthenium phthalocyanine (RuPc) fabricated on a silver substrate pre-modified with a monolayer of 4-mercaptopyridine (PySH) or 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (BPENB) was studied by ultraviolet-visible (UV-Vis) and surface enhanced Raman scattering (SERS) spectroscopy. PySH or BPENB was used as a ligand to link RuPc since they not only modify the silver substrate, but also deliver a pyridyl group pointing out from the silver surface. Therefore, we can explore the relationship between the structure and orientation of metallophthalocyanine and the substrate modified by the two kinds of organic-monolayers with the different conjugates and molecular lengths. UV-Vis bands due to the organic-monolayer (PySH or BPENB) modified silver films shift to longer wavelengths and a new band arising from the metallophthlocyanine appears, suggesting the binding of RuPc to PySH/BPENB, as well as the interaction between the marcocycle of RuPc and the ring of PySH/BPENB. Vibrational bands arising from both the RuPc and PySH/BPENB moieties appear clearly in the SERS spectra of the RuPc-PySH/BPENB composite films, indicating that RuPc is successfully assembled on the top of PySH/BPENB film. The shifts and relative intensity changes of bands due to PySH or BPENB in the SERS spectra imply the binding of the metallophthalocyanine to the pyridyl group in the composite films. Furthermore, the comparison of the SERS spectra revealed that the orientations of PySH and BPENB in the two kinds of composite films are different; the BPENB moiety in the RuPc-BPENB composite film is more perpendicular to the silver surface compared with the PySH moiety in the RuPc-PySH composite film.     

High-density silver nanoparticle film with temperature-controllable interparticle spacing for a tunable surface enhanced Raman scattering substrate

The formation of high-density silver nanoparticles and a novel method to precisely control the spacing between nanoparticles by temperature are demonstrated for a tunable surface enhanced Raman scattering substrates. The high-density nanoparticle thin film is accomplished by self-assembling through the Langmuir-Blodgett (LB) technique on a water surface and transferring the particle monolayer to a temperature-responsive polymer membrane. The temperature-responsive polymer membrane allows producing a dynamic surface enhanced Raman scattering substrate. The plasmon peak of the silver nanoparticle film red shifts up to 110 nm with increasing temperature. The high-density particle film serves as an excellent substrate for surface-enhanced Raman spectroscopy (SERS), and the scattering signal enhancement factor can be dynamically tuned by the thermally activated SERS substrate. The SERS spectra of Rhodamine 6G on a high-density silver particle film at various temperatures is characterized to demonstrate the tunable plasmon coupling between high-density nanoparticles.     

Novel method for preparing controllable and stable silver particle films for surface-enhanced Raman scattering spectroscopy

A new surface-enhanced Raman scattering (SERS) active substrate has been developed based on our previous study. Small silver nanoparticles on a quartz slide can be enlarged by using a mixture of commercially available reagents called Silver Enhancer and Initiator. The optical properties and characteristics of the new substrate have been investigated by ultraviolet-visible (UV-Vis) spectroscopy and atomic force microscopy (AFM). The results indicate that the small silver nanoparticles grow and some silver aggregates emerge on the quartz slide after the slide is immersed into the Silver Enhancer and Initiator Mixture (SEIM). The average diameter of the silver nanoparticles on the substrate becomes approximately double after the immersion into SEIM for 20 s. 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (BPENB) was used as a Raman probe to evaluate the enhancement ability of the new silver substrate. It has been found that the SERS intensity can be increased about 10 times by using the substrate treated by SEIM compared with that without being treated by SEIM. Interestingly enough, the SERS enhancement increases with time. This may be due to the reorganization of silver nanoparticles on the quartz surface. The new substrate can remain active for more than 90 days. The adsorption mode of BPENB on the new substrate and the dependence of the BPENB configurations on the concentration of BPENB in methanol solution have also been investigated by SERS or UV-Vis spectroscopy. The SERS spectra of a self-assembled monolayer (SAM) BPENB film adsorbed on a silver substrate treated by SEIM show that BPENB molecules are chemically absorbed through the Ag-N bond. Consequently, a nearly perpendicular orientation of BPENB on the silver surface is proposed. The SERS spectra of BPENB SAMs on the new substrates fabricated from methanol solutions with different concentrations are compared. The concentration dependence of the SERS spectra reveals that the BPENB molecules are adsorbed on the silver film as monomers when the film is prepared from the solution with a lower concentration (<4 x 10(-6) M) and as aggregates when it is prepared from the solution with a higher concentration (>1 x 10(-5) M).     

Preparation of silver nanoparticles by photo-reduction for surface-enhanced Raman scattering

A substrate for surface-enhanced Raman scattering (SERS) has been developed. Based on the surface-catalyzed reduction of Ag⁺ by citrate on the silver nanoparticles surface under light irradiation, small silver seeds on a quartz slide can be enlarged. The optical properties and characteristics of the silver films have been investigated by ultraviolet-visible spectroscopy, scan electron microscope and atomic force microscopy (AFM). The results indicate that the particle size and shape are different at different reduction time. At the first 3 h, some triangular and hexagonal nanoparticles formed; with the reduction proceeding, the shape of the silver particles became irregular and the size became larger. The silver films obtained are very suitable as SERS active substrate. The relationship between SERS intensity and the reduction time has been investigated for 1,4-bis[2-(4-pyridyl)ethenyl]-benzene molecule adsorbed on the silver film. The SERS intensity reached a maximum at 8 h reduction. The AFM measurements indicate that roughness features with an average size of 100 nm are present on the surface, which yielded the strongest SERS signal. Pyridine was used as a probe molecule to investigate the enhancement factor (EF) of the silver films. According to the formalism of Tian and co-workers, the EF of the silver films is estimated to be 3.4 × 10⁵. The silver film that can remain active for more than 50 days would seem to be suitable for various analytical applications.     

Palladium and gold nanoparticle array films formed by using self-assembly of block copolymer

The well-arrayed Pd and Au nanoparticle thin films were successfully prepared by making use of self-assembled PS-b-P4VP block copolymer (BCP) as a mask for the reduction of PdCl2 deposited on glass substrate. The films consisted of spherialcal nanoparticles with an average diameter of about 45 nm. For monitoring the size, shape and array formation of Pd nanopaticle films, this procedure was proved better to the conventional process in which PdCl2 impregnated in the channels of self assembled BCP film is reduced to form nanoparticle array. This observations of Pd nanoparticle array film formation is supported by the AFM and UV-VIS studies of Au nanoparticle array films formed by conventional method.     

A biomimetic approach to the deposition of ZrO2 films on self-assembled nanoscale templates

Zirconium oxide thin films were deposited on a phosphonate-terminated self-assembled monolayer (SAM) on a single crystal silicon substrate by a hydrolysis of zirconium sulfate solution in acid environment at 80 °C. The ZrO₂ films consist of tetragonal ZrO₂ crystallites with a size of 5–10 nm. Surface nucleation and attraction between the SAM surface and bulk precipitates in solution can explain the film formation. In both mechanisms, the surface functionality of the SAM plays a crucial role. This deposition approach was inspired by biomineralization through controlled deposition of inorganic solids on an ordered organic matrix. Microstructures and mechanical properties of the ZrO₂ thin films were studied using scanning electron microscope (SEM), cross-sectional transmission electron microscope (TEM) and nanoindentation. Microstructures were tailored at different stages of the film growth, as well as with processing parameters and substrate surface conditions. The nanoindentation modulus and hardness of the as-deposited ZrO₂ films were much lower than those of the bulk ZrO₂. The addition of extra pressure during this process, however, restores mechanical properties of ZrO₂ films.     

银纳米颗粒单层膜的组装及其SERS特性研究

用柠檬酸三钠还原硝酸银制备银溶胶,再添加己烷和乙醇,银纳米颗粒会组装在水面上。利用LB拉膜机滑障沿水面压缩银纳米颗粒,使得银纳米颗粒紧密有序地排列在水面上。把这层银纳米颗粒转移到硅衬底上,即得到一种密集排列的银纳米颗粒单层膜SERS基底,采用扫描电子显微镜（SEM）研究该基底的表面形貌,并以罗丹明6G（Rh6G）作为探针分子检测其SERS活性,结果表明,银纳米颗粒具有较好的均一性和聚集度,且Rh6G在该单层膜基底上得到了非常好的SERS效应。     

Optical switch from silver nanocomposite thin films

Silver nanoparticles capped with sodium alginate were assembled into thin films by using the layer-by-layer dipping technique. Composite films were built by sequential dipping of a glass slide in either anionic alginate capped nanoparticles or cationic Poly(diallyldimethylammonium chloride) (PDADMAC). The growth of the film was characterized using UV-Vis spectroscopy by monitoring the increase in absorbance at 420 nm which correspond to the silver nanoparticles plasmon band. The final films formed onto glass slides displayed and interesting color shift upon exposure to water or to a less polar solvent such as ethanol. In this research, changes in spectral absorbance of the nanoparticles film were monitored as a function of ethanol content (0, 20, 40, 60, 80 and 100%) in water. The color shift from yellow to red color was explained by the changes in the dielectric constant of the silver nanoparticles surrounding medium which induce a shift in their plasmon band absorbance. These composite thin films displayed fast color change and could therefore be used in sensing application as well as for optical switches.     

Glucose sensing using near-infrared surface-enhanced Raman spectroscopy: gold surfaces, 10-day stability, and improved accuracy

This research presents the achievement of significant milestones toward the development of a minimally invasive, continuously monitoring, glucose-sensing platform based on the optical quantitation of glucose in interstitial fluid. We expand our initial successes in the measurement of glucose by surface-enhanced Raman scattering (SERS), demonstrating substantial improvements not only in the quality and optical properties of the substrate system itself but also in the robustness of the measurement methodology and the amenability of the technique to compact, diode laser-based instrumentation. Herein, we compare the long-term stability of gold to silver film over nanosphere (AuFON, AgFON) substrates functionalized with a partitioning self-assembled monolayer (SAM) using both electrochemical and SERS measurements. AuFONs were found to be stable for a period of at least 11 days. The switch to AuFONs not only provides a more stable surface for SAM formation but also yields better chemometric results, with improved calibration and validation over a range of 0.5-44 mM (10-800 mg/dL). Measured values for glucose concentrations in phosphate-buffered saline (pH approximately 7.4) based on 160 independent SERS measurements on AuFONs have a root-mean-square error of prediction of 2.7 mM (49.5 mg/dL), with 91% of the values falling within an extended A-B range on an expanded Clarke error grid. Furthermore, AuFONs exhibit surface plasmon resonances at longer wavelengths than similar AgFONs, which make them more efficient for SERS at near-infrared wavelengths, enabling the use of low-power diode lasers in future devices.     

Large-scale homogeneously distributed Ag-NPs with sub-10 nm gaps assembled on a two-layered honeycomb-like TiO(2) film as sensitive and reproducible SERS substrates

We present a surface-enhanced Raman scattering (SERS) substrate featured by large-scale homogeneously distributed Ag nanoparticles (Ag-NPs) with sub-10?nm gaps assembled on a two-layered honeycomb-like TiO(2) film. The two-layered honeycomb-like TiO(2) film was achieved by a two-step anodization of pure Ti foil, with its upper layer consisting of hexagonally arranged shallow nano-bowls of 160?nm in diameter, and the lower layer consisting of arrays of about fifty vertically aligned sub-20?nm diameter nanopores. The shallow nano-bowls in the upper layer divide the whole TiO(2) film into regularly arranged arrays of uniform hexagonal nano-cells, leading to a similar distribution pattern for the ion-sputtered Ag-NPs in each nano-cell. The lower layer with sub-20?nm diameter nanopores prevents the aggregation of the sputtered Ag-NPs, so that the Ag-NPs can get much closer with gaps in the sub-10?nm range. Therefore, large-scale high-density and quasi-ordered sub-10?nm gaps between the adjacent Ag-NPs were achieved, which ensures homogeneously distributed 'hot spots' over a large area for the SERS effect. Moreover, the honeycomb-like structure can also facilitate the capture of target analyte molecules. As expected, the SERS substrate exhibits an excellent SERS effect with high sensitivity and reproducibility. As an example, the SERS substrate was utilized to detect polychlorinated biphenyls (PCBs, a kind of persistent organic pollutants as global environmental hazard) such as 3,3',4,4'-pentachlorobiphenyl (PCB-77) with concentrations down to 10(-9)?M. Therefore the large-scale Ag-NPs with sub-10?nm gaps assembled on the two-layered honeycomb-like TiO (2) film have potentials in SERS-based rapid trace detection of PCBs.     

Nano-silver mediated polymerization of pyrrole: synthesis and gas sensing properties of polypyrrole (PPy)/Ag nano-composite

Thermal polymerization of pyrrole was performed using silver nitrate as source of silver ions followed by its conversion to Polypyrrole (PPy)/Ag nano-comoposites without using any external oxidizing agent or solvent. The formation of PPy was monitored by UV-Visible absorption spectroscopy showing a band at approximately 464 nm. XRD measurement confirmed characteristic peaks for face centered cubic (fcc) silver and presence of PPy at 2 theta of approximately 23 degrees suggesting the formation of PPy/Ag nanocomposite. Transmission electron microscopy (TEM) images showed non-aggregated spherical Ag nano-particles of about 5-10 nm. PPy/Ag thick film acts as a NH3 sensor at 100 degrees C, a H2S sensor at 250 degrees C and CO2 sensor at 350 degrees C. The thick films showed capability to recognize various gases at different operating temperature.     

铜合金表面均三嗪二硫醇与硅烷复合自组装薄膜的制备及其耐蚀性

采用自组装技术,在铜合金表面制备了单一6-N,N-二丁基胺-1,3,5-三嗪-2,4-硫醇(DB)和3-巯基丙基三甲氧基硅烷(MPTES)自组装薄膜及二者的复合自组装薄膜。通过傅里叶变换红外光谱(FT-IR)、接触角测量、极化曲线和盐水浸泡实验(0.5M NaCl)对铜合金表面的自组装薄膜的特性进行了表征。结果表明:与未处理的铜合金相比,经复合自组装薄膜修饰的铜合金表面接触角由85.8°上升到107.3°,提高了铜合金表面的疏水性;红外光谱结果也表明复合自组装薄膜在铜合金表面的形成;极化曲线测试和盐水试验均表明了该复合自组装薄膜有效地提高了铜合金的耐腐蚀能力。     

Electrochemical synthesis using a self-assembled Au nanoparticle template of dendritic films with unusual wetting properties

This report describes the electrochemical preparation of dendritic silver films with unusual wetting properties coming from the use of a self-assembled gold nanoparticle (Au NP) template. It shows that the Au NP self-assembled monolayer on the highly ordered pyrolytic graphite (HOPG) surface is responsible for the formation of the dendritic morphology, which is not observed for the same deposition conditions on a bare HOPG substrate. An interesting evolution of the wetting properties of these films during the electrodeposition process is observed. Field emission scanning electron microscopy (FEGSEM), energy-dispersive spectrometry (EDS), x-ray photoelectron spectroscopy (XPS) and contact angle measurements are used to reveal the dendritic structure of the deposited silver film at a later stage of the electrodeposition process. They also reveal surprising wetting properties in terms of hydrophobic surface.     

Highly aligned epitaxial nanorods with a checkerboard pattern in oxide films

One of the central challenges of nanoscience is fabrication of nanoscale structures with well-controlled architectures using planar thin-film technology. Herein, we report that ordered nanocheckerboards in ZnMnGaO4 films were grown epitaxially on single-crystal MgO substrates by utilizing a solid-state method of the phase separation-induced self-assembly. The films consist of two types of chemically distinct and regularly spaced nanorods with mutually coherent interfaces, approximately 4 x 4 x 750 nm3 in size and perfectly aligned along the film growth direction. Surprisingly, a significant in-plane strain, more than 2%, from the substrate is globally maintained over the entire film thickness of about 820 nm. The strain energy from Jahn-Teller distortions and the film-substrate lattice mismatch induce the coherent three-dimensional (3D) self-assembled nanostructure, relieving the volume strain energy while suppressing the formation of dislocations.     

[101]取向Li掺杂ZnO薄膜光学性能的研究

采用射频磁控溅射法在玻璃衬底上制备了[101]取向的Li:ZnO薄膜, 研究了该薄膜的光学性能随热处理温度变化的规律. 结果表明, 399nm的发光峰是由Li的杂质能级引起; 与[002]取向的薄膜相比, 未经热处理的[101]薄膜其光学带隙大, 且出现了380nm附近的带边发射(NBE) 峰; 在560～580℃热处理下, 其晶胞变小、光学带隙变窄、360nm 左右的带间发光峰红移; 当热处理温度升至610℃时, 薄膜中再次出现380nm的NBE峰.     

Surface-enhanced Raman scattering dendritic substrates fabricated by deposition of gold and silver on silicon

This paper reports a study on the preparation of gold nanoparticles and silver dendrites on silicon substrates by immersion plating. Firstly, gold was deposited onto silicon wafer from HF aqueous solution containing HAuCl4. Then, the silicon wafer deposited gold was dipped into HF aqueous solution of AgNO3 to form silver coating gold film. Scanning electron microscopy reveals a uniform gold film consisted of gold nanoparticles and rough silver coating gold film containing uniform dendritic structures on silicon surface. By SERS (surface-enhanced Raman scattering) measurements, the fabricated gold and silver coating gold substrates activity toward SERS is assessed. The SERS spectra of crystal violet on the fabricated substrates reflect the different SERS activities on gold nanoparticles film and silver coating gold dendrites film. Compared with pure gold film on silicon, the film of silver coating gold dendrites film significantly increased the SERS intensity. As the fabrication process is very simple, cost-effective and reproducible, and the fabricated silver coating gold substrate is of excellent enhancement ability, spatial uniformity and good stability.     

Plasmonic enhancement of fluorescence on silver nanoparticle films

The localized plasmon controlled fluorescence has been discussed by comparing the fluorescence enhancement of dyes on different shaped silver nanoparticle self-assembled films. A trilayer structure, composed of a silver nanoparticle monolayer, a proper thickness polyelectrolyte spacing layer and a dye-adsorbed layer, was constructed to study the plasmon enhanced fluorescence properties. The effective coupling of the plasmon band with the excitation or emission of dye resulted in different enhancement factors. Moreover, the plasmon enhanced fluorescence resonance energy transfer (FRET) of two dyes was observed. The FRET efficiency of the spherical silver nanoparticle self-assembled film had a 2.8-fold increase. The improvement of FRET efficiency via localized surface plasmons would increase the sensitivity of FRET-based bioassays.     

A reusable surface-enhanced Raman scattering (SERS) substrate prepared by atomic layer deposition of alumina on a multi-layer gold and silver film

A thermally stable, reusable surface-enhanced Raman scattering (SERS) substrate consisting of a gold/silver bi-layer film with a protective alumina coating is reported. The film is synthesized by thermally evaporating sequential layers of gold and silver followed by coating an ultra-thin alumina layer using atomic layer deposition. The use of gold as the foundational layer improves the thermal stability of the metal bi-layer film while providing the additional ability to tune the SERS response. Deposition of the thin alumina overlayer on the bi-layer film creates a SERS substrate capable of enduring multiple high-temperature exposures to 400 °C with minimal loss of enhancement capabilities. We demonstrate the multi-use capability of the substrate by measuring the SERS spectrum of rhodamine 6G followed by a thermal treatment at 400 °C to remove the analyte. A representative substrate was used to acquire SERS spectra of rhodamine 6G up to five repeat measurements, thus establishing the reusability of this relatively simple, inexpensive, and stable substrate.     

Synthesis of silver nanoparticles in a polyvinylpyrrolidone (PVP) paste, and their optical properties in a film and in ethylene glycol

Silver nanoparticles were synthesized in a paste of polyvinylpyrrolidone formed after mixing PVP with acetone and a small volume of aqueous silver nitrate under magnetic stirring. A film made with the material was characterized by UV-vis spectroscopy. The obtained spectrum shows a single peak at 438 nm, arising from the surface plasmon absorption of silver colloids. This result clearly indicates that silver nanoparticles are embedded in PVP. When the pre-treated PVP-Ag colloid is dissolved in ethylene glycol, the UV-vis spectrum of the resulting dispersion shows an absorption peak at 433 nm, whose maximum absorption blue shifts to 416 nm after 18 days of agitation. The silver nanoparticles have an average particle size of 4.12 nm. Because the IR band assigned to the carbonyl group of the PVP shifts to longer wavelengths, the interaction of this polymer with silver nanoparticles seems to take place through the carbonyl oxygen.     

Controlled layer-by-layer formation of ultrathin TiO2 on silver island films via a surface sol-gel method for surface-enhanced Raman scattering measurement

A surface sol-gel process has been demonstrated to be an effective method for the surface modification of silver island films as unique SERS substrates for monitoring molecular adsorption on a dielectric titania surface. This layer-by-layer approach allows control of the thickness of the dielectric surface with a monolayer precision on silver surfaces. The enhancement of Raman scattering from adsorbed Rhodamine 6G molecules is inversely proportional to the thickness of the titania film, which is consistent with the decay of electromagnetic enhancement. Despite a reduction in the sensitivity of the film, a substantial improvement in the film was achieved as a result of the enhanced stability of this substrate compared to the silver island film without a TiO(2) coating.