Spectroscopic and electrochemical properties of thin solid films of yttrium bisphthalocyanine

Langmuir—Blodgett (LB) and evaporated thin solid films of the yytrium bisphthalocyanine complex (YPc₂) have been prepared on various substrates. Cyclic voltammograms of films are discussed and the electrochromic effect on LB films is reported. A detailed spectroscopic characterization of the YPc₂ material is given using resonance Raman scattering (RRS), surface-enhanced resonance Raman scattering (SERRS), transmission and reflection absorption FT-IR spectroscopy and UV—vis spectra. The spectroscopic characterization of the chemical and electrochemical oxidations products of YPc₂ films and solutions was carried out by in situ UV—vis spectroscopy. Potential applications are discussed.     

Surface enhanced resonance Raman scattering imaging of Langmuir-Blodgett monolayers of bis (benzimidazo) thioperylene.

The synthesis, spectroscopic characterization and surface-enhanced spectroscopy of a new electro active organic material bis (benzimidazo) thioperylene (Monothio BZP) are reported. Langmuir monolayers of Monothio BZP were successfully formed on water subphase and characterized by the pi-A surface-pressure area isotherm. Langmuir-Blodgett (LB) monomolecular layers of Monothio BZP were fabricated onto glass substrates and onto silver island films for surface-enhanced spectroscopic studies. The results of surface-enhanced resonance Raman scattering (SERRS), SERRS imaging and surface-enhanced fluorescence (SEF) studies for Monothio BZP LB monolayers are reported. Raman imaging (global imaging and point-by-point mapping) of the SERRS signal for a single monomolecular layer on silver islands were obtained using the 514.5 nm laser line. The SERRS imaging permits a visualization of the variation of the SERRS intensity across of the rough metal surface. The SEF was recorded for the excimer emission of aggregates in the LB film. The distance dependence and the enhancement factor of SEF were determined using fatty acid spacing layers. A temperature dependence study of the LB monolayer SERRS and SEF spectra was carried out between -190 degrees and + 200 degrees C confirming the thermal stability of the LB monolayer on silver. The specificity and the sensitivity of SERRS signal on metal island films was probed using mixed LB films with 0.01% molecular ratio of Monothio BZP in Arachidic Acid (AA). The micro-Raman SERRS spectra from ca. 10(-3) attomole of the dye were recorded.     

Surface-enhanced spectroscopy of Langmuir—Blodgett films of N-octyl,N′-isobutyl-3,4:9,10-perylene-bis(dicarboximide)

The infrared, resonant Raman and surface-enhanced resonant Raman spectra of N-octyl, N′-isobutyl-3,4:9,10-perylene-bis(dicarboximide) (PBDC) were obtained and the aggregation of PBDC molecules was studied using surface-enhanced fluorescence. Langmuir—Blodgett (LB) films of the neat dye as well as mixed layers with arachidic acid, were prepared and transferred to glass slides and surface-enhanced active surfaces for spectroscopic characterization. A strong red shifted excimer emission was characteristic of LB layers of the neat material and of the thin solid films formed by dipping a glass slide into a solution containing the dye and a volatile solvent. However, using mixed LB monolayers of PBDC and arachidic acid, the surface-enhanced fluorescence of the monomer was observed. The surface-enhanced scattering was measured for both neat and mixed LB layers.     

Surface enhanced fluorescence and Raman imaging of Langmuir-Blodgett azopolymer films

The spectroscopic properties and surface-enhanced spectra of Langmuir-Blodgett (LB) films of methacrylic homopolymer (HPDR13) are presented. It is shown that LB film displays strong fluorescence attributed to the spatial restrictions imposed by its structure. The emission is observed in conjunction with photoisomerization, a process clearly demonstrated by the formation of surface-relief gratings in the LB film [C.R. Mendon?a et al., Macromolecules 32 (1999) 1493]. Surface-enhanced Raman scattering (SERS), Surface-enhanced resonance Raman scattering (SERRS) and surface-enhanced fluorescence (SEF) were observed for LB films of HPDR13 deposited onto silver island films. SERS measurements were also carried out on a sample fabricated with one monolayer LB film deposited onto silver islands followed by one overlayer of silver (LB sandwiched between two layers of silver islands). The polymer interacts very weakly with the metal surface (physisorption), and the enhancement effect is determined by the local electric field enhancement. The strong SERS and SERRS signals were suitable for micro-Raman imaging. Line, area mapping and global images of the LB monolayer on silver island are reported. The transfer ratio in the fabrication of the LB suggests a homogeneous coating of the silver islands, thereby the chemical images show the variation of the SERS intensity due to surface enhancement.     

Spectroscopic characterization and Langmuir-Blodgett films of a novel azopolymer material

Spectroscopic characterization and fabrication of Langmuir and Langmuir-Blodgett (LB) films of an azopolymer-pyridine (PAzPy) are reported. UV-visible absorption and fluorescence spectra, Fourier transform infrared (FTIR) spectra, and Raman spectra were recorded. The vibrational assignment of the observed spectra is supported by a complete geometry optimization, followed by vibrational frequency and intensity computations of both the trans and cis forms of the monomer (AzPy) using density functional theory at the B3LYP 6-31G(d,p) level of theory. Langmuir monolayers of the polymer (PAzPy) were formed at the water-air interface, and LB films of high quality were formed onto solid substrates. The polymer LB films were investigated by surface-enhanced Raman scattering.     

Molecular Orientation and Structural Characterization of Ultrathin Films of C12AzoNaph(1,4)C6N-SDS Studied by FT-IR and NIR-SERS Spectroscopies

IntroductionAzobenzene- containing long- chain fatty acidsand their ammonium amphiphiles have recentlyaroused a great interest of some researchersbecause of their promising photochromicproperties[1— 6 ] . In order to understand theinteresting physical properties the LB films withazo chromophores show,a structure- functionrelationship of the films must be explored.Thusfar,infrared spectroscopy has been usedextensively for the investigations of molecularaggregation,orientation and structuralch…     

Vibrational and surface-enhanced vibrational spectra of 6-nitrochrysene

The infrared and Raman spectra of solids and thin solid films of 6-nitrochrysene, its electronic spectra, and resonance Raman scattering (RRS) obtained with UV-laser excitation at 325 nm are reported. The vibrational assignment is supported by ab initio computations at the B3LYP/6-311G(d, p) level of theory. The molecular organization in nanometric films evaporated onto smooth metal surfaces of silver and copper was probed using reflection-absorption infrared spectroscopy (RAIRS). The results of the surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA) obtained from nanometric films evaporated onto silver island films are also discussed. It was found that the molecule efficiently interacts with silver island film surfaces, and that the interaction leads to extensive photochemical reaction at the metal surface under laser illumination.     

Raman spectroscopic investigation of the single-monolayer Langmuir-Blodgett film of C16NaphOH and C10AzoNaphC4N-SDS

Raman spectra were measured for Langmuir-Blodgett (LB) films of C(16)NaphOH and C(10)AzoNaphC(4)N-SDS on Calcium Fluorite substrate for the first time. In order to find out favorable excitation condition, Raman spectra of the single and multi-monolayer LB films excited at different lines at 244, 514, 633 and 778 nm are recorded and compared in the present study. Raman spectrum of the monolayer LB film of C(16)NaphOH excited by 244 nm demonstrate that excellent signal to noise is achieved even for one monolayer LB film with an extremely short integrating time as 60 s because of being resonantly enhanced, while no meaningful spectra were recorded under the same condition for the monolayer LB film of C(10)AzoNaphC(4)N-SDS because of burning. Using a HeNe 633 nm excitation the problem with strong substrate fluorescence was partially solved, since under these conditions this fluorescence is mainly outside the fingerprint region of the LB film molecules (1000-2000 cm(-1)). Therefore by using the HeNe laser excitation, Raman spectra with high signal to noise ratio of LB films of C(16)NaphOH were collected and shown in this paper. These findings stress again the necessity to define an appropriate Raman system for this special application of LB film diagnosis.     

Single molecular detection of a perylene dye dispersed in a Langmuir-Blodgett fatty acid monolayer using surface-enhanced resonance Raman scattering

The Langmuir-Blodgett (LB) monolayer technique was used to fabricate single molecule LB monolayer containing bis(phenethylimido)perylene (PhPTCD), a red dye dispersed in arachidic acid (AA) with an average doping of 1 molecule per microm2. The monolayer was transferred onto Ag island films to obtain spatially resolved surface-enhanced resonance Raman scattering (SERRS) spectra. The mixed LB monolayers were fabricated with a concentration, on average, of 1, 6, 19 and 118 PhPTCD molecules per microm2 in AA. The AA provides a two-dimensional host matrix whose background signal does not interfere with the detection of the probe molecule's SERRS signal. The properties of the single molecule detection were investigated using micro-Raman with a 514.5-nm laser line. The Ag island surfaces coated with the LB monolayer were mapped with spatial steps of 3 microm and global chemical imaging of the most intense SERRS band in the spectrum was also recorded. The SERRS and surface-enhanced fluorescence (SEF) of the neat and single molecule LB monolayer were recorded in a temperature range from liquid nitrogen to + 200 degrees C. Neat PhPTCD LB monolayer spectra served as reference for the identification of characteristic signatures of the single molecule behavior. The spatial resolution of Raman-microscopy experiments, the multiplicative effect of resonance Raman and SERRS, and the high sensitivity of the new dispersive Raman instruments, allow SERRS to be part of the family of single molecular spectroscopies.     

The role of cavity sites in surface-enhanced Raman scattering

Thermal desorption spectra (TDS) of pyridine from silver films deposited in ultra high vacuum are reported. Marked differences in the TDS are seen depending on the deposition conditions and the thermal history of the films, which have been correlated with surface-enhanced Raman scattering (SERS). These results as well as some of the observations in electrochemical systems are discussed in light of the recent Xe probe analysis carried out by Albano et al.     

Characterization and surface-enhanced Raman spectral probing of silver hydrosols prepared by two-wavelength laser ablation and fragmentation

A four step Ag foil laser ablation-Ag nanoparticle fragmentation procedure in ultrapure water was carried out both under argon and in air. Pulses of a high power Nd/YAG laser were used for laser ablation (1064 nm) and for the three step Ag hydrosol treatment in the absence of Ag foil in the sequence 1064-532-1064 nm. Transmission electron microscopy (TEM) and surface plasmon (SP) extinction spectra provide evidence of Ag nanoparticle fragmentation in the second and third step of the procedure carried out under argon. While polydispersity of Ag hydrosol increases in the second step, both the polydispersity and the mean size of the nanoparticles are reduced in the third step. Qualitative and quantitative surface-enhanced Raman scattering (SERS)/surface-enhanced resonance Raman scattering (SERRS) spectral probing of systems with Ag hydrosols and the selected adsorbates at 514.5 nm excitation shows that Ag hydrosols obtained in the second step of the preparation procedure carried out in air are the most suitable substrates for SERS/SERRS experiments performed at this excitation wavelength.     

An ionic surfactant-mediated Langmuir-Blodgett method to construct gold nanoparticle films for surface-enhanced Raman scattering

A gold nanoparticle film for surface-enhanced Raman scattering (SERS) was successfully constructed by an ionic surfactant-mediated Langmuir-Blodgett (LB) method. The gold film was formed by adding ethanol to a gold colloid/hexane mixture in the presence of dodecyltrimethylammonium bromide (DTAB). Consequently, gold nanoparticles (AuNPs) assembled at the water/hexane interface due to the decrease in surface charge density of AuNPs. Since DTAB binds the gold surface by a coulombic force, rather than a chemical bonding, it is easily replaced by target molecules for SERS purposes. The SERS enhancement factor of the 80 nm gold nanoparticle film was approximately 1.2 × 10(6) using crystal violet (CV) as a Raman dye. The SERS signal from the proposed DTAB-mediated film was approximately 10 times higher than that from the octanethiol-modified gold film, while the reproducibility and stability of this film compared to an octanethiol-modified film were similar. This method can also be applied to other metal nanostructures to fabricate metal films for use as a sensitive SERS substrate with a higher enhancement factor.     

Ultra thin films of nanocrystalline Ge studied by AFM and interference enhanced Raman scattering

Initial growth stages of the ultra thin films of germanium (Ge) prepared by ion beam sputter deposition have been studied using atomic force microscope (AFM) and interference enhanced Raman scattering. The growth of the films follows Volmer-Weber growth mechanism. Analysis of the AFM images shows that Ostwald ripening of the grains occurs as the thickness of the film increases. Raman spectra of the Ge films reveal phonon confinement along the growth direction and show that the misfit strain is relieved for film thickness greater than 4 nm. Dedicated to Professor C N R Rao on his 70th birthday     

化学气相沉积法制备ZnO纳米结构薄膜及其SERS活性研究

提供了半导体作为光、电和生物等功能材料的表面和界面信息, 同时也为SERS的研究开拓了新的领域.     

Spectroscopic studies on molecular recognition capabilities of a nucleolipid bearing thymine headgroup to adenosine

The Langmuir-Blodgett (LB) films of octadecanoyl ester of 1-(2-carboxyethyl) thymine deposited from pure water and aqueous adenosine subphases were investigated by ultraviolet-visible (UV-vis), Fourier transform infrared-attenuated total reflection (FTIR-ATR), and Fourier transform surface-enhanced Raman scattering (FT-SERS) spectroscopy. The obtained spectral results indicate that the adenosine molecules in the subphase can be transferred onto solid substrates by LB techniques as a result of the formation of base pairs at the air/water interface. UV-vis spectra alternations indicated that, with increasing adenosine concentration in subphase, more adenosine molecules were recognized by nucleolipid monolayer and were transferred onto the quartz substrates. The closed-packing of the constituent molecules facilitates the photodimerization of the thymine moieties in the headgroup under ultraviolet irradiation. FTIR-ATR results suggest that the hydrocarbon chains of nucleolipid in the LB films deposited from pure water and aqueous adenosine take on a close-packed all trans conformation. By analyzing the FT-SERS spectra results, it can be deduced that the orientation of nucleobase in the headgroup is different before and after the recognition effect occurred. For LB film deposited from pure water, the nucleobases are lying flat on the silver substrates; whereas for LB film deposited from aqueous adenosine, the base pairs take an end-on adsorption on silver substrate.     

Surface-enhanced Raman scattering characteristics of 4-nitrobenzenethiol adsorbed on palladium and silver thin films

Palladium is an important catalytic metal, and it is desirable to develop a surface-enhanced Raman scattering (SERS) technique to investigate the reagent and product species adsorbed on its surface. Unfortunately, Pt-group metals, e.g., Pt and Pd, have been commonly considered as non- or weak-SERS-active substrates. In this work, Ag and Pd thin films were deposited very efficiently and evenly onto the surface of glass substrates by using only corresponding metal nitrate salts (AgNO₃ and Pd(NO₃)₂) with butylamine in ethanolic solutions. In this process, pure ethanol was used for Ag deposition, while an ethanol–water (8:2) mixture was used for Pd deposition. The as-prepared Ag and Pd films exhibited SERS activity over a large area. The surface-induced photoconversion capabilities of these Ag and Pd films were then tested on 4-nitrobenzenethiol by means of SERS. It was found that at least under visible laser irradiation, the surface-catalyzed photoreaction occurs more readily on a Ag film than on a Pd film for the conversion of 4-nitrobenzenethiol to 4-aminobenzenethiol, even though Pd is known to be an important transition metal with high catalytic activity.     

Noble-metal nanostructures for controlling surface plasmons and sensing molecules

Arrays of nanoapertures in thin silver film were fabricated by deposition of metal through a self-organizing distribution of polystyrene nanospheres. We demonstrate that both the surface-enhanced Raman scattering (SERS) and fluorescence decay of probe molecules are strongly dependent on the plasmonic environment exhibited as fabricated nanostructures.     

Surface enhanced vibrational spectra of thymine

Surface-enhanced vibrational spectroscopy (SEVS) is discussed using 5-methyluracil (thymine) as a model compound. Surface-enhanced Raman scattering (SERS) and surface-enhanced infrared (SEIR) are reported and a characterization of thymine adsorbed onto silver island films is provided. The thymine SERS spectra obtained using silver colloids, silver roughened electrodes and silver island films are remarkably different due to several binding possibilities of thymine during chemical adsorption onto a silver surface. It is shown that laser induced photo dissociation may lead to further changes in the recorded spectra of the adsorbate. The surface enhanced-infrared (SEIR) spectra of thymine on silver island are reported here for the first time. The infrared spectra of thymine films were also been obtained to help the assignment of molecular vibrations in the surface enhanced spectra.     

Organic vapor sensing properties and characterization of α-naphthylmethacrylate LB thin films

Determination of organic vapor sensing properties of α-Naphthylmethacrylate (α-NMA) monomer based Langmuir-Blodgett (LB) thin films was aimed in this study. LB thin film fabrication was performed on quartz glass and quartz crystal substrates in order to investigate the characterization and organic vapor properties of α-NMA materials by using UV-Visible, Atomic Force Microscopy (AFM) and Quartz Crystal Microbalance (QCM) techniques. π-A isotherm graph was taken and a suitable surface pressure value were primarily determined as 13?mN m^?1 for successful α-NMA LB thin film fabrication. Transfer ratio value was found to be ≥ 0.93 for quartz glass and quartz crystal substrates. The typical frequency shift per layer was obtained as 16.93?Hz/layer and the deposited mass onto a quartz crystal was calculated as 271.30?ng/layer (1.02?ng mm^?2). The sensing responses of α-NMA LB films against dichloromethane, chloroform, toluene and m-xylene were measured by QCM system. Dichloromethane created the maximum shift in the resonance frequency than other organic vapors used in this study. Results exhibited that α-NMA LB thin films were potential candidates for organic vapor sensing applications, especially high sensitive detection of dichloromethane at room temperature.     

由组分可控的LB膜前驱物法制备Y2O3稳定立方相ZrO2的超薄陶瓷膜

由有机LB膜技术发展了一种制备组分、厚度可控的无机超薄陶瓷膜的方法.以Zr、 Y的β-二酮络合物的作为"表面离子"代替传统的亚相离子,沉积它们与花生酸的混合LB膜.并将它作为前驱物,经臭氧处理和热处理,成功制得了Y2O3稳定的立方相ZrO2超薄膜(YSZ).用X射线衍射(XRD)、 X射线光电子能谱(XPS)等手段研究了YSZ薄膜的相结构和其组成.结果表明,超薄陶瓷膜中Zr与Y的含量比率控制得很好,且形成Y2O3稳定的立方相ZrO2.说明这种方法可以成功地用来制备组分和膜厚均可控的纳米陶瓷膜.