等离子体源辅助磁控溅射法低温(200℃)制备多晶硅薄膜

利用电感耦合等离子体辅助中频直流脉冲磁控溅射技术在200℃成功制备出多晶硅薄膜.详细介绍了等离子体源辅助磁控溅射技术制备多晶硅的工艺过程,并对辅助等离子体源放电功率对硅薄膜结晶度的影响进行了研究.利用拉曼散射、X射线衍射、傅里叶红外光谱对所制备的硅薄膜进行了表征.     

Nanophotonic crescent moon structures with sharp edge for ultrasensitive biomolecular detection by local electromagnetic field enhancement effect

We present novel gold nanophotonic crescent moon structures with a sub-10 nm sharp edge, which can enhance local electromagnetic field at the edge area. The formation of unconventional nanophotonic crescent moon structure is accomplished by using a sacrificial nanosphere template and conventional thin film deposition method, which allows an effective batch nanofabrication and precise controls of nanostructure shapes. Unique multiple scattering peaks are observed in a single gold nanocrescent moon with dark-field white light illumination. A 785 nm near-infrared (NIR) diode laser was used as the excitation source to induce the amplified scattering field on the sharp edge of the single gold nanocrescent moon. The Raman scattering spectrum of Rhodamine 6G molecules adsorbed on the single gold nanocrescent moon are characterized, and the Raman enhancement factor of single gold nanocrescent moon is estimated larger than 10(10), which suggests the potential applications of gold nanocrescent moons in ultrasensitive biomolecular detection and cellular imaging using surface enhanced Raman spectroscopy.     

Broadband coherent anti-Stokes Raman spectroscopy characterization of polymer thin films

Broadband coherent anti-Stokes Raman spectroscopy (CARS) is demonstrated as an effective probe of polymer thin film materials. A simple modification to a 1 kHz broad bandwidth sum frequency generation (SFG) spectrometer permits acquisition of CARS spectra for polymer thin films less than 100 nm thick, a dimension relevant to organic electronic device applications. CARS spectra are compared to the conventional Raman spectra of polystyrene and the resonance-enhanced Raman spectra of poly(3-hexylthiophene). The CARS spectra obtained under these conditions consistently demonstrate enhanced signal-to-noise ratio compared to the spontaneous Raman scattering. The sensitivity of the CARS measurement is limited by the damage threshold of the samples. The dielectic properties of the substrate have a dramatic effect on the detected signal intensity. For ultrathin films, the strongest signals are obtained from fused silica surfaces. Similar to surface-enhanced Raman scattering (SERS), Au also gives a large signal, but contrary to SERS, no surface roughening is necessary.     

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.     

Distinguishing individual vibrational fingerprints: single-molecule surface-enhanced resonance raman scattering from one-to-one binary mixtures in Langmuir-Blodgett monolayers

Here, it is demonstrated that similar chemical species within a multicomponent sample can be distinguished, down to the single-molecule level, by means of their surface-enhanced vibrational fingerprints. Surface-enhanced resonance Raman scattering spectra and 2D spatial intensity maps are recorded from thin Ag nanoparticle films coated with fatty acid Langmuir-Blodgett monolayers containing one-to-one binary mixtures, at varying concentrations, of two dye molecules of similar absorption and scattering cross section (n-pentyl-5-salicylimidoperylene and octadecylrhodamine B). The results reveal the change in the distribution of the two dyes within the monolayer, and the breakdown of ensemble spectral averaging, which occur as the single-molecule regime is approached. It is found that the unimolecular level is reached when 1-10 molecules of each dye occupy the 1-microm2 scattering areas probed by the laser. These signals are attributed to the rare spatial coincidence of isolated target analyte molecules and localized electromagnetic hot spots in the nanostructured metal film. The bianalyte nature of the samples provides strong corroborative support for the attribution of spectra to single molecules at high dilution, while the effect of domain formation/aggregation is found to be important at higher concentrations.     

Laser marking on microcrystalline silicon film

We present a compact dot marker using a CW laser on a microcrystalline silicon (Si) thin film. A laser annealing shows a continuous crystallization transformation from nano to a large domain (> 200 nm) of Si nanocrystals. This microscale patterning is quite useful since we can manipulate a two-dimentional (2-D) process of Si structural forms for better and efficient thin-film transistor (TFT) devices as well as for photovoltaic application with uniform electron mobility. A Raman scattering microscope is adopted to draw a 2-D mapping of crystal Si film with the intensity of optical-phonon mode at 520 cm(-1). At a 300-nm spatial resolution, the position resolved the Raman scattering spectra measurements carried out to observe distribution of various Si species (e.g., large crystalline, polycrystalline and amorphous phase). The population of polycrystalline (poly-Si) species in the thin film can be analyzed with the frequency shift (delta omega) from the optical-phonon line since poly-Si distribution varies widely with conditions, such as an irradiated-laser power. Solid-phase crystallization with CW laser irradiation improves conductivity of poly-Si with micropatterning to develop the potential of the device application.     

Normal and surface-enhanced Raman spectroscopy of nitroazobenzene submonolayers and multilayers on carbon and silver surfaces

Raman and ultraviolet-visible (UV-Vis) absorption spectra were obtained for nitroazobenzene (NAB) chemisorbed on smooth and rough silver, and they were compared to published spectra for NAB on sp(2) hybridized pyrolyzed photoresist film (PPF) surfaces. High signal-to-noise ratio Raman spectra were obtained for 4.5 nm thick NAB films on PPF and smooth Ag due to significant enhancement of the NAB scattering relative to that observed in solution. The UV-Vis spectra of chemisorbed NAB exhibited a significant shift toward longer wavelength, thus bringing the NAB absorption closer to the 514.5 nm laser wavelength. The red shift was larger for PPF than for smooth Ag, consistent with the approximately 5x stronger Raman signal obtained on PPF. Deposition of Ag onto quartz without a chromium adhesion layer produced a rough Ag surface that enhanced the Raman spectrum of chemisorbed NAB by a factor of approximately 1000, as expected for roughened Ag due to electromagnetic field enhancement. The strong Raman signal permitted observation of NAB at low coverage and revealed changes in the NAB spectrum as the film progressed from submonolayer to multilayer thicknesses. Finally, deposition of Ag onto PPF/NAB samples through a metal grid produced Ag squares on top of the NAB, which enhanced the Raman scattering of the NAB layer by a factor of approximately 100. Deposition of a final conducting film on the Ag squares should permit in situ observation of a wide range of molecules in operating molecular electronic junctions.     

Characterization of the growth of sol-gel derived Ba---Ti---O thin films by laser Raman spectroscopy

The isothermal growth kinetics of sol-gel derived BaTi₅O₁₁ thin films has been studied by laser Raman spectroscopy. Thin films of the precursors were spin coated on silicon wafers with platinum or gold overlayers. The films were then annealed isothermally, and Raman spectra were recorded in situ. The time-dependent intensity changes of the Raman bands could be analyzed in terms of Avrami models. The interaction of the BaTi₅O₁₁ film with the platinum or gold overlayers during heat treatment apparently increased the Raman intensity by a factor of about 100.     

Intracavity laser spectroscopy for the identification of nanomedia

The optical absorption and emission spectra of heterogeneous plasma formations involved in the thermal synthesis of carbon-based nanomaterials have been studied. A characteristic relationship between parameters of the plasma-assisted synthesis of carbon nanotubes (CNTs) and the spectrum of giant Raman scattering is revealed. Operation of the intracavity laser spectroscopy setup in a near-field microscopy (tip-enhanced Raman spectroscopy) regime was observed. In this regime, a CNT formed in the laser plasma plays the role of a probe capable of enhancing the intensity of emission due to the Raman scattering.     

Characterization of MBa2Cu3O7-x thin films by Raman microspectroscopy

Thin film embodiments of MBa2Cu3O7-x (MBCO, M = yttrium or a rare-earth metal) prepared by several different deposition methods on a variety of substrates were investigated by Raman microspectroscopy. Several of the unique characterization capabilities of Raman spectroscopy in the analysis of MBCO thin films are highlighted by the results of these investigations. The Raman active phonons of the orthorhombic and tetragonal forms of MBCO that are most useful for characterization of textured MBCO films are diagrammed and discussed. A rapid procedure for qualitative texture mapping of MBCO thin films using Raman microscopy techniques is presented, and a new approach for investigating phase separation at the sub-micrometer level in MBCO thin films based on curve resolution of the MBCO Cu2 phonon is described. The assignment of a particular feature often observed in Raman spectra of MBCO films to cation disorder is reinforced by results of a cation substitution study. The depth of penetration of the laser into MBCO films and the type of information that can be obtained by varying the extent of defocusing of the laser are also discussed.     

Thin film deposition on plastic substrates using silicon nanoparticles and laser nanoforming

Reduced melting temperature of nanoparticles is utilized to deposit thin polycrystalline silicon (c-Si) films on plastic substrates by using a laser beam without damaging the substrate. An aqueous dispersion of 5 nm silicon nanoparticles was used as precursor. A Nd:YAG (1064 nm wavelength) laser operating in continuous wave (CW) mode was used for thin film formation. Polycrystalline Si films were deposited on flexible as well as rigid plastic substrates in both air and argon ambients. The films were analyzed by optical microscopy for film formation, scanning electron microscopy (SEM) for microstructural features, energy dispersive spectroscopy (EDS) for impurities, X-ray photoelectron spectroscopy (XPS) for composition and bond information of the recrystallized film and Raman spectroscopy for estimating shift from amorphous to more crystalline phase. Raman spectroscopy showed a shift from amorphous to more crystalline phases with increasing both the laser power and irradiation time during laser recrystallization step.     

Transmission fourier transform Raman spectroscopy of pharmaceutical tablet cores

Transmission Fourier transform (FT) Raman spectroscopy of pharmaceutical tablet cores is demonstrated using traditional, unmodified commercial instrumentation. The benefits of improved precision over backscattering Raman spectroscopy due to increased sample volume are demonstrated. Self-absorption effects on analyte band ratios and sample probe volume are apparent, however. A survey of near-infrared (NIR) absorption spectra in the FT-Raman spectral range (approximately 0 to 3500 wavenumber shift from 1064 nm, or 1064 to 1700 nm) of molecules with a wide range of NIR-active functional groups shows that although absorption at the laser wavelength (1064 nm) is relatively small, some regions of the Raman spectrum coincide with NIR absorbances of 0.5 per cm or greater. Fortunately, the pharmaceutically important regions of the Raman shift spectrum from 0 to 600 cm(-1) and from 1400 to 1900 cm(-1) exhibit low self-absorption for most organic materials. A statistical analysis of transmission FT-Raman noise in spectra collected from different regions of a pharmaceutical tablet provides insight into both spectral distortion and reduced sampling volume caused by self-absorption.     

N1s Electron Binding Energies of CN_x Thin Films Grown by Magnetron Sputtering at Different Temperature

Carbon nitride thin films deposited using dc unbalanced magnetron sputtering system have been analyzed by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT1R) and Raman spectroscopy. The XPS data show that N1s binding states depend on substrate temperature Ts, in which the peak at 400.0 eV increases with Ts, whereas the peak at 398.3 eV decreases with Ts slightly On the basis of XPS, FT1R and Raman spectra, the assignment of N1s electron binding energies was made. The peak at 400.0 eV is attributed to N atoms bonded to sp2 coordinated C atoms. The peak at 398.3 eV is attributed to N atoms bonded to sp3 coordinated C atoms as well as N C bonds.     

Orientation effects in waveguide resonance Raman spectroscopy of monolayers

In this paper we study the effect of molecular orientation on the observed Raman spectra in waveguide Raman spectroscopy. Depolarization ratios differ from those in 'normal' Raman spectroscopy due to the polarization properties of the guiding modes that excite the Raman scattering. Waveguide Raman spectra of submonolayers of cytochrome c and NiOEP were recorded using different polarization settings. The observed depolarization ratios strongly deviate from those obtained in bulk Raman spectra. Using the derived equations for the depolarization ratios, the preferred orientation angle of the molecules can be obtained from the observed depolarization ratios. From these results we first conclude that high-quality spectra of sub-monolayers can be obtained using waveguide Raman spectroscopy and secondly, that these spectra can be used to determine the preferred orientation of the molecule with respect to the waveguide surface.     

Hole-enhanced Raman scattering

Stokes and anti-Stokes non-resonant hole-enhanced Raman scattering (HERS) spectra with high signal-to-noise ratio (S/N) are reported for the first time for aqueous phase R6G molecules adsorbed onto random nanoholes in thin gold films. Compared to conventional surface-enhanced Raman scattering from nanometric gold colloid particles, HERS exhibits higher strength gain, exceptional reproducibility, simple and reliable substrate preparation, and excellent mechanical stability. By correlating the hole density with Raman scattering gain, we determined optimum HERS gain for 50 nm diameter holes at approximately 100 holes/microm(2). Providing a Raman substrate with uniform "hot spots", we expect that HERS will make the quantitative Raman analysis of biological molecules possible.     

Selective Formation of Size-Controlled Silicon Nanocrystals by Photosynthesis in SiO Nanoparticle Thin Film

The SiO_x thin film with a thickness of about 1 mum was formed on a GaAs substrate by bar-coating with the organic solution of the SiO_x nanoparticles (~40 nm). The as-formed SiO_x thin film consists of the SiO_x nanoparticles; thus the thin film is macroscopically discontinuous and is referred to as a nanoparticle thin film. Although there were no silicon (Si) nanocrystals in the as-formed SiO_x nanoparticle thin film, Si nanocrystals were observed by Raman scattering measurement after the thin film was exposed to the laser beam. The growth of Si nanocrystals by laser irradiation is referred to as photosynthesis. The photosynthesis of Si nanocrystals is found to be a self-limiting process. After the average size reaches a certain value, further increase of irradiation time or laser power does not increase the average size. The photosynthesis is similar to the thermal synthesis of Si nanocrystals from SiO_x but much faster and low-temperature growth of Si nanocrystals from SiO _x. Furthermore, the laser irradiation makes nanoparticles larger by merging. This suggests a possibility of low-temperature formation of a Si-nanocrystal array embedded in a SiO₂ thin film. Such a structure has many potential device applications     

KrF excimer laser crystallization of silicon thin films

A KrF excimer laser operating at 249 nm has been employed to crystallize silicon thin films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) and by RF magnetron sputtering on Corning glass and SiO₂. All films display a substantial improvement in crystallinity after ELC with the optimum laser fluence for as-deposited ECR films being higher than for sputtered films. This is probably related to the presence of Si-H_x bonds in the former. A pronounced bimodality in the Raman spectra of some amorphous, as-deposited ECR samples has been observed after laser crystallization where, in addition to the peak at 520cm^-1, a strong peak at 509cm^-1 is also present. Such behavior has not been reported previously to our knowledge in ELC silicon films. Interestingly, the XRD spectra of these samples do not exhibit any peaks suggesting the films are composed of nano-grain material. The dehydrogenation of ECR films by ELC has been demonstrated to be substantial, the hydrogen content typically decreasing from ~30 at % in an as-deposited film to ~10 at % after a single low fluence laser shot. Raman spectroscopy has shown that the film bonding changes from predominantly Si-H₂ to Si-H after ELC. Electrical resistivity measurements of phosphorus-doped films show a controllable and repeatable change with laser fluence. The results in this paper show that it is possible to crystallize and controllably change the electrical characteristics of ECR PECVD produced silicon thin films by ELC.     

Spectral and quantum chemical examination of the Si clusters nascent inside the SiO bulk

In the present communication the results of the synthesis, the quantum chemical (QC) and the spectral examination of the SiO thin film and powder are reported. The QC and Raman studies indicate the formation of the Si clusters inside the bulk of the SiO protoparticle at the very first stages of its gas-phase growth. Infrared, Raman, inelastic neutron scattering and electron spin resonance spectra for the synthesized SiO thin films and the commercial sample have been recorded and simulated in order to verify the theoretical model. The QC calculated radial distribution function and vibrational spectra reproduce well the experimental ones.     

Microstructures of microcrystalline silicon thin films prepared by hot wire chemical vapor deposition

Undoped hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared at low temperature by hot wire chemical vapor deposition (HWCVD). Microstructures of the μc-Si:H films with different H₂/SiH₄ ratios and deposition pressures have been characterized by infrared spectroscopy X-ray diffraction (XRD), Raman scattering, Fourier transform (FTIR), cross-sectional transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The crystallization of silicon thin film was enhanced by hydrogen dilution and deposition pressure. The TEM result shows the columnar growth of μc-Si:H thin films. An initial microcrystalline Si layer on the glass substrate, instead of the amorphous layer commonly observed in plasma enhanced chemical vapor deposition (PECVD), was observed from TEM and backside incident Raman spectra. The SAXS data indicate an enhancement of the mass density of μc-Si:H films by hydrogen dilution. Finally, combining the FTIR data with the SAXS experiment suggests that the Si---H bonds in μc-Si:H and in polycrystalline Si thin films are located at the grain boundaries.     

On-line characterization of YBCO coated conductors using Raman spectroscopy methods

The use of Raman spectroscopy for on-line monitoring of the production of superconducting YBa2Cu3O6+X (YBCO) thin films on long-length metal tapes coated with textured buffer layers is reported for the first time. A methodology is described for obtaining Raman spectra of YBCO on moving tape exiting a metal-organic-chemical-vapor-deposition (MOCVD) enclosure. After baseline correction, the spectra recorded in this way show the expected phonons of the specific YBCO crystal orientation required for high supercurrent transport, as well as phonons of non-superconducting second-phase impurities when present. It is also possible to distinguish YBCO films that are properly textured from films having domains of misoriented YBCO grains. An investigation of the need for focus control on moving tape indicated that focusing of the laser on the surface of the highly reflective YBCO films exiting the MOCVD enclosure tends to produce aberrant photon bursts that swamp the Raman spectrum. These photon bursts are very likely a consequence of optical speckle effects induced by a combination of surface roughness, crystallographic texture, and/or local strain within the small grain microstructure of the YBCO film. Maintaining a slightly out-of-focus condition provides the best signal-to-noise ratio in terms of the obtained Raman spectra. In addition to examining moving tape at the post-MOCVD stage, Raman spectra of the film surface can also be recorded after the oxygen anneal performed to bring the YBCO to the optimum superconducting state. Consideration is given to data processing methods that could be adapted to the on-line Raman spectra to allow the tagging of out-of-specification tape segments and, at a more advanced level, feedback control to the MOCVD process.