氧化锌薄膜的拉曼光谱研究

利用拉曼光谱结合X射线衍射分析对未掺杂和掺杂的ZnO薄膜，陶瓷薄膜进行了研究，ZnO薄膜及ZnO陶瓷薄膜均由sol-gel法制备，掺杂组份有Bi2O3,Sb2O3,MnO和Cr2O3等。结果表明，未掺杂的薄膜的ZnO主晶相均表现出显著的定向生长特征，其拉曼光谱特征谱峰为437cm^-1，谱峰强度随薄膜退火温度的提高略有增强，掺杂后ZnO的拉曼谱峰发生了红移，掺Bi2O3后ZnO的拉曼谱峰由347cm^-1移质移至434cm^-1，掺Sb2O3后ZnO的拉曼谱峰移至435cm^-1，而掺杂Bi2O3,Sb2O3,MnO和Cr2O3等组份的ZnO陶瓷薄膜的ZnO拉曼谱峰则移至434cm^-1，说明掺杂元素进入了ZnO晶格，引起了晶格的变化，ZnO薄膜性能不仅受次晶相组成的影响，而且受因掺杂元素进入而引起的ZnO晶格畸变的影响。     

Fourier transform Raman spectroscopy of thin films

Conventional Raman measurements of dyes in the visible region exhibit resonant effects which enhance the Raman scattering cross-section of the chromophores by several orders of magnitude but make scattering from other parts of the molecules, such as the hydrocarbon chains, unobservable. Taking advantage of the benefits inherent to Fourier transform (FT) spectroscopy, Raman spectra can now be measured routinely with an FT IR spectrometer and a continuous wave Nd:YAG laser. By coupling the laser excitation into a thin film waveguide, we have recently observed FT Raman spectra of a thin film of polystyrene. The advantages of using integrated optics with FT Raman spectroscopy for Langmuir-Blodgett films of dye molecules are also discussed.     

Quantitative secondary neutral mass spectroscopy of thin films

A secondary ion mass spectrometer, having a liquid metal primary ion beam capable of focusing down to below 100 nm, has been adapted so that it can operate in conventional secondary ion or secondary neutral analysis mode. An electron beam is used to ionize the neutral species in the secondary neutral mass spectroscopy (SNMS) mode. Optimum operating conditions are reported including the use of an energy filter, which is shown to reduce background signals significantly. Typical results for various types of thin film coatings are reported including semiconductor materials, multilayer structures, metal oxides and metal alloys. A comparison of the SNMS data with that obtained in the secondary ion mass spectroscopy mode shows that the new technique provides more reliable quantitative data.     

Photoconductivity spectroscopy in hydrogenated microcrystalline silicon thin films

Steady-state photoconductivity and sub-bandgap absorption measurements by the dual-beam photoconductivity (DBP) method were carried out on undoped hydrogenated microcrystalline silicon thin films prepared by VHF-PECVD and hot-wire chemical vapor deposition. The results are compared with those of the constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS). It is found that DBP, CPM, and PDS provide complementary data on the optoelectronic processes in microcrystalline silicon.     

Dielectric and Raman spectroscopy of MWCVD diamond thin films

The dielectric properties of diamond thin films obtained on silicon substrates by microwave plasma-assisted chemical vapour deposition (MWCVD) have been measured in the frequency range from 0.1 to 10³ kHz at different temperatures up to 150 C. The experimental results have been discussed in terms of the many body theory for dielectric relaxation in solids. Dielectric parameters as well as the d.c. conductivity of the samples have been correlated with the morphology and diamond content in the films, respectively detected from scanning electron microscopy (SEM) and Raman spectroscopy. The calculated activation energies for the dielectric relaxation mechanism agree with those obtained from other measurement techniques used in the electrical characterization of diamond films.     

Cavity ringdown spectroscopy of thin films in the mid-infrared

To demonstrate the potential of the cavity ringdown technique in mid-infrared spectroscopy of thin film samples, we measured absorption losses in a C60 film on a BaF2 substrate using a tunable optical parametric amplifier source. With a Brewster angle sample geometry, we achieved a fractional loss sensitivity as small as 1.3 x 10(-7) with 1.5 cm(-1) resolution, an improvement in sensitivity of 2 orders of magnitude compared to standard Fourier transform infrared methods. At an absorption sensitivity of 5 x 10(-7), spectra of several C60 overtone lines were recorded.     

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.     

Scanning tunneling microscopy and spectroscopy of C70 thin films

Scanning tunneling microscopy of C₇₀ films deposited on HOPG and gold substrates has been carried out to investigate the 2D packing, defects and disorder. Besides providing direct evidence for orientational disorder, high resolution images showing the carbon skeleton as well as the molecular arrangement in a solid solution of C₇₀ and C₆₀ are presented. Tunneling conductance measurements indicate a small gap in the C₇₀ film deposited on HOPG substrate.     

Ultrafast pump-probe surface plasmon resonance spectroscopy of thin gold films

A time-resolved reflection pump-probe method was combined with a surface plasmon resonance technique in Kretschmann geometry for the investigation of ultrafast light-induced processes in thin films. Transient changes in the gold layer's reflectivity were observed when the layer was excited by 3 ps duration pulses with photon energy exceeding the interband transition and by probing with photon energy close to the interband transition. Comparison of the experimental and modeling results has shown that the imaginary part of the dielectric function of gold increases linearly during excitation, whereas the real part remains unchanged. The decay of the light-induced changes has two components. The first component is faster than the pulse duration, and the second is much longer than 1.5 ns; they are related to cooling of the electron plasma and lattice, respectively.     

Diffusion studies in Cr-Pt thin films using Auger electron spectroscopy

The diffusion of Cr through a thin film of Pt has been studied using Auger electron spectroscopy. The diffusion couples were prepared by the evaporation of 1400 Å of Cr onto Si(111) substrates followed by the deposition of 2000 Å of Pt. The substrates were not heated intentionally during the film depositions. Diffusion anneals in the temperature range 700°–850°K were carried out in an ultrahigh vacuum system in situ while Auger spectra were being recorded. Auger spectra from the Pt surface were taken periodically while the sample was held at a constant temperature and the signal from the Cr impurity was recorded as a function of time.The reciprocal of the times t resulting in equal peak-to-peak height ratios of the chromium 529 eV Auger transition to the platinum 64 eV Auger transition were plotted against the reciprocal of the temperatures T of the anneals. These results yielded an effective diffusion coefficient of Cr through Pt which is described by D′ = 1.02 × 10^-2 exp (-1.69 eV/kT)     

Phase sensitivity of Raman spectroscopy analysis of CVD titania thin films

Photocatalytic titania thin films deposited on float glass by chemical vapor deposition were analyzed by transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and X-ray diffraction. Raman spectroscopy results indicate its phase sensitivity in the presence of trace amount of anatase. This suggests a preferable method of using Raman spectroscopy to characterize mixed phases of titania thin films, especially when titania coatings are deposited on other crystalline oxide materials, for example, tin oxide.     

Infrared reflection spectroscopy of thin films on highly oriented pyrolytic graphite

The properties of highly oriented pyrolytic graphite (HOPG) as a substrate for external reflection infrared spectroscopy in the mid-infrared region were investigated. Clean HOPG substrates, physisorbed hydrocarbon multilayers, and chemisorbed monolayers of p-substituted aryl radicals on HOPG were used as samples, and the experimental spectra were compared and complemented with the results of spectral simulations. From reflectivity measurements of clean HOPG surfaces with polarized light as a function of the light incidence angle and the frequency, the anisotropic optical constants n (refractive index) and k (absorption index) were determined for in-plane and out-of-plane directions with respect to the graphite basal plane. These constants express the semimetallic properties of HOPG, indicated by an intermediate reflectivity between a typical metal and a dielectric substrate and by asymmetric, distorted peak shapes in adsorbate film spectra, which represent a transition state between symmetrical, positive absorptions on metals and inverted, negative peaks on dielectric substrates. Regarding spectral sensitivity and surface selection rules, HOPG behaves much like a metal and is therefore an equally suitable substrate for external reflection infrared (IR) measurements.     

Optical properties of CdTe thin films studied by photothermal deflection spectroscopy

Photothermal deflection spectroscopy (PDS) was used to analyze CdTe thin films which are to be used to construct solar cells. It was found that CdTe thin films grown on a conducting SnO₂ layer deposited on glass show deviations from a stoichiometric composition due to an excess of tellurium. This non-stoichiometry modifies the absorption spectrum obtained from the PDS measurements.     

AC impedance spectroscopy of porous silicon thin films containing metallic cations

Thin porous silicon (PS) films were prepared by HF/HNO₃ vapor etching on silicon wafers. The infiltration of metallic cations inside the porous silicon matrix followed by slow heating in air leads to an interesting electrical and optical physical phenomena. Al³⁺, Cu⁺, K⁺, Li⁺ metallic cations as chloride or as nitrate solutions are infiltrated inside the silicon porous matrix. After annealing in air at 500 °C during 2 h a structure was achieved in order to measure the Nyquist diagram corresponding to the cations embedded in PS/silicon. The real and imaginary parts of the whole structure depend on the voltage bias and on the frequency. Those signify that the junction is a Schotky-barrier junction.

From the variation of Ln(σT) versus absolute temperature T, where σ is the conductivity, we have deduced the activation energy of the metallic impurities in the [100 °C–400 °C] temperature range. We have found that the activation energies are of about 0.19 eV, 0.25 eV, 0.49 eV and 0.71 eV for Cu⁺, K⁺, Al³⁺ and Li⁺ cations respectively. These kinds of structures are suitable for gas sensing, optical sensing or for the fabrication of fuel cell membranes.     

Auger electron spectroscopy study of the oxidation of Gd-Tb-Fe magnetooptical thin films

The oxidation mechanism and oxide layer structure of Gd-Tb-Fe magnetooptical thin films at room temperature and annealing temperatures of 120, 140 and 160 °C were studied by Auger electron spectroscopy. The results demonstrate that the thickness and structure of oxide layers and oxidation mechanism and magnetooptic properties were affected by the annealing temperature and oxygen exposure.