Low energy (⩽ 100 eV) sputtering of thin molybdenum nitride films

Molybdenum nitride films formed by 100 eV N⁺₂ bombardment to saturation of polycrystalline Mo have been sputtered to high fluence by normally incident 100 eV Ar⁺ and He⁺ and 15 eV Ne⁺ while the surface nitrogen concentration was monitored by Auger electron spectroscopy (AES). The penetration distance of nitrogen atoms during film formation and subsequent sputtering is assumed to be small enough that AES will detect, to some degree, all of the nitrogen in the film. The nitrogen AES signal decays exponentially to unsputterable levels for the 15 eV Ne⁺ and 100 eV He⁺ cases and decays bi-exponentially to near the bulk contamination level for the 100 eV Ar⁺ case. The results are interpreted according to existing concepts, but the kinetics of nitrogen loss is modeled using a two-layer adaptation of the standard model for adsorbate monolayer sputtering kinetics. Fitting our proposed model to the data yields apparent cross-sections which are interpreted as composites of cross-sections for experimentally indistinguishable elementary processes; these elementary cross-sections for each process are geometrical averages on the polycrystalline surface. Processes considered, in addition to nitrogen sputtering, include bombardment-induced transport of nitrogen within the film and sputtering of the Mo lattice itself.     

The absorption band at 1.128 eV of copper phthalocyanine films

We deposited copper phthalocyanine (CuPc) films on (100) silicon wafers by means of a vacuum evaporation method and investigated the absorption characteristics by means of photoacoustic (PA) spectroscopy. It was verified that we excluded the PA signal originated in the silicon substrate with the chopping frequency of 200 Hz when the thickness of the CuPc film was 4.4 μm. We then detected an absorption band at 1.128 eV (1.1 μm). This band is possibly related to the charge transfer between Cu atoms and adsorbed oxygen molecules. PACS 78.66.Qn; 78.20.Hp     

Optical absorption studies of copper phthalocyanine thin films

The optical absorption of thermally evaporated copper phthalocyanine (CuPc) was studied in the UV-VIS-NIR region. The absorption spectra recorded in the UV-VIS region show two well-defined absorption bands of the phthalocyanine molecules, namely, the Soret (B) and the Q-band . The Q-band shows its characteristic splitting (Davydov splitting) of the main absorption peak in the metal phthalocyanine correlates with the relative tendencies of the metal to out-of-plane bonding. Some of the important spectral characteristics such as the molar extinction coefficient (ε_molar), the oscillator strength (f), the electric dipole strength (q²) and absorption half-bandwidth (Δλ) of the principle optical transitions were evaluated. The analysis of the spectral behavior of the absorption coefficient α in the absorption region revealed two indirect allowed transitions with corresponding energies 2.95±0.03 and 1.55±0.02 eV.The spectra of the infrared absorption allow characterization of vibration modes for the powder, as-deposited material and thin films of CuPc annealed at 423 K for two hours. Discussion of the obtained results and their comparison with the previous published data are also given.     

Optical constants and thermocoloration of pulsed laser deposited molybdenum oxide thin films

Molybdenum oxide thin films were prepared by pulsed laser deposition. The as-deposited films were dark. Annealing the films in air at 400 °C resulted in transparent films. These films were further annealed in vacuum at 300 and 400 °C to investigate thermocoloration. The structural, chemical, and optical properties of the films were determined. All films were predominantly amorphous. The air-annealed films were nearly stoichiometric. However, after annealing in vacuum at 400 °C, the films became oxygen-deficient. The transmittance of the films progressively decreased as the vacuum-annealing temperature increased, indicating stronger coloration of the films. The optical constants were determined from the transmittance measurements. Both the refractive index and extinction coefficient increased upon vacuum annealing. However, the band gap slightly decreased after vacuum annealing.     

Optical absorption in polycrystalline thin films of magnetite at room temperature

Polycrystalline thin films of magnetite have been prepared to allow the measure of their absorption coefficient. Results are dealt with the hopping small polarons scheme. The case of free carriers is also considered.     

Competition between band and hopping carrier transport in Ge : Mn thin films

Regularities of hole transport and its correlation with percolation magnetism caused by localized carriers simultaneously involved in the formation of the magnetic and electrical properties of Ge: Mn thin films are investigated. It is established that at temperatures of T > 22 K the activationless band carrier transport occurs in the Ge: Mn samples (2 at % Mn). At low temperatures, the hopping mechanism with a variable hopping length works.     

Optical properties and electronic transitions of SnO2 thin films by reflection electron energy loss spectroscopy

Optical properties of SnO₂ thin films in the 4–60 eV energy range are determined by reflection electron energy loss spectroscopy. Bulk and surface electron loss functions, real and imaginary parts of the dielectric function, refraction index, extinction and absorption coefficients are obtained from the analysis of the electron energy loss spectra. Electronic transitions are identified through the interpretation of the optical data. The samples (250–500 nm thick) were produced by ion beam-induced chemical vapor deposition. It is found that the compacity of the SnO₂ thin films affects their optical properties and therefore the relative intensity of the observed electronic transitions. The advantages of this method to determine optical properties of thin films are discussed. Inelastic mean free paths (6.2, 17 and 41 Å for electrons traveling in SnO₂ with kinetic energies of 300, 800 and 2000 eV, respectively) are obtained from the corresponding inelastic electron scattering cross-sections.     

Thickness transitions in thin films: The equilibrium

The thermodynamic and thickness equilibria of planar solid, liquid or gaseous thin films are described in terms of the film excess chemical potential μ_ex. A general formula is given which relates μ_ex to the short- and/or long-range surface forces associated with the two film surfaces and the dependence of the film specific surface free energy σ on the film thickness h is expressed through μ_ex. The conditions under which the thin films are in stable or metastable thermodynamic equilibrium are analyzed and it is shown that the metastable thin films are subject to thickness transitions involving abrupt changes of h. The thin film thickness equilibrium, i.e. the coexistence between two films of different thickness, is also considered and the film equilibrium chemical potential characterizing this equilibrium is determined by means of μ_ex and σ.     

立方氮化硼薄膜的光学带隙

用射频溅射法在p型Si(100)衬底上沉积立方氮化硼(c-BN)薄膜,薄膜的成分由傅里叶变换红外谱标识,用紫外-可见分光光度计测量了c-BN薄膜的反射光谱,利用K-K(Kramers-Kroning)关系从反射谱计算出c-BN薄膜的光吸收系数,进而确定c-BN薄膜的光学带隙.对于立方相含量为55.4%的c-BN薄膜,光学带隙为5.38eV. 关键词： 立方氮化硼薄膜 光学带隙 K-K关系     

Optical absorption coefficient of the first series transition metals between 20 and 130 eV

Experimental electron-energy loss spectra are used to calculate in a rather accurate way the complex dielectric constant and consequently the optical absorption coefficient.     

Optical absorption and electrical conductivity of flash evaporated CuGaTe2 thin films

The optical absorption edge of CuGaTe₂ thin films in the energy range 1 to 2·3 eV was studied. The characteristic band gaps were found to be 1·23 eV and 1·28 eV whereas the acceptor ionization energy was 170 meV. Electrical conductivity measurements were carried out in the temperature range 300–550 K and two acceptor states with ionization energies 400 meV and 140 meV were found. The origin of acceptor states is explained based on covalent model.     

Glass transitions and dynamics in thin polymer films: dielectric relaxation of thin films of polystyrene

The glass transition temperature T(g) and the temperature T(alpha) corresponding to the peak in the dielectric loss due to the alpha process have been simultaneously determined as functions of film thickness d through dielectric measurements for polystyrene thin films supported on glass substrate. The dielectric loss peaks have also been investigated as functions of frequency for a given temperature. A decrease in T(g) was observed with decreasing film thickness, while T(alpha) was found to remain almost constant for d>d(c) and to decrease drastically with decreasing d for d相似文献   

Optical absorption and band structure of PbTe

It is shown that the rigid band model cannot be applied to the sodium tungsten bronzes outside of the cubic range. The origin of the band gap states observed in the semiconducting range is discussed.     

Preparation and characterization of molybdenum diselenide thin films

MoSe₂ layers, synthesized by annealing a molybdenum foil under selenium pressure, have been investigated by scanning electron microscopy, X-ray analysis, electron spectroscopy (XPS) and electrical resistance measurements. It has been found that stoichiometric layers are obtained after appropriate processing. The films crystallize in the hexagonal structure. The crystallites develop preferentially along the c axis. The binding energies deduced from the XPS lines were found to be in good agreement with those of the reference powder. The electrical resistance is governed by hopping conduction in the low temperature range (80–250 K) and by grain boundary scattering mechanisms at higher temperatures.     

Optical and structural comparison between nitrogen-doped and oxygen-rich ZnO thin films

A ZnO thin film reactively sputtered at high oxygen pressure (O-rich) was compared to a nitrogen-doped ZnO (ZnO:N) thin film using optical and structural spectroscopies. X-ray diffraction measurements confirmed a high (0002) preferential orientation for both films. Absorption measurements revealed two intra-band-gap absorptions in addition to observed free exciton (FX) and neutral acceptor–bound exciton features in both films. Binding energies of the FXs were calculated to be 65 and 69 meV, respectively, for the ZnO:N and O-rich thin films at 15 K. Photoluminescence measurements revealed nearly the same characteristics, i.e. that the deep level emission is dominant. Recombination lifetime values of 577.35 and 797.46 ps were measured for ZnO:N and O-rich thin films, respectively.     

Phase transitions and domain structures in thin ferroelectric films

Recent advances in technology made available high quality thin ferroelectric films and ferroelectric–paraelectric multilayers. But understanding of the properties of these systems is far from being complete. In particular, it is not clear why various anomalies observed at phase transitions here are different from those in high quality bulk systems. The aim of the paper is to discuss some specific features of ferroelectric phase transitions in thin films and multilayers which are taken into account only partially by the theory. The discussion is limited to revealing the character of ferroelectric state forming just after the transition, i.e. if it is single-domain or multi-domain, if it is single-phase or two-phase. First, thin films with electrodes and on a substrate are discussed. The role of non-ideality of electrodes in realization of one of the first pairs of possibilities is emphasized. A more recent idea is that even for ideal electrodes a domain formation is possible when some conditions on the electrode–ferroelectric interface and the material constants of the material are met. This seems to be quite possible for the considered systems. Clamping by the substrate may lead to formation of a two-phase state which is practically unexplored for very thin films on substrates. Second, ferroelectric–paraelectric multilayers are considered which are more challenging for theoretical study than the thin films. Indeed, despite periodicity in the composition the domain structures are almost never periodic along the multilayer. The non-ideality of electrodes seems to lead to practical impossibility of single-domain ferroelectric phase transition in the multilayers of the considered type.     

Optical properties,electronic band structure,and vibrational spectrum of thin C60-TPP films

This paper reports on the first synthesis of thin films of the fullerene-mesotetraphenylporphyrin molecular complex, C₆₀-TPP, a promising material for molecular photonics devices. The spectral response of film transmittance in the visible and IR ranges, as well as of photoluminescence, has been measured. An additional absorption band at 1.70 eV originating from intermolecular transfer of photoexcited electrons has been observed. Ab initio quantum-mechanical calculations of the optimized geometry and electronic band spectra of tetraphenylporphyrin (TPP) and the C₆₀-TPP complex have been performed, which corroborate the optical spectroscopy measurements.     

Optical absorption and dispersion characterizations of CuGaSe2 thin films prepared by flash evaporation technique

Thin films of CuGaSe₂ have been prepared by flash evaporation technique. The optical properties of the prepared films were investigated using spectrophotometric measurements of the transmittance and reflectance at normal incidence of light in the wavelength range from 400 to 2500 nm. The optical constants as refractive index, n, and absorption index, k, were calculated and found to be independent of film thickness in the range of the film thickness 132–423 nm. The analysis of the photon energy against the absorption coefficient showed three direct optical transitions (one of them is allowed while the others are forbidden). This direct transition was ascribed to the crystal field and spin orbital splitting of the upper most valence band. The crystal field and spin orbital splitting of CuGaSe₂ were found to be ? 0.15 eV and 0.45 eV, respectively. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–DiDomenico (WD) model. The single oscillator energy (E_o), the dispersion energy (E_d), the high frequency dielectric constant (ε_∞), the lattice dielectric constant (ε_L) and the ratio of free charge carrier concentration to the effective mass (N / m*) were estimated. The capacitance–voltage measurements of CuGaSe₂/p-Si heterojunction showed that the diode is abrupt junction diode. The carrier concentration and the built-in voltage were estimated. The current–voltage characteristics of the device under illumination were investigated and photovoltaic properties of the device were evaluated.