Vacuum-deposited poly(o-methoxyaniline) thin films: Structure and electronic properties

Thin poly(o-methoxyaniline) (POMA) films have been formed by thermovacuum deposition in the temperature range of 350–450 °C and at a pressure of 5 × 10^?5 Torr. The structure properties of vacuum deposited POMA films according to FTIR and UV–VIS spectra are similar to those observed for the emeraldine form of polyaniline. Current–voltage characteristics (I–V) of sandwichtype device ITO/POMA/A1 possess rectifying properties with the ideality factor ≈4 at room temperature. On the basis of the dependence of conductivity on frequency in the frequency range of 10 Hz to 1 MHz, it is shown that the Pollack–Pohl current flow hopping mechanism dominates in a polymer film; such mechanism is typical of non-ordered systems.     

Dielectric properties of bis(2,4 pentanedionato)copper(II) crystalline films grown on Si substrate for low-k applications

Bis(acetylacetonato)copper(II) thin films were prepared by sublimation at about 245 °C in vacuum on p-Si and glass substrates for dielectric and optical investigations. They were characterized by the X-ray diffraction (XRD) and energy-dispersion X-ray fluorescence (EDXRF) methods. The XRD pattern reveals that the prepared films were polycrystalline of monoclinic P2₁/n structure. The optical absorption spectrum of the prepared film was not identical to that of the molecular one, which identified by a strong absorption peak at 635 nm. The onset energy of the optical absorption of the complex was calculated by using Hamberg et al. method, which is usually used for common solid-state semiconductors and insulators. The dielectric properties for the complex as insulator were investigated on samples made in form of a metal-insulator-semiconductor (MIS) structure. The dielectric properties were studied in frequency range 1–1000 kHz and temperature range 298–333 K. The dielectric relaxation was analyzed in-terms of dielectric modulus M¹(ω). Generally, the present study shows that films of the complex grown on Si substrate are a promising candidate for low-k dielectric applications; it displays low-k value around 1.7 ± 0.1 at high frequencies.     

Optical properties of tin sulphide (SnS) thin film estimated from transmission spectra

Thin films of tin sulphide (SnS) were deposited on tin oxide conducting glass substrates by thermal evaporation technique. The transmission spectrum of the SnS film in the wavelength range from 300 to 1100 nm has been obtained. X-ray diffraction has been used to determine the structure of the films. The film thickness and refractive index have been estimated from the transmission spectra. The results showed that the refractive index of the SnS thin films is thickness independent in the wavelength range 590 ≤ λ ≤ 1100 nm and found to be ~ 1.72. This result indicates that the SnS thin films are homogeneous and isotropic. The energy band gaps were found to be between 1.06 and 1.32 eV, which is in good agreement with literature values. The energy dependence of the obtained refractive index is also investigated.     

Films thickness effect on structural and optoelectronic properties of hydrogenated amorphous germanium (a-Ge:H)

Thin films of hydrogenated amorphous germanium (a-Ge:H) deposited at high growth rate by radiofrequency (RF) glow discharge with 1 sccm GeH₄ diluted in 40 sccm H₂ have been studied. The effect of the films thicknesses on the defect density and on the structural parameters was carefully investigated by means of infrared spectroscopy, optical transmission measurements, and the photothermal deflection spectroscopy (PDS) technique. The results of this investigation show that when the films thicknesses increase, the total hydrogen content (C_H) decreases and the hydrogen-bonding configuration changes. The results of these changes appear clearly on the defects density and on the microstructure parameter of the films, while the disorder parameter E_OV and the optical gap E_T remain practically constant (E_OV ≈ 45 ± 2 meV, E_T = 1.08 ± 0.02 eV). The improvement of these parameters is mainly due to the incorporation of the hydrogen in the bulk of the material as the monohydride groups (Ge-H) rather than the polyhydride groups (Ge-H₂ and Ge-H_2n) when the films thicknesses increase.     

I–V Characteristics of tris(2,4-pentanedionato)manganese(III) thin films

Amorphous thin films of tris(acetylacetonate)manganese(III) were deposited on Si(P) substrates by thermal sublimation in vacuum. The deposited films were probed with X-ray fluorescence. Their electrical properties were studied as insulators for Al/Mn(acac)₃/Si(P) metal–insulator–semiconductor devices. Those devices were characterized by the measurement of the gate-voltage dependence of their capacitance, from which the relative permittivity (RP) and density of the charges in the insulator were determined. It was found that values of the RP of tris(acetylacetonate)manganese(III) films grown on Si(P) wafers were in the range of 30–40, which can be find applications in gate related technological uses. The dc-electrical conduction in the complex film was studied at room temperature and in temperature range of (293–325 K). It was found that the data of the as-deposited films follow the trap-charge-limited space-charge-limited conductivity (TCL-SCLC) mechanism, while the data of the annealed sample in vacuum of about 10⁻³ Pa at about 100 °C for 10 min obey the Richardson–Schottky (RS) mechanism. The parameters of both mechanisms were determined. It was concluded that the density of charged defects in the insulating film is critically determined the mechanism of the current-transfer.     

Infrared spectroscopy of Li-diborate glassy thin films

This work presents a structural investigation of Li-borate thin film electrolytes prepared by rf-sputtering from targets having the nominal Li₂O–2B₂O₃ composition. Thin films of ca. 1 μm were deposited on Si wafers and gold-covered Si substrates under argon, and their infrared spectra were measured in the 30–5000 cm⁻¹ range. The measured spectra of thin films were compared with those calculated on the basis of the infrared properties of the bulk Li-diborate glass and by considering all optical effects in the film/substrate system. The results showed that the thin films have the key structural features of the bulk glass, but exhibit also differences in the short-range order structure and in the Li ion-site interactions. These findings were discussed in terms of cooling rate differences between melt-quenching for bulk glass and sputtering for thin films.     

Characterizations of pulsed laser deposited SiC thin films

Thin films of silicon carbide (SiC) were prepared using pulsed laser deposition (PLD) on Si(1 0 0) substrates at a temperature of 370 °C. Various structural characterizations showed the development of short-range SiC precipitates in the films. These films were annealed isochronally at temperatures of 800 °C, 1000 °C and 1200 °C for 2 h under an inert environment. Thermally induced crystalline ordering of SiC into β-SiC phase was investigated by X-ray diffraction (XRD), Raman spectroscopy and Fourier transforms infrared (FTIR) spectroscopic measurements. In addition to the crystallization of SiC films, high temperature annealing resulted in the dissolution of carbon clusters found in the as-grown films.     

Analysis of the absorption and emission spectra of poly(p-phenylene vinylene) films thermally converted at a relatively low temperature

In this work, we studied the absorption and emission spectra of spin-coated poly(p-phenylene vinylene) (PPV)–dodecylbenzenesulfonic counter-ion (DBS) films. The PPV–DBS films were obtained from a soluble precursor polymer thermally converted to PPV over a comparatively short time interval (30 min), and at low temperature (110 °C), conditions that yielded films with few structural defects. The line shape of the absorption spectra of the films deposited on glass substrates was analyzed by assuming a Gaussian distribution of segments along the main chain of PPV, and a conjugation degree between 3 and 15 units. For emission studies, only PPV segments with a high conjugation degree or a lower energy gap (HOMO–LUMO transition) contributed to the feature of the spectra.     

Structural and optical properties of ZnO thin films deposited onto ITO/glass substrates

ZnO films were prepared by post deposition thermal oxidation in the ambient atmosphere of metallic Zn films (d = 100–170 nm) vacuum evaporated onto unheated indium tin oxide (ITO)-coated glass substrates. To study the effect of the substrate position during the Zn film deposition on the microstructure and optical properties (transmittance, reflectance and absorbance) of as obtained ZnO films, two set of Zn samples simultaneously deposited onto horizontally and obliquely arranged substrates were prepared. The as obtained ZnO films had a polycrystalline wurtzite structure, those obtained from normally deposited Zn films having a higher c-axis preferred orientation and a lower optical transmittance in the visible wavelength range. The optical band-gap was found to be of 3.14 eV for oxidized normally deposited virgin Zn films and of 3.16 eV for those obliquely deposited.     

Optical and electrical properties of as-prepared and annealed (Se80Te20)100 − xAgx (0 ≤ x ≤ 4) ultra-thin films

Optical and electrical properties of the (Se₈₀Te₂₀)_100 ? xAg_x (0 ≤ x ≤ 4) ultra-thin films have been studied. The ultra-thin films were prepared by thermal evaporation of the bulk samples. Thin films were annealed below glass transition temperature (328 K) and in between glass transition temperature and crystallization temperature (343 K). Thin films annealed at 343 K showed crystallization peaks for Se–Te–Ag phases in the XRD spectra. The transmission and reflection of as-prepared and annealed ultra-thin films were obtained in the 300–1100 nm spectral region. The optical band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical band gap increases, but the refractive index, extinction coefficient, real and imaginary dielectric constant decrease with increase in Ag content. The optical band gap and refractive index show the variation in their values with increase in the annealing temperature. The extinction coefficient increases with increasing annealing temperature. The surface morphology of ultra-thin films has been determined using a scanning electron microscope (SEM). The measured dc conductivity, under a vacuum of 10^? 5 mbar, showed thermally activated conduction with single activation energy in the measured temperature range (288–358 K) and it followed Meyer–Neldel rule. The dc activation energy decreases with increase in Ag content in pristine and annealed films. The results have been analyzed on the bases of thermal annealing effects in the chalcogenide thin films.     

Sol–gel derived highly transparent and conducting yttrium doped ZnO films

This paper reports the structural, electrical and optical properties of Yttrium doped zinc oxide (YZO) thin films deposited on Corning (7059) glass substrates by spin coating technique. A precursor solution of ZnO, 0.2 M in concentration was prepared from zinc acetate dissolved in anhydrous ethanol with diethanolamine as a sol gel stabilizer. Yttrium nitrate hexahydrate (Y₂NO₃ · 6H₂O) was used as the dopant (3 wt%) in the present study. The films of different thickness in the range (200–500 nm) were prepared. The films were annealed in air at 450 °C for 1 h. It was observed that the c-axis orientation improves and the grain size increases as is indicated by an increase in intensity of the (0 0 2) peak and the decrease in the FWHM with the increase of film thickness. The resistivity decreased sharply from 2.8 × 10⁻² to 5.8 × 10⁻³ Ω-cm as the thickness increased from 200 to 500 nm. However, the average transmittance decreased from 87% to 82.6% as the film thickness increased to 500 nm. The lowest sheet resistance of ∼120 Ω/□ was obtained for the 500 nm thick film.     

Nanostructural and optical features of amorphous AlxSi0.45−xO0.55 (0 ⩽ x ⩽ 0.05) thin films prepared by RF-magnetron sputter techniques

The nanostructural, chemical, and optical features of Al_xSi_0.45−xO_0.55 (0 ⩽ x ⩽ 0.05) thin films were investigated in terms of Al concentration and post-deposition annealing conditions; the films were prepared by co-sputtering a Si main target and Al-chips, and the annealing was carried out at temperatures of 400–1100 °C. The a-Si_0.45O_0.55 films prepared without Al-chips and annealed at 800 °C contain ∼3.5 nm-sized Si nanocrystallites. The photoluminescence (PL) intensity as well as the volume fraction of Si nanocrystallites increased with increasing the concentration of Al to a certain level. In particular, the intensity of the PL spectra of the Al_0.025Si_0.425O_0.550 films which were annealed at 800 °C increased significantly at wavelengths of ∼580 nm. It is highly likely that the observed increase in the PL intensity is caused by the raise in the total volume of the ∼3.5 nm-sized nanocrystallites in the films. The addition of Al as well as the post-deposition annealing allow adjustment and control of the nanostructural and light-emission features of the a-SiO_x films.     

Copper nitride (Cu3N) thin films deposited by RF magnetron sputtering

The copper nitride thin films were prepared on glass substrate by RF magnetron sputtering method. At pure nitrogen atmosphere, the nitrogen flow rate affects the copper nitride thin films’ structures. Only a little part of nitrogen atoms insert into the body center of Cu₃N structure and parts of nitrogen atoms insert into Cu₃N crystallites boundary at higher nitrogen flow rate. But the indirect optical energy gap, E_opg, decreases with increasing nitrogen flow rate. The typical value of E_opg is 1.57 eV. In a nitrogen and argon mixture atmosphere, when the nitrogen partial was less than 0.2 Pa at 50 sccm total flow rate, the (1 1 1) peak of copper nitride appears. Thermal decomposition temperature of Cu₃N thin films deposited in pure nitrogen and 30 sccm flow rate was less than 300 °C. The surface morphology was smooth.     

Evaluation of structural and mechanical properties of aluminum oxide thin films deposited by a sol–gel process: Comparison of microwave to conventional anneal

Thin films of Al₂O₃ have been deposited on polished silica glass substrates at room temperature by sol–gel dip coating technique followed by two different exposure methods. One set was annealed at different temperatures ranging from 200 °C to 800 °C for 10 h and a second set was exposed to microwave (2.45 MHz) radiation at different powers for 10 min. The lower temperature and shorter time with microwave irradiation might be ascribed to the activating and facilitating effect of microwaves on solid phase diffusion. Unlike other preparation methods, microwave heating is generally quite faster, and energy efficient. X-ray diffraction (XRD) and scanning electron microscopy (SEM), energy dispersive X-ray analysis techniques have been employed to characterize structural, morphological and elemental compositions of the films. Adhesion strength failure measurements on films performed by scratch test in progressive loading sequence have shown critical loads up to 25 N (partial perforation) for both annealed films and films exposed to microwave irradiation. Nanohardness indentation tests of the films exposed (800 W) to microwave have shown hardness of 8.3 GPa with elastic modulus of 120 GPa compared to the conventional annealed film (800°) of 4.5 GPa with elastic modulus of 90 GPa.     

Amorphous to crystalline transition and optoelectronic properties of nanocrystalline indium tin oxide (ITO) films sputtered with high rf power at room temperature

ITO thin films were deposited on quartz substrates by the rf sputtering technique using various rf power keeping the substrates at room temperature. The influence of rf power on the structural, electrical, optical and morphological properties was studied by varying the rf power in the range 50–350 W. X-ray diffraction results show an amorphous – crystalline transition with nano grains. At a power of 250 W, the ITO film showed preferential orientation along (4 0 0) peak. It is observed from the optical transmission studies that the optical band gap increased from 3.57 to 3.69 eV when the rf power was increased from 50 to 250 W. The resistivity value is minimum and grain size is maximum for the ITO film deposited at 250 W. The X-ray photoelectron spectroscopy (XPS), Energy dispersive X-ray (EDX) and Atomic force microscopy AFM results confirm that the ITO films are stoichiometric and the surface contained nano-sized grains distributed uniformly all over the surface. It can be concluded that the ITO film deposited at room temperature with 250 W rf power, can provide the required optical and electrical properties useful for developing optoelectronic devices at lower temperatures.     

Characteristics of p-type nanocrystalline silicon thin films developed for window layer of solar cells

Different rf-power and chamber pressures have been used to deposit boron doped hydrogenated silicon films by the PECVD method. The optoelectronic and structural properties of the silicon films have been investigated. With the increase of power and pressure the crystallinity of the films increases while the absorption decreases. As a very thin p-layer is needed in p–i–n thin film solar cells the variation of properties with film thickness has been studied. The fraction of crystallinity and thus dark conductivity vary also with the thickness of the film. Conductivity as high as 2.46 S cm⁻¹ has been achieved for 400 Å thin film while for 3000 Å thick film it is 21 S cm⁻¹. Characterization of these films by XRD, Raman Spectroscopy, TEM and SEM indicate that the grain size, crystalline volume fraction as well as the surface morphology of p-layers depend on the deposition conditions as well as on the thickness of the film. Optical band gap varies from 2.19 eV to 2.63 eV. The thin p-type crystalline silicon film with high conductivity and wide band gap prepared under high power and pressure is suitable for application as window layer for Silicon thin film solar cells.     

Electrochemical deposition of ZnO film and its photoluminescence properties

ZnO thin films were prepared by the electrochemical deposition method on conductive substrates. The as-deposited film was ZnO crystallites of the wurzite structure highly oriented along the (0 0 2) plane. The specific crystalline morphology may be attributed to the growth mechanism through the orientation attachment mode, which is one of the characteristics peculiar for the present process, because the terrace has been clearly observed in high-resolution AFM images. The film shows high transmittance and an optical band gap energy of 3.3 eV. After annealing in N₂ or Ar, strong green emission was observed, which should be related to the generation of singly ionized oxygen defects. Improving emission intensity further by optimizing the annealing conditions, this method may be promising to replace the traditional method for preparation of ZnO green phosphor.     

Fabrication and characterization of transparent conductive ZnO:Al thin films prepared by direct current magnetron sputtering with highly conductive ZnO(ZnAl2O4) ceramic target

Using a highly conductive ZnO(ZnAl₂O₄) ceramic target, c-axis-oriented transparent conductive ZnO:Al₂O₃ (ZAO) thin films were prepared on glass sheet substrates by direct current planar magnetron sputtering. The structural, electrical and optical properties of the films (deposited at different temperatures and annealed at 400°C in vacuum) were characterized with several techniques. The experimental results show that the electrical resistivity of films deposited at 320°C is 2.67×10⁻⁴ Ω cm and can be further reduced to as low as 1.5×10⁻⁴ Ω cm by annealing at 400°C for 2 h in a vacuum pressure of 10⁻⁵ Torr. ZAO thin films deposited at room temperature have flaky crystallites with an average grain size of ∼100 nm; however those deposited at 320°C have tetrahedron grains with an average grain size of ∼150 nm. By increasing the deposition temperature or the post-deposition vacuum annealing, the carrier concentration of ZAO thin films increases, and the absorption edge in the transmission spectra shifts toward the shorter wavelength side (blue shift).     

Thermo-mechanical behavior of uniaxially drawn and crystallized poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) films

Thermo-mechanical properties of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) films in the amorphous state, uniaxially stretched and thermally crystallized were compared and show different microstructure–property relationships. The glass transition temperature shifts to higher temperatures when films are stretched above T_g at 160 °C, in relation with a crystallinity increase and subsequent confinement effects of the amorphous phase, but films stretched below T_g at 100 °C show an opposite trend while drawing. This is discussed in relation with the highly mobile structural state arising from plastic deformation of the amorphous phase. The confinement effects were particularly assessed by the estimation of a ‘rigid amorphous fraction’ (RAF). Crystallinities and RAF were estimated from DSC data for the uniaxially drawn and thermally crystallized films respectively. It was observed that the RAF was higher in thermally crystallized films than in uniaxially drawn samples in relation to a lamellar semi-crystalline morphology. In addition to this detailed thermo-mechanical characterizations, low stress creep measurements were carried out during heating scans. They can be related to the microstructure and thermal transitions of the films. In particular, for the uniaxially stretched films, the measured shrinkage decreases when the draw ratio increases because the crystalline entities developed during the draw process are locking the chain motions.     

Absorption and luminescence in amorphous SixGe1-xO2 films fabricated by SPCVD

Optical absorption and photoluminescence of Ge-doped silica films fabricated by the surface-plasma chemical vapor deposition (SPCVD) are studied in the 2–8 eV spectral band. The deposited on silica substrate films of about 10 μm in thickness are composed as x·GeO₂-(1-x)·SiO₂ with x ranging from 0.02 to 1. It is found that all as‐deposited films do not luminesce under the excitation by a KrF (5 eV) excimer laser, thus indicating lack of oxygen deficient centers (ODCs) in them. After subsequent fusion of silicon containing (x < 1) films by a scanning focused CO₂ laser beam absorption band centered at 5 eV as well as two luminescence bands centered at blue (3.1 eV) and UV (4.3 eV) wavelengths arise, highlighting the formation of the ODCs. The excitation of unfused SPCVD films by an ArF (6.4 eV) excimer laser yields a luminescence spectrum with two bands typical for the ODCs, but with a faster decay kinetics. Intensities of these bands grow up with samples cooling down to a temperature of 80–60 K. Unfused films excited by the ArF laser also demonstrate luminescence due to recombination of a trapped charge resulted from the excitation of localized electron states of the glass network. In the unfused GeO₂ film luminescence related to a self-trapped exciton (STE) typical for GeO₂ crystals with α-quartz structure is observed. The observed STE luminescence can be indicative of the crystalline fraction availability in the film. Whereas GeO₂ crystals are known as not containing twofold coordinated germanium, a polycrystalline inclusion in the SPCVD GeO₂ film serves as a factor explaining the absence of any spectroscopic manifestation of this type of defects in it even after fusion. On the other hand, lack of STE luminescence in other unfused films with x < 1 testifies truly amorphous state of the matter in them.