Structural modification of fullerene thin films by highly charged iron ions

In this paper, the results of structural modification of fullerene thin films bombarded by highly charged iron ions (Fe⁶⁺) are presented. The properties of as-deposited and irradiated fullerene thin films have been investigated by Raman spectroscopy, UV/Vis spectrophotometry and atomic force microscopy (AFM). The results of Raman spectroscopy have indicated structural changes of irradiated thin films depending on fluences. It was found that iron doped fullerene films are dominated by sp³ rather than sp² after bombardment which might be due to formation of nanodiamond structures. AFM analysis showed that the ion beam had destroyed the surface ordering. The optical band gap was found to be in the range of 0.6 to 1.4 eV for irradiated films by Fe⁶⁺ ions at the highest fluences. PACS 61.48.+c; 78.30.-j; 79.20.Rf     

Swift heavy ion induced modifications in cobalt doped ZnO thin films: Structural and optical studies

Modifications in the structural and optical properties of 100 MeV Ni⁷⁺ ions irradiated cobalt doped ZnO thin films (Zn_1−xCo_xO, x = 0.05) prepared by sol-gel route were studied. The films irradiated with a fluence of 1 × 10¹³ ions/cm² were single phase and show improved crystalline structure with preferred C-axis orientation as revealed from XRD analysis. Effects of irradiation on bond structure of thin films were studied by FTIR spectroscopy. The spectrum shows no change in bonding structure of Zn-O after irradiation. Improved quality of films is further supported by FTIR studies. Optical properties of the pristine and irradiated samples have been determined by using UV-vis spectroscopic technique. Optical absorption spectra show an appreciable red shift in the band gap of irradiated Zn_1−xCo_xO thin film due to sp-d interaction between Co²⁺ ions and ZnO band electrons. Transmission spectra show absorption band edges at 1.8 eV, 2.05 eV and 2.18 eV corresponding to d-d transition of Co²⁺ ions in tetrahedral field of ZnO. The AFM study shows a slight increase in grain size and surface roughness of the thin films after irradiation.     

Influence of assisted ion energy on surface roughness and mechanical properties of boron carbon nitride films synthesized by DIBSD

The BCN thin films were produced by dual ion beam sputtering deposition (DIBSD). The influence of assisted ion energy on surface roughness and mechanical properties of BCN films were investigated. The surface roughness was determined by atomic force microscopy (AFM) and the mechanical properties of BCN firms were evaluated by nano-indentation in N₂ gas. The composition, structure and chemical bonding of the BCN thin films were analyzed by using energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), laser Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). These films appeared as amorphous structure. As a result, the BCN films with the smoothest surface (R_a = 0.35 nm and R_p-v = 4.4 nm) and the highest nano-hardness of 30.1 GPa and elastic modulus of 232.6 GPa were obtained at 200 eV and 12 mA with N₂:Ar = 1:1, and the chemical composition of this BCN film was 81 at.% B, 14 at.% C and 5 at.% N. Moreover, several bonding states such as B-N, B-C and C-N were observed in BCN thin films.     

Blue-cathodoluminescent layers synthesis by high-dose N, C and B SiO2 implantation

Thermal silicon oxide layers have been implanted at 600 °C with N⁺+C⁺, N⁺+B⁺ and N⁺+C⁺+B⁺ ions. Two different implantation doses have been chosen in order to introduce peak concentrations at the projected range comparable to the SiO₂ density. Some pieces of the samples have been annealed in conventional furnace at 1200 °C for 3 h. After annealing, cathodoluminescence measurements show in all cases a main broad band centered at 460 nm (2.7 eV). High doses of C implantation give rise to an intensity attenuation. Phases formed in the oxides have been investigated by Fourier transform infrared spectroscopy before and after annealing. The spectra suggest that N incorporates as BN and probably as a ternary BCN phase in the triply implanted samples, while C seems to bond mainly with B. Boron is also bonded to O in B-O-Si configuration. Depth structure and quantitative composition of the films were deduced from fittings of the spectroscopic ellipsometry measurements.     

Mn doped ZnO nanostructured thin films prepared by ultrasonic spray pyrolysis method

Mn-doped ZnO thin films with different percentage of Mn content (0, 1, 3 and 5 at.%) and substrate temperature of 350 °C, were deposited by a simple ultrasonic spray pyrolysis method under atmospheric pressure. We have studied the structural and optical properties by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and ultra-violet visible near infrared (UV–Vis-NIR) spectroscopy. The lattice parameters calculated for the Mn-doped ZnO from XRD pattern were found to be slightly larger than those of the undoped ZnO, which indicate substitution of Mn in ZnO lattice. Compared with the Raman spectra for ZnO pure films, the Mn-doping effect on the spectra is revealed by the presence of additional peak around 524 cm⁻¹ due to Mn incorporation. With increasing Mn doping the optical band gap increases indicating the Burstein–Moss effect.     

The effects of xenon ion irradiation on the photoluminesce behavior of poly(p-cresolformaldeyde)/diazonaphtoquinone thin films

In the present paper, we investigate the origin of photoluminescence (PL) and the changes in the optical properties: refractive index and absorption coefficient, in poly(p-cresolformaldeyde) and diazonaphtoquinone thin films irradiated with Xe ions. Films 400 nm thick have been irradiated with 800 keV Xe²⁺ ions in a fluence range from 10¹³ to 6 × 10¹⁵ Xe cm⁻². The structural modifications were followed by the techniques of nuclear reaction analysis, elastic recoil detection analysis, Rutherford backscattering, Fourier transform infrared and Raman spectroscopies. The PL behavior was characterised with 488 nm excitation wavelength. The pristine films show emission with maxima of the main bands located at 635, 720 and 830 nm. For fluences up to 10¹⁴ Xe cm⁻², the photoluminescence intensity increases with the irradiation fluence. The chain mobility lowering, characterized by the crosslinked structure, explains this behavior in organic systems. Other possible contribution for increasing of PL intensity, at these fluences, is the presence of oxygen trapped in the polymer chains by the dangling bonds. At intermediate and higher fluences, the photoluminescence starts to decrease. At fluences higher than 10¹⁴ Xe cm⁻², irreversible changes of the organic structure occur and they are characterized by large losses of oxygen and hydrogen, transforming the material into amorphous carbon films. The loss of photoluminescent behavior is associated with the light absorption characteristics of the amorphous carbon structure. This conclusion is supported by the observed increase of the refractive indexes and absorption coefficients, obtained in the infrared region, as well as by the Raman results. Also, the effect of irradiation modifying the refractive index in the infrared region suggests the application of these films as waveguide in this region of wavelength.     

Characterization of hydrogenated amorphous carbon thin films by end-Hall ion beam deposition

Pure hydrogenated amorphous carbon (α-C:H) and nitrogen doped hydrogenated amorphous carbon (α-C:H:N) thin films were prepared using end-Hall (EH) ion beam deposition with a beam energy ranging from 24 eV to 48 eV. The composition, microstructure and mechanical properties of the films were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning probe microscopy (SPM), and nano-scratch tests. The films are uniform and smooth with root mean square roughness values of 0.5-0.8 nm for α-C:H and 0.35 nm for α-C:H:N films. When the ion energy was increased from 24 eV to 48 eV, the fraction of sp³ bonding in the α-C:H films increased from 36% to 55%, the hardness increased from 8 GPa to 12.5 GPa, and the Young's modulus increased from 100 GPa to 130 GPa. In the α-C:H:N films, N/C atomic ratio, the hardness and Young's modulus of the α-C:H:N films are, 0.087, 15 and 145 GPa, respectively. The results indicate that both higher ion energy and a small amount of N doping improve the mechanical properties of the films. The results have demonstrated that smooth and uniform α-C:H and α-C:H:N films with large area and reasonably high hardness and Young's modulus can be synthesized by EH ion source.     

Investigations on structural, vibrational, morphological and optical properties of CdS and CdS/Co films by ultrasonic spray pyrolysis

CdS and CdS/Co films have been deposited on glass substrates by an ultrasonic spray pyrolysis method. The effects of Co incorporation on the structural, optical, morphological, elemental and vibrational properties of these films were investigated. XRD analysis confirmed the hexagonal wurtzite structure of all films and had no impurity phase. While CdS film has (0 0 2) as the preferred orientation, CdS/Co films have (1 1 0) as the preferred orientation. The direct optical band gap was found to decrease from 2.42 to 2.39 eV by Co incorporation. The decrease of the direct energy gaps by increasing Co contents is mainly due to the sp-d exchange interaction between the localized d-electrons of Co²⁺ ions and band electrons of CdS. After the optical investigations, it was seen that the transmittance of CdS films decreased by Co content. The Raman measurements revealed two peaks corresponding to the 1LO and 2LO modes of hexagonal CdS. The vibrational modes of Cd-S were obtained in the wavenumber range (590-715 cm⁻¹) using Fourier transform infrared spectroscopy (FTIR). The elemental analysis of the film was done by energy dispersive X-ray spectrometry.     

Low voltage electrodeposition of diamond like carbon (DLC)

Attempt has been made to deposit diamond like carbon (DLC) films from ethanol through electrodeposition at low voltages (80-300 V) at 1 mm interelectrode separation. The films were characterized by atomic force microscopy (AFM), Scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and Auger electron Spectroscopy (AES). AFM investigations revealed the grain sizes are of tens of nanometers. The films were found to be continuous, smooth and close packed. Presence of peaks at 2958, 2929 and 2869 cm⁻¹ in FTIR spectrum indicates the bonding states to be of predominantly sp³ type (C-H). Raman spectroscopy analysis revealed two broad bands at ∼1350 and ∼1570 cm⁻¹. The downshift of the G-band of graphite is indicative of presence of DLC. Analysis of the Raman spectra for the samples revealed an improvement in the film quality with increase in the voltage. Micro Raman investigations indicate the formation of diamond phase at the deposition potential of 80 V. The sp² contents the films calculated from Auger electron spectra were calculated and were found to be 31, 19 and 7.8% for the samples prepared at 80, 150 and 300 V, respectively. A tentative mechanism for the formation of DLC has been proposed. These results indicate the possibility of deposition of DLC at low voltage.     

X-ray diffraction and photoelectron spectroscopy study of swift heavy ion irradiated Mn/p-Si structure

The electronic structure and interfacial chemistry of thin manganese films on p-Si (1 0 0) have been studied by photoelectron spectroscopy measurements using synchrotron radiation of 134 eV and from X-ray diffraction data. The Mn/p-Si structures have been irradiated from swift heavy ions (∼100 MeV) of Fe⁷⁺ with a fluence of 1 × 10¹⁴ ions/cm². Evolution of valence band spectrum with a sharp Fermi edge has been obtained. The observed Mn 3d peak has been related to the bonding of Mn 3d-Si 3sp states. Mn 3p (46.4 eV), Mn 3s (81.4 eV) and Si 2p (99.5 eV) core levels have also been observed which show a binding energy shift towards lower side as compared to their corresponding elemental values. From the photoelectron spectroscopic and X-ray diffraction results, Mn₅Si₃ metallic phase of manganese silicide has been found. The silicide phase has been found to grow on the irradiation.     

Carbon nitride films by RF plasma assisted PLD: Spectroscopic and electronic analysis

Carbon nitride (CNx) thin films have been grown on Si 〈1 0 0〉 by 193 nm ArF ns pulsed laser ablation of a pure graphite target in a low pressure atmosphere of a RF generated N₂ plasma and compared with samples grown by PLD in pure nitrogen atmosphere. Composition, structure and bonding of the deposited materials have been evaluated by X-ray photoelectron spectroscopy (XPS), and Raman scattering. Significant chemical and micro-structural changes have been registered, associated to different nitrogen incorporation in the two types of films analyzed. The intensity of the reactive activated species is, indeed, increased by the presence of the bias confined RF plasma, as compared to the bare nitrogen atmosphere, thus resulting in a different nitrogen uptake in the growing films. The process has been also investigated by some preliminary optical emission studies of the carbon plume expanding in the nitrogen atmosphere. Optical emission spectroscopy reveals the presence of many excited species like C⁺ ions, C atoms, C₂, N₂; and CN radicals, and N₂⁺ molecular ions, whose relative intensity appears to be increased in the presence of the RF plasma. The films were also characterised for electrical properties by the “four-probe-test method” determining sheet resistivity and correlating surface conductivity with chemical composition.     

Photoluminescence, FTIR and X-ray diffraction studies on undoped and Al-doped ZnO thin films grown on polycrystalline α-alumina substrates by ultrasonic spray pyrolysis

Undoped and aluminum-doped zinc oxide (ZnO) thin films have been grown on polycrystalline α-alumina substrates by ultrasonic spray pyrolysis (USP) technique using zinc acetate dihydrate and aluminum chloride hexahydrate (Al source) dissolved in methanol, ethanol and deionized water. A number of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and photoluminescence (PL) were used to characterize the obtained ZnO thin films. It was seen that the orientation changed with increase in substrate temperature. During the ZnO deposition Zn source reacted with polycrystalline α-Al₂O₃ substrate to form an intermediate ZnAl₂O₄ spinel layer. It has been interestingly found that the intensity of green emission at 2.48 eV remarkably increased when the obtained ZnO:Al films were deposited at 380 °C. The FTIR absorbance intensity of spectroscopic band at 447±6 cm⁻¹ is very sensitive to oxygen sublattice disorder resulting from non-stoichiometry, which is consistent with the result of PL characterization.     

Characterization of BCN films synthesized by radiofrequency plasma enhanced chemical vapor deposition

Boron carbonitride (BCN) films have been synthesized on Si(1 0 0) substrate by radio frequency plasma enhanced chemical vapor deposition using tris-(dimethylamino)borane (TDMAB) as a precursor. The deposition was performed at the different RF powers of 400-800 W, at the working pressure of 2×10⁻¹ Torr. The formation of the sp²-bonded BCN phase was confirmed by Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy measurements showed that B atoms were bonded to C and N atoms to form the BCN atomic hybrid configurations with the chemical compositions of B₅₂C₁₂N₃₆ (sample 1; prepared at the RF power of 400 W), B₅₂C₁₀N₃₈ (sample 2; at 500 W) and B₄₆C₁₈N₃₆ (sample 3; at 800 W), respectively. Near-edge X-ray absorption fine structure (NEXAFS) measurements indicated that B atoms were bonded not only to N atoms but also to C atoms to form various configurations of sp²-BCN atomic hybrids. The polarization dependence of NEXAFS suggested that the predominant hybrid configuration of sp²-BCN films oriented in the direction perpendicular to the Si substrate.     

Structural modifications of diamond like carbon films induced by MeV nitrogen ion irradiation

Diamond-like carbon (DLC) films were deposited on Si(1 0 0) substrates using plasma deposition technique. The deposited films were irradiated using 2 MeV N⁺ ions at fluences of 1×10¹⁴, 1×10¹⁵ and 5×10¹⁵ ions/cm². Samples have been characterized by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). Analysis of Raman spectra shows a gradual shift of both D and G band peaks towards higher frequencies along with an increase of the intensity ratio, I(D)/I(G), with increasing ion fluence in irradiation. These results are consistent with an increase of sp² bonding. XPS results also show a monotonic increase of sp²/sp³ hybridization ratio with increasing ion fluence. Plan view TEM images show the formation of clusters in the irradiated DLC films. HRTEM micrographs from the samples irradiated at a fluence of 5×10¹⁵ ions/cm² show the lattice image with an average interplanar spacing of 0.34 nm, revealing that the clusters are graphite clusters. The crystallographic planes in these clusters are somewhat distorted compared to the perfect graphite structure.     

Matrix assisted pulsed laser evaporation of cinnamate-pullulan and tosylate-pullulan polysaccharide derivative thin films for pharmaceutical applications

We have demonstrated the successful thin film growth of two pullulan derivatives (cinnamate-pullulan and tosylate-pullulan) using matrix assisted pulsed laser evaporation (MAPLE). Our MAPLE system consisted of a KrF* laser, a vacuum chamber, and a rotating target holder cooled with liquid nitrogen. Fused silica and silicon (1 1 1) wafers were used as substrates. The MAPLE-deposited thin films were characterized by transmission spectrometry, profilometry, atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The deposited layers ranged from 250 nm to 16.5 μm in thickness, depending on the laser fluence (0.065-0.5 J cm⁻²) and number of pulses applied for the deposition of one structure (1500-13,300). Our results confirmed that MAPLE was well-suited for the transfer of cinnamate-pullulan and tosylate-pullulan.     

High-conductive nanocrystalline silicon with phosphorous and boron doping

Intrinsic, P- and B-doped hydrogenated amorphous silicon thin films were prepared by plasma-enhanced chemical vapor deposition technique. As-deposited samples were thermally annealed at the temperature of 800 °C to obtain the doped nanocrystalline silicon (nc-Si) films. The microstructures, optical and electronic properties have been evaluated for the undoped and doped nanocrystalline films. X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of the substitutional boron and phosphorous in the doped films. It was found that thermal annealing can efficiently activate the dopants in films accompanying with formation of nc-Si grains. Based on the temperature-dependent conductivity measurements, it was shown that the activation of dopant by annealing increased the room temperature dark conductivity from 3.4 × 10⁻⁴ S cm⁻¹ to 5.3 S cm⁻¹ for the P-doped films and from 1.28 × 10⁻³ S cm⁻¹ to 130 S cm⁻¹ for the B-doped films. Meanwhile, the corresponding value of conductivity activation energies was decreased from 0.29 eV to 0.03 eV for the P-doped films and from 0.3 eV to 5.6 × 10⁻⁵ eV for the B-doped films, which indicated the doped nc-Si films with high conductivity can be achieved with the present approach.     

Effect of Cr implantation on structural and optical properties of AlN thin films

Molecular beam epitaxy (MBE) grown AlN thin layer on sapphire substrates have been implanted with Cr⁺ ions for various dose from 10¹³ to 10¹⁵ cm⁻². The analyses were carried out by an X-ray diffractometer (XRD), Raman spectroscopy, a spectrophotometer and spectroscopic ellipsometry (SE) for structural and optical analyses. E₂(high) and A₁(LO) Raman modes of AlN layer have been observed and analyzed. The behavior of Raman shift and the variation in intensity and in peak width of Raman modes as a function of ions flux are explained on the basis of chromium substituting aluminum atom and implantation-induced lattice damage. Both Raman and X-ray analyses reveal that the incorporation of chromium atoms increases in the host lattice with the increasing of Cr ions fluence. The band gap energy was determined by using transmission spectra. It was found that the band gap energy decreases as the ion dose increases. The band gap of the unimplanted AlN is 6.02 eV and it decreases down to 5.92 eV for the Cr⁺-implanted AlN with a ion dose of 1×10¹⁵ cm⁻². Optical properties such as optical constants of the samples were examined by using a spectroscopic ellipsometer. It was observed that the refractive index (n) decreases with the increasing of ion dose.     

Microwave-assisted synthesis and optical property of CdMoO4 nanoparticles

Microwave-assisted synthesis is a novel method used to synthesize CdMoO₄ nanoparticles in propylene glycol. The effects of reaction time and microwave power on phase, morphologies, and optical properties of CdMoO₄ nanoparticles were studied, using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and UV-visible spectroscopy. The present analyses proved that these crystalline powders were scheelite-type tetragonal structured CdMoO₄, with the crystallite size of 14-20 nm, and 4.51-4.73 eV band gaps, controlled by the synthetic conditions.     

Evidence of the primary-color photoluminescence in ion (H,H,C) irradiated and thermal annealed SrTiO3

We have measured photoluminescence (PL) spectrum of (1) thermal-annealed SrTiO₃/Si thin film and undoped SrTiO₃ single crystal; (2) SrTiO₃ single crystal irradiated by high energy (3 MeV) proton, deuterium, and He ion beams and (3) SrTiO₃ single crystal irradiated by low energy (60 keV) H⁺ and C⁻ ions. Two PL emissions are induced in (1) and (2) at visible frequencies 3 and 2.45 eV, while another PL peak is induced at 2 eV in (3). When compared with our previous PL experiments on high-temperature annealed SrTiO₃/SiO₂/Si thin film and 3 MeV proton (H⁺) irradiated STO single crystal, these results confirm that the three PL emissions with blue (3 eV), green (2.45 eV), and red-orange (2 eV) frequencies originate indeed from SrTiO₃. These primary-color PL effect induced at room-temperature makes STO a strong candidate material for future oxide-based optoelectronic application.     

Effects of rf power on surface-morphological, structural and electrical properties of aluminium-doped zinc oxide films by magnetron sputtering

Aluminium-doped zinc oxide (ZnO:Al) films were prepared by magnetron sputtering at different radio-frequency powers (P_rf) of 50, 100, 150 and 200 W. The properties of the films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Raman microscopy, and spectrophotometry with the emphasis on the evolution of compositional, surface-morphological, optical, electrical and microstructural properties. XPS spectra showed that within the detection limit the films are chemically identical to near-stoichiometric ZnO. AFM revealed that root-mean-square roughness of the films has almost linear increase with increasing P_rf. Optical band gap E_gopt of the films increases from 3.31 to 3.51 eV when P_rf increases from 50 to 200 W. A widening E_gopt of the ZnO:Al films compared to the band gap (∼3.29 eV) of undoped ZnO films is attributed to a net result of the competition between the Burstein-Moss effect and many-body effects. An electron concentration in the films was calculated in the range of 3.73 × 10¹⁹ to 2.12 × 10²⁰ cm⁻³. Raman spectroscopy analysis indicated that well-identified peaks appear at around 439 cm⁻¹ for all samples, corresponding to the band characteristics of the wurtzite phase. Raman peaks in the range 573-579 cm⁻¹ are also observed, corresponding to the A₁ (LO) mode of ZnO.