High-energy heavy-ion induced physical and surface-chemical modifications in polycrystalline cadmium sulfide thin films

The effect of high electronic energy deposition on the structure, surface topography, optical properties, and electronic structure of cadmium sulfide (CdS) thin films have been investigated by irradiating the films with 100 MeV Ag⁺⁷ ions at different ion fluences in the range of 10¹²–10¹³ ions/cm². The CdS films were deposited on glass substrate by thermal evaporation, and the films studied in the present work are polycrystalline with crystallites preferentially oriented along (002)-H direction. It is shown that swift heavy ion (SHI) irradiation leads to grain agglomeration and hence an increase in the grain size at low ion fluences. The observed lattice compaction was related to irradiation induced polygonization. The optical band gap energy decreased after irradiation, possibly due to the combined effect of change in the grain size and in the creation of intermediate energy levels. Enhanced nonradiative recombination via additional deep levels, introduced by SHI irradiation was noticed from photoluminescence (PL) analysis. A shift in the core levels associated with the change in Fermi level position was realized from XPS analysis. The chemistry of CdS film surface was studied which showed profound chemisorption of oxygen on the surface of CdS.     

Swift heavy ion induced surface modifications in nano-crystalline Li-Mg ferrite thin films

The swift heavy ion (190 MeV Au¹⁴⁺) induced modifications in surface morphologies of the nanocrystals of ferrite thin films have been extensively studied through the images of atomic force microscopy (AFM). In most of the irradiated films significant features like, the ditch and dike structures, have been observed through out the surface. We try to explain the observed changes on the basis of thermal spike model followed by momentum transfer induced lateral mass transport. In addition to these changes some new and interesting features have been noticed after irradiation in 8F and 9F ferrite thin films. These new features are attributed to sputtering phenomenon due to the presence of defects like latent tracks.     

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.     

Structural and optoelectronic properties of antimony tin sulphide thin films deposited by thermal evaporation techniques

Thin films of SnSb₂S₄ have been prepared on glass substrate by using thermal evaporation techniques. The films were annealed in argon gas at low pressure in sealed glass ampoules at 85 °C, 150 °C, 275 °C and 325 °C. XRD of the films reveal that the low temperature annealed films are poly crystalline while the as deposited films and high annealed films are in amorphous states. There is no adequate variation in the photoconductivity response of the amorphous and crystalline phases. The transmittance of the films is low and having no transmittance below 740 nm. The band gap calculated by ellipsometry technique is in the range of 1.82–3.1 eV. The films have n-type conductivity but the film annealed at 325 °C show p-type conductivity.     

Structural modifications of AlInN/GaN thin films by neon ion implantation

To study ion beam induced modifications into MOCVD grown wurtzite AlInN layers, neon ions were implanted on the samples with four doses ranging from 10¹⁴ to 9×10¹⁵ ions/cm²$9\times {10}^{15}\text{ions}/{\text{cm}}^2$. Structural characterization was carried out by X-ray diffraction and Rutherford backscattering spectroscopy (RBS) techniques. XRD analysis revealed that GaN related peak for all samples remains at its usual Bragg position of 2θ=34.56°$2\theta =34.56\mathrm{°}$ whereas a shift in AlInN peak takes place from its position of 2θ=35.51°$2\theta =35.51\mathrm{°}$ for as-grown sample. Rutherford back scattering (RBS) analysis indicated that peak related to Ga atoms in capping layer provided evidence of partial sputtering of GaN cap layers. Moreover, Al peak position is shifted towards lower channel side and width of the signal is increased after implantation, which pointed to the inwards migration of Al atoms away from the AlInN surface. The results suggested that partial sputtering of cap layer has taken place without uncovering the underneath AlInN layer.     

Studies on surface deformation of copper sulphide thin films by holographic interferometry technique

Holographic interferometry technique used to study the surface deformation of electrodeposited copper sulphide thin films on stainless steel substrate is here presented. It is concerned with the formation and interpretation of fringe patterns, which appears when a wave generated at some earlier time and stored in a hologram is later reconstructed by interfering with comparison wave. The proposed technique uses double exposure holographic interferometry (DEHI) together with simple mathematical relation, which allows immediate finding of stress, mass deposited and thickness of thin film. It must be further noted that, fringe spacing changes with time of deposition as well as solution concentration. The structural study (XRD) is carried out for the confirmation.     

The quantum size effect in thin antimony films

Thin antimony films have been epitaxially deposited at 350K onto cleavage surfaces of mica at different residual gas pressures between 10^?5 and 10^?9 torr, and their resistivity ? measured as a function of film thicknessd≦500Å at temperaturesT=110K andT=300K. The ?(d) characteristics of films deposited at residual gas pressures of about 10^?6 torr with condensation rates of about 1Å/s showed generally decreasing slopes as film thicknesses increased, but irregularities in detail. The ?(d) characteristics of films deposited at 10^?8 torr with the same condensation rate decreasing with increasingd, too, show no such irregularities but very small regular variations of ?(d) with constant oscillation length Δd between the maxima, and decreasing amplitudes with increasingd. These variations are better recognizable in a modified ?(d) graph. We tend to interprete these variations by the quantum size effect as we found oscillation lengths and amplitudes compatibel with theory.

     

The quantum size effect in thin antimony films

Thin antimony films have been epitaxially deposited at 350K onto cleavage surfaces of mica at different residual gas pressures between 10⁻⁵ and 10⁻⁹ torr, and their resistivity ∂ measured as a function of film thicknessd≦500? at temperaturesT=110K andT=300K. The ∂(d) characteristics of films deposited at residual gas pressures of about 10⁻⁶ torr with condensation rates of about 1?/s showed generally decreasing slopes as film thicknesses increased, but irregularities in detail. The ∂(d) characteristics of films deposited at 10⁻⁸ torr with the same condensation rate decreasing with increasingd, too, show no such irregularities but very small regular variations of ∂(d) with constant oscillation length Δd between the maxima, and decreasing amplitudes with increasingd. These variations are better recognizable in a modified ∂(d) graph. We tend to interprete these variations by the quantum size effect as we found oscillation lengths and amplitudes compatibel with theory.     

Synthesis and characterisation of co-evaporated tin sulphide thin films

Tin sulphide films were grown at different substrate temperatures by a thermal co-evaporation technique. The crystallinity of the films was evaluated from X-ray diffraction studies. Single-phase SnS films showed a strong (040) orientation with an orthorhombic crystal structure and a grain size of 0.12 μm. The films showed an electrical resistivity of 6.1 Ω cm with an activation energy of 0.26 eV. These films exhibited an optical band gap of 1.37 eV and had a high optical absorption coefficient (>10⁴ cm^-1) above the band-gap energy. The results obtained were analysed to evaluate the potentiality of the co-evaporated SnS films as an absorber layer in solar photovoltaic devices. PACS 78.40.Fy; 68.60.-p; 61.10.Nz; 68.55.-a; 78.66.-w     

Swift heavy ion irradiation-induced modifications of tris-(8-hydroxyquinoline)aluminum thin films

Tris-(8-hydroxyquinoline)aluminum (Alq₃), one of the most widely used light emitting and electron transport materials in organic luminescent devices, has been synthesized. Alq₃ thin films have been deposited by a thermal evaporation process on glass substrates. The effect of swift heavy ion (SHI) irradiation using 40 MeV Li³⁺ on the Alq₃ thin films has been studied by UV-visible, infrared, photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. From TRPL studies, it is found that the PL of Alq₃ thin films arises from two species corresponding to its two geometrical isomers, namely facial and meridional having two different life times. It is also confirmed that the PL and lifetimes of excitons decrease with the increase of ion fluences of SHI of 40 MeV Li³⁺, indicating a transfer of exciton energy to unstable cationic Alq₃ species generated by SHI irradiation.     

Ion implantation doping of zinc sulphide thin films

This letter reports on the ion implantation doping of zinc sulphide thin films with terbium, erbium and manganese and shows that the resultant cathode-excited emission is characteristic of the implanted ion.     

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.     

Structure, surface morphological and opto-electronic properties of zinc sulphide thin films deposited by dip method

ZnS thin films have been deposited by dip technique using succinic acid as a complexing agent. The structural and morphological characterizations of films have been investigated by X-ray diffraction, scanning electron microscope. X-ray pattern shows crystalline has hexagonal structure. The films show that good optical properties high absorption and band gap value was found to be 3.7 eV. The specific conductivity of the film was found to be in order of 10⁻⁵ (Ω cm)⁻¹ and showing n-type conduction.     

Morphological and optical characterization of thermally evaporated copper sulphide thin films

Thin films of Cu₂S on opaque gold layers and quartz substrates at the temperature of 393 K were deposited by a thermal evaporation technique. The surface morphology of the Cu₂S thin films at different thicknesses is investigated by AFM. It is seen that all the films are composed of highly coordinated spherical nano-sized particles well adhered to the substrate. The transmittance and reflectance spectra of Cu₂S thin films on the quartz substrate were recorded by a UV–visible spectrophotometer. The results show that the thermally evaporated Cu₂S thin films have the characteristic transmittance and reflectance suitable for optoelectronic applications. The stoichiometry and surface morphology of a grown Cu₂S thin film were confirmed by energy-dispersive X-ray spectroscopy (EDAX) and scanning electron microscopy (SEM), respectively. The dependence of the refractive index and the extinction coefficient on the photon energy for both the surface film and the opaque gold layer have been determined by ellipsometry. From the spectral behaviour of the absorption coefficient at two distinct absorption regions, a dual-band scheme of optical absorption for a Cu₂S thin film is described. The indirect and direct edges of Cu₂S are found to be about at 0.91 eV and 2.68 eV, respectively.     

Analysis of material modifications induced during laser damage in SiO2 thin films

The damage mechanisms in silica thin films exposed to high fluence 1064 nm nano-second laser pulses are investigated. The thin films under study are made with different techniques (evaporation and sputtering, with and without ion assistance) and the results are compared. The material morphological, optical and structural modifications are locally analyzed with optical microscopy and profilometry, photoluminescence and absorption microscopies. These observations are made for fluences near and above the laser damage threshold, and also in the case of multiple pulse irradiations. An increase in absorption in and around the damages is observed, as well as the generation of different defects that we spatially resolve with absorption and luminescence mappings.     

Silicon negative ion implantation induced vacancy defects in thermally grown SiO2 thin films

ABSTRACT

Thermally grown SiO₂ thin films on a silicon substrate implanted with 100?keV silicon negative ions with fluences varying from 1?×?10¹⁵ to 2?×?10¹⁷ ions cm^?2 have been investigated using Electron spin resonance, Fourier transforms infrared and Photoluminescence techniques. ESR studies revealed the presence of non-bridging oxygen hole centers, E′-centers and P_b-centers at g-values 2.0087, 2.0052 and 2.0010, respectively. These vacancy defects were found to increase with respect to ion fluence. FTIR spectra showed rocking vibration mode, stretching mode, bending vibration mode, and asymmetrical stretching absorption bands at 460, 614, 800 and 1080?cm^?1, respectively. The concentrations of Si–O and Si–Si bonds estimated from the absorption spectra were found to vary between 11.95?×?10²¹ cm^?3 and 5.20?×?10²¹ cm^?3 and between 5.90?×?10²¹ cm^?3 and 3.90?×?10²¹ cm^?3, respectively with an increase in the ion fluence. PL studies revealed the presence of vacancies related to non-bridging oxygen hole centers, which caused the light emission at a wavelength of 720?nm.