Swift heavy ion irradiation induced modification of structure and surface morphology of BiFeO3 thin film

BiFeO₃ (BFO) thin films of thickness about 800 nm deposited on Si (100) substrates by sol–gel spin coating method were irradiated by 200 MeV Ag ions. Modification of structure and surface morphology of the films under irradiation was studied using glancing incidence X-ray diffraction (GIXRD) and atomic force microscope (AFM). Fluence dependence of GIXRD peak intensity indicated formation of 10 nm diameter cylindrical amorphous columns in crystalline BFO due to 200 MeV Ag ion irradiation. AFM analysis indicated that the pristine film consists of agglomerated grains with diffuse grain boundary. Irradiation led to reduced agglomeration of the grains with the formation of sharper grain boundaries. The rms roughness (σ _rms) estimated from AFM analysis increased from 6·2 in pristine film to 12·7 nm when the film irradiated at a fluence of 1 × 10¹¹ ions cm ^???2 . Further irradiation led to decrease of σ _rms which finally saturated at a value of 7–8 nm at high ion fluences. The power spectral density analysis indicated that the evolution of surface morphology of the pristine film is governed by the combined effect of evaporation condensation and volume diffusion processes. Swift heavy ion irradiation seems to increase the dominance of volume diffusion in controlling surface morphology of the film at high ion fluences.     

Modifications induced by silicon and nickel ion beams in the electrical conductivity of zinc nanowires

This paper presents the modification in electrical conductivity of Zn nanowires under swift heavy ions irradiation at different fluences. The polycrystalline Zn nanowires were synthesized within polymeric templates, using electrochemical deposition technique and were irradiated with 80 MeV Si⁷⁺ and 110 MeV Ni⁸⁺ ion beams with fluence varying from 1 × 10¹² to 3 × 10¹³ ions/cm². I–V characteristics of exposed nanowires revealed a decrease in electrical conductivity with increase in ion fluence which was found to be independent of applied potential difference. But in the case of high fluence of Ni ion beam (3 × 10¹³ ions/cm²), electrical conductivity was found to increase with potential difference. The analysis found a significant contribution from grain boundaries scattering of conduction electrons and defects produced by ion beam during irradiation on flow of charge carriers in nanowires.     

Preparation and luminescence characteristics of LiYF4: Tm3+/Dy3+ single crystals for white-light LEDs

Tm³⁺ /Dy³⁺ co-doped LiYF₄ single crystals were synthesized by using vertical Bridgman method in sealed Pt crucibles. When excited by a proper UV-light, the crystals show blue emission band centered at 485 nm, which overlaps between the transition of Tm³⁺ (¹G₄ → ³H₆) and Dy³⁺ (⁴F_9/2 → ⁶H_15/2) ions, and yellow band of 573 nm ascribed to Dy³⁺ (⁴F_9/2 → ⁶H_13/2) ions. Both chromaticity coordinates and photoluminescence intensity vary with the excitation wavelengths and the concentration of rare earth dopants. A white light can be achieved from Tm³⁺ (0.6 mol%), Dy³⁺ (2.25 mol%) co-doped LiYF₄ crystal with chromaticity coordinates of x ≈ 0.2836, y ≈ 0.3229, and color temperature T _c = 8419 K by the excitation of a 350 nm light. It indicates that this crystal can be a potential candidate for the UV-light excited white-light emitting diodes.     

Effect of swift heavy ion irradiation on bare and coated ZnS quantum dots

The present study compares structural and optical modifications of bare and silica (SiO₂) coated ZnS quantum dots under swift heavy ion (SHI) irradiation. Bare and silica coated ZnS quantum dots were prepared following an inexpensive chemical route using polyvinyl alcohol (PVA) as the dielectric host matrix. X-ray diffraction (XRD) and transmission electron microscopy (TEM) study of the samples show the formation of almost spherical ZnS quantum dots. The UV-Vis absorption spectra reveal blue shift relative to bulk material in absorption energy while photoluminescence (PL) spectra suggests that surface state and near band edge emissions are dominating in case of bare and coated samples, respectively. Swift heavy ion irradiation of the samples was carried out with 160 MeV Ni¹²⁺ ion beam with fluences 10¹² to 10¹³ ions/cm². Size enhancement of bare quantum dots after irradiation has been indicated in XRD and TEM analysis of the samples which has also been supported by optical absorption spectra. However similar investigations on irradiated coated quantum dots revealed little change in quantum dot size and emission. The present study thus shows that the coated ZnS quantum dots are stable upon SHI irradiation compared to the bare one.     

GaN optical degradation during high energy Sn<Superscript>5+</Superscript> ion irradiation

GaN(0001) epilayers grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD) have been irradiated with 75 MeV Sn⁵⁺ ions at the fluences of 10¹¹, 10¹², and 10¹³ ions/cm². Structural and optical studies reveal that GaN epilayer withstands 75 MeV Sn⁵⁺ ion irradiations up to 10¹¹ ions/cm² ion fluences. High resolution X-ray diffraction results showed that the FWHM corresponding to (0002) plane increased from 227 to 279 arc-seconds after Sn-ions irradiation. Red shift was observed in the yellow luminescence (YL) emission by photoluminescence (PL), corresponds to the concentration of ion fluences. Donor-bound exciton (DBE) and free exciton (FE^A, FE^B and FE^C) emissions were observed for as-grown and irradiated GaN samples up to 10¹² ions/cm² at 2K PL measurements. Free excitons are dominated by low-temperature PL measurements for as-grown and irradiated GaN samples at 10¹¹ and 10¹² ion fluences. Atomic force microscopy images show the RMS roughness increases with increasing Sn-ion fluences by removing as-grown GaN surface defects.     

Effects of proton irradiation on the microstructure and mechanical properties of Amosic-3 silicon carbide minicomposites

One dimensional Amosic-3 silicon carbide fiber reinforced silicon carbide matrix composites (SiC_f/SiC minicomposites) prepared by chemical vapor infiltration were irradiated with 2.8 MeV proton ions. The ion fluences were 1.0 × 10¹⁷ and 1.5 × 10¹⁷ cm⁻² at room temperature and 300 °C, respectively. The microstructure and mechanical properties were investigated before and after proton irradiation. Raman spectra showed no evident change in Amosic-3 fibers regardless of irradiation temperature, which is confirmed by high resolution transmission electron microscopy observation. Pyrolytic carbon interphase showed slightly expansion after 300 °C irradiation, however, no microstructure changes were observed in SiC matrix. Moreover, it can be deduced that no irradiation induced changes in mechanical properties were observed after present proton irradiation.     

Swift heavy ion irradiation effect on Cu-doped CdS nanocrystals embedded in PMMA

Semiconductor nanocrystals (NCs) have received much interest for their optical and electronic properties. When these NCs dispersed in polymer matrix, brightness of the light emission is enhanced due to their quantum dot size. The CdCuS NCs have been synthesized by chemical route method and then dispersed in PMMA matrix. These nanocomposite polymer films were irradiated by swift heavy ion (SHI) (100 MeV, Si⁺⁷ ions beam) at different fluences of 1 × 10¹⁰ and 1 × 10¹² ions/cm² and then compared their structural and optical properties by XRD, atomic force microscopy, photoluminescence, and UV-Vis spectroscopy before and after irradiation. The XRD spectra showed a broad hump around 2θ ≈ 11·83° due to amorphous PMMA and other peaks corresponding to hexagonal structure of CdS nanocrystals in PMMA matrix. The photoluminescence spectra shows a broad peak at 530 nm corresponding to green emission due to Cu impurities in CdS. The UV-Vis measurement showed red shift in optical absorption and bandgap changed from 4·38–3·60 eV as the irradiation fluency increased with respect to pristine CdCuS nanocomposite polymer film.     

Effect of 80 MeV oxygen ion beam irradiation on the properties of CdTe thin films

Polycrystalline CdTe thin films were irradiated with 80 MeV oxygen (O⁶⁺) ions for various fluences and its effect on the composition, structure, surface topography and optical properties have been investigated. The as-grown films are found to be slightly Te-rich in composition and there is no significant change in the composition after irradiation. X-ray diffraction analysis shows a high degree of crystallite orientation along the (111) plane of cubic phase CdTe. Upon irradiation a large decrease in intensity of the (111) plane and a small shift in the peak position has been resulted. The shift in the peak position is correlated with the change in the residual stress. The surface roughness of the films get increased after irradiation. A decrease in the grain size was observed after irradiation due to ion-induced recrystallization. The optical band gap energy decreased from 1.53 eV for as-grown film to 1.46 eV upon irradiation. The photoluminescence (PL) spectrum is dominated by the defect band and the effect of irradiation has been discussed and correlated with the observed change in the XRD peak position and optical band gap.     

Synthesis of zirconium silicide in Zr thin film on Si and study of its surface morphology

Zirconium silicide was synthesized on Si (100)/zirconium interface by means of swiftly moving 150 MeV Au ion beam. Thin films of zirconium (~60 nm) were deposited on Si (100) substrates in ultra high vacuum conditions using the electron-beam evaporation technique. The system was exposed to different ion fluencies ranging from 3 × 10¹³ to 1 × 10¹⁴ ions/cm² at room temperature. Synthesized zirconium silicide thin film reasonably affects the resistivity of the irradiated system and for highest fluence of 1 × 10¹⁴ ions/cm² resistivity value reduces from 84.3 to 36 μΩ cm. A low resistivity silicide phase, C-49 ZrSi₂ was confirmed by X-ray analysis. Schottky barrier height was calculated from I–V measurements and the values drops down to 0.58 eV after irradiation at 1 × 10¹⁴ ions/cm². The surface and interface morphologies of zirconium silicide were examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM shows a considerable change in the surface structure and SEM shows the ZrSi₂ agglomeration and formation of Si-rich silicide islands.     

Structural study, photoluminescence, and photocatalytic activity of semiconducting BaZrO3:Bi nanocrystals

Wide band gap nanocrystalline bismuth doped barium zirconate is synthesized by a facile hydrothermal method at 100 °C. The obtained cubic perovskites are characterized by powder X-ray diffraction (XRD), UV-VIS diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy, and photocatalytic activity. The estimated band gap in the 2.4-4.9 eV range, depending on Bi concentration, suggests nanocrystalline BaZrO₃:Bi as a useful visible-light activated photocatalyst under excitation wavelengths <800 nm. Displacement of main XRD pattern peaks suggest that bismuth ion mostly substitutes into Zr⁴⁺ sites within the BaZrO₃ host lattice. It is found that BaZrO₃:Bi decomposes methylene blue (MB) under both UV and visible light irradiation. The photocatalyst efficiency depends strongly on Bi content and induced defects.     

Photoelectron spectroscopy study of Mn/n-Si interfacial structure

The Mn/n-Si interfacial structure is susceptible to intermixing even at room temperature. To investigate the chemistry as a result of the intermixing, valence band and core level photoelectron spectroscopy of Mn/Si has been carried out using synchrotron radiation of 134 eV energy and Al K_α X-ray (λ = 1,486.6 Å) source. The fabricated structures have also been irradiated from swift heavy ions (Fe⁷⁺ of ~100 MeV) to investigate the ion beam mixing in such structures. Valence band photoelectron spectroscopy with 134 eV photons shows the evolution of Mn3d, Mn3p and Si2p levels with a shifting towards lower binding energy side compared to their elemental values of the binding energy. This binding energy shift shows the formation of chemical compound of Si and Mn. Evolution of Si2p core level prior to and after the swift heavy ion irradiation shows strong chemical reactivity of manganese thin film with silicon. Deconvolution of Mn3d valence band has shown the formation of silicide phase due to the hybridization of Mn3d and Si3sp states. Mn2p core level study shows that the oxide and silicide formation takes place during the growth and for successive etching, oxide part is decreasing whereas silicide part is increasing.     

Synthesis and luminescence of Dy3+-activated NaSrPO4 phosphors for novel white light generation

The Dy³⁺-doped NaSrPO₄ phosphor powders have been synthesized by solid state reaction. All samples were verified to be in a pure NaSrPO₄ phase by X-ray diffraction analysis for all the Dy³⁺ doping concentrations. The room temperature excitation spectra of NaSrPO₄:Dy³⁺ phosphors illustrated that they could easily be excited by UV–Visible light corresponding f ? f transitions of Dy³⁺. The photoluminescence spectra exhibit two main bands centered at 481 nm (blue) and 573 nm (yellow), which originate from the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺, respectively. The two bands combined to form a white light with the chromaticity coordinates varying with the concentrations of Dy³⁺. The chromaticity coordinates were measured and mapped in the Commission International de L’Ecllairage 1931 diagram, indicating that they distributed around (0.30, 0.34) of the colorless point D65. The dependence of luminescence intensity onto Dy³⁺ concentration was investigated and the concentration quenching mechanism for NaSrPO₄:Dy³⁺ was discussed.     

Irradiation effects on AlGaN HFET devices and GaN layers

AlGaN/GaN heterostructure field effect transistors (HFETs) were irradiated with protons as well as carbon, oxygen, iron and krypton ions of high (68 and 120 MeV) and low (2 MeV) energy with fluences in the range from 1 × 10⁷ to 1 × 10¹³ cm^?2. High energy irradiation with protons, carbon and oxygen produced no degradation in devices while krypton irradiation at the fluence of 1 × 10¹⁰ cm^?2 resulted in a small reduction of 2% in the transconductance. Similarly, for GaN samples irradiated with protons, carbon and oxygen at high energy no changes were seen by XRD, PL and Hall effect, while changes in lattice constant and a reduction in PL intensity were observed after irradiation with high energy krypton. Low energy irradiation with carbon and oxygen at a fluence of 5 × 10¹⁰ cm^?2 results in small change in the device performance while remarkable changes in device characteristics are seen at a fluence of 1 × 10¹² cm^?2 for carbon, oxygen, iron and krypton irradiation. Similarly changes are also observed by XRD, PL and Hall effect for the thick GaN layer irradiated at the fluence of 1 × 10¹² cm^?2. The device results and GaN layer properties are strongly correlated.     

Irradiation induced grain growth and surface emission enhancement of chemically tailored ZnS : Mn/PVOH nanoparticles by Cl<Superscript>+9</Superscript> ion impact

Manganese doped zinc sulfide nanoparticles are fabricated on polyvinyl alcohol dielectric matrix. They are bombarded with energetic chlorine ions (100 MeV). The size of the crystallites is found to increase with ion fluence due to melting led grain growth under ion irradiation. The increased size as a result of grain growth has been observed both in the optical absorption spectra in terms of redshift and in electron microscopic images. The photoluminescence (PL) study was carried out by band to band excitation (λ_ex = 220 nm) upon ZnS : Mn, which results into two emission peaks corresponding to surface states and Mn⁺² emission, respectively. The ion fluence for irradiation experiment so chosen were 1 × 10¹¹, 5 × 10¹¹, 5 × 10¹² and 10¹³ Cl/cm².     

Nanostructure, optical and photoluminescence properties of Zn1−xNixO nanoclusters by co-precipitation method

Zn_1?xNi_xO (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) nanoclusters have been successfully synthesized by co-precipitation method. The synthesized samples have been characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV–visible spectrophotometer and Fourier transform infrared spectroscopy. The XRD and SEM measurements reveal that the prepared undoped and Ni-doped nanoclusters have different microstructure without changing a hexagonal wurtzite structure. The calculated average crystalline size from XRD measurement decreases from 37.5 to 26.6 nm for x = 0 to 0.05 which was confirmed by SEM micrographs. The change in lattice parameters, micro-strain, shift of XRD peaks and the blue shift of energy gap from 3.18 to 3.33 eV (ΔE_g = 0.15 eV) for Ni = 0–0.02 and red shift of E_g from 3.33 to 3.14 eV (ΔE_g = 0.19 eV) for Ni = 0.02 to 0.05 reveal the substitution of Ni²⁺ ions into Zn–O lattice. The presence of functional groups and the chemical bonding are confirmed by FTIR spectra. The shift of NBE UV emission between 374 and 395 nm, the shift of green band emission between 517 and 531 nm, the change in intensity and the broadening effect in the photoluminescence spectra confirms the substitution of Ni²⁺ ions into the Zn–O lattice. Ni-doped ZnO system shows a great pledge for the fabrication of nano-optoelectronic devices like tunable light emitting diode in the near future.     

Surface hardening in N<Superscript>+</Superscript> implanted polycarbonate

The influence of low energy nitrogen ions on the surface hardness of polycarbonate has been studied by implanting some of these specimens with 100 keV N⁺ ions at a beam current of 1 μA/cm² in the dose range of 1 × 10¹⁵ to 1 × 10¹⁷ ions cm^?2. Knoop microhardness has been found to be increased nearly 24 times at a load of 9.8 mN, for the dose of 1 × 10¹⁷ ions cm^?2. The structural changes occurred in implanted specimens were studied by Raman analysis, UV–Visible spectroscopy, and X-ray diffraction techniques. Raman studies point toward the formation of a structure resembling hydrogenated amorphous carbon. Disordering in the surface structure (I _D/I _G ratio) has also been found to increase with ion fluence using Raman technique. UV–Visible spectroscopic analysis shows a clear enhancement in Urbach energy (disorder parameter) from a value of 0.61 eV (virgin sample) to 1.72 eV (at a fluence of 1 × 10¹⁷ N⁺ cm^?2) with increasing ion dose. The increase in Urbach energy has been found to be correlated linearly with the increase in Knoop microhardness number. Results of X-ray diffraction analysis also indicate disordering in implanted layers as a result of implantation. In the present work, the possible mechanism behind the formation of harder surfaces due to implantation has been discussed in detail.     

Enhanced performance of 4,4′-bipyridine-doped PVDF/KI/I<Subscript>2</Subscript> based solid state polymer electrolyte for dye-sensitized solar cell applications

Pure (PVDF/KI/I₂) and 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolytes were prepared by solution casting method using N,N-dimethylformamide (DMF) as solvent. The solid state polymer electrolytes were characterized by the powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), AC-impedance, dielectric measurements and scanning electron microscopy (SEM) analysis. The crystallinity of the solid state polymer electrolytes was analyzed by PXRD measurement. The functional groups of the solid state polymer electrolytes were confirmed by FTIR analysis. The AC-impedance analysis was carried out to calculate the ionic conductivity of the solid state polymer electrolytes. The ionic conductivity value of pure (PVDF/KI/I₂) and 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolytes are 2.00?×?10^?6 S cm^?1 and 4.60?×?10^?5 S cm^?1, respectively. The dielectric properties of solid state polymer electrolytes were calculated by using the dielectric measurements. From the SEM analysis, the surface morphology of the solid state polymer electrolytes was analyzed. The power conversion efficiencies of pure (PVDF/KI/I₂) and 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolytes are 1.8% and 4.4%, respectively. 4,4′-bipyridine-doped PVDF/KI/I₂ solid state polymer electrolyte has higher power conversion efficiency due to its increased amorphous nature and ionic mobility.     

Effect of SHI irradiation on the morphology of SnO2 thin film prepared by reactive thermal evaporation

SnO₂ thin films prepared by reactive thermal evaporation on glass substrates were subjected to 120 MeV Ag⁹⁺ ion irradiation. The surface topography progression using the swift heavy ion irradiation was studied. It shows creation of unique surface morphologies and regular structures on the surface of the SnO₂ thin film at particular fluences. Field Emission Scanning electron microscopy (FE-SEM) and Atomic force microscopy (AFM) are used for investigating the effect of Ag ions at different fluences on the surface of SnO₂. The morphological changes suggest that ion assisted/induced diffusion process play a significant role in the evolution of nanostructures on SnO₂ surface. The roughness increases from 9.4 to 14.9 with fluence upto 1 × 10¹² ions/cm² and beyond this fluence, the roughness decreases. Ion-beam induced recrystallization at lower fluences and amorphization or disordering of crystals at higher fluences are understood based on the thermal spike model.     

Structural,optical and electrical properties of ion beam irradiated cadmium selenate nanowires

Present study is related to the synthesis of cadmium selenate nanowires via template-assisted electrodeposition approach and their characterization before and after lithium (Li³⁺) ion beam irradiation. Energy-dispersive X-ray analysis and X-ray diffraction study confirmed the synthesis of cadmium selenate nanowires with monoclinic structure. Electrical properties were examined with current–voltage (I–V) source meter using two-probe method. The electrical conductivity augmentation was perceptible for semiconducting nanowires with the increase in the ion beam fluence. The band gap of pristine nanowires was found to be 1.96 eV, while the red shift was observed in the optical band gap of ion irradiated nanowires and it approaches to the value of 1.31 eV at last fluence. In XRD spectra, no evidence was found of phase change or shifting in ‘2θ’ position or evolution of any new peak. However, variation in the peak intensities was noticed that could be the result of movement of plane orientation. This study revealed that the defects induced by the ion irradiation and variation in potential gradient with fluence plays a major role in the alteration of the optical and electrical properties of the semiconducting nanowires.     

Enhancement in CO gas sensing properties of hydroxyapatite thick films: Effect of swift heavy ion irradiation

This paper investigates the effect of swift heavy ion (SHI) irradiation on surface morphology of Hydroxyapatite (HAp) thick films and modification in gas sensing characteristics. The HAp nanopowder is synthesized by wet chemical process and the thick films are prepared by screen printing technique. These films are irradiated with Ag⁷⁺ ions with energy of 100 MeV at different fluences ranging from 3 × 10¹⁰ to 3 × 10¹³ ions/cm². X-ray diffraction and atomic force microscopy tools are employed to examine the phase and surface modification in HAp thick films due to swift heavy ion irradiation. The ion irradiation study shows that crystallinity decreases and grain size changes with increase in ion fluence. A precise study on gas sensing is carried out to confirm operating temperature of HAp thick film sensor to detect CO gas. Saturation region of the film with increasing gas concentration and other parameters such as response and recovery time are also investigated from the point of view of using HAp films as a sensor device. SHI irradiated HAp thick film shows enhancement in the gas response and saturation limit for CO gas. Furthermore, the irradiated HAp film shows fast response and recovery time for CO gas. The study concludes that nanoceramic HAp thick film is an excellent CO gas sensor at an operating temperature of 195 °C.