Photoluminescence and optical properties of He ion bombarded ultra-high molecular weight polyethylene

Ion bombardment is a suitable tool to improve the physical and chemical properties of polymer surface. In this study UHMWPE samples were bombarded with 130 keV He ions to the fluences ranging from 1 × 10¹² to 1 × 10¹⁶ cm⁻². The untreated and ion beam modified samples were investigated by photoluminescence, and ultraviolet-visible (UV-vis) spectroscopy. Remarkable decrease in integrated luminescence intensity with increasing ion fluences was observed. The reduction in PL intensity with increase of ion fluence might be attributed to degradation of polymer surface and formation of defects. The effect of ion fluence on the optical properties of the bombarded surfaces was characterized. The values of the optical band gap E_g, and activation energy E_a were determined from the optical absorption. The width of the tail of the localized states in the band gap (E_a) was evaluated using the Urbach edge method. With increasing ion fluences a decrease in both the energy gap and the activation energy were observed. Increase in the numbers of carbon atoms (N) in a formed cluster with increasing the He ion fluence was observed.     

Effect of swift (∼100 MeV) heavy ion irradiation on surface morphology and electronic transport in Fe film on Si substrate

Fe film (∼50 nm) have been deposited on pSi substrate by electron beam evaporation technique. The bilayers have been irradiated by 100 MeV Fe⁷⁺ ions having fluences of 1 × 10¹³, 1 × 10¹⁴ and 5 × 10¹⁴ ions cm⁻². SEM study of the unirradiated devices show surface modifications having a annular structures. From XRD study of the bilayer, it is observed that grain size has reduced from 70 to 25 nm after the irradiation for a fluence of 1 × 10¹⁴ ions cm⁻². Moreover electronic transport data of the bilayer show practically no effect on the current flow for a fluence of 1 × 10¹³ ions cm⁻² irradiation whereas for 1 × 10¹⁴ ions cm⁻² fluence, there is very significant change in current flow (by two orders in magnitude) across the bilayer. However, for a higher fluence of irradiation 5 × 10¹⁴ ions cm⁻², the bilayer becomes highly resistive. It has been found from the above observations that the fluence of 1 × 10¹⁴ ions cm⁻² of swift heavy ion irradiation is a optimum fluence.     

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.     

Study of nitrogen ion implantation and diffusion phenomena on thin chromium layers followed by the atomic force microscopy and secondary ion mass spectroscopy techniques characterization

This research investigates the effect of ion implantation dosage level and further thermal treatment on the physical characteristics of chromium coatings on Si(1 1 1) substrates. Chromium films had been exposed to nitrogen ion fluencies of 1 × 10¹⁷, 3 × 10¹⁷, 6 × 10¹⁷ and 10 × 10¹⁷ N⁺ cm⁻² with a 15 keV energy level. Obtained samples had been heat treated at 450 °C at a pressure of 2 × 10⁻² Torr in an argon atmosphere for 30 h. Atomic force microscopy (AFM) images showed significant increase in surface roughness as a result of nitrogen ion fluence increase. Secondary ion mass spectroscopy (SIMS) studies revealed a clear increased accumulation of Cr₂N phase near the surface as a result of higher N⁺ fluence. XRD patterns showed preferred growth of [0 0 2] and [1 1 1] planes of Cr₂N phase as a result of higher ion implantation fluence. These results had been explained based on the nucleation-growth of Cr₂N phase and nitrogen atoms diffusion history during the thermal treatment process.     

Thermal evolution of vacancy defects induced in sintered UO2 disks by helium implantation

A slow positron beam coupled with Doppler broadening (DB) spectrometer was used to measure the low- and high-momentum annihilation fractions, S and W, respectively, as a function of positron energy in UO₂ disks implanted with different 1 MeV ³He fluences and annealed in ArH₂ or in vacuum. The S(E) and W(E) behaviors indicate that for fluences in the range from 2 × 10¹⁴ to 2 × 10¹⁶³He cm⁻², the vacancy defects distribution evolves with the annealing temperature in the range from 264 to 700 °C under ArH₂. This evolution is found to be dependent on the ³He fluence implanted in the sintered UO₂ disks. For the lowest fluence of 2 × 10¹⁴³He cm⁻², the S(W) plot with positron energy as the running parameter suggests that only the concentration of vacancy defects decreases when annealing temperature increases. For the highest implantation fluences (from 5 × 10¹⁵ to 2 × 10¹⁶³He cm⁻²) the S(W) plot suggests that the nature of the vacancy defects changes in the annealing temperature range from 260 to 400 °C. Measurements performed in implanted UO₂ disks annealed in vacuum have revealed a partial recovery of the vacancy defects possibly due to their recombination with mobile oxygen interstitials. The role of the hydrogen infusion into the disk is also discussed.     

Impact of 100 MeV Au on the surface of relaxed Si0.5Ge0.5 alloy films studied by atomic force microscopy

We demonstrate a gradual surface modification process of relaxed Si_0.5Ge_0.5 alloy films by 100 MeV Au beam with fluence varying between 5 × 10¹⁰ and 1 × 10¹² ions/cm² at 80 K by means of atomic force microscopy (AFM). Presence of Ge quantum dots (QDs) was found in the virgin sample. The disappearance of the QDs were noticed when the samples were irradiated with a fluence of 5 × 10¹⁰ ions/cm². Craters were found developing at a fluence of 1 × 10¹¹ ions/cm². Apart from the evolution of the craters, blisters were also detected at a fluence of 1 × 10¹² ions/cm². Variation of the average root mean square value of the surface roughness as a function of fluence was examined.     

Formation of nanodots on oblique ion sputtered InP surfaces

Using a field emission gun based scanning electron microscopy, we report the formation of nanodots on the InP surfaces after bombardment by 100 keV Ar⁺ ions under off-normal ion incidence (30° and 60° with respect to the surface normal) condition in the fluence range of 1 × 10¹⁶ to 1 × 10¹⁸ ions cm⁻². Nanodots start forming after a threshold fluence of about 1 × 10¹⁷ ions cm⁻². It is also seen that although the average dot diameter increases with fluence the average number of dots decreases with increasing fluence. Formation of such nanostructured features is attributed due to ion-beam sputtering. X-ray photoelectron spectroscopy analysis of the ion sputtered surface clearly shows In enrichment of the sputtered InP surface. The observation of growth of nanodots on the Ar⁺-ion sputtered InP surface under the present experimental condition matches well with the recent simulation results based on an atomistic model of sputter erosion.     

Phase formation by ion beam mixing in the Ti/Si multilayer system

The irradiation effect of 350 MeV Au⁺ ions on Ti/Si multilayers has been studied using Rutherford backscattering spectroscopy, X-ray reflectivity (XRR) and grazing incidence X-ray diffraction (GIXRD). Intermixing effects have been studied as a function of fluences of 0.46 × 10¹⁴, 1.82 × 10¹⁴ and 4.62 × 10¹⁴ cm⁻². Rutherford backscattering spectra (RBS) confirm mixing at the interface. X-ray reflectivity patterns show damage at the interfaces with the absence of a continuous fringe pattern at high fluence doses in comparison to the pristine interface. Mixing leads to titanium di-silicide (TiSi₂) phase formation as a shown by grazing incidence X-ray diffraction patterns. The observed intermixing is attributed to energy deposited by the incident ions in the electronic system of the target. Swift heavy ion irradiation induced intermixing increases with fluence.     

SHI induced silicide formation and surface morphology at Co/Si system

Ion beam mixing is a useful technique to produce modifications at the surface and interface of the solid material. In the present work, ion beam induced modifications at Co/Si interface using 120 MeV Au-ion irradiation has been studied at ion fluences in the range of 10¹² to 10¹⁴ ions/cm² by secondary ion mass spectroscopy (SIMS) technique and calculated mixing efficiency at the interface. Silicide formation has been discussed on the basis of swift heavy ion (SHI) irradiation induced effects. Surface morphology and roughness of irradiated system with fluence 5 × 10¹³ and 1 × 10¹⁴ ions/cm² is studied by scanning tunneling microscopy (STM). Roughness of the surface shows marks of melting process and confirms the appearance of some pinholes in the reacted Co/Si system. Comparative study was also undertaken on annealed sample at 300 °C and then irradiated at a dose 1 × 10¹⁴ ions/cm².     

Surface roughness and power spectral density study of SHI irradiated ultra-thin gold films

Quantitative roughness and microstructural analysis of as-deposited and swift heavy ion (SHI) (107 MeV Ag and 58 MeV Ni) irradiated 10 and 20 nm thick Au films were performed by atomic force microscopy (AFM). Power spectral density (PSD) analysis was done from the AFM images. The energies chosen for the two different ions eliminated the velocity effect of SHI in materials modification. The rms roughness estimated from the AFM data did not show either monotonic increase or decrease with ion fluences. Instead, it increased at low fluences and decreased at high fluences for 20 nm thick film. In 10 nm film, the roughness first increased with ion fluence, then decreased and again increased at higher fluences. Though the 10 and 20 nm films exhibited very different patterns of rms roughness variation with ion fluence, the pattern of variation in both cases was identical for Ni and Ag beams. The PSD analysis for both 10 and 20 nm films (pristine and irradiated) showed similar variation of low frequency roughness with ion fluence as that of the rms roughness. In the high frequency regime, PSD analysis suggests that surface morphology of the irradiated samples is governed by the combined effect of evaporation-recondensation and diffusion dominated processes.     

Pulsed Nd:YAG laser depositions of ITO and DLC films for OLED applications

Indium-tin oxide (ITO) films deposited on heated and non-heated glass substrates by a pulsed Nd:YAG laser at 355 nm and ∼2.5 J/cm² were used in the fabrication of simple organic light-emitting diodes (OLEDs), ITO/(PVK + Alq₃ + TPD)/Al. The ITO was deposited on heated glass substrates which possessed resistivity as low as ∼3 × 10⁻⁴ Ω cm, optical transmission as high as ∼92% and carrier concentration of about ∼5 × 10²⁰ cm⁻³, were comparable to the commercial ITO. Substrate heating transformed the ITO microstructure from amorphous to polycrystalline, as revealed by the XRD spectrum. While the polycrystalline ITO produced higher OLED brightness, it was still lower than that on the commercial ITO due to surface roughness. A DLC layer of ∼1.5 nm deposited on this ITO at laser fluence of >12.5 J/cm² improved its device brightness by suppressing the surface roughness effect.     

Change of sheet resistance of high purity alumina ceramics implanted by Cu and Ti ions

High purity alumina ceramics (99% Al₂O₃) was implanted by copper ion and titanium ion in a metal vapour vacuum arc (MEVVA) implanter, respectively. The influence of implantation parameters was studied varying ion fluence. The samples were implanted by 68 keV Cu ion and 82 keV Ti ion with fluences from 1 × 10¹⁵ to 1 × 10¹⁸ ions/cm², respectively. The as-implanted samples were investigated by scanning electron microscopy (SEM), glancing X-ray diffraction (GXRD), scanning Auger microscopy (SAM), and four-probe method. Different morphologies were observed on the surfaces of the as-implanted samples and clearly related to implantation parameters. For both ion implantations, the sheet resistances of the alumina samples implanted with Cu and Ti ion fluences of 1 × 10¹⁸ ions/cm², respectively, reached the corresponding minimum values because of the surface metallization. The experimental results indicate that the high-fluence ion implantation resulted in conductive layer on the surface of the as-implanted high purity alumina ceramics.     

Effects of swift heavy ion irradiation on the electrical characteristics of Au/n-GaAs Schottky diodes

Metal-semiconductor diode of Au/n-GaAs is studied under the irradiation of swift heavy ion (SHI) beam (80 MeV ¹⁶O⁶⁺), using in situ current-voltage characterization technique. The diode parameters like ideality factor, barrier height, and leakage current are observed to vary with irradiation fluence. Significantly, the diode performance improves at a high fluence of 2 × 10¹³ ions cm⁻² with a large decrease of reverse leakage current in comparison to the original as deposited sample. The Schottky barrier height (SBH) also increases with fluence. At a high irradiation fluence of 5 × 10¹³ ions cm⁻² the SBH (0.62 ± 0.01 eV) is much larger than that of the as deposited sample (0.55 ± 0.01 eV). The diode parameters remain stable over a large range of irradiation up to fluence of 8 × 10¹³ ions cm⁻². A prominent annealing effect of the swift ion beam owing to moderate electronic excitation and high ratio of electronic energy loss to the nuclear loss is found to be responsible for the improvement in diode characteristics.     

Structure and tribological performance by nitrogen and oxygen plasma based ion implantation on Ti6Al4V alloy

Ti6Al4V alloy was implanted with nitrogen-oxygen mixture by using plasma based ion implantation (PBII) at pulsed voltage −10, −30 and −50 kV. The implantation was up to 6 × 10¹⁷ ions/cm² fluence. The changes in chemical composition, structure and hardness of the modified surfaces were studied by XPS and nanoindentation measurements. According to XPS, it was found that the modified layer was predominantly TiO₂, but contained small amounts of TiO, Ti₂O₃, TiN and Al₂O₃ between the outmost layer and metallic substrate. Surface hardness and wear resistance of the samples increased significantly after PBII treatment, the wear rate of the sample implanted N₂-O₂ mixture at −50 kV decreased eight times than the untreated one. The sample implanted N₂-O₂ mixture showed better wear resistance than that of the sample only implanted oxygen at − 50 kV. The wear mechanism of untreated sample was abrasive-dominated and adhesive, and the wear scar of the sample implanted at −50 kV was characterized by abrasive wear-type ploughing.     

Luminescence studies on swift heavy ion irradiated nanocrystalline aluminum oxide

Pellets of nanocrystalline aluminum oxide synthesized by a combustion technique are irradiated with 120 MeV Au⁹⁺ ions for fluence in the range 5×10¹¹-1×10¹³ ions cm⁻². Two photoluminescence (PL) emissions, a prominent one with peak at ∼525 nm and a shoulder at ∼465 nm are observed in heat treated and Au⁹⁺ ion irradiated aluminum oxide. The 525 nm emission is attributed to F₂²⁺-centers. The PL intensity at 525 nm is found to increase with increase in ion fluence up to 1×10¹² ions cm⁻² and decreases beyond this fluence. Thermoluminescence (TL) of heat-treated and swift heavy ion (SHI) irradiated aluminum oxide gives a strong and broad TL glow with peak at ∼610 K along with a weak shoulder at 500 K. The TL intensity is found to increase with Au⁹⁺ ion fluence up to 1×10¹³ ions cm⁻² and decreases beyond this fluence.     

Damage formation in Ge during Ar and He implantation at 15 K

Ar⁺ and He⁺ ions were implanted into Ge samples with (1 0 0), (1 1 0), (1 1 1) and (1 1 2) orientations at 15 K with fluences ranging from 1×10¹¹ to 1×10¹⁴ cm⁻² for the Ar⁺ ions and fluences ranging from 1×10¹² to 6×10¹⁵ cm⁻² for the He⁺ ions. The Rutherford backscattering (RBS) technique in the channelling orientation was used to study the damage built-up in situ. Implantation and RBS measurements were performed without changing the target temperature. The samples were mounted on a four axis goniometer cooled by a close cycle He cryostat. The implantations were performed with the surface being tilt 7° off the ion beam direction to prevent channelling effects. After each 300 keV Ar⁺ and 40 keV He⁺ implantation, RBS analysis was performed with 1.4 MeV He⁺ ions.For both the implantation ions, there is about no difference between the values found for the damage efficiency per ion for the four different orientations. This together with the high value (around 5 times higher than that found in Si), gives rise to the assumption of amorphous pocket formation per incident ion, i.e. direct impact amorphization, already at low implantation fluences. At higher fluences, when collision cascades overlap, there is a growth of the already amorphized regions.     

Silicon substrate temperature effects on surface roughness induced by ultrafast laser processing

We report the effect of substrate temperature (T_sub) in the range 300-900 K on the surface roughness of silicon wafer resulted from femtosecond laser ablation. The surface roughness observed at the laser fluences less then 0.3 J/cm² increases with increasing T_sub. However, the surface roughness decreases with increasing T_sub for the laser fluences between 0.5 and 1.0 J/cm². If the laser fluence is higher than 2.0 J/cm², the surface roughness is independent of T_sub. The effect of T_sub on the surface roughness can be understood in terms of the temperature dependence of optical absorption coefficient of silicon substrate, which eventually alters a mechanism underlying the fs-laser-material ablation process between optical penetration and thermal diffusion processes.     

Influence of oxygen partial pressure on the properties of pulsed laser deposited nanocrystalline zirconia thin films

ZrO₂ thin films were deposited at various oxygen partial pressures (2.0 × 10⁻⁵-3.5 × 10⁻¹ mbar) at 973 K on (1 0 0) silicon and quartz substrates by pulsed laser deposition. The influence of oxygen partial pressure on structure, surface morphology and optical properties of the films were investigated. X-ray diffraction results indicated that the films are polycrystalline containing both monoclinic and tetragonal phases. The films prepared in the oxygen partial pressures range 2.0 × 10⁻⁵-3.5 × 10⁻¹ mbar contain nanocrystals of sizes in the range 54-31 nm for tetragonal phase. The peak intensity of the tetragonal phase decreases with the increase of oxygen partial pressures. Surface morphology of the films examined by AFM shows the formation of nanostructures. The RMS surface roughness of the film prepared at 2.0 × 10⁻⁵ mbar is 1.3 nm while it is 3.2 nm at 3.5 × 10⁻¹ mbar. The optical properties of the films were investigated using UV-visible spectroscopy technique in the wavelength range of 200-800 nm. The refractive index is found to decrease from 2.26 to 1.87 as the oxygen partial pressure increases from 2.0 × 10⁻⁵ to 3.5 × 10⁻¹ mbar. The optical studies show two different absorption edges corresponding to monoclinic and tetragonal phases.     

Vacancy profiles and clustering in light-ion-implanted GaN and ZnO

We present experimental results obtained in H-implanted GaN and He- and Li-implanted ZnO. The ion energies were varied in the range 100-850 keV, and the implantation fluences in the range 5 × 10¹³ to 1 × 10¹⁸ cm⁻². In addition, conventional and flash anneals at temperatures 500-1400 °C were performed on the ZnO samples. The data obtained with a slow positron beam show that vacancy clusters are formed in as-implanted samples with fluences above 1 × 10¹⁷ cm⁻². Below this value only single vacancies are detected after implantation, but vacancy clusters can be formed and subsequently dissociated by thermal annealings.     

Ionoluminescence and photoluminescence studies of Ag ion irradiated kyanite

Ionoluminescence (IL) of kyanite single crystals bombarded with 100 MeV swift Ag⁸⁺ ions with fluences in the range 1.87-7.5×10¹¹ ions/cm² has been studied. A pair of sharp IL peaks at ∼689 and 706 nm along with broad emission in the region 710-800 nm are recorded in both crystalline and pelletized samples. Similar results are recorded in Photoluminescence (PL) of pelletized kyanite bombarded with same ions and energy with fluences in the range 1×10¹¹-5×10¹³ ions/cm² with an excitation of 442 nm laser beam. The characteristic pair of sharp emission peaks at 689 and 706 nm in both IL and PL is attributed to luminescence centers activated by Fe²⁺ and Fe³⁺ ions. The reduction in IL and PL bands intensity with increase of ion fluence might be attributed to degradation of Si-O (2ν₃) bonds, present on the surface of the sample.