Search

Grain size driven effects on electronic excitation-induced structural modifications have been investigated in nanocrystalline (NC) Nd2Zr2O7 on irradiation with 100 MeV iodine ions. Characterizations have been performed with in situ x-ray diffraction, Raman spectroscopy, and plane-view high-resolution transmission electron microscopy techniques. NC-powders of Nd2Zr2O7 were synthesized by auto gel-combustion and sintered at different temperatures to obtain different grain-sized samples. XRD analysis of the smallest grain-sized sample reveals the highest order–disorder transition (from pyrochlore to a more radiation-resistant phase; anion-deficient fluorite) rate at initial ion fluences followed by least amorphization at higher ion fluences. A strong correlation of the transformation build-up with the double ion impact model confirms the two step amorphization process in NC-Nd2Zr2O7 with the disordered anion-deficient fluorite structure as an intermediate phase. TEM result supports the formation of circular ion track consisting of randomly distributed regions (anion-deficient fluorite structure and amorphous regions), surrounded by a microstrain induced defect-rich pyrochlore superstructure. Lesser ordering at cationic sites and a relatively larger number of grain boundaries are responsible for the highest radiation tolerance exhibited by the smallest grain-sized sample. The present study reports a relatively higher radiation stability of NC-ternary pyrochlore oxide, Nd2Zr2O7, with a grain size of a few tens of nm, which establishes its application as a potential inert matrix for nuclear applications.

Crystalline Si films incorporated with Al are important for applications in microelectronics and solar cells. In this paper, we report on the morphology of crystalline Si surfaces in Al/amorphous-Si bilayer thin films under ion beam irradiation at 100 °C. Micro-Raman and transmission electron microscopy studies show that best crystallization is achieved at a fluence of 1 × 1012 ions cm−2. The contact angle of Si surfaces (after chemically etched unreacted Al), referred to as absorber surfaces, decreases with increasing ion fluence. These surfaces are hydrophobic in nature and the hydrophobicity decreases with increasing ion fluence. Fractal and multifractal analysis of atomic force microscopy images, along with system energy/unit cell and Laplace pressure calculations, supports our observations. Moreover, the calculated multiple scattering cross sections of light, along with reflectivity measurements, indicate that absorber surfaces of best crystalline films have the lowest reflectivity. The present results suggest that such surfaces having low optical reflectance and a hydrophobic nature can be used as photon absorber layers for advanced solar cell devices.

Solar-blind photodetectors are critically important for civil and military applications. Several of these applications, such as space exploration and nuclear energy infrastructure, demand the use of a photodetector under extreme environments. In this paper, we have studied the radiation hardness and device performance of amorphous and polycrystalline gallium oxide thin films against heavy ion (Ag7+) irradiation with a high energy of 100 MeV. Gallium oxide thin films show great tenacity against massive and highly energetic ions. The amorphous and polycrystalline phases undergo structural and morphological changes that initially induce degradation in the device performance. Nano-pore like structures are formed in the amorphous film, while the polycrystalline film shows the destruction of large crystallites. The responsivity of the photodetector device reduces fourfold in the amorphous phase; however, a sixfold reduction in the performance is observed in the polycrystalline phase of the gallium oxide photodetector. The degradation is attributed to the annealing of pre-existing optical defects that are otherwise responsible for the huge photoconductive gain in the detector and confirmed by photoluminescence studies. The effect of self-annealing at room temperature and annealing at moderate temperature is investigated to recover the irradiated photodetector devices. Partial recovery in the polycrystalline based photodetector and two orders of magnitude enhanced responsivity and an almost twice faster response time compared to the control photodetectors in the amorphous phase are observed. This work investigates the effect of heavy and energetic ions on the performance of gallium oxide based solar-blind photodetector and provides the guideline to use high energy irradiation as a tool for defect engineering.

Yttria stabilized zirconia pellets with different crystallite sizes were irradiated with 80 MeV Ag6+ ions at room temperature and 1000 K to understand the effect of crystallite size/material microstructure and irradiation temperature on the radiation tolerance against high energy heavy ions [where electronic energy loss (Se) dominates]. XRD and Raman spectroscopy measurements reveal that, irrespective of the irradiation temperature, the nano-crystalline samples suffered more damage when compared with the bulk-like sample. A reduction in the irradiation damage, i.e., improvement in the radiation tolerance, was observed for all the samples irradiated at 1000 K. The reduction in the damage, however, was remarkably higher for the nano-crystalline samples compared with the bulk-like sample, and hence the difference in the damage between the bulk-like and nano-crystalline samples was also significantly lower at 1000 K than that at room temperature. The irradiation damage, against Se, was thus found to be critically dependent on the interplay between the irradiation temperature and the crystallite size. These results are explained on the basis of the “in-elastic thermal spike” model by taking into consideration the combined effects of crystallite size and environmental (irradiation) temperature on the electron-phonon coupling strength and the lattice thermal conductivity and hence on the resulting thermal spike. These results, besides being crucial from the fundamental prospect of comprehending the size and temperature dependent radiation damage against Se, may also be important from the perspective of designing highly nano-crystalline materials for applications in various radiation environments.

Self-aligned ZnO nanorods (NRs) were grown on n-Si(100) substrate by RF sputtering techniques. The NRs are uniformly grown on 2-inch wafer along [0001] direction. Single-crystalline wurtzite structure of ZnO NRs was confirmed by X-ray diffraction. The average diameter, height, and density of NRs are found 48 nm, 750 nm, and 1.26 × 1010 cm−2, respectively. The current-voltages (I-V) characteristics of ZnO NRs/Si heterojunction (HJ) were studied in the temperature range of 120–300 K and it shows a rectifying behavior. Barrier height (ϕB) and ideality factor (η) were estimated from thermionic emission model and found to be highly temperature dependent in nature. Richardson constant (A*) was evaluated using Richardson plot of ln(Io/T2) versus q/kT plot by linear fitting in two temperature range 120–180 K and 210–300 K. Large deviation in Richardson constant from its theoretical value of n-Si indicates the presence of barrier inhomogeneities at HJ. Double Gaussian distribution of barrier height with thermionic...

Softening and stiffening of phonons in rutile titanium dioxide films are investigated by in situ micro-Raman studies during energetic ion irradiation. The in situ study minimized other possible mechanisms of phonon dynamics. Initial softening and broadening of Raman shift are attributed to the phonon confinement by structural defects and loss of stoichiometry. The stiffening of A1g mode is ascribed to large distortion of TiO6 octahedra under the influence of lattice strain in the (110) plane, which gives rise to lengthening of equatorial Ti-O bond and shortening of apical Ti-O bond. The shortening of apical Ti-O bond induces stiffening of A1g mode in the framework of the bond-order-length-strength correlation mechanism.

In this study, in-situ X-ray diffraction has been carried out to investigate the effect of temperature and pressure on hydrogen induced lattice parameter variation in size selected Pd-Ag and Pd-Cu alloy nanoparticles. The nanoparticles of three different mobility equivalent diameters (20, 40, and 60 nm) having a narrow size distribution were prepared by gas phase synthesis method. In the present range of temperature (350 K to 250 K) and pressure (10−4 to 100 millibars), no α (H/Pd ≤ 0.03) ↔ β (H/Pd ≥ 0.54) phase transition is observed. At temperature higher than 300 °C or pressure lower than 25 millibars, there is a large difference in the rate at which lattice constant varies as a function of pressure and temperature. Further, the lattice variation with temperature and pressure is also observed to depend upon the nanoparticle size. At lower temperature or higher pressure, size of the nanoparticle seems to be relatively less important. These results are explained on the basis of the relative dominance of physical absorption and diffusion of H in Pd alloy nanoparticles at different temperature and pressure. In the present study, absence of α ↔ β phase transition points towards the advantage of using Pd-alloy nanoparticles in applications requiring long term and repeated hydrogen cycling.

A detailed structural study involving in situ glancing angle x-ray diffraction (GAXRD) analysis carried out on Pd nanoparticle and thin film samples at hydrogen concentrations of 2%, 5%, and 10% over temperature ranging from −100 to 55 °C and hydrogen pressures ranging from 250 to 1000 mbars is reported. Variation in the lattice constant has been interpreted in terms of hydrogen content in α and β PdHx phases, and decrease in XRD peak intensity has been interpreted in terms of hydrogen induced degradation in crystalline quality and temperature induced lattice disorder. It is observed that Pd–H interaction is strongly influenced by the temperature and pressure dependences of physisorption, chemisorption, and diffusion. These results show that the increased surface area, interparticle gaps, and electronic enhancement result in enhanced Pd–H interaction in case of nanoparticles. In addition, the presence of single β phase and lower crystallinity degradation is observed in the case of Pd nanoparticles in comp...

This study is carried out to verify the role of thin film microstructure in determining the energy relaxation processes of swift heavy ions in CdS polycrystalline thin films. Two sets of CdS thin film samples, differing in their microstructures, prepared using thermal evaporation and spray pyrolysis, are irradiated with 100 MeV Ag ions using Pelletron accelerator. It is observed that the effects produced differ significantly in the two films. For the evaporated films, defect annealing dominates for lower irradiation fluences but at higher fluences the effects due to defect creation and their migration are dominant. A transformation from the metastable cubic to hexagonal phase together with the creation of a significant amount of compressive strain is seen in these films for irradiation at the highest fluence. The optical absorption of the samples shows an increase in band gap from 2.34 eV for the as grown film to 2.43 eV for the sample irradiated at the highest fluence that is further confirmed by photoluminescence (PL) studies. In contrast, the spray deposited samples undergo a significant improvement of crystalline quality for all fluences as shown by an increase in x-ray diffraction peak intensity, sharper optical absorption edge, reduction in defect PL intensity, and removal of asymmetry in the line shape of the longitudinal optical phonon on its lower wavenumber side in Raman spectra.