Electronic Energy Loss Values Research Articles

Study of Ion Velocity Effect on the Band Gap of CVD-Grown Few-Layer MoS2.

The present work reports on a simple chemical vapor deposition (CVD) technique that employs alkali halide (NaCl) to synthesize high-quality few-layer MoS2 by reducing growth temperature from 850 to 650 °C, and its ion irradiation study for band gap modification. The Raman peak position difference of A1g to E12g of ≈24.5 cm-1 for the synthesized MoS2 corresponds to a few layers (<5 monolayers) of MoS2 on the substrate, as also confirmed by atomic force microscopy (AFM). The optical image shows the continuous distribution of flakes throughout the substrate and the average area of flakes ≈0.2 μm2 as confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Swift heavy-ion (SHI) irradiation at 60, 100, and 150 MeV ion energies of 1 × 1012 ions/cm2 ion fluence have been used to modify the band gap in few-layer MoS2. The ions with two different energies are chosen at two sides of the Bragg peak of energy loss curve in such a way as to have the same value of electronic energy loss (Se) but different ion energies to examine the velocity effect for the ion-induced modification. The absorbance peaks for 60 and 150 MeV irradiated samples show the same effect in the band gap modification.

Radiation stability of CBD grown nanocrystalline CdS films against ion beam irradiation for solar cell applications

Here we investigate the effect of swift heavy ion irradiation (SHII) on various properties of chemical bath deposited nanocrystalline CdS (nCdS) thin films. For this purpose, nCdS films are exposed to the varying ion fluences (1 × 1011–1 × 1014 ion/cm2) of 80 MeV O6+ ions. Glancing angle X-ray diffraction (GAXRD) and micro-Raman studies confirm almost negligible structural transformation in CdS after ion irradiation even at highest fluence i.e. 1 × 1014 ion/cm2. GAXRD, micro-Raman spectroscopy, field emission scanning electron microscopy and UV–Visible absorption spectroscopy studies suggest that the structure, shape and size of the particles as well as band gap of the nCdS films remain unaltered upon irradiation. The quality of the films and their radiation hardness is investigated by optical as well as electrical properties using photoluminescence spectroscopy and Hall measurements respectively. The films are found to be radiation resistant for 80 MeV O6+ ion irradiation as compared to other heavy radiations. The stability of various properties of nCdS films under the impact of SHII may be due to lesser or comparable value of electronic energy loss (Se) to the threshold value of Se. Radiation hardness of nCdS thin films is a good sign for fabrication of high performance, radiation stable and long lasting solar cell for extraterrestrial applications.

Electronic energy loss of protons and deuterons in multi-walled carbon nanotubes

Results of measurements of electronic energy loss for few keV protons and deuterons interacting with multi-walled carbon nanotubes are presented. Analyses of the energy loss distributions, for both type of ions, show a particular shape which is due to the cylindrical geometry of the nanotubes. These distributions can be explained in detail by a Monte Carlo simulation program that includes elastic and inelastic processes and the geometrical properties of the nanotubes. The electronic energy loss values obtained from this study are proportional to the ion velocity, but are lower than the corresponding values for amorphous carbon. This indicates that the ion-nanotube interaction is affected by the electronic and crystalline structure of the nanotubes. Comparisons with experimental values for different types of C targets and with recent theoretical calculations were also done.

Synthesis of Tin Nanoparticles by Swift Heavy Ion Irradiation of Films on Quartz Substrates

In this paper we investigate nano-particle synthesis by irradiation of 25 nm tin films deposited on quartz substrate, with 45 MeV Li3+ ions and 100 MeV O7+ ions. Ion fluences in the range 1×1011 to 1×1013 ions/cm2 are used. Morphological changes driven by ion irradiation include substantial changes in surface roughness, and narrowing of the majority particle size from several hundred nm to tens of nm is observed. The films are characterized by AFM, XRD and RBS, which provide information about the changes in surface topography, crystallinity and surface composition respectively, resulting from ion irradiation. In this system, sputtering is found to be the dominant mechanisms driving structural change, (despite the use swift heavy ions in the MeV energy range, where electronic energy loss is significant) and we have quantified the extent of material loss. The consequences of nuclear and electronic energy loss values upon irradiation by the two different ion beams are also discussed.

Properties of ion track in polystyrene irradiated with high energy 56Fe ions

Polystyrene (PS) films were irradiated with 1.157GeV 56Fe ions at room temperature to fluences of 1×1012ions/cm2 at various electronic energy loss values. Ultraviolet–visible (UV–vis) spectra were measured to investigate the optical properties of the irradiated materials. Optical constants of virgin and irradiated PS were evaluated in the UV–vis frequence range through fitting of UV–vis spectra with the multi-Lorentz model. Furthermore, effective medium theory was applied to evaluate the optical constants of materials in the ion track area. It is found that the refractive index of ion track material decreased significantly in the ultraviolet–visible range whereas its extinction coefficient increased. Gas atom release and carbon atom conglomerating are believed to be the reason. The extracted track radius and its variation with electronic energy loss values are in good agreement with earlier studies.

Amorphization of nanocrystalline monoclinic ZrO2 by swift heavy ion irradiation

Bulk ZrO(2) polymorphs generally have an extremely high amorphization tolerance upon low energy ion and swift heavy ion irradiation in which ballistic interaction and ionization radiation dominate the ion-solid interaction, respectively. However, under very high-energy irradiation by 1.33 GeV U-238, nanocrystalline (40-50 nm) monoclinic ZrO(2) can be amorphized. A computational simulation based on a thermal spike model reveals that the strong ionizing radiation from swift heavy ions with a very high electronic energy loss of 52.2 keV nm(-1) can induce transient zones with temperatures well above the ZrO(2) melting point. The extreme electronic energy loss, coupled with the high energy state of the nanostructured materials and a high thermal confinement due to the less effective heat transport within the transient hot zone, may eventually be responsible for the ionizing radiation-induced amorphization without transforming to the tetragonal polymorph. The amorphization of nanocrystalline zirconia was also confirmed by 1.69 GeV Au ion irradiation with the electronic energy loss of 40 keV nm(-1). These results suggest that highly radiation tolerant materials in bulk forms, such as ZrO(2), may be radiation sensitive with the reduced length scale down to the nano-metered regime upon irradiation above a threshold value of electronic energy loss.

Impedance studies on high energy Li 3+ irradiated PZT thin films

The ferroelectric Pb(Zr 0.48Ti 0.52)O 3 (PZT) thin films prepared by the pulsed laser deposition technique were studied for their response to high energy lithium ion irradiation through impedance spectroscopy. The Debye peaks, observed in the impedance and modulus plots of irradiated films, shifts towards higher frequencies compared to those of unirradiated films. This is equivalent to the trend observed with increase in temperature in the unirradiated films due to the dielectric relaxation. The irradiated films showed a decrease in the grain resistance compared to the unirradiated films. The activation energy of dielectric relaxation increases from 1.25 eV of unirradiated film to 1.62 eV of irradiated film. The observed modifications in the irradiated film were ascribed to the modifications in the grain structure due to the high value of electronic energy loss.

Thermal spike effect on defect evolution in NaCl irradiated with light and heavy ions at 8 and 300 K

Single crystals of NaCl were irradiated at room temperature and at 8K with energetic heavy ions (12C, 50Ti, 58Ni, 74Kr, 152Sm, 197Au, 208Pb and 238U) of 50–2600MeV providing mean electronic energy loss values from 0.7 to 19keV/nm. The creation and evolution of color centers were investigated as a function of fluence and temperature by in situ absorption spectroscopy and thermo-stimulated luminescence, complemented by thermal annealing and optical bleaching. For irradiations at 8K, primary hole centers are observed which typically annihilate at temperatures between 10 and 80K. The efficiency of color center creation at 8K strongly depends on the energy loss of the ions and is several times higher for U and Au ions than for C and Ti ions. Thermal spike estimations, taking into account the finite velocity of heat propagation, assign these effects to thermal stimulated separation of color centers in the genetic Frenkel pairs.

Neutral atom sputtering yields from Gd 3Ga 5O 12 and Y 3Fe 5O 12 garnets: Observation of a velocity effect

The effects of swift heavy ions in insulators, leading e.g. to the appearance of latent tracks, have been extensively studied. In particular, it has been shown that at a fixed value of electronic stopping power the damage cross-section in the yttrium iron garnet (Y 3Fe 5O 12) is larger for low energy ions than for high energy ions. This is the so-called “velocity effect” in the damage creation in the electronic stopping power regime. In order to verify if such a velocity effect also exists for atoms sputtering, the total sputtering yields of yttrium iron garnet (Y 3Fe 5O 12) and gadolinium gallium garnet (Gd 3Ga 5O 12) irradiated at high energy with a lead beam of 19.3 MeV/u, were measured using the catcher technique. The sputtered particles, were collected upon an aluminum foil placed in front of the target and the impurities deposited on the collectors were analysed by Rutherford backscattering. By comparison with previous measurements of the sputtering yield for the same electronic energy loss value at lower velocity, we clearly observed an important velocity effect: the sputtering yield is higher at low velocity than at high velocity.

Heavy-ion induced defects in phlogopite imaged by scanning force microscopy

A new geological dating method uses alpha-recoil tracks (ART) created by the natural α-decay of U, Th, and their daughter products. When visualizing ART by optical microscopy, the age range is restricted to the last 10 6 a. Recording of etched ART by scanning force microscopy (SFM) enables the access to track densities beyond 10 8 cm −2 and thus extends ART dating to ages >10 6 a. In the present work, natural radiation damage induced by ions was simulated by irradiating phlogopite samples, originating from Quaternary and Tertiary volcanic rocks of the Eifel (Germany) and Kerguelen Islands (Indian Ocean), with U, Ni (11.4 MeV/u), Xe, Cr, Ne (1.4 MeV/u), and Bi (200 keV) ions. Before and after irradiation and etching with HF, the phlogopite surfaces were imaged by SFM. On freshly cleaved natural phlogopite, latent ART, located near to the cleavage plane, form small hillocks. In addition, numerous similar hillocks develop in air, not related to ART since they do not transform to etch pits. Due to these hillocks, whose origin is still unknown, it is presently not possible to study latent ART with SFM. A further kind of hillock arises after irradiation with energetic heavy ions. The damage trails created by these ions are etchable, providing hexagonal etch pits in the case of U, Xe and Cr ions, whereas the pits of Ni, Ne and Bi ion tracks are triangular. The transition from triangular to hexagonal shape occurs between the electronic energy loss values 5.4 and 8.1 keV/nm for Ni and Cr ions, respectively, coinciding with a sharp increase of the track etch velocity.

Chemical modifications of polymer films induced by high energy heavy ions

Polymer films including polyethylene terephthalate (PET), polystyrene (PS) and polycarbonate (PC) were irradiated at room temperature with ions of 35 MeV/u 40Ar, 25 MeV/u 84Kr, 15.1 MeV/u 136Xe and 11.4 MeV/u 238U to fluences ranging from 9×10 9 to 5.5×10 12 ions/cm 2. The radiation-induced chemical changes of the materials were investigated by Fourier-transform infrared (FTIR) and ultraviolet/visible spectroscopies. It is found that the absorbance in the ultraviolet and visible range induced by all irradiations follows a linear relationship with fluence. The radiation-induced absorbance normalized to one particle increases slowly with increasing of electronic energy loss below about 8 keV/nm followed by a sharp increase up to about 15 keV/nm above which saturation is reached. FTIR measurements reveal that the materials suffer serious degradation through bond breaking. The absorbance of the typical infrared bands decays exponentially with increase of ion fluence and the bond-disruption cross-section shows a sigmoid variation with electronic energy loss. In PET loss of crystallinity is attributed to the configuration transformation of the ethylene glycol residue from trans into the gauche. Alkyne end groups are induced in all the materials above certain electronic energy loss threshold, which is found to be about 0.8 keV/nm for PS and 0.4 keV/nm for PC. The production cross-section of alkyne end group increases with increasing of electronic energy loss and shows saturation at high electronic energy loss values. It is concluded that not only the physical processes but also the chemical processes of the energy deposition determine the modification of polymer.

Modification of polyethylene terephthalate under high-energy heavy ion irradiation

Polyethylene terephthalate films were irradiated with high-energy heavy ions to fluences ranging from 9×10 9 to 5.5×10 12 ions/cm 2. The radiation-induced changes in molecular and crystalline structures were investigated by the Fourier-transform infrared (FTIR) spectroscopy and the X-ray diffraction measurement. FTIR spectra measurements reveal that the material suffers serious degradation through bond breaking. The absorbance of the typical infrared bands decays exponentially with increase of ion fluence and the bond-disruption cross-section shows a sigmoid variation with the electronic energy loss. The semi-crystalline structure of the material is destroyed by the irradiation with processes that are electronic energy loss dependent. At lower electronic energy loss values the amorphization is closely related to the destruction of the trans-configuration of the ethylene glycol residue. At high electronic energy loss, however, other processes determine the amorphization.

Effect of 30 Mev Li 3+ ion and 8 MeV electron irradiation on n-channel MOSFETs

The effect of 30 v MeV Li 3+ ion and 8 v MeV electron irradiation on the threshold voltage ( V TH ), the voltage shift due to interface trapped charge ( j V Nit ), the voltage shift due to oxide trapped charge ( j V Not ), the density of interface trapped charge ( j N it ), the density of oxide trapped charge ( j N ot ) and the drain saturation current ( I D v Sat ) were studied as a function of fluence. Considerable increase in j N it and j N ot , and decrease in V TH and I D v Sat were observed in both types of irradiation. The observed difference in the properties of Li 3+ ion and electron irradiated MOSFETs are interpreted on the basis of energy loss process associated with the type of radiation. The study showed that the 30 v MeV Li 3+ ion irradiation produce more damage when compared to the 8 v MeV electron irradiation because of the higher electronic energy loss value. High temperature annealing studies showed that trapped charge generated during ion and electron irradiation was annealed out at 500 v °C.