Photoinduced Modifications of the Structure and Microhardness of Fullerite C60

The wavelength dependence, temperature limits, time and depth evolution of the photoinduced hardening of C60 crystals in air have been investigated by microindentation and dislocation mobility methods. Two photopolymerized phases, which differ in the hardness and thermal stability, are found to appear. We suggest that formation of fullerene dimers (ie. C120) in pristine fullerite and growth of C120O phase in oxygenated fullerite via [2+2] photoaddition reaction is responsible for it. It has been found from depth distribution data of the hardness that the C120O phase is located in oxygen-contaminated subsurface layer of 0.8–1 μm and appears under illumination at 290–330 K.

LiF crystals irradiated with 150MeV Kr ions: Peculiarities of color center creation and thermal annealing

Abstract Color centers in LiF crystals are studied under irradiation at room temperature with 150 MeV Kr ions in the fluence (Φ) range of 1010–1014 ions/cm2 with a beam current density of 10, 50, and 100 nA/cm2, corresponding to flux of 4.46 × 109, 2.23 × 1010 and 4.46 × 1010 ions/(cm2 × s), respectively. At Φ ⩾ 3 × 1012 ions/cm2 besides F and Fn centers also charged F 3 + centers are created. Thermal annealing of irradiated LiF crystals with Φ ⩾ 1013 ions/cm2 at 400 K leads to a decrease of F centers (due to annihilation with H centers) and an enhancement of complex Fn color centers (neutral and charged) due to interaction with thermally activated anion vacancies. Annealing LiF crystals at…

Hardening and formation of dislocation structures in LiF crystals irradiated with MeV–GeV ions

Abstract Material modifications of LiF crystals irradiated with Au, Pb and Bi ions of MeV to GeV energy are studied by means of microindentation measurements and dislocation etching. Above a critical irradiation fluence of 10 9 ions/cm 2 , the microhardness can improve by a factor of 2 in the bulk and by more than 3 on the surface. Radiation-induced hardening follows the evolution of the energy loss along the ion path. Annealing experiments indicate that complex defect aggregates created in the tracks play a major role for the hardness change. Evidence for severe structural modifications is found when etching indentation impressions in highly irradiated crystals leading to similar pattern a…

Interface Diffusion Controlled Sintering of Atomically Clean Surfaces of Metals

Nanoindentation and Raman Spectroscopic Study of Graphite Irradiated with Swift238U Ions

Modifications of the structure and mechanical properties of the isotropic fine-grained graphite R6650 irradiated with 2.6 GeV 238U ions at fluences up to 1013 ions/cm2 at room temperature are studied. A strong ion-induced increase of Young's modulus and hardness is observed that points to the formation of a hard form of carbon. Raman spectra ascertain the disordering of graphite and its transformation to glassy carbon.

Atmosphere-Induced Effect in Microhardness, Dislocation Mobility and Plasticity of C60and Graphite Crystals

Abstract Formation of hard, brittle and toluene-insoluble near-surface layer (∼0.3 μm) of C60 crystals under atmospheric exposure was observed. Similar atmosphere-induced effect was found for graphite crystals and might also be expected for other molecular solids. Data on ageing kinetics of C60 and graphite crystals are presented. Variation of hardness with indentation depth can be described by the microhardness model for bilayer medium with different mechanical properties. Specific feature of C60 and graphite crystals is that no size effect appears in the intrinsic microhardness and dislocation mobility characteristics in the indentation depth range of 0.6–4μm.

Deformation behavior and interfacial sliding in carbon/copper nanocomposite films deposited by high power DC magnetron sputtering

Abstract Amorphous carbon–copper nanocomposite films with a carbon content from 7 to 40 at.% have been deposited onto steel, silicon and glass substrates using a high power (> 60 W/cm 2 ) and high-rate DC magnetron sputtering technique. XRD, Raman spectroscopy and TEM results confirm that the deposited films consist of copper nanograins (size

Formation of dislocations in LiF irradiated with 3He and 4He ions

Influence of the irradiation with 13.5 MeV 3He and 5 MeV 4He ions on the micro-structure and mechanical properties of LiF single crystals was studied. The depth profiles of nanoindentation, dislocation mobility, selective chemical etching and photoluminescence served for the characterization of damage. Strong ion-induced increase of hardness and decrease in dislocation mobility at the stage of track overlapping due to accumulation of dislocations and other extended defects was observed. At high fluences (1015 ions/cm2) the hardness saturates at about 3.5 GPa (twofold increase in comparison to a virgin crystal) thus confirming high efficiency of light projectiles in modifications of structur…

Mechanical Properties of Deformed Interfaces in Bimetallic Joints

Swift heavy ion induced modifications of luminescence and mechanical properties of polypropylene/ZnO nanocomposites

Abstract The effect of irradiation with 150 MeV Kr ions at fluencies 10 11 and 10 12  ions/cm 2 on luminescence of PP/ZnO nanocomposites and PP matrix has been studied. In unirradiated composite the luminescence is comparatively weak and is contributed mainly by the excitonic luminescence of ZnO. Irradiation of nanocomposite and PP matrix leads to a strong increase of luminescence intensity in a wide spectral range of 360–600 nm. It follows from the obtained results that the enhancement of luminescence originates mainly from the broken bonds in PP matrix. Ion-induced scission of polymer bonds and fragmentation of polymer chains is deduced also from the nanoindentation tests which show a rem…

PHOTOINDUCED HARDENING AND REDUCTION OF DISLOCATION MOBILITY IN C60SINGLE CRYSTALS: THE WAVELENGTH DEPENDENCE

An increase of the microhardness and decrease of the dislocation mobility in C60 single crystals after light-irradiation in the wavelength range of 150–900nm in air has been observed giving evidence for photo-induced change in bonding. Efficiency of C60 phototransformation was found to increase with decreasing the wavelength.

Color centers and nanodefects in LiF crystals irradiated with 150MeV Kr ions

Abstract The modifications of structure, optical and nano-mechanical properties of LiF crystals after irradiation with 150-MeV Kr +14 ions at a fluence of 6 × 10 12  ions cm −2 have been studied using optical absorption spectroscopy, scanning electron and atomic force microscopy, and nanoindentation. Optical spectroscopy shows the saturation of F centers and a comparatively high number of F n centers. AFM and SEM imaging reveals a nanostructured region with columnar nanocrystallites (size 30–90 nm). Nanostructuring occurs in depths up to 10 μm, where the ion energy loss surpasses a critical threshold of about 10 keV/nm. At a lower energy loss a zone enriched with dislocations is observed. S…

Nanoindentation response analysis of Cu-rich carbon–copper composite films deposited by PVD technique

Abstract The micromechanical properties of sputter deposited amorphous carbon–copper (a-C/Cu) composite films with different carbon content (6.8–19.8 at.%) were investigated. Atomic force and electron microscopy studies confirmed that the a-C/Cu films have a two-phase microstructure of amorphous sp 2 /sp 3 -bonded carbon as a composite matrix with embedded copper nanocrystallites encapsulated in a graphene shell. Load–displacement curves obtained in nanoindentation experiments followed Meyer's law with the exponent varying slightly within the interval 2.0–2.2 depending on the penetration depth and carbon content. The reverse indentation size effect was observed which was most likely the res…

Hardening in LiF induced by fast Ni ions and recovery of properties under annealing

The recovery of hardness and optical absorbance of LiF crystals irradiated with 640 MeV nickel ions under annealing at 450–810 K is investigated. Recovery of the hardness of irradiated crystals is initiated at temperatures above 530 K, at which a transition from a complex absorption spectrum to a spectrum with only one broad peak at 275 nm is observed. Activation energy of 0.13 eV ± 0.02 eV, which is close to that necessary for migration of H centers, is obtained from the annealing data. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Polymerization and Damage of C60 Single Crystals under Low Fluency Laser Irradiation

Photo-induced hardening, substructure formation and damage of C 60 single crystals under the 632.8 nm He-Ne laser irradiation in air at a power density of 1.47 mW/mm 2 was investigated by microhardness and AFM methods. Photo-induced formation of the dislocation substructure and crystallographically oriented crack patterns on the (111) face due to lattice contraction on polymerization were observed. Two phototransformed states: soft (400-450 MPa) and hard (650-1000 MPa) are found to appear under laser-irradiation. Hard fullerite is created in the subsurface layer < 1 μm at the saturation stage of phototransformation. It softens to 400-450 MPa at 340 K and reverts to non-polymerized state at …

Hardening and long-range stress formation in lithium fluoride induced by energetic ions

Abstract LiF crystals were irradiated with Au, Pb, Bi and S ions in the energy range 400–2300 MeV and studied by means of Vickers microindentation. Remarkable hardening effects are observed which depend on the applied fluence and ion species, and correlate with the ion energy loss along the ion path. Structural investigations reveal irradiation-induced stress extending deep into the adjacent non-irradiated crystal and leading to the formation of dislocations. X-ray diffraction measurements of the irradiated crystals show a decrease of the lattice constant indicating the presence of internal stress.

Color centers and structural damage in LiF induced by 150 MeV Kr ions

Color centers and evolution of structure defects were investigated in LiF crystals irradiated at room temperature with 150 MeV 84Kr ions with a beam current of 10nA/cm2 in the fluence range 1011 - 1014 ions/cm2 at the cyclotron accelerator DC-60 (Astana, Kazakhstan). At the fluence of 1011 ions/cm2, SEM imaging revealed mainly formation of etchable ion tracks. Above this fluence, severe structural modifications in the irradiated layer were observed which include the ion-induced formation of dislocations and grains with nano-scale dimensions. The role of fluence in the concentration of electronic color centers and structural modifications is discussed.

Depth profiles of aggregate centers and nanodefects in LiF crystals irradiated with 34 MeV 84Kr, 56 MeV 40Ar and 12 MeV 12C ions

I. Manika, J. Maniks and R. Zabels acknowledge the national project IMIS2. A. Dauletbekova, A. Akilbekov, M. Zdorovets and A. Seitbayev acknowledge the GF AP05134257of Ministry of Education and Science the Republic of Kazakhstan.

Energy loss and fluence dependency of swift‐ion‐induced hardening in LiF

The depth profiles of the hardening effects of LiF irradiated with swift Au, Pb, Bi, Kr, Ni and S ions of MeV-GeV energy have been studied as a function of ion penetration depth. For all projectiles, the hardness increases scaling with the range of ions and depending on ion fluence and energy loss. Heavy ions (Au, Pb, Bi), for which the energy loss noticeably exceeds the threshold of about 10 keV/nm for severe track core damage, cause uniform increase of hardness in the entire irradiated layer. For irradiations with lighter S, Ni, Kr ions, the hardening displays strong depth dependence. Ion-induced hardening is related to pinning of dislocations by defect aggregates (possibly small Li collo…

Formation of dislocations and hardening of LiF under high-dose irradiation with 5–21 MeV 12C ions

R. Zabels, I. Manika, J. Maniks, and R.Grants acknowledge the national project IMIS2, and A. Dauletbekova, M. Baizhumanov, and M. Zdorovets the Ministry of Education and Science of the Republic of Kazakhstan for the financial support.

Photo‐Induced Polymerization and Stress Effects in Fullerite C60

Abstract Modifications of the structure and hardness of fullerite C60 crystals under stresses generated during photo‐induced polymerization are investigated.

Modification of LiF structure by irradiation with swift heavy ions under oblique incidence

The structural modifications of LiF irradiated with swift heavy ions under oblique angles have been investigated using AFM, SEM, chemical etching, nanoindentation and optical absorption spectroscopy. LiF crystals were irradiated under incidence angles of 30 and 70 degrees with 2.2 GeV Au (fluence 57?l011 ions-cm2) and 150 MeV Kr ions (fluence 1012?1014 ions?cm?2). Structural study on sample cross-sections shows that two damage regions ? (1) nanostructured zone and (2) dislocation ? rich zone, which are typical for irradiations at normal incidence, appear also in samples irradiated under oblique angles. However in the latter case a more complex structure is formed that leads to stronger ion-…

&lt;title&gt;Effect of light exposure on dislocation mobility in fullerite C60 crystals&lt;/title&gt;

The illumination-time evolution and the wavelength dependence of the photoinduced changes in dislocation mobility on the (111) face of C60 single crystals in air for the wavelength range 150 - 900 nm and power densities 0.2 - 2 mW/cm2 has been investigated. The results show that the light exposure in air leads to the decrease of the dislocation mobility. The magnitude of the effect as a function of the illumination time was investigated and a two-stage relationship was obtained. The ultraviolet light was found to be more effective than the visible light in the photoinduced reduction of dislocation mobility and solubility. In the wavelength range of 150 - 700 nm, the reduction of dislocation…

Surface processing of TlBr single crystals used for radiation detectors

Abstract The processing method for obtaining the high-quality surfaces of TlBr single crystals, providing removal of a mechanically destroyed surface layer by chemical etching, is developed. The crystals grown from the melt of purified materials by the Bridgman–Stockbarger method were used for the experiments. The Vickers microhardness as a structure-sensitive technique was used in a study of the crystal quality and properties of the plastically deformed surface layer created by cutting. It was shown that even under highly accurate conditions of cutting, the depth of the work-hardened surface layer with a high density of dislocations, vacancies and other structural defects exceeds 20 μm. Th…

A review of colour center and nanostructure creation in LiF under heavy ion irradiation

A study of radiation damage in LiF crystals under irradiation with MeV–GeV energy ions, from 12C to 238U, at temperatures varying from 8 to 300 K, depending on the ion energy, energy loss and irradiation temperature, is presented. For light ions (12C, 14N) at low fluences, it is mainly color centers that are created. Increasing the fluence leads to the overlapping of tracks and the creation of more complex color centers, defect aggregates and dislocations. For ions with an energy loss above a threshold value (dE/dx = 10 keV nm−1) the tracks exhibit a central core damage region with a radius of 1–2 nm, surrounded by an extended halo which mainly contains single color centers. In this case, i…

Investigation of heavy ion tracks in LiF crystals by dislocation mobility method

Abstract The track damage created in LiF by swift heavy ions was studied using methods of dislocation mobility and track etching. The crystals were irradiated with Bi and Pb ions of a specific energy of 11 MeV/u at fluences between 10 7 and 10 10  cm −2 . The measurements on cross-sections cleaved parallel to the irradiated surface showed continuity of the track etching for the depth up to 70% of the ion range. In deeper layers, numerous etch pits had a flat-bottomed shape indicating the discontinuities of the track structure. At this stage, a decrease of the ion-induced effect in dislocation mobility was observed. The observed reduction of the efficiency of ion tracks as obstacles for disl…

Dislocation mobility study of heavy ion induced track damage in LiF crystals

Track damage created in LiF crystals by swift U, Kr, Xe and Ni ions with a specific energy of 11.1 MeV/u was studied using dislocation mobility measurements, track etching, SEM, AFM and optical microscopy. The results demonstrate continuity of etching of U tracks while discontinuities of etching are observed in the case of Xe ions. The relationship between the track structure and dislocation mobility in irradiated crystals is discussed. The dislocation mobility technique can serve as a highly sensitive method for track core damage studies.

Nanostructuring and strengthening of LiF crystals by swift heavy ions: AFM, XRD and nanoindentation study

Abstract Modifications of the structure and micromechanical properties of LiF crystals under high-fluence irradiation (10 11 –10 13  ions cm −2 ) with swift C, Ti, Au and U ions of the specific energy of 11.1 MeV/u have been studied. In the case of heavy ions (U, Au), the AFM and SEM results reveal the bulk nanostructure consisting of columnar grains with nano-scale dimensions (50–100 nm). For lighter C ions the structure enriched with prismatic dislocation loops has been observed. High-resolution XRD reciprocal space maps for nano-structured LiF expose a mosaic-type structure with low-angle boundaries between grains.

MeV–GeV ion induced dislocation loops in LiF crystals

Abstract Formation of prismatic dislocation loops and evolution of dislocation structure in LiF crystals irradiated with swift 238U and 36S ions of specific energy 11 MeV/u at fluences up to 1013 ions cm−2 has been investigated using chemical etching and AFM. It has been shown that prismatic dislocations are formed in the stage of track overlapping above threshold fluences Φ ≈ 109 U cm−2 and Φ ≈ 1010 S cm−2. The diameter of dislocation loops reaches 600–1000 nm for 238U ions and 200 nm for 36S ions. The dislocations created by 238U ions are arranged in rows along the direction of ion beam, whereas 36S ions create freely distributed dislocation loops each of them being oriented along the ion…

Swift-ion-induced hardening and reduction of dislocation mobility in LiF crystals

Ion-induced change in Vickers hardness and arm length of dislocation rosettes created by indentation on the (1 0 0) face of LiF crystals was studied. The irradiations were performed using swift U, Bi and Ni ions with a specific energy of 11 MeV per nucleon at fluences between 106 and 1013 ions cm−2. Remarkable effects of the ion-induced hardening and reduction of dislocation arm length were observed above the threshold fluences of about 109–1010 ions cm−2 and 106–107 ions cm−2, respectively. The products of track core damage and aggregates of single defects in the halo of overlapping tracks are responsible for the effects. The results are analysed using the Orowan's model of dislocation imp…

Effect of in Doping on the ZnO Powders Morphology and Microstructure Evolution of ZnO:In Ceramics as a Material for Scintillators

Transparent ZnO ceramics are of interest for use as material for high-efficiency fast scintillators. Doping ZnO ceramics in order to improve complex of their properties is a promising direction. In the present research, the role of indium in the ZnO nanopowders surface interactions and in the change of microstructures and photoluminescence (PL) characteristics of sintered cera-mics is considered. Undoped and 0.13 wt% In doped ZnO ceramics are obtained by hot pressing sintering. It has been found that indium leads to the transition of initially faceted ZnO particles to rounded, contributing to good sintering with formation of diffusion active grain boundaries (GBs). Unlike ZnO ceramics, ZnO:…

Atmosphere-induced change of microhardness and plasticity of C60 single crystals and polycrystalline films

Abstract The effect of air exposure and visible light illumination on the microhardness, plasticity and dislocation mobility in the C60 single crystals was investigated. Microhardness values for defined structural states of the fullerene (pristine, oxygen-intercalated, photo-oxidized) are reported. It has been shown that oxygen intercalation in the fullerene lattice during air-aging in the dark results in the suppression of dislocation mobility. However, only a slight increase in the hardness of oxygenated samples was observed. A remarkable increase in the hardness and decrease in the plasticity of the C60 crystals under illumination-assisted air exposure was noted. Photochemical transforma…

&lt;title&gt;Formation of dislocations and hardening of LiF crystals irradiated with energetic Au, Bi, Pb, and S ions&lt;/title&gt;

The irradiation of LiF crystals with Au, Pb, Bi, and S ions in the range of 400 - 2200 MeV leads to a remarkable increase of the hardness. The effect appears for Bi and Pb ions at fluences above 109 ions/cm2 and for S ions above 1010 ions/cm2. The increase of hardness follows the energy loss and is related to the formation of defects along the ion path. Defect complexes, clusters and aggregates with nanoscale dimensions serve as strong obstacles for dislocations and cause dispersion strengthening. Structural investigations reveal the generation of long-range stress in the adjacent non-irradiated part of the crystal. Close to the implantation zone, the stress exceeds the yield strength, caus…

Depth profiles of damage creation and hardening in MgO irradiated with GeV heavy ions

This work has been performed within the framework of the EUROfusion Enabling Research project: ENR-MFE19.ISSP-UL-02 “Advanced experimental and theoretical analysis of defect evolution and structural disordering in optical and dielectric materials for fusion applications”. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

&lt;title&gt;Indentation creep and stress relaxation in amorphous As-S-Se and As-S films&lt;/title&gt;

The indentation creep in as-deposited and photopolymerized As- S-Se and As-S films has been investigated. The results show pronounced relaxation of mechanical stresses in the films at room temperature. The relationship (sigma) equals B (epsilon) m between the deformation rate and the stress is observed and the values of the deformation rate sensitivity exponent m < 1 are found. The creep rate was found to be dependent on deposition conditions of layers, applied indentation load, structural state of the material and light irradiation during the creep test.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.