Study of defect evolution by TEM with in situ ion irradiation and coordinated modeling

The paper describes a novel transmission electron microscopy (TEM) experiment with in situ ion irradiation designed to improve and validate a computer model. TEM thin foils of molybdenum were irradiated in situ by 1?MeV Kr ions up to ～0.045 displacements per atom (dpa) at 80°C at three dose rates ?5?×?10^?6, 5?×?10^?5, and 5?×?10^?4?dpa/s – at the Argonne IVEM-Tandem Facility. The low-dose experiments produced visible defect structure in dislocation loops, allowing accurate, quantitative measurements of defect number density and size distribution. Weak beam dark-field plane-view images were used to obtain defect density and size distribution as functions of foil thickness, dose, and dose rate. Diffraction contrast electron tomography was performed to image defect clusters through the foil thickness and measure their depth distribution. A spatially dependent cluster dynamic model was developed explicitly to model the damage by 1?MeV Kr ion irradiation in an Mo thin foil with temporal and spatial dependence of defect distribution. The set of quantitative data of visible defects was used to improve and validate the computer model. It was shown that the thin foil thickness is an important variable in determining the defect distribution. This additional spatial dimension allowed direct comparison between the model and experiments of defect structures. The defect loss to the surfaces in an irradiated thin foil was modeled successfully. TEM with in situ ion irradiation of Mo thin foils was also explicitly designed to compare with neutron irradiation data of the identical material that will be used to validate the model developed for thin foils.     

Electrical and structural properties of the swift heavy ion irradiated Au/n-GaAs schottky barrier diodes

Abstract

Au/n-GaAs Schottky Barrier Diodes (SBDs) have been fabricated on LEC grown silicon doped (100) GaAs single crystals. The SBDs were irradiated using high energy (120 MeV) silicon ion with fluences of 1 × 10 ¹¹ and 1 × 10¹² ions/cm². Current-Voltage (I-V) characteristics of unirradiated and irradiated diodes were analyzed. The change in the reverse leakage current increases with increasing ion fluence. This is due to the irradiation induced defects at the interface and its increase with the fluence. The diodes were annealed at 573 and 673 K. to study the effect of annealing. The rectifying behavior of the irradiated (fluence of 1 × 10¹² ions/cm¹²) SBDs improves upon as the annealing temperature increases and is attributed to the in situ self-annealing during irradiation. Scanning Electron Microscopic analysis was carried out on the irradiated samples to delineate the projected range and to observe defects.     

Field ion and scanning tunnel microscopy studies of surface and bulk defects in carbon and silicon

Complex study of surface and bulk defects was performed by field ion and scanning tunnel microscopy. Specimens were irradiated by 20-to 50-keV He⁺, Ar⁺, and Bi⁺ ions at room temperature. The irradiation fluences were between 10¹⁸ and 10²⁰ ion m⁻². Calculated parameters of depletion zones and atomic displacement cascades were compared with theoretical estimates. It was shown that controlled ion bombardment of material surface is an effective tool for fabricating field-emission cathodes for vacuum microelectronics.     

Optical properties of metal nanoparticles synthesized in a polymer by ion implantation: A review

Polymer composite layers irradiated by 30-keV Ag⁺ ions with doses from 3.1×10¹⁵ to 7.5×10¹⁶ cm^?2 and an ion current of 4 µA/cm² are investigated. The composites were examined using Rutherford backscattering (RBS), transmission electron microscopy (TEM), and optical spectroscopy. As follows from electron microscopy and electron microdiffraction data, ion implantation is a promising tool for synthesizing silver nanoparticles in the surface region. The optical density spectra taken of these composites demonstrate that the silver nanoparticles exhibit unusually weak plasma resonance. The formation of silver nanoparticles in layers carbonized by ion implantation is considered. Based on the Mie theory, optical extinction spectra for silver particles in the polymer and carbon matrices are simulated and optical spectra for complex silver core-carbon sheath nanoparticles are calculated. The physics behind the experimental optical spectra of the composite is discussed.     

Comparative study on low energy ion beam modification of thermoplastic polymers

ABSTRACT

Polycarbonate (PC) and polyethylene terephthalate (PET) thermoplastic polymer films were irradiated by low energy ion beams such as 100 keV Hydrogen (H⁺) ions and 350 keV Nitrogen (N⁺) ions at varied fluence from 1?×?10¹³ ions/cm² to 5?×?10¹⁴ ions/cm². The depth profile concentration of ions was calculated using Stopping and Range of Ions in Matter (SRIM) software code. Fourier Transform Infrared (FTIR) technique shows decrement in the intensity of peaks and disappearance of peaks mainly related to carbonyl stretching at 1770?cm^?1 and C–C stretching at 1500?cm^?1. Scanning electron microscopy (SEM) of irradiated polymers showed the formation of pores. X-ray diffraction (XRD) analysis has showed decrease in the intensity indicating the decrease in crystallinity after irradiation. Mechanical studies revealed that the molecular weight and microhardness decrease with increase in ion fluence due to increase in chain scission. The contact angle increased with increase in ion fluence indicating the hydrophobic nature of polymer after irradiation. Antibiofilm activity test of irradiated films shows resistance to Salmonella typhi (S. typhi) pathogen responsible for typhoid. The study shows that Nitrogen ion induces more damage compared to Hydrogen ions and PC films get more modified than PET films.     

Field ion microscopy of ion-implanted alloys

In this review we describe research in which field ion microscopy is used for the first time for a precision investigation of the structural and phase changes that occur in the surface layers of ordered and aging alloys as a result of implantation with ions of different gases. It is established that when ordered and aging solid solutions are irradiated with gas ions with an energy of 15–40 keV and doses of 10¹³–10¹⁸ ion/cm² a structural phase transition occurs in the surface volume of the alloys. Radiationally disordered zones in the case of order-disorder transitions and ordered zones in the case of the reverse transition are detected and their dimensions are found. The atomic structure of the defects formed due to ion implantation are studied, these include radiationally disordered regions, dislocation configurations, dislocation loops and barriers, and also complexes of these defects localised in small volumes, and the segregation of atoms of one of the components. The structure of these defects in regions of single cascades of atomic displacements, their dimensions and mutual arrangement and their crystal-geometric characteristics are determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii. Fizika, No. 5, pp. 41–58, May, 1994.     

Formation of bubbles and blisters in hydrogen ion implanted polycrystalline tungsten

ABSTRACT

Tungsten (W) has been regarded as one of the most promising plasma facing materials (PFMs) in fusion reactors. The formation of bubbles and blisters during hydrogen (H) irradiation will affect the properties of W. The dependence of implantation conditions, such as fluence and energy, is therefore of great interest. In this work, polycrystalline tungsten samples were separated into two groups for study. The thick samples were implanted by 18?keV H₃⁺ ions to fluences of 1?×?10¹⁸, 1?×?10¹⁹ and 1?×?10²⁰ H⁺/cm², respectively. Another thick sample was also implanted by 80?keV H₂⁺ ions to a fluence of 2?×?10¹⁷ H⁺/cm² for comparison. Moreover, the thin samples were implanted by 18?keV H₃⁺ ions to fluences of 9.38?×?10¹⁶, 1.88?×?10¹⁷ and 5.63?×?10¹⁷ H⁺/cm², respectively. Focused ion beam (FIB) combined with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for micro-structure analysis, while time-of-flight ion mass spectrometry (ToF-SIMS) was used to characterize the H depth profile. It is indicated that bubbles and blisters could form successively with increasing H⁺ fluence. H bubbles are formed at a fluence of ～5.63?×?10¹⁷ H⁺/cm², and H blisters are formed at ～1?×?10¹⁹ H⁺/cm² for 18?keV H₃⁺ implantation. On the other hand, 80?keV H₂⁺ ions can create more trapping sites in a shallow projected range, and thus enhancing the blisters formation with a relatively lower fluence of 2?×?10^17?H⁺/cm². The crack-like microstructures beneath the blisters are also observed and prefer to form on the deep side of the implanted range.     

Simulation of high fluence fast neutron damage with heavy ion bombardment

316 stainless steel has been irradiated with 5 MeV Cu ions to a fluence of 2 × 10¹⁶ ions/cm² at 500°C. Transmission electron microscopy of this sample reveals that 6 × 10¹⁵ voids/cm² of average diameter equal to 180 Å were produced. A method for correlating the fluence of ions with equivalent neutron fluences is described. This method predicts that the Cu bombardment in this study should produce a microstructure similar to that found in steel irradiated with 2–5 × 11²² neutrons/cm². A comparison of the ion produced voids with those found after previous neutron irradiation experiments confirms this prediction.     

Formation of ordered helium pores in amorphous silicon subjected to low-energy helium ion irradiation

Thin transparent (for transmission electron microscopy, TEM) self-supported Si(001) films are irradiated on the (110) end face by low-energy (E=17 keV) He⁺ ions at doses ranging from 5×10¹⁶ to 4.5×10¹⁷ cm⁻² at room temperature. The TEM study of the irradiated Si films along the ion range shows that an a-Si layer forms in the most heavily damaged region and helium pores (bubbles) with a density of up to 3×10¹⁷ cm⁻³ and 2–5 nm in diameter nucleate and grow across the entire width of this layer. The growth of nanopores in the a-Si layer is accompanied by their linear ordering into chains oriented along the ion tracks. The absence of pores in the region that remains crystalline and has the maximal concentration of implanted helium is explained by the desorption of helium atoms from the thin film during the irradiation. After annealing at 600°C, the volume of immobile pores in the remaining a-Si layer increases owing to the capture of helium atoms from the amorphous matrix. Solid solution is shown to be the prevalent state of the helium implanted into the amorphous silicon. Linear features with a diameter close to 1 nm and density of about 10⁷ cm⁻¹ discovered in the helium-doped a-Si layer are identified as low-energy He⁺ ion tracks.     

Effect of 100 MeV O7+ ions irradiation on ethanol sensing response of nanostructures of ZnO and SnO2

Tin dioxide nanoparticles and zinc oxide nanorods were synthesized chemically and thick film gas sensors on alumina substrates were fabricated of these materials. Morphology and crystallite size of synthesized powders were investigated by TEM. The fabricated sensors were irradiated with 100 MeV O⁷⁺ ions at fluences of 1×10¹¹, 1×10¹² and 1×10¹³ ions/cm². The X-ray diffraction analysis of the samples before and after ion bombardment was performed for structural characterization. The sensing response to ethanol before and after irradiation was carried out for each fabricated sensor. Investigation revealed that irradiated SnO₂ based sensor’s response and response time increased significantly. Results show that ZnO based sensor exhibit strong resistance to damage caused by ion irradiation which might be due to defects annihilation.     

Neon gas imaging of gold in the field ion microscope

An improved field ion microscope (FIM) technique has been developed for the neon gas imaging of gold specimens. The technique produces images which are stable at best image voltage at a tip temperature (T_T) of 30 K or less. The first stage of the technique consisted of the development of an end form at 55 K in the presence of a partial pressure of air (～ 2 × 10^?8 Torr gauge pressure) and neon gas (～ 3 × 10^?5 Torr gauge pressure) followed by further field evaporation at 28 K. The second stage involved neon gas imaging of the previously developed end form in a baked FIM in a background pressure of (0.5 to 3) × 10^?9 Torr. The FIM images obtained in conjunction with the field ionization characteristic curves showed that there is a working range (in the sense defined by Southon and Brandon). A detailed study was made of artifact vacancies detected in the {203}, {321}, {315}, {421}, {671} and {731} planes, and it was found that at 28 K their concentration was < 2.5 × 10^?3 at.fr. Approximately 191,000 atomic sites were examined for artifact vacancies. The artifact vacancy concentrations measured in the present study were a factor of 13 to 60 lower than those measured earlier by Schmid and Balluffi who employed a background pressure of ～ 5 × 10^?8 Torr in their FIM. Hence, the artifact vacancy concentrations detected in gold are dependent upon the background partial pressure employed in the FIM. This latter result plus the result that the images are only stable in ultra-high vacuum (UHV) conditions indicates the need for UHV conditions for the successful imaging of gold surfaces.     

Swift heavy ion induced structural modification and photo-luminescence in CaS:Bi nanophosphors

CaS:Bi nanocrystalline powder of average grain size 35 nm was prepared by wet chemical co-precipitation method and irradiated with 100 MeV oxygen ions at fluences between 1×10¹² and 1×10¹³ ion/cm². The irradiation induced damage and modifications were studied using X-ray Diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. With the increase in ion fluences, the crystallinity of CaS was destroyed upto 25.9 % for the reflection (200) and 21.1 % for the reflection (220) and the peaks broadens at a much faster rate due to grain breaking process. Structural parameters such as grain size, strain and dislocation density have shown a significant change after ion irradiation. The effects of different dopant concentrations on PL emission intensity after irradiation were also investigated. A blue shift of the photoluminescence peak with increasing ion fluence was noticed and was also ascribed to a decrease in the CaS grain size.      

Field ion microscopy of metal-metal contacts

Tungsten-platinum and platinum-platinum mechanical contacts were investigated using field ion microscopy. A clean field evaporated field ion microscope tip served as one contact member, and a fiat outgassed platinum foil was used as the other. The experiments were conducted in-situ using an ultra-high-vacuum field ion microscope pumped to 2 × 10^?10 Torr before being backfilled to 5 × 10^?4 Torr of helium or neon for imaging. A refined contact device was employed having an ultimate applied load resolution of 5 micromg. In contrast to previous results, gross tip deformation could be avoided, while the contact area could clearly be seen against the untouched parts of the tip. It was found in most cases that the damage to the tip at the contact interface extended only 5–15 Å deep, and that this damage depth was independent of both the magnitude of the applied load and the size of the contact area. The functional variation of the contact area with the applied load was found to be in basic agreement with the Hertz theory of elastic deformation. Fundamental limitations on the minimum observable size of the contact area due to impact are discussed.     

Heavy ion irradiation-induced phase transformation in polycrystalline Dy2O3

Radiation damage effects in polycrystalline pellets of the rare earth sesquioxide Dy₂O₃ irradiated with 300?keV Kr²⁺ ions were studied by combining grazing incidence X-ray diffraction (GIXRD) with transmission electron microscopy (TEM). Radiation damage was introduced using 300?keV Kr²⁺ ions to fluences up to 1?×?10²⁰?Kr?m^?2 at cryogenic temperature. GIXRD and cross-sectional TEM observations revealed that the crystal structure of the irradiated Dy₂O₃ transformed from a cubic, so-called C-type rare earth sesquioxide structure to a monoclinic, B-type rare earth sesquioxide structure upon ion irradiation. In addition, TEM and high-resolution electron microscopy (HREM) indicated that the transformed surface Dy₂O₃ layer adopts an epitaxial orientation relationship with the substrate Dy₂O₃.     

Effect of 50 MeV Li+3 and 80 MeV C+5 ions’ beam irradiation on the optical,structural, chemical and surface topographic properties of PMMA films*

The self-standing films of polymethyl methacrylate (PMMA) were irradiated under vacuum with 50?MeV lithium (Li³⁺) and 80?MeV carbon (C⁵⁺) ions to the fluences of 3?×?10¹⁴, 1?×?10¹⁵, 1?×?10¹⁶ and 1?×?10¹⁷ ions µm^?2. The pristine and irradiated samples of PMMA films were studied by using ultraviolet–visible (UV–Vis) spectrophotometry, Fourier transform infrared, X-ray diffractrometer and atomic force microscopy. With increasing ion fluence of swift heavy ion (SHI), PMMA suffers degradation, UV–Vis spectra show a shift in the absorption band from the UV towards visible, attributing the formation of the modified system of bonds. E_g and E_a decrease with increasing ion fluence. The size of crystallite and crystallinity percentage decreases with increasing ion fluence. With SHI irradiation, the intensity of IR bands and characteristic bands of different functional groups are found to shift drastically. The change in (E_g) and (N) in carbon cluster is calculated. Shifting of the absorption band from the UV towards visible along with optical activity and as a result of irradiation, some defects are created in the polymer causing the formation of conjugated bonds and carbon clusters in the polymer, which in turn lead to the modification in optical properties that could be useful in the fabrication of optoelectronic devices, gas sensing, electromagnetic shielding and drug delivery.     

Optical and electrical properties of swift heavy ion beam-irradiated polycarbonate/polystyrene bilayer films

Polycarbonate/polystyrene bilayer films prepared by solvent-casting method were irradiated with 55 MeV carbon ion beam at different fluences ranging from 1×10¹¹ to 1×10¹³ ions cm^?2. The structural, optical, surface morphology and dielectric properties of these films were investigated by X-ray diffraction (XRD), UV–visible spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, optical microscopy and dielectric measurements. The XRD pattern shows that the percentage of crystallinity decreases while inter-chain separations increase with ion fluence. UV–visible spectroscopy shows that the energy band gap decreases and the number of carbon atoms in nanoclusters increase with the increase in ion fluences. The refractive index is also found to decrease with the increase in the ion fluence. Optical microscopy shows that after irradiation polymeric bilayer films color changes with ion fluences. The FTIR spectra evidenced a very small change in cross-linking and chain scissoring at high fluence. Dielectric constant decreases while dielectric loss and AC conductivity increase with ion fluences.     

Spectroscopic studies of copper and carbon ion irradiated polypropylene

The samples of polypropylene (PP) have been irradiated with 120 MeV ⁶⁴Cu⁹⁺ and 70 MeV ¹²C⁵⁺ ion beams, with the fluence ranging from 1 × 10¹³ to 1 × 10¹¹ ions/-cm⁻². UV-VIS and FTIR techniques have been used to study the chemical and optical properties of these irradiated polymers. UV spectra revealed that the optical-gap energy decreases by 54 % with copper ion irradiation at the fluence of 1 × 10¹³ ions/cm², whereas at the same fluence, carbon beam decreases the optical-gap energy by 20%. FTIR analysis of ion irradiated samples revealed the presence of -OH, C = O and C = C bonds. Alkyne formation has been observed only in the case of copper ion irradiation.      

Swift heavy ion provoked structural, optical and electrical properties in SnO2 thin films

SnO₂ thin films grown on glass substrates at 300 ^°C by reactive thermal evaporation and annealed at 600 ^°C were irradiated by 120 MeV Ag⁹⁺ ions. Though irradiation is known to induce lattice disorder and suppression of crystallinity, we observe grain growth at a certain fluence of irradiation. X-ray diffraction (XRD) revealed the crystalline nature of the films. The particle size estimated by Scherrer’s formula for the irradiated films was in the range 10–25 nm. The crystallite size increases with increase in fluence up to 1×10¹² ions?cm^?2, whereas after that the size starts decreasing. Atomic force microscope (AFM) results showed the surface modification of nanostructures for films irradiated with fluences of 1×10¹¹ ions?cm^?2 to 1×10¹³ ions?cm^?2. The UV–visible spectrum showed the band gap of the irradiated films in the range of 3.56 eV–3.95 eV. The resistivity decreases with fluence up to 5×10¹² ions?cm^?2 and starts increasing after that. Rutherford Backscattering (RBS) reveals the composition of the films and sputtering of ions due to irradiation at higher fluence.     

Studies of some physical properties of PrFe0.7Ni0.3O3 thin films after 200 MeV Ag15+ irradiation

PrFe_0.7Ni_0.3O₃ thin films (thickness ~ 200 nm) were prepared by pulsed laser ablation technique on LaAlO₃ substrate. These films were irradiated with 200?MeV Ag¹⁵⁺ ions at various fluencies, ranging from 1 × 10¹¹ to 1 × 10¹² ions/cm². These irradiated thin films were characterized by using X-ray diffraction, dc conductivity, dc magnetization and atomic force microscopy. These films exhibit orthorhombic structure and retain it even after irradiations. The crystallite size (110–137?nm), micro strain (1.48 × 10^?2–1.75 × 10^?2 line^?2?m^?4) and dislocation density (79.7 × 10¹⁴–53.2 × 10¹⁴ line/m²) vary with ion fluencies. An enhancement in resistivity at certain fluence and then a decrease in its value (0.22175–0.21813?Ω?cm) are seen. A drastic change in observed magnetism after ion irradiation is seen. With ion irradiation, an increase in surface roughness, due to the formation of hillocks and other factors, is observed. Destruction of magnetic domains after irradiation can also be visualized with magnetic force microscopy and is in close agreement with magnetization data. The impact on various physical properties in these thin films after irradiation indicates a distortion in the lattice structure and consequently on single-particle band width caused by stress-induced defects.     

Superior tolerance of Ag/Ni multilayers against Kr ion irradiation: an in situ study

Monolithic Ag and Ni films and Ag/Ni multilayers with individual layer thickness of 5 and 50?nm were subjected to in situ Kr ion irradiation at room temperature to 1 displacement-per-atom (a fluence of 2?×?10¹⁴?ions/cm²). Monolithic Ag has high density of small loops (4?nm in diameter), whereas Ni has fewer but much greater loops (exceeding 20?nm). In comparison, dislocation loops, ～4?nm in diameter, were the major defects in the irradiated Ag/Ni 50?nm film, while the loops were barely observed in the Ag/Ni 5?nm film. At 0.2?dpa (0.4?×?10¹⁴?ions/cm), defect density in both monolithic Ag and Ni saturated at 1.6 and 0.2?×?10²³/m³, compared with 0.8?×?10²³/m³ in Ag/Ni 50?nm multilayer at a saturation fluence of ～1?dpa (2?×?10¹⁴?ions/cm²). Direct observations of frequent loop absorption by layer interfaces suggest that these interfaces are efficient defect sinks. Ag/Ni 5?nm multilayer showed a superior morphological stability against radiation compared to Ag/Ni 50?nm film.