Ion Bombardment Research Articles

Disorder and cavity evolution in single-crystalline Ge during implantation of Sb ions monitored in-situ by spectroscopic ellipsometry

Ion implantation has been a key technology for the controlled surface modification of materials in microelectronics and generally, for tribology, biocompatibility, corrosion resistance and many more. To form shallow junctions in Ge is a challenging task. In this work the formation and accumulation of shallow damage profiles was studied by in-situ spectroscopic ellipsometry (SE) for the accurate tracking and evaluation of void and damage fractions in crystalline Ge during implantation of 200-keV Sb + ions with a total fluence up to 1016 cm−2 and an ion flux of 2.1 × 1012 cm−2s−1. The consecutive stages of damage accumulation were identified using optical multi-layer models with quantitative parameters of the thickness of modified layers as well as the volume fractions of amorphized material and voids. The effective size of damaged zones formed from ion tracks initiated by individual bombarding ions can be estimated by numerical simulation compared with the dynamics of damage profiles measured by ion beam analysis and ellipsometry. According to our observations, the formation of initial partial disorder was followed by complete amorphization and void formation occurring at the fluence of about 1 × 1015 cm−2, leading to a high volume fraction of voids and a modified layer thickness of ≈200 nm by the end of the irradiation process. This agrees with the results of numerical simulations and complementary scanning electron microscopy (SEM) measurements. In addition, we found a quasi-periodic time dependent behavior of amorphization and void formation represented by alternating accelerations and decelerations of different reorganization processes, respectively. For the understanding and prevention of adverse void formation and for controlled evolution of subsurface nanocavities or cellular surface texture the in-situ monitoring of the dynamics of structural damage accumulation by the developed SE method is essential.

Elaboration and characterization of porous ultrathin gold films grown by ion beam assisted deposition

The growth of ultrathin gold layers on a silicon substrate is performed with an unconventional ion beam assisted deposition. In this setup, evaporated gold flow and ion beam flux are perpendicular. 5 and 10 nm thick gold were deposited on tilted samples with the assistance of an argon ion beam at energies of 70 and 150 eV. We explored the evolution of surface morphology, mainly roughness and porosity, with ion bombardment for two gold thicknesses. We have also extrapolated Young’s modulus of these ultrathin layers by means of high-frequency acoustic measurements in the 90–260 MHz range. We also investigated the evolution of wettability of our structures with ion bombardment as well as their electrical and optical responses.

Surface state change influence’s theoretical approach of pressed iron on hollow cathode discharge characteristics: first results of plasma heating reproducibility for sintering purposes

In this work first results of the plasma heating process reproducibility for sintering purposes of pressed iron powder sample was investigated analyzing changes on the current-voltage characteristics of pulsed direct current (dc) Ar + H2 hollow cathode discharges sequentially carried out. For this purpose, the temperature of a sample acting as central cathode was varied by changing the switched-on time (duty cycle) of the pulse, via plasma species bombardment (ions and fast neutrals), which typically occurs in both cathode cylindrical surfaces that constitute the annular (hollow cathode) glow discharge, and measured by a thermocouple inserted in the central cathode sample holder. After two sequential plasma heating experiments, the third one practically reproduced the measured plasma parameters evidenced in the second heating, and the respective heating curves as a function of the time have led to similar current-voltage characteristics suggesting the iron sample sintering in non-isothermal way. Principles comprising plasma-surface interface and metallurgical-physical-chemical reactions, powder surface aspects, thermodynamic properties, metallurgical transformation of the pressed sample, and hollow cathode discharge properties are presented and discussed. The main points considered in the present approach are related to plasma (oxygen-affected plasma ionization, high ionization and excitation rate, and the intense light radiation of the annular glow discharge), thermodynamics (oxidation-reduction reactions, electron work function, sintering driving force, and surface energy), and powder (particle size distribution, morphology, specific surface, and iron recrystallization). To the best of the author’s knowledge, it is the first time that it is brought to the light the changes on hollow cathode discharge characteristics while an iron sample acting as the central cathode of an annular glow discharge is subjected to distinct heating steps on the temperature range of 20 to ∼1250 °C, leading it to have its sintering initiated.

Transparent Conductive Oxide Sputtering Damage on Contact Passivation in Silicon Heterojunction Solar Cells with Hydrogenated Nanocrystalline Silicon

Mitigating the adverse effect of transparent conductive oxide (TCO) sputtering on the passivation quality of the heterojunction contact is very critical for achieving high‐efficiency silicon heterojunction (SHJ) solar cells. Herein, n‐type ultra‐thin (5 nm) nanocrystalline silicon (nc‐Si:H) is utilized as a contact layer in rear‐junction SHJ solar cells. It is revealed that the TCO sputtering damage on the contact layer is caused by the ion bombardment during the sputtering process and cannot be fully recovered by low‐temperature annealing. A more severe passivation deterioration is observed for the devices with nc‐Si:H(n) having a higher microstructure factor. This result is explained by an increased ion penetration depth in the porous nc‐Si:H film. By applying denser nc‐Si:H(n) in SHJ solar cells, the front silicon film stack shows more resilience to sputter damage, yielding a remarkable cell performance on the M2‐size wafer with certificated power conversion efficiency (η) of 23.87%. The sputter damage on nc‐Si:H by TCO in SHJ solar cells is explored in depth for the first time from the perspective of silicon thin films.

Radiolysis of Cytosine at Cryogenic Temperatures by Swift Heavy Ion Bombardments

Radiolysis of Cytosine at Cryogenic Temperatures by Swift Heavy Ion Bombardments

Measuring sub-surface spatially varying thermal conductivity of silicon implanted with krypton

The thermal properties of semiconductors following exposure to ion irradiation are of great interest for the cooling of electronic devices; however, gradients in composition and structure due to irradiation often make the measurement difficult. Furthermore, the nature of spatial variations in thermal resistances due to spatially varying ion irradiation damage is not well understood. In this work, we develop an advancement in the analysis of time-domain thermoreflectance to account for spatially varying thermal conductivity in a material resulting from a spatial distribution of defects. We then use this method to measure the near-surface (≲1 μm) thermal conductivity of silicon wafers irradiated with Kr+ ions, which has an approximate Gaussian distribution centered 260 nm into the sample. Our numerical analysis presented here allows for the spatial gradient of thermal conductivity to be extracted via what is fundamentally a volumetric measurement technique. We validate our findings via transmission electron microscopy, which is able to confirm the spatial variation of the sub-surface silicon structure, and provide additional insight into the local structure resulting from the effects of ion bombardment. Thermal measurements found the ion stopping region to have a nearly 50× reduction in thermal conductivity as compared to pristine silicon, while TEM showed the region was not fully amorphized. Our results suggest this drastic reduction in silicon thermal conductivity is primarily driven by structural defects in crystalline regions along with boundary scattering between amorphous and crystalline regions, with a negligible contribution being due to implanted krypton ions themselves.

Analysis of Incorporation of Ion-Bombarded Nickel Ions with Silicon Nanocrystals for Microphotonic Devices

Nanotechnology is playing a greater role in biomedical engineering. Microphotonic technology is on another side, having faster growth with more requirements. The nanocrystals are a part of nanotechnology which uses silicon for manufacturing. These silicon nanocrystals have the optical property mostly used in microphotonic devices. Silicon nanocrystals are of biocompatibility with less toxicity. Therefore, the advancement in the silicon nanocrystal helps develop more microphotonic devices for biological purposes. One critical factor of silicon nanocrystal is the surface defects or surface imperfections. Surface passivation is the method employed for rectifying this disadvantage of silicon nanocrystal. Another major thing is that silicon nanocrystals are size dependent. So proper variation on the surface is required for yielding high performance of the nanocrystal. After characterizing the surface of the silicon nanocrystal, ion bombardment can occur. Nickel is a lustrous white chemical element which is less reactive when it is of a smaller size. So ion bombardment of nickel ion on the surface of the silicon nanocrystal can be done to improvise the performance of the microphotonic devices. Nearly there is an excess of 20 a.u. of photoluminescence intensity yielded. The relative fluorescence is also increased by 150 a.u. This research work enhanced the silicon nanocrystal using ion bombardment of nickel ion, which increased energy traps resulting in more intensities.

Sputtering of GaAs target under Bim+ cluster ions bombardment

The yield of secondary ions and neutral Ga atoms, converted into positive ions on the surface of an Ir emitter was measured during the bombardment of a GaAs target with cluster ions Bim+ (m = 1–5) in the energy range 1–10 keV. A non-additive increase in the yield of secondary ions was observed with an increase in the number of atoms in the bombarding ions. An estimated calculation of the ionization probability of gallium during sputtering has been carried out. A decrease in the ionization probability with an increase in the number of atoms in the bombarding cluster ions was found.

Structural and chemical changes in He+ bombarded polymers and related performance properties

The paper presents the effect of He+ ion irradiation of selected polymeric materials: poly(tetrafloroethylene), poly(vinyl chloride), ethylene-propylene-diene monomer rubber, nitrile-butadiene rubber, styrene-butadiene rubber, and natural rubber, on their chemical composition, physical structure, and surface topography. The modification was studied by scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and differential scanning calorimetry. Irradiation with a high-energy ion beam leads to the release of significant amounts of hydrogen from the surface layer, resulting in an increase in cross-linking that manifests itself by shrinkage of the surface layer, which in turn causes significant stresses leading to the formation of a crack pattern on the polymer surface. The development of microroughness is combined with oxidation. Shallow range of the ions makes the modified layer “anchored” in the substrate via bulk macromolecules, assuring its good durability and adhesion to elasto-plastic substrates. Changes in the surface layer were manifested by the modification of functional properties of the polymers. The hardness of the layer subjected to the ion irradiation process increases even up to 10 times. After modification with the ion beam, a significant decrease in frictional forces was also observed, even up to 5–6 times. The microscopic analysis of wear traces confirmed that the wear resistance also significantly increased. However, ion bombardment of polymeric materials caused a reduction in their mechanical strength (despite the range limited to the surface layer of the order of micrometers) and electrical resistance, which has a negative impact on the possibility of using the materials in some applications.

Effects of He-ion bombardment on the ferroelectric and dielectric properties of BaHf0.17Ti0.83O3 films

Focused helium ion bombardment provides an effective means to modify the properties of ferroelectric materials. This work systematically investigates the effect of helium ion bombardment on the structural, ferroelectric, and dielectric properties of relaxor BaHf0.17Ti0.83O3 thin films at different bombardment doses in the range of 1 × 1012 to 7 × 1015 ions/cm2. The films show more defects and slightly expanded out-of-plane lattice parameters with an increase in dose. Despite helium ion bombardment introducing more defects and structural disorder in the system, the bombardment-induced dipole polarization leads to enhanced ferroelectricity. Our findings highlight energetic helium ion bombardment as an effective way to enhance the ferroelectricity of relaxor materials.

Band gap engineering of the top layer of mica by organized defect formation

We report the narrowing of bandgap of the topmost layer of muscovite mica by low energy Ar+ ion beam induced defect formation. Variation of sputtering rate of the constituent elements of mica leads to organized defects creation. The first principle (DFT) calculation shows a bandgap of 4.63 eV for a single layer of muscovite mica, whereas the absence of specified atoms in that layer results in a reduction of bandgap to 1.3 eV. To examine the change of bandgap of a single mica layer, the top most layer of the muscovite mica is selected, and controlled atomic vacancies are created by low energy Ar+ ion sputtering at glancing angle. The bombarding ion energy and incidence angle are chosen by Monte Carlo Simulation (SRIM) to create the desired defects on the top most layer. Removal of the constituent atoms is probed by X-ray photoelectron spectroscopy and the change in bandgap is experimentally estimated by UV-Vis reflectance spectroscopy and conducting Atomic Force Microscopy (c-AFM). The experimental measurements of bandgap change are found to be consistent with the first principle calculation. The key features of bandgap alteration of the top layer of muscovite mica by ion induced sputtering are discussed.

Negative ion beam bombardment of a protic ionic liquid: Alleviating surface charging and damage and analyzing the surface of organic insulating materials

Positive ion beams are widely used in surface processing and analysis; however, serious surface charging can occur in the case of insulating materials. To address this issue, we investigate bombardment effects of ionic liquid negative ions emitted from the tip of a sharp needle wetted with the protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate. Experimental results show that the potential of an electrically floating metal target bombarded with the ionic liquid negative ions is slightly higher (about 1 V) than that of a front electrode, indicating that the target potential can be controlled by adjusting the potential of a nearby electrode. We also investigate the application of the negative ion bombardment in secondary ion mass spectrometry. Two types of insulating materials, polytetrafluoroethylene and polyethylene glycol, are analyzed. Experimental results show that the negative ion bombardment allows one to analyze organic insulating materials by adjusting sample bias potential, without charge neutralization such as electron flooding. Results obtained show that the ionic liquid negative ion beam is a useful tool for alleviating sample charging and damage because tens of negatively charged low-energy constituent atoms hit a surface locally and simultaneously. The ionic liquid negative ion bombardment is shown to have the advantages of both negative and polyatomic ion bombardment.

Molecular dynamics study on the role of Ar ions in the sputter deposition of Al thin films

Compressive stresses in sputter deposited thin films are generally assumed to be caused by forward sputtered (peened) built-in particles and entrapped working gas atoms. While the former are assumed to be predominant, the effect of the latter on interaction dynamics and thin film properties is scarcely clarified (concurrent or causative). The overlay of the ion bombardment induced processes renders an isolation of their contribution impracticable. This issue is addressed by two molecular dynamics case studies considering the sputter deposition of Al thin films in Ar working gas. First, Ar atoms are fully retained. Second, they are artificially neglected, as implanted Ar atoms are assumed to outgas anyhow and not alter the ongoing dynamics significantly. Both case studies share common particle dose impinging Al(001) surfaces. Ion energies from 3 to 300 eV and Al/Ar+ flux ratios from 0 to 1 are considered. The surface interactions are simulated by hybrid reactive molecular dynamics/force-biased Monte Carlo simulations and characterized in terms of mass density, Ar concentration, biaxial stress, shear stress, ring statistical connectivity profile, Ar gas porosity, Al vacancy density, and root-mean-squared roughness. Implanted Ar atoms are found to form subnanometer sized eventually outgassing clusters for ion energies exceeding 100 eV. They fundamentally govern a variety of surface processes (e.g., forward sputtering/peening) and surface properties (e.g., compressive stresses) in the considered operating regime.

Formation of pseudo-hexagonal pyramidal structures on (111) crystallographic surfaces of cubic PbTe crystals by ion sputtering

On the example of the PbTe compound we present the results of the study of the interplay between the crystallographic orientation of the surfaces of high reticular density and easy cleaving of the crystals of cubic symmetry and the shape of surface structures induced by prolonged ion sputtering. We found that in case of right combination of the crystallographic orientation of both the sputtering surface and the planes of high reticular density in the aggregate with easy cleaving of the crystals, the pyramidal structures of pseudo-hexagonal shape can be formed on the sputtering surface of cubic crystals. In case of PbTe these are the surfaces of (111) crystallographic orientation subject to the presence of sputter-resistant protective shields on them. When the protective shields are destroyed, the hexagonal structures are transformed into trihedral pyramids. The pseudo-hexagonal pyramidal structures are characterized by indistinct edges and terrace-shaped lateral facets, whereas the facets of the trihedral pyramids, into which they are transformed during the ion bombardment, are mirror-smooth. We prove that: (a) the maximally sharpened pseudo-hexagonal pyramids, ion-induced on PbTe (111) sputtering surfaces, are formed as a result of self-organization of the crystallographic planes of the family {0ī2}, the reticular density of which directly follows the reticular density of the plane of the sputtered surface; (b) the roughness of the lateral facets of pseudo-hexagonal pyramids, as well as the mirroring of the facets of the trihedral pyramids is due to the impact of crystallographic planes of the {100}family, which are the planes of the greatest reticular density and easiest cleaving for PbTe crystals.

24.4% industrial tunnel oxide passivated contact solar cells with ozone-gas oxidation Nano SiOx and tube PECVD prepared in-situ doped polysilicon

Ozone-gas oxidation (OGO) technology, capable of integrating into tube plasma-enhanced chemical vapor deposition (PECVD) technology, is developed to prepare the Nano SiO x layer for tunnel oxide passivated contact (TOPCon) solar cells in this work. The effects of gas flow, oxidation temperature, and annealing temperature on passivation quality are investigated. The X-ray photoelectron spectroscopy (XPS) indicates that OGO SiO x possesses a Si 4+ proportion of about 20%, higher than the nitric acid oxidized (NAOS) SiO x and plasma-assisted N 2 O oxidation (PANO) SiO x . The implied open-circuit voltage ( iV oc ) of the hydrogenated lifetime sample is promoted to more than 740 mV with the highest value of 748 mV, corresponding to a lowest single-sided saturation current density ( J 0,s ) of 3.1 fA/cm 2 . The contact resistivity extracted from the Cox-Strack method is < 9 mΩ cm 2 as the annealing temperature is more than 840 °C. Finally, we prepared the large-sized TOPCon solar cells with an average efficiency of 24.37% and a maximum efficiency of 24.41%, respectively. The above work shows that the tube PECVD technology integrated with ozone gas oxidation has the potential for the mass-production TOPCon industry. • Ozone-gas oxidation (OGO) technology is integrated into tube PECVD technology. • OGO SiO x and P-doped a-Si:H can be prepared by the same graphite-boat carrier. • OGO SiO x shows a high proportion of Si 4+ without ion bombardment. • The highest iV oc of 748 mV corresponding to the lowest J 0,s of 3.1 fA/cm 2 . • Average efficiency of 158.75 mm TOPCon cells reaches ∼24.4%.

Environmentally safe layered crystal produced from hazardous chemical elements: TlPb2BrI4, a new promising detector material

Exploring better Gamma, X-Ray and IR-Mid-R detectors, adequately sensitive to ambient temperatures and environmental conditions, is highly desirable. Therefore, following this path, we present detecting opportunities, based on data of experimental and theoretical investigation of the electronic and optical properties, photocurrent behavior at different bias voltages as well as the reflection for the He-Cd cw laser after irradiation by three different IR laser wavelengths, for recently grown TlPb2BrI4 single crystal with strong anisotropic, two-dimensional (2D) layered structure. The X-ray photoelectron spectroscopy brings data on binding energy values of core levels of TlPb2BrI4 for both as-grown and Ar+-ion-treated crystal surfaces as well as for elucidation of the energy distribution of the valence electronic states. In opposite to well-known IR-detector materials, TlPb2BrI4 crystal surface shows high chemical stability concerning Ar+-ion bombardment. Further, we carry out ab initio band-structure calculations to gain curves of total and partial densities of states and to elucidate the principal optical constants of TlPb2BrI4. The present studies indicate that, in spite of the fact that the TlPb2BrI4 crystal contains two very hazardous/toxic chemical elements, thallium and lead; however, it is chemically stable and reveals very low hygroscopic behavior when being exposed to environmental conditions.

Effects of Pre-Annealing on the Radiation Resistance of ZnO Nanorods

Ion implantation is usually used for semiconductor doping and isolation, which creates defects in semiconductors. ZnO is a promising semiconductor and has a variety of applications, such as for use in transparent electronics, optoelectronics, chemical and biological sensors, etc. In this work, ZnO nanorods were grown on Si (100) substrates by the process of chemical bath deposition and then annealed in an O2 atmosphere at 350 and 600 °C for 1 h to introduce different kinds of defects. The as-grown nanorods and the nanorods that annealed were irradiated simultaneously by 180 keV H+ ions at room temperature with a total dose of 8.0×1015 ions/cm2. The radiation effects of the H+ ions, effects of the pre-existed defects on the radiation resistance, and the related mechanisms under irradiation were investigated. The crystal and optical properties of the ZnO nanorods after H+ ion irradiation were found to depend upon the pre-existed defects in the nanorods. The existence of the appropriate concentration of oxygen interstitials in the ZnO nanorods caused them to have good radiation resistance. The thermal effects of irradiation played an important role in the property variation of nanorods. The temperature of the nanorods under 180 keV H+ ion bombardment was around 350 °C.

Comparative study regarding the sputtering yield of nanocolumnar tungsten surfaces under Ar+ irradiation

Nanostructured tungsten has been proposed as a promising option for plasma facing materials in future fusion reactors, because compared to conventional tungsten it shows advantages such as a better radiation resistance and, in particular, a retardation of tungsten-fuzz growth. Besides these aspects, the sputtering yield of nanostructured tungsten under ion bombardment is of interest, since it would affect the atomic density of tungsten emitted into the fusion plasma, which leads to radiative heat losses. In this work, we present a multiscale approach for investigating the sputtering yield of nanocolumnar tungsten surfaces under 1 keV and 2 keV ${\mathrm{Ar}}^{+}$ irradiation. Our results cover experiments and also computational simulations, which operate either on the basis of the binary collision approximation and ray tracing or use a full molecular dynamics implementation. In our studied case, both computational approaches can predict the sputtering yield of nanocolumnar tungsten surfaces very well. In comparison to flat W, we observe a much reduced dependence on the ion incidence angle, similar as reported for conventional rough surfaces in literature. However, an additional global reduction of the sputtering yield was identified, which can be attributed to geometrical redeposition effects between the separated nanocolumns. These results support the applicability of nanocolumnar tungsten as a first wall coating.

Residual stress and tribological behavior of hydrogen-free Al-DLC films prepared by HiPIMS under different bias voltages

Hydrogen-free Al-DLC films were prepared by HiPIMS technology under different bias voltages through an AlC composite target. Surface and cross-sectional morphologies, chemical composition, microphase structure and bonding state, residual stress, hardness and elastic modulus, friction coefficient and wear resistance of Al-DLC films were investigated to study the influences of substrate bias voltage. Results show that bias voltage decreased film roughness (Ra) from 3.83 nm to 1.16 nm through ion bombardment. The increase of negative bias voltage improved film disorder and altered the content of sp3 bonds. However, the existence of sp3 bonds should not be responsible for residual stress. Local distortions generated by film disorder together with the mismatch between film and substrate give rise to residual compressive stress in Al-DLC films. Film hardness is in the range of 10 GPa to 17 GPa which is affected by the content of sp3 bonds and film disorder. The lowest wear rate of Al-DLC film is 6.07 × 10−8 mm3/Nm. Besides graphitization, friction can also generate more sp3 bonds at wear interface between Al-DLC film and the counterpart ball.

Influence of ion irradiation-induced defects on phase formation and thermal stability of Ti0.27Al0.21N0.52 coatings

The influence of changes induced by ion irradiation on structure and thermal stability of metastable cubic (Ti,Al)N coatings deposited by cathodic arc evaporation is systematically investigated by correlating experiments and theory. Decreasing the nitrogen deposition pressure from 5.0 to 0.5 Pa results in an ion flux-enhancement by a factor of three and an increase of the average ion energy from 15 to 30 eV, causing the stress-free lattice parameter to expand from 4.170 to 4.206 Å, while the chemical composition of Ti0.27Al0.21N0.52 remains unchanged. The 0.9% lattice parameter increase is a consequence of formation of Frenkel pairs induced by ion bombardment, as revealed by density functional theory (DFT) simulations. The influence of the presence of Frenkel pairs on the thermal stability of metastable Ti0.27Al0.21N0.52 is investigated by scanning transmission electron microscopy, differential scanning calorimetry, atom probe tomography and in-situ synchrotron X-ray powder diffraction. It is demonstrated that the ion flux and ion energy induced formation of Frenkel pairs increases the thermal stability as the Al diffusion enabled crystallization of the wurtzite solid solution is retarded. This can be rationalized by DFT predictions since the presence of Frenkel pairs increases the activation energy for Al diffusion by up to 142%. Hence, the thermal stability enhancement is caused by a hitherto unreported mechanism - the Frenkel pair impeded Al mobility and thereby retarded formation of wurtzite solid solution.