Low Energy Ion Beam Irradiation Research Articles

LSPR anisotropy minimization by sequential growth of Ag nanoparticles on nanoripple patterned Si surface for SERS Application

The present work describes the formation of low-aspect-ratio Ag nanoparticles (NPs) arrays by sequential deposition of Ag from different growth directions on a nanoripple-patterned Si substrate, produced by low-energy ion beam irradiation. It is observed that the growth of Ag-NPs on ripple surfaces is direction-dependent due to the asymmetric ridge of the ripple pattern. This asymmetric ridge can be utilized to tune the shape of NP from elongated to spherical and in turn, assists in minimizing the LSPR anisotropy. The Finite-Difference-Time-Domain (FDTD) simulations demonstrate that the interparticle gap, major, and minor axis combinations of a NP are crucial in minimizing anisotropic near-field interaction. NPs grown perpendicular to the ripple from either direction lead to an elongated chain of nanoparticles; however, if a proper combination of sequential growth times is chosen then the aspect ratio of NPs can be tuned from elongation to spherical ones. Interestingly, a LSPR shift of 209 nm was observed when NPs are grown for 60 min on ripple patterns from one direction only. On the other hand, it reduces to 54 nm when NPs are sequentially grown for 30 min from each of directions, perpendicular to the ripples. SERS measurements also evidence a minimized anisotropic nature in sequentially grown NP arrays; hence, the growth direction as well as optimized growth times together can be used to control the LSPR anisotropy of NP arrays which can be used to fabricate such isotropic SERS substrates.

Correlation between structural, morphological, and electrical transport properties of nano-dimensional Tellurium thin film by low energy ion beam irradiation

Tellurium (Te), an emerging semiconductor material, exhibits intriguing physical properties in low-dimensional forms. This study investigates the structural, morphological, and transport properties of low-dimensional Te thin film deposited by physical vapor deposition after 400 keV Kr2+ ion irradiation with varying fluences of 1 × 1013, 5 × 1013, and1 × 1014 ions-cm−2. The X-ray diffraction (XRD) pattern reveals the hexagonal phase of pristine Te. As ion fluence increases, intensity of the XRD peaks decreases and the full-width half maxima (FWHM) increases, indicating a reduction in crystallinity. The intensity of the Raman peak decreases upon irradiation, resulting in a red shift in the spectra of the irradiated sample. The evolution of morphology at different fluences has been examined with atomic force microscopy (AFM) measurements. The results indicate the segregation of grains and an increase in root mean square (RMS) roughness from 2.59 pm to 5.11 pm with ion fluence up to 5 × 1013 ions-cm−2. At the highest fluence, i.e., 1 × 1014 ions-cm−2, there is an agglomeration of grains, and hence a decrease in RMS roughness to 3.92 pm is observed. The DC resistivity measurement indicates the semiconducting nature of all films. Additionally, this measurement signifies the rapid decrease in activation energy at both band-to-band conduction and nearest neighbour hopping (NNH) conduction. Following irradiation, Hall measurement demonstrates a decrease in the concentration of charge carriers and an increase in resistivity due to scattering originating from grain boundaries. However, when the fluence is increased to 1 × 1014 ions-cm−2, there is a reduction in resistivity and an increase in carrier concentration with enhanced Hall mobility in comparison to pristine Te. Therefore, this study showcases that low-energy ion irradiation has a significant impact on the modification of the structure, morphology, and electrical transport properties of semiconducting Te thin film.

Cone array formation on Si surfaces by low-energy He plasma irradiation with magnetron sputtering pre-deposited Ta

Low-energy ion beam irradiation, combined with the introduction of impurities, presents a promising approach for nanopatterning silicon (Si) surfaces. In this research, we investigate the surface evolution of Si (100) surfaces irradiated by 75 eV helium (He) plasma, in the presence of tantalum (Ta), traditionally regarded as an impurity incapable of initiating pattern formation, as evidenced in prior studies. The Ta impurities are pre-deposited onto the Si surfaces using the magnetron sputtering method, which offers a more controlled and quantifiable approach compared with the conventional co-deposition route. After irradiation at 800 K, dense cone arrays are produced on the Si surface. The growth of the cones is explored for fluence spanning (1–10) × 1025 m−2. The cross-sectional scanning electron microscope images indicate that the cone lengths and base width are well characterized by t1/2 dependence. The kinetics of the cone growth follow Fick’s law, characterized by an effective diffusive mechanism with the coefficients of diffusion: D = 6.49 ± 0.83 × 10−16 m−2 s−1. Transmission electron microscope observations reveal that the cone has distinct inner and outer parts with different microstructures and a clear interface. The growth mechanism of these cones is elucidated as a composite process involving preferential sputtering, the destabilizing influence of He bubbles, and the migration of adatoms.

Defect-engineered MnO2 nanoparticles by low-energy ion beam irradiation for enhanced electrochemical energy storage applications

Defect-engineered MnO2 nanoparticles by low-energy ion beam irradiation for enhanced electrochemical energy storage applications

Effect of low-energy ion-beam irradiation on the structure and electron transport of monolayer MoS2

The presence of vacancies in two-dimensional (2D) materials, such as monolayer MoS2 (1L-MoS2), significantly affects their structural and electronic properties. In this study, 1L-MoS2 was irradiated with an Ar+ ion beam to introduce vacancies in a controlled manner. A complementary study that combines multiple evaluations was performed to verify the role of vacancies in the structural and electronic properties of MoS2. Raman spectroscopy and conductivity measurements reveal that the S vacancies, introduced into the MoS2 lattice prior to Mo vacancies at the lower dose region, cause electron-doping. The E’ lattice vibration mode was more sensitive to vacancies than the A’1 mode. According to photoluminescence studies, irradiating Ar+ at a lower dose of less than 3.8 × 1013 cm−2 does not change the band gap and only introduces mid-gap states, which is consistent with the smaller and larger influences of vacancies in carrier scattering and doping, respectively, in the electrical conductivity.

Comparative wettability study of bulk and thin film of polytetrafluoroethylene after low energy ion irradiation

A comparative wettability study was carried out on bulk polytetrafluoroethylene (PTFE) and physical vapor deposited PTFE-like thin films using low-energy Argon ion beam irradiation. Both bulk PTFE and PTFE-like thin film surfaces were irradiated with the beam energy of 300 and 800 eV for 5 min. The angle of incidence of the ion beam was varied from 0° to 70° with respect to the surface normal. Ion beam irradiation produced the tilted sharp-edged microstructures on PTFE sheets elongated in the direction of the beam. After irradiation with 800 eV at 20°, the bulk PTFE sheet became superhydrophobic, the water contact angle increased from 105° to 157°, and again decreased to 132° after irradiation at 70° Whereas nanoripple-like patterns formed on PTFE-like thin films after ion beam irradiation. The maximum wavelength of such ripples was found to be 212 nm for an 800 eV irradiated surface at an angle of 50° Beyond this angle, a clear transition from ripple to facet-like patterns was observed. The contact angles of the irradiated thin film were found to be varying from 105° to 112° up to 30° irradiation and again decreased to 83° after irradiation at 70° PTFE thin film showed strong anisotropic wettability behavior with a variation of 12° of contact angle values perpendicular to the ion beam direction, and water droplets did not roll off from the surface like in the case of bulk PTFE. X-ray photoelectron spectroscopy revealed that the bulk PTFE had C−C, and CF2 bonding on the surface, whereas PTFE thin films formed additional CF, CF‒CFn, and CF3 bonding, which was not observed in the bulk PTFE. After irradiation, additional CF-CFn and CF3 bonding in bulk PTFE were observed. However, in the case of thin films, ion irradiation causes severe chain scission, crosslinking, and defluorination of the surface.

Texturization of polycrystalline titanium surfaces after low-energy ion-beam irradiation: Impact on biocompatibility

In this study, the impact of low-energy (1 keV) Ar+ ion-beam irradiation on the morphology of polycrystalline Ti disks was investigated. Targets were prepared by cutting and mechanically polishing commercial rods. The surface topographies before and after irradiation were characterized by scanning electron microscopy (SEM) and mechanical profilometry. Irradiation was performed using a wide range of incident angles (αi) from normal to grazing geometries at a total dose of 1018 ions/cm2. SEM analysis of the irradiated Ti targets revealed clear texturing with various attainable surface morphologies depending on αi. The surface features varied from ripples within patches with fingerprint-like patterns (0 ≤ αi ≤ 60°) to oriented structures parallel to the direction of the ion beam, such as pillar/tip structures (65 ≤ αi ≤ 75°) and shallow ripples (αi ≈ 80°). This morphological selectivity could be attributed to the competitive diffusive and erosive regimes, where the lateral uniformity of the morphology was affected by the limited size of the crystal grains. Finally, the wettability and biocompatibility of the characteristic topographies were evaluated, and the results indicated improved performance of the ion-beam-textured surfaces compared to the untreated ones.

Design and simulation of a low-energy single ion irradiation system for micro/nano-biosample investigation

A low-energy single ion irradiation system is developed in its initiation in Thailand to follow one of the trends in novel ion beam technology exploitation. Single ion irradiation of materials is a highly technological development of ion beam technology. The developed single ion irradiation systems worldwide are primarily in the MeV-energy range and for single cell studies, and recently the trend has been extended to the low-energy range (< 100 keV) but focused on microelectronic applications. Based on our previous research on low-energy ion beam irradiation of biological cells and DNA, we design and simulate a low-energy single ion implantation system, aiming at eventual construction of such a novel ion beam apparatus for applications to the biological studies. In the system, the ion energy is decreased to orders < 1 keV by the existing deceleration lens, then the low-energy ion beam passes through µm slits, and finally, low-energy single ions are obtained by beam scanning with appropriate frequencies from scanner plates and detected by a single ion detection device. Conceptual design, calculation and simulation of this single ion system are presented.

Tailoring of the Distribution of SERS-Active Silver Nanoparticles by Post-Deposition Low-Energy Ion Beam Irradiation.

The possibility of controlled scalable nanostructuring of surfaces by the formation of the plasmonic nanoparticles is very important for the development of sensors, solar cells, etc. In this work, the formation of the ensembles of silver nanoparticles on silicon and glass substrates by the magnetron deposition technique and the subsequent low-energy Ar+ ion irradiation was studied. The possibility of controlling the sizes, shapes and aerial density of the nanoparticles by the variation of the deposition and irradiation parameters was systematically investigated. Scanning electron microscopy studies of the samples deposited and irradiated in different conditions allowed for analysis of the morphological features of the nanoparticles and the distribution of their sizes and allowed for determination of the optimal parameters for the formation of the plasmonic-active structures. Additionally, the plasmonic properties of the resulting nanoparticles were characterized by means of linear spectroscopy and surface-enhanced Raman spectroscopy. Hereby, in this work, we demonstrate the possibility of the fabrication of silver nanoparticles with a widely varied range of average sizes and aerial density by means of a post-deposition ion irradiation technique to form nanostructured surfaces which can be applied in sensing technologies and surface-enhanced Raman spectroscopy (SERS).

Role of mass redistribution on nanoripple formation and propagation: A molecular dynamics simulation study

Molecular dynamics (MD) is a tool suitable for investigating the formation of nanoscale patterns under low-energy ion beam irradiation. To focus on the role of impact-induced mass redistribution in ripple formation and propagation, an MD method was used in this paper to study the morphological change of a silicon surface under continuous bombardment with 30-eV argon. The atomic-scale dynamics processes of ripple formation and propagation are discussed in detail. The migration rate of surface atoms obtained as a function of an ion incidence angle by analyzing the migration of surface atoms can provide a reasonable explanation for the smooth-to-unstable mode transition of the silicon surface. The propagation of low-energy ion-induced ripples is investigated for the first time, and the ripple propagation velocities associated with four different incidence angles (40°, 50°, 60°, and 70°) are presented. The propagation velocity increases with the incidence angle, and the propagation direction is always in accordance with the incidence direction. This study can help further understand the formation and propagation mechanisms of nanoscale ripples in the experiments and provide a guide for the development and optimization of the theoretical model.

Structural changes induced in graphene oxide film by low energy ion beam irradiation

Graphene oxide consists of sp3 hybridization due to the presence of different oxygen containing functional groups on its edges and basal planes. However, its sp3/sp2 hybridization can be tuned by various methods. Ion beam irradiation can also be one of the methods to optimize sp2/sp3 hybridization for its desirable properties. In this work, graphene oxide films were irradiated with 100 keV Argon ions at different fluences varying from 1013 to 1016 ions/cm2. Synchrotron X-ray diffraction (XRD) measurements showed an increase in crystallinity at low fluence of 1013 ions/cm2. Raman spectroscopy qualitatively determines the defects induced by ion beam in graphene oxide. Also, identification of different groups and their removal at different ion fluences was done using Fourier transform infra-red spectroscopy technique.

Heavy carrier doping by hydrogen in the spin-orbit coupled Mott insulator Sr2IrO4

Highly efficient carrier doping into the spin-orbit coupled Mott insulator ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ is achieved by low-energy hydrogen ion beam irradiation at low temperature. We demonstrate that heavy doping of hydrogen into a ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ epitaxial thin film induces a large increase in conductivity by band-filling control via electron doping, which is confirmed by Hall effect measurements. The introduction of a large amount of hydrogen and its distribution along the depth direction are clarified by nuclear reaction analysis. The doped interstitial and substitutional hydrogens act as electron donors with minimum perturbation to the lattice, as evidenced by crystal structural analysis and first-principles calculations of the defect formation energy for doped hydrogen. The hydrogen-doping method offers a strategy toward realization of novel quantum phases in strongly correlated spin-orbit entangled systems.

Tuning surface wettability of molybdenum oxide nanorod mesh by low energy ion beam irradiation

In this work, we have studied low energy argon ion-induced modification of surface wetting property of molybdenum dioxide nanorod mesh. The nanorods were deposited on a conductive silicon substrate using a spin coating process. The coated thin films were irradiated at two different fluences of 5 × 1016 and 1 × 1017 ions cm−2, respectively. With increasing ion doses, the nanorods tend to bend slightly and a kinky structure is observed in a cross-geometry. While the surface of the as-deposited sample is hydrophilic, the irradiated surface alters into hydrophobic. We have analyzed the morphological and structural properties of the surface in detail to realize the initial and altered wetting properties. Furthermore, the dynamical variations in the contact angle on the molybdenum dioxide surfaces are further investigated to understand the interactions between the water droplet, the sample surface, and the atmosphere. We foresee that such altered surfaces can be helpful to fabricate corrosion-resistant devices.

Nanopatterning of Weak Links in Superconducting Oxide Interfaces.

The interface between two wide band-gap insulators, LaAlO and SrTiO (LAO/STO), hosts a quasi-two-dimensional electron gas (q2DEG), two-dimensional superconductivity, ferromagnetism, and giant Rashba spin-orbit coupling. The co-existence of two-dimensional superconductivity with gate-tunable spin-orbit coupling and multiband occupation is of particular interest for the realization of unconventional superconducting pairing. To investigate the symmetry of the superconducting order parameter, phase sensitive measurements of the Josephson effect are required. We describe an approach for the fabrication of artificial superconducting weak links at the LAO/STO interface using direct high-resolution electron beam lithography and low-energy argon ion beam irradiation. The method does not require lift-off steps or sacrificial layers. Therefore, resolution is only limited by the electron beam lithography and pattern transfer. We have realized superconducting weak links with a barrier thickness of 30–100 nm. The barrier transparency of the weak links can be controlled by the irradiation dose and further tuned by a gate voltage. Our results open up new possibilities for the realization of quantum devices in oxide interfaces.

Bacterial Envelope Damage Inflicted by Bioinspired Nanostructures Grown in a Hydrogel.

Surface-associated bacterial communities, known as biofilms, are responsible for a broad spectrum of infections in humans. Recent studies have indicated that surfaces containing nanoscale protrusions, like those in dragonfly wings, create a hostile niche for bacterial colonization and biofilm growth. This functionality has been mimicked on metals and semiconductors by creating nanopillars and other high aspect ratio nanostructures at the interface of these materials. However, bactericidal topographies have not been reported on clinically relevant hydrogels and highly compliant polymers, mostly because of the complexity of fabricating nanopatterns in hydrogels with precise control of the size that can also resist aqueous immersion. Here, we report the fabrication of bioinspired bactericidal nanostructures in bacterial cellulose (BC) hydrogels using low-energy ion beam irradiation. By challenging the currently accepted view, we show that the nanostructures grown in BC affect preferentially stiff membranes like those of the Gram-positive bacteria Bacillus subtilis in a time-dependent manner and, to a lesser extent, the more deformable and softer membrane of Escherichia coli. Moreover, the nanostructures in BC did not affect the viability of murine preosteoblasts. Using single-cell analysis, we demonstrate that indeed B. subtilis requires less force than E. coli to be penetrated by nanoprobes with dimensions comparable to those of the nanostructured BC, providing the first direct experimental evidence validating a mechanical model of membrane rupture via a tension-induced mechanism within the activation energy theory. Our findings bridge the gap between mechano-bactericidal surfaces and low-dimensional materials, including single-walled carbon nanotubes and graphene nanosheets, in which a higher bactericidal activity toward Gram-positive bacteria has been extensively reported. Our results also demonstrate the ability to confer bactericidal properties to a hydrogel by only altering its topography at the nanoscale and contribute to a better understanding of the bacterial mechanobiology, which is fundamental for the rational design bactericidal topographies.

Ion beam engineering in WO3-PEDOT: PSS hybrid nanocomposite thin films for gas sensing measurement at room temperature

This work focus upon influence of low energy ion beam irradiation on the physico-chemical, structural and optical properties of (Glass/WO3-PEDOT: PSS) hybrid thin films. The hybrid nanocomposites were synthesized by uniform dispersion of 1 wt% and 5 wt% WO3 nanoparticles in PEDOT: PSS conducting polymer solution. The hybrid films were irradiated with low energy Ar4+ (700 keV) beam at fluence 1 × 1015 ions.cm−2 and 1 × 1016 ions.cm−2 in IUAC, New Delhi, India. The particle size was determined to be 63 nm–33 nm (1 wt% hybrid film) and 62–61 nm (5 wt% hybrid film) using Scherer’s formula. The band gap for pristine and irradiated films of 1 wt% (2.34–2.18 eV) and 5 wt% (2.39–2.14 eV) were calculated from Tauc’s relation. FTIR and Raman spectroscopy analysis confirmed the formation of chemical bonds and carbonization of film at higher fluences. The change in properties of hybrid nanocomposite material by ion irradiation may be useful for sensing applications. The sensor response of pristine and irradiated hybrid composite films was studied from liquefied petroleum gas (LPG) at room temperature.

Silicone-based modified layer obtained by low-energy nitrogen ion beam as diaphragm for environmental transmission electron microscope

Amorphous silicon carbonitride (a-SiCN) films were prepared with surface-modified layers of silicone resin and silicone grease, fabricated by low-energy nitrogen ion beam irradiation, for use as diaphragms in an environmental-cell transmission electron microscope (E-TEM). Conditions used during nitrogen ion irradiation for surface modification of silicone polymers were accelerating voltages of 0.8–1.5 kV, ion current densities of 0.70–2.10 μA/cm2, and ion doses of 4.8–8.0 × 1016 ions/cm2. The modified layers, obtained by etching the unmodified layers with hexane, were evaluated by X-ray photoelectron spectroscopy (XPS). The atomic ratio of nitrogen was higher in the modified layer using silicone grease than in the modified layer using silicone resin. The best thinnest and nitriding condition on the silicone grease was obtained through nitrogen ion irradiation using is the case of an accelerating voltage of 0.8 kV, an ion current density of 0.7 μA/cm2, and an ion dose of 4.8 ions/cm2. However, the silicone-grease-based modified layer exhibited much more deflection than the silicone-resin-based modified layer. This is thought to be because the non-modified layer of silicone resin is a tougher material than silicone grease.

Precise tuning chemistry and tailoring defects of graphene oxide films by low energy ion beam irradiation

Precise tuning chemistry and tailoring nanopores of graphene oxide (GO) thin films are vital for their application for liquid and gas separation. In this work, ultra-thin GO films with thicknesses of about 150 nm were prepared and then modified by a low energy carbon ion beam with ion fluences ranging from 1 × 1015 ions·cm−2 to 1 × 1017 ions·cm−2. An ion fluence of 1 × 1016 ions·cm−2 is a threshold for the changes to the surface geometry (i.e. the chemical state and the consequent morphology) of the GO films. Moreover, X-ray photoelectron spectroscopy (XPS) reveals that oxygen loss in ion beam-induced reduction of GO films was mainly by the elimination of the unstable CO species. Raman spectroscopy indicates that a mass of defects with a mean defect distance of about 1.4 nm was generated in GO films by C+ irradiation. According to SRIM simulation, an average of 208 carbon vacancies were created in the GO film per impinging C+. These results suggest that low energy carbon ion beam irradiation is promising for simultaneously reducing and drilling nanoscale pores on GO surfaces in a controllable manner, which could be used for engineering GO-based separation membranes.

Effect of Mixed Ions and Ion Irradiation on Ionic Conductivity of Solid Polymer Electrolytes

It is a well known fact that conductivity in case of solid polymer electrolytes (SPEs) is due to hopping of ions assisted by the segmental motion of polymer chains. It is observed that the ionic conductivity in SPEs increases with increase in the concentration of ions. After certain critical concentration the conductivity starts decreasing due to the formation of ion pairs. In this work, an attempt is made to identify the concentration at which ion pair formation occurs and hence improve conductivity by incorporating two different ions (salts) in the polymer matrix. SPEs with mixed conducting species PEOxLiBryNaBr with different concentration of salts have been prepared and investigated. Also an attempt is made to modify the crystalline phase of the host polymer by low energy ion beam (Oxygen ion, O+1 with energy 100 keV) irradiation. These observations place ion irradiation as an effective tool in improving ionic conductivity in SPEs. Using X-ray diffraction spectra and the temperature dependent conductivity studies of SPEs, the effect of mixed ions and ion irradiation on the ionic conductivity of SPEs is investigated and presented.

Role of Hierarchical Protrusions in Water Repellent Superhydrophobic PTFE Surface Produced by Low Energy Ion Beam Irradiation

The surface wettability of polytetrafluoroethylene (PTFE) was investigated with low energy Ar+ ion beam irradiation varied from 300 eV to 800 eV both at normal and oblique angle of incidence (0°–70°) and at a low irradiation time of few 10 s of seconds. A remarkable change in surface wettability was observed, surface became hydrophobic to superhydrophobic just at 800 eV energy and in 30 s time. A systematic increase in the contact angle was observed with increase in beam energy and irradiation time. For a given ion energy and a threshold irradiation time, the hierarchical protrusions developed that leads to the rolling and bouncing of water droplet even on the horizontal PTFE surface. For the above energy range, the rolling speed was found to be in the range of ~19–31 mm/s. This induced wetting behaviour due to ion irradiation leads to the Cassie-Baxter state as confirmed by the calculation of sliding angle, contact angle hysteresis (CAH) and surface free energy (SE). The CAH values were found to be reduced from 18° for untreated surface (SE ~ 20 mN/m) to 2° for 800 eV, 180 s irradiated surface (SE ~ 0.35 mN/m) at normal incidence.