Low-energy Ion Beam Research Articles

Extraction and transport of low-energy Ar ion beams with a broad cross-section

Low-energy argon (Ar) ion beams were accelerated from a quiescent discharge in a custom-designed ion reservoir. Around 100 eV Ar ion beams were extracted from an ion source with different multi-cusp magnetic field configurations through a 4-cm diameter two-electrode extraction system. Langmuir probe measurements correlated the source plasma characteristics to the extracted ion beam properties that were determined using a retarding potential analyzer and a moving Faraday cup. The ion extractor configuration allowed primary electrons from the ion reservoir to seep downstream to neutralize the space-charge of the Ar ions. The broad cross-section ion beam system is designed for material synthesis and surface modification.

Production of low-energy SiCH3+ and SiC2H7+ ion beams for 3C-SiC film formation by selecting fragment ions from dimethylsilane

Fragment ions produced from dimethylsilane (DMS) in a Bernas-type ion source were investigated. Dominant fragment ions were identified to be CH3+, Si+, SiH3+, SiCH3+, and SiC2H7+. We mass-selected SiCH3+ and SiC2H7+ ions and then produced low-energy SiCH3+ and SiC2H7+ ion beams. Subsequently, these ion beams were used to irradiate Si(111) substrates at 800 °C. The energies of SiCH3+ and SiC2H7+ ions were set at 100 eV. We found that the irradiation of these ions led to the deposition of silicon carbide (3C-SiC) films on the Si substrates. For comparison, SiC film formations on Si(111) substrates were also attempted by the chemical vapor deposition (CVD) method using DMS. The X-ray photoelectron spectroscopy measurements showed that atomic ratios of C to Si (C/Si ratio) of the films obtained by the irradiation of SiCH3+ and SiC2H7+ ion beams were 1.2 and 1.2, respectively. Conversely, the C/Si ratio of the film obtained by CVD was 1.9. Raman spectroscopy showed that the film obtained by CVD included diamond-like carbon. These results suggest that the low-energy mass-selected ion beam deposition technique using DMS-derived fragment ions is practicable for the 3C-SiC deposition on Si substrates.

Physiological and molecular responses of the root system of indica–japonica intersubspecific tetraploid rice seedlings to ion beam stress

Low-energy ion beam bombardment can induce various biological effects on plants, including stimulation, damage, and mutation. However, the physiological and molecular mechanisms of the stress effects of indica–japonica intersubspecific tetraploid rice seedlings roots in response to ion implantation are not fully understood. In this work, indica–japonica intersubspecific tetraploid rice seeds were implanted with different doses of ion beam to explore the responses of their seedling roots. The investigation found that that high-dose ion implantation significantly reduced the total root length, root surface area, total root volume and root tips number, significantly increased MDA content in roots, and interfered with the expression level of IAA biosynthesis and transport related genes. Under low-dose radiation, the antioxidant enzyme activity in the roots of intersubspecific tetraploid rice increased significantly compared with the control, and remained at a high level during 5–15 days of culture, without significant change. Meanwhile, the expression of IAA biosynthesis and transportation related genes were up-regulated, and the IAA content was significantly increased, which was 20.12% higher than that of the control, which finally made the root activity significantly higher than that of the parents. The aforementioned results will be useful for further research on the physiological and molecular mechanisms of indica–japonica intersubspecific tetraploid rice seedlings roots to ion beam stress.

(Invited) Reactions on Metal Surface and Diketone Induced By Gas Cluster Ions during Atomic Layer Etching

Gas cluster ion beams (GCIB), which consists of several thousands of gaseous atoms or molecules, have been used as novel low-energy ion beams for surface processing and analysis. Since thousands of low-energy (several eV) atoms bombard a surface at the same time and the same position, the bombarded area experiences transient high-temperature and high-pressure conditions, which enhance sputtering of atoms or enhance surface reactions. In recent years, we have been investigating to apply GCIB as energetic ions for atomic layer etching. We have reported ALE of transition metals (Cu and Ni) with GCIB irradiations and diketone (acetylacetone and hexafluoroacetone). We separated each etching step as following; (1) adsorption of diketone molecules on metal oxide, (2) evacuation of residual vapor, (3) irradiation of oxygen GCIB to remove metal oxide. By using 5 keV oxygen GCIB (~ 2eV/molecules), thin layer of nickel oxide with adsorbed acetylacetone is removed. There is no physical sputtering at this energy region, which realizes self-limiting ALE process. From in-situ XPS study, Ni oxide with adsorbed diketone molecules can be removed by Ar-GCIB irradiation. It means that other oxidation method can be used to form metal oxide, and Ar-GCIB can be used for the removal steps. In this talk, we will report surface reactions between metals and diketone induced by gas cluster ion irradiations, and etching characteristics of various metals using GCIB irradiation and diketone.

Development, installation, and offline-beam testing of a chopping and deflecting system for the High Current Injector at IUAC

A chopping and deflecting system (CDS) has been designed, fabricated, and tested to provide the chopped beam with various frequencies, to the experimental facilities of the Inter-University Accelerator Centre (IUAC), New Delhi. The CDS comprises four pairs of deflecting electrodes with an ascending gap from 15 mm to 21 mm to achieve the utmost effective electric field and the highest current within the same input voltage. The design, physical structure, and slit location of CDS have been verified with various simulation codes. The 90-degree beamline of a low energy ion beam facility was extended to install and test the CDS assembly to validate its electric design. The beamline was aligned using theodolite and dimensions measurement was carried out using a coordinate measuring machine (CMM). A floating type-high voltage power supply has been developed indigenously to apply the DC voltage across the four pairs of deflecting electrodes, and the amount of deflection was measured accordingly at slit location. A beam profile digitizer was used to measure the precise beam deflection within the error of ~ 0.25 mm. The measured beam deflection matches very well with the simulated value. The measured data shows that the amount of beam deflection is independent of the charge state, energy, and mass of the charged particle beam. The various ion beams of different energy, charge state, and mass were injected into the CDS system to verify the accuracy, precision, and repeatability of the measurements. The ion beam test results extend the capability of CDS to use as an electrostatic charge state analyzer. The beam test results reveal that deflection voltage directly depends on the ratio of energy to charge state (E/q). The development, installation, and offline-beam test are discussed in the article.

Direct ion-beam deposition of Ag nanoparticles using a solid-state silver ion source

Ion beam technology has shown itself worth to be an efficient method to produce nanoparticles embedded in dielectrics for photoelectronic devices. However, direct ion-beam deposition of nanoparticles (NPs) on the surface of dielectrics is rarely reported because the conventional metal ion source runs into difficulties to generate low energy (<10 keV) ion-beams. Herein, Ag NPs are directly deposited on the surface of Si substrates using the recently developed solid electrolyte ion source (SEIS), which possesses advantages of compactness, simple working conditions, and ability of emitting ion-beam at an energy of few keV. The composition, morphology and size of the synthesized Ag NPs are studied. Precise control of the NPs size including in-plane diameter and height is achieved by a modulation of the ion implantation dose. Localized maskless deposition of metal films on semiconductor surface is also expected using the SEIS device.

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.

Nitrogen ion beam thinning of a-SiCN diaphragm for environmental cell prepared by low-energy ion beam enhanced chemical vapor deposition

An amorphous silicon carbonitride (a-SiCN) diaphragm for environmental cell transmission electron microscopy (E-TEM) was fabricated by ion-beam-induced chemical vapor deposition (LEIBICVD) with Ar+ ions accelerated by 1.5 kV and hexamethyldisilazane (HMDSN). The diaphragms were applied to a KBr substrate or a Cu grid with 100-μm-diameter holes. Then, the deposited film was irradiated by N+ ions accelerated at 1.5 kV for thinning and nitriding. Optical microscopy revealed that the diaphragm deflection decreased with increasing N+ ion dose. These films, which were observed by E-TEM, were amorphous and transparent to an electron beam accelerated to 300 kV and caused no charging. Fourier transform infrared spectra and X-ray photoelectron spectra revealed that higher N+ ion doses helped to eliminate organic compounds and hydrogen, and promoted the formation of Si–N and C–N bonds in diaphragms. A diaphragm with a 15 nm film thickness after etching by N+ ion irradiation was successfully developed that could resist a differential pressure of 0.3 MPa.

Investigating the effects of broad ion beam milling to sedimentary organic matter: Surface flattening or heat-induced aromatization and condensation?

Previous work has proposed transfer of kinetic heat energy from low-energy broad ion beam (BIB) milling causes thermal alteration of sedimentary organic matter, resulting in increases of organic matter reflectance. Whereas, other studies have suggested the organic matter reflectance increase from BIB milling is due to decreased surface roughness. To test if reflectance increases to sedimentary organic matter (vitrinite) caused by BIB milling were related to molecular aromatization and condensation, Raman and Fourier transform infrared (FTIR) spectroscopies were used to evaluate potential compositional changes in the same vitrinite locations pre- and post-BIB milling. The same locations also were examined by atomic force microscopy (AFM) to determine topographic changes caused by BIB milling (as quantified by the areal root-mean-square roughness parameter Sq). Samples consisted of four medium volatile bituminous coals. A non-aggressive BIB milling approach was used with conditions of 5 min, 4 keV, 15°incline, 360° rotation at 25 rpm and 100% focus (1.5 kV discharge; ∼100 μA). This gentle BIB milling caused vitrinite reflectance (VRo) increases of 12 to 36% of the original values determined optically before milling (average 26% increase). When molecular proxies from FTIR (A- and C-factor, branching ratio) were plotted against each other for the same vitrinite locations pre- and post-milling, mean data points for each sample generally lie within error of a 1:1 line. Likewise, mean Raman thermal proxy [full-width half maximum of G-band (G-FWHM), Raman band separation (RBS) and D1/G band intensity ratio] values were similar for pre- and post-milled locations, also plotting within error of a 1:1 line. AFM confirms the majority (24 of 36) of pre- and post-ion milled surface pairs were smoother (lower Sq values) after BIB milling. These results are interpreted to indicate VRo increase induced by the gentle BIB milling conditions used in this study is an effect of decreased diffuse reflectance due to flatter surfaces, causing more photons to reflect directly back to the detector. Little evidence was observed for molecular aromatization and condensation of vitrinite molecules following BIB milling (with the conditions used). The presence of milling-induced artifacts, including differential milling effects dependent on location and the development of self-organized patterned structures, indicate much work remains in standardization of BIB milling before its promulgation as a routine sample preparation technique for organic petrography. These results provide better understanding of anthropogenic-induced changes to geological samples caused by the now widespread adoption of BIB milling as a disruptive innovation in sample preparation.

Impact of low energy ion beams on the properties of rr-P3HT films

Two types of ions (fluorine and titanium) are implanted into films of regio-regular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT) spin-coated on glass substrates with subsequent annealing in argon atmosphere to modify their electrical properties and structure. The ion energy and fluence were within 0.2–40 keV and 1013–1015 cm−2 respectively. The dc resistance enhances after the intensive ion beam treatment while the ac impedance decreases. Ti ion implantation with 40 keV energy and 1014 cm−2 fluence induces decrease of the ac impedance by almost two orders of magnitude and appearance of the molecular hydrogen features in 1H NMR spectrum. The UV–VIS spectra of the films are blue shifted after their exposal to the ion beams, which correlates with the presence of oxygen. The ratio of the oxygen to carbon peak intensities (ξ=O1s/C1s) in the XPS spectra is proposed as a measure for the local partial disturbance of the film. EPR spectra demonstrate formation of the paramagnetic states with g factor <2, which is accompanied with the down-field shift of the NMR spectrum. The ion beams are found to have no significant etching effect as per results of the film thickness measurements and AFM images.

Synthesis of nanoclusters and quasy one-dimensional structures in glow discharge at T ≈ 2 K

The present article considers the phenomena observed in ultracold multimodal dusty plasma generated in the glow discharge cooled with superfluid helium. It was shown that intense sputtering of the clay insert due to focused beams of low energy electrons and ions produces a total flow ∼100 ng s−1 of sputtered materials at the power released in the discharge less than 0.1 W at T ⩽ 2 K. The synthesis rates for nanoclusters (∼10 ng s−1) and filaments (∼1 ng s−1) were estimated for the first time. Fast growth of quasy one-dimensional structures, the filaments with high aspect ratio, ∼100, in ultracold plasma was explained by self-assembly of polarizable materials in strongly inhomogeneous electric fields. The intense broadband emission stimulated by laser excitation of the filaments synthesized was assigned to carbon quantum dots, domains enriched with carbon. The key parameters of the nanocluster cloud were determined for the first time. The nanocluster concentration was estimated as high as 1012÷1013 nanocluster/m3. Charging of nanoclusters in plasma produced a stable uprising nanocluster flow (∼108 cluster/s) driven by external electrostatic field and observable due to laser light scattering on dust acoustic waves developed within the flow. Temporal variations of the nanocluster concentration caused changes of the interparticle distance in the dusty plasma structure composed of CeO2 particles. It was found that the particles trapped in the structure had the mean size of about 2 μm and much narrower size distribution in comparison with the very broad initial distribution.

Design of a Novel Pixelated Residual Gas Ionization Profile Monitor for the 320 kV high-voltage platform at IMPCAS

In this paper, a Pixelated Residual Gas Ionization Profile Monitor (RGIPM) has been proposed for the 320 kV High-Voltage Platform at the Institute of Modern Physics, Chinese Academy of Sciences. Beam profile monitoring in both the horizontal and vertical directions is realized in one-meter length. A compact microchannel plate (MCP) detector with an array of the Topmetal-II− pixel ASIC as the anode is proposed for the device. The spatial resolution of the detector is expected to be comparable to the intrinsic pixel size of the anode. Compensation electric and magnetic fields have been integrated into the RGIPM to minimize the influence of the measurement fields on the transportation of low energy ion beams. This paper presents the test results of a prototype of the MCP detector and the study on the electric and magnetic fields.

Ion beam modified TiO2 nanotubular bio-interface for electrochemical detection of L-tyrosine towards smart bandage application

One of the common complications diagnosed in Diabetes Mellitus (DM) patients is Diabetic Foot Ulcers (DFUs). It is a condition wherein the deep tissues located in the lower limb undergo inflammation and infection due to neurological abnormalities (neuropathy) and various degrees of vascular diseases (angiopathy). The concentration of l-tyrosine (Tyr) rises abruptly in DFUs, and therefore may be used as an indicator for early monitoring of the patient’s condition during the onset of diabetic foot disease. Herein, we report the electrochemical enzymatic detection of Tyr using low energy ion beam modified titania nanotube (TiNT) thin films with nitrogen (N+) and gold (Au−) ions. Electrochemical Impedance Spectroscopy (EIS) analysis was performed to investigate the levels of Tyr using ion beam modified TiNT thin film electrodes. The modified electrodes exhibited excellent sensor performances with Au-TiNT and N-TiNT within the Tyr concentration range of 100 fM −500 μM with limit of detection (LoD)1.76 nM and 1.25 nM respectively and response time ∼ 1 min. The results indicate that low energy ion beam modified TiNT/enzyme bio-electrodes can potentially be employed as a highly sensitive and portable sensor for real-time detection of l-tyrosine in wound fluids for the development of a smart bandage.

Activating photosensitivity in polycrystalline PbSe via in-situ oxygen ion beam induction

An in situ O+ beam method for preparing mid-infrared sensitive polycrystalline lead selenide thin films has been demonstrated. By interaction with low energy ion beam, the optical band gap of the material can be adjusted to the extent that it is more suitable for absorption and detection of mid-infrared photons. The structural properties and the Urbach energy as low as 1.1 meV both suggest a well-ordered microstructure with high crystallinity. The preliminary optoelectronic measurements suggest its mid-IR sensitivity and a comparable responsivity of 0.62 A/W at 3.0 μm. Unlike the traditional thermal diffusion, this method therefore provides a rapid material sensitization and only requires a low temperature annealing without oxygen or iodine. This method may provide a new low-cost and easy-processing approach to fabricate mid-IR photosensitive lead chalcogenides.

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.

Creating thin magnetic layers at the surface of Sb2Te3 topological insulators using a low-energy chromium ion beam

The surfaces of Sb2Te3 topological insulator crystals were implanted using a 40 keV chromium ion beam. To facilitate uniform doping, the Sb2Te3 was passivated with a thin TiO2 film before the implantation step. The resulting chemical structure was studied using atomic-resolution transmission electron microscopy. A fluence of 7 × 1015 ions/cm2 at 40 keV lead to amorphization of the Sb2Te3 surface, with chromium predominantly incorporated in the amorphous layer. Heating to 200 °C caused the amorphous region to recrystallize and led to the formation of a thin chromium-rich interfacial layer. Near-edge x-ray absorption spectroscopy indicates a uniform valence state of Cr3+ throughout, with no evidence of metallic clustering. High-temperature superparamagnetic behavior was detected up to 300 K, with an increased magnetic moment below 50 K.

Tuning optical properties of atomically heterogeneous systems created by plasma-based low-energy ion beams.

The optical properties (reflectivity, transmissivity, and absorptivity) of metallic thin films (MTFs) of copper, silver, gold, and aluminum upon irradiation by low-energy (∼0.5keV) inert gaseous argon (Ar+) ion beams are investigated using UV-VIS-NIR spectrophotometry. The optical constants (real and imaginary parts of the refractive index) of both pristine as well as irradiated MTFs are measured by employing the pseudo-Brewster angle technique. The implanted low-energy Ar+ ions modify the dielectric constant of pure MTFs, which in turn changes the refractive index and therefore alters the optical properties of MTFs. Results indicate that the reflectivity decreases, whereas the transmissivity increases with Ar+ ion fluence. Absorptivity, calculated using the energy conservation law, increases with ion fluence. The optical modification of MTFs is discussed in light of Maxwell-Garnett theory, and possible applications are outlined.

Bismuth adducted intact molecular ions [M + Bi]+ under low-energy bismuth cluster ion beams

The authors propose the use of a low-energy (sub-keV/atom) bismuth cluster ion beam for time-of-flight secondary ion mass spectrometry (TOF-SIMS). 2 keV Bi3+ at an incident angle of 65° generated bismuth-adducted secondary molecular ions [M + Bi]+, which are not observed under normal TOF-SIMS conditions. This low-energy Bi primary ion beam was used for the depth profiling of Irganox1010/Irganox1098 multilayered organic thin films. [M + Bi]+ gave a better dynamic range for both Irganox1010 and Irganox1098 layers. The results suggest that a 2 keV Bi3+ ion beam is more suitable for the depth profiling of organic thin films than a 54 keV Bi3++ ion beam of typical TOF-SIMS conditions.

Local smoothing of optical aluminum surfaces by reactive ion beam etching

Ion beam finishing techniques are commonly used for improvement of surface error topography of optical devices. Optical aluminum surfaces after manufacturing by single-point diamond turning meet the requirements for applications in the infrared spectral range. However, optics used for applications in the short-wavelength visible and ultraviolet spectral range demand improved surface qualities. To overcome the limitations mainly caused by structural and compositional inhomogeneities of aluminum alloys, a reactive ion beam machining process using oxygen and nitrogen operating gas is applied. This technology enables direct surface machining while preserving the initial roughness up to a 1-μm etching depth using low-energy ion beams. Moreover, the use of oxygen allows us to smooth the surface in the microroughness regime. Based on Monte-Carlo simulations and roughness evolution measured by atomic force microscopy, a more detailed discussion of the ion beam process is presented. Hence, a model scheme for direct smoothing of high-frequency surface features is suggested.

Physiological and Molecular Responses of the Aboveground Part of Indica–Japonica Intersubspecific Tetraploid Rice Seedlings to Ion Beam Stress

Low-energy ion beam bombardment can induce various biological effects on plants, including stimulation, damage, and mutation. However, the physiological and molecular mechanisms of the biological effects of ion implantation are not fully understood. In this article, ion beam implantation was performed on Indica–Japonica intersubspecific tetraploid rice seeds to explore the responses of their seedlings. The investigation found that the aboveground part development of rice seedlings was inhibited, radiation damage was induced, and the metabolic accumulation and expression of abscisic acid (ABA) was disturbed by implantation with large doses of the low-energy $\text{N}^{+}$ beam. The activities of the antioxidant enzymes and proline (Pro) content were also increased by low-dose ion implantation induction. The malondialdehyde (MDA) content in seedlings under ion implantation was markedly higher than those of controls, and increased with the increase of ion beam irradiation doses. Transcriptional expression analysis of selected genes revealed that partly ABA anabolism genes associated with ABA production were significantly upregulated in seedlings in response to ion implantation. The aforementioned results will be useful for further research on the physiological and molecular mechanisms of Indica–Japonica intersubspecific tetraploid rice to ion beam stress.