Low-energy Electron Irradiation Research Articles

Probing low-energy electron induced DNA damage using single photon ionization mass spectrometry

Single photon ionization mass spectrometry (SPI MS) followed by gel electrophoresis was developed for investigation of low-energy electron (LEE) induced DNA damage. This method detects neutral species generated from DNA molecules during LEE irradiation. The neutral yields are then correlated with single strand breaks (SSBs) and double strand breaks (DSBs) as a function of incident electron energy. Specifically, fragments with masses of m/z=27, 68 and 69 show resonance structure between 6–12 and 15–25eV which is similar to that observed in the SSB and DSB probabilities. These fragments are likely associated with sugar damage and dissociative electron attachment (DEA) channels. Other fragments with masses of m/z=45, 56, 67 and 70 show a monotonic increase at threshold energies around 10–12eV, indicating the possible role of direct dissociative excitation or ionization. Resonance structure above the 10–12eV threshold for fragments with masses of m/z=43, 44, 67 and 70 are also observed and can be associated with compound states in the continuum and core-excited excitations. The results support the contention that DEA resonances localized on DNA sub-units can lead to damage, especially at energies below the ionization threshold. Damage also occurs due to direct dissociative excitation and dissociative ionization.

A study on the electric properties of single-junction GaAs solar cells under the combined radiation of low-energy protons and electrons

Displacement damage induced by charged particle radiation is the main cause of degradation of orbital-service solar cells, while the radiation-induced ionization shows no permanent damage effect on their electrical properties. It is reported that in single crystal silicon solar cells, low-energy electron radiation does not exert permanent degradation of their properties, but the fluence of electron radiation exerts an influence on the damage magnitude under the combined radiation of protons and electrons. The electrical properties of the single-junction GaAs/Ge solar cells were investigated after irradiation by sequential and synchronous electron and proton beams. Low-energy electron radiation showed no effects on the change of the solar cell properties during sequential or synchronous irradiation, implying ionization during particle radiation could not exert influence on the displacement damage process to the solar cells under the experimental conditions.

Interface Engineering and Direct Bonding of Lithium Tantalate Crystals

A method for modifying the surface free energy of lithium tantalate (LT) ferroelectric crystals is reported. Ultraviolet illumination and low-energy electron irradiation have been used for tuning the surface free energy (wettability) resulting in a wide range of contact angles (6 deg to 87 deg). The ultraviolet (UV) illumination makes the LT crystal surface superhydrophilic while the low-energy electron irradiation decreases the surface wetting. Fabrication of various wetting configurations allows demonstration of high-quality direct bonding of LT plates with hydrophilic polar faces.

Threshold Energy of Low-Energy Irradiation Damage in Single-Walled Carbon Nanotubes

Low-energy electron and photon irradiation cause damage in single-walled carbon nanotubes. In this work, irradiation effects of photons (hν<20 eV) in an ultra-high vacuum were systematically studied. The threshold energy of the low-energy irradiation damage was evaluated to be about 6 eV. Less damage was observed at 8 eV, which seems to be due to a small optical absorption coefficient at that energy.

Electron beam induced orientation selective epitaxial growth of CeO2(100) layers on Si(100) substrates by dc reactive sputtering

From studies on the epitaxial growth of CeO2 layers on Si(100) substrates using reactive dc magnetron sputtering, it has been found that the epitaxial CeO2 layer with (100) or (110) orientation is selectively grown by controlling substrate bias and the growth rate. In order to develop this technology into two dimensional orientation selectivity, we attempt to grow CeO2(100) by low energy electron irradiation, as an alternative way to substrate bias application. It proved that electron beams in two energy regions of 30 ~ 40 and 80 ~ 100 eV are effective on preferential growth of CeO2(100) layers. Interfacial structures of CeO2(100)/Si(100) are studied using cross-sectional transmission electron microscopy.

Interface modification and bonding of lithium tantalate crystals

Intermolecular interactions defined by surface free energy of solids are a critical factor affecting adhesion and bonding of the materials. An experimental technique for surface free energy and related properties (wettability and adhesion) modification has been developed and applied to lithium tantalate ferroelectric crystals. The method is based on combination of ultraviolet illumination and low-energy electron irradiation. These two techniques provide controllable wettability tailoring in a wide range of contact angles of 6°–87°. Fabrication of various wetting configurations of contacted and bonded lithium tantalate (LT) pair plates, such as hydrophilic/hydrophilic, hydrophilic/hydrophobic, and hydrophobic/hydrophobic, allows us to demonstrate direct bonding for modified hydrophilic polar LT faces.

Mass spectrometry investigation of the degradation of polyethylene terephtalate induced by low-energy (

Polyethylene terephtalate (PET) thin films were damaged by low-energy (0–100 eV) electron irradiation to simulate the degradation of this polymer in electronic devices. The products formed were analyzed by mass spectrometry. The emission of anions from the polymer surface is associated with dissociative electron attachment (DEA) and dipolar dissociation (DD) for H −, and with DD for O −. The monotonic emission rise in O − desorption as a function of incident electron energy is produced by mid-chain C–O–C cleavage, leading to chain scission. The signal of the positive mass fragments showed only a monotonic increase with electron energy. In this case, chemical recombination with hydrogen atoms also leads to chain scission.

Modification of Alkaneselenolate Monolayers by Low-Energy Electrons

The effect of low-energy (50 eV) electron irradiation on alkaneselenolate (AS) self-assembled monolayers (SAMs) was studied by synchrotron-based X-ray photoelectron spectroscopy and near-edge X-ray...

Deep Levels in Electron-Irradiated n- and p-type 4H-SiC Investigated by Deep Level Transient Spectroscopy

The authors have investigated deep levels in electron-irradiated n- and p-type 4H-SiC epilayers by deep level transient spectroscopy (DLTS). By low-energy electron irradiation at 116 keV, the Z1/2 and EH6/7 concentrations are increased in n-type samples, and the concentrations are almost unchanged after annealing at 950°C for 30 min. In p-type samples, the unknown centers, namely EP1 and EP2, are introduced by irradiation. By annealing at 950°C, the unknown centers are annealed out. The HK4 center (EV + 1.44 eV) is increased by the electron irradiation and subsequent annealing at 950°C. The dependence of increase in the trap concentrations by irradiation (NT) on the electron fluence reveals that NT for the Z1/2 and EH6/7 centers is in proportional to the 0.7 power of electron fluence, while the slope of the plot is 0.5 for the HK4 center. The Z1/2 and EH6/7 centers show similar annealing stage and are thermally stable up to 1500-1600°C, while the HK4 center is annealed out at about 1350°C. The Z1/2 and EH6/7 centers may be derived from a same origin (single carbon vacancy: VC) but different charge state. The HK4 center may be a complex including VC.

Electron-induced surface modification of hydroxyapatite-coated implant

Here, the authors report on surface free energy modulation of a hydroxyapatite-coated titanium femoral implant that is performed by a newly-developed method using a low-energy electron irradiation. They observe pronounced increase of hydrophobicity of irradiated samples that occurs in several stages and is characterized by various mechanisms. Bacterial adhesion on electron modified hydroxyapatite samples is studied, by considering different approaches. The authors show that bacterial adherence is selective and depends on the surface free energy components, which were determined from detailed surface free energy analysis. The selective bacterial adhesion, together with the ability to define the surface energy properties, suggests that this newly-developed method opens an avenue for protection of implants from bacterial infections.

Toward the In Situ Remediation of Carbon Deposition on Ru-Capped Multilayer Mirrors Intended for EUV Lithography: Exploiting the Electron-Induced Chemistry

The realization of next-generation extreme ultraviolet (EUV) lithography depends on the application of Ru-capped multilayer mirrors. Under EUV irradiation, carbon deposition due to the presence of hydrocarbons in the vacuum environment rapidly degrades mirror reflectivity, thus preventing implementation of this technology. We show that in the presence of low-energy electron irradiation, which corresponds to the photoelectron energy distribution encountered in practice, very low pressures (∼10-5 mbar) of NO or O2 are effective for oxidative removal of carbon from contaminated ruthenium surfaces at ambient temperature. This procedure leads to the net accumulation of oxygen on and beneath the metal surface. Subsequent exposure of the resulting Ru surface to CO under electron irradiation leads to efficient removal of this oxygen, again at ambient temperature. Carbon removal rates on the order of ∼4.5 × 10-5 nm s-1 are achievable, showing that sequential (or simultaneous) application of electron-induced oxidation and reduction reactions provides a viable strategy for remediation (or mitigation) of EUV mirror contamination under operating conditions.

Electron-induced wettability modification

The pioneering works by Lippmann [Ann. Chim. Phys. 5, 494 (1875)] and Frumkin [Actual. Sci. Ind. 373, 5 (1936)] reported on electrowetting phenomenon. It was shown that electric potential, applied to an interface between a conducting liquid droplet and solid surface, strengthened the wetting effect. Here, we describe pronounced decrease of wettability induced by a low-energy electron irradiation. We observe this effect in many materials of different origins. The proposed theory of this phenomenon explains the found growth of the hydrophobicity under an electron irradiation by decreasing solid/liquid and solid/vapor interfacial free energies, when reduction of the latter is always higher. This theory considers the droplet shape dependence on the incident electron charge density and energy of the incident electrons, as well as on the liquid and solid origins. The results of calculations are in a good agreement with the experimental data obtained for water droplet on amorphous silicon dioxide. The effect of the decrease of the wettability, induced by an electron irradiation at low incident charge, is completely reversible after subjection of the electron-irradiated material to ultraviolet illumination, which restores its initial wettability state.

Doping of boron carbides with cobalt, using cobaltocene

The decomposition of cobaltocene under low energy electron irradiation appears facile, and evidence suggests that the decomposition products lead to an increase in the carrier concentration in semiconducting boron carbides. Using cobaltocene to introduce dopants, we fabricated a semiconducting boron carbide homojunction

Investigation of carrier lifetime in 4H-SiC epilayers and lifetime control by electron irradiation

Carrier lifetimes in 4H-SiC epilayers are investigated by differential microwave photoconductivity decay measurements. When the Z1∕2 concentration is higher than 1013cm−3, the Z1∕2 center works as a recombination center. In this case, carrier lifetimes show positive dependence on the injection level (number of irradiated photons). On the other hand, other recombination processes such as surface recombination limit the lifetime when the Z1∕2 concentration is lower than 1013cm−3. In this case, carrier lifetimes have decreased by increasing the injection level. By controlling the Z1∕2 concentration by low-energy electron irradiation, the lifetime control has been achieved.

Tailored polymer microlenses on treated glass surfaces

Integrating arrayed biosensors (biochips) or micro- and nanofluidic devices with readout systems is an important step towards their realization in lab-on-a-chip devices. To this end, we present a straightforward method of fabricating polymer microlenses in precise locations, with desired optical characteristics, using a combination of two methods: surface energy tuning using low-energy electron irradiation, to control the numerical aperture, and time-controlled nanofountain pen deposition of polymer microlenses, to control the focal length. The authors demonstrate the tuning of focal length between 8 and 20μm with numerical apertures between 0.16 and 0.26.

Radiation resistance of boron nitride and related ceramics to low-energy electron irradiation

The radiation resistance of heat-proof ceramics based on boron nitride (BN + Si3N4 and BN + SiO2), which are proposed to be used as structural materials in space ion engines, to low-energy electron irradiation has been investigated.

Wettability study of modified silicon dioxide surface using environmental scanning electron microscopy

The wettability analysis is often used to characterize a surface in micro and nanometer scale. At these small scales, effects of the contact line tension are also expected to play a significant role. Wettability effect is studied using environmental scanning electron microscopy on silicon dioxide surface modified by a low-energy electron irradiation method. Electron-induced wettability variation and patterning at micrometer scale on silicon dioxide substrate allow investigating the contact angle dependence on the water droplet line curvature and calculating values of the line tension of a three-phase system (solid-liquid-vapor) of about 10−9 J/m that is consistent with theoretical estimations. It is found that the sign of the line tension alters from positive for hydrophilic surface to negative for hydrophobic one.

Probing induced defects in individual carbon nanotubes using electrostatic force microscopy

Structural defects greatly affect the electronic properties of single wall carbon nanotubes (CNT’s), for instance by increasing the sensitivity to their environment; an effect which can be utilized for better performance of CNT based chemical sensors. Here we show that electrostatic force microscopy (EFM) can be used as a non-invasive technique for probing defects in individual CNT’s supported on insulating substrates. The technique is demonstrated by monitoring the change in EFM signal upon intentionally inducing defect by an oxygen plasma etch, and is applied to assess the quality of as-grown CNT samples and to study the effect of exposing CNT’s to the low energy electron irradiation of a scanning electron microscope (SEM).

Scanning tunneling microscope observation of plasmid DNA under electron irradiation at8–40eV

The structural changes in plasmid DNA adsorbed onto graphite following low-energy electron irradiation were investigated. Using a scanning tunneling microscope (STM), we observed networks or islands of DNA consisting of entangled molecules and compared the shapes of the DNA before and after electron irradiation at $8--40\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ field emitted from the tip of the STM. The shape of the DNA changed depending on the electron energy. Electrons with very low energy, such as 8 or $13\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, extended the area of a DNA island, while the electrons at 18 or $38\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ degraded it. Both types of changes tend to saturate as the electron dose increases. We also discuss the above results in terms of the chemical reactions, such as strand breaks or molecular dissociation, induced by low-energy electrons.

Electron beam induced orientation selective epitaxial growth of [formula omitted] layers on Si(1 0 0) substrates

From studies on the epitaxial growth of CeO 2 layers on Si(1 0 0) substrates using reactive DC magnetron sputtering, it has been found that the epitaxial CeO 2 layer with (1 0 0) or (1 1 0) orientation is selectively grown by controlling substrate bias and the growth rate. Optimum bias for the CeO 2 (1 0 0) layer growth was ± 15 V . In order to develop this technology into two-dimensional orientation selectivity, we attempt to grow CeO 2 (1 0 0) by low energy electron irradiation, as an alternative way to substrate bias application. It proved that electron beams in two energy regions of 30–40 and 80–100 eV are effective on preferential growth of CeO 2 (1 0 0) layers.