Ar Ion Bombardment Research Articles

Characterization of Schottky-diode X/[formula omitted]-ray detectors based on CdTe crystals with different uncompensated impurity concentrations

The Schottky-diode X/ γ-ray detectors based on semi-insulating p-like CdTe single crystals with four values of uncompensated impurity concentration (N≈ 2 × 1012 cm−3, 2 × 1011 cm−3, 1 × 1011 cm−3, 4 × 1010 cm−3) were developed and characterized by I-V measurements at low reverse bias (0.005–100 V) and detection of 137Cs and 241Am radioisotope emission spectra. All the detectors were fabricated by the same technique using vacuum evaporation of a Cr electrode (rectifying contact) and chemical deposition of an Au electrode (Ohmic contact) onto the B- and A-face of CdTe(111) crystals, respectively, pre-treated with Ar-ion bombardment. The change of the charge transport mechanism from over-barrier (thermionic) to generation current along with the analysis of the temperature dependence of the differential resistivity evidenced a high concentration of deep level impurities near the middle of the semiconductor bandgap. The detection efficiency η of the detectors was calculated using the corrected expressions for the coordinate dependence of the electrical field strength in a diode which took into account the fact that the depletion region width exceeded the CdTe crystal thickness at higher bias voltages. It was shown that the dependence η(N) decreased with increasing N without a maximum corresponding to an optimal value Nopt as reported earlier. The Cr/CdTe/Au Schottky-diode detectors, fabricated using CdTe with the lowest N, demonstrated the highest energy resolution (0.6% @662 keV and 7.5% @59.5 keV) and it degraded when crystals with higher N were used.

Nucleation retardation of cubic boron nitride films caused by the addition of oxygen in argon‑nitrogen sputtering gas

Cross-sectional transmission electron microscopy (TEM) was employed to study the effect of the additive oxygen gas on the microstructure of boron nitride (BN) films especially focusing on the intervening turbostratic BN (tBN) layer's behavior. Films in this study were deposited on diamond coated Si substrates, which were biased with negative voltages, using an unbalanced magnetron sputtering method with a boron carbide target. Various amounts of oxygen were added into argon‑nitrogen mixed sputtering gas. TEM showed that the tBN intervening layer was also observed to form prior to cubic BN (cBN) layer formation for all films, irrespective of oxygen addition. The tBN layer thickness increased with increasing oxygen content. This thickness increase implied that the addition of oxygen delayed cBN phase nucleation. On the other hand, the alignment of the hexagonal BN planes in the tBN layer, estimated from FTIR spectra, was observed to be enhanced with increasing oxygen content. Such alignment enhancement is considered as a result of oxygen adsorption on the tBN layer surface, which suppresses breaking sp2 bonds caused by Ar ion bombardments. The suppression of the sp2 bond breakage, consequently, causes the difficulty of forming sp3 bonds and delays the cBN phase nucleation.

Enhancing the quality of self-organized nanoripples by Ar-ion bombardment of a bilayer system

Ion bombardment (IB) is a promising nanofabrication technique for producing nanoripples. A critical issue that restricts the application of IB is the limited quality of IB-induced nanoripples. Photoresist (PR) and antireflection coating (ARC) are of technological relevance for lithographic exposure processes. Moreover, to improve the quality of IB-induced self-organized nanoripples, in this study, a PR/ARC bilayer was bombarded at an incidence angle of 50°. The surface normalized defect density and power spectral density, obtained via scanning atomic force microscopy, indicate the superiority of the PR/ARC bilayer nanoripples over those of single PR or ARC layers. The growth mechanism of the improved nanoripples, deciphered via the temporal evolution of the morphology, involves the following processes: (i) formation of a well-grown IB-induced nanoripple prepattern on the PR, (ii) transfer of nanoripples from the PR to the ARC, forming an initial ARC nanoripple morphology for subsequent IB, and (iii) conversion of the initial nonuniform ARC nanoripples into uniform nanoripples. In this unique method, the angle of ion-incidence should be chosen so that ripples form on both PR and ARC films. Overall, this method facilitates nanoripple improvement, including prepattern fabrication for guiding nanoripple growth and sustainable nanoripple development via a single IB. Thus, the unique method presented in this study can aid in advancing academic research and also has potential applications in the field of IB-induced nanoripples.

BCl3/Ar plasma etching for the performance enhancement of Al-doped ZnO thin films

Al-doped ZnO (AZO) has attracted significant attention as a transparent electrode with low cost, high transmittance, high electrical conductivity, and excellent mechanical flexibility. A high-resolution patterning process is required for its application to next-generation displays, which can be achieved through the plasma etching process. In this study, we investigated the etching mechanism for Al-doped ZnO thin films in a BCl3/Ar-based plasma system and observed the performance of the thin-film surface after the etching process. The etch rate of the AZO thin films was highest at BCl3/Ar = 25:75, and increased as the power of the radio frequency source and bias increased. The etching mechanism was elucidated through optical emission and X-ray photoelectron spectroscopic analyses and confirmed to be the interaction between the bombardment of Ar ions and the chemical reaction of Cl and Cl2 radicals. BCl3-based plasma etching induces various changes in the properties of the AZO thin-film surface. The surface of the AZO thin film becomes very smooth, the work function increases by approximately 200 meV, and the bandgap increases by approximately 0.03 eV after the etching process in BCl3-based plasma. In addition, the electrical properties, such as sheet resistance and carrier mobility, are significantly improved. The results of this study may be applied for the development of high-performance optical and electronic devices.

Negative effect of cations out-diffusion and auto-doping on switching mechanisms of transparent memristor devices employing ZnO/ITO heterostructure

An excessive unintentional out-diffused In atom into the switching layer is a potential threat to the switching stability of memristor devices having indium tin oxide (ITO) as the electrode. We suggest that the physical factor (bombardment of Ar ions and bombardment-induced localized heat during ZnO deposition) and chemical factor (bonding dissociation energy, point defects, and bond length of atoms) are responsible for promoting the out-diffusion. The In atom acts as dopant in the ZnO lattice that degenerates the ZnO insulative behavior. Furthermore, the In ions take part in the conduction mechanism where they may compete with other mobile species to form and rupture the filament, and hence, deteriorate the switching performance. We propose a facile UV/O3 (UVO) treatment to mitigate such damaging effects. The device fabricated on the UVO-treated ITO substrate exhibits significant switching parameter improvement than that of the device manufactured on untreated ITO. This work delivers an insight into the damaging effect of out-diffusion and auto-doping processes on the reliability of memristor devices.

Strengthening ultrathin Si3N4 membranes by compressive surface stress

In this work, the effect of compressive surface stress on thin film membrane fracture was studied by bulge test. In order to create membranes with compressive residual stress at the surface, low-pressure chemical vapor deposition (LPCVD) Si3N4 membranes were coated with a 1−8 nm compressive SiNx adlayer or subjected to Ar-ion bombardment. Fracture strength analysis, done using finite element method and Weibull distribution, and microscope inspection of failed membranes showed that the pressure limit of the membranes is determined by the intrinsic fracture mode, caused by high stress induced at the membrane edge near the top surface. By creating compressive residual stress at the membrane surface, the maximum stress induced by the applied pressure was reduced and the fracture strength of the Si3N4 was increased from 17.3 GPa to 18.3 GPa. As a result, membranes with a compressive surface showed a 50 % increase in pressure limit, from 5 kPa/nm to 7.5 kPa/nm.

Surface modification and structure evolution of aluminum under argon ion bombardment

The surface properties is an important factor in the surface activated bonding of aluminum. The effect of argon (Ar) bombardment on the surface properties of aluminum was investigated in this work. The changes in surface chemical composition, wettability and structure were analyzed. The results revealed that the AlO bonds of surface oxide film were broken by Ar ion bombardment. The positive aluminum ions (Al+) and oxygen radicals (O*) produced by breaking of AlO bonds could react with the adsorbed water molecules to form hydrophilic hydroxyl (OH groups) and AlOH groups, which improved the wettability of aluminum surface. A large number of dislocations and subgrains with lattice distortion accumulated in the bombard-induced modification layer near the surface. The stress distribution on the surface was transformed from tensile stress into compressive stress with the bombardment power enhanced. The simulation results showed that the regular structure was broken and the point defects were produced from the collision. In the later stage of collision, most of the disordered atoms rearranged with the point defects annihilated, and finally a crater with several stable point defects was left near the surface.

In situ surface analysis of an ion-energy-dependent chlorination layer on GaN during cyclic etching using Ar+ ions and Cl radicals

Gallium nitride (GaN) semiconductor devices must be fabricated using plasma etching with precise control of the etching depths and minimal plasma-induced damage on the atomic scale. A cyclic process comprising etchant adsorption and product removal may be suitable for this purpose but an understanding of the associated etching surface reactions is required. The present work examined the formation of a chlorinated layer based on Cl radical adsorption on a GaN surface in conjunction with Ar ion irradiation. This research employed beam experiments and in situ x-ray photoelectron spectroscopy. The results show that N atoms are preferentially desorbed during exposure to Ar ions to produce Ga-rich layers at depths of 0.8 and 1.1 nm at an Ar ion dosage on the order of 1016 cm−2 and ion energies of 116.0 and 212.6 eV, respectively. Subsequent exposure of the irradiated Ga-rich layer to Cl radicals removes some Ga atoms and produces a chlorinated layer over the GaN surface. This chlorinated layer has a thickness on the order of 1 nm following Cl radical dosages on the order of 1019 cm−2. This study of plasma-treated surfaces is expected to assist in developing means of controlling the etching depth during the atomic layer etching of GaN via Ar ion bombardment.

Plasma resistance of sintered and ion-plated yttrium oxyfluorides with various Y, O, and F composition ratios for use in plasma process chamber

Yttrium oxyfluoride was developed for use in the plasma process chamber using various corrosive gases. In this paper, sintered yttrium oxyfluorides with various Y, O, and F composition ratios (YxOyFz) and ion-plated YOF and Y5O4F7 films were prepared, and the physical etching behavior due to Ar ion bombardment and NF3/Ar plasma resistance was investigated. It was found that the etching rate of the sintered yttrium oxyfluoride due to the bombardment of Ar ions with an energy of 500 eV decreased as the oxygen composition ratio in the samples decreased, i.e., F-rich yttrium oxyfluoride had better resistance against energetic-ion bombardment. It was also found that the surface roughness of sintered YOF and Y5O4F7, both of which had the stable phases, was much smoother after Ar ion bombardment than that of yttrium oxyfluorides without the stable phase. NF3/Ar plasma resistance was also investigated. For the sintered yttrium oxyfluoride, both YOF and Y5O4F7 showed good resistance against the NF3/Ar plasma, where the ideal stoichiometric atomic composition ratio could be kept even after plasma irradiation. For both as-deposited ion-plated YOF and Y5O4F7 films, the F composition ratio was slightly smaller than the ideal stoichiometric ratios, suggesting that some amount of fluorine was escaped from the starting materials of YOF and/or Y5O4F7 during the ion-plated film deposition processes. After NF3/Ar plasma irradiation, F composition ratios were increased for both ion-plated YOF and Y5O4F7 films, and the atomic composition ratio becomes closer to the ideal stoichiometric ratios for both films.

Precision measurements of the gradient of the Casimir force between ultraclean metallic surfaces at larger separations

We report precision measurements of the Casimir interaction at larger separation distances between the Au-coated surfaces of a sphere and a plate in ultrahigh vacuum using a much softer cantilever of the dynamic atomic-force-microscope-based setup and two-step cleaning procedure of the vacuum chamber and test body surfaces by means of UV light and Ar-ion bombardment. Compared to the previously performed experiment, two more measurement sets for the gradient of the Casimir force are provided, which confirmed and slightly improved the results. Next, additional measurements have been performed with a factor-of-two larger oscillation amplitude of the cantilever. This allowed the obtainment of meaningful results at much larger separation distances. The comparison of the measurement data with theoretical predictions of the Lifshitz theory using the dissipative Drude model to describe the response of Au to the low-frequency electromagnetic field fluctuations shows that this theoretical approach is experimentally excluded over the distances from 250 to 1100 nm (i.e., a major step forward compared to the previous work where it was excluded up to only 820 nm). The theoretical approach using the dissipationless plasma model at low frequencies is shown to be consistent with the data over the entire measurement range from 250 to 1300 nm. The possibilities to explain these puzzling results are discussed.

Study of ion bombardment of SiC ceramics: Surface and interfacial reaction modification

Ar ion bombardment was conducted to modify the SiC surface microstructures, which had a vital effect on the interfacial microstructure and shear property of brazing joints. The amorphous layer with thickness of ∼120 nm was formed on the bombarded surface, accompanied with plenty of dislocations and twins beneath the amorphous layer. Reliable SiC/AgCu-Ti/SiC joints were brazed in vacuum at 900 °C for 10 min, and the interfacial microstructure was investigated by SEM, EDS and TEM in detail. When the ion bombarded SiC was used as substrates, the microstructure of brazing beam was optimized as SiC / Ti5Si3 + TiC mixed layer / Ag(s,s) + Cu(s,s) containing TiCu / Ti5Si3 + TiC mixed layer / SiC, in which the interfacial stratification was eliminated compared to the conventional SiC brazing. The shear strength was improved to 30.9 MPa with ion bombardment, which was ∼72.6 % higher than that of the original SiC joints without ion bombardment. The proposed Ar ion bombardment method provides a novel way to modify the brazability of ceramics.

Depletion Region in Cr/CdTe/Au Schottky Diode X- and $\gamma$ -Ray Detectors

The electrical and spectral characteristics of the Cr/cadmium telluride (CdTe)/Au structures with a Schottky contact at the Cr–CdTe interface and near ohmic contact at the Au–CdTe interface were studied. The Schottky diodes were fabricated using high-resistivity CdTe(111) single-crystal wafers with different thicknesses (0.5–2 mm) after preliminary chemical etching and also additional surface treatment by Ar-ion bombardment was employed. Electronic parameters such as the concentration of uncompensated impurities, width of the space-charge region, and the thickness of the depletion region were calculated based on the comparison of the voltage dependences of the photopeak heights in the 241Am isotope spectra excited from the Schottky contact side and ohmic contact side, respectively. The obtained Cr/CdTe/Au Schottky diodes with low leakage current [a few nanoampere (nA) at 1000–1500 V] show promise as high-energy resolution spectroscopic X-/gamma ( $\gamma $ )-ray detectors.

Impact of pre-existing disorder on radiation defect dynamics in Si

The effect of pre-existing lattice defects on radiation defect dynamics in solids remains unexplored. Here, we use a pulsed beam method to measure the time constant of defect relaxation for 500 keV Ar ion bombardment of Si at 100 °C with the following two representative types of pre- existing lattice disorder: (i) point defect clusters and (ii) so-called “clamshell” defects consisting of a high density of dislocations. Results show that point defect clusters slow down defect relaxation processes, while regions with dislocations exhibit faster defect interaction dynamics. These experimental observations demonstrate that the dynamic aspects of damage buildup, attributed to defect trapping-detrapping processes, can be controlled by defect engineering.

Growth of MWCNTs on Plasma Ion-Bombarded Thin Gold Films and Their Enhancements of Ammonia-Sensing Properties Using Inkjet Printing

Multiwalled carbon nanotubes (MWCNTs) have been synthesized on thin gold (Au) films using thermal chemical vapor deposition (CVD). The films were evolved to catalytic Au nanoparticles (Au NPs) by plasma argon (Ar) ion bombardment with a direct current (DC) power of 216 W. The characteristics of the MWCNTs grown on Au catalysts are strongly dependent on the growth temperature in thermal CVD process. The MWCNTs were then purified by oxidation (550°C) and acid treatments (3 : 1 H2SO4/HNO3). After purifying the MWCNTs, they were dispersed in deionized water (DI water) under continuous sonication. The MWCNT solution was then ultrasonically dissolved in a conducting polymer mixture of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to prepare for an electronic ink. The ink was deposited onto the flexible and transparent plastic substrates such as polyethylene terephthalate (PET) with fabricated silver interdigitated electrode using two methods such as drop-casting and inkjet printing to compare in the detection of ammonia (NH3) and other volatile organic compounds (VOCs) at room temperature. Based on the results, the gas response, sensitivity, and selectivity properties of MWCNT-PEDOT:PSS gas sensor for NH3 detection are significantly enhanced by using inkjet printing technique. The sensing mechanism of fabricated gas sensor exposed to NH3 has been also proposed based on the swelling behaviour of polymer due to the diffusion of NH3 molecules into the polymer matrix. For the MWCNTs, they were mentioned as the conductive pathways for the enhancement of gas-sensing signals.

3D flower-like defected MoS2 magnetron-sputtered on candle soot for enhanced hydrogen evolution reaction

Exploring highly efficient, cost-effective and stable electrocatalysts for hydrogen evolution reaction (HER) based on naturally abundant elements is of great interest but still a challenge. As is generally known, molybdenum disulfide (MoS2) represents a promising catalyst to replace the state of the-art platinum (Pt) for HER, but an effective way of applying it is yet unknown due to a significant resistance between basal planes. Herein, for the first time, a novel nanostructure with three-dimensional (3D) flower-like defected MoS2 nanosheets grown directly on candle soot by magnetron sputtering with Ni foam as a supporter was developed, and it displayed excellent catalytic activity and stability. On the one hand, the bombardment of Ar ions in the deposition system could effectively etch the inert basal plane, leading to the formation of defects and steps to increase the active edge sites. On the other hand, the resistance of MoS2-based electrocatalysts decreased due to the unique topographic structure and the existence of 1T-MoS2 phase, and also the composite was superhydrophilic which is beneficial to the contact of the solid-liquid interface. The as-prepared 3D MoS2/candle soot/Ni foam (NF + CS + MoS2) composite has an overpotential of 56 mV at the current density of 10 mA cm−2 and a small Tafel slope of 49 mV decade-1. This present work provides new insight into the large-scale production of chemically active MoS2-based catalysts for HER.

Fabrication, Characterization and Ar-Ions Bombardment for the Non-Flaking CuO Nanowires Synthesized on Copper Foam by Thermal Oxidation

Fabrication, Characterization and Ar-Ions Bombardment for the Non-Flaking CuO Nanowires Synthesized on Copper Foam by Thermal Oxidation

Quantitative evaluation of high-energy O− ion particle flux in a DC magnetron sputter plasma with an indium-tin-oxide target

O− ion flux from the indium tin oxide (ITO) sputter target under Ar ion bombardment is quantitatively evaluated using a calorimetry method. Using a mass spectrometer with an energy analyzer, O− energy distribution is measured with spatial dependence. Directional high-energy O− ion ejected from the target surface is observed. Using a calorimetry method, localized heat flux originated from high-energy O− ion is measured. From absolute evaluation of the heat flux from O− ion, O− particle flux in order of 1018 m−2 s−1 is evaluated at a distance of 10 cm from the target. Production yield of O− ion on the ITO target by one Ar+ ion impingement at a kinetic energy of 244 eV is estimated to be 3.3 × 10−3 as the minimum value.

Crystallization mechanism of Fe78Si13B9 amorphous alloy induced by ion bombardment

The crystallization behavior of Fe78Si13B9 amorphous alloys induced by Ar ion bombardment was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. The crystallization process of amorphous alloys can be controlled by adjustment of ion incident angles (θ), beam density and substrate temperature. The compressive stress caused by ion bombardment will result in the decrease of critical nucleation energy and induce the crystallization of amorphous alloy even at very low temperature, and the thermal effect converted from energetic ions will improve the crystallization of amorphous alloys. The crystallization process of amorphous alloy induced by ion bombardment was a stress induced phase transformation process assisted by thermal effect.

Simulation of sputtering from ion-beam-roughened carbon surfaces

ABSTRACTEffects of ion-induced surface roughness on sputtering of amorphous carbon under ion bombardment are studied by means of binary-collision computer simulation in a wide range of incidence angles. Most simulations refer to 1–10 keV Ar ion bombardment, and sinusoidal ripple morphology is assumed. It is shown that surface roughness is a key factor to achieve quantitative agreement with experiment. The simulation results are compared with the analytical estimates of the yield from sine-shaped and ridged surfaces based on continuum models of ion sputtering. Some deviations between the results are discussed.

Effects of the Ar and He dilution gas mixture ratio on the hardness of a-C:H films synthesized by atmospheric pressure plasma enhanced chemical vapor deposition

Hydrogenated amorphous carbon (a-C:H) films synthesized by atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) possess a low hardness because of the large amount of incorporated hydrogen. To increase the hardness of these a-C:H films, detachment of the hydrogen is accomplished using Ar ion bombardment during the deposition process. Herein, a-C:H films were deposited by AP-PECVD and the effects of varying the dilution gas mixing ratio of Ar and He on the hardness of the a-C:H films were investigated. As the Ar ratio in the mixture gas increased from 0% to 20%, the hardness of the films increased from 0.8 to 2.7 GPa. Furthermore, as the Ar ratio increased, the metastable He atoms in the plasma decreased, the intensity of the CHx peaks related to the hydrogen decreased, and the surface roughness of the films increased. These results imply that Ar ion bombardment at the film surface occurred and was caused by the Penning effect of metastable He and Ar atoms. The hardness of the a-C:H films synthesized by AP-PECVD was increased by the dilution of Ar and He gases because the hydrogen content of the films was decreased via the Ar ions generated by the Ar and He mixture gases.