Increase Of Acceleration Voltage Research Articles

From macro-measure of Franck–Hertz curves to micro-collisions between electrons and argon atoms

A Franck–Hertz experiment is adopted in our undergraduate laboratory by using a cylindrical tetrode tube filled with argon vapor. The Franck–Hertz curves, i.e. the variation of the anode current via the accelerating voltage, are experimentally measured, and the key roles of the filament voltage, the control voltage, and the retarding voltage played in the experiments are studied. Diagrams of the micro-elastic/inelastic collisions between the electrons and argon atoms, which are of significance for students to build a connection between the macroscopic measurements and microscopic collisions occurring inside the Franck–Hertz tube, are schematically presented based on the experimental results. The peak/valley interval in the experimental Franck–Hertz curves of argon vapor increases as the accelerating voltage increases. The results further suggest that the lowest excitation energy of an argon atom cannot be exactly derived from the experimental results since all the four sub energy levels within the first excitation energy state of the argon atom are involved in the inelastic electron–atom collisions.

イオンビーム援用傾斜機能性TiNコーティングを施したチタン合金の摩耗およびフレッティング疲労特性

The effect of functionally graded TiN coating on the wear and fretting fatigue behavior of titanium alloy was investigated. The two kinds of monolayer TiN coatings and three kinds of functionally graded TiN coatings were deposited on Ti-6Al-4V alloy substrate using an ion beam assisted deposition technique. Monolayer TiN coating was fabricated by an electron beam evaporation of titanium and simultaneous nitrogen ion bombardment at the acceleration voltage of 0.2 or 2.0 keV. The later consisted of top TiN layer and functionally graded layer. During the fabrication of functionally graded layer, the mixing ratio of nitrogen and argon gas that were used for the generation of ion beam increased stepwisely. The mixed layer formed by ion beam bombardment became thicker by an increase in acceleration voltage. The adhesion and wear resistance improved with an increase in the acceleration voltage. Moreover, inserting the functionally graded layer with the layer thickness of 250 nm improved them significantly. However, further increase in graded layer thickness deteriorated the adhesion and wear resistance. The fretting fatigue life was evaluated by a four-point bending fatigues test. The fretting fatigue life of specimen coated with monolayer TiN film was longer than that of uncoated specimen. The TiN coating with functionally graded layer was the most effective to improve the fretting fatigue life. It was concluded that the insert of functionally graded layer with appropriate layer thickness is effective way for improvement of wear and fretting fatigue behavior.

Fretting Fatigue Behavior of Titanium Alloy Coated with Functionally Graded Ti/TiN Film

The influence of functionally graded TiN coating on fretting fatigue behavior of titanium alloy was investigated. The coating was deposited using an ion beam assisted deposition technique. TiN film was fabricated by an electron beam evaporation of titanium and simultaneous nitrogen ion bombardment. An acceleration voltage of ion beam was set at 0.2 or 2.0 keV. The functionally graded layer was fabricated by varying the mixing ratio of nitrogen/argon ion beam. The mixed layer became thicker by an increase in acceleration voltage. The adhesive strength and wear resistance were improved with an increase in the acceleration voltage. Moreover, they were significantly improved by inserting the functionally graded layer. The fretting fatigue tests were conducted using a four-point bending fatigue testing machine. The fretting fatigue life of specimen coated with monolayer TiN film was longer than that of uncoated specimen. The TiN coating with functionally graded layer was the most effective to improve the fretting fatigue life.

GaN‐based p–i–n X‐ray detection

AbstractGaN‐based p–i–n X‐ray detectors have been fabricated. We observed using SEM that the surface of a GaN sample has a large number of hexagonal defects. The SEM results show that GaN itself contains numerous screw dislocations that will be the flow channel of leakage current, which in turn increased the reverse‐bias leakage current of detectors. We have observed a two‐step increase in X‐ray photocurrent, which is caused by two different detection mechanisms: photovoltaic and photoconductive, and the total photocurrent (Jp) to dark current (Jd) ratio is about 27.7 times and the net photocurrent is about 2.52 µA at 110 V reverse bias. As the X‐ray accelerating voltage increases, the photocurrent has a sublinear trend.

Formation of amorphous carbon on the surface of poly(ethylene terephthalate) by helium plasma based ion implantation

The surface modification of poly(ethylene terephthalate) (PET) by helium plasma based ion implantation (He PBII) was studied. The effect of the main process parameters (acceleration voltage, fluence and fluence rate) on the alterations of the surface chemical composition and structure were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. According to SRIM calculations, at ion energies above 2 keV the stopping power of PET for He + ions is dominated by the electronic component and the contribution of the nuclear component is relatively small. Degradation of the ester group and carbonisation were observed by XPS due to elimination of O-rich fragments. The total C-content of the modified layer increased with the increase of fluence rate and acceleration voltage of particles, enabling the purposeful alteration of the surface composition. A strong broadening was detected in the Raman spectrum between 1000 and 1700 cm −1, testifying to the intense formation of amorphous carbon. The area ratio of the D (∼1410 cm −1) to G (∼1570 cm −1) band increased with the increase of particle fluence and the increase of acceleration voltage, offering the possibility of tailoring the chemical structure of the amorphous carbon layer created by the He PBII treatment.

Estimation of suitable condition for observing copper–phthalocyanine crystalline film by transmission electron microscopy

The decay of the electron diffraction intensity of a copper–phthalocyanine crystalline film was quantitatively measured at room temperature by transmission electron microscopy (TEM) as a function of current density and beam diameter. The measurements revealed that the critical dose increases with decreasing current density, decreasing beam diameter and increasing acceleration voltage. Generally, the damage process only depends on the electron dose. However, the temperature rise of the copper–phthalocyanine enhances the damage process. The relationship between damage and acceleration voltage has been measured, and the result shows that an increase in acceleration voltage decreases the damage. The relationship between image contrast and acceleration voltage was also measured using a single-wall carbon nanotube (SWNT) as a radiation-insensitive substitute for the copper–phthalocyanine in order to obtain atomic-level images. The results revealed that image contrast increases with decreasing acceleration voltage. Using these oppositely behaving results, the most suitable voltage for observing copper–phthalocyanine crystalline films was estimated. The results show that low acceleration voltages should be used for imaging to achieve the minimum specimen resolution limit.

Diagnostics of neutral species in the low-angle forward-reflected neutral beam etching system

The reactive ions extracted from an ion gun were neutralized by reflecting the ions at the angle of 5° on the reflector installed in front of the ion gun. Their neutralization characteristics were investigated for SF6 as a function of acceleration voltage and RF power of the ion gun. When the ion current density was measured as a function of acceleration voltage and RF power of the ion gun using a Faraday cup for both with and without the reflector, the ion current density measured with the reflector was drastically decreased to 99.7% compared to those measured without the reflector suggesting the neutralization of most of the reflected ions. The reactive ions extracted from the ion gun were SF+, SF2+, SF3+ and SF5+. After the reactive ions were reflected at the reflector, the species were neutralized and changed to F2, SF, SF2, SF3 and SF5. The increase of acceleration voltage of the ion gun increased the lower mass peaks such as SF2, SF and F2 and decreased the higher mass peaks such as SF3 and SF5 suggesting the formation of lower mass neutrals at the reflector by the cracking and neutralization of the higher mass ions such as SF3+ and SF5+. The formation of F2 was significant with the increase of the acceleration voltage.

Etch damage evaluation of low-angle, forward-reflected neutral beam etching

In the fabrication of nano-scale silicon-based devices, any process-related damage such as electrical charging and surface modification remaining during the processing may cause serious problems due to the size limitation of the devices. Therefore, etching processes with no or negligible damage are required. In this study, an energetic reactive neutral beam of SF6 was formed using a low-angle, forward-reflected neutral beam technique and the etch properties of SiO2 and possible neutral beam-induced damage were investigated. The result showed that, when the neutral beam was formed by the low-angle reflection of the reactive ions generated by the ion gun, most of the reactive ions were neutralized after the reflection at the reflector. When SiO2 was etched with the energetic reactive neutral beams of SF6, the increase of acceleration voltage and SF6 gas flow rates applied to the ion gun increased the SiO2 etch rate possibly due to the increase of energy and flux of the neutrals at the reflector, respectively. Using the neutral beam, a SiO2 etch rate higher than 22 nm/min could be obtained. Also, when etch damage was estimated by measuring the breakdown voltage of SiO2 after the exposure to the oxygen neutral beam, no noticeable damage of SiO2 could be observed.

Studies of Ag films deposited using partially ionized beam deposition

Partially ionized beam deposition, in which the starting material Ag is evaporated form a crucible with a restricted nozzle, partially ionized by electron bombardment, and the ions accelerated to the deposition substrate, has been used to deposit Ag films on both Si(111) and Si(100) substrates. Characterization of the deposited films has been carried out by x‐ray diffraction, scanning electron microscopy, α‐step roughness, Auger electron spectroscopy, and ellipsometry. As a comparison, Ag films deposited without ion acceleration and by evaporated conventionally from an open crucible were also investigated. Highly textured Ag films with strong (111) orientation on Si(111) have been obtained at high accelerating voltage Va=4 kV. The surface flatness improves and the resistance of the films to impurity diffusion from the surface increases as the accelerating voltage increases.

Intensity distribution of scintillation produced by high-energy electrons

As a basis of yttrium aluminum garnet (YAG)-TV image-recording systems scintillation properties of single-crystal phosphors (YAG (Y 2Al 5O 12)), yttrium compound (YAlO 3, Y 2SiO 5), powder phosphors and plastic scintillators have been studied in the electron energy range 40 keV – 1 MeV. The scintillation light is measured by a photomultiplier and a pulse height analyzer. All of the energy of 100 kV electrons is absorbed in a single crystal of 100 μm thick and the distribution of pulse heights of light outputs produced by many electrons shows a single peak. However, the distribution changes drastically as the accelerating voltage increases. At 300 kV two peaks appear in the pulse height distribution and at higher accelerating voltage such as 800 kV only one single peak with low pulse height remains. These distributions for high-energy electrons are due to the energy loss of electrons which penetrate the scintillator without much deflection. The variance of the pulse height distribution gives the detective quantum efficiencies which are about 0.9 for 100 kV and about 0.55 for 1000 kV. The energy conversion coefficient is estimated to be 0.01 for the YAG scintillator.

Characterization by Photoluminescence of ICB-Grown CuInSe2 Thin Films

CuInSe2 thin films were prepared by the ICB (ionized cluster beam) technique on glass substrates. It is found that the apparent grain size increased more than 1 µm when Cu cluster is ionized, even in In-excess CuInSe2 films which usually shows a specular surface with a small grain size of less than 0.2 µm. These films were characterized by photoluminescence (PL) spectra employing Ar and YAG lasers as excitation sources. In those films with a slightly In-excess composition, the 0.85 eV-peak was observed, which has been correlated with the good solar cells performance. The PL peak gained intensity with the increase of acceleration voltage of In-cluster up to 2 kV. It is concluded that ICB is a promising technique for preparation of good quality CuInSe2 thin films for solar cells.

Electron-beam-pumped lasing in epitaxial ZnSe thin films

We have observed lasing in ZnSe thin films grown epitaxially on (100) GaAs substrates under pulsed electron beam excitation in the transverse geometry. Films were grown using both molecular beam epitaxy (MBE) and organometallic vapor phase epitaxy (OMVPE). These films have been characterized using low-temperature photoluminescence (PL) and electrical transport measurements, as well as optical and electron microscopy. Lasing thresholds as low as 1 A/cm2 have been determined for MBE-grown films (films thickness 4 μm, accelerating voltage 40 kV, temperature 16 K, pulse length 100 ns). This threshold rose with increasing temperature, but lasing could be observed at temperatures as high as 295 K. In spite of many similarities between the PL and electrical properties of the MBE and OMVPE films, our measurements on the latter films indicate that the lasing thresholds are somewhat higher in these materials (≥2x), but that the differences diminish as the electron accelerating voltage increases. Correlations between the lasing thresholds and other measured properties of the two materials are discussed. We find that the higher thresholds in the OMVPE films are due to increased cavity losses resulting from scattering by the textured film surfaces.

Atomic structure of ultrafine catalyst particles resolved with a 200-keV transmission electron microscope

Small atomic assemblies (diameter 10–100 A) possess several unusual physical and catalytic properties1–9. Speculations regarding the crystalline nature of individual particles of supported metals dispersed to this degree, as well as colloidal metallic sols, date back to Faraday's researches on divided metals. Interest has been renewed following the demonstration10,11 that metals could readily be prepared in colloidal form. Similarly, binary semiconductors such as CdS exhibit novel properties which are of potential value in photoelectrochemistry. Thus, the electronic band-gap of bulk CdS is 2.4 eV, whereas a CdS cluster of ∼18° diameter—corresponding to one of the ‘magic agglomeration numbers’—has a band-gap closer to 3.4 eV. Moreover, the conduction-band edges of such ultrafine semiconductors functioning as microelectrodes are sufficiently shifted to favour the photoreduction of H+ (as gaseous H2) from water4. Reliable methods are needed to probe the ultrastructure of very fine particles, especially as such methods can elucidate the nature of many other ultrafine materials. Examples of such materials are: (1) bimetallic systems8, such as Pt/Ir on oxide supports for the catalytic re-forming of hydrocarbons to improve octane ratings; (2) semiconductors such as TiO2 overlaid with comminuted Pt for the photocleavage of water12,14; (3) dispersed Rh or Pt on oxide supports for controlling automobile exhausts15; and (4) large clusters of transition metal and noble metals of the type Au55 [P(C6H5)3]12Cl6, which bridge the gap between molecular and extended metallic structures6. High-resolution electron microscopy is a possibility as it probes structures directly in real-space16–18. Very-high-voltage transmission electron microscopes (TEM), operating between 400 and 1,500 keV, would provide the best interpretable resolution; however, they cannot usually be fitted with in situ micro-analytical facilities based on X-ray emission—essential for sample characterization of mixed phases—and voltage stability is harder to achieve as accelerating voltage increases. Here we report results obtained with a modified commerical 200-keV TEM. A new type of side-entry specimen stage permits the investigation of atomic arrays in minute assemblies of Au and in colloidal catalysts of Pt, such as those used in photoredox processes4,19,20. These are shown to be crystalline but relatively rich in disordered regions, both within their bulk and on their surface.