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In high numerical aperture (NA) extreme ultraviolet lithography, which is used to implement a finer linewidth of 10 nm or lower, serious problems arise in patterning as the NA increases. To alleviate such problems, a thin absorber and a multilayer with good reflective efficiency and improved pattern quality are required. To develop an effective EUV photomask for the commercialization of high-NA systems, we determined the optimal ruthenium (Ru)/silicon (Si) multilayer structure using a phase-shift mask (PSM) absorber. A Ru/Si multilayer d R u = 2.2 nm , d S i = 4.7 nm using PSM as an absorber has a smaller best-focus range and placement error compared to the molybdenum (Mo)/silicon (Si) multilayer. At the same time, it provides improved image contrast, enabling more stable patterning. Even when the number of layers of the Ru/Si multilayer was reduced, it was confirmed that the reflectance efficiency and image quality were maintained.

High-performance GaAs tunnel diodes (TDs) are fabricated by using Si delta-doping technique. The GaAs TDs exhibited a high peak tunnel-current density of 2,735 A/cm2 and low specific resistivity of 1.46 × 10−4 Ωcm2. However, the performance of the GaAs TDs deteriorated once the amount of Si delta doping exceeded a certain limit, which has been rarely reported elsewhere. Detailed analyses and numerical simulations of GaAs TDs with various amounts of Si delta doping prove that Si amphoteric behavior governs the performance limit. GaAs TDs with precisely controlled Si delta doping are suitable for cutting-edge tandem solar cell applications.

We examined the structural and optical properties of a crown-shaped quantum well (CSQW) to suppress nonradiative recombination. To reduce carrier loss in defect traps at the well/barrier interface, the CSQW was designed to concentrate carriers in the central region by tailoring the bandgap energy. Temperature-dependent photoluminescence measurements showed that the CSQW had a high activation energy and low potential fluctuation. In addition, the long carrier lifetime of the CSQW at high temperatures can be interpreted as indicating a decrease in carrier loss at defect traps.

The lasing characteristics of three-guide coupled rectangular ring laser containing active and passive sections were investigated numerically and experimentally. The rectangular laser cavity consists of four low-loss total internal reflection mirrors and an output coupler made from three passive coupled waveguides. The laser having active section lengths of 350 µm and total cavity lengths of 780 µm was fabricated. The lasing threshold current in the clockwise circulating direction is approximately 35 mA, while that in the counterclockwise circulating direction is around 40 mA under continuous wave operation. The lasing characteristics are bidirectional operation of the single mode with a side mode suppression ratio better than 27 dB.

We examined the impact that the electrode/(Ba,Sr)TiO3 (BST) interface structures have on electric properties by investigating the electrical conduction mechanism of the BST thin-film capacitors with Pt and Au top electrodes. The BST thin films were prepared on the Pt bottom electrode/glazed Al2O3 substrate by chemical solution deposition (CSD). The dielectric property of the as-deposited Pt/BST/Pt capacitor had a large frequency dispersion and the leakage current properties deteriorated because the Pt top electrode/BST interface structure is rough. However, by post-annealing for 30 min at 400 � C after the top electrode was deposited, the frequency and temperature properties improved. The Schottky barrier height at the Pt top electrode/BST interface was 1.03 eV and that at the Au/BST interface was 0.73 eV, which indicated that its electrical conduction mechanism depends on the Schottky emission model. The dielectric constant, tan � , and tunability of the Au/BST/Pt capacitor are 200, 0.0178, and 53.7% (at 214 kV/cm, 6.0 V), respectively, which showed excellent dielectric properties. This suggests that highquality BST films for application to tunable microwave devices can be formed on a very inexpensive glazed Al2O3 substrate. [DOI: 10.1143/JJAP.47.7494]

A micro-electro-mechanical-systems (MEMS)-based IR spectrometer has been designed and fabricated. The proposed micro-spectrometer consists of multi-slit grating and bolometric IR detector array. The grating is used for dispersion of an incident optical radiation into different wavelength components. The grating structure is patterned by reactive ion etching (RIE) of aluminum deposited on dielectric membrane, which is fabricated over silicon wafer. The IR detector part adopts a resistive bolometer that changes its resistance due to the temperature increment. The presence of IR at the specific wavelength can be detected by noticing the resistance change when temperature increases due to an incident IR ray. Vanadium oxide is adopted for resistive bolometer of IR spectrometer in this work because of its higher temperature coefficient of resistance (TCR) which is needed for the better sensitivity. Two parts that composes the MEMS-based IR spectrometer, aluminum multi-slit grating and thermal-type vanadium oxide IR detector, are processed independently and bonded as a final step.

Dual grating interferometric (DGI) lithography which can be operate in the usage of an incoherent EUV light source is proposed. Thus, the DGI exposure method can combine with a stand alone EUV source, such as laser produced plasma and discharge produced plasma. Therefore, this exposure system becomes a compact one for the evaluation of resolution and LER in a EUV resist.

We have studied a pixel-isolated phase-separated composite organic film (PI-PSCOF). This PI-PSCOF is used for anisotropic phase separation from ferroelectric liquid crystals (FLCs) and prepolymer materials using an appropriate UV intensity variation. In this device, the FLC molecules are isolated in the pixels where FLCs are surrounded by the interpixel vertical polymer walls and the horizontal polymer films on the upper substrate. These devices show very short response time and very high mechanical durability against external pressure. We also compared the pure FLC, conventional phase-separated composite film (PSCOF) and PI-PSCOF mode in terms of their electrooptic characteristics and X-ray layer structure measurements. Compared with the PSCOF mode, PI-PSCOF exhibits good electrooptical behaviors. Consequently, we achieved an excellent device scheme suitable for flexible substrates, using the PI-PSCOF mode and expect that this PI-PSCOF scheme will be one of the powerful and promising new FLC display modes, particularly applicable to flexible FLC display modes.

The pi-cell is one of the candidates for replacing the twisted nematic (TN) and in-plane switching (IPS) modes. It has a fast switching speed and a good viewing angle owing to its self-compensated director configuration. In this paper, we report the optimized conditions for polymer-network stabilization to prevent the bend state from transforming into the (transitioning) splay state. Excellent electro-optical characteristic were obtained by optimizing various conditions: monomer concentrations in liquid crystal (LC), UV intensity, curing time, curing voltage, curing temperature and the retardation of the compensation film. Scanning electron microscopy (SEM) images revealed the structures of the stabilized polymer network in a pi-cell, which is the key factor for maintaining the bend state.

The authors report X-ray scattering experiments on phase-separated composite organic film (PSCOF) structures mixed with ferroelectric liquid crystals (FLCs). We discuss the effect of the local layer structure in a PSCOF cell on the ratio of the concentration between prepolymer and liquid crystals. The ratio of optimized concentration in terms of optical characteristics for a PSCOF liquid crystal display are 30 wt % for prepolymer (NOA65) and 70 wt % for FLCs (Felix). We found that the layer structure in a ferroelectric liquid crystal cell made of 30 wt % NOA65 and 70 wt % Felix is a tilted-bookshelf layer structure. The angles 15 and 17° are the tilted-bookshelf angles at 65 and 58 °C, respectively. These layer tilt angles are almost same as the molecular tilt angles of ferroelectric liquid crystals in the Sm C* phase. We understand that this result comes from compensating for layer buckling. We consider that the PSCOF-mode local layer structure is an excellent solution to the problem of zig-zag defects and mechanical shock for application in future televisions and plastic ferroelectric liquid crystal displays (FLCDs).

To improve the performance of shallow trench isolation chemical–mechanical polishing (STI-CMP) in terms of the removal selectivity of oxide and nitride films and the formation of surface defects, we investigated the effects of the calcination and milling process conditions during ceria slurry synthesis. We have focused on the effects of particle size distribution, the large-particle size, and the dispersion stability in a ceria slurry. We determined the optimum bead size for milling and appropriate calcination temperatures in order to obtain a reasonable particle distribution, with lower numbers of fine primary particles and large, agglomerated particles, in ceria slurry. This was achieved by reducing the quantity of aggregated particles during milling and two-step calcination process generating higher-density particles. These results can be qualitatively explained by abrasive collisions occurring between the milling beads and the decarbonation of cerium carbonate through diffusion during the manufacturing process used for the ceria slurry.

Through chemical mechanical polishing (CMP) tests using polycrystalline silicon (polysilicon) and oxide blanket film wafers, the effects of alkaline agents added to colloidal silica slurries were investigated. With increasing concentration of the alkaline agent, a decreasing trend after an initial increase in the polysilicon removal rate was found, along with a low oxide removal rate, enabling high selectivity. The surface roughness similarly became worse and then better with increasing concentration of the alkaline agent. The results suggest a mechanism in which hydroxide bonds to the Si surface of the abrasives in the slurry and OH- attaches to the polysilicon surface. The silanol group induces high polarization and thus weakens the Si–Si back bonds. These results can be qualitatively explained in terms of the chemical reaction between the polysilicon surface and the alkaline agent in the slurry, according to the hydrophobicity and hydrophylicity as indicated by contact angle measurements.

It has been reported that wafer nanotopography has a substantial impact on oxide film thickness variation after chemical mechanical polishing (CMP). Currently, shallow trench isolation (STI) is the preferred isolation scheme for device manufacturing, where STI CMP has become an essential process. Studies on nanotopography effects when using fumed silica slurries have been reported. This research examines the impact of nanotopography on the remaining oxide film thickness variation with varying surfactant concentrations in and molecular weights of the nano-ceria slurries used in STI CMP. Higher surfactant concentration and molecular weight lead to higher remaining oxide film thickness variation induced by wafer nanotopography.

The dependencies of the electrical characteristics of n-metal–oxide–semiconductor field-effect transistors (n-MOSFETs) on the nano-scale Si thickness (

An investigation of Smith–Purcell radiation is carried out with a three-dimensional particle-in-cell simulation. The simulation model consists of a rectangular grating with limited length and width, which is driven by a single electron bunch, a train of periodic bunches, and a continuous beam. Smith–Purcell radiation is observed and distinguished from an evanescent wave, which travels near the surface of the grating. We found that the evanescent wave has a frequency lower than the allowed minimum Smith–Purcell frequency, and does not radiate until it reaches the ends of the grating. It is also shown that superradiant radiation can be excited by periodic electron bunches. With the present parameters, superradiant radiations are emitted at higher harmonics of the bunch frequency and at corresponding Smith–Purcell angles. The initially continuous beam can be bunched by the interaction with the evanescent wave when the beam current is above a certain threshold, and consequently induces the superradiant Smith–Purcell radiation. The threshold current is derived as well.

We investigate the properties of a multimode-interference (MMI) coupled ring cavity resonator with total-internal-reflection (TIR) mirrors and a semiconductor optical amplifier (SOA) in an InGaAsP material system. The TIR mirrors were fabricated by the self-aligned process with a loss of about 1.4 dB per mirror. The resulting free spectral range (FSR) was approximately 0.8 nin (97 GHz) near 1569 rim. The on-off ratio and the full width at half maximum (FWHM) were 8 dB and 0.152 nm, respectively, corresponding to a finesse of 5.2 and a Q factor of 10,322. Hence, such resonators can be directly integrated with other devices making possible the fabrication of compact and highly functional photonic integrated circuits.

A frequency converter based on a BaxSr1-xTiO3 (x=0.5) (BST) film was successfully realized using the nonlinearity of the film. Frequency conversion occurred due to the distortion of a signal across the BST film, because the relation between electric charge and external bias is nonlinear in the film. Frequency conversion at low frequency from 2 to 6 MHz and 4 to 12 MHz was realized using a parallel-plate BST capacitor. Frequency conversion at high frequency from 500 MHz to 1 GHz was demonstrated, yielding a conversion loss of 30 dB at an input power of 19 dBm. The conversion loss of the frequency converter can be improved by increasing the input power on a BST film.

Metal oxide nanoparticles are embedded in a polyimide matrix by a chemical reaction between a metal thin film and polyamic acid. The electrical characteristics of ZnO nanoparticles are investigated with a floating gate capacitor structure by capacitance–voltage (C–V) measurement. The C–V characteristics resulting from metal deposition modulation and the existence of a SiO2 layer are also investigated. As a result, ZnO particles with a SiO2 tunneling barrier show a C–V hysteresis voltage gap of 2.8 V at 300 K. ZnO particles directly located on a Si substrate show a C–V hysteresis width of 1.5 V at 80 K. This electrical characterization is discussed for applications to nano floating-gate memory devices.

The effect of the calcination process for cerium carbonate, a precursor of ceria, on the degree of synthesis and colloidal properties of ceria particles in aqueous media, which greatly influence shallow trench isolation (STI) chemical mechanical planarization (CMP) performance, was investigated. A two-step calcination process, consisting of decarbonation and crystal growth, resulted in a higher degree of synthesis for the same crystal size, a narrower particle size distribution, and better dispersion of the ceria particles, than conventional one-step calcination. These properties enhanced certain aspects of STI CMP performance, leading to a higher oxide removal rate, a better selectivity between oxide and nitride, and fewer defects, including remaining particles.

The dependencies of the non-Prestonian behavior of ceria slurry with anionic surfactant on the size and concentration of abrasive particles were investigated by performing chemical mechanical polishing (CMP) experiments using blanket wafers. We found that not only the abrasive size but also the abrasive concentration with surfactant addition influences the non-Prestonian behavior. Such behavior is clearly exhibited with small abrasive sizes and a higher concentrations of abrasives with surfactant addition, because the abrasive particles can locally contact the film surface more effectively with applied pressure. We introduce a factor to quantify these relations with the non-Prestonian behavior of a slurry. For ceria slurry, this non-Prestonian factor, βNP, was determined to be almost independent of the abrasive concentration for a larger size and a smaller weight conentration of abrasive particles, but it increased with the surfactant concentration for a smaller size and a higher concentration of abrasives with surfactant addition.

Hot-carrier effects in body-tied fin-type field effect transistors (FinFETs) are investigated. As the gate bias increases, coupling effects of two gates facing each other suppress the lateral channel electric field more effectively at double gate metal oxide FETs (MOSFETs) than at single gate MOSFETs. In double gate FinFETs, this effect is even further enhanced when the fin width is narrowed. The substrate current produced by an impact ionization process becomes large as fin width increases. In the generalized substrate current model, the maximum substrate current bias condition is approximately VG/VD~0.5. However, in the double-gate FinFETs, it was (VG-VT)/VD~0.3. There are two competing stress conditions: the maximum substrate current condition, and the maximum gate current condition. Device degradation is compared for various fin widths after both type of stress. It was found that the maximum substrate current stress condition degraded the device more significantly. The narrow fin is more immune to both stress biases than the wide fin. Thus, the narrow fin is appropriate for further device scaling and reliability. The supply voltage which corresponds to a 10-years lifetime was 1.31 V for the worst hot-carrier stress case.

The charging tendency of a Zn2SiO4:Mn2+ phosphor surface was modified in order to improve the discharging characteristics of green cell in an ac-plasma display panel (ac-PDP). The zinc silicate (Zn2SiO4:Mn2+) green-emitting phosphor was coated with magnesium oxide (MgO), which has a positive charge on the surface. After fabricating a green cell with MgO-coated Zn2SiO4:Mn2+, the electrical and optical properties were examined. It was found that the dynamic voltage margin could be increased while decreasing address time. This may be ascribed to a change in the charging tendency of Zn2SiO4:Mn2+ phosphor by the MgO coating, which makes stable wall-charge accumulation possible. When Zn2SiO4:Mn2+ phosphor was coated with 1.3 wt% MgO, the address time was decreased to 1.2 µs and the address voltage lowered to 25 V without any misfiring problem, compared with those of a noncoated Zn2SiO4:Mn2+ phosphor layer. The luminescence intensity of the green cell using the MgO-coated phosphor layer was also improved by 10%.

In e-beam projection lithography (EPL) systems, the relativistic focus condition was derived and compared with the nonrelativistic focus condition to investigate the effect of a large acceleration field related to the initial energy and emission angle of an electron emitted from a cathode. The difference in confusion disk between the relativistic and nonrelativistic limits was 180 nm when 1 eV was used as the initial energy of the electron. The variation in the initial energy of the electron was more sensitive to change the confusion disk than the acceleration field. In this comparison, the focusing parameters are used as follows: axial magnetic field, 0.5 T, distance between the mask layer and the workpiece, 2 mm and emission angle of the electron, 30°.

Due to its ability to produce nanosized patterns on large area substrates with high throughput, UV curing nanoimprinting lithography is a promising technology for nanosized pattern fabrication. However, for it to become a technology for the mass production of nanosized patterns, we must first show that UV curing imprint lithography can produce a uniform layer with minimal residue. In this study, a pressurized chamber imprinting system was used. Isotropic pressure was applied to insure effective delivery of pressing force and uniform pressing. A UV curable resin, consisting of a perfluorinated acrylate and a photo-initiator, was used. The factors determining residual layer thickness in UV curing imprint lithography were investigated. To obtain imprinted patterns with no residual layer, a thin and uniform initial resin layer and pressurized imprinting must be used to rearrange the resin effectively. The high fidelity transfer of various patterns as small as 150 nm with no residual layer was successfully demonstrated by controlling the initial resin thickness at an imprint pressure of 15 atm.

The reverse selectivity of nanosized ceria slurry for the damascene gate chemical mechanical planarization (CMP) process has been investigated. The relationship between the electrokinetic behaviors of abrasive ceria particles and the plasma-enhanced tetraethylorthosilicate (PETEOS), and CVD Si3N4 films in an aqueous medium were observed to determine the reverse selectivity performance in the CMP process. The surface potentials of abrasive and PETEOS/CVD Si3N4 films were found to have different surface charges in certain pH regions and these differences were found to be key parameters in the selective removal performance of damascene gate CMP process. The ceria slurry with polymeric additives showed reverse selectivity with a low PETEOS removal rate and a high CVD Si3N4 film removal rate.

By considering the physical characteristics of ceria particles, the factors affecting the chemical mechanical planarization (CMP) performance for shallow trench isolation (STI) were investigated. Ceria powders were synthesized by calcination at temperatures of 400, 600, 700, 800, and 900°C. The influence of the calcination temperature on the physical characteristics, such as the crystallinity, grain size, porosity, morphology and high-resolution lattice images of the ceria particles, were investigated, and a correlation between the physical characteristics and the electrokinetic behaviors of the ceria particles in aqueous suspending media was also investigated to identify the relationship with CMP performance. Grain size increased with calcination temperature, as did the removal rate of plasma-enhanced tetraethylorthosilicate (PETEOS) film with slurries including these particles. The results indicate that the grain size of ceria particles is one of the key parameters controlling the removal rate and uniformity of PETEOS film.

The interactions between buried defects and impurities formed by MeV-level nitrogen ion implantation in silicon have been investigated. The interactions between the oxygen atoms in a CZ Si wafer and the defects introduced during annealing after implantation are discussed in terms of the amount, nature, morphology, and depth distribution of the defects. Oxygen atoms are found to be gettered in two different regions in the implanted layers. A shallow oxygen peak appears in regions near the surface (between 0.5 and 1.5 µm). A deep oxygen peak is also observed at locations with secondary defects, which mainly consist of elongated dislocation loops and dislocation networks. In this case, the gettered oxygen content is not especially influenced by the amount or nature of the generated defects. Rather, there is a good correlation between the gettered oxygen amount and the mismatch stress induced by the atomic radius difference.

In a ceria slurry with an ionic surfactant, the grain size and particle size of the poly-crystalline abrasives were controlled independently by changing the calcination temperature and the mechanical milling time, respectively, during abrasive synthesis. A chemical mechanical polishing (CMP) experiment using the slurry showed that the oxide removal rate increased with both the grain size and the abrasive particle size, while the nitride removal rate was independent of both. On the other hand, examination of the nanotopography impact showed that the planarization efficiency increased with decreasing abrasive size but was independent of the grain size.

We investigated the nanotopography impact on the post-chemical mechanical polishing (post-CMP) oxide thickness deviation (OTD) and the non-Prestonian behavior of ceria slurry with a surfactant. Not only the surfactant but also the slurry abrasive size influenced the non-Prestonian behavior and the nanotopography impact. We created a one-dimensional numerical simulation of the nanotopography impact by taking account of the non-Prestonian behavior of the slurry, and good agreement with the experimental results was obtained. After examining the mechanism of oxide surface planarization during CMP, an index to relate the non-Prestonian behavior of the slurry to the nanotopography impact was developed.

We used a blank chemical mechanical polishing (CMP) test to examine the dependence of nanotopography impact on surfactant concentration in three ceria slurries differing in abrasive size. We found that the magnitude of film thickness variation after CMP increased with the surfactant concentration in case of the smaller abrasives but for the case of larger abrasive was almost independent of the surfactant concentration. This result was explained with a model based on the passivation layer of the surfactant adsorbed on the oxide film surfaces during polishing.

In the fabrication of the practical helix slow wave structure (SWS), the misalignment or the dielectric constant variation in its support is not avoidable and, thus, causing azimuthal asymmetry in the structure. Therefore, the analysis of the asymmetric structure becomes an important issue. In this study, rigorous field analysis of a general asymmetric helical SWS was done by considering the structure as a helix supported by n wedge shaped dielectric supports, enclosed in a metal envelope. To consider the angular harmonic effect, the dielectric was not smoothed out. Using the present theory, the dispersion characteristics of the asymmetric helical structure were obtained. The study of the dispersion characteristics of the asymmetric structure revealed the stopband characteristics near the π-phase-shift point. This result was compared with that obtained from 3D FEM code, high frequency structure simulator (HFSS) and found to be in good agreement. It was also found that the asymmetry in the structure lowered the phase velocity and the cut-off frequency but increased the stopband width.

A stationary 1-D nonlinear code based on Lagrangian disk model is developed on the basis of a simple set of analytical expressions to study nonlinear dynamics in the helix slow-wave structure used in a traveling wave tube. The loss profiles such as triangular and Gaussian types are modeled as stairsteps and a simple formula is developed to found the loss at a plane for such loss profile. In contrast to the earlier works in nonlinear theory, at present, no numerical method is used at any stage. The method, introduced in this work, is general in nature because it can handle (a) multi-section structure with sever, (b) different loss profiles, namely, center (Gaussian) and tip (triangular: increasing or decreasing), (c) space charge effect on the electrons, (d) backward waves arising due to reflections, etc. Accuracy of the theory and code is verified with comparison of the computed present results with the results from simulation code MAGIC and published elsewhere and found to be in good agreement. The generation and suppression of the harmonic power are studied for a typical structure. It is found that the introduction of resynchronization section of the reduced pitch enhances the fundamental power with the reduction of the second harmonic power. In addition, the method can be used for any helix slow-wave-structure consisting of homogeneous/inhomogeneous dielectric support rods in isotropic/anisotropic overall metallic enclosure, because the axial propagation constant and interaction impedance obtained for any structure and model such as sheath and tape helix approximations or from any simulation codes can be used as the input in the program to make the code more general.

Through a chemical mechanical polishing (CMP) test using oxide and nitride blanket film wafers, we investigated the effect of adding an anionic surfactant to a ceria slurry, especially at very dilute concentrations (less than 0.2 wt%). The removal rate trend, which decreases with increasing surfactant concentration, was compared with the variation in the electrokinetic behavior of the ceria abrasives dispersed in the slurry. The removal rate transition did not coincide with the changes in the zeta potential or the secondary particle size distribution of the abrasives. This suggests that the electrostatic effect is not the dominant factor in the removal rate with ceria slurry. It is also found that abrasive size influences removal rate trend versus surfactant concentration, and that oxide removal follows Preston's law but nitride removal shows non-Prestonian behavior. To explain the result qualitatively, we have proposed a hydrodynamic model in which a particle travels through the viscous fluid and approaches the film surface.

Ceria powders were synthesized by two different methods, solid-state displacement reaction and wet chemical precipitation, and the influence of the physical characteristics of cerium oxide on the removal rate of plasma-enhanced tetraethylorthosilicate (PETEOS) and chemical vapor deposition (CVD) nitride films in chemical mechanical planarization (CMP) was investigated. The fundamental physicochemical property and electrokinetic behavior of ceria particles in aqueous suspending media were investigated to identify the correlation between the colloidal property of ceria and the CMP performance. The surface potentials of two different ceria particles are found to have different isoelectric point (pHiep) values and differences in physical properties of ceria particles such as porosity and density were found to be the key parameters in CMP of PETEOS films. Ceria powders synthesized by the solid-state displacement reaction method yielded a higher removal rate of PETEOS and higher selectivity than powders synthesized by the wet chemical precipitation method.

To reveal the mechanism behind the high oxide-to-nitride removal selectivity of ceria slurry in shallow trench isolation (STI) chemical mechanical polishing (CMP), we examined the effects of the abrasive morphology and the concentration of surfactant added to control the selectivity. A slurry with small abrasives showed a more drastic drop in the oxide removal rate as the surfactant concentration increased, compared to a slurry with large abrasives. For the nitride removal rate, however, both slurries showed the same trend. These results can be qualitatively explained from the movement of abrasives though the layer of surfactant adsorbed on the film surface.

The characteristics of an axis-encircling electron beam using an annular Pierce-type electron gun are calculated analytically. The analytical calculation is carried out by considering the initial canonical angular momentum spreads at the cathode and the crossing of the electron beam with the magnetic flux line before the magnetic cusp. The analytically calculated characteristics of an axis-encircling electron beam such as the axial velocity spread, the velocity ratio, the Larmor radius, and the guiding center radius are in good agreement with the simulated result obtained using an electron trajectory program. In this comparison, a 30 kV, 1.0 A electron beam is used with a peak magnetic flux density of 4.38 kG using the magnetic field with a single cusp. The result obtained by this analysis also shows that the electron beam with a fairly low axial velocity spread of less than 1% can be realized by employing a suitable distance between the cathode and magnetic cusp.

Using numerical simulations, a wideband (>1.5 octave) vane loaded helix traveling-wave tube (TWT) was studied, the output section of which is provided with a `positively' phase velocity tapered helix portion, in which the helix pitch is made to linearly increase with distance towards the output end for reasonably high efficiency values. As compared to a device with a conventional 'negatively' phase velocity tapered helix portion, which gives an efficiency hike only in a narrow band of frequency, the positively tapered device provided a wideband efficiency improvement. Also, over the band, it provided a higher efficiency and a lower second harmonic content than a device with a nontapered portion. Factors such as the beginning position of the taper from the input and the amount of taper were considered in the optimum design for improving efficiency and reducing the second harmonic content of the device.