摘要:

The composition and structure of crystalline silicon implanted with carbon ions at high dose were studied using spectroscopic ellipsometry. A brief description of our spectroscopic ellipsometer system and the modeling method adopted for the analysis of the data are included. The crystal damage caused by carbon‐ion implantation in the as‐implanted sample was characterized as an amorphous region of atomic or chemical mixture of silicon and carbon atoms. The recrystallization of Si and the formation of crystalline silicon carbide on annealing these specimens at 800 °C and 1000 °C were investigated through similar spectroscopic ellipsometry studies.

ISSN:0021-8979    

DOI:10.1063/1.345304

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper is concerned with a basic study of optical cavitation or cavitation induced by a high intensity laser beam. The work deals with the collective behavior of several bubbles induced independently and simultaneously. The experimental setup to produce and to visualize bubbles and shock waves in the liquid (water) is described. Bubbles dynamics in an infinite medium is displayed in sequential photographs (framing and streak). The visualizations show such interesting results as strong asymmetries, deformations, attraction or repulsion, and premature implosion due to bubble‐interface/shock‐wave‐radiated‐upon‐collapse impact.

ISSN:0021-8979    

DOI:10.1063/1.345305

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The propagation of a normal shock wave into the CO2‐N2‐He gas mixture seeded with solid particles is analyzed. The translation‐vibration and vibration‐vibration molecular energy exchange processes in the gas mixture are included in the analysis. The results indicate the creation of population inversions due to these processes in the relaxation region behind the shock wave for transitions at 50 and 22 &mgr;m in CO2molecules. The presence of solid particles in the flow is found to be advantageous for observing the laser radiation behind the shock wave. Effects of the frozen shock Mach number, the particle size, the particle‐to‐gas mass loading ratio, and the laser gas mixture composition on the population inversions are discussed.

ISSN:0021-8979    

DOI:10.1063/1.345306

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Surface plasmon microscopic pictures recorded as a function of the angle of incidence of the coupling laser beam can be quantitatively evaluated and yield optical thicknesses of ultrathin coatings with an areal resolution of 5×5 &mgr;m2. This is demonstrated for a lipid monolayer transferred to a solid support in its phase transition region. The coexisting amorphous and crystalline domains can be analyzed simultaneously.

ISSN:0021-8979    

DOI:10.1063/1.345307

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A quasilinear theory of the self‐consistent evolution of the electron‐beam distribution and radiation field within a free‐electron laser is presented. The relativistic electron beam propagates through an ideal helical wigglerB0=−Bw(cos kwzeˆx+sin dwzeˆy), for which the transverse gradients ∂/∂x=0=∂/∂yhave been neglected. The transverse variation of both the transverse‐polarized radiation field and the electron‐beam distribution have also been neglected. Additionally, the electron beam is assumed to be sufficiently tenuous that the longitudinal space‐charge potential &dgr;&fgr; is negligible and the Compton approximations are applicable. The resulting asymptotic expression for the spectral energy density is used to evaluate the efficiency and saturated radiation power in a variety of parameter regimes relevant to experiments.

ISSN:0021-8979    

DOI:10.1063/1.345308

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In a Smith–Purcell amplifier, the guiding magnetic field couples the TE and TM modes. However, for an incident TM wave it is shown that the scattered TM waves can be determined with the induced TE waves neglected, the latter being treated within a first‐order approximation. The response function of the amplifier for the TM waves is derived, and the dependence of its poles on the intensity of the guiding magnetic field is investigated. It is found that there are five poles, two of them complex, irrespective of the guiding field intensity and related to the ‘‘pure’’ slow‐wave‐structure poles; two other poles may be complex only if the cyclotron frequency is below a ‘‘cutoff’’ (determined explicitly) and resemble ‘‘gyrotron’’ poles. The cutoff is shown to be proportional to the shift (due to collective effects) in the radiation wave vector. The first pair of poles emerges from the longitudinal electronic oscillation, while the second pair corresponds to the transverse oscillation. The real pole into which the gyrotronlike poles degenerate is precisely the third pole, which occurs in slow‐wave structures under strong magnetic fields. By a suitable choice of the magnetic field a 10% increase is obtainable in the gain of the amplifier; this optimal field is determined and shown, within the relevant range of parameters, to be linear with the device length.

ISSN:0021-8979    

DOI:10.1063/1.345309

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A method to determine large optical absorption coefficients of liquids from the amplitude ratio of acoustic waves generated under rigid‐ and free‐boundary conditions is presented. This has been examined both experimentally and theoretically, taking into account the attenuation of the pulse amplitude ratio with the increased acoustic path length due to attenuation effects. Although the proposed method was tested in a narrow wavelength interval and close to the limit of precision of the experimental arrangement, the results show quantitative agreement with the literature values.

ISSN:0021-8979    

DOI:10.1063/1.345310

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Some properties of laser‐generated plasma emission in the soft x‐ray region (0.1 keV<h&ngr;<1.5 keV) are presented. Detailed spectral distributions are reported for several kinds of materials (carbon, aluminum, titanium, copper, zinc, molybdenum, tin, tungsten, and lead). Dependence of x‐ray emission on focal size and target thickness is also studied. The experiments were carried out at a laser intensity of a few times 1012W/cm2using Nd‐doped phosphate zigzag glass slab laser (8 J/40 ns, &lgr;=1.054 &mgr;m). As an application of the laser‐generated plasma x rays, the sensitivity of FBM‐120 resist for x‐ray lithography was measured and a 0.25‐&mgr;m‐wide space mask pattern was replicated.

ISSN:0021-8979    

DOI:10.1063/1.345311

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Chemical species responsible for diamond growth were examined byinsitumethods using a microwave plasma jet from Ar‐H2‐CH4/C2H2. Irrespective of the reactants, diamond was successfully deposited, and morphology was likely to depend only upon the carbon equivalent concentration in the gas phase. Emission spectroscopy revealed that the C2radical was the main emissive species in the plasma, and that its vibration temperature was estimated to be about 5000 K with little dependence on the axial position. Moreover, emission from just above the substrate showed a considerably lower concentration ratio of H atom to C, including radicals, than the case of low‐pressure microwave plasma. On the other hand, mass spectroscopy mainly detected CH4and C2H2in the species impinging on a substrate. The importance of kinetic processes in a boundary layer was strongly emphasized.

ISSN:0021-8979    

DOI:10.1063/1.345312

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Etch rates of tantalum in tetrafluoromethane‐oxygen and hexafluoroethane‐oxygen rf glow discharges were measuredinsituas functions of pressure, reactor residence time, temperature, and applied plasma power. A dramatic increase in the etch rate was observed as the pressure increased. In addition, two distinct temperature regimes occurred in Arrhenius plots. Such data suggest strong effects due to heat of reaction in the Ta/CF4‐O2etch system. The observed etch‐rate pressure dependence can be explained by assuming first‐order kinetics for the reaction of fluorine atoms with tantalum. Evidence for etch‐rate quenching at high pressures due to an increase in the deposition of an inhibiting fluorocarbon surface layer is presented.

ISSN:0021-8979    

DOI:10.1063/1.345313

出版商:AIP    

年代:1990

数据来源: AIP