摘要:

ZnO (zinc oxide) thin films have been prepared by using rf magnetron sputtering on a SiO2/Si substrate. The crystallographic properties and optical properties were investigated. It is shown that the ZnO films exhibit strongc‐axis orientation. The standard deviation of thecaxis was obtained less than 1°. The optical propagation loss was less than 2 dB/cm (TE0mode) in a 0.6‐&mgr;m‐thick film. To achieve the ZnO films with low light propagation loss, it was found that we must take into account not onlyc‐axis orientation of ZnO films but also the density of ZnO films.

ISSN:0021-8979    

DOI:10.1063/1.354091

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The third‐order nonlinear optical susceptibility &khgr;(3)(−3&ohgr;;&ohgr;,&ohgr;,&ohgr;) of propylmethylpolyazine thin films as measured by the third harmonic generation is reported. The &khgr;(3)(−3&ohgr;;&ohgr;,&ohgr;,&ohgr;) values of propylmethylpolyazine that possess statistically alternating methyl and propyl substituents on the carbon atoms along the conjugated chain were found to be 8.0×10−12esu off resonance at 1.5 &mgr;m fundamental radiation. The interesting third‐order nonlinear properties presumably originate from the unique periodicity of the main &pgr;‐electron‐conjugated polyazine backbone.  

ISSN:0021-8979    

DOI:10.1063/1.353837

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Laser induced ultrasonic standing waves are observed in molecular beam deposited ZnSe thin films using the transient grating technique. This observation is attributed to a very short trapping time for single photon absorption in the band tail. The period of the standing wave is used to determine the acoustic phonon velocity in the ZnSe thin film which indicates that it is longitudinal acoustic phonons which are excited.

ISSN:0021-8979    

DOI:10.1063/1.353838

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The Stark broadening parameters of the 1990.53, 2631.55, 2669.17, 2816.18, 3900.68, and 5593.23 A˚ lines of Al(II) have been measured in a plasma produced by ablation with a Nd:YAG laser of an aluminum target. In order to obtain suitable experimental conditions for the homogeneity and stability of the plasma a study of the spatial and temporal plasma evolution in helium, argon, and nitrogen at different pressures was made. The broadening parameters were obtained with the aluminum target placed in molecular nitrogen at 1000 mbar, which provides appropriate measurements conditions. The Al(II) 4663.05 A˚ line was used to determine the electron density in all cases. For this line the Stark shift parameter has been measured. Contributions to broadening arising from mechanism different than Stark broadening were estimated for every studied line.

ISSN:0021-8979    

DOI:10.1063/1.353839

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The numerical plasma torch model of D. A. Scott, P. Kovitya, and G. N. Haddad [J. Appl. Phys.66, 5232 (1989)], in which both the arc and plume regions are included in the computational domain, has been extended to treat the effect of the mixing of the plasma gas with the ambient gas. Both laminar diffusion and turbulent mixing are considered. The predictions of the model are compared with laser‐scattering measurements of the temperature distribution in the plume of a plasma torch, for the case in which the plasma gas is argon and the ambient gas is air at atmospheric pressure. Good agreement is found between the measurements and the predictions of the model. The rapid decay in plume temperature away from the exit of the torch nozzle is shown to be mainly due to cooling by air entrained by turbulent mixing. TheK‐&egr; turbulence model is found to adequately approximate the turbulence phenonema involved.

ISSN:0021-8979    

DOI:10.1063/1.353840

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In plasma source ion implantation (PSII), a target to be implanted is immersed in a weakly ionized plasma and pulsed to a high negative voltage. Plasma ions are accelerated toward the target and implanted in its surface. In this article, two factors in the analysis of these discharges are examined for the first time: (1) displacement current across the expanding sheath results in increased implant current and decreased implanted ion energy, with respect to existing models; and (2) ion depletion around the target due to high pulse repetition rates results in decreased implant current and dose. These effects are studied with analytic models and particle‐in‐cell simulations. Simulation results are compared to previously published PSII models.

ISSN:0021-8979    

DOI:10.1063/1.353841

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Plasmas are generated in a low ionization potential gas, tetrakis(dimethylamino)ethylene (TMAE) vapor through a one‐photon ionization process by an ultraviolet laser beam at a 193 nm wavelength. The TMAE plasma characteristics are studied by means of a Langmuir probe and microwave scattering. A new method is used to measure the 193 nm ultraviolet (UV) photon absorption cross section in TMAE. It is determined to be 1.1±0.3×10−17cm2from the axial profile of electron density. The temporal evolution of electron temperature is measured. A peak electron density ofne=5×1013/cm3and peak electron temperature ofTe=1 eV are measured at 500 mTorr TMAE pressure. The plasma decay process is studied, and the electron‐ion recombination coefficient is measured to be 5.4±0.5×10−6cm3/s. A theoretical model is derived to describe the photon flux and the one photon ionization process. An application of a TMAE plasma as a mirror for microwave reflections is proposed.

ISSN:0021-8979    

DOI:10.1063/1.353842

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

This article describes the results of measurements of the plasma parameters, plasma potential &Fgr;, positive ion densityn+ , electron densityne, electron temperatureTe, and electron energy distribution function (EEDF)f(&egr;) within and near the electrostatic particle traps in an argon process plasma. The measurements have been made with a tuned Langmuir probe at a constant set of system parameters: 250 W, 13.56 MHz power, 15 mTorr, and 10 sccm flow of Ar. The electrostatic traps have precisely defined boundaries characterized by a sharp increase in &Fgr; of about 6 V as we have described elsewhere. We show here that during an initial mapping period of 0–10 min after the rf power is turned abruptly on (10 min are required to map 48 points),n+is continuous across a trap boundary as areneandTe.kTe/e≊6.5 eV uniformly throughout the mapped region. If the mapping is repeated later att=30–40 min whilen+is still continuous and does not show any change in its values in time,nehas decreased by 42% within the trap compared to the region outside the trap which we call the ambient plasma region. Also,kTe/ehas increased within the trap to 8 eV while the ambient plasma remains at 6.5 eV. If the mapping is again repeated att=60–70 min,nehas decreased by 56% of its value in the ambient plasma andkTe/ehas increased within the trap to 10 eV. This picture is consistent with the postulation that we have made previously that the trap initially contains few particles and is created by the system configuration and not particles; the trap then slowly fills with negatively charged particles. In order to maintain charge neutrality within the trapnemust decrease. Also, since the particles allow recombination to occur on their surfaces, the electron temperature must increase within the trap in order that generation can keep up with increased recombination. Finally, the EEDF appears to be Maxwellian in the ambient plasma but non‐Maxwellian within the trap. In both cases, the EEDF has an attenuated high energy tail.

ISSN:0021-8979    

DOI:10.1063/1.353843

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

It is shown that J. Lothe’s theorem [Philos. Mag.15, 353 (1967)] is also valid for piezoelectric materials by replacing the energy factor. Its proof follows L. M. Brown’s procedure [Philos. Mag.15, 363 (1967)]. The forces on dislocation bends in lithium niobate are numerically calculated.

ISSN:0021-8979    

DOI:10.1063/1.353844

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Afterexsituetching with various solutions of hydrofluoric acid (HF) and ammonium fluoride (NH4F) Si(111) samples are transferred into ultrahigh vacuum with an ultrafast load‐lock and characterized by scanning tunneling microscopy (STM): Concentrated HF selectively removes any surface oxide and, thus chemically prepares the initially burried, isotropically rough Si/SiO2interface while highly buffered HF (i.e., NH4F) attacks bulk silicon anisotropically. After a rapid homogenization of the chemical surface termination (HF: various hydrides, fluorine, ...) towards a perfect, unreconstructed monohydride phase, Si(111)‐(1×1):H, NH4F etching leads to a time‐dependent transformation of isotropic roughness into a pattern of triangular etch defects with monohydride steps perpendicular to <2¯11≳ due to a preferential removal of lower‐coordinated atomic defect sites. A predominant atomic step structure due to sample miscut (vicinal surfaces with azimuth ≠<2¯11≳) can oppose the anisotropic NH4F etching: At low step density (small polar angle of miscut) a meandering of atomic steps with straight monohydride portions is observed while at high step density strong step‐step interaction counterbalances anisotropic removal and forces an etching by a homogeneous flow of (nonmonohydride) steps along the macroscopic misorientation. Local findings obtained with STM are compared to macroscopically averaged results from a simultaneous quantitative analysis of low‐energy electron diffraction profiles.  

ISSN:0021-8979    

DOI:10.1063/1.353845

出版商:AIP    

年代:1993

数据来源: AIP