摘要:

The two-photon absorption (TPA), TPA-induced frequency upconversion emission, and two-photon-pumped (TPP) lasing properties of a new dye,trans-4[p-(N-hydroxyethylN-methylamino)stryryl]-N-methylpyridinium iodide (abbreviated as ASPI) were experimentally investigated. This new dye has a moderate TPA cross section (&sgr;2≈3.9×20−20cm4/GW in benzyl alcohol), but exhibits a low lasing threshold and high lasing efficiency when pumped with a 1064 nm pulsed laser beam. Furthermore, the TPA-induced fluorescence yield is strongly dependent on the polarity of the solvent, making it a promising dye for sensing applications. The spectral, temporal, and spatial structures as well as the output/input characteristics of the TPP cavity lasing and the superradiant (cavityless) lasing are systematically measured using a 1 cm path quartz cuvette filled with the ASPI solution or a doped polymer rod. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the ∼615 nm upconverted cavity lasing energy was found to be as high as ∼17&percent;. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364303

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A Beer’s law expression for the penetration depth of ultraviolet radiation in a concentrated suspension of scattering particles is used to model the depth of cure for a suspension of ceramic particles in a medium of photocurable monomers. The cure depth is predominantly controlled by the square of the refractive index difference between the ceramic particles and the medium,&Dgr;n2=(np−n0)2. A secondary effect on the cure depth is the ratio of the interparticle spacing to the ultraviolet wavelength. Theoretical results agree with experimental data for 0.40–0.50 volume fraction ceramic-filled suspensions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364311

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effects of ion collisions in the plasma sheath on etch profiles of a long trench is modeled. The pattern transfer step is for trilayer lithography where the photoresist etches down to a silicon dioxide mask and the trench is etched in the substrate. The etch rate in the ion flux-limited regime varies as the ion energy flux which is calculated from the ion velocity distribution function. The form of the ion velocity distribution function consists of a sum of drifted Maxwellians. This sum fits experimental data for ion energy distribution functions with angular dependence for an argon plasma by a simulated annealing optimization procedure. Etch rate expressions for a drifted Maxwellian in a collisionless sheath are extended to the collisional sheath. The etch profiles are computed numerically by integration of characteristic equations for the profile points and by numerical computation of the profile at a given time. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363918

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A carbon-nitride compound with defect zincblende structure (P4¯3m) has been discovered in samples prepared by a chemical precursor route. Crystallographical (high-resolution electron microscopy and electron nanodiffraction) and electron energy loss measurements has been performed to identify the material as cubic zincblende with C3N4composition. Nanoindentation indicates a high elastic recovery and hardness. The results agree with detailedab initiocalculations on metastable structures and compressibility. Our synthesis method is projected to be a process that could produce large quantities of material by controlling the chemical strategy. The new compound has potential applications for high hardness, elasticity and thermal conductivity materials and thin films. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364301

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of fluorine upon the annealing behavior at 450–500 °C of BF2+implanted layers on silicon wafers was investigated by measurement of the sheet resistance, the carrier profile, and the crystallinity. The junction leakage current was also measured. Approximately one order of magnitude retardation in the average regrowth rate and lower electrical activation of implanted boron were observed in BF2+implanted layers as compared with B+implanted preamorphized layers. However, a leakage current level as low as 1.97×10−9A/cm2was measured, which is about three orders of magnitude less than reported in the literature. This result was obtained in the BF2+implanted siliconp+njunction at an annealing temperature as low as 500 °C by employing ultraclean ion implantation techniques. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364444

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the lattice sites of ion-implanted radioactive33P in natural IIa diamond using the emission channeling technique.33P ions were implanted at room temperature with 30 keV and a rather low dose of 1011cm−2and the implanted samples were annealed in vacuum to 1200 °C. From the channeling effects of the emitted &bgr;−particles measured for all principal axial directions we obtain a fraction of 70±10&percent; of substitutional P, a vanishing fraction on tetrahedral interstitial sites and a 30&percent; random fraction. Possible displacements of the P atoms from ideal substitutional sites must be below 0.2 Å. This demonstrates that P is a substitutional impurity in diamond and efficient substitutional P doping of diamond can be accomplished by a conventional implantation and annealing procedure if low implantation doses are chosen. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363919

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electron-induced amorphization of coesite was studied as a function of irradiation temperature byin situtransmission electron microscopy at an incident energy of 200 keV. Electron-induced amorphization of coesite is induced by an ionization mechanism and is mainly dominated by an interface-mediated, heterogeneous nucleation-and-growth controlled process. Amorphous domains nucleate at surfaces, crystalline-amorphous (c-a) interfaces, and grain boundaries. This is the same process as the interface-mediated vitrification of coesite by isothermal annealing above the thermodynamic melting temperature (875 K), but below the glass transition temperature (1480 K). The interface-mediated amorphization of coesite by electron irradiation is morphologically similar to interface-mediated thermodynamic melting. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363920

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new damage function suitable for metals under dynamic loading, based on the physical statistics of microvoids in metals and the law of conservation of energy, is presented in this article. This new damage model has a sound physical or theoretical foundation and fewer adjustable or empirical parameters than most existing models. Several hydrodynamic elastic-plastic numerical modeling experiments that use this damage function combined with the proper constitutional equations have been conducted by us and the results are in good agreement with previously published experimental results on different metals with different geometries. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363921

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A series of experiments have been conducted on metals subjected to planar impact loading in which a biaxial stress state and a uniaxial strain state is induced. Longitudinal and transverse stresses have been measured in copper, iron, and mild steel, using manganin stress gauges. The results have been used to calculate shear stress from the difference between the stress components. Results indicate that copper displays an increase in shear stress with pressure, showing similar trends to other work. An increase in dislocation density has been suggested as a possible mechanism. Iron shows a constant shear stress with increasing pressure, again in accordance with other workers. Finally, mild steel has been observed to have a significant increase in shear stress with increasing pressure. The inclusion of a hard second phase in the microstructure is thought to produce a large amount of dislocation debris, again explaining the observed hardening. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363967

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The specific heatcand the heat powerWexchanged by a Deuterated Potassium Dihydrogen Phosphate ferroelectric-ferroelastic crystal have been measured simultaneously for both decreasing and increasing temperature at a low constant rate (0.06 K/h) between 175 and 240 K. The measurements were carried out under controlled uniaxial stresses of 0.3 and 4.5±0.1 bar applied to face (110). AtTt=207.9K, a first order transition is produced with anomalous specific heat behavior in the interval where the transition heat appears. This anomalous behavior is explained in terms of the temperature variation of the heat power during the transition. During cooling, the transition occurs with coexistence of phases, while during heating it seems that metastable states are reached. Excluding data affected by the transition heat, the specific heat behavior agrees with the predictions of a 2-4-6 Landau potential in the range of 4–15 K belowTtwhile logarithmic behavior is obtained in the range fromTtto 1 K belowTt.Data obtained under 0.3 and 4.5 bar uniaxial stresses exhibit the same behavior. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363922

出版商:AIP    

年代:1997

数据来源: AIP