摘要:

Erbium doped materials are of great interest in thin film integrated optoelectronic technology, due to theirEr3+intra-4femission at 1.54 &mgr;m, a standard telecommunication wavelength. Er-doped dielectric thin films can be used to fabricate planar optical amplifiers or lasers that can be integrated with other devices on the same chip. Semiconductors, such as silicon, can also be doped with erbium. In this case the Er may be excited through optically or electrically generated charge carriers. Er-doped Si light-emitting diodes may find applications in Si-based optoelectronic circuits. In this article, the synthesis, characterization, and application of several different Er-doped thin film photonic materials is described. It focuses on oxide glasses (pureSiO2,phosphosilicate, borosilicate, and soda-lime glasses), ceramic thin films (Al2O3,Y2O3,LiNbO3), and amorphous and crystalline silicon, all doped with Er by ion implantation. MeV ion implantation is a technique that is ideally suited to dope these materials with Er as the ion range corresponds to the typical micron dimensions of these optical materials. The role of implantation defects, the effect of annealing, concentration dependent effects, and optical activation are discussed and compared for the various materials. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366265

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Using the well explored endoreversible heat engine as an example, this article shows how an endoreversible model fits the general framework of nonlinear nonequilibrium thermodynamics. The heuristic power of endoreversible thermodynamics is stressed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365829

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The static friction regime of an atomic force microscope tip on a soft material is analyzed. A mechanical model shows that the experimental response is characteristic of the complex modulus of the sample. Moduli deduced from experiments on styrene-butadiene films compare favorably with macroscopically determined ones. Small discrepancies can be attributed to the imprecise knowledge of the mechanical properties of the cantilever. Relative measurements should, however, be accurately made. Spatial resolution depends on mechanical and adhesive properties of the material. For the experiments shown, the resolution is a few microns. Contrary to others, this method is little dependent on the geometrical properties of the tip end since in this regime the tip is deeply intruded in the material. It applies on thin films and heterogeneous materials and provides a new method for determining the mechanical properties at a local scale. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365834

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Optically induced oxidation of hydrogen-passivated silicon surfaces using a scanning near-field optical microscope was achieved with both uncoated and aluminum-coated fiber probes. Line scans on amorphous silicon using uncoated fiber probes display a three-peak profile after etching in potassium hydroxide. Numerical simulations of the electromagnetic field around the probe–sample interaction region are used to explain the experimental observations. With an aluminum-coated fiber probe, lines of 35 nm in width were transferred into the amorphous silicon layer. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365847

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Titanium oxide thin films have been deposited by thermal evaporation in vacuum and then have been analyzed before and after a suitable thermal annealing in order to test their application inNH3gas-sensing technology. In particular, spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of titanium oxide thin films. The structure and the morphology of such material have been investigated by high resolution electron microscopy and small area electron diffraction. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365848

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photonic band gap materials are holograms with extremely high refractive index contrasts. The refractive index function can be approximated by a small number of plane waves, as a consequence of the photonic crystal periodicity. Photonic crystals can hence be constructed with a simple holographic recording of a very small number of optical plane waves, and appear in this regard as the simplest holograms. Various photonic band gap structures are theoretically analysed and those concepts are illustrated experimentally with the fabrication of a two-dimensional triangular lattice in GaAs. The extension of the method to the three-dimensional diamond structure is discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365849

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The local structures of amorphousGe0.52Te0.48andPd0.01Ge0.17Sb0.26Te0.56were examined by extended x-ray absorption fine structure. In amorphous GeTe film, only Ge atoms were observed in the nearest-neighbor of Te atoms. The average coordination number around Te atoms in amorphous GeTe is 1.5 which is close to twofold coordination. These results support a chemically ordered structure model. In amorphous PdGeSbTe film, Ge and Sb (and/or Te) atoms were observed in the nearest-neighbor of Te atoms at distances of 2.61 and 2.84 Å, respectively. Debye–Waller factors of the Te–Ge bonds in TeGe and PdGeSbTe are 0.076 and 0.081 Å, respectively, and are larger than that of Te-(Sb and/or Te); 0.063 Å. From these results, we argue that the softened Te–Ge bond plays an important role in the elementary process of crystallization of GeTe and PdGeSbTe alloys. The total average coordination number of Pd atoms in amorphous PdGeSbTe alloy is 4.0. This result suggests Pd atoms play the role of cross-linking element. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365850

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A self-consistent computer model was used to simulate the plasma kinetics (radially resolved) and parametric behaviour of an 18 mm bore (6 W) copper vapour laser for a wide range of optimum and non-optimum operating conditions. Good quantitative agreement was obtained between modelled results and experimental data including the temporal evolution of the4p2P3/2,4s22D5/2and4s22D3/2Cu laser level populations derived from hook method measurements. The modelled results show that the two most important parameters that affect laser behaviour are the ground state copper density and the peak electron temperature Te.For a given pulse repetition frequency (prf), maximum laser power is achieved by matching the copper atom density to the input pulse energy thereby maintaining the peak Teat around 3 eV. However, there is a threshold wall temperature (and copper density) above which the plasma tube becomes thermally unstable. At low prf(<8 kHz), this thermal instability limits the attainable copper density (and consequently the laser output power) to values below the optimum for matching to the input pulse energy. For higher prf values(>8 kHz), the copper density can be matched to the input pulse energy to give maximum laser power because the corresponding wall temperature then falls below the threshold temperature for thermal instability. For prf>14 kHz, the laser output becomes highly annular across the tube diameter due to a severe depletion of the copper atom density on axis caused by radial ion pumping. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365851

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present linewidth measurements on AlGaAs double heterostructure lasers as a function of temperature and power. The data, which plot observed linewidth as a function of reciprocal power, reveal decreasing slopes and increasing vertical axis intercepts, or power independent linewidths, with falling temperature, consistent with previous experimental observation [D. Welford and A. Mooradian, Appl. Phys. Lett.40, 560 (1982)]. To explain the power independent linewidth broadening observed in these continuous wave single frequency lasers, we propose that carrier heating processes create a thermal nonequilibrium between electrons and the semiconductor lattice, and that this leads to a power dependent linewidth enhancement factor. From a carrier thermal model we find that the power independent linewidth is mediated by the longitudinal optical (LO)-phonon lifetime(&tgr;LO);as&tgr;LOis increased (for example, by decreasing the lattice temperature), the noneqilibrium condition is enhanced, and, consequently, the power independent linewidth increases. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365852

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This paper addresses the fundamental problem of how to connect a heat generating volume to a point heat sink by using a finite amount of high-conductivity material that can be distributed through the volume. The problem is one of optimizing the access (or minimizing the thermal resistance) between a finite-size volume and one point. The solution is constructed by covering the volume with a sequence of building blocks, which proceeds toward larger sizes (assemblies), hence, the “constructal” name for this approach. Optimized numerically at each stage are geometric features such as the overall shape of the building block, its number of constituents, and the internal distribution of high-conductivity inserts. It is shown that in the optimal design, the high-conductivity material has a distribution with the shape of a tree. Every aspect of the tree architecture is deterministic: the shapes of the largest assembly and all its constituents, the number of branches at each level of assembly, the relative position of building blocks in each assembly, and the relative thicknesses of successive branches. The finer, innermost details of the tree architecture (e.g., the branching angle) have a negligible effect on the overall thermal resistance. The main conclusion is that the structure, working mechanism, and minimal resistance of the tree network can be obtained deterministically, and that the constrained optimization of access routes accounts for the macroscopic structure in nature. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365853

出版商:AIP    

年代:1997

数据来源: AIP