Volume 93, Issue 10, 15 May 2003
- lasers, optics, and optoelectronics (pacs 42)
- plasmas and electrical discharges (pacs 51-52)
- structural, mechanical thermodynamic, and optical properties of condensed matter (pacs 61-68, 78)
- electronic structure and transport (pacs 71-73)
- magnetism and superconductivity (pacs 74-76)
- dielectrics and ferroelectricity (pacs 77)
- nanoscale science and design
- device physics (pacs 85)
- interdisciplinary and general physics (pacs 1-41, 43-47, 79, 81-84, 89-99)
- 47th annual conference on magnetism and magnetic materials
- symposium on building bridges: magnetic modeling at different length and time scales
- inductive recording heads: design and materials
- nanostructured hard magnetic materials i: exchange coupled systems
- structured materials: interface properties
- amorphous/nanocrystalline soft magnetic materials i
- recording modeling, systems, and theory i
- magnetic microscopy and imaging i
- exchange bias i: materials
- hysteresis modeling and applications
- crystalline alloys
- perpendicular magnetic recording i
- magnetic semiconductors i
- micromagnetic methods and thermal effects
- exchange bias ii: new materials
- other half-metallics i
- magnetoelectronic devices
- electronic structure
- spin dynamics and relaxation i: permalloy films and structures
- hard magnetic materials i
- magneto-optic materials i
- new magnetic materials i
- recording modeling, systems, and theory ii
- magnetic tunnel junctions ii
- interactions in particle arrays
- instrumentation and measurement techniques i
- molecular nanomagnets i
- crystalline alloys and ferrite dynamics
- fundamental properties
- l10 nanoparticle media
- amorphous/nanocrystalline soft magnetic materials ii
- structured materials: multilayer films and superlattices
- electronic structure and itinerant magnetism
- symposium on biological applications of magnetic nanostructures
- magnetic memory and elements
- magnetoresistive heads
- novel fabrication methods
- spin manipulation
- cmr: structure and orbital ordering
- low-dimensional systems i
- thin film recording media i
- magnetic nanostructures and arrays
- micromagnetics and field computation
- ferrites and garnets
- magnetic tunnel junctions iii
- symposium on relaxation in magnetic thin films and devices
- biological applications: particles and sensors
- nanostructured hard magnetic materials ii
- spin excitations and transport in nanostructures i
- structured materials: magnetic anisotropy
- phase transitions and frustrated systems
- magnetic semiconductors ii
- giant magnetoresistance and spin valves i
- exchange bias iii: characterization
- perpendicular magnetic recording iii: modeling and performance
- thin film recording media ii
- magnetic tapes and magneto-optics
- molecular nanomagnets ii
- kondo, heavy fermions, and correlated systems
- perpendicular magnetic recording iii
- magnetic semiconductors iii
- small magnetic structures
- giant magnetoresistance and spin valves ii
- other half-metallics
- hard magnetic materials ii
- ferrites, garnets, and other microwave materials
- magnetic tunnel junctions and other half-metallics
- anisotropic magnetoresistance, hall effect, and magnetoimpedance
- nanostructured hard magnetic materials iii
- perpendicular magnetic recording iv: media
- critical phenomena, spin glasses, and superconductivity
- symposium on louis neel: retrospective and new developments
- structured materials: magnetic structures and electronic properties
- symposium on single electron devices
- magnetic sensors (not for recording)
- spin dynamics and relaxation ii: multilayers and thin films
- new magnetic materials ii
- cmr: transport and manetoresistance
- correlated electron systems
- magnetic tunnel junctions: materials and applications
- giant magnetoresistance and spin valves iii
- spin excitation and transport in nanostructures ii
- magnetic fluids
- thin film recording media iii
- magneto-elastic materials i
- new applications
- magnetic microscopy and imaging ii
- instrumentation and measurement techniques ii
- magnetic tunnel junctions iv
- ballistic magnetoresistance and spin transfer
- magnetic noise
- microwave and millimeter wave devices
- exchange bias iv: characterization
- magneto-elastic materials ii
- hard magnet processing and applications
- head-media interface and tribology
- structured materials: ultrathin films and surface effects
- spin dynamics and relaxation
- low-dimensional systems ii
- power and control magnetics
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
93(2003); http://dx.doi.org/10.1063/1.1568533View Description Hide Description
We have studied the photoluminescence properties of as-grown epitaxial layers grown on GaAs containing 0.6%, 1.77%, and 2.8% nitrogen. We found laser emission from thick nm) layers exhibiting the characteristic lasing properties of random lasers. This is unusual because random lasers have so far only been associated with highly disordered or random media. We believe that high gain in combination with structural inhomogeneities that are evident in these layers, can explain the random lasing in such epitaxial layers.
Asymptotic analysis of dispersion characteristics in two-dimensional metallic photonic band gap structures93(2003); http://dx.doi.org/10.1063/1.1568530View Description Hide Description
We present a self-consistent technique for the asymptotic analysis of dispersion curves in two-dimensional metallic photonic band gapstructures representing square and triangular arrays of metal rods. The technique is applicable for the structures with rod radii which are small compared to the distance between the rods and to the wavelength (λ). The induced current and charge distributions on the rods are expressed self-consistently in terms of the electromagnetic wave field. The dispersion characteristics are calculated for the TE and TM modes. The results are in agreement with those obtained previously using the Photonic Band GapStructure Simulator code.
93(2003); http://dx.doi.org/10.1063/1.1568548View Description Hide Description
We have proposed and demonstrated an economical technique to fabricate a three-dimensional layer-by-layer photonic band gapstructure in the infrared wavelengths. An organic polymer template structure, an inverse layer-by-layer photonic crystalstructure, is assembled using the microtransfer molding technique. This template is infiltrated with sol-gel or nanoparticle titanium oxide slurry, then later removed by heat treatment at a temperature range of 550–800 °C. This method can be extended to fabricatephotonic crystals operating at optical and ultraviolet frequencies.
93(2003); http://dx.doi.org/10.1063/1.1568150View Description Hide Description
We report on the effect of different aperture shapes on the power output of a very small aperture laser (VSAL) fabricated from commercial edge-emitting laser diodes and correlate the results to the layer structure and polarization of the optical field. A waveguide theory is used to explain the experimental observations. We show that the shape of the aperture has a significant effect on the VSAL output power. In particular shapes exploiting the asymmetry of the laser can achieve much higher throughput over square apertures while keeping the aperture area constant. This work also indicates the validity of analyzing near-field small apertures as cutoff waveguide structures.
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
Dynamics of ozone and OH radicals generated by pulsed corona discharge in humid-air flow reactor measured by laser spectroscopy93(2003); http://dx.doi.org/10.1063/1.1567796View Description Hide Description
The dynamics of ozone and OH radicals are studied in pulsed corona discharge plasma in a humid-air environment. Ozone density is measured by the laser absorption method, and OH density is measured by the laser-induced fluorescence(LIF) method. A 100-ns pulsed corona discharge occurs between a series of 25 needle electrodes and a plate electrode. After the pulsed discharge, the time evolutions of ozone and OH densities are measured in humid air or a humid nitrogen-oxygen mixture. Results show that the addition of 2.4% water vapor to dry air reduces ozone production by a factor of about 6, and shortens the ozone formation time constant from 30 to 6 μs. Water vapor may reduce atomic oxygen levels leading to the decreased production of ozone by reaction. The LIFmeasurement for OH radicals shows that OH density is approximately constant for 10 μs after the pulsed discharge, then decays by recombination reaction and reactions with the discharge products of oxygen, such as ozone or atomic oxygen. Absolute OH density is estimated; it is about in streamers at 10 μs after discharge in the mixture.
Effects of assistant anode on planar inductively coupled magnetized argon plasma in plasma immersion ion implantation93(2003); http://dx.doi.org/10.1063/1.1568151View Description Hide Description
The enhancement of planar radio frequency (RF) inductively coupled argon plasma is studied in the presence of an assistant anode and an external magnetic field at low pressure. The influence of the assistant anode and magnetic field on the efficiency of RF power absorption and plasma parameters is investigated. An external axial magnetic field is coupled into the plasmadischarge region by an external electromagnetic coil outside the discharge chamber and an assistant cylindrical anode is inserted into the discharge chamber to enhance the plasmadischarge. The plasma parameters and density profile are measured by an electrostatic Langmuir probe at different magnetic fields and anode voltages. The RF power absorption by the plasma can be effectively enhanced by the external magnetic field compared with the nonmagnetized discharge. The plasma density can be further increased by the application of a voltage to the assistant anode. Owing to the effective power absorption and enhanced plasmadischarge by the assistant anode in a longitudinal magnetic field, the plasma density can be enhanced by more than a factor of two. Meanwhile, the nonuniformity of the plasma density is less than 10% and it can be achieved in a process chamber with a diameter of 600 mm.
93(2003); http://dx.doi.org/10.1063/1.1568158View Description Hide Description
A low-input capacitance emissive probe heated by a laser has been used to investigate frequency-modulated electric potentials in a radio-frequency (rf)glow discharge plasma. An excellent time-response ability of our probe system to a sharp potential change was confirmed by potential measurements with applying a step function voltage to the plasma. The electric field distribution as the first derivative of the potential distribution obtained by the probe method was compared with that by the laser optogalvanic spectroscopy to ensure the reliability of the measurements in the sheath region. The probe method was applied to directly monitor a temporal variation of axial potential and electric field distributions between two parallel-plate electrodes in a rf argon plasma. The formation of ion sheath regions on both electrode surfaces was confirmed at any phase in a rf cycle. The results were consistent with a one-dimensional model for potential and electric field distributions in the sheath region.
- STRUCTURAL, MECHANICAL THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER (PACS 61-68, 78)
93(2003); http://dx.doi.org/10.1063/1.1565690View Description Hide Description
In this paper is reported a general and accurate binary-collision-approximation- (BCA-)based Monte Carloion implantation model for implants into crystalline silicon. The combination of an improved semiempirical electronic stopping power model and Ziegler-Biersack-Littmark universal potential enables us to simulate a wide variety of implant species with only two different electronic stopping parameters for different implant species. With the model parameters fixed for a given implant species, excellent agreement is found with experimental secondary ion mass spectroscopy data for the energy range from sub-keV to above 10 MeV, and for different implant directions including random equivalent orientation, 〈100〉, 〈111〉, and 〈110〉 channeling directions. When compared with other BCA-based Monte Carlo simulators, it is demonstrated that more accurate results can be obtained for ultralow energy and very high energy implants. Furthermore, it is shown that, while the existing ion implantation simulators with the electronic stopping power based on the effective charge theory fail to predict the long tails of the deeply channeled implant species (such as Al), our model can predict these long tails successfully. Finally, an efficient damage model is also presented, which requires only one additional free parameter to accurately account for the damage accumulation and dechanneling effect. For high dose implants, substantial speed improvement over MARLOWE-based Monte Carlo simulators is observed.
93(2003); http://dx.doi.org/10.1063/1.1564280View Description Hide Description
Electron spin resonance(ESR) and Raman spectra measurements are carried out on and films both as grown and implanted with W and Ni ions with doses ranged from to The as-grown films have small concentration of paramagnetic centers with a spin density of Upon implantation a significant increase in of centers with and was observed. These defects are ascribed to dangling bonds in the silicon substrate and in the carbon film, respectively. The correlation between variation of value with implantation dose and behavior of D and G band position and their intensity ratio in the visible Raman spectra is observed. The effects are attributed to changes in the systems and hydrogen loss due to ion induced annealing of the carbon films at high ion doses. The temperature and concentration dependencies of the ESR line shape and linewidth are explained using the mechanism of motional narrowing over the temperature range 4.2–300 K. Low temperature anisotropy of the g value is found in the ESR spectra and is explained as arising from the dipole–dipole interaction in the infinitely thin films.
93(2003); http://dx.doi.org/10.1063/1.1567060View Description Hide Description
A distributed electron cyclotron resonanceplasma reactor powered by a microwave generator operating at 2.45 GHz was used to deposit a-C:H films at room temperature on rf biased 〈100〉 Si substrates. Modifying substrate bias, substrate current density and composition of the precursor gas enabled the average deposited energy density to be varied. The physical properties of a-C:H were investigated using atomic force microscopy(AFM), x-ray photoelectron spectroscopy, and electron energy loss spectroscopy(EELS). The experimental results were correlated with the predictions of the binary collision theory. The influence of the deposited energy density on the nucleation and growth processes was investigated using both pure and mixed with Ar. The nucleation process is shown to be stimulated by high energy density cascades generated by and ions. For the pure acetylene plasma, the AFM topography displays a random network of circular, crater-like objects close to 1 μm in diameter. These objects are associated with plastic flow of a-C:H and are attributed to the transversal hypersonic shock waves generated by overlapping binary collision cascades. EELS analysis shows that an increasing ion current density applied under constant substrate bias leads to an increased hybridized carbon fraction. The effect is attributed to interference between the shock waves triggered by individual ions and the corresponding high pressure transients. The probability of a dynamic overlap of order i between shock waves is estimated under the assumption that in order to modify the quantum state and bonding type, the overlap must occur during the wave propagation time τ. The observed evolution of the hybridized fraction is consistent with theoretical predictions for and a propagation time ps, indicating that shock waves are generated during the cascade’s lifetime. Analysis of the AFM images shows that once the shock wave comes to rest, the subsequent nucleation of the hybridized component is controlled by the tensile stress-mediated nucleation process.
93(2003); http://dx.doi.org/10.1063/1.1566471View Description Hide Description
A discrete dislocationplasticityanalysis of plastic deformation in metalthin films caused by thermal stress is carried out. The calculations use a two-dimensional plane-strain formulation with only edge dislocations.Single crystalfilms with a specified set of slip systems are considered. The film-substrate system is subjected to a prescribed temperature history and a boundary value problem is formulated and solved for the evolution of the stress field and for the evolution of the dislocationsstructure in the film. A hard boundary layer forms at the interface between the film and the substrate, which does not scale with the film thickness and thus gives rise to a size effect. It is found that a reduction in the rate of dislocation nucleation can occur abruptly, which gives rise to a two-stage hardening behavior.
93(2003); http://dx.doi.org/10.1063/1.1563295View Description Hide Description
The temperature-dependent behavior of excitonic photoluminescence observed in ZnO/MgZnO multiple quantum wells(MQWs) in the temperature range of 5–300 K is described. In a MQWgrown by laser molecular-beam epitaxy, the luminescence was dominated by localized exciton (LE) emission throughout the whole temperature range studied. Luminescence of free excitons (FEs) was not observed. A simple rate equation is used to describe the quenching of LE emission. The activation energy for LE luminescence quenching is of the order of the localization energy of excitons, suggesting that the thermionic emission of the LEs out of the localization potentials leads to nonradiative recombination. In a MQW having lower barriers, the luminescence was dominated by LE emissions at low temperatures, while the FE transition was dominating emissions at temperatures above 175 K. A rate equation assuming one nonradiative recombination channel is used to describe the quenching of the transitions observed. The activation energy for LE luminescence quenching deduced in this sample is also of the order of the localization energy of excitons. The temperature dependences of FE emission intensities are also discussed by using a simple rate equation in which a thermal release effect of LEs toward FEs is taken into account.
93(2003); http://dx.doi.org/10.1063/1.1565190View Description Hide Description
We developed the annealing method for the activation of the ion-implanted dopants in siliconcarbide using excimer laser irradiation. The electrical activation efficiency of the dopants drastically improved while the substrate temperature was kept in the range of 500–700 °C during laser irradiation. A “multiple energy irradiation method” realized the annealing of the implanted layer without ablation of the surface atoms and without redistribution of the dopants that were usually observed in the case of furnaceannealing above 1500 °C. We have obtained a very low sheet resistance namely, 164.7 Ω/□, of the phosphorus ion-implanted layer in 4H-SiC by excimer laserannealing. This value is comparable to that of the furnace-annealed substrate at 1500 °C.
93(2003); http://dx.doi.org/10.1063/1.1565174View Description Hide Description
Several Al–Ni multilayers were prepared where the Ni thickness was varied in order to (i) detect Nidiffusion in Al and Al diffusion in Ni and (ii) determine the compounds that form at the interface during deposition at room temperature. X-ray absorption spectroscopy was carried out at the K edge of Ni to identify the local atomic arrangement around this atom. Magnetic measurements allowed the detection of pure Ni among nonmagnetic compounds. At the Al/Ni interface,Ni diffuses in Al whereas no Al diffusion in Ni was observed at the Ni/Al interface.Nidiffusion in Al results in the formation of a disordered aluminide over a thickness of about 1.7 nm, then pure Ni growth takes place in the form of islands.
93(2003); http://dx.doi.org/10.1063/1.1563844View Description Hide Description
The interface of zirconium oxide thin films on silicon is analyzed in detail for their potential applications in the microelectronics. The formation of an interfacial layer of with graded Zr concentration is observed by the x-ray photoelectron spectroscopy and secondary ion mass spectrometryanalysis. The as-deposited sample is thermally stable up to 880 °C, but is less stable compared to the samples. Post-deposition annealing in oxygen or ammonia improved the thermal stability of as-deposited to 925 °C, likely due to the oxidation/nitridation of the interface. The as-deposited film had an equivalent oxide thickness of with a dielectric constant of and a leakage current of at −1.5 V. Upon oxygen or ammonia annealing, the formation of and at the interface reduced the overall dielectric constants.
Self-assembled InAs quantum dots formed by molecular beam epitaxy at low temperature and postgrowth annealing93(2003); http://dx.doi.org/10.1063/1.1566457View Description Hide Description
Self-assembled InAs quantum dots are grown at low temperature (LT) by molecular beam epitaxy(MBE) on GaAs substrates. The growth is in situ monitored by reflection high-energy electron diffraction, and ex situ evaluated by atomic force microscopy for the morphological properties, and by high-resolution x-ray diffraction for the structural properties. While two monolayers as-grown LT InAs layers exhibit shallow mounds due to the low adatom migration length at low temperature, well-developed InAs dots are formed after postgrowth annealing above The structural quality of the LT GaAs matrix grown on top and of the embedded InAs dot layer is improved when a 3 nm GaAs interlayer is deposited (at on the InAs dots and subsequently annealed at before LT GaAs overgrowth. These high structural quality LT-grown InAs dots are considered for applications in high-speed optical modulators and switches operating at low power by combining the high optical nonlinearity of quantum dots with the ultrafast optical response provided by LT growth in MBE.
93(2003); http://dx.doi.org/10.1063/1.1567057View Description Hide Description
Soft ultraviolet laserdesorption of neutral and ionized Si atoms was investigated at 355 nm for fluences ranging from the desorption threshold (85 up to 165 The sensitivity of resonance ionizationmass spectrometry enabled the number of sputtered particles to be studied at a very low emission level corresponding to only several 100 atoms. For such a low emission yield, the ejected atoms keeps the memory of the laser–surface interaction mechanism during their flight in the ultrahigh vacuum condition. The velocity distribution of neutrals was measured for different fluences and were well fitted by a set of 2 Maxwellian functions at each fluence. From these fits it appears that the primary mechanisms involved in laser desorption are both a thermal process and an electronic one.
Sequence of Mg segregation, grain growth, and interfacial MgO formation in Cu–Mg alloy films on during vacuum annealing93(2003); http://dx.doi.org/10.1063/1.1566451View Description Hide Description
Cu-alloy films are being explored for integrated circuits, for creating low-resistivity interconnects with stabilized metal/dielectric interfaces via solute segregation, and for interfacial reactions. Here, we describe the pathways of microstructure evolution in supersaturated Cu– 5–12 at. % Mgfilms, and phase formation at the interface during annealing. The as-deposited films consist primarily of a Cu–Mg solid solution with trace amounts of orthorhombic Upon annealing to Mg segregates to the surface and the Cu–Mg grains grow from an average size of 20 to 60 nm, resulting in a ∼25%–40% decrease in filmresistivity. In the same temperature regime, phase dissolves and fcc forms. Upon annealing to higher temperatures, Mg segregates to the film/silica interface, reduces and forms fcc MgO on the silica side of the interface. The Si released by this interfacial reaction diffuses into the metal film resulting in a ∼40%–190% increase in resistivity, for films with 8–12 at. % Mg, respectively. These results are of relevance for understanding microstructure evolution in alloy films and exploring the use of Cu alloys as interconnects in integrated circuits.
Recombination kinetics in wide gap electroluminescent conjugated polymers with on-chain emissive defects93(2003); http://dx.doi.org/10.1063/1.1566091View Description Hide Description
We analyze the experimental dependence of temporally and spectrally resolved electroluminescence(EL) from polyfluorene-based light-emitting diodes on electric field and temperature. The blue band in the ELspectrum is caused by emission from the polymer backbone, while the low-energy green emission results from on-chain keto defects, which act as traps for electrons. Although the time and temperature dependencies of the blue and green emission could be explained by the kinetics of redistribution of trapped holes and electrons in energy and space, the increase of the blue-to-green delayed emission ratio with increasing field strength appears to result from a difference in the nature of recombination. We propose that the formation of blue-emitting singlet excitons from close electron–hole pairs after turn-off is impeded by an energy barrier, in contrast to the formation of green-emitting excitons.
93(2003); http://dx.doi.org/10.1063/1.1567803View Description Hide Description
Micro-light emitting diode(LED) arrays with diameters of 4 to 20 μm have been fabricated and were found to be much more efficient light emitters compared to their broad-area counterparts, with up to five times enhancement in optical power densities. The possible mechanisms responsible for the improvement in performance were investigated. Strain relaxation in the microstructures as measured by Raman spectroscopy was not observed, arguing against theories of an increase in internal quantum efficiency due to a reduction of the piezoelectric field put forward by other groups. Optical microscope images show intense light emission at the periphery of the devices, as a result of light scattering off the etched sidewalls. This increases the extraction efficiency relative to broad area devices and boosts the forward optical output. In addition, spectra of the forward emitted light reveal the presence of resonantcavity modes [whispering gallery (WG) modes in particular] which appear to play a role in enhancing the optical output.