A control volume derivation of the energy equation for LII modeling

This paper considers the unsteady energy equation for a particle undergoing processes relevant to laser-induced incandescence. The energy equation is derived using both an integral control volume formalism and a differential approach. Confusion in the previous literature over the form of the energy equation is traced to the evaluation of the energy flux terms to and from the particle surface. Terms such as the heat of sublimation or heat of combustion are shown to arise naturally in both the control volume and differential derivations. Problems associated with the confusion regarding the flux terms resulting in incorrect energy equations are also identified.     

Crackless linear through-wafer etching of Pyrex glass using <Emphasis Type="Italic">liquid-assisted</Emphasis> CO<Subscript>2</Subscript> laser processing

Pyrex glass etching is an important technology for the microfluid application to lab-on-a-chip devices, but suffers from very low etching rate and mask-requiring process in conventional HF/BOE wet or plasma dry etching as well as thermal induced crack surface by CO₂ laser processing. In this paper, we applied the liquid-assisted laser processing (LALP) method for linear through-wafer deep etching of Pyrex glass without mask materials to obtain a crackless surface at very fast etching rates up to 25 μm/s for a 20 mm long trench. The effect of laser scanning rate and water depth on the etching of the 500 μm thick Pyrex glass immersed in liquid water was investigated. The smooth surface without cracks can be achieved together with the much reduced height of bulge via an appropriate parameter control. A mechanism of thermal stress reduction in water and shear-force-enhanced debris removal is discussed. The quality improvement of glass etching using LALP is due to the cooling effect of the water to reduce the temperature gradient for a crackless surface and natural convection during etching to carry away the debris for diminishing bulge formation. An erratum to this article can be found at     

Impurity doping in silicon nanowires synthesized by laser ablation

Boron (B) or phosphorus (P) doped silicon nanowires (SiNWs) were synthesized by laser ablation. Local vibrational modes of B were observed in B-doped SiNWs by micro-Raman scattering measurements at room temperature. Fano broadening due to a coupling between the discrete optical phonon and a continuum of interband hole excitations was also observed in the Si optical phonon peak for B-doped SiNWs. An electron spin resonance signal due to conduction electrons was observed only for P-doped SiNWs. These results prove that B and P atoms were doped in substitutional sites of the crystalline Si core of SiNWs during laser ablation and electrically activated in the sites.     

Gadolinium scandate as an alternative gate dielectric in field effect transistors on conventional and strained silicon

Long channel n-type metal oxide semiconductor field effect transistors on thin conventional and strained silicon on insulator substrates have been prepared by integrating gadolinium scandate as high-κ gate dielectric in a gate last process. The GdScO₃ films were deposited by electron beam evaporation and subsequently annealed in oxygen atmosphere. Electrical characterization of readily processed devices reveals well behaved output and transfer characteristics with high I _on/I _off ratios of 10⁶–10⁸, and steep inverse subthreshold slopes down to 66 mV/dec. Carrier mobilities of 155 cm²/Vs for the conventional and 366 cm²/Vs for the strained silicon substrates were determined.     

Modeling the dynamics of one laser pulse surface nanofoaming of biopolymers

Self standing films of biopolymers like gelatine, collagen, and chitosan irradiated with single nanosecond or femtosecond laser pulse easily yield on their surface, a nanofoam layer, formed by a cavitation and bubble growth mechanism. The laser foams have interesting properties that challenge the molecular features of the natural extracellular matrix and which make them good candidates for fabrication of artificial matrix (having nanoscopic fibers, large availability of cell adhesion sites, permeability to fluids due to the open cell structure). As part of the mechanistic study, the dynamics of the process has been measured in the nanosecond timescale by recording the optical transmission of the films at 632.8 nm during and after the foaming laser pulse. A rapid drop 100→0% taking place within the first 100 ns supports the cavitation mechanism as described by the previous negative pressure wave model. As modeled a strong pressure rise (∼several thousands of bar) first takes place in the absorption volume due to pressure confinement and finite sound velocity, and then upon relaxation after some delay equal to the pressure transit time gives rise to a rarefaction wave (negative pressure) in which nucleation and bubble growth are very fast.     

Laser-induced incandescence: excitation and detection conditions,material transformations and calibration

Successful implementation of laser-induced incandescence (LII) relies upon judicious choice of excitation and detection conditions. Excitation conditions encompass choice of excitation wavelength and laser fluence. Detection conditions include choice of detection wavelength, spectral band pass about the central wavelength, detection delay and duration relative to the excitation laser pulse usually corresponding to the peak of the signal intensity. Examples of applying these parameters to LII are illustrated by way of examples: soot/polycyclic aromatic hydrocarbon and metal aerosol systems. Tradeoffs must be recognized. Laser-induced chemical and structural changes of the aerosol must be considered, particularly in light of heterogeneous aerosols. Diagnostics of such changes are outlined as they will affect interpretation of the LII signal. Finally, calibration (for LII) must be chosen to be appropriate for aerosols from practical sources as they may be mixed organic and inorganic composition. A research paper in response to the call for papers from the Third International Discussion Meeting and Workshop on Laser-Induced Incandescence July 30th–August 1st, Ottawa, Canada (2008).     

The effects of pulsed laser injection seeding and triggering on the temporal behavior and magnitude of laser-induced incandescence from soot

The effect of sub-nanosecond fluence fluctuations and triggering on time-resolved laser-induced incandescence (LII) from soot has been studied using an injection-seeded pulsed Nd:YAG laser that produces a smooth laser temporal profile. Without injection seeding, this multi-mode laser generates pulses with large intensity fluctuations with sub-nanosecond rise times. The experimental results described here demonstrate that at fluences below 0.6 J/cm² LII signals are insensitive to fluence fluctuations on nanosecond time scales. At fluences above 0.6 J/cm² fluctuations in the laser profile cause the rising edge of the LII profile to move around in time relative to the center of the laser pulse causing a broader average profile that shifts to earlier times. Such fluctuations also lead to a decrease in the average LII temporal profile by up to 12% at a fluence of 3.5 J/cm². A timing jitter on the trigger of the data acquisition, such as that produced by triggering on the laser Q-switch synchronization pulse, has a negligible effect on the shape and temporal maximum of the LII signal. Additional jitter, however, considerably reduces the peak of the LII temporal profiles at fluences as low as 0.15 J/cm². Neither fast fluence fluctuations nor trigger jitter have a significant effect on gated LII signals, such as those used to infer soot volume fraction.     

Experimental beta-decay energies of very neutron-rich isobars with mass numbers A=101 and A=102

TheQ -values of¹⁰¹Rb,^101,102Sr and^101,102Y have been measured for the first time at the mass separator ISOLDE by means of-coincidence techniques with a plastic scintillation detector telescope and a large Ge(HP)-detector. For some of these nuclei, also new details of their decay schemes could be derived from the measured-decay properties. The experimental results are discussed, as far as the systematics of two-neutron separation energies derived from them is concerned. In addition, the nuclear masses deduced from theseQ -values are compared with the predictions of recent mass calculations.Dedicated to Prof. Dr. Peter Armbruster on the occasion of his 60th birthday     

Signal of new physics and chemical composition of matter in core-crossing neutrinos

We consider the non-standard matter effect in flavor conversion of neutrinos crossing the core of the Earth. We show that oscillations of core-crossing neutrinos with E≳0.5 GeV can well be described by first order perturbation theory. We show that due to the non-standard matter effect a varying chemical composition in the Earth can modify the neutrino flavor conversion by 100%. The effects of CP violating phases in non-standard neutral current interactions are emphasized in particular.     

The effects of chemical etching of porous silicon on Raman spectra

We have investigated the effects of chemical etching on Raman spectra of porous silicon. The as-anodized porous silicon consisted mainly of crystalline silicon, as indicated by the Raman spectra. The background in the spectrum was strong, indicating that the porous silicon surface was rough due to the presence of pores. When chemical etching was performed five times, the Raman spectrum revealed the presence of spherically shaped nanocrystalline silicon whose diameter was around 3.5 nm. Further chemical etching, however, extinguished the nanocrystallites, in addition to smoothing the surface morphology.     

Thermal analysis of InP-based quantum cascade lasers for efficient heat dissipation

We have theoretically investigated the thermal characteristics of double-channel ridge–waveguide InGaAs/InAlAs/InP quantum cascade lasers (QCLs) using a two-dimensional heat dissipation model. The temperature distribution, heat flow, and thermal conductance (G _th) of QCLs were obtained through the thermal simulation. A thick electroplated Au around the laser ridges helps to improve the heat dissipation from devices, being good enough to substitute the buried heterostructure (BH) by InP regrowth for epilayer-up bonded lasers. The effects of the device geometry (i.e., ridge width and cavity length) on the G _th of QCLs were investigated. With 5 μm thick electroplated Au, the G _th is increased with the decrease of ridge width, indicating an improvement from G _th=177 W/K⋅cm² at W=40 μm to G _th=301 W/K⋅cm² at W=9 μm for 2 mm long lasers. For the 9 μm×2 mm epilayer-down bonded laser with 5 μm thick electroplated Au, the use of InP contact layer leads to a further improvement of 13% in G _th, and it was totally raised by 45% corresponding to 436 W/K⋅cm² compared to the epilayer-up bonded laser with InGaAs contact layer. It is found that the epilayer-down bonded 9 μm wide BH laser with InP contact layer leads to the highest G _th=449 W/K⋅cm². The theoretical results were also compared with available obtained experimentally data.     

Derivation of a temperature-dependent accommodation coefficient for use in modeling laser-induced incandescence of soot

This paper presents a derivation of an expression to estimate the accommodation coefficient for gas collisions with a graphite surface, which is meant for use in models of laser-induced incandescence (LII) of soot. Energy transfer between gas molecules and solid surfaces has been studied extensively, and a considerable amount is known about the physical mechanisms important in thermal accommodation. Values of accommodation coefficients currently used in LII models are temperature independent and are based on a small subset of information available in the literature. The expression derived in this study is based on published data from state-to-state gas-surface scattering experiments. The present study compiles data on the temperature dependence of translational, rotational, and vibrational energy transfer for diatomic molecules (predominantly NO) colliding with graphite surfaces. The data were used to infer partial accommodation coefficients for translational, rotational, and vibrational degrees of freedom, which were consolidated to derive an overall accommodation coefficient that accounts for accommodation of all degrees of freedom of the scattered gas distributions. This accommodation coefficient can be used to calculate conductive cooling rates following laser heating of soot particles.     

Muonic x-ray intensity measurements on a highT c superconductor

Muonic x-ray spectra from the high-T _c superconductor YBa₂Cu₃O_6.95 have been measured in the superconducting and normal states. No significant differences were found between the two spectra when comparing the intensities of 27 lines.Dedicated to Prof. Dr. H. J. Mang on the occasion of his 60th birthday     

Systematic studies of fission fragment kinetic energy distributions by Langevin simulations

Fission fluctuation-dissipation dynamics of heavy nuclei has been studied using Langevin Monte Carlo simulations. The covariant form of the fission transport equation and the coefficients related to it are investigated. To learn about the influence of the dynamics from the ground state to the saddle point on the kinetic energy distributions we have studied various systems and compared the calculations both starting from the ground state and from the saddle point. Both the mean total kinetic energy of the fission fragments and its variances can fit with the experimental values in terms of a finite neck radius as scission condition.This work was supported by the National Natural Science Foundation of China.     

Beta decay of very neutron-rich110Mo studied at the new IGISOL facility

The decay of the new activity¹¹⁰Mo (t_1/2=0.30(4).s) has been observed at the new IGISOL separator. Multiscaled singles,--t and -y-t coincidences were recorded. The decay scheme suggests I=2⁺ for the ground state of the daughter nucleus¹¹⁰Tc. Three 1⁺ levels are fed with logft values below 5, indicating no drastic change among Mo and Ru decays at the middle of the neutron shell. This experiment confirms the expectation that the new IGISOL facility will allow the identification of one or two new more neutron-rich isotopes per element in this region.Supported by the Academy of Finland.     

Polycrystalline silicon films obtained by hot-wire chemical vapour deposition

Silicon films were deposited at moderate substrate temperatures (280–500° C) from pure silane and a silane-hydrogen mixture (10% SiH₄, 90% H₂) in a hotwire CVD reactor. The morphology, structure and composition of the samples were studied with scanning electron microscopy, transmission electron microscopy, transmission electron diffraction, X-ray diffraction, Raman spectroscopy and secondary ion mass spectrometry. The sample deposited at 500° C with pure silane has an amorphous structure, whereas the samples obtained from silane diluted in hydrogen have a polycrystalline structure, even that grown at the lowest temperature (280° C). Polycrystalline samples have a columnar structure with 0.3–1 m crystallite sizes with preferential orientation in [220] direction. Deposition rates depend on the filament-substrate distance and range from 9.5 to 37 Å/s for the polycrystalline samples. The high quality of the polycrystalline samples obtained makes the hot-wire technique very promising. Moreover, it is expected to be easily scaled up for applications to large-area optoelectronic devices and to photovoltaic solar cells.     

Transient 3D/2D simulation of laser-induced ablation of silicon

A numerical software has been developed to simulate heating, enthalpy-based phase changes and ablation of silicon during pulsed or continuous-wave laser irradiation. The unsteady heat transfer equation is solved by finite differences in two or three dimensions with full resolution of the thin liquid layer. An intelligent adaptive grid refinement and a semi-analytic treatment of the surface elements have been implemented to simulate laser cuts with lots of laser pulses in moderate computing time. The code has been successfully verified by comparisons with an analytic solution and with experimental data. Details of the mathematical model, the implementation in Matlab^®and comparisons with experimental laser cuts are presented in this paper.     

Dense stars with exotic configurations

In this paper, we consider dense stars with configurations expected from the SU(3)_C×SU(2)_W× U(1) standard model of strong and electroweak interactions. Following a recent suggestion that strange matter, a form of (uds) quark matter, may be the true ground state of hadronic matter, we investigate the prospect for the existence of dense stars consisting partially, or entirely, of strange matter by comparing the relative stability between neutron matter and strange matter. It is found that the restriction on the maximum star mass holds in all cases, including a pure strange star, a pure neutron star, and a neutron star with a quark core. It is also found that the choice of both the bag constantB and the strong coupling constant _s has a decisive effect on the relative stability between strange matter and neutron matter. For currently accepted values of (B, _s), anA= dense starcannot consist entirely,nor partially, of strange matter. Nevertheless, such conclusion may be subject to change if corrections ofO ( _s ² ) or other effects are taken into account. Finally, we use the framework of Tolman, Oppenheimer, and Volkoff to analyze two cases of boson stars: gluon stars and stars consisting of massive scalar particles (massive bosons). It is found that, in the case of gluon stars, the presence of the bag constant in the QCD vacuum yields results very similar to that found in quark stars. On the other hand, soliton stars consisting of massive bosons exist if there is some background pressure which plays the role similar to the bag constant for lowering the matter pressure. The stability problem for both gluon stars and soliton stars is briefly discussed.     

Influence of spatial laser energy distribution on evaluated soot particle sizes using two-colour laser-induced incandescence in a flat premixed ethylene/air flame

Time-resolved laser-induced incandescence (LII) has been developed rapidly during the last decade as a useful non-intrusive technique for particle size determination. Still several parameters should be investigated in order to improve the accuracy of LII for particle sizing and the spatial distribution of the laser energy is one of these. Generally a top-hat profile is recommended, as this ensures a uniform heating of all particles in the measurement volume. As it is generally not straightforward to create a uniform beam profile, it is of interest to establish the influence of various profiles on the evaluated particle sizes. In this work we present both an experimental and a theoretical investigation of the influence of the spatial profile on evaluated sizes. All experiments were carried out using a newly developed setup for two-colour LII (2C-LII) which provides online monitoring of both the spatial and temporal profile as well as the laser pulse energy. The LII measurements were performed in a one-dimensional premixed sooting ethylene/air flame, and evaluated particle sizes from LII were compared with thermophoretically sampled soot particles analysed using transmission electron microscopy (TEM). The results show that although there is some influence of the spatial laser energy distribution on the evaluated particle sizes both in modelling and experiments, this effect is substantially smaller than the influence of the uncertainties in gas temperature and the thermal accommodation coefficient.     

Mounting-induced strains in red-emitting (Al)InGaP laser diodes tuned by pressure

The hydrostatic pressure behavior of red-emitting diode lasers packaged on Si, AlN, and diamond submounts is studied in the 0–2 GPa range by emission and photocurrent spectroscopy. Photocurrent spectroscopy allows for simultaneous measurement of the InGaP quantum well and (Al_0.5Ga_0.5)_0.5In_0.5P waveguide. A broadening of the absorption edge of the waveguide is observed for all devices and explained by the pressure-induced direct-to-indirect transition in this material. For the QW resonance, distinct differences are observed for differently packaged devices. Thus, very low pressure tuning rates are demonstrated for devices packaged on diamond and AlN submounts and explained by the presence of shear strain components. Consistently we find the device packaged on Si to be least affected by the strain caused by the pressure cycling.