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81.
M. Eryürek M. H. Güven 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(2):221-228
The solid-liquid phase transitions of Lennard-Jones clusters LJN
(N=39–55) were simulated by a microcanonical molecular dynamics method using
Lennard-Jones potential, and their thermodynamic quantities were calculated.
The caloric curves of clusters (except N=42) have S-bend. To understand this
behaviour, configurational and total entropies were evaluated, and dents on
the entropy curves were taken as a sign of negative heat capacity. The heat
capacities were evaluated for N=39–55 clusters using configurational entropy
data. The potential energy distributions have bimodal behaviour for all
clusters in the given range at the melting temperature. The distinct melting
behaviour of LJ42 was explained by the topology of the potential energy
surface by examining the isomer distributions at phase transitions for
LJ39-LJ55. The isomer distributions were found to be a useful way
to interpret this behaviour and melting dynamics in general. Melting
temperature, latent heat and entropy change upon melting values were
reported and are consistent with literature values and values calculated
from bulk thermodynamic properties. The dependence of these quantities on
the size of the clusters was examined and it is found that latent heat is
the key quantity to determine the magic numbers. 相似文献
82.
83.
The specific heat of the super carbon nanotube (ST) was investigated by the molecular structure mechanics method. At given temperature, it was found that the specific heat of the ST is a fixed value and is almost independent both of the length, diameter and of chirality of the ST. By comparing the influences of the chirality of the ST on its mechanical properties, electronic properties and thermal properties as well, we find that the chirality effects on the physical properties of STs can be neglected. This result may be regarded as a universal law for the physical properties of STs. 相似文献
84.
The transmission of ArF laser pulses in virgin fused silica (type III) samples changes during N = 106 pulses at an incoming fluence Hin = 5 mJ cm−2 pulse−1. The related absorption is determined by the pulse energy absorption coefficient α(N, Hin) using a modified Beer’s law, yielding initial values αini around 0.005 cm−1, a maximum αmax ? 0.02 cm−1 at N = 103-104 and stationary values 0.0045 cm−1 ? αend ? 0.0094 cm−1 after N ≈ 6 × 105 pulses. The development α(N, Hin = const.) is simulated by a rate equation model assuming a pulse number dependent E′ center density E′(N). E′(N) is determined by a dynamic equilibrium between E′ center generation and annealing. Generation occurs photolytically from the precursors ODC II and unstable SiH structures upon single photon absorption and from strained SiO bonds via two-photon excitation. Annealing in the dark periods between the laser pulses is dominated by the reaction of E′ with H2 present in the SiO2 network. The development α(N, Hin = const.) is observed for the very first sample irradiation only (virgin state). The values αend are not accessible by simple spectrophotometer measurements. 相似文献
85.
For increasing the packing density of electronic devices and enabling 3D wiring, new concepts of interconnection for flexible circuit boards are required. The backside wiring is one innovative concept which, however, requires interconnections from the back to the front side by means of vias.Results on backside opening of polymer foils for exposing a thin metal film deposited at the front side are presented. For the experiments, a thin polyimide foil covered with a thin molybdenum metal film was used. By using mask projection of a pulsed UV-laser beam (248 nm, 20 ns) polymer foil was ablated. The laser ablation process must be adjusted in the manner to avoid damage of the thin metal film, to prevent cones formation at laser ablation, but still enabling the clean ablation of the polymer. The influence of process parameters on the backside opening is discussed and compared with theoretical estimations of the laser-induced temperatures. Using a two-step ablation process applying first high fluences to ablate the main part of the foil and finishing with low laser fluence turns out to be advantageous. This backside opening (BSO) can be used to perform an electrical contact from the backside. 相似文献
86.
M. Zimbone G. Litrico M. Barbera G. A. Baratta G. Foti 《Applied physics. B, Lasers and optics》2009,94(1):29-32
The defects produced in 4H-SiC epitaxial layers by irradiation with 200-keV H+ were characterized by low-temperature photoluminescence. These defects induce sharp luminescent lines, the so-called alphabet
lines. Their intensity shows an evolution under UV-laser irradiation not previously observed. By monitoring the change in
the resulting photoluminescence spectra versus time, we distinguish two original ‘families’ of peaks called PB1 and PB2. They display a different, and opposite, behaviour with laser irradiation but they are strongly correlated. In particular,
the recovering rate of the PB1 family and the growth rate of the PB2 family are the same, indicating a structural rearrangement of defects. 相似文献
87.
In this paper, the interaction between the inhomogeneous and anisotropic cloak covered infinitely long PEC circular cylinder
and the parallel electric-line-source is investigated in detail. First, the permittivity and permeability tensors of the cloak
are defined according to Pendry’s model, then the wave equation in the metamaterial cloak is derived; second, the far/near
properties of the model are investigated, and using the boundary conditions the electromagnetic fields of the whole region
are calculated analytically; finally, based on the analytical expressions, the electric fields of the whole region are demonstrated
through numerical results which show the effects of invisibility. Finally, the effects of loss on the performance of the invisible cloak are investigated. 相似文献
88.
Irini Michelakaki Stavros Pissadakis 《Applied Physics A: Materials Science & Processing》2009,95(2):453-456
The effect of 193 nm excimer laser radiation on the Knoop hardness and the elastic modulus of an ultra-phosphate glass is
presented here. The experimental results reveal that the glass matrix undergoes a significant softening and volume dilation
process for highly accumulated energy doses, where the Knoop hardness reduces by more than 15%, while following a single photon
absorption rule. Further, during the early stages of the exposure a slight hardening process is observed. Finally, the elastic
modulus is correlated with respect to the measured Knoop hardness. 相似文献
89.
We report on a new Laser Rapid Thermal Annealing (Laser-RTA) technique for one-step bandgap engineering at selected areas
of quantum semiconductor wafers. The technique is based on using a 150 W 980 nm fiber coupled laser diode and a 30 W TEM00
1064 nm Nd:YAG laser for background heating and ‘writing’, respectively, the regions of the quantum well intermixed (QWI)
material. The implementation of a 3D Finite Element Method for modeling of laser induced temperature profiles allows for the
design of processing schemes that are required for accurate bandgap engineering at the wafer level. We demonstrate that arbitrary
shaped lines of the QWI material can be fabricated with the Laser-RTA technique in InGaAs/InGaAsP quantum well microstructures. 相似文献
90.
Alessandra Ciapponi Stéphanie Palmier Jean-Yves Natoli Laurent Gallais 《Journal of luminescence》2009,129(12):1786-1789
Hafnia thin films for high-power optical coatings have been characterized by photoluminescence pumped by 4.66 eV photons and photothermal deflection measurements. These data are compared to the statistical laser damage behavior in order to find correlations between destructive and non-destructive characterizations. Thin films have been produced at two thicknesses and using different thin-film deposition techniques typically employed for optical coating fabrication: EBD (HfO2 target), EBD (Hf target), RLVIP and DIBS. The photoluminescence spectra show significant differences depending on the deposition techniques and thicknesses. EBD films show significant luminescence but the luminescence of ion-assisted films could not be distinguished from the uncoated substrate. All EBD coating spectra could be described by a linear combination of four bands. Further, XRD measurements show that the 255-nm-thick films had a relatively high crystallinity: EBD films contained the monoclinic phase and the ion-assisted films contained oriented nanocrystals of orthorhombic hafnia. The presence of orthorhombic phases indicates high compressive strain quenching the photoluminescence of these samples. 相似文献