排序方式: 共有138条查询结果,搜索用时 15 毫秒
111.
Manish Prasad Patrick F. Conforti Barbara J. Garrison 《Applied Physics A: Materials Science & Processing》2008,92(4):877-881
Experimental and theoretical studies of laser ablation of polymers, under various processing conditions, have identified many
possible photoexcitation pathways and consequently many likely processes responsible for the onset of ablation. We investigate
the role of these processes—namely the thermal, mechanical and chemical processes—occurring in a polymeric substrate during
UV irradiation. Molecular dynamics simulations with an embedded Monte Carlo-based reaction scheme were used to study ablation
of Poly (methyl methacrylate) at 157 nm. Laser-induced heating and chemical decomposition of the polymeric substrate are considered
as ablation pathways. For the heating case, the mechanism of ejection is thermally driven limited by the critical number of
bonds broken. This fragmentation process is well reproduced by the existing bulk photothermal ablation model. Alternatively,
if the photon energy goes toward direct bond breaking, it initiates chemical reactions, polymer unzipping, and formation of
gaseous products leading to near complete decomposition, loss of strength and cohesiveness of the top layers of the polymeric
substrate. The ejection of small gaseous molecules weakens and hollows out the substrate, facilitating liftoff of larger fragments
of material. These larger clusters are thermally ejected and the photochemical ablation process can be described by the two-step
model proposed by Kalontarov. 相似文献
112.
M. Rabah D. Rached R. Khenata N. Moulay 《Journal of Physics and Chemistry of Solids》2008,69(11):2907-2910
We report local density-functional calculations using the full-potential linearized muffin-tin orbital method (FP-LMTO) for platinum carbide (PtC) in the, rock-salt (B1), zinc-blende (B3), wurtzite (B4), nickel-arsenide (B8) and PbO (B10) structures. The ground state properties such as the equilibrium lattice constant, elastic constants, the bulk modulus and its pressure derivative of PtC in these phases are determined and compared with available experimental and theoretical data.Our calculations show that the ground state phase of PtC to be zinc-blende (B3) structure at zero pressure and the nickel-arsenide (B8) structure is a high-pressure phase. The transition pressures at which this compound undergoes the structural phase transition from (B3) to (B8) and from (B3) to (B1) are found to be 34.25 and 51.28 GPa, respectively. The highest bulk modulus values in the nickel-arsenide (B8), zinc-blende (B3), rock-salt (B1) and PbO (B10) structures indicate that PtC is a hard material. 相似文献
113.
Patrick F. Conforti Manish Prasad Barbara J. Garrison 《Applied Physics A: Materials Science & Processing》2008,92(4):1037-1041
Molecular dynamics (MD) simulations are used to study the interactions of photons with a poly(methyl methacrylate), or PMMA,
substrate and point thermal absorbers. The point thermal absorbers are embedded within the polymer matrix which can be excited
and transfer energy to the surrounding particles through an internal vibrational mode. Using a fluence above the ablation
threshold, two excitation channels are studied—one includes a direct heating of the polymer and the other includes the excitation
of the thermal absorbers. Although the yield of ejected particles is similar for both simulations, the plume composition differs.
For the simulation of the excitation of the point thermal absorbers, the plume consists of a greater number of smaller substrate
fragments due to local high temperature regions. 相似文献
114.
采用对函数进行环形分解的技术和对算子进行截断的方法,得出分数次积分算子Is在齐次双权Morrey-Herz空间上的有界性。 相似文献
115.
讨论了如下定义的带粗糙核的超奇异积分算子:
TΩ,α,hf(x)=p.v.∫R^nh(|y|)(Ω(y′))/(|y|^n+a)f(x-y)dy
的(Lα^p(ω),L^p(ω))有界性,推广了已有的结果.这里0≤α〈1,1〈p〈∞,Ω为H^q(S^n-1)中的函数,q=(n-1)/(n-1+α),且h(|y|)∈△γ(R+)={supR〉0 R-1∫0^R (|h(t)|^γdt) },γ〉1,ω是某类径向权. 相似文献
116.
A novel electroless method of producing porous silicon carbide (PSiC) is presented. Unlike anodic methods of producing PSiC, the electroless process does not require electrical contact during etching. Rather, platinum metal deposited on the wafer before etching serves as a catalyst for the reduction of a chemical oxidant, which combined with UV illumination injects holes into the valence band, the holes subsequently participating in the oxidation and dissolution of the substrate. The etchant is composed of HF and K2S2O8 in water. Various porous morphologies are presented as a function of etchant concentration, time of etching, and SiC polytype. Wafer quality is of the utmost concern when utilizing the electroless wet etchant, since defects such as stacking faults, dislocations, and micropipes have a large impact on the resulting porous structure. Results of imaging and spectroscopic characterization indicate that the porous morphologies produced in this manner should be useful in producing sensors and porous substrates for overgrowth of low dislocation density epitaxial material. 相似文献
117.
H. Katayama-Yoshida T. KoyanagiH. Funashima H. HarimaA. Yanase 《Solid State Communications》2003,126(3):135-139
Based on ab initio electronic structure calculation using a super-cell FLAPW method, we propose a new valence control method for the fabrication of low-resistive p-type and transparent conducting oxides of Delafossite CuAlO2. We propose a Cu-vacancy doping method with decreasing the Cu-vapor pressure and with increasing the oxygen vapor pressure, or, Be- or Mg-acceptor doping method at the Al-site with decreasing the Al-vapor pressure and with increasing the Cu-vapor pressure. The heavily doped p-type CuAlO2 indicates the two-dimensional nested Fermi surfaces, which originate from the layered O-Cu-O dumbbell. Nested Fermi surfaces may cause possibly a lattice instability or a transparent superconductivity rather than magnetism. 相似文献
118.
Analysis of low-temperature photoluminescence measurements performed on single silicon nanocrystals is presented. The luminescence emission linewidth of Si nanocrystals is found to be less than thermal broadening at low temperature, confirming the atomic-like nature of their energetic states. Beside the main peak the low-temperature spectra reveal a ∼6 meV replica, the origin of which is discussed. For some of the investigated dots, we also observe a ∼60 meV transverse optical (TO) phonon replica. The regular arrangement of individual nanocrystals used in this work enables combined high-resolution transmission electron microscopy (TEM) and low-temperature photoluminescence characterization of the same single quantum dot. 相似文献
119.
We present valence electron Compton profiles calculated within the density-functional theory using the all-electron full-potential projector augmented-wave method (PAW). Our results for covalent (Si), metallic (Li, Al) and hydrogen-bonded ((H2O)2) systems agree well with experiments and computational results obtained with other band-structure and basis-set schemes. The PAW basis set describes the high-momentum Fourier components of the valence wave functions accurately when compared with other basis set schemes and previous all-electron calculations. 相似文献
120.
This paper describes elaboration of two dimensional photonic crystal structures based on Thue–Morse sequence. Our results establish that the optical properties of these aperiodic multilayer systems can be tailored by adjusting either the radius of some cells of the proposed structure or defect characteristics. We introduce a resonant cavity in the proposed structure to select desirable wavelengths for filtering. Bandwidth of selected wavelengths are about 1 nm and suitable for communication applications. Also, our simulations show that efficiency of the proposed structure is enough. The total footprint of proposed filter is 331.24 μm2, therefore it is suitable to be integrated in all optical chips. 相似文献