Sparse field level set method for non-convex Hamiltonians in 3D plasma etching profile simulations

Level set method [S. Osher, J. Sethian, J. Comput. Phys. 79 (1988) 12] is a highly robust and accurate computational technique for tracking moving interfaces in various application domains. It originates from the idea to view the moving front as a particular level set of a higher dimensional function, so the topological merging and breaking, sharp gradients and cusps can form naturally, and the effects of curvature can be easily incorporated. The resulting equations, describing interface surface evolution, are of Hamilton-Jacobi type and they are solved using techniques developed for hyperbolic equations. In this paper we describe an extension of the sparse field method for solving level set equations in the case of non-convex Hamiltonians, which are common in the simulations of the profile surface evolution during plasma etching and deposition processes. Sparse field method itself, developed by Whitaker [R. Whitaker, Internat. J. Comput. Vision 29 (3) (1998) 203] and broadly used in image processing community, is an alternative to the usual combination of narrow band and fast marching procedures for the computationally effective solving of level set equations. The developed procedure is applied to the simulations of 3D feature profile surface evolution during plasma etching process, that include the effects of ion enhanced chemical etching and physical sputtering, which are the primary causes of the Hamiltonian non-convexity.     

Φ90mm圆盘延伸机前卡钢分析

探讨了造成Φ90mm圆盘延伸机前卡钢的原因,分析了轧件轧制过程中的第一、第二次咬入的受力情况,提出了预防前卡钢的措施。该措施实施后,基本消除了前卡钢现象。     

Characteristics of copper oxide films deposited by PBII&D

Copper oxide films were deposited by plasma based ion implantation and deposition using a copper antenna as rf sputtering ion source. A gas mixture of Ar + O₂ was used as working gas. During the process, copper that was sputtered from the rf antenna reacted with oxygen and was deposited on a silicon substrate. The composition and the chemical state of the deposited films were analyzed by XPS. The structure of the films was detected by XRD. It is observed that Cu₂O film has been prepared on the Si substrate. It is found that the microstructure of the deposited film is amorphous for the applied voltage of − 5 kV. The surface layer of the deposited films is CuO. This is because the surface layer absorbs the oxygen from ambient air after the treated sample was removed from the vacuum chamber. An appropriate applied voltage, 2 kV under the present conditions, brings the lowest resistance. It is also seen that the maximum absorbance of the deposited films moves to a lower wavelength with increased applied voltage.     

PHON: A program to calculate phonons using the small displacement method

The program phon calculates force constant matrices and phonon frequencies in crystals. From the frequencies it also calculates various thermodynamic quantities, like the Helmholtz free energy, the entropy, the specific heat and the internal energy of the harmonic crystal. The procedure is based on the small displacement method, and can be used in combination with any program capable to calculate forces on the atoms of the crystal. In order to examine the usability of the method, I present here two examples: metallic Al and insulating MgO. The phonons of these two materials are calculated using density functional theory. The small displacement method results are compared with those obtained using the linear response method. In the case of Al the method provides accurate phonon frequencies everywhere in the Brillouin Zone (BZ). In the case of MgO the longitudinal branch of the optical phonons near the centre of the BZ is incorrectly described as degenerate with the two transverse branches, because the non-analytical part of the dynamical matrix is ignored here; however, thermodynamic properties like the Helmholtz free are essentially unaffected.

Program summary

Program title: PHONCatalogue identifier: AEDP_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEDP_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 19 580No. of bytes in distributed program, including test data, etc.: 612 193Distribution format: tar.gzProgramming language: Fortran 90Computer: Any Unix, LinuxOperating system: UnixRAM: Depends on super-cell size, but usually negligibleClassification: 7.8External routines: Subprograms ZHEEV and DSYEV (Lapack); needs BLAS. A tutorial is provided with the distribution which requires the installation of the quantum-espresso package (http://www.quantum-espresso.org)Nature of problem: Stable crystals at low temperature can be well described by expanding the potential energy around the atomic equilibrium positions. The movements of the atoms around their equilibrium positions can then be described using harmonic theory, and is characterised by global vibrations called phonons, which can be identified by vectors in the Brillouin zone of the crystal, and there are 3 phonon branches for each atom in the primitive cell. The problem is to calculate the frequencies of these phonons for any arbitrary choice of q-vector in the Brillouin zone.Solution method: The small displacement method: each atom in the primitive cell is displaced by a small amount, and the forces induced on all the other atoms in the crystal are calculated and used to construct the force constant matrix. Supercells of ∼100 atoms are usually large enough to describe the force constant matrix up to the range where its elements have fallen to negligibly small values. The force constant matrix is then used to compute the dynamical matrix at any chosen q-vector in the Brillouin zone, and the diagonalisation of the dynamical matrix provides the squares of the phonon frequencies. The PHON code needs external programs to calculate these forces, and it can be used with any program capable of calculating forces in crystals. The most useful applications are obtained with codes based on density functional theory, but there is no restriction on what can be used.Running time: Negligible, typically a few seconds (or at most a few minutes) on a PC. It can take longer if very dense meshes of q-points are needed, for example, to compute very accurate phonon density of states.     

The measurement of the dielectric and optical properties of nano thin films by THz differential time-domain spectroscopy

As feature sizes of circuits and devices approach 100 nm and chip frequencies climb into the upper GHz to THz range, it becomes increasingly important to have a convenient method of characterizing properties of thin dielectric films in the GHz to THz frequency range. THz time-domain spectroscopy provides a non-contact, non-destructive and highly sensitive optical tool to characterize the dielectric and optical properties of micron to nanometer scaled thin films at GHz and THz frequencies. The measurement of the dielectric and the optical properties of nanometer scaled dielectric films is performed using the THz differential time-domain spectroscopy. The real and imaginary parts of the complex dielectric constants and the optical constants of a variety of nano thin films are measured at GHz and THz frequencies.     

2-(苯甲基)-7-氯茚并[1,2-e][1,3,4]噁二嗪-2,4a(3H,5H)-二羧酸4a甲酯的合成

以5-氯-1-茚酮为起始原料,经羰基化、不对称氧化、腙化和缩合反应合成了高效杀虫剂茚虫威的关键中间体2-(苯甲基)-7-氯茚并[1,2-e][1,3,4]噁二嗪-2,4a(3H,5H)-二羧酸4a甲酯。以5-氯-1-茚酮计,产品总收率达61.1%,产品结构经核磁共振分析验证。探讨了原料配比、溶剂的选择、氧化剂等因素对反应收率的影响。     

Implementing peridynamics within a molecular dynamics code

Peridynamics (PD) is a continuum theory that employs a nonlocal model to describe material properties. In this context, nonlocal means that continuum points separated by a finite distance may exert force upon each other. A meshless method results when PD is discretized with material behavior approximated as a collection of interacting particles. This paper describes how PD can be implemented within a molecular dynamics (MD) framework, and provides details of an efficient implementation. This adds a computational mechanics capability to an MD code, enabling simulations at mesoscopic or even macroscopic length and time scales.     

Implantation effects of low energy H and D ions in germanium at −120 °C and room temperature

Germanium was implanted with 5 keV H and D ions at −120 °C or room temperature and thermally annealed in several steps. The samples were analysed at various stages by atomic force microscopy, ion channeling and Raman spectroscopy of Ge-H/D local vibration modes. The results are discussed in comparison with those in the well studied silicon. In general, the evolution of the different types of defects, in germanium at a given temperature, tends to be similar to that of the corresponding defects in silicon at 100-300 °C higher temperature. However, the behaviour of the defects detected by ion channeling (interstitials, lattice distortions) often appears unrelated to the chemical evolution measured by Raman scattering and to the temperature and isotope dependence of blistering.     

Fabrication of amorphous silicon films for arrayed waveguide grating application

Amorphous silicon (a-Si) optical films were deposited on a silicon substrate by ICP-PECVD at the temperature of 300 °C, using argon (Ar) and silane (SiH₄) as gas precursors, with the influences of precursors' flow rate, RF power and operating vacuum pressure on the optical properties and microstructure evolutions of a-Si films as the object of our investigation in this study. Optical characteristics of a-Si films indicated that optimum refractive index and extinction coefficient at 1550 nm wavelength can be achieved by using the process parameters of argon/silane flow rate of 400 sccm, RF power wattage of 40 W with an operating vacuum pressure of 60 Pa, respectively. Microstructure evolutions show that the few defects and silicon nano-crystallized structures existing in a-Si films might increase the extinction coefficient. We strongly suggest adopting the optimum process parameters and thermal annealing to fabricate a rib-type a-Si arrayed waveguide grating device with 8 channels and 1.6 nm channel spacing; and its coupling loss and propagation loss were about − 0.74 dB and − 0.14 dB/cm, respectively.