Influence of resists on reactive ion etching

In the course of plasma etching we can observe a loading effect, i.e. the etch rate depends on the size of the etched surface exposed to the plasma. This phenomenon was explained according to Mogab by the plasma active etch species depletion via a rapid etch reaction. But there exist more coomplicated systems, for example SiO₂-photoresist SCR17-CHF₃, where the SiO₂ surface can be etched and a polymer layer can grow on the photoresist surface. The etching of SiO₂ is also influenced by different resists in the case of differences in their chemical structure. The degree of electrode coating with a resist influences both the etch rate of the masking layer. This may be used for the control of the etching selectivity in the SiO₂-resist system independently of other process parameters.The author is grateful to Mr. Z. Pokorný for his help in preparing the SiO₂ layers used in all experiments.     

On ricci-pseudosymmetric hypersurfaces in spaces of constant curvature

Results in Mathematics - This article studies the conditions of pseudosymmetry and Ricci-pseudosymmetry, realizedon hypersurfaces of semi-Riemannian spaces of constant curvature. In particular, we...     

Rearrangements in neutron shell closures far from stability

A survey of experimental results obtained at GANIL (Caen, Prance) on the study of the properties of very neutron-rich nuclei (Z = 6–20, A = 20–60) near the neutron drip line and resulting in an appearance of further evidence for the new magic number N = 16 is presented. Very recent data on mass measurements of neutron-rich nuclei at GANIL and some characteristics of binding energies in this region are discussed. Nuclear binding energies are very sensitive to the existence of nuclear shells and together with the measurements of instability of doubly magic nuclei ¹⁰He and ²⁸0 they provide information on changes in neutron shell closures of very neutron-rich isotopes. The behaviour of the two-neutron separation energies S_2n derived from mass measurements gives a very clear evidence for the existence of the new shell closure N = 16 for Z = 9 and 10 appearing between 2s_1/2 and ld_3/2 orbitals. This fact, strongly supported by the instability of C, N and O isotopes with N > 16, confirms the magic character of N = 16 for the region from carbon up to neon while the shell closure at N = 20 tends to disappear for Z ≤ 13. Decay studies of these hardly accessible short-lived neutron-rich nuclei from oxygen to silicon using the in-beam γ-ray spectroscopy are also reported.     

Synthesis of poly(tetrahydrofuran)‐b‐polystyrene block copolymers from dual initiators for cationic ring‐opening polymerization and atom transfer radical polymerization

A dual initiator (4‐hydroxy‐butyl‐2‐bromoisobutyrate), that is, a molecule containing two functional groups capable of initiating two polymerizations occurring by different mechanisms, has been prepared. It has been used for the sequential two‐step synthesis of well‐defined block copolymers of polystyrene (PS) and poly(tetrahydrofuran) (PTHF) by atom transfer radical polymerization (ATRP) and cationic ring‐opening polymerization (CROP). This dual initiator contains a bromoisobutyrate group, which is an efficient initiator for the ATRP of styrene in combination with the Cu(0)/Cu(II)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system. In this way, PS with hydroxyl groups (PS‐OH) is formed. The in situ reaction of the hydroxyl groups originating from the dual initiator with trifluoromethane sulfonic anhydride gives a triflate ester initiating group for the CROP of tetrahydrofuran (THF), leading to PTHF with a tertiary bromide end group (PTHF‐Br). PS‐OH and PTHF‐Br homopolymers have been applied as macroinitiators for the CROP of THF and the ATRP of styrene, respectively. PS‐OH, used as a macroinitiator, results in a mixture of the block copolymer and remaining macroinitiator. With PTHF‐Br as a macroinitiator for the ATRP of styrene, well‐defined PTHF‐b‐PS block copolymers can be prepared. The efficiency of PS‐OH or PTHF‐Br as a macroinitiator has been investigated with matrix‐assisted laser desorption/ionization time‐of‐flight spectroscopy, gel permeation chromatography, and NMR. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3206–3217, 2003     

Left symmetric left distributive operations on a group

We study equational theories of several left symmetric left distributive operations on groups. Normal forms of terms in the variety of LSLD groupoids, LSLD medial groupoids, LSLD idempotent groupoids and LSLD medial idempotent groupoids are found. Received October 11, 2001; accepted in final form December 9, 2004.     

Quantum chemical study of the electronic structure of NaX and NaY zeolites1

The CNDO/2 method is employed to determine S_III type positions for the location of Na cations in the faujasite zeolites. The minimum energy path of Na migration between these positions exhibiting an energy banier of 20 kJ/mol has been calculated.     

Computer analysis of coherent electric vibrations in biological systems

The Fröhlich condensed state may be created in the system of vibration modes if the energy supply is above the critical one. A model of a vibration system of a limited number of modes in the frequency range 0·1–4 THz with uniform density of state function and limited energy in the condensed state (saturation) is used for computer simulation. Energy stored in particular modes is calculated as a function of energy supply and energy leakage to the heat bath. The energy stored in the condensed state may be greater than the thermal energy of the system. In the saturated condensed state the stored energy is independent of energy supply. In the vicinity of the critical energy supply the change of the supply of the order of 10% switches on or off the condensed state. The interaction between systems with condensed states leads to interaction forces. Dependent on various conditions these forces may be attractive or repulsive.     

Einige Experimente zur Erfassung der Kontaktzone in Einem Membranstosswellenrohr

In order to get some information on the position and the contact front profile miniature double-electrode systems working in glow regime in the test gas have been used. The arrival of shock front and contact front have been detected reliably and resolved in time and space. Experimental results proved to be in good agreement with independent thin-film thermometer and interferometric measurements. The profile of the contact surface seems to be relatively flat. Only near to the wall substantial disturbances have been found which need further investigation.

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Einige Experimente zur Erfassung der Kontaktzone in Einem Membranstosswellenrohr

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DDR-69 Jena, Fröblestieg 3, G.D.R.

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Pukinovo n. 9, Praha 6, Czechoslovakia.

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Verstorben am 1. 12. 1971. Durch seinen Tod verloren die koautoren einen wertvollen Kollegen und lieben Freund.

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Herrn Dipl.-Ing. J. Blaha CSc. danken wir für die Durchführung der interferometrischen Messung und für die Bereitstellung der Interferenz-Aufnahme.     

On mean reward variance in semi-Markov processes

As an extension of the discrete-time case, this note investigates the variance of the total cumulative reward for the embedded Markov chain of semi-Markov processes. Under the assumption that the chain is aperiodic and contains a single class of recurrent states recursive formulae for the variance are obtained which show that the variance growth rate is asymptotically linear in time. Expressions are provided to compute this growth rate.