Plasma etching: From micro- to nanoelectronics

The role of plasma etching in the semiconductor technology upon switching from the microscale to the nanoscale dimensions is discussed. The continuing miniaturization has led to impossibility of simple scaling and further use of the conventional materials of silicon microelectronics. New materials and functional elements of integrated circuits call for revision of the existing plasma etching processes and development of novel processes. This situation brings plasma etching along with photolithography to the forefront of nanoelectronics technology.     

The singlet state in the Hubbard model with U=∞

We discuss, in connection with the problem of the ground state in the Hubbard model with U=∞, the normal (nonmagnetic) N-state of a system over the entire range of electron concentrations n≤1. It is found that in a one-particle approximation, e.g., in the generalized Hartree-Fock approximation, the energy ε ₀(n) of the N-state is lower than the energy ε _FM(n) of a saturated ferromagnetic state for all values of n. Using the random phase approximation we calculate the dynamical magnetic susceptibility and show that the N-state is stable for all values of n. A formally exact representation is derived for the mass operator of the one-particle electron Green’s function, and its expression in the self-consistent Born approximation is obtained. We discuss the first Born approximation and show that when correlations are taken into account, the attenuation vanishes on the Fermi surface and the electron distribution function at T=0 acquires a Migdal discontinuity, whose magnitude depends on n. The energy of the N-state in this approximation is still lower than ε _FM(n) for n<1. We show that the spin correlation functions are isotropic, which is a characteristic feature of the singlet states of the system. We calculate the spin correlation function for the nearest neighbors in the zeroth approximation as a function of n. Finally, we conclude that the singlet state of the system in the thermodynamic limit is the ground state. Zh. éksp. Teor. Fiz. 114, 2130–2144 (December 1998)     

Hyperactivated resistance in TiN films on the insulating side of the disorder-driven superconductor-insulator transition

We investigate the insulating phase that forms in a titanium nitride film in a close vicinity of the disorder-driven superconductor-insulator transition. In zero magnetic field the temperature dependence of the resistance reveals a sequence of distinct regimes upon decreasing temperature crossing over from logarithmic to activated behavior with the variable-range hopping squeezing in between. In perpendicular magnetic fields below 2 T, the thermally activated regime retains at intermediate temperatures, whereas at ultralow temperatures, the resistance increases faster than that of the thermally activated type. This indicates a change of the mechanism of the conductivity. We find that at higher magnetic fields the thermally activated behavior disappears and the magnetoresistive isotherms saturate towards the value close to quantum resistance h/e ². The article is published in the original.     

Microscopic model of the coexistence of superconductivity and ferromagnetism in the hybrid ruthenate-cuprate oxide RuSr2GdCu2O8

A microscopic t-J-I model with competing antiferromagnetic (J) and ferromagnetic (I) exchange interactions is proposed for strongly correlated electrons in RuSr₂GdCu₂O₈. It is assumed that for CuO₂ layers and for RuO₂ layers. A superconducting solution of $d_{x^2 - y^2 }$ symmetry was obtained for the CuO₂ layers while competition between ferromagnetism and p-type triplet superconducting pairing is obtained for RuO₂ layers. It is shown that the RuO₂ layers have a lower carrier concentration in the Hubbard subband formed by coupled ((d _xy -p)-π) orbitals compared with a bulk Sr₂RuO₄ crystal, which leads to stabilization of the ferromagnetic state in the RuO₂ layer.     

Superhigh resolution spectroscopy in methane with cold molecules

Use of optical selection of cold particles in saturated absorption spectroscopy is discussed. Owing to this we observed directly the splitting of a methane absorption line (=3.39 m) due to recoil effect in a light beam of 0.5 cm in diameter. The obtained width of nonlinear resonance of about 1 kHz corresponds to an effective temperature of particles of about 10^–1 K. The new direct absolute frequency measurement of the central hyperfine component of theF ₂ ⁽²⁾ line in methane (7–6 transition) made under these conditions gave the following value 88376181600.7±0.5 kHz. The behaviour of the resonance intensity of saturated absorption in the transit-time conditions is analysed. It has been shown that with an absorption cell inside a cavity the saturation resonance intensity in the transit-time region increases sharply.     

Estimation of microblock sizes in mosaic crystals according to fast electron radiation characteristics

The possibilities of a previously proposed technique for determining the characteristic sizes of microblocks in mosaic a??-class crystals have been analyzed. Determination is performed according to the ratio between the measured and calculated values for the diffraction suppression of the fixed-energy bremsstrahlung yield. The limits of applicability of the technique have been revealed. It is demonstrated that the technique can be implemented in an electron accelerator with the average energy E _e ?? 30?C40 MeV and long baselines making it possible to use crystal-diffraction spectrometers. The influence of microblock sizes on coherent electromagnetic processes in real crystals is discussed.     

Influence of crystal mosaicity on the X-radiation characteristics observed at a small angle to the particle velocity direction

b-class mosaic crystals, including pyrolytic graphite, are widely used as neutron and X-ray mono-chromators in experimental physics and ensure a more intense yield of monochromatic radiation than do perfect crystals. A new technique that has been proposed for calculating the X-ray reflectivity of these crystals via the Monte Carlo method is implemented. According to this technique, repeated reflections of photons inside crystals and the experiment geometry can be correctly estimated for an arbitrary mosaicity distribution.