Using two experimental techniques, we studied single crystals of the 122-FeAs family with almost the same critical temperature, T sub(c). We investigated the temperature dependence of the lower ...critical field H sub(c1) (T) of a Ca sub(0.32) Na sub(0.68) Fe sub(2) As sub(2) (T sub(c) approximate 34k) single crystal under static magnetic fields H parallel to the c axis. The temperature dependence of the London penetration depth can be described equally well either by a single anisotropic s-wave-like gap or by a two-gap model, while a d-wave approach cannot be used to fit the London penetration depth data. Intrinsic multiple Andreev reflection effect spectroscopy was used to detect bulk gap values in single crystals of the intimate compound Ba sub(0.65) K sub(0.35) Fe sub(2) As sub(2), with the same T sub(c). We estimated the range of the large gap value Delta sub(L) = 6-8 meV (depending on small variation of T sub(c)) and its a k space anisotropy of about 30%, and the small gap Delta sub(S) approximate 1.7 + or - 0.3 meV. This clearly indicates that the gap structure of our investigated systems more likely corresponds to a nodeless s-wave two gaps.
The structure of the superconducting order parameter of weakly underdoped BaFe
1.92
Ni
0.08
As
2
pnictides with the critical temperature
T
c
≈ 18.2 K has been determined. Two microscopic ...superconducting order parameters—the small superconducting gap Δ
S
(0) and, supposedly, the edges of the large gap with anisotropy in the
ab
plane
and
—have been determined at
T
≪
T
c
, together with their temperature dependences, using incoherent multiple Andreev reflection spectroscopy. It has been shown that the determined temperature dependence of the lower critical field
H
c1
(
T
) can be described in the two-band approximation both within the so-called alpha model (using experimental Δ
S
(0),
, and
values) and using the temperature dependences Δ
S
(
T
) and
obtained by multiple Andreev reflection spectroscopy under the assumption of a fairly strong anisotropy of the small superconducting gap, where the experimental Δ
S
(0) value is taken as the outer edge of its angular distribution.
A comparative study of residual thermal effects in aluminum following ns- and fs-laser ablation shows a surprisingly similar trend in their behavior, despite many differences between ns and fs ...laser-matter interactions. At laser fluences above the ablation threshold where plasmas are produced and at a sufficiently high ambient gas pressure, an enhanced coupling of pulsed laser energy to the sample occurs. This effect appears to be a universal phenomenon for both ns- and fs-laser ablation in gas media. Furthermore, in contrast to the common belief that residual thermal energy is negligible in fs-laser ablation, our study shows that up to 70% of the incident pulse energy can be retained in the sample following single-pulse fs-laserablation in 1-atm air. In both ns- and fs-laser ablation, the major factors governing thermal energy coupling to the sample are the laser fluence and ambient gas pressure. Residual thermal energy deposition decreases with reducing ambient gas pressure.
Abstract
Deterioration of the operation parameters of p-type Si surface-barrier detector and Si(Li) p-i-n detector upon irradiation by alpha-particles was investigated. The detectors were irradiated ...at room temperature up to a total number of the registered α-particles
N
α
equal to 6 × 10
9
. Prolonged irradiation has resulted in a deterioration of the detectors energy resolution ability and it was found that the increase of α-peaks broadening can be described by a linear function of
N
α
with a slope Δσ/Δ
N
α
∼ (1.4–1.8) × 10
–9
keV/α for both detectors. Resolution deterioration was associated with the increase of the detectors leakage current, which proceeds linearly with the number of absorbed α-particles with the slope ΔI/Δ
Nα
∼ (7-17) × 10
-17
A/α. The increase of the detectors reverse current was related with appearance of radiation-induced defect level at 0.56 eV above the valence band.
Subject of Research. We study the methods for determination of the physical and mechanical characteristics of materials based on parameters recording of a solid body-indenter impact interaction with ...the surface of the material under test. Among the methods considered, the method of dynamic indentation was chosen for further research. With the development of computing devices and electronic element base this method acquires new opportunities and advantages over the other methods of nondestructive testing. They are: the possibility of portable implementation of the device, an unrestricted control of products, the possibility of F-h diagrams construction and others. Method. We consider the application of the developed algorithm for the primary processing of a measuring signal obtained from a primary transducer under dynamic indentation. The results of the algorithm are compared with the results obtained from the ISPG-1 dynamic indentation device, previously developed at the Institute of Applied Physics of the National Academy of Sciences of Belarus. The results of the measuring signal processing were also compared with the results of computer simulation of the process of shock contact interaction by the finite element method. Main Results. An algorithm for processing of dynamic indentation primary signals is proposed. A model of dynamic indentation process is proposed. It is shown that the developed algorithm and model are efficient and show similar results in comparison with the results obtained with the existing dynamic indentation device. Practical Relevance. The obtained results can be used in the development of the domestic analogue of the dynamic indentation device.
The results of kinetic modeling by the Monte Carlo method of sputtering heavy d-metals of Ir, Os, and W group by nitrogen N
+
ions with energy in the range of 0.5–2.5 keV are presented. The ...coefficients of physical ion sputtering, the average sputtered atom energies, the reflection coefficients of the bombarding ions in the form of neutral nitrogen atoms, and the depth of ion penetration into the target were calculated. The calculations were performed for one-, two- and three-element targets, the partial ion sputtering coefficients of these metals were determined, and the influence of the surface binding energy on the ion sputtering parameters of individual target elements was studied. The calculations were performed for an Al target to compare the ion sputtering parameters of heavy d-metals and light aluminum. Despite the strong difference between the surface binding energy for these metals, their sputtering coefficients are of the same order of magnitude due to the fact that nitrogen ions penetrate deeper into aluminum and the exit of the recoil atoms from the target is impeded. The reflected or backscattered neutralized nitrogen atoms represent the second type of atomic particles emitted from the target. The coefficients of reflection of the bombarding nitrogen particles from the heavy metals and aluminum are determined.
Photoelectric properties of MIS tunnel diodes produced on high-resistive p-type silicon wafers with thin aluminium nitride AlN insulator layer and Pd or Al metal gate electrodes were investigated. It ...was found that synthesized AlN films possess a fixed positive charge, which leads to the creation of near-surface inversion layer in silicon substrate. The ratio of the photocurrent to the dark current K = Iph / Idark (on / off ratio) was found to depend on the gate electrode material, illumination intensity and the applied reverse bias. For studied MIS structures K ratio varied from 10 4 to 10 5 and was two orders of magnitude higher than that for the control MS structure without the insulator layer. High on / off ratio of such MIS structures with AlN tunnelling insulator promotes their application as an effective photodetectors in optoelectronics.
We discuss the synthesis, characterization, and comprehensive study of Ba-122 single crystals with various substitutions and various superconducting transition temperatures. We use five complementary ...techniques to obtain a self-consistent set of data on the superconducting properties of Ba-122. A major conclusion of our work is the coexistence of two superconducting condensates differing in the electron-boson coupling strength. The two gaps that develop in distinct Fermi surface sheets are nodeless in the kxky plane and exhibit s-wave symmetry; the two-band model suffices for the description of the main parameters of the superconducting state. A moderate interband coupling and a considerable Coulomb repulsion in the description of the two-gap superconducting state of barium pnictides favor the s++ model.
We present direct measurements of the superconducting order parameter in nearly optimal FeSe Te single crystals with the critical temperature
T
C
≈ 14 K. Using the intrinsic multiple Andreev ...reflection effect (IMARE) spectroscopy and measurements of the lower critical field, we directly determined two superconducting gaps, Δ
L
≈ 3.3−3.4 meV and Δ
S
≈ 1 meV, and their temperature dependences. We show that a twoband model fits well the experimental data. The estimated electron–boson coupling constants indicate a strong intraband and a moderate interband interaction.
Using incoherent multiple Andreev reflection effect spectroscopy, the gap structure of superconducting
(the 122-Se family) and the temperature evolution of the features caused by Andreev transport in ...I(V) and
d
I(V)/
d
V curves of planar SnS-contacts formed in this compound: the Andreev excess current
at
and the Andreev zero-bias conductance
are studied for the first time. The magnitude of the superconducting order parameter
meV is determined. The possibility of describing the obtained results within the available theoretical models is discussed.
PDF
