Difference approach to the analysis of resistivity recovery data for irradiated short-range ordered alloys

Electrical resistivity recovery (RR) data for irradiated concentrated alloys typically consist of two inseparable parts, one resulting from defect annihilation and the other from short-range order (SRO) effects. These parts exhibit different behaviour and often follow opposite trends. Therefore, in this case, analysis of RR data within the conventional method is too complicated. A new approach to data analysis of such a two-component RR is proposed. The approach involves a new quantity, the difference RR (DRR), which is composed of RR dependences of two similar samples irradiated to different defect concentrations. It is shown that the SRO formation proper and the stages corresponding to the onset of long-range migration of Frenkel pair defects, formed in each part of RR, can be clearly related to certain features of the DRR plots. This interrelationship allows detecting and identifying these stages in each part of RR separately. The validity of the approach is illustrated by analysis of the available pairwise RR data for Fe–16Cr–20Ni and Fe–4Cr alloys. It makes it possible to detect the small contribution from the SRO formation to RR in Fe–4Cr, which we failed to observe previously. It is shown that stage III of Fe–4Cr, which has a negligible contribution to the part of RR induced by defect annihilation, is clearly observed in the part induced by SRO formation.     

Recovery of electrical resistivity,short-range order formation and migration of defects in electron-irradiated Fe–4Cr alloy doped with carbon

Resistivity recovery (RR) data of Cr4 alloy doped with carbon (Cr4C) after irradiation with 5 MeV electrons are presented and compared with RR data of non-doped Cr4 alloy. Analysis of the defect- and short-range order-induced parts of RR has confirmed the proposed earlier scheme of the evolution of Frenkel pair defects on post-irradiation anneal in Cr4 and Cr9. Vacancies start free migration around 205–210?K; however, the related peak of stage III is invisible in conventional RR plots. Interstitials atoms (IAs) trapped in stage I at configurations of several Cr atoms start their long-range migration at 220?K. Migrating vacancies are captured by carbon atoms in Cr4C while IAs are not. Dissociation of vacancies from carbon atoms at 350?K gives rise to a decoration of carbon atoms with Cr atoms. Indications are seen that a release of vacancies captured by atoms of residual nitrogen takes place around 250–260?K.     

Role of nickel and manganese in recovery of resistivity in iron-based alloys after low-temperature proton irradiation

This study investigates the recovery of electric resistivity in pure iron, Fe–0.6Ni and Fe–1.5Mn as related to isochronal annealing following 1 MeV proton irradiation at lower temperature than 70 K, focusing on the relationship between solute atoms and irradiation defects. Both nickel and manganese prevent stage I_D recovery, which corresponds to correlated recombination. Stage II recovery is also changed by the addition of a solute, which corresponds to the migration of small interstitial clusters. In both pure iron and Fe–0.6Ni, no evident difference was observed in the stage III region, which corresponds to the migration of vacancies. In contrast, two substages appeared in the Fe–1.5Mn at a higher temperature than stage III_B appeared in pure iron. These substages are considered to represent the release of irradiation-induced defects, which was trapped by manganese.     

One-dimensional migration of interstitial clusters in SUS316L and its model alloys under electron irradiation

The one-dimensional (1D) migration of interstitial clusters in austenitic stainless steel SUS316L and its model alloys, namely, Fe–18Cr–13Ni, Fe–18Cr–13Ni–0.012C, and Fe–18Cr–13Ni–1.7Mn (mass %), was examined using in situ observation by high-voltage electron microscopy. Such 1D migration was confirmed to occur along the ?110? direction at irregular intervals in all these alloys under 1250-kV electron irradiation at room temperature. The frequency of 1D migration was found proportional to electron beam intensity, and was about 1/10 that in high-purity iron under the same irradiation intensity. The distance of 1D migration in the four alloys was less than 10?nm, which was much shorter than that in high-purity iron. No clear difference in the frequency or distance of 1D migration was observed among the four alloys, suggesting that minor solute/impurity elements have no apparent effect on 1D migration in SUS316L.     

Fabrication of Fe-doped TiO2 nanoparticles and investigation of photocatalytic decolorization of reactive red 198 under visible light irradiation

In this research, Fe-doped TiO₂ nanoparticles with various Fe concentrations (0. 0.1, 1, 5 and 10 wt%) were prepared by a sol–gel method. Then, nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDX), BET surface area, photoluminescence (PL) spectroscopy and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-particles was evaluated through degradation of reactive red 198 (RR 198) under UV and visible light irradiations. XRD results revealed that all samples contained only anatase phase. DRS showed that the Fe doping in the titania induced a significant red shift of the absorption edge and then the band gap energy decreased from 3 to 2.1 eV. Photocatalytic results indicated that TiO₂ had a highest photocatalytic decolorization of the RR 198 under UV irradiation whereas photocatalytic decolorization of the RR 198 under visible irradiation increased in the presence of Fe-doped TiO₂ nanoparticles. Among the samples, Fe-1 wt% doped TiO₂ nanoparticles showed the highest photocatalytic decolorization of RR198 under visible light irradiation.     

Analysis of the effect of the energy of interatomic interaction and the structure of Fe-Cr alloys on the processes of radiation-induced segregation after ion etching

We present the results of a comparative analysis of profiles of the radiation-induced segregation of chromium after irradiation of model alloys Fe-(9, 11, 14) at % Cr by He⁺ ions with the energy of 30 keV with fluences 10¹⁹–10²¹ ions/m² at 450°C and data on varying the moduli of normal elasticity and the structure of these alloys depending on the Cr concentration. It is shown that an interstitial migration mechanism is the determining factor in the case of chromium segregation near the surface. A correlation between the character of varying the elasticity moduli, order, and value of surface segregation and swelling of the Fe-Cr alloys depending on the Cr concentration is established.     

Blue–violet photoluminescence from colloidal suspension of nanocrystalline silicon in silicon oxide matrix

We report room temperature visible photoluminescence (PL), detectable by the unaided eye, from colloidal suspension of silicon nanocrystals (nc-Si) prepared by mechanical milling followed by chemical oxidation. The PL bands for samples prepared from Si wafer and Si powder peak at 3.11 and 2.93 eV respectively, under UV excitation, and exhibit a very fast (～ns) PL decay. Invasive oxidation during chemical treatment reduces the size of the nc-Si domains distributed within the amorphous SiO₂ matrix. It is proposed that defects at the interface between nc-Si and amorphous SiO₂ act as the potential emission centers. The origin of blue–violet PL is discussed in relation to the oxide related surface states, non-stoichiometric suboxides, surface species and other defect related states.     

Stage III-recovery of cold worked high-purity aluminium determined with a low-temperature calorimeter

Using a low-temperature calorimeter annealing effects were investigated in high-purity aluminium of varying grades of purity (Al 99.99, Al 99.999 and Al 99.9999) which had been subjected to deformation by torsion at liquid nitrogen. For the purpose of comparison, some residual resistivity measurements were performed on deformed and quenched Al 99.999.The calorimetric signals comprises two consecutive peaks (low-temperature peak and high-temperature peak) for each degree of deformation and purity. The low-temperature peak, with a maximum at 200 K-210 K, lies in the temperature range stage III, well-known from isochronous resistivity measurements. The effective activation energy of the annealing defects in this peak has the valueQ _m=0.62 eV/atom averaged over all degrees of deformation and purity, and is thus close to the known values of the activation energy of vacancy migration. Throughout the high-temperature peak, the position of which on the temperature scale depends strongly on the degree of deformation and purity, the processes of primaty recrystallization and dislocation recovery take place in the material. The coincidence of this peak with the changes of mechanical and electrical properties are in accordance with this interpretation. Thus to the usual nomenclature for isochronous resistance measurements, one may designate this peak a stage V reaction peak.In this paper the particular results of the low-temperature peak (stage III peak) are analysed and discussed. Then the experimental data are compared with the literature data derived from other measuring procedures.     

Surface acoustic-wave-induced magnetoresistance oscillations in a two-dimensional electron gas

We study the geometrical commensurability oscillations imposed on the resistivity of 2D electrons in a perpendicular magnetic field by a propagating surface acoustic wave (SAW). We show that, for omega相似文献   

Ⅱ-Ⅵ族碲化物体单晶低温光致发光谱研究

采用熔体法生长Ⅱ-Ⅵ族碲化物体单晶时,不同的生长条件及热经历过程会导致生长态晶体材料中,占主导的点缺陷类型存在较大的差异,进而影响了晶体的物理性能及器件的使用。低温光致发光(PL)谱作为一种无损检测方法,可以用于研究不同条件下生长的Ⅱ-Ⅵ族碲化物体单晶中的点缺陷和杂质的能级状态。对比富Te条件下生长的未掺杂ZnTe和CdTe晶体在8.6 K下的PL谱可以发现,电阻率较低的p型ZnTe晶体,其PL谱中,电子到中性受主复合发光峰(e, A0)强度高于施主-受主对复合发光峰(DAP),而高电阻率阻n型CdTe晶体则刚好相反,这可能是由于生长速率及降温过程的热经历不同导致占主导的本征点缺陷类型不同造成的。按化学计量比生长的未掺杂CdZnTe晶体,其PL谱中自由激子发光峰(D0, X)占主导,而(e, A0)峰强度高于DAP峰,变温PL谱测试表明当温度高于15 K时,(e, A0)峰与DAP峰逐渐叠加在一起。In掺杂导致在富Te条件下生长的CdZnTe晶体的PL谱中产生明显的A中心复合发光峰,与导带的能量差约为0.15 eV,主要与In补偿Cd空位形成的复合体[In+_CdV2-_Cd]-有关,且其强度与In掺杂元素的含量成正比。     

On factors affecting alloy clustering in In0.52Al0.48As layers grown on InP substrates by molecular beam epitaxy

Growth of In_0.52Al_0.48As epilayers on InP (100) substrates by molecular beam epitaxy at a wide range of substrate temperatures (470 - 550 °C) and V/III flux ratios is carried out. Low temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) measurements showed a strong dependence of the PL and XRD linewidths and lattice-mismatch on the substrate temperature. Minimum PL and XRD linewidths and lattice-mismatch were found to occur at substrate temperatures between ≈ 500 - 520 °C. The XRD intensity ratios (I_epi/I_sub) were generally higher within the same substrate temperature range at which the lattice-mismatch was the lowest. XRD rocking-curves of samples grown at low temperatures showed the main epilayer peak to be a composition of smaller peaks which can strongly indicate the presence of alloy clustering. PL spectra taken at increasing temperatures showed the quenching of the main emission peak followed by the evolution of a distinct peak at lower energy, possibly associated with carrier localization due to the presence of lattice disorder. Within the range of V/III flux ratios investigated (32 to 266), the lowest PL linewidth of 14 meV was recorded for the samples grown at a V/III ratio of 160. The lattice-mismatch between the epilayer and the substrate for these samples was also found to be relatively insensitive to changes in the V/III flux ratios.     

Competing ferromagnetism and superconductivity on FeAs layers in EuFe2(As0.73P0.27)2

We have measured the spin-polarized electron momentum density distributions of EuFe2(As0.73P0.27)2 by magnetic Compton scattering (MCS) measurements. For the first time, we show direct evidence of competing ferromagnetism and superconductivity (SC) on FeAs layers in this iron pnictide system. The MCS orbitalwise decomposition of the density distributions reveals that between 16 and 19 K, the spin-polarized Fe-3d character is enhanced (as the ferromagnetic character supersedes superconducting character), where the resistivity shows a maximum, reentrant SC-like peak, at 18 K. The spin polarization of the Fe-3d orbital, enhanced by ferromagnetic Eu ions, suppresses the SC around 18 K, while at other temperatures the system indeed exhibits SC where the Fe-3d spin polarization is suppressed or collapses.     

Optical properties of vertically aligned self-assembled InGaAs quantum dot layers on (311)A/B and (100) GaAs substrates

In this work, we present substrate orientation effects on optical properties in vertically stacked In_0.5Ga_0.5As layers grown by molecular beam epitaxy on (311)A/B and reference (100) GaAs substrates. Samples were grown for different GaAs spacer thicknesses. The spacer thickness variation shows the influence on PL spectra for all planes. The differences in peak shape, peak position, amplitude and integrated luminescence have been observed for all surfaces. These differences suggest that indium migration in spacer layers is caused by the strain fields induced by islands buried below, and is different at the three surfaces. Vertical electronic coupling between quantum dots is confirmed by photoluminescence temperature dependence.     

Influence of Grain Boundaries on the Electrical Conductivity of Copper Alloys

Technical Physics - The experimentally found insensitivity of the resistivity of Cu–Cr and Cu–Cr–Zr alloys to structural modifications in alloy specimens subjected to severe...     

Angular distribution of photoluminescence as a probe of bose condensation of trapped excitons

Recent experiments on two-dimensional exciton systems have shown that excitons collect in shallow in-plane traps. We find that Bose condensation in a trap results in a dramatic change of the exciton photoluminescence (PL) angular distribution. The long-range coherence of the condensed state gives rise to a sharply focused peak of radiation in the direction normal to the plane. By comparing the PL profile with and without Bose condensation, we provide a simple diagnostic for the existence of a Bose condensate. The PL peak has strong temperature dependence due to the thermal order parameter phase fluctuations across the system. The angular PL distribution can also be used for imaging vortices in the trapped condensate. Vortex phase spatial variation leads to destructive interference of PL radiation in certain directions, creating nodes in the PL distribution that imprint the vortex configuration.     

8—羟基喹啉金属螯合物的吸收光谱和发射光谱

测量了一系列８－羟基喹啉金属螯合物的吸收谱和发射谱，发现当喹啉螯合不同的金属阳离子，其各类光谱有不同程度的红移，本文经验地给出了８－羟基喹啉金属螯合物发射谱和吸收谱移动的规律并分析了金属离子影响光谱原因。     

Mössbauer spectroscopic studies of Fe-20 wt.% Cr ball milled alloy

Interesting differences were noticed in the alloying process during ball milling of Fe-10 wt.% Cr and Fe-20 wt.% Cr alloys by ⁵⁷Fe Mössbauer spectroscopic studies. In both cases, there is almost no diffusion of Fe in Cr or vice versa up to 20 h of milling time. As the powders are milled for another 20 h substantive changes occur in the Mössbauer spectra showing atomic level mixing. But the two compositions behave differently with respect to alloying. Fe-20 wt.% Cr sample does not differ much in the hyperfine field distribution as it is milled from 40 to 100 h. On the other hand, the hyperfine field distribution keeps on changing with milling time for Fe-10 wt.% Cr sample even up to 100 h of milling. The average crystallite size is found to be 7.5 nm for Fe-10 wt.% Cr and 6.5 nm in Fe-20 wt.% Cr after milling.     

Measurement of internal friction and shear modulus of aluminium-magnesium alloy after neutron irradiation at 78 K

The internal friction and shear modulus of polycrystalline Al + 3 at.% Mg was studied as a function of temperature after fast neutron irradiation, at liquid nitrogen temperature (78 K). The initial increase of shear modulus after irradiation is mainly due to the dislocation pinning of the irradiation induced defects. The further increase of shear modulus during annealing is caused by the bulk-effect. The recovery of shear modulus up to room temperature is similar to that of the residual electrical resistivity after a low temperature neutron irradiation. However, we may point out that in contrast to stage II, in stage III we observe a recovery of shear modulus that is distinctly more pronounced than that of electrical resistivity. The temperature dependence of internal friction, before irradiation, shows a peak at 230 K. After neutron irradiation we observe no peak in the temperature region, from 90 K to 300 K.     

High-Density Effects on the Exciton Systems and Their Dynamical Behavior in Al x Ga 1− x As/AlAs Quantum Wires

In Al x Ga 1 m x As/AlAs quantum wire (QWR) structures, the lower lying indirect exciton (IE) photoluminescence (PL) peak shows remarkable blue-shift under intense light-excitation contrary to the higher lying direct exciton (DE) PL band with very small blue-shift, although the two kinds of exciton states consist of the common hole state. In time-resolved PL spectra in the type-II QWR of x = 0.4, the DE PL band appears at an earlier stage without peak-shift and the excitons relax to the IE state making the IE PL peak dominant with time evolution. The blue-shift of the IE peak in a quasi equilibrium after the relaxation seriously depends on the excitation density. The origin of the blue-shift is explained in terms of many-body effects including band-bending effect due to the electric field induced by spatially separated electrons and holes in the QWR structures.     

Anomalous Electrical Conductivity and Magnetization in Fe–Cr–Ni Austenite–Martensite Alloys

Technical Physics - We have measured the temperature dependence of the resistivity and magnetization of a special steel of the Fe–Cr–Ni austenite–martensite class in a wide...