Exciton photoluminescence from ZnO layers produced by laser-induced gas breakdown processing

The plasma of optically-excited gas breakdown has been used to treat a Zn target in atmospheric pressure gases (air, O₂, N₂, Ar). The breakdown is produced near the target by a pulsed CO₂ laser radiation, yielding to a local erosion of the target under the irradiation spot and the formation of a porous nanostructured layer, consisting of ZnO nanoscale spheres. We show that the produced nanostructured layers exhibit an intense exciton emission band in the ultraviolet range (380–385 nm), while defect-related photoluminescent bands were weak and could be completely removed by varying the fabrication parameters. Properties of the produced layers were found to be very promising for the development of optoelectronic devices. PACS 81.16.Mk; 81.05.-t     

Investigation of perceptual constancy in the temporal-envelope domain

The ability to discriminate complex temporal envelope patterns submitted to temporal compression or expansion was assessed in normal-hearing listeners. An XAB, matching-to-sample-procedure was used. X, the reference stimulus, is obtained by applying the sum of two, inharmonically related, sinusoids to a broadband noise carrier. A and B are obtained by multiplying the frequency of each modulation component of X by the same time expansion/compression factor, alpha (alphain[0.35-2.83]). For each trial, A or B is a time-reversed rendering of X, and the listeners' task is to choose which of the two is matched by X. Overall, the results indicate that discrimination performance degrades for increasing amounts of time expansion/compression (i.e., when alpha departs from 1), regardless of the frequency spacing of modulation components and the peak-to-trough ratio of the complex envelopes. An auditory model based on envelope extraction followed by a memory-limited, template-matching process accounted for results obtained without time scaling of stimuli, but generally underestimated discrimination ability with either time expansion or compression, especially with the longer stimulus durations. This result is consistent with partial or incomplete perceptual normalization of envelope patterns.     

Process Parameters Optimization,Characterization, and Application of KOH-Activated Norway Spruce Bark Graphitic Biochars for Efficient Azo Dye Adsorption

In this work, Norway spruce bark was used as a precursor to prepare activated biochars (BCs) via chemical activation with potassium hydroxide (KOH) as a chemical activator. A Box–Behnken design (BBD) was conducted to evaluate and identify the optimal conditions to reach high specific surface area and high mass yield of BC samples. The studied BC preparation parameters and their levels were as follows: pyrolysis temperature (700, 800, and 900 °C), holding time (1, 2, and 3 h), and ratio of the biomass: chemical activator of 1: 1, 1.5, and 2. The planned BBD yielded BC with extremely high SSA values, up to 2209 m²·g⁻¹. In addition, the BCs were physiochemically characterized, and the results indicated that the BCs exhibited disordered carbon structures and presented a high quantity of O-bearing functional groups on their surfaces, which might improve their adsorption performance towards organic pollutant removal. The BC with the highest SSA value was then employed as an adsorbent to remove Evans blue dye (EB) and colorful effluents. The kinetic study followed a general-order (GO) model, as the most suitable model to describe the experimental data, while the Redlich–Peterson model fitted the equilibrium data better. The EB adsorption capacity was 396.1 mg·g⁻¹. The employment of the BC in the treatment of synthetic effluents, with several dyes and other organic and inorganic compounds, returned a high percentage of removal degree up to 87.7%. Desorption and cyclability tests showed that the biochar can be efficiently regenerated, maintaining an adsorption capacity of 75% after 4 adsorption–desorption cycles. The results of this work pointed out that Norway spruce bark indeed is a promising precursor for producing biochars with very promising properties.     

Improving impossible-differential attacks against Rijndael-160 and Rijndael-224

Impossible-differential attacks are a very efficient form of cryptanalysis against block ciphers. In this paper, we improve the existing impossible-differential attacks against Rijndael-160 and Rijndael-224.     

The nature of the predominant acceptors in high quality zinc telluride

We report very sharp bound exciton luminescence spectra in high quality melt-grown very lightly compensated ZnTe, p-type with N_A-N_D in the low 10⁺¹⁵ cm^-3. Bound exciton localisation energies at seven shallow neutral acceptors with E_A between ~55 and ~150 meV are very insensitive to E_A. Optical absorption and dye laser luminescence excitation spectroscopy were necessary to obtain a full separation of the transitions due to different acceptors, together with a study of certain ‘two-hole’ luminescence satellites in which the acceptor is left in a series of orbital states after bound exciton decay. Two shallow acceptors are P_Te and As_Te, a third possibly Li_Zn while a fourth, relatively prominent in our best undoped crystals, may be a complex. A deeper, 150 meV acceptor, frequently reported in the ZnTe literature and electrically dominant in most of our undoped crystals has the Zeeman character of a point defect. We present clear evidence from our spectra that this energy does not represent the binding of a single hole at a doubly ionized cation vacancy, a popular attribution since 1963. This acceptor may be covered by another impurity, possibly Cu_Zn. We also report bound phonon effects, lifetime broadening of excited bound exciton states and observe a single unidentified donor with E_D ~18.5 meV. This energy is determined using selective dye laser excitation at the weak neutral donor bound exciton line and from the onset of valence band to ionized donor photo-absorption.     

Size dependent photoluminescence from Si nanoclusters produced by laser ablation

We report a photoluminescence study of silicon nanoclusters deposited by laser ablation. This technique allows to obtain clusters with a reduced size dispersion. Taking advantage of that as well as of the possibility to tune selectively the cluster size relatively to the preparation parameters, we are able to make a fine correlation between the emission band and the corresponding emitting size. The photoluminescence band can be tuned in a wide spectral region spreading from the near ultraviolet to the near infrared depending on preparation conditions. The correlation with atomic force microscopy measurements provides a size dependence of the luminescence which is fully consistent with the quantum confinement interpretation. To our knowledge, we present here the first observation of a wide spectral range tuning of the emission bands of nanocrystalline silicon by using a dry technique compatible with clean vacuum processing.     

Average life of oxygen vacancies of quartz in sediments

Average life of oxygen vacancies of quartz in sediments is estimated by using the ESR(electron spin resonance) signals of E' centers from the thermal activation technique. The experi-mental results show that the second-order kinetics equation is more applicable to the life estima-tion compared with the first order equation. The average life of oxygen vacancies of quartz from4895 to 4908 deep sediments in the Tarim Basin is about 10~(18) a at 27℃.     

Structural Surface Features of Paramagnetic Multifunctional Nanohybrids Based on Silver Oleic Acid

Sols of core–shell silver nanoparticles (AgNPs) are synthesized by electrochemical method. The method provides the ability to adjust the particle size by changing both the concentration of oleic acid and the residence time τ₀ in the organic phase. We synthesized AgNPs with oleic acid (OA) concentration of 0.25% (AgNPs & 0.25% OA) and 0.75% (AgNPs & 0.75% OA). These nanoparticles have been studied using modern physical–chemical methods. Differential thermal analysis curves indicate the chemical nature of bond ligand in the secondary shell; this conclusion is confirmed by quantum chemical simulation and semi-empirical calculation. In the electron paramagnetic resonance spectra of silver-containing sols AgNPs & 0.25% OA and AgNPs & 0.75% OA complex wide asymmetric signals of 500–800 G and g-factor of 2.09–2.13 are recorded, in addition, in the spectra of AgNPs with bilayer the pronounced ferromagnetic contribution is observed. The change of the oleic acid layers of the particles affects the dimension of the nanocrystallites that are being formed and the manifestation of their magnetism.

Trial registration number and date of registration JCS-P-20-03-0188.R1, 22-Sep-2020 (02-Mar-2020)

Graphic Abstract

     

Synthesis of Glutamic Acid-based Cluster Galactosides and Their Binding Affinities with Liver Cells

Structurally well defined di-, tri- and tetra-valent cluster galactosides were synthesized in a convenient way.Oligo-glutamic acids were assembled as scaffolds. The presence of amine groups in these three ligands is expected to couple with drugs or genes for delivery. The binding affinities of these cluster galactoses to liver cells were determined by in vitro binding studies. Among them, the tetravalent cluster galactose (19) showed the highest affinity to liver cell. It is therefore a promising targeting device for the specific delivery of drugs or genes to parenchymal liver cells.     

分光光度法测定海洋生物体中的铜

本文提出采用浓HNO_3-H_2O_2在低温常压下消化海洋生物样品的新方法,其特点是使用试剂简单,操作方便,节省时间,方法可靠。还介绍使用正交设计法试验了影响测铜灵敏度的主要因素。认为测定样品时,选择pH8.0～8.5、隐蔽剂10ml、铜试剂5 ml为最佳条件。本法还分别作了方法验证,结果良好。