More on the frequency spectrum of an artificial amorphous solid

Summary In a previous paper on the same subject an analysis of the frequency spectrum of an amorphous Lennard-Jones solid, as determined by methods of molecular dynamics by Rahman and collaborators, was given. There the general form of the spectrum was considered. Here we show how the analysis of the spectrum can be refined so as to allow a separation of the contribution of the propagating waves from the contribution of that fraction of atomic oscillations that do not possess propagational character. It is thus possible to bring indirectly into evidence bands of transverse and longitudinal waves, contributing a nonnegligible fraction of atomic motion.     

Statistical simulation of the structure of amorphous alloys

Summary The total and partial distribution functions of a metalloid/transition-metal amorphous alloy (Fe₈B₁₅) have been calculated by means of a ?nonstandard? hard-sphere dense-random-packing model. Based on these results, a comparison with the ?canonical? dense-random-packing model is discussed.

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Riassunto Si presenta un calcolo delle funzioni di distribuzione radiale parziali e totali di una lega metallo-metalloide amorfa (lega Fe-B) generate mediante simulazione numerica. La struttura viene realizzata tramite un modello ad impaccamento di sfere rigide basato su criteri di crescita probabilistici. I risultati sono confrontati con il modello ad impaccamento denso e casuale (dense random packing) ?canonico? di Bennet.

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Резюме Вьічисляются полньіе и парциональньіе функции распределения для аморфного сплава ?металлоид-переходной металл? (Fe₈B₁₅), используя ?нестандартную⎴ модель плотной случайной упаковки твердых сфер. Полученные результаты сравниваются с результатами ?канонической? модели плотной случайной упаковки.

     

On the frequency spectrum of an artificial amorphous solid

Summary The frequency spectrum of an amorphous Lennard-Jones solid, as determined by molecular-dynamics methods, is entirely different from that of a crystalline solid of the same nature, although its radial distribution function shows the environment of each atom to be similar in both cases. Such a disparity is interpreted in terms of a preponderance of the effects of the local forces (i.e. those between direct neighbours) which, in the case of the amorphous solid, is supposed to take place because of the absence of long-range co-ordination among individual atomic motions. To give the observed spectrum, this feature combines with a structure in which atomic clusters of different radii seem to coexist.

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Riassunto Lo spettro di frequenza di un solido amorfo costituito da atomi che interagiscono secondo un potenziale di Lennard-Jones risulta, secondo ricerche di dinamica molecolare, del tutto diverso da quello di un solido cristallino della stessa natura. D'altra parte la funzione di distribuzione radiale non mostra, nella regione del picco principale, cioè quella dei vicini diretti, nessuna significativa deviazione dalla normale struttura del solido cristallino. Questa disparità degli effetti di quelle che sono essenzialmente le stesse forze è interpretabile in termini di una quasi indipendenza delle oscillazioni locali che si unisce, per dare il caratteristico spettro osservato, ad una peculiare struttura nella quale coesistono gruppi sferici di atomi vicini aventi raggi, entro certi limiti, diversi.

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Резюме Частотный спектр аморфного твердого тела Леннарда-Джонсона, определяемЫй методами молекулярной динамики, оказЫвается полностью отличнЫм от частотного спектра кристаллического твердого тела той же природЫ; хотя радиальные функции распределения показывают, что окружение каждого атома является сходным в обоих случаях. Таксе несоответствие интерпретируется в терминах преобладания эффектов локальных сил (t.e. сил между соседними атомами), которое, как предполагается, имеет место в случае аморфного твердого тела, t.e. отсутствуют длиннодействуюшие корреляции между движениями отдельных атомов. Чтобы получить наблюдаемый спектр, эта особенность комбинируется со структурой, в которой сосуществуют атомные кластеры различных радиусов.

     

Anomalous interaction between phonons and IVAP-originated two-level systems

Summary The first-principle dynamics of IVAP-originated two-level systems is developed with reference to phonon-scattering and thermally activated processes. It is shown that the anomalous coupling term βδ, appearing in the phonon-IVAP interaction, originates from the elastic polarity ξ characteristic of the IVAP-like defects. The formal expressions for the quantities of interest, such as the resonant-scattering rate of phonons and the time-dependent density of TLS states, are given analytically. Since the tunnelling-atom theory is a limit case (β=0) of the present general approach, a point-by-point comparison with the standard formalism of tunnelling-originated TLS is performed. This work was partially supported by Ministero della Pubblica Istruzione.     

A statistical approach to the serial condensation of amorphous clusters

Summary A numerical simulation is proposed of extended closepacked systems of hard spheres obtained by serial deposition. The process takes into account a random contribution to the growth of the aggregate; in this way, without using relaxation potential methods, it was possible to reproduce, even for large systems, the splitting of the second peak in the pair correlation function, evidenced both by experimental arrangements of hard spheres and by measurements on amorphous alloys.

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Riassunto Si presenta un metodo di simulazione numerica per la generazione di una struttura amorfa compatta basato sulla deposizione in sequenza di sfere rigide identiche. Il processo di crescita dell’aggregato è basato su criteri probabilitisci ed ha permesso di riprodurre, senza dover ricorrere a tecniche di rilassamento, lo sdoppiamento del secondo picco della funzione di correlazione delle coppie, presente sia nelle misure su metalli amorfi che negli aggregati sperimentali di sfere rigide.

     

非线性光学中的新型有机和聚合分子材料

近年来的研究成果表明在非线性光学中一些有机和聚合分子材料与相应的无机晶体、半导体如LiNbO₃、GaAs等相比较,具有许多优越性。本文介绍了一些有机和聚合分子材料的非线性光学效应,包括模拟,离散和双稳现象及其潜在的应用。然后描述了几种这类晶体与薄膜材料的制备技术,其中LB膜沉积是制备超薄有机聚合膜的有效方法。     

Development of organic light‐emitting diodes for electro‐optical integrated devices

Organic light‐emitting diodes (OLEDs) are discussed for electro‐optical integrated devices that are used for optical signal transmission. Organic optical devices including polymeric optical fibers are used for optical communication applications to realize polymeric electro‐optical integrated devices. The OLEDs were fabricated by vacuum process, i.e. the organic molecular beam deposition (OMBD) technique or a solution process on a polymeric or a glass substrate, for comparison. Optical signals faster than 100 MHz have been created by applying pulsed voltage directly to the OLED utilizing rubrene doped in 8‐hydoxyquinolinum aluminum (Alq₃), as an emissive layer. OLEDs fabricated by solution process utilizing rubrene doped in carrier‐transporting materials have also discussed. OLEDs utilizing polymeric materials by solution process are also fabricated and discussed. Moving‐picture signals are transmitted utilizing both vacuum‐ and solution‐processed OLEDs, respectively.     

Behavior of Deuterium in Boron Films Covered by Oxygen-Containing Layer

Boron is an attractive candidate of the first wall coating materials in fusion reactors. The behavior of deuterium implanted into boron films has been studied . This paper reports the effect of thin oxygen-containing boron layer on the behavior of deuterium im- planted into boron film by X-ray photoelectron spectroscopy （XPS） and thermal desorption spectroscopy （TDS）.     

Nanocomposite‐based stretchable optics

Stretchable and conformable optical devices open up very exciting perspectives for the fabrication of systems incorporating diffracting and optical power in a single element. Supersonic cluster beam implantation of silver nanoparticles in an elastomeric substrate grooved by molding allows effective fabrication of cheap and simple stretchable optical elements able to withstand thousands of deformations and stretching cycles without any degradation of their optical properties. The nanocomposite‐based reflective optical devices were characterized both morphologically and optically showing excellent performances and stability compared to similar devices fabricated with standard techniques. The nanocomposite‐based devices can therefore be applied to arbitrary curved nonoptical grade surfaces in order to achieve optical power and to minimize aberrations like astigmatism. The high resilience of the nanocomposite material on which the devices are based allows them to be peeled and reused multiple times.     

Microstructured Ultrathin HDPE Films Prepared by Selective Oriented Recrystallization

The recrystallization behavior of surface-modified melt-drawn HDPE thin films having a vacuum-evaporated carbon layer was studied by means of transmission electron microscopy and electron diffraction. The results show that, by surface modification with the carbon layer, the orientation of the melt-drawn highly oriented HDPE film can be preserved after complete melting and subsequent recrystallization for any condition. Based on the orientation maintenance phenomenon of the carbon-coated preoriented HDPE films, micrometer-structured, thin HDPE films with well-defined oriented and nonoriented structures were prepared by selectively coating the melt-drawn-oriented HDPE thin film with the help of a micrometer-structured mask and subsequent melt recrystallization. A potential application of the thus prepared micrometer-structured HDPE thin films stems from the fact that they exhibit conspicuous different birefringence between the areas with and without carbon coating under polarized optical microscopy. This may provide us with a new route toward polarization-dependent displays.     

Influence of the Morphology of Lysozyme‐Shelled Microparticles on the Cellular Association,Uptake, and Degradation in Human Breast Adenocarcinoma Cells

The ultrasound‐assisted self‐assembly and cross‐linking of lysozyme at the water–air and water–perfluorohexane interfaces are shown to produce lysozyme‐shelled hollow microbubbles (LSMBs) and microcapsules (LSMC), respectively. The arrangement of lysozyme at the air–liquid or oil–liquid interfaces is accompanied by changes in the bioactivity and conformational state of the protein. The interaction of LSMB and LSMC with human breast adenocarcinoma cells (SKBR3) is studied. LSMB and LSMC are phagocyted by cells within 2 h without exerting a cytotoxic activity. The cellular internalization kinetics of LSMB and LSMC and the effects on cell cycle are evaluated using flow cytometry. Evidence for the internalization of microparticles and degradation within the cell are also monitored by confocal and scanning electron microscopic analyses. The integrity of cell membrane and cell cycle is not affected by LSMBs and LSMCs uptake. These studies show that the positively charged LSMB and LSMC are not cytotoxic and can be readily internalized and degraded by the SKBR3 cells. LSMBs and LSMCs show a different uptake kinetics and intracellular degradation pattern due to differences in the arrangement of the protein at the air–liquid or oil–liquid interfaces.     

Demonstration of polycrystalline thin film coatings on glass for spin Seebeck energy harvesting

The spin Seebeck effect, a newly discovered phenomena, has been suggested as a potential ‘game changer’ for thermoelectric technology due to the possibility of separating the electric and thermal conductivities. This is due to a completely different device architecture where, instead of an arrangement of p‐ and n‐type pillars between two ceramic blocks, a thermopile could be deposited directly onto a magnetic film of interest. Here we report on the spin Seebeck effect in polycrystalline Fe₃O₄:Pt bilayers deposited onto amorphous glass substrates with a view for economically viable energy harvesting. Crucially, these films exhibit large coercive fields (197 Oe) and retain 75% of saturation magnetisation, in conjunction with energy conversion comparable to epitaxially grown films. This demonstrates the potential of this technology for widespread application in harvesting waste heat for electricity.     

Light emissions from a silicon nanocrystal thin film prepared by phase separation of hydrogen silsesquioxane

We report a facile method to prepare thin film of Si nanocrystals embedded SiO₂ (Si-NC:SiO₂) by annealing a photoresist of hydrogen silsesquioxane (HSQ) at 1100 °C in nitrogen via a phase separation process. The spatial density, photoluminescence intensity, the photoluminescence efficiency and electroluminescence intensity of Si-NC of the sample made from HSQ, or HSQ sample, were 15.0, 5.5, 1.5 and 7.9 times as large as those of the sample made by a traditional method of annealing SiO_x (1<x<2), or SiO_x sample, respectively. Meanwhile, the turn-on voltage of electroluminescence of the HSQ sample was only 3.8 eV, which was more than 2 times smaller than that of the SiO_x sample. The results of this work may find application in developing high brightness Si light sources.     

等离子辅助后处理对锰掺杂氮化钛薄膜磁特性的影响

The ferromagnetic manganese doped TiN films were grown by plasma assisted molecular beam epitaxy on MgO(001) substrates. The nitrogen concentration and the ratio of manganese at Ti lattice sites increase after the plasma annealing post treatment. TiN(002) peak shifts toward low angle direction and TiN(111) peak disappears after the post treatment. The lattice expansion and peak shift are mainly ascribed to the reduction of nitrogen vacancies in films. The magnetism was suppressed in as-prepared sample due to the pinning effect of the nitrogen vacancies at defect sites or interface. The magnetism can be activated by the plasma implantation along with nitrogen vacancies reduce. The decrease of nitrogen vacancies leads to the enhancement of ferromagnetism.     

宽带隙薄膜材料场电子发射研究的背景、现状和问题

介绍了以金刚石为代表的宽带隙薄膜材料场电子发射研究背景和现状,对金刚石、类金刚石（ＤＬＣ）、立方氮化硼（ｃ－ＢＮ）、氮化铝（Ａ１Ｎ）和碳化硅（ＳｉＣ）薄膜场电子发射研究的进展进行了评述,着重介绍了发射性能与薄膜的结构特征、杂质含量和处理方法间的关系,并讨论了研究中存在的问题。     

Aspects of “low field” magnetotransport in epitaxial thin films of the ferromagnetic metallic oxide SrRuO3

Epitaxial thin films of the conductive ferromagnetic oxide SrRuO₃ were grown on an (0 0 1) SrTiO₃ (STO) substrate by using DC sputtering technique. The magnetic and magnetoresistive properties of the films were measured by applying the magnetic field both perpendicular (out-of-plane) and parallel (in-plane) to the film plane and ever maintaining the direction of the applied field perpendicular to that of the transport current. The films grown on an (0 0 1) STO substrate showed identical magnetization properties in two orthogonal crystallographic directions of the substrate, [1 0 0]_S and [0 0 1]_S (in-plane and out-of-plane geometry), which suggests the presence of a multi domain structure within the plane of the film. For such samples, no anisotropic field (hard axis) along de [0 0 1]s direction, i.e., perpendicular to the film-plane could be detected. Nevertheless, a distinguishable temperature dependent out-of-plane anisotropic magnetoresistance (MR) along with strong temperature dependent low field hysteretic MR(H) behavior was detected for the studied films. A negative MR ratio MR(T)=[ρ(μ₀H=9 T; T)−ρ( μ₀H=0 T; T)]/ρ( μ₀H=0 T; T) on the order of a few percent, with maximums of 6% and 4% (right at the Curie temperature, T_C 160 K) was calculated for an in-plane and out-of plane measuring geometry, respectively. In addition there is an equally strong MR effect at low temperatures, which might be related to the temperature dependence of the magnetocrystalline anisotropy together with a magnetization rotation. Both the MR(T) behavior and the achieved values (except for T<30 K) are similar to those obtained on SrRuO₃ films grown on 2° miscut (0 0 1) STO substrates with the current parallel to the field and parallel to the direction, which was identified as the easier axis for magnetization.     

Impact of the Structural Changes on the Fracture Behavior of Naturally Weathered Low-Density Polyethylene (LDPE) Films

Weathering of LDPE films was performed in a sub-Saharan facility in Laghouat, Algeria. Ageing led to a rapid change of the physicochemical properties resulting from the alteration of the material's microstructure. XRD revealed the progressive increase of the crystallinity ratio and the thickness of the crystalline lamellae as well. SEM revealed the presence of white particles, which look like crystalline phase emerging from the surface of the film. The oxidation and crystallinity varied according to a concentration gradient across the thickness. The impact of the microstructural changes on the mechanical properties was highlighted based on the essential work of fracture (EWF) method. There was a progressive decrease of the total energy of fracture and a lowering of the net stress (σ_net) and the (β_wp) term. Nevertheless, this loss of the mechanical properties was characterized by a rapid transition from a ductile mode of failure to a very brittle mode.     

Photoconductive studies on electron beam evaporated CdSe films

Thin CdSe films were electron beam evaporated. The CdSe powder synthesized in the laboratory by a chemical method was used as source for the deposition of films. Clean glass and titanium substrates were used as substrates. The substrate temperature was varied in the range of 30-250 °C. X-ray diffraction studies indicated polycrystalline hexagonal structure. The band gap was 1.65 eV. The grain size was 15-30 nm with increase of substrate temperature. Photoconductive cells fabricated with the doped and undoped films have exhibited high photosensitivity and high signal to noise ratio. The current voltage characteristics were linear.     

Biodegradable Catalase-Modified Micelles as Ultrasound Contrast Agents for Inflammation Detection

Overproduction of hydrogen peroxide (H₂O₂) is a characteristic feature for inflammation and cancer. Ultrasonography is a safe and effective clinical diagnosis method to identify inflammation, yet a fully biodegradable ultrasound contrast agent (UCA) system that is able to reflect the pathophysiological level of H₂O₂ at diseased tissue with high sensitivity is still scarce. Herein, a self-assembled biodegradable catalase-modified poly(ethylene glycol)₄₄-b-poly(lactic acid)₁₀₀ (PEG-b-PLA) micelle (Cat-PEG-PLA) is presented as a sensitive ultrasound contrast agent. It is found that the imaging effect of Cat-PEG-PLA is remarkable with an obvious enhancement of ultrasound echogenic signal even in an ultralow (0.33 × 10⁻³ m ) inflammation-relevant H₂O₂ concentration environment, close to or even lower than the reported lowest ultrasound detectable concentration limits. The ultrasonography of collagen-induced arthritis rat model’s articular cavity by the Cat-PEG-PLA micelle platform is demonstrated, showing highly promising results. Therefore, with superior detection sensitivity and contrast, the system detects H₂O₂ in arthritis rat model with full biodegradability, providing a novel, safe, and translatable platform for arthritis diagnosis.