Optical and electrical properties of undoped and doped Ge nanocrystals

Size-dependent photoluminescence characteristics from Ge nanocrystals embedded in different oxide matrices have been studied to demonstrate the light emission in the visible wavelength from quantum-confined charge carriers. On the other hand, the energy transfer mechanism between Er ions and Ge nanocrystals has been exploited to exhibit the emission in the optical fiber communication wavelength range. A broad visible electroluminescence, attributed to electron hole recombination of injected carriers in Ge nanocrystals, has been achieved. Nonvolatile flash-memory devices using Ge nanocrystal floating gates with different tunneling oxides including SiO2, Al2O3, HfO2, and variable oxide thickness [VARIOT] tunnel barrier have been fabricated. An improved charge storage characteristic with enhanced retention time has been achieved for the devices using VARIOT oxide floating gate

Effects of IL-8 up-regulation on cell survival and osteoclastogenesis in multiple myeloma

[EN]IL-8 promotes cancer cell growth, survival, angiogenesis, and metastasis in several tumors. Herein, we investigated the sources of IL-8 production in multiple myeloma (MM) and its potential roles in MM pathogenesis. We found that bone marrow cells from patients with MM secreted higher amounts of IL-8 than healthy donors. IL-8 production was detected in cultures of CD138+ plasma cells and CD138(-) cells isolated from bone marrows of MM patients, and in three of seven human myeloma cell lines (HMCLs) analyzed. Interactions between MM and stromal cells increased IL-8 secretion by stromal cells through cell-cell adhesion and soluble factors. Interestingly, 1L8 expression also increased in HMCLs, stromal cells, and osteoclasts after treatment with the antimyeloma drugs melphalan and bortezomib. In fact, the effect of bortezomib on IL-8 production was higher than that exerted by stromal-MM cell interactions. Addition of exogenous IL-8 did not affect growth of HMCLs, although it protected cells from death induced by serum starvation through a caspase-independent mechanism. Furthermore, IL-8 induced by stromal-MM cell interactions strongly contributed to osteoclast formation in vitro, because osteoclastogenesis was markedly reduced by IL-8 specific neutralizing antibodies. In conclusion, our results implicate IL-8 in myeloma bone disease and point to the potential utility of an anti IL-8 therapy to prevent unwanted effects of IL-8 up-regulation on survival, angiogenesis, and osteolysis in MM.Spanish RTICC, Spanish Association against Cancer (AECC), the INNOCAMPUS Program , Spanish ISCIII-FIS (PI12/02591) and FEDER, Regional Council from Castilla y León (Consejería de Educación) and the Network of Centers for Regenerative Medicine and Cellular Therapy from Castilla y León

A comprehensive review of techniques for natural fibers as reinforcement in composites::preparation, processing and characterization

Designing environmentally friendly materials from natural resources represents a great challenge in the last decade. However, the lack of fundamental knowledge in the processing of the raw materials to fabricate the composites structure is still a major challenge for potential applications.Natural fibers extracted from plants are receiving more attention from researchers, scientists and academics due to their use in polymer composites and also their environmentally friendly nature and sustainability. The natural fiber features depend on the preparation and processing of the fibers. Natural plant fibers are extracted either by mechanical retting, dew retting and/or water retting processes. The natural fibers characteristics could be improved by suitable chemicals and surface treatments. This survey proposes a detailed review of the different types of retting processes, chemical and surface treatments and characterization techniques for natural fibers. We summarize major findings from the literature and the treatment effects on the properties of the natural fibers are being highlighted

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Synergistic effect of various intermolecular interactions on self-assembly and optoelectronic behaviour in co-crystals/salts of tetrabromoterephthalic acid: a report on their structure, theoretical study and Hirshfeld surface analysis

The rational design of organic opto-electronic materials has been one of the prime focuses in recent times, and halogen interactions have become a major tool in crystal engineering to design multi-component organic co-crystals/salts. Tetrabromoterephthalic acid (TBTA), which is able to participate in both hydrogen bonding and halogen bonding, has been used as a co-crystallizing agent to synthesize four different organic co-crystals/salts, TBTA-3-bromopyridine (co-crystal I), TBTA·TBTA 2− -2(2-aminopyridine + )·2H 2 O (co-crystal salt II), TBTA − -4-aminopyridine + ·H 2 O (salt III) and TBTA·TBTA 2− -2(nicotinamide + )·2H 2 O (co- crystal salt IV), by a conventional solvent evaporation method. These compounds were characterized by single-crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD) and spectral and thermal studies. Molecular and supramolecular structural analyses reveal that TBTA interacts with the pyridyl-containing co-formers through hydrogen bonding and exploits several types of halogen bonding (Br⋯O, Br⋯H, Br⋯Br, Br⋯π interactions etc.) and π⋯π interactions to assemble in the solid state. TBTA utilizes Br⋯π interactions to assemble with other co-formers while it utilizes Br⋯O interactions and preferably type I Br⋯Br interactions to assemble with each other in these co-crystals/salts. The supramolecular behaviour of TBTA within these co-crystals/salts analyzed by Hirshfeld surface analysis and associated 2D fingerprint plots also corroborates the crystallographic supramolecular structural patterns. Theoretical analysis has been carried out for geometry optimization and bandgap calculations which were then compared with the optical bandgap values. Charge-separated hydrogen bonding and π⋯ interactions (Br⋯π and π⋯π interactions) have a significant impact on the optical and electrical properties of these samples. Solid-state luminescence studies reveal that all compounds show a blue shift. Electrical conductivity measurements on the ITO/sample/Al sandwich structures of these supramolecular complexes reveal Schottky barrier diode behaviour and photoresponsivity under illumination

Photo-responsive Schottky Diode Behavior of a Donor-Acceptor Co-crystal with Violet Blue Light Emission

Herein, we report the crystal structure, supramolecular structure, electronic transport property and optoelectronic behaviour of a co-crystal made of tetrabromoterephthalic acid (TBTA) and quinoxaline (QUIN) (1:1). The sample has been characterized by thermogravimetric analysis and spectral techniques. Moreover, the theoretical analysis on noncovalent interactions, optical properties and band structure of the co-crystal has been performed. The co-crystal has been crystallized in orthorhombic system with P nma space group and the constituent molecules assemble in the solid state by using O- H···N hydrogen bonding, π···π, Br···π and Br···O interactions. The ground state geometry optimization over the hydrogen bonded dimer by DFT method indicates that TBTA acts as the donor and QUIN as the acceptor within the self-assembled co-crystal. According to UV- vis spectroscopic study the bandgap of the co-crystal is ~ 3.18 eV. In solid state it exhibits a broad emission band with maxima at 405 nm while in aqueous medium its photoluminescence emission peaks are obtained at 350 and 403 nm. The values of average fluorescence lifetime of the sample in aqueous medium are 3.38 ns at 352 nm and 4.94 ns at 403 nm. Under UV-irradiation, the co-crystal emits violet-blue light. The emission spectra in solution phase shows relative quantum yield of 0.018. Band structure calculation indicates that the co-crystal is a p-type semiconductor with bandgap of 2.835 eV. Due to its semiconducting character, the ITO/Co-crystal/Al sandwiched structured device acts as a Schottky barrier diode with rectification ratio, ideality factor, barrier height and series resistance of 41, 1.36, 0.70 eV, and 26.97 KΩ, respectively. The current through the device increases substantially under visible light exposure. Upon visible light illumination the values of electrical conductivity, mobility, carrier concentration increases by 35 (± 0.5), 54 (± 0.5) and 6 (± 0.5) %, respectively, with respect to dark condition. It has been shown that π···π and hydrogen bonding interaction can play crucial role in producing donor-acceptor (D-A) type co-crystal, semiconducting behaviour can be incorporated in organic co-crystal utilizing π···π and hydrogen bonding interactions and weak intermolecular π···π, Br···π and Br···O interactions can act as the pathway for electrical conduction