Graphene oxide (GO) can be used as an electron acceptor for polymeric solar cells but still band gap matching for electron donor and acceptor demands more study. The generation of the exciton in such ...materials is intimately related to the optical band gap. However, exciton dissociation is related to transport band gap that controls the device performance, particularly the open circuit voltage and short circuit current. Therefore, the modulation of the optical gap is useful because it results into tuning of the transport gap. The interest of the present work is to study the reduction of graphene oxide (GO) at room temperature, using environmental friendly reagents like glucose, fructose and ascorbic acid for the modulation of a band gap. It has been found that glucose and fructose function effectively only in presence of NH4OH. Although ascorbic acid can reduce GO alone, NH4OH speeds up the reaction. The optical band gap of GO can be reduced and tuned effectively from 2.7eV to 1.15eV.
Novel Al-based nanocomposites reinforced with multi-walled carbon nanotubes were produced by mechanical milling. Next, pressure-less sintering at 823
K under vacuum and hot extrusion at 773
K were ...carried out. The interface between Al matrix and the multi-walled carbon nanotubes was examined using transmission electron microscopy. The values of yield strength (
σ
y), maximum strength (
σ
max) and microhardness Vickers (HVN) of the composites were evaluated and reported as a function of carbon nanotubes content. The concentration of multi-walled carbon nanotubes has an important effect on the mechanical properties of the nanocomposite. Formation of aluminum carbide in the nanocomposites was observed. Possible strengthening mechanisms are presented and discussed.
Enhancement of the discharge capacity and cycle life of lead–acid batteries demands the innovative formulation of positive and negative electrode pastes that can be achieved through the modifications ...in the leady oxide morphology and the use of additives to control characteristics such as grain size, specific surface area, electrical conductivity, and chemical reactivity. In the present work, we describe a methodology for the improvement of the cycle life of lead oxide electrodes by the addition of multi-walled carbon nanotubes (MWCNT) and high-energy ball milling of leady oxide obtained by Barton and Sovema reactors. Positive and negative electrodes were produced and tested by cycling at constant discharge current. An improvement of 110% on the number of cycles over the unaltered Sovema electrode, and 168% over Barton electrode were found and attributed to the cured electrode morphology and the improved conductivity introduced by the addition of MWCNT. Symmetrical cells of high energy ball-milled leady oxide electrodes with MWCNT withstood 528 cycles, retaining more usable charge than its counterparts.
Graphic abstract
The materials intended for organic photovoltaics and organic electronics require specific properties, such as conjugation along backbones, good solubility in organic solvents and a suitable band gap. ...Graphene oxide holds a high indirect optical band gap of 3 eV and a hydrophilic behavior. However, based on the fact that the graphene oxide band gap is related to the C/O ratio, chemical reduction and functionalization must be performed to obtain the proper characteristics that are required for organic applications. Here an efficient approach for chemically modified graphene oxide as a low-cost alternative for organic semiconductor materials was developed. The two synthesized materials (functionalized reduced graphene oxide and functionalized reduced graphene oxide decorated with silver nanoparticles) exhibited a 65% and 52% band gap decrease respectively, compared to graphene oxide. Moreover, both materials were soluble in organic solvents at high concentrations 10 mg mL−1, turning them suitable for many applications, including organic electronics, with the additional advantage of being a solution process avoiding restacking of layers.
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In this work, multiple narrow and highly intense ultraviolet (UV) electroluminescent (EL) bands were observed in light emitting capacitors (LECs) using silicon rich oxide (SRO) films as active layer. ...Besides, the effect of a thin silicon rich nitride (SRN) film on top of the SRO (as SRN/SRO bilayer) layer was also studied. LECs were fabricated using simple metal–insulator–semiconductor (MIS) structures with indium tin oxide (ITO) and aluminum as gate and substrate electrodes, respectively. SRO and SRN films contain 41.85±1.1 and 46.96±1.1at% of silicon, respectively. Both structures exhibited a resistance switching (RS) behavior from a high conduction state (HCS) to a low conduction state (LCS), enhancing an intense UV EL. This RS behavior produces structural changes in the active layer and probably in the ITO contact. Seven narrow bands with half-peak width of 7±0.6nm at ~250, 270, 285, 305, 325, 415 and 450nm were clearly observed once the LCS was reached. These bands could be related to a combination of emissions through defects inside SRO (252, 288.2 and 415nm), and characteristic radiation of neutral tin (252.39 and 286.33nm), neutral indium (271.02, 303.93 and 325.85nm), single (444.82nm) and doubly ionized indium (403.07nm). Furthermore, red EL was observed at the HCS and it was similar to the PL spectra indicating the same radiative process involved. The charge transport is improved when the SRN/SRO bilayer is used as active layer in the LEC. An EL band at ~590nm is observed when the SRN/SRO bilayer is formed at both conduction states. This band has been observed before and attributed to transitions from the minimum conduction band to K° centers in SRN films. The conduction mechanism responsible of the EL at both conduction states was also studied.
Photovoltaic solar panel for a hybrid PV/thermal system Zakharchenko, R.; Licea-Jiménez, L.; Pérez-Garcı́a, S.A. ...
Solar energy materials and solar cells,
05/2004, Letnik:
82, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
The hybrid PV–thermal system was studied, with the photovoltaic panel (PVP) area much smaller than that of the solar collector. Performance of the different panels in the system was investigated, in ...particular, those made of crystalline (c-) Si,
α-Si and CuInSe
2 as well as different materials and constructions for the thermal contact between the panel and the collector. Our conclusion is that the PVP for application in a hybrid system needs a special design providing efficient heat extraction from it. PVP was designed and made. Its study has shown that this design provides the high electrical and thermal efficiency of the hybrid system.
The electro-optical properties of metal-oxide-semiconductor devices with embedded Si nanoparticles in silicon-rich (4at.%) oxide films have been studied. Devices show intense visible continuous ...luminescence not only in the regular metal-oxide-semiconductor configuration, but when biased via surface electrodes (floating substrate) separated 10μm. Electroluminescence manifests as extremely bright randomly scattered discrete spots on the gate area or the periphery of the devices depending on the bias direction. The mechanism responsible for the surface-electroluminescence has been related to the recombination of electron–hole pairs injected through enhanced current paths within the silicon-rich oxide film.
► Silicon rich oxide (SRO) based metal-oxide-semiconductor like luminescent devices. ► Electroluminescence (EL) in floating-substrate, horizontal electrodes configuration. ► EL is observed as multiple shining spots with surface electrodes. ► Preferential current paths established in the SRO between several electrodes.
A recently reported solvent spraying technique was used herein for incorporation of multi-walled carbon nanotubes (MWCNTs) on unidirectional carbon fiber/epoxy prepregs. The role of the agglomerates ...reduction of oxidized MWCNTs on Mode-I interlaminar fracture toughness (G
IC
) of laminated composites was investigated using double cantilever beam tests. Multiscale laminate composites were fabricated using MWCNTs without and with an acid oxidation, agglomerates reduction (AR) and a sequential treatment based on oxidation and AR. For comparison, specimens without MWCNTs were also prepared and tested. Fourier transform infrared analysis shows evidence of an important amount of oxygenated functional groups on the surface of as-received and oxidized MWCNTs. The results also show Mode-I fracture toughness improvements for all the laminated composites compared to reference samples. A substantial 52% increase in the average G
IC
initiation was achieved for laminated composites reinforced with oxidized AR-MWCNTs prepared with only 0.05 wt.% MWCNTs.
Carbon nanotube/2024 aluminum alloy (CNT/Al2024) composites were fabricated with a combination of mechanical alloying (MA) and powder metallurgy routes. Composites were microstructurally and ...mechanically evaluated at sintering condition. A homogeneous dispersion of CNTs in the Al matrix was observed by a field emission scanning electron microscopy. High-resolution transmission electron microscopy confirmed not only the presence of well dispersed CNTs but also needle-like shape aluminum carbide (Al4C3) crystals in the Al matrix. The formation of Al4C3 was suggested as the interaction between the outer shells of CNTs and the Al matrix during MA process in which crystallization took place after the sintering process. The mechanical behavior of composites was evaluated by Vickers microhardness measurements indicating a significant improvement in hardness as function of the CNT content. This improvement was associated to a homogeneous dispersion of CNTs and the presence of Al4C3 in the aluminum alloy matrix.
► The 2024 aluminum alloy was reinforced by CNTs by mechanical alloying process. ► Composites were microstructural and mechanically evaluated after sintering condition. ► The greater the CNT concentration, the greater the hardness of the composites. ► Higher hardness in composites is achieved at 20h of milling. ► The formation of Al4C3 does not present a direct relationship with the milling time.
A photorefractive effect at the wavelength of 1064
nm is demonstrated for a composite consisting of an aromatic polyimide and carbon single wall nanotubes. The two-beam gain coupling coefficient and ...the net gain coefficient are equal to 90 and 65
cm
−1, respectively, at 80
V/μm for a nanocomposite containing 0.25
wt% crude nanotube material. The refractive index modulation measured at
E
0
=
50
V/μm is close to Δ
n
=
0.004.
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