Inelastic neutron scattering due to acoustic vibrations confined in nanoparticles: theory and experiment

The inelastic scattering of neutrons by nanoparticles due to acoustic vibrational modes (energy below 10 meV) confined in nanoparticles is calculated using the Zemach-Glauber formalism. Such vibrational modes are commonly observed by light scattering techniques (Brillouin or low-frequency Raman scattering). We also report high resolution inelastic neutron scattering measurements for anatase TiO2 nanoparticles in a loose powder. Factors enabling the observation of such vibrations are discussed. These include a narrow nanoparticle size distribution which minimizes inhomogeneous broadening of the spectrum and the presence of hydrogen atoms oscillating with the nanoparticle surfaces which enhances the number of scattered neutrons.Comment: 3 figures, 1 tabl

Assessment of Food Security Situation of Tiv Farming households in Nigeria

The fact that several households are engaged in farming does not translate directly to them being food secured, this is because of the food security entails all people at all times having both physical and economic access to sufficient food to meet their dietary needs for a productive and healthy life. The study therefore, assessed the food security situation and living conditions of Tiv farming households. Respondents were drawn from farming households in Benue, Taraba and Nasarawa States. Data was collected from 315 heads of households using interview schedule, and the data were analysed using means and food security index. The study found that enhanced ICT use (M=2.47) and increased competition (M=2.40) were perceived conditions that were found to be attributed to their agricultural operations. The analysis of food security situation shows that majority (64.1%) of these households were food secured. This could be because of those strategies for ensuring food security is working for majority of the families. Also on the strategies put in place to ensure households’ food security were the use of high yielding crop varieties (M= 1.60), mixed cropping (M=1.53) and use of early maturing crop varieties. Therefore the study recommends that governments in these states should support various extension agencies involved in the dissemination of these technologies that enhance the food security of the farmers

On a biphononic origin of the 1125 cm^(-1) absorption band in cuprous oxide

We report on the IR spectroscopic studies in both reflection (50-900 cm^{-1}) and transmission (900-3000 cm^{-1}) mode of the vibration spectrum of the cuprous oxide. A detailed analysis based on a comparison of the temperature dependences of the absorption band at 1125 cm^{-1} and of IR and Raman active fundamental vibrations results in assignment of the former to a biphonon.Comment: 5 pages, 5 figures (to appear in Phys.Lett. A

Assessment of Food Security Situation of Tiv Farming households in Nigeria

The fact that several households are engaged in farming does not translate directly to them being food secured, this is because of the food security entails all people at all times having both physical and economic access to sufficient food to meet their dietary needs for a productive and healthy life. The study therefore, assessed the food security situation and living conditions of Tiv farming households. Respondents were drawn from farming households in Benue, Taraba and Nasarawa States. Data was collected from 315 heads of households using interview schedule, and the data were analysed using means and food security index. The study found that enhanced ICT use (M=2.47) and increased competition (M=2.40) were perceived conditions that were found to be attributed to their agricultural operations. The analysis of food security situation shows that majority (64.1%) of these households were food secured. This could be because of those strategies for ensuring food security is working for majority of the families. Also on the strategies put in place to ensure households’ food security were the use of high yielding crop varieties (M= 1.60), mixed cropping (M=1.53) and use of early maturing crop varieties. Therefore the study recommends that governments in these states should support various extension agencies involved in the dissemination of these technologies that enhance the food security of the farmers

Synthesis and Microstructural Properties of Fe-TiO 2 Nanocrystalline Particles Obtained by a Modified Sol-Gel Method

Abstract. A series of iron/titanium oxide nanocrystalline particles with Fe/Ti molar ratios up to 0.15 were synthesized by a modified sol-gel technique using Ti(IV)-isopropoxide and anhydrous Fe(II)-acetate. The precursors were mixed and subsequently hydrolyzed with water molecules generated in situ by an esterification reaction between acetic acid and ethanol. As-synthesized samples were amorphous for XRD, independently of the relative amount of doped iron. The undoped samples and samples with the molar ratio Fe/Ti = 0.01, treated at up to 500 • C, contained anatase as the dominant phase and rutile as the minor phase. The samples with the Fe/Ti molar ratio of 0.15, treated at the same temperature, contained anatase (major phase), rutile (minor phase) and a very small amount of an unidentified phase. The crystallite size of the dominant phase in the samples was estimated from the XRD line broadening using the Scherrer formula. Thermogravimetric analysis showed that weight loss was accelerated and completed at lower temperatures as the relative concentration of iron in the Fe-TiO 2 samples increased. The strong exothermic peak in the DTA curve between 300 and 450 • C in the undoped TiO 2 sample shifted to the lower temperatures and became much more asymmetrical with increased iron doping. This DTA peak corresponded to the amorphous-to-anatase-transition and it included several steps such as (i) the thermal degradation of strongly bound organic molecules, (ii) the condensation of unhydrolyzed -OR groups, (iii) the sintering and growth of particles and (iv) the rearrangement of newly formed chemical bonds. The center of the most intense Raman band of the E g mode at 143.8 cm −1 in the undoped TiO 2 sample continually shifted to higher wave numbers and the full-width at half maximum increased with iron doping. Transmission electron microscopy revealed decrease of the mean particle size from 16.3 nm in undoped sample to 9.7 nm in the highest iron doped sample. The particle size distribution becomes * To whom all correspondence should be addressed. 6Šijaković-Vujičić et al. narrower with iron doping. The narrowest particle size distribution was found in sample with the Fe/Ti molar ratio of 0.05, calcined at 500 • C. Scanning electron microscopy of undoped samples calcined at 580 • C showed irregular aggregates having a relatively flat surface. On the contrary, the samples doped with 15 mol% of iron and treated at the same temperature exhibited a non-uniform sponge-like surface with distributed micrometer holes

Rare-earth-activated glasses for solar energy conversion

The solar cells efficiency may be improved by better exploitation of the solar spectrum, making use of the down-conversion mechanism, where one high energy photon is cut into two low energy photons. The choice of the matrix is a crucial point to obtain an efficient down-conversion process with rare-earth ions. When energy transfer between rare earth ions is used to activate this process, high emission and absorption cross sections as well as low cut-off phonon energy are mandatory. In this paper we present some results concerning 70SiO2-30HfO2 glass ceramic planar waveguides co-activated by Tb3+/Yb3+ ions, fabricated by sol gel route using a top-down approach, and a bulk fluoride glass of molar composition 70ZrF4 23.5LaF3 0.5AlF3 6GaF3 co-activated by Pr3+/Yb3+ ion. Attention is focused on the assessment of the energy transfer efficiency between the two couples of rare earth ions in the different hosts

Novel Tm3+-doped fluorotellurite glasses with enhanced quantum efficiency

In this paper, new highly Tm3+-doped tellurite glasses with host composition 75TeO2-xZnF2-yGeO2-12PbO-3Nb2O5 [x(5-15), y(0-5) mol%] are presented and compared to the Tm-doped tellurite glasses based on the traditional host composition: 75TeO2-20ZnO-5Na2O mol%. Enhanced quantum efficiency from 3F4 level was observed for the proposed glasses and thermal stability and viscosity values make them suitable for optical fiber drawing. Besides the host composition, substantial influence of Tm3+ concentration on luminescence and lifetime of excited 3F4 and 3H4 states were discusse

Enhanced near-infrared response of nano- and microstructured silicon/organic hybrid photodetectors

Heterojunctions between an organic semiconductor and silicon are an attractive route to extending the response of silicon photodiodes into the near infrared (NIR) range, up to 2000 nm. Silicon-based alternatives are of interest to replace expensive low band-gap materials, like InGaAs, in telecommunications and imaging applications. Herein, we report on the significant enhancement in NIR photodetector performance afforded by nano- and microstructuring of p-doped silicon (p-Si) prior to deposition of a layer of the organic semiconductor Tyrian Purple (TyP). We show how different silicon structuring techniques, namely, electrochemically grown porous Si, metal-assisted chemical etching, and finally micropyramids produced by anisotropic chemical etching (Si μP), are effective in increasing the NIR responsivity of p-Si/TyP heterojunction diodes. In all cases, the structured interfaces were found to give photodiodes with superior characteristics as compared with planar interface devices, providing up to 100-fold improvement in short-circuit photocurrent, corresponding with responsivity values of 1–5  mA/W in the range of 1.3–1.6 μm. Our measurements show this increased performance is neither correlated to optical effects, i.e., light trapping, nor simply to geometric surface area increase by micro- and nanostructuring. We conclude that the performance enhancement afforded by the structured p-Si/organic diodes is caused by a yet unresolved mechanism, possibly related to electric field enhancement near the sharp tips of the structured substrate. The observed responsivity of these devices places them closer to parity with other, well-established, Si-based NIR detection technologies