First-principles study and electronic structures of Mn-doped ultrathin ZnO nanofilms

The first-principles density functional calculation is used to investigate the electronic structures and magnetic properties of Mn-doped and N-co-doped ZnO nanofilms.The band structure calculation shows that the band gaps of ZnO films with 2,4,and 6 layers are larger than the band gap of the bulk with wurtzite structure and decrease with the increase of film thickness.However,the four-layer ZnO nanofilms exhibit ferromagnetic phases for Mn concentrations less than 24% and 12% for Mn-doping performed in the whole layers and two layers of the film respectively,while they exhibit spin glass phases for higher Mn concentrations.It is also found,on the one hand,that the spin glass phase turns into the ferromagnetic one,with the substitution of nitrogen atoms for oxygen atoms,for nitrogen concentrations higher than 16% and 5% for Mn-doping performed in the whole layers and two layers of the film respectively.On the other hand,the spin-glass state is more stable for ZnO bulk containing 5% of Mn impurities,while the ferromagnetic phase is stable by introducing the p-type carriers into the bulk system.Moreover,it is shown that using the effective field theory for ferromagnetic system,the Curie temperature is close to the room temperature for the undamped Ruderman-Kittel-Kasuya-Yoshida（RKKY） interaction.

Electronic and magnetic structures of V-doped zinc blende Zn_(1-x)V_xN_yO_(1-y) and Zn_(1-x)V_xP_yO_(1-y)

Electronic and magnetic structures of zinc blende ZnO doped with V impurities are studied by first-principles calculations based on the Korringa-Kohn-Rostoker （KKR） method combined with the coherent potential approximation （CPA）. Calculations for the substitution of O by N or P are performed and the magnetic moment is found to be sensitive to the N or P content. Furthermore, the system exhibits a half-metallic band structure accompanied by the broadening of vanadium bands. The mechanism responsible for ferromagnetism is also discussed and the stability of the ferromagnetic state compared with that of the paramagnetic state is systematically investigated by calculating the total energy difference between them by using supercell method.

Morphological, Structural, Thermal and Tensile Properties of High Density Polyethylene Composites Reinforced with Treated Argan Nut Shell Particles

High Density Polyethylene （HDPE） composites reinforced with treated bio-filler from Argan-Nut Shell （ANS） at various filler contents are prepared by extrusion and injection molding processes. The microstructures of the composites are charac- terized by Fourier Transform Infrared Spectroscopy （FTIS） and Scanning Electron Microscopy （SEM）; the thermal stability is analyzed by Thermogravimetric Analysis （TGA）, and their mechanical properties are investigated by dynamical mechanical analysis and rheological testing. The morphological and structural results indicate an improvement in adhesion between the ANS fillers and HDPE matrix upon alkali treatment. The mechanical properties of the composites show a significant increase in young＇s modulus with the addition of filler, a gain of 58% is marked compared to neat polymer, Thermal analysis reveals that the incorporation of bio-filler in polymer results in a decrease in decomposition temperatures. This research offers an ecological alternative to upgrade the valorization of abundant and unexploited Moroccan resources. In addition, the possibility of finding uses for ANS in composite manufacturing will help open new markets for what is normally considered waste or for use in low value products.

Mechanical and Thermal Properties of Polypropylene Reinforced with Almond Shells Particles： Impact of Chemical Treatments

Polypropylene （PP） matrix composites reinforced with chemically treated Almond Shell （AS） particles with and without compatibilizer （PP-g-MA） was prepared by a twin-screw extrusion at loading of 20 wt.% AS particles. Two types of chemical treatments （alkali treatment with sodium hydroxide and etherification with dodecane bromide） of the particles were carried out to improve the interface adhesion between particles and PP matrix. Results show that chemical modifications of AS particles affect the mechanical and viscoelastic properties of AS/PP composites. The composites reinforced with alkali treated particles and the compatibilized matrix lead to a notable increase in the Young＇s modulus （14%） compared to the composites with untreated AS particles. The ductility of composite was also evaluated by the yield strain, and results show a notable increase （31%） compared to that of composites with untreated particles. The thermal stability increased with the use of etherification （385 ℃）, with gains in the temperature up to 23 ℃ compared to neat PP （362 ℃）. The achieved results show that the AS/PP composites can be used in several applications. A thermoplastic matrix compsite mixed with treated AS particles appears to be a good alternative to obtain environmentally friendly products.

Production and Characterization of High Density Polyethylene Reinforced by Eucalyptus Capsule Fibers

In this work, Eucalyptus Capsule Fibers （ECF） are proposed as a new natural fiber reinforcement to produce bio-composites due to their biological origin, specific smell and color. High Density Polyethylene （HDPE） is used as the matrix to compare three reinforcement types, raw ECF, alkali treated ECF, and ECF treated with PE-graft-maleic anhydride （PE-g-MA） as a coupling agent at three concentrations （5 wt.%, 10 wt%, and 15 wt%）. A complete set of characterization is performed including tension, torsion, hardness, Melt Flow Index （MFI）, Attenuated Total Reflection Fourier Transform Infrared Spectroscopy （ATR-FTIR）, Contact Angle （CA）, Scanning Electron Microscopy （SEM）, Thermogravimetric Analysis （TGA） and Dynamic Mechanical Analysis （DMA）. The results show that the best mechanical and rheological improvements are obtained by using the coupling agent with alkali treated fibers.

First-principles prediction of the magnetism of 4f rare-earth-metal-doped wurtzite zinc oxide

Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functional theory based on the full-potential linear augmented plane wave （FP-LAPW） method as implemented in the Wien2k code. In this approach the generalized gradient approximation （GGA） was used for the exchange-correlation （XC） potential. Our results showed that the substitution of RE ions in ZnO induced spins polarized localized states in the band gap. Moreover, the studied DMSs compounds retained half metallicity at dopant concentration x=0.625%for most of the studied elements, with 100%spin polarization at the Fermi level （EF）. The total magnetic moments of these compounds existed due to RE 4f states present at EF, while small induced magnetic moments existed on other non-magnetic atoms as well. Finally, the energy difference between far and near configurations was investigated. It was found that the room temperature ferromagnetism was possible for RE-doped ZnO at near configuration. Since the RE-RE separation was long enough （far configuration） for magnetic coupling, the system became paramagnetic or antiferromagnetic ground state.

Laminated Epoxy Biocomposites Based on Clay and Jute Fibers

Jute/epoxy hybrid laminated biocomposites were manufactured by using Illite clay particles at various content （5 wt.% - 20 wt.%）. The effects of hybridization on the morphology, structure, and mechanical properties were investigated. The properties of the biocomposites reinforced with jute fibers were mainly influenced by the interfacial adhesion between the jute fibers and the epoxy matrix. An alkali treatment was applied to improve the interfacial fiber-matrix adhesion and thus obtaining better mechanical properties. Besides the chemical treatment, epoxy hybridization using clay particles also had a strong effect on the overall properties of laminated biocomposites. The mechanical properties of the jute/epoxy biocomposites reinforced with Illite clay increased with clay content, up to an optimum value at 15 wt.%. The average technique and the laminates theory were performed to validate the coherence of the elastic moduli between the calculated and experimental values. A difference between the experimental and predicted data was observed, which was attributed to the simplifying assumptions made in both models. The laminates theory gave better overall predictions.