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This study reports on the synthesis of highly oriented chromium triiodide (CrI3) magnetic inclusions inside nano/microfibres with a polyethylene oxide matrix, prepared by the electrospinning technique. The structural, microstructural and spectroscopic analysis shows uniformly dispersed CrI3 nanosized inclusions inside the fibres, presenting a C2/m monoclinic structure at room temperature, where their c-axis is perpendicular to the fibre mat plane and the ab layers are in-plane. Analysis of the magnetic properties show that the samples have a ferromagnetic-paramagnetic phase transition at ∼55-56 K, lower than that of bulk CrI3. Noticeably, a field-driven metamagnetic transition is observed below ∼45 K, from M versus H curves, when the applied magnetic field is perpendicular to the fibre mat plane, while it is strongly reduced when the field is in-plane. This anisotropic behaviour is attributed to the field-induced changes from antiferromagnetic to ferromagnetic interlayer magnetic moment alignment along the CrI3 c-axis stacked layers. These CrI3 electrospun fibres then show an efficient cost-effective route to synthesize magnetic composite fibres with highly oriented van der Walls inclusions, for spintronic applications, taking advantage of their anisotropic 2D layered materials properties., We are grateful to the Fundacao Para a Ciencia e a Tecnologia (FCT) for the financial support through the Physics Centers of the Universities of Minho and Porto (Ref. UIDB/04650/2020) and projects UTAPEXPL/NTec/0046/2017, NORTE-01-0145-FEDER-028538 and PTDC/FIS-MAC/29454/2017. J H Belo thanks FCT for the Grant SFRH/BD/88440/2012, the project PTDC/FIS-MAC/31302/2017 and his contract DL57/2016 reference SFRH-BPD-87430/2012. J P Araujo and J H Belo thank the funding from the project, with reference POCI-01-0145-FEDER-032527. V B Isfahani acknowledges a Post-Doc grant from the project NORTE-01-0145-FEDER-028538. L Boddapati acknowledges the Nano TRAIN for Growth II program by the European Commission through the Horizon 2020 Marie Sklodowska-Curie COFUND Programme and support provided by the International Iberian Nanotechnology Laboratory. We are gratefull to Professor Michael Belsley, of the Physics Department at Minho University, for the fruitfull discussions on the manuscript.

This work is supported by FCT with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalizacao (POCI) with the reference project POCI-01- 0145-FEDER-006941, and by the strategic projects UID/FIS/04650/2013 and PEST – C/QUI/UI0686/2013. EMFV is grateful for financial support through the FCT grant SFRH/BPD/95905/2013.

This work reports the fabrication and characterization of lithium cobalt oxide films (LiCoO2) on flexible Kapton® substrate. LiCoO2 is commonly used as cathode of lithium microbatteries but needs an annealing of 700 °C, which is not compatible with most flexible substrates. LiCoO2 films were deposited by reactive RF sputtering followed by an annealing process at 400 °C for 1 h in vacuum and air atmospheres both in silicon and Kapton® substrates. Raman spectroscopy, X-ray diffraction patterns and scanning electron microscopy images were used to evaluate samples crystallinity and morphology. Films fabricated in Kapton® and silicon substrates were compared., This work was financial supported by FEDER/COMPETE and FCT funds with the Project PTDC/EEA-ELC/114713/2009, strategic Project PEst-C/FIS/UI607/2013, PEst-C/QUI/UI0686/2013 and UID/EEA/04436/2013, first author scholarship SFRH/BD/78217/2011 and third author scholarship SFRH/BPD/95905/2013.

Raman spectroscopy results obtained for undoped and Al- and/or Mn-doped ZnO thin films produced by RF-sputtering are reported. The effect of the doping method (either co-sputtering or ion implantation), the dopant type, and its concentration on the Raman-active vibrational modes in these films were studied in detail. The results are discussed with focus on the peak shifts and broadening, and on the doping-induced relaxation of the symmetry selection rules. A particular attention is paid to the 520–530 cm−1 Raman band observed in all Mn containing samples and a simple theoretical model and arguments are presented in support of its relation to the local (gap) phonon mode produced by Mn atoms substituting Zn in the cationic sublattice of the ZnO crystal.

In this work, a novel customized shadowed off-axis deposition set-up is used to perform an original study of Ge nanoparticles (NPs) formation in an inert Ar gas atmosphere by pulsed laser deposition at room temperature varying systematically the background Ar gas pressure (Pbase(Ar)), target-substrate distance (d) and laser repetition rate (f). The influence of these parameters on the final NPs size distributions is investigated and a fairly uniform droplets-free and non-agglomerated NPs distribution with average height 〈h〉 = 2.8 ± 0.6 nm is obtained for optimized experimental conditions (Pbase(Ar) = 1 mbar; d = 3 cm; f = 10 Hz) with a fine control in the NPs density (from 3.2 × 109 cm -2 to 1.1 × 1011 cm-2). The crystalline quality of as-deposited NPs investigations demonstrate a strong dependence with the Ar gas pressure and a crystalline to amorphous phase volume fraction χc > 50% is found for Pbase(Ar) = 2 mbar. The NPs functionality for charge trapping applications has been successfully demonstrated by capacitance-voltage (C-V) electrical measurements. © 2013 Elsevier B.V. All rights reserved., This work has been partially funded by: (i) FEDER funds through the COMPETE program “Programa Operacional Factores de Competitividade” and by Portuguese funds through Portuguese Foundation for Science and Technology (FCT) in the frame of the Project PTDC/FIS/70194/2006; (ii) Scientific and Technological Cooperation Program between Portugal (FCT) and Morocco (CNRST)-2010/2011; (iii) European COST MP0901-NanoTP Action. E.M.F.V. and S.R.C.P. are grateful for financial support through FCT/POPH grants SFRH/BD/45410/2008 and SFRH/BPD/73548/2010, respectively. J.M.-S. is grateful for financial support through grant CSICJAE-DOC-070/01.

With the aim of producing materials with enhanced optical and photocatalytic properties, titanate nanotubes (TNTs) modified by cobalt doping (Co-TNT) and by Na+ -> Co ion-exchange (TNT/Co) were successfully prepared by a hydrothermal method. The influence of the doping level and of the cobalt position in the TNT crystalline structure was studied. Although no perceptible influence of the cobalt ion position on the morphology of the prepared titanate nanotubes was observed, the optical behaviour of the cobalt modified samples is clearly dependent on the cobalt ions either substituting the Ti4+ ions in the TiO 6 octahedra building blocks of the TNT structure (doped samples) or replacing the Na+ ions between the TiO6 interlayers (ion-exchange samples). The catalytic ability of these materials on pollutant photodegradation was investigated. First, the evaluation of hydroxyl radical formation using the terephthalic acid as a probe was performed. Afterwards, phenol, naphthol yellow S and brilliant green were used as model pollutants. Anticipating real world situations, photocatalytic experiments were performed using solutions combining these pollutants. The results show that the Co modified TNT materials (Co-TNT and TNT/Co) are good catalysts, the photocatalytic performance being dependent on the Co/Ti ratio and on the structural metal location. The Co(1%)-TNT doped sample was the best photocatalyst for all the degradation processes studied., The authors thank Fundação para a Ciência e Tecnologia (FCT) for financial support under the projects PTDC/CTM-NAN/113021/2009, UID/MULTI/00612/2013, UID/CTM/04540/2013, UID/FIS/04650/2013 and SFRH/BD/101220/2014. XPS analyses were performed at CEMUP– Centro de Materiais da Universidade do Porto.

In this work, we report on the production of Ge nanoparticles (NPs) in an inert Ar gas atmosphere by pulsed laser deposition (PLD) at room temperature (RT). The direct deposition of energetic particles/droplets resulting from the ablation process of the target material has been avoided by using an original and customized off-axis shadow mask (shadowed off-axis) deposition set-up where the NPs deposition on the substrate takes place by means of scattering between the NPs formed in the vapor phase and the background Ar atoms. It is found that the Ar gas pressure parameter has a relevant role in the crystallization process, with better crystallinity obtained as the background Ar pressure is raised for the given experimental conditions. © Springer-Verlag 2012

Thin films composed by (BaTiO3)1-x-(NiFe2O4)x with different nickel ferrite concentrations (x) have been deposited by pulsed laser ablation on platinum covered Si(001) substrates. The films structure was studied by X-ray diffraction and Raman spectroscopy. It was found that the NiFe2O4 phase unit cell was expanded along the growth direction of the films, with a lattice parameter that increased with increasing NiFe2O4 concentration. The opposite behavior was observed on the BaTiO3 phase, with an expansion of its unit cell that lowered with increasing x. The presence of the strain in the films induced a redshift of the Raman peaks of NiFe2O4 that decreased with increasing NiFe2O4 concentration. Cation disorder in the nickel ferrite was observed for lower x, where the nanograins are more isolated and subjected to more strain, which was progressively decreased for higher NiFe2O4 content in the films. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ge nanocrystals (NCs) embedded in Al2O3 were grown by RF-sputtering. X-ray diffraction, high resolution transmission electron microscopy, and Raman spectroscopy techniques were used to characterize the stresses on the NCs. While small NCs ( 17 nm) demonstrated a compressive stress effect. This could be linked to the crystal structure of the adjacent Al2O3 matrix.

A Raman spectroscopy study of doped versus undoped ZnO layers is presented. The layers were grown by RF magnetron sputtering and the doping with Al, Sb and Mn was achieved by ion implantation with subsequent annealing. First-order Raman response measured under λ=488 nm excitation is discussed. It is shown that doping with any of the impurities used in this work produces a strong enhancement of the longitudinal optical (LO) phonon band, which is attributed to the intra-band Frohlich mechanism. In addition, doping with Mn results in an extra mode located at 530 cm-1, tentatively attributed to a local vibrational mode of Mn substituting Zn in the lattice sites. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A study on the structure, electrical and optical properties of ZnO thin films produced by r.f. magnetron sputtering and implanted either with phosphorous (P) or antimony (Sb) is reported in this work. Raman spectroscopy, X-ray diffraction, optical transmittance and Hall effect measurements have been employed to characterize the samples. X-ray diffraction and Raman scattering patterns confirm that, after a 500 degrees C annealing, the doped films keep a polycrystalline nature with (002) preferred orientation. These films are very transparent and Hall effect results show that all have p-type conduction, despite doping ion and dose. The electric resistivity reaches values of 0.012 (omega cm) and 0.042 (omega cm) for the P and Sb-doped samples, respectively.

In this work we report a study on the structure, optical and electrical properties of P, Sb and Al implanted ZnO thin films that had been produced by r.f. magnetron sputtering. The influence of the different replacing atoms on the structure and properties of the films has been explored. Looking for the best annealing conditions, two different annealing temperatures (300 degrees C and 500 degrees C) have been employed. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction, transmittance and d.c conductivity measurements have been used to characterize the samples. X-ray diffraction and Raman scattering patterns confirm that after annealing, doped films keep a polycrystalline nature with (002) preferred orientation. These films remain very transparent and the electrical conductivity increases significantly after the 500 degrees C annealing, reaching 10.90 (Omegacm)(-1) in the P-doped, 10.33 (Omegacm)(-1) in the Al-doped and 0.56 (Omegacm)(-1) in the Sb-doped samples.

Authors thanks in particular the help of Professor T.H. Metzger scientific responsible of ID01 beamline at ESRF Grenoble for XRD data. Also authors would like to thank Dr. A.Chahboun for reading the manuscript and valuable remarks.One of the authors, M.Mamor is grateful for the support of Sultan Qaboos University., In this paper we report on the structural, optical and electrical properties of CdSe nanocrystals (NCs) embedded in silica matrix grown by the rf-magnetron sputtering technique with subsequent annealing under argon flux. Grazing incidence X-ray diffraction (GIXD), Photoluminescence (PL) and Raman spectroscopy, as well as current-voltage (I-V) measurements were used to characterize the CdSe NCs. The PL spectra of annealed samples demonstrate the presence of peaks in the range of 550-620 rim, indicating the quantum confinement effect in CdSe NCs. This quantum confinement effect in CdSe NCs was also confirmed by Raman spectroscopy. Finally, I-V behavior was explained by different concentrations and sizes of CdSe NCs., European Commission through project called SEMINANO under the contract NMP4-CT-2004-505285, Project POCTI/FIS/56930/2004 financed by Portuguese Foundation for Science and Technology (FCT)., FCT grant SFRH/BPD/26532/2006, FCT grant SFRH/BD/29657/2006, European Synchrotron Radiation Facility (ESRF), Grenoble, France, Project MA-128

CdSe nanocrystals (NCs) embedded in a solid SiO2 matrix were fabricated by RF-sputtering technique. Raman and photoluminescence spectroscopy illustrated the NCs size dependent confinement effect. The CdSe NCs charging effects were electrically characterized by means of capacitance–voltage measurements. A memory effect was demonstrated through memory window measurements.

Ge NCs have attracted considerable attention because of their potential applications in nonvolatile memory and integrated optoelectronics. A number of groups have already proposed integrate flash memories based on Ge NCs embedded SiO2 matrix. Since Al2O3 presents a high dielectric constant comparatively to SiO2, it is a good candidate to replace silica in flash memory systems, and therefore improve their performances. Moreover, Al2O3 presents good mechanical properties, and supports high temperature, which leads it to be an ideal material for Si processing conditions. However, a few studies have been reported on Ge NCs embedded in Al2O3 matrix.

Germanium (Ge) nanocrystals (NCs) embedded in alumina thin films were produced by deposition on fused silica and silicon (111) substrates using radio-frequency (RF) magnetron sputtering. The films were characterised by both Raman and X-ray diffraction (XRD) spectroscopy. The deposition conditions were optimised in order to obtain crystalline Ge nanoparticles. In as-deposited films, the typical NC size was ∼3 nm as estimated by means of X-ray diffraction. Raman spectra taken from as-deposited films revealed both amorphous and crystalline semiconductor phases. Annealing was performed in order to improve the crystallinity of the semiconductor phase in the films. After a 1 h annealing at 800 °C the mean NC size estimated from the XRD data and Raman spectra increased to ∼6.5 nm. An increase in the crystallinity of the Ge phase was also confirmed by the Raman spectroscopy data.

The authors are grateful to Prof. R. Correia (Univ. de Aveiro) for help in performing the Raman experimental work. Accepted version (9 January 2007), Ge nanocrystals (NCs) embedded in aluminum oxide were grown by RF-magnetron sputtering. Raman, high resolution transmission electron microscopy (HRTEM), selected area diffraction (SAD), and X-ray diffraction (XRD) techniques confirmed good cristallinity of the NCs from samples annealed at 800 °C. The average NC size was estimated to be around 7 nm. Photoluminescence (PL) measurements show an emission related to the NCs. The temperature dependence of the PL confirms the confinement phenomenon in the Ge NCs., Project number POCTI/FIS/56930/2004 and STRP 505285-1 SEMINANO., FCT grant SFRH/BPD/11650/2002.

Gas-phase phosphorous and boron doping of hydrogenated nanocrystalline thin films deposited by HWCVD at a substrate temperature of 150 °C on flexible-plastic (polyethylene naphthalate, polyimide) and rigid-glass substrates is reported. The influence of the substrate, hydrogen dilution, dopant concentration and film thickness on the structural and electrical properties of the films was investigated. The dark conductivity of B- and P-doped films (σd = 2.8 S/cm and 4.7 S/cm, respectively) deposited on plastic was found to be somewhat higher than that found in similar films deposited on glass. n- and p-type films with thickness below ∼ 50 nm have values of crystalline fraction, activation energy and dark conductivity typical of doped hydrogenated amorphous silicon. This effect is observed both on glass and on plastic substrates.

Nanocomposite thin films composed by (BaTi03) 1-x -(CoFe 2 O 4 ) x with different cobalt ferrite concentrations (x) have been deposited by pulsed laser ablation on platinum covered Si(001) substrates. The films structure was studied by X-ray diffraction and Raman spectroscopy. It was found that the CoFe 2 O 4 phase unit cell was compressed along the growth direction of the films, and it relaxed with increasing x. The opposite behavior was observed in the BaTiO 3 phase where the lattice parameters obtained from the X-ray measurements presented a progressive distortion of its unit cell with increasing x. The presence of the strain in the films induced a blueshift of the Raman peaks of CoFe 2 O 4 that decreased with increasing CoFe 2 O 4 concentration. Cation disorder in the cobalt ferrite was observed for lower x, where the nanograins are more isolated and subjected to more strain, which was progressively decreased for higher CoFe 2 O 4 content in the films.

This paper gives an overview of theoretical and experimental results on Raman-active optical phonon modes confined in nearly spherical nanocrystals (NCs) of polar semiconductor materials with cubic crystal structure. A systematic consideration of the effect of reduced dimensionality on both electrons and phonons is presented. The theoretical approach is based on a continuum lattice dynamics model and the effective mass approximation for electronic states in the NCs. Calculated resonant and non-resonant Raman scattering spectra are compared to experimental data stressing the effects of phonon confinement, type of excitation, polaron correction to the exciton spectrum enhanced because of the reduced dimensionality, and individual features of the NC material. Copyright © 2007 John Wiley & Sons, Ltd.

In this paper we report on the structural properties of as-grown CdS nanoparticles embedded in Al2O3 films produced by a magnetron RF-sputtering technique. Grazing incidence X-ray diffraction together with high-resolution transmission electron microscopy (HRTEM) and electron diffraction were used to study the crystallinity and morphology of the CdS nanocrystals. Depending on the deposition parameters, elongated or spherical nanocrystals were grown. HRTEM shows evidence of the growth of CdS nanocrystals at room temperature with sizes in the range of 3–8 nm, and indicates that the nanocrystals formed in the cubic phase during the early stages of the deposition process. Stress-free films were formed under selected deposition conditions. r 2002 Elsevier Science B.V. All rights reserved.

Fundacao para a Ciencia e a Tecnologia (FCT) - PTDC/FIS/70194/2006, SFRH/BPD/64850/2009 (FCT grant)

Absorption of far-infrared (FIR) radiation and Raman scattering in CdTe nano-crystals (spherical quantum dots (QDs) of several nanometers in size) and Cd 54 Te 32 (SCH 2 CH 2 OH) 8- 32 clusters prepared by colloidal synthesis were studied. Raman spectra of both QDs and clusters are dominated by a peak situated slightly below the bulk CdTe LO phonon frequency. Experimental FIR transmittance spectra of films containing CdTe clusters show a broad band between the bulk TO and LO phonon frequencies, while there is only a single dip at the Frohlich frequency observed for larger QDs. These observations are in agreement with the results of our numerical lattice dynamics calculations and previously published theoretical results based on a continuous model. It is suggested that the lattice dynamics of very small clusters is similar to that of large crystallites in the sense that there still exists the dispersion of optical vibration frequencies within the LO-TO band of bulk material.

13 pags., 9 figs., 3 tabs., In this work, we report on the production of regular (SiGe/SiO) multilayer structures by conventional RF-magnetron sputtering, at 350 °C. Transmission electron microscopy, scanning transmission electron microscopy, raman spectroscopy, and x-ray reflectometry measurements revealed that annealing at a temperature of 1000 °C leads to the formation of SiGe nanocrystals between SiO thin layers with good multilayer stability. Reducing the nominal SiGe layer thickness (t ) from 3.5-2 nm results in a transition from continuous SiGe crystalline layer (t ∼ 3.5 nm) to layers consisting of isolated nanocrystals (t ∼ 2 nm). Namely, in the latter case, the presence of SiGe nanocrystals ∼3-8 nm in size, is observed. Spectroscopic ellipsometry was applied to determine the evolution of the onset in the effective optical absorption, as well as the dielectric function, in SiGe multilayers as a function of the SiGe thickness. A clear blue-shift in the optical absorption is observed for t ∼ 2 nm multilayer, as a consequence of the presence of isolated nanocrystals. Furthermore, the observed near infrared values of n = 2.8 and k = 1.5 are lower than those of bulk SiGe compounds, suggesting the presence of electronic confinement effects in the nanocrystals. The low temperature (70 K)hotoluminescence measurements performed on annealed SiGe/SiO nanostructures show an emission band located between 0.7-0.9 eV associated with the development of interface states between the formed nanocrystals and surrounding amorphous matrix., This work was partially funded by: (i) FEDER funds through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011; (ii) the transnational access framework of the ANNA Eu Project (Contract No. 026134-RII3) through the funding of the ANNA_- TA_UC9_RP006 proposal; (iii) UID/CTM/50025/2013 and (iv) UID/FIS/04650/2013. EMFV is grateful for financial support through the FCT and POPH of the grant SFRH/ BPD/95905/2013. The authors would like also to thank engineer José Santos for technical support at the Thin Film Laboratory

This paper reports on the changes in the structural and morphological features occurring in a particular type of nanocomposite thin-film system, composed of Au nanoparticles (NPs) dispersed in a host TiO2 dielectric matrix. The structural and morphological changes, promoted by in-vacuum annealing experiments of the as-deposited thin films at different temperatures (ranging from 200 to 800 C), resulted in a well-known localized surface plasmon resonance (LSPR) phenomenon, which gave rise to a set of different optical responses that can be tailored for a wide number of applications, including those for optical-based sensors. The results show that the annealing experiments enabled a gradual increase of the mean grain size of the Au NPs (from 2 to 23 nm), and changes in their distributions and separations within the dielectric matrix. For higher annealing temperatures of the as-deposited films, a broad size distribution of Au NPs was found (sizes up to 100 nm). The structural conditions necessary to produce LSPR activity were found to occur for annealing experiments above 300 C, which corresponded to the crystallization of the gold NPs, with an average size strongly dependent on the annealing temperature itself. The main factor for the promotion of LSPR was the growth of gold NPs and their redistribution throughout the host matrix. On the other hand, the host matrix started to crystallize at an annealing temperature of about 500 C, which is an important parameter to explain the shift of the LSPR peak position to longer wavelengths, i.e. a red-shift., FEDER funds through the program COMPETE—Programa Operacional Factores de Competitividade; Karlsruhe Nano Micro Facility (KNMF), a Helmholtz Research Infrastructure at KIT; ELETTRA Synchrotron Radiation Center for the measurements at the SAXS beamline; European COST Actions MP0901-NanoTP, This work is sponsored by FEDER funds through the program COMPETE - Programa Operacional Factores de Competitividade - and by national funds through FCT – Fundação para a Ciência e a Tecnologia-, under the projects PEst-C/FIS/UI607/2013, PEst-C/CTM/LA0025/2013 and PEst-C/EME/UI0285/2013. The authors would like also to thank the support by: (i) Karlsruhe Nano Micro Facility (KNMF), a Helmholtz Research Infrastructure at KIT; (ii) ELETTRA Synchrotron Radiation Center for the measurements at the SAXS beamline; (iii) European COST Actions MP0901-NanoTP and (iv) European Community as an Integrating Activity 'Support of Public and Industrial Research Using Ion Beam Technology (SPIRIT project)' under EC contract no. 227012. M.B. acknowledges support from the Croatian Ministry of Science, Higher Education and Sport, (project number 098-0982886-2895).

Non-resonant Raman spectroscopy studies of a set of CdS films annealed at different temperatures were performed and showed a direct correlation between the width of the Raman peak produced by CdS-like optical phonons and the crystalline quality of the semiconductor phase probed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). In order to decribe the Raman lineshape a model proposed by Trallero-Giner et al (1998 Phys. Rev. B 57 4664) was used, which considers optical phonons confined in small semiconductor spheres with a size distribution. The model is shown to give a good reproduction of the spectra of samples where the semiconductor phase is most crystalline. However, it required too large values of phonon damping to fit the spectra of several other samples, which, according to XRD and TEM data, do contain CdS nano-crystallites. This large broadening of the Raman peak was considered as inhomogeneous, i.e. associated with disorder. Numerical lattice dynamics calculations were performed for 2D binary clusters of arbitrary shape and three kinds of disorder were considered, (i) random variation of the Cd–S bond frequency from one nano-crystallite to another, (ii) cluster shape irregularities and (iii) fluctuations of the nearest-neighbour interaction constant within one cluster. It is shown that ‘ensemble disorder’ (i) can be responsible for a shoulder above the bulk CdS phonon frequency observed for some of our samples. The effect of shape disorder (ii) is similar to that of the size dispersion producing some inhomogeneous broadening of the peak. In addition, it gives rise to an extra low-frequency mode originating from the top of the acoustic band. The force constant’s disorder (iii) is shown to result in a stronger asymmetric broadening of the Raman peak., Fundação para a Ciência e a Tecnologia (FCT)

The non-resonant nonlinear optical properties of CdS nanocrystals (NCs) embedded in silica (i) and forming matrix-free (MF) almost close-packed films (ii) were studied using the Z-scan technique. Among the group (i), samples containing NCs covered with a HgS and CuS shell were investigated. The highest value of the nonlinear refractive index n2 1⁄4 1.85 10– 6 cm2/W was measured for the MF films. This number exceeds by far the value typical for bulk CdS and cannot be explained in terms of thermally induced nonlinearity. Strong enhancement of local fluctuations of the electro-magnetic field in MF films where NCs form aggregates or clusters is suggested to explain this result. Within the group (ii), an enhancement of the nonlinearity was observed under pulsed irradiation for both CdS/HgS and CdS/CuS nanoparticles, compared to CdS NCs without a shell.

Absorption of far-infrared (FIR) radiation in very small CdSe crystallites (quantum dots, QDs) via excitation of confined dipolar vibrational modes was studied, both theoretically and experimentally. Spatial quantisation of optical phonons was analysed in the framework of a continuum model, which couples the phonon amplitude to the electrostatic potential via the Fro¨ hlich interaction. The frequencies and oscillator strengths of the dipole-active optical vibration modes are presented calculated for a spherical QD, and for the first time for II–VI QDs these quantised modes were observed experimentally. Another effect studied in this work is the influence of the QD concentration on the FIR absorption of their ensemble. It is shown that the dipole–dipole interaction becomes very important in dense QD ensembles and leads to smearing of the structure in the CdSe phonon band as the QD concentration increases., Fundação para a Ciência e a Tecnologia (FCT)

Ge nanocrystals embedded in silicon dioxide (SiO2) films were prepared using the magnetron rf-sputtering technique. The films were characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and optical transmission measurements. It was determined from X-ray diffractograms that the Ge particles have a diamond structure. The mean diameter of the nanocrystals was estimated to be between 30 and 80 A ˚ . XPS measurements showed that the Ge nanocrystals were very little oxidised. For the crystalline Ge particles, the size dependence of the Raman spectra of the TO phonon mode was observed. The increase in the line-width and the shift of the peak position to lower frequencies with decrease in their size are explained theoretically from quantum confinement effects of phonons. Optical transmission spectra clearly display a marked blue shift of the edge of the absorption band compared to bulk crystalline Ge, which is attributed to quantum size effects. # 1999 Elsevier Science S.A. All rights reserved.

The authors would like to thank Professor David Barber (University of Essex) for his helpful discussions and critical reading of this manuscript, and Engineer José Santos for technical support at Thin Film Laboratory., The charge storage behavior of nanostructures based on Si1−xGex (0 ≤ x ≤ 1) nanocrystals (NCs) in an Al2O3 matrix was investigated. The structures have been grown by RF magnetron sputtering and subsequently annealed at temperatures ranging from 700 ºC to 1000 ºC for 30 min in nitrogen ambient. The stoichiometry of the SiGe NCs and the alumina crystalline structure were found to be significantly dependent on the RF power and the annealing temperature. The sizes of the SiGe NCs and their distribution were investigated by grazing incidence small angle X-ray scattering (GISAXS). The capacitance-voltage (C-V) and conductance-voltage (G-V) measurements were performed to investigate the charge trapping characteristics of the memory structures. The C-V hysteresis width depends on variations in the crystalline structure resulting from different annealing temperatures. It is also shown that charge injection is governed by the Fowler-Nordheim tunnel mechanism for higher electric fields., European COST Actions MP0901-NanoTP, European COST Actions MP0903-NanoAlloy, ELETTRA Synchrotron Radiation Center for the measurements at the SAXS beamline, FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Projects PEST-C/FIS/UI607/2011 and PEst-C/CTM/LA0025/2011, E.M.F.V. is grateful for financial support through the FCT and POPH of the Grant SFRH/BD/45410/2008, M.B. acknowledges support from the Ministry of Science Education and Sports, Republic Croatia (Project No. 098-0982886-2895).

We report the synthesis, structural and ferroelectric characterization of continuous well-aligned nanofibres of barium titanate produced by the electrospinning technique. The fibres with average diameter of 150-400 nm consist of connected nanoparticles of BaTiO3 stacked together to form the shape of a long filament. The tetragonal phase in the obtained nanofibres was revealed by the x-ray diffraction and Raman spectroscopy and has been also confirmed by the second harmonic generation (SHG) and piezoresponse force microscopy (PFM). The temperature dependence of the SHG in the vicinity of the paraelectric-ferroelectric phase transition suggests that barium titanate nanofibres are indeed ferroelectric with an apparent glass-like state caused by metastable polar nanoregions. The existence of domain structure and local switching studied by PFM present clear evidence of the polar phase at room temperature., This work has been done in the framework of the CIENCIA-2007 programme (reference UMINHO-CF-06) and was financially supported by the European Regional Development Fund (ERDF) through Programa Operacional Factores de Competitividade (COMPETE: FCOMP-01-0124-FEDER-014628), by the Portuguese Foundation for Science and Technology (FCT) (PTDC/CTM-NAN/114269/2009, PTDC/CTM-NAN/115125/2009, PTDC/CTM-CER/115085/2009, PTDC/CTM/105597/2008, PTDC/CTM/099415/2008) and by the strategic project PEST-C/FIS/UI607/2011., info:eu-repo/semantics/publishedVersion

The oThe oxidation of phenol, cychohexanol and hydroquinone has been screened in the presence of copper(II) complexes with the Schiff‐base salen ligand, 1,5‐bis[(E)‐5‐chloro‐2‐hydroxybenzylideneamino]‐1H‐imidazole‐4‐carbonitrile, and encapsulated into NaY zeolite by using two different methods. The new heterogeneous catalysts were characterized by SEM, XRD, FTIR, EPR and Raman spectroscopy as well as by chemical analysis. The structures of the copper(II) complexes were proposed on the basis of theoretical studies (DFT). The catalytic activities of the encapsulated copper(II) complexes in NaY were compared with their homogeneous counterparts. The results show higher or similar substrate conversion when compared with the free complex in all the reactions tested. After their use in catalytic reaction, these catalysts were found to be reusable without loss of activity., I. K. B. thanks the Fundação para Ciência e Tecnologia (FCT) for a contract under the program Ciência 2007. The authors are grateful to Dr. A. S. Azevedo for collecting the powder diffraction data. The authors thank the FCT and the European Fund for Regional Development (FEDER, COMPETE‐QREN‐EU) for financial support to the Research Centre (CQ/UM PEst‐C/QUI/UI0686/2011, FCOMP‐01‐0124‐FEDER‐022716) and to the financial support from the NMR Portuguese Network (PT NMR, Bruker Avance III 400, Univ. of Minho).

In this paper, we report on the electrical properties of metal–oxide–semiconductor (MOS) capacitors containing a well-confined 8 nm-thick SiGe amorphous layer (a-SiGe) embedded in a SiO2 matrix grown by RF magnetron sputtering at a low temperature (350 ºC). Capacitance–voltage measurements show that the introduction of the SiGe layer leads to a significant enhancement of the charge trapping capabilities, with the memory effect and charge retention time larger for hole carriers. The presented results demonstrate that amorphous floating-gate SiGe layers embedded in SiO2 may constitute a suitable alternative for memory applications., This study was partially funded by: (i) European COST Actions MP0901-NanoTP and MP0903-NanoAlloy; (ii) FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology in the framework of the Strategic Project PEST-C/FIS/UI607/2011; (iii) the transnational access framework of the ANNA Eu Project (Contract No 026134-RII3) through the funding of the ANNA_TA_UC9_RP006 proposal. EMFV is grateful for financial support through the FCT and POPH of the grant SFRH/BD/45410/2008. JMS is grateful for financial support through the Spanish CSIC JAE-DOC-070/01 program co-funded by FSE. The authors would also like to thank Engineer Jose Santos for technical support at the Thin Film Laboratory., The authors would also like to thank Engineer José Santos for technical support at the Thin Film Laboratory.

In this work, we investigate the structural and photoluminescence (PL) properties of (SiGe+Al2O3)/Al2O3 multi-layer films with layer thicknesses in the range of a few nanometres. The films were prepared by magnetron sputtering deposition at room temperature followed by an annealing process to promote the formation of small SiGe nanocrystals (NCs) (∼3 to 5 nm) embedded between ultra-thin (∼6 nm thickness) Al2O3 layers. Our results show that the structural and compositional properties of the films can be tuned by changing the RF-power. It is found that nearly spherical and well confined isolated SiGe NCs (∼5 nm) are obtained for an RF-power value of 80 W. The PL properties of the films were studied and optical emission in the blue visible wavelength region was observed. © 2013 IOP Publishing Ltd., JMS is grateful for financial support through the Spanish CSIC JAE-DOC-070/01 programme co-funded by FSE. SIM acknowledges support by the Spanish MICINN/MEC (projects TEC2011-29120-C05- 03 and CONSOLIDER INGENIO CSD2009-00013) and the Junta de Andalucía (PAI research group TEP-120; project P08-TEP-03516).

In this work, we report on the synthesis of Ge nanocrystals (NCs) by pulsed laser deposition (PLD) at room temperature (RT) in an argon atmosphere without any further annealing process. Our results show that functional thin films of crystalline Ge nanoparticles with spherical shapes can be obtained by PLD directly on alumina layers deposited on n-doped Si (100) substrates. In addition, we also demonstrate that a uniform size distribution of NCs with an average diameter of about 3 nm and a density of 2.3x10^11 cm^-2 can be obtained by optimizing a shadow mask set-up, where a solid disk is introduced between the target and the substrate. Charge/discharge effects in Ge NCs deposited on a high-k amorphous alumina layer are also evidenced by conductive atomic force microscopy, which makes them suitable for memory applications., This work has been fully funded through the project PTDC/FIS/70194/2006 financed by the Portuguese Foundation for Science and Technology (FCT), European COST MP0901-NanoTP and COMPETE. SRCP, EMFV, and JMS are grateful for financial support through FCT grants SFRH/BD/29657/2006, SFRH/BD/45410/2008, and SFRH/BPD/64850/2009, respectively. We would like to thank David J. Barber, Augusto Lopes, Ana J. Martins, and Jose Santos for scientific discussion and technical support., European COST MP0901-NanoTP, COMPETE

Continuous nanofibers of barium titanate (BaTiO3) with average diameter of 150–300 nm have been produced by means of mutual sol-gel and electrospinning routines with subsequent calcination step. The structural characterization of the obtained nanofibers has been performed by XRD and Raman spectroscopy. Their individual grain and domain structures were studied by piezoresponse force microscopy (PFM). The results show that the fibers consist of stacked tetragonal ferroelectric BaTiO3 grains with average size of about 50–100 nm and random initial orientations. The piezoelectric response is similar to that obtained for domain model in ferroelectric tetragonal perovskites., Fundação para a Ciência e a Tecnologia PDTC/CTM/099415/2008,PDTC/CTM-NAN/114269/2009

Thin Zn0.98Mn0.02O films were grown by pulsed laser deposition on glass substrates under oxygen pressure. The structural properties were studied by X-ray diffraction and Raman techniques, while the conductivity was characterized by the Hall effect. The oxygen pressure during the growth seems to govern the structural and the electrical properties of the thin Zn0.98Mn0.02 films. In fact, the micron size grain and the resistivity of the Zn0.98Mn0.02O increase with the partial oxygen pressure. However, no evident effect was observed on the magnetic behavior. Electronic structure calculations were performed and magnetic moment carried by Mn atom was computed as well., Fundação para a Ciência e a Tecnologia (FCT) - PTDC/FIS/098943/2008, bolsa SFRH/BPD/26532/2006, European Commission through project ELIARE NETWORK SUDOE INTERREG IV B (2009-2011), Scientific and Technological Cooperation Program (CNRST)-2010/2011

Dipole-active optical phonons confined in nearly spherical InP quantum dots (QDs) were studied theoretically and experimentally. Spatial quantization of the phonon modes in an InP QD was considered theoretically by solving the coupled continuous equation of motion and Poisson equation. It is shown that, when the Frohlich frequency falls into the gap between the bulk LO and TO phonon bands, a gap mode appears, which contains most of the dipole oscillator strength. Accordingly, the shape of the far-infrared (FIR) absorption spectra does not change with the QD size. This conclusion has been confirmed by our experimental FIR spectroscopy studies on films of InP QDs prepared by colloidal synthesis.

In this article, we present an investigation of (Ge + SiO2)/SiO2 multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures. The structural properties were investigated by transmission electron microscopy, grazing incidence small angles X-ray scattering, Rutherford backscattering spectrometry, Raman, and X-ray photoelectron spectroscopies. We show a formation of self-assembled Ge clusters during the deposition at 250°C. The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution. The crystallization of the clusters was achieved at annealing temperature of 700°C., FEDER - COMPETE - “Programa Operacional Factores de Competitividade", British Council and the Council of the Portuguese Rectores - Bilateral Cooperation Program BC/CRUP - B 26/08, ELETTRA Synchrotron Radiation Center through the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no 226716, European COST MP0901-NanoTP Action, Croatian Ministry of Science Higher Education and Sport (project number 098-0982886-2866), Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/29657/2006, PTDC/FIS/70194/2006, Scientific and Technological Cooperation Program (CNRST)-2010/2011)

Antimony telluride (Sb2Te3) is a chalcogenide material used in thermoelectric applications. The deposition of thin films of Sb2Te3 requires a precisely controlled process to achieve a desirable high thermoelectric figure of-merit. The optimization of the thermal co-evaporation process for p-type Sb2Te3 thin-film onto plastic substrates (Kapton© polyimide) for thermoelectric applications is reported. The influence of deposition parameters and composition on thermoelectric properties was studied, seeking optimal thermoelectric performance. Energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy all confirmed the formation of Sb2Te3 thin films. Seebeck coefficient (up to 190 μVK−1), in-plane electrical resistivity (8–15 μΩm), carrier concentration (1×10^19–7×10^19 cm−3) and Hall mobility (120–180 cm2V−1s−1) were measured at room temperature for the best Sb2Te3 thin-films., Fundação para a Ciência e a Tecnologia (FCT) FCT/PTDC/EEA-ENE/66855/2006

Si1-xGex nanocrystals (NCs), embedded in Al2O3 matrix, were fabricated on Si (100) substrates by RF magnetron sputtering technique with following annealing procedure at 800 C, in nitrogen atmosphere. The presence of Si1-xGex NCs was confirmed by grazing incidence X-ray diffraction (GIXRD), grazing incidence small angle X-ray scattering (GISAXS) and Raman spectroscopy. The influence of the growth conditions on the structural properties and composition of Si1-xGex NCs inside the alumina matrix was analyzed. Optimal conditions to grow Si1-xGex (x~0.8) NCs sized between 3 and 4 nm in Al2O3 matrix were established., Portuguese Foundation for Science and Technology (FCT) - SFRH/BD/45410/2008, SFRH/BD/29657/2006 and SFRH/BPD/26532/2006, ELETTRA and European Community under EU Contract No.RII3-CT-2004-506008 for the measurements at the SAXS beamline (Proposal 2008345), European Cost Action MP0901-NanoTP ”Designing novel materials for nanodevices: From Theory to Practise, Scientific and Technological Cooperation Program between Portugal (FCT) and Morocco (CNRST)-2010/2011, Ministry of Science Education and Sports, Republic Croatia (project number 098-0982886-2866)

Raman spectroscopy results obtained under visible (non-resonant) and UV (resonant) excitation for nanocrystalline ZnO, ZnO:Mn and ZnO:Mn:Al thin films grown by radio frequency magnetron sputtering are presented and compared. The origin of the multiple longitudinal optical (LO) phonon Raman peaks, strongly enhanced under resonance conditions, and the effects of the dopants on them are discussed in the framework of the ‘cascade’ model. It is suggested that the observed suppression of the higher-order LO phonon lines for ZnO:Mn:Al is caused by the dissociation of excitons in the heavily n-type doped material. On the basis of the cascade model interpretation of the higher-order Raman peaks in the resonant spectra, the LO phonon frequencies for wavevectors away from the gamma point are evaluated and compared topreviously published phonon dispersion curves., Financial support from the FCT through project PTDC/FIS/72843/2006 is acknowledged.

We report on the structural and electrical properties of Mn-doped ZnO/Al2O3 nanostructures produced by the pulsed laser deposition technique. Grazing incidence small angle x-ray scattering (GISAXS) and Rutherford backscattering spectrometry revealed the multilayered structure in as-deposited samples. Annealing of the nanostructures was shown to promote the formation of nanocrystals embedded in the Al2O3 matrix, as was evidenced by GISAXS and high resolution transmission microscopy. Particle-induced x-ray emission analysis showed a doping of 8 at.% Mn in ZnO. Grazing incidence x-ray diffraction and Raman spectroscopy demonstrated that the nanocrystals have the pure wurtzite ZnMnO crystalline phase. Resonant Raman scattering displayed an increase of intensity of the 1LO mode as well as broadening of the 2LO mode related to the size effect. Capacitance-voltage measurements showed carrier retention with a voltage shift higher than those reported for similar systems., Project PTDC/FIS/098943/2008 financed by the Portuguese Foundation for Science and Technology (FCT), European Commission through projects COST Action MP0901-NanoTP and Eliare Network Sudoe Interreg IV-B, Scientific and technological cooperation programme between Portugal (FCT) and Morocco (CNRST) 2010/2011, European Synchrotron Radiation Facility, Grenoble, France, Project SI-1780 for the use of beamline ID10B for GISAXS and GIXRD measurements., FCT grant SFRH/BPD/26532/2006

The kinetics of the isothermal crystallization from the melt of α- and γ-poly(vinylidene fluoride), PVDF, and the corresponding melting behaviour has been investigated. The crystallization kinetics was evaluated on the basis of the theory of Avrami. The variation of the microstructure of the samples crystallized at different temperatures was monitored along time by optical microscopy with polarized light. The correlation between microstructure and kinetic parameters allows tailoring the microstructure of the polymer by choosing specific crystallization conditions. Infrared spectroscopy and Raman spectroscopy show the appearance of the γ-phase for higher crystallization temperatures., The authors thank the Portuguese FCT Grants PTDC/CTM/73030/2006, PTDC/CTM/69316/2006 and NANO/NMed-SD/0156/2007. V.S. thanks the FCT for the SFRH/BPD/63148/2009 grant.

Zn 1- x Mn x O ( x = 0.01, 0.02, 0.05, 0.1, and 0.15) powders were prepared by solid-state reaction processes. The structural and magnetic properties of the powders were investigated. X-ray diffraction (XRD) analysis of the samples indicates the presence of wurtzite crystal structure similar to pure ZnO and absence of any other secondary phase till 5% Mn doping. This suggests that doped Mn 2+ ions substitute Zn 2+ sites. However, Raman results revealed the presence of secondary phase even at very low Mn doping (2%), which demonstrates that Mn does not incorporate completely the ZnO lattice. The powders exhibit ferromagnetism at low temperatures and paramagnetic at room temperature. Transition from ferromagnetic to paramagnetic is highlighted by measurements at 230 K.

Alumina films containing gold nanoparticles (NPs) were grown by magnetron radio frequency (rf) sputtering technique. They were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and optical absorption spectroscopy. It is suggested that the increase of the contrast of surface plasmon resonance band after annealing is connected with increasing of electron free mean pass in Au NPs rather than with change in particle size distribution. The absorption spectra of the nanocomposites have been modelled taking into account a correction of the dielectric constant for electron mean free path limitation., Project Acções Integradas Luso-Britânicas Acção Nº B-50/05., FCT grant SFRH/BPD/18098/2004

In this paper, Ge/Al"2O"3 multilayer systems were grown by pulsed laser ablation. The grown samples were annealed at 900^oC to promote the formation of Ge nanocrystals. Rutherford backscattering spectroscopy and transmission electron microscopy confirmed the presence of a multilayer system. Grazing incidence small angles X-ray scattering technique demonstrates the formation of Ge nanoclusters formed between alumina layers. Room temperature I-V measurements showed weak carrier trapping in the system. This was explained by the leakage caused by Ge diffusion through the multilayer.

ZnO:Mn transparent thin films (thickness b1 μm) with the Mn contents ranging from 1.8 to 3.25 at.% were grown by RF magnetron co-sputtering. The films are nanocrystalline, with wurtzite-structure grains of a typical size of 20 nm and with a preferential orientation of the c-axis perpendicular to the surface. According to the Raman spectroscopy data, Mn mostly substitutes Zn in the lattice sites. In spite of these factors, the nanostructure and the Mn(Zn) substitution, that are considered favorable for ferromagnetism in this material, both magnetic resonance and Faraday effect measurements show paramagnetic behavior of the ZnO:Mn films and the absence of ferromagnetic order at room temperature., FCT throughproject PTDC/FIS/72843/2006

We report on the formation of a regularly ordered void lattice with a void size of about 4 nm in an alumina matrix. The voids were formed by thermal treatment of a well-ordered three-dimensional Ge quantum dot lattice formed earlier by self-assembled growth in an alumina matrix during magnetron sputtering codeposition of Ge+Al2O3. During the subsequent annealing the germanium atoms were lost from the film and so voids were produced. The positions of the voids are ordered in the same way as the Ge quantum dots that were present before annealing, while their sizes can be controlled by the deposition parameters.

Hydrogenated amorphous and nanocrystalline silicon thin films deposited by Hot Wire (HW) and Radio-Frequency Plasma-Enhanced (RF) Chemical Vapor Deposition were Er-bium-implanted. Their pre-implantation structural properties and post-implantation optical properties were studied and cor-related. After one-hour annealing at 150ºC in nitrogen atmos-phere only amorphous films showed photoluminescence (PL) activity at 1.54 μm, measured at 5 K. After further annealing at 300oC for one hour, all the samples exhibited a sharp PL peak positioned at 1.54 m, with a FWHM of ~5 nm. Amorphous films deposited by HW originated a stronger PL peak than corresponding films deposited by RF, while in na-nocrystalline films PL emission was much stronger in sam-ples deposited by RF than by HW. There was no noticeable difference in Er3+ PL activity be-tween films implanted with 1x1014 atoms/cm2 and 5x1015 at-oms/cm2 Er doses., FCT for a post-doctorate grant (SFRH/BPD/14919/2004)