Papers by Ana Maria Botelho Rego
Experimental Methods in the Physical Sciences, 2001
... 4. PHOTONIC AND ELECTRONIC SPECTROSCOPIES FOR THE CHARACTERIZATION OF ORGANIC SURFACES AND OR... more ... 4. PHOTONIC AND ELECTRONIC SPECTROSCOPIES FOR THE CHARACTERIZATION OF ORGANIC SURFACES AND ORGANIC MOLECULES ADSORBED ON SURFACES Ana MariaBotelho do Rego, Luis Filipe Vieira Ferreira centro de Qufmica-Ffsica Molecular ...
Photochemical & Photobiological Sciences, Jan 1, 2006
The Journal of Physical Chemistry B, 2008
We present results from high-resolution electron energy loss spectroscopy (HREELS) and XPS studie... more We present results from high-resolution electron energy loss spectroscopy (HREELS) and XPS studies of self-assembled monolayers of DNA. The monolayers are well-organized and display sharp vibrational peaks in the HREEL spectra. The electrons interact mainly with the backbone of the DNA. The XPS results indicate that, in most of the samples studied, the phosphates on the DNA are not charged.
Materials Research Bulletin, 2010
Doped TiO 2 particles were synthesized by solid grinding and sol–gel methods. The ensuing powders... more Doped TiO 2 particles were synthesized by solid grinding and sol–gel methods. The ensuing powders were analysed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ground state diffuse reflectance absorption spectroscopy (GSDR). The doped ...
Materials Chemistry and Physics, 2012
ZnO is a natural n-type widespread semiconductor with wide direct bandgap of 3.37 eV, large excit... more ZnO is a natural n-type widespread semiconductor with wide direct bandgap of 3.37 eV, large exciton bending energy (60 meV) and high optical gain (300 cm −1 ). One dimensional ZnO nanomaterials such as nanowires or nanorods have focused much attention due to their multifunctionality in optoelectronic devices, gas sensing, piezoelectricity and thin film transistors for transparent and flexible electronics. Solution-phase chemical synthesis of nanomaterials has several important advantages, as low temperatures, high versatility, low cost, simple equipments and handling.
Macromolecules, 2001
High-resolution electron energy loss spectroscopy (HREELS) is applied to study film surfaces of t... more High-resolution electron energy loss spectroscopy (HREELS) is applied to study film surfaces of two silicon-based polymers having methyl and/or phenyl rings as pendant groups: poly(diphenylsiloxane) and poly(methylphenylsilane). These spectra are compared with those obtained by infrared absorption, Raman scattering, and UV/vis absorption spectroscopy for the polymer bulk. Both vibrational and electronic spectra of these two polymers exhibit common features corresponding to the phenyl pendant group excitations. Positions of peaks appearing in HREELS vibrational spectra correspond well to infraredand Raman-active modes of the polymer bulk. Electronic losses also correspond to the electronic excited states of phenyl groups cited in the literature. Differences related to secondary emission and accumulation of relaxed electrons are assigned to the electronic structure of the film. The absence of a loss corresponding to the excitation of polysilane chain is related to a trapping mechanism.
Langmuir, 2008
Ultrathin films of cellulose were functionalized with iron protoporphyrin IX (FePP). Spin-coating... more Ultrathin films of cellulose were functionalized with iron protoporphyrin IX (FePP). Spin-coating allows the production of silylated cellulose films in a controlled way. Cellulose regeneration is achieved through the hydrolyzation of the silane groups, exposing the film to acidic vapors. To enhance the reactivity of the cellulose surface to the protoporphyrin, carbonyldiimidazole (CDI) was used as an activator. The effect of different spacers on the porphyrin grafting such as 1,8-diaminooctane and 1,4-phenylenediamine was studied. The highest level of cellulose functionalization with FePP was achieved when both the cellulose film and FePP were activated by CDI and a diaminoalkane was used as a spacer between the surface and the FePP. ATR/MIR (attenuated total reflection in multiple internal reflections) was performed in situ to follow the kinetics of the different chemical reactions with the cellulose surface. ATR/MIR proved again to be a powerful tool for probing the surface reaction. X-ray photoelectron spectroscopy permitted the elemental analysis of the cellulose surface after the chemical modification.
Journal of Electron Spectroscopy and Related Phenomena, 1997
High resolution electron energy loss spectroscopy (HREELS) was used to study vibrational and elec... more High resolution electron energy loss spectroscopy (HREELS) was used to study vibrational and electronic excitations induced by electrons in polystyrene thin films cast on silicon substrates. In order to deduce the nature of the interaction mechanisms involved, differential cross-sections of vibrational and electronic excitations were measured as a function of the incident electron energy and of the geometrical configuration of the experiment. Vibrational excitations were compared with the very strong bands of infrared and Raman spectra. Losses produced by impact interaction correspond mostly to Raman active modes; those produced by dipole interaction correspond mostly to infrared active modes. Electronic excitations leading to triplet or singlet excited states and having constant widths around 0.7 eV were detected. In this case, pronounced resonance mechanisms are involved, mainly in geometrical configurations far from specular conditions, showing the existence of transient negative ions centred at the maxima found for the excitation functions. The resonant mechanisms decline as specular conditions are reached. Losses having widths increasing with incident energy are assigned to interband transitions. Finally, structures at fixed kinetic energies, appearing in all spectra, are associated with the relaxation of slow electrons occupying conduction band levels with high density of states before escaping to the vacuum. ᭧ 1997 Elsevier Science B.V.
The effect of different mild post-annealing treatments in air, at 270 ◦C, for 4–6 min, on the opt... more The effect of different mild post-annealing treatments in air, at 270 ◦C, for 4–6 min, on the optical, electrical,
structural and chemical properties of copper sulphide (CuxS) thin films deposited atroomtemperature
are investigated. CuxS films, 70nm thick, are deposited on glass substrates by vacuum thermal evaporation
from a Cu2S:S (50:50 wt.%) sulphur rich powder mixture. The as-deposited highly conductive
crystalline CuS (covellite) films show high carrier concentration (∼1022 cm−3), low electrical resistivity
(∼10−4 cm) and inconclusive p-type conduction. After the mild post-annealing, these films display
increasing values of resistivity (∼10−3 to ∼10−2 cm) with annealing time and exhibit conclusive p-type
conduction. An increase of copper content in CuxS phases towards the semiconductive Cu2S (chalcocite)
compound with annealing time is reported, due to re-evaporation of sulphur from the films. However,
the latter stoichiometry was not obtained, which indicates the presence of vacancies in the Cu lattice.
In the most resistive films a Cu2O phase is also observed, diminishing the amount of available copper
to combine with sulphur, and therefore the highest values of optical transmittance are reached (65%).
The appearance on the surface of amorphous sulphates with annealing time increase is also detected as a
consequence of sulphur oxidation and replacement of sulphur with oxygen. All annealed films are copper
deficient in regards to the stoichiometric Cu2S and exhibit stable p-type conductivity.
Transparent and conductive/semiconductive undoped indium oxide (InOx) thin films were deposited a... more Transparent and conductive/semiconductive undoped indium oxide (InOx) thin films were deposited at room temperature. The deposition
technique used is the radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium (In) in the presence
of oxygen. The influence of oxygen partial pressure on the properties of these films is presented. The oxygen partial pressure varied
between 3 · 102 and 1.3 · 101 Pa. Undoped InOx films, 100 nm thick, deposited at the oxygen partial pressure of 6 · 102 Pa show a
conductive behaviour, exhibit an average visible transmittance of 81%, a band gap around 2.7 eV and an electrical conductivity of about
1100 (X cm)1. For oxygen pressures greater than 6 · 102 Pa, semiconductive films are obtained, maintaining the visible transmittance.
Films deposited at lower pressures are conductive but dark. From XPS data, films deposited at an oxygen partial pressure of 6 · 102 Pa
show the highest amount of oxygen in the film surface and the lowest ratio between oxygen in the oxide crystalline and amorphous phases.
Journal of Physical Chemistry B, Jan 1, 2005
Thin Solid Films, 2011
In the present study, black chromium coatings were electrodeposited from a 1-butyl-3-methylimidaz... more In the present study, black chromium coatings were electrodeposited from a 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF 4 ]) solution containing Cr(III) under potentiostatic control on copper substrates. The electrochemical behavior of the electrolyte was studied by cyclic voltammetry. The reduction of Cr(III) species in the solution is a two-step process, from Cr(III) to Cr(II) and from Cr(II) to Cr(0). The potential of each reaction shifts positively with the increase of the electrolyte temperature. The parameters for the electrodeposition of black chromium films were optimized. Homogeneous black chromium films with spectrally selective optical properties were produced by applying a potential of −1.5 V for 1800 s, at an electrolyte temperature of 85°C. The coatings consist of a mixture of chromium oxide/hydroxide and metallic chromium. They are amorphous and present a sub-micrometric granular structure.
Polymer, 2003
X-ray photoelectron spectroscopy (XPS) applied to the study of fluorinated polymer surfaces prese... more X-ray photoelectron spectroscopy (XPS) applied to the study of fluorinated polymer surfaces presents several problems related both to peak assignment and to degradation. In this work, we analyse extensively the question of XPS peak assignments in this kind of surfaces. We conclude that in this kind of surfaces using binding energy differences between fluorine and carbon is better than using absolute binding energies. Also a useful relation between fluorine photoelectron energy vs. polymer composition expressed through the atomic ratio fluorine/carbon (F/C) was found. A protocol for data treatment is proposed and applied to a XPS study of the degradation induced by X-ray on high-density polyethylene surfaces modified by direct fluorination. Results obtained for the degradation, namely the atomic ratio F/C obtained by two different methods, combined with angle resolved X-ray photoelectron spectroscopy (ARXPS) were used to study the fluorine concentration profile in depth, producing self-consistent results. q .pt (A.M. Botelho do Rego).
Macromolecules, 1994
Manuel Rei War' Laboratoire de Spectrochimie Infrarouge et Raman (CN... more Manuel Rei War' Laboratoire de Spectrochimie Infrarouge et Raman (CNRS), 2 rue Henri Dunant, F-94320 Thiais, France ... Ana Maria Botelho do Rego and Jose Lopes da Silva Centro de Quimica-Fsica Molecular da UTL, Instituto Superior T&cnico, Av. Rouisco, Pais, ...
Langmuir, 2010
A method to produce hybrid systems of cellulose ultrathin films containing immobilized silver nan... more A method to produce hybrid systems of cellulose ultrathin films containing immobilized silver nanoparticles (Ag NPs) generated and grown at the surface is presented. Ag NPs were produced via a mild wet chemistry technique on cellulose ultrathin films spin-coated on GaAs substrates and on modified films after grafting of diaminoalkanes activated by N,N 0 -carbonyldiimidazole. Appended amine groups operate as anchoring centers of the silver NPs enabling selective generation and immobilization of Ag NPs. The different phases of the modification process were followed by Fourier transform infrared spectroscopy (FTIRS) in attenuated total reflection in multiple internal reflections (ATR/MIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The generation of NPs is observed even on untreated cellulose surfaces with sizes ranging from 7 to 30 nm but not specifically at the surface. For modified surfaces with diaminoalkanes, higher NP density regions including extensive plates are obtained, which are specifically located at the film extreme surface. The highest NP density is achieved when the NP generation is performed on these modified surfaces in the presence of a carboxylic salt.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2012
ABSTRACT The atomic composition of layer-by-layer (LbL) films of the conductive polyelectrolyte p... more ABSTRACT The atomic composition of layer-by-layer (LbL) films of the conductive polyelectrolyte poly(o-methoxyaniline) (POMA) alternated with the strong polyelectrolyte poly(styrene sulfonate) (PSS) was obtained from X-ray photoelectron spectroscopy (XPS), in order to study the influence of sodium chloride concentration of PSS aqueous solutions on the degree of ionization of polyelectrolytes in the film structure. The results revealed that the degree of ionization for both weak and strong polyelectrolytes decreases with NaCl concentration while the relative amount of counterions/co-ions increases. A larger number of ions, in comparison with the number of polylectrolytes ionic groups, indicate the formation of NaCl nanocrystals in the LbL film. However, results showed that some Cl atoms are being used in an extra chlorination chemical reaction with POMA. The number of water molecules retained in the films decreases with salt at a rate lower than that of the degree of ionization indicating that water molecules are close to salt ions. Moreover, the ratio water molecules per sodium assumes a value of 4 for films prepared without salt, which is the typical hydration number value for NaCl in solution, and decreases linearly with salt concentration pointing out to nanocrystals increase in size with salt concentration.
Carbohydrate Polymers, 2011
Films and fibres of cellulose were functionalised with silver and gold nanoparticles directly gen... more Films and fibres of cellulose were functionalised with silver and gold nanoparticles directly generated on the surface. The present method lays on the cellulose surface pre-modification, replacing some of the hydroxyl groups by amino functions, which selectively act as the seed coordination sites. Nanoparticles can then grow through the interaction with aqueous dilute solutions of AgNO 3 or NaAuCl 4 at room temperature, without adding any reducing agent. The procedure offers the advantage of limiting the generation of nanoparticles to the cellulose surface, leaving the dispersion medium completely exempt of them. The cellulose pre-modification also ensures chemical anchoring of the nanoparticles to the surface, avoiding any risk of particle desorption and extending the lifetime of the resulting hybrid materials. Evidence of the formation of the NPs on the cellulose surfaces was supported by FE-SEM, AFM, XPS and XRD. The method is simple and reproducible.
Carbohydrate Polymers, 2009
Surface grafting of different amino derivatives was carried on under mild condition using N,N 0 -... more Surface grafting of different amino derivatives was carried on under mild condition using N,N 0 -carbonyldiimidazole (CDI) as an activator. The action of a diamine or a triamine on previously activated cellulose fibres proceeds by the reaction of one amine function giving rise to a carbamate derivative. The other terminal amino groups remained available for further reaction. In particular, their activation with CDI generates a reactive carboxamide able to condense with an aliphatic amine through a urea linkage. Evidence for the occurrence of the reaction at each modification step was confirmed by Fourier Transform Infrared Spectroscopy (FTIRS) and X-ray photoelectron spectroscopy (XPS). The contact angle measurement, using water as a probe, was used to explore the evolution of the surface wettability for the different modification sequences. It was shown that the contact angle value is determined by the ratio between polar and methylene groups and by the spatial arrangement of the molecule on the surface.
Experimental Methods in the Physical Sciences, 2001
... 4. PHOTONIC AND ELECTRONIC SPECTROSCOPIES FOR THE CHARACTERIZATION OF ORGANIC SURFACES AND OR... more ... 4. PHOTONIC AND ELECTRONIC SPECTROSCOPIES FOR THE CHARACTERIZATION OF ORGANIC SURFACES AND ORGANIC MOLECULES ADSORBED ON SURFACES Ana MariaBotelho do Rego, Luis Filipe Vieira Ferreira centro de Qufmica-Ffsica Molecular ...
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Papers by Ana Maria Botelho Rego
structural and chemical properties of copper sulphide (CuxS) thin films deposited atroomtemperature
are investigated. CuxS films, 70nm thick, are deposited on glass substrates by vacuum thermal evaporation
from a Cu2S:S (50:50 wt.%) sulphur rich powder mixture. The as-deposited highly conductive
crystalline CuS (covellite) films show high carrier concentration (∼1022 cm−3), low electrical resistivity
(∼10−4 cm) and inconclusive p-type conduction. After the mild post-annealing, these films display
increasing values of resistivity (∼10−3 to ∼10−2 cm) with annealing time and exhibit conclusive p-type
conduction. An increase of copper content in CuxS phases towards the semiconductive Cu2S (chalcocite)
compound with annealing time is reported, due to re-evaporation of sulphur from the films. However,
the latter stoichiometry was not obtained, which indicates the presence of vacancies in the Cu lattice.
In the most resistive films a Cu2O phase is also observed, diminishing the amount of available copper
to combine with sulphur, and therefore the highest values of optical transmittance are reached (65%).
The appearance on the surface of amorphous sulphates with annealing time increase is also detected as a
consequence of sulphur oxidation and replacement of sulphur with oxygen. All annealed films are copper
deficient in regards to the stoichiometric Cu2S and exhibit stable p-type conductivity.
technique used is the radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium (In) in the presence
of oxygen. The influence of oxygen partial pressure on the properties of these films is presented. The oxygen partial pressure varied
between 3 · 102 and 1.3 · 101 Pa. Undoped InOx films, 100 nm thick, deposited at the oxygen partial pressure of 6 · 102 Pa show a
conductive behaviour, exhibit an average visible transmittance of 81%, a band gap around 2.7 eV and an electrical conductivity of about
1100 (X cm)1. For oxygen pressures greater than 6 · 102 Pa, semiconductive films are obtained, maintaining the visible transmittance.
Films deposited at lower pressures are conductive but dark. From XPS data, films deposited at an oxygen partial pressure of 6 · 102 Pa
show the highest amount of oxygen in the film surface and the lowest ratio between oxygen in the oxide crystalline and amorphous phases.
structural and chemical properties of copper sulphide (CuxS) thin films deposited atroomtemperature
are investigated. CuxS films, 70nm thick, are deposited on glass substrates by vacuum thermal evaporation
from a Cu2S:S (50:50 wt.%) sulphur rich powder mixture. The as-deposited highly conductive
crystalline CuS (covellite) films show high carrier concentration (∼1022 cm−3), low electrical resistivity
(∼10−4 cm) and inconclusive p-type conduction. After the mild post-annealing, these films display
increasing values of resistivity (∼10−3 to ∼10−2 cm) with annealing time and exhibit conclusive p-type
conduction. An increase of copper content in CuxS phases towards the semiconductive Cu2S (chalcocite)
compound with annealing time is reported, due to re-evaporation of sulphur from the films. However,
the latter stoichiometry was not obtained, which indicates the presence of vacancies in the Cu lattice.
In the most resistive films a Cu2O phase is also observed, diminishing the amount of available copper
to combine with sulphur, and therefore the highest values of optical transmittance are reached (65%).
The appearance on the surface of amorphous sulphates with annealing time increase is also detected as a
consequence of sulphur oxidation and replacement of sulphur with oxygen. All annealed films are copper
deficient in regards to the stoichiometric Cu2S and exhibit stable p-type conductivity.
technique used is the radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium (In) in the presence
of oxygen. The influence of oxygen partial pressure on the properties of these films is presented. The oxygen partial pressure varied
between 3 · 102 and 1.3 · 101 Pa. Undoped InOx films, 100 nm thick, deposited at the oxygen partial pressure of 6 · 102 Pa show a
conductive behaviour, exhibit an average visible transmittance of 81%, a band gap around 2.7 eV and an electrical conductivity of about
1100 (X cm)1. For oxygen pressures greater than 6 · 102 Pa, semiconductive films are obtained, maintaining the visible transmittance.
Films deposited at lower pressures are conductive but dark. From XPS data, films deposited at an oxygen partial pressure of 6 · 102 Pa
show the highest amount of oxygen in the film surface and the lowest ratio between oxygen in the oxide crystalline and amorphous phases.