Time filter

Source Type

Osorio H.M.,University of Zaragoza | Osorio H.M.,Laboratorio Of Microscopias Avanzadas Lma | Martin S.,University of Zaragoza | Lopez M.C.,University of Zaragoza | And 7 more authors.
Beilstein Journal of Nanotechnology | Year: 2015

Monolayer Langmuir-Blodgett (LB) films of 1,4-bis(pyridin-4-ylethynyl)benzene (1) together with the "STM touch-to-contact" method have been used to study the nature of metal-monolayer-metal junctions in which the pyridyl group provides the contact at both molecule-surface interfaces. Surface pressure vs area per molecule isotherms and Brewster angle microscopy images indicate that 1 forms true monolayers at the air-water interface. LB films of 1 were fabricated by deposition of the Langmuir films onto solid supports resulting in monolayers with surface coverage of 0.98 × 10-9 mol·cm-2. The morphology of the LB films that incorporate compound 1 was studied using atomic force microscopy (AFM). AFM images indicate the formation of homogeneous, monomolecular films at a surface pressure of transference of 16 mN·m-1. The UV-vis spectra of the Langmuir and LB films reveal that 1 forms two dimensional J-aggregates. Scanning tunneling microscopy (STM), in particular the "STM touch-to-contact" method, was used to determine the electrical properties of LB films of 1. From these STM studies symmetrical I-V curves were obtained. A junction conductance of 5.17 × 10-5 G0 results from the analysis of the pseudolinear (ohmic) region of the I-V curves. This value is higher than that of the conductance values of LB films of phenylene-ethynylene derivatives contacted by amines, thiols, carboxylate, trimethylsilylethynyl or acetylide groups. In addition, the single molecule I-V curve of 1 determined using the I(s) method is in good agreement with the I-V curve obtained for the LB film, and both curves fit well with the Simmons model. Together, these results not only indicate that the mechanism of transport through these metal-molecule-metal junctions is non-resonant tunneling, but that lateral interactions between molecules within the LB film do not strongly influence the molecule conductance. The results presented here complement earlier studies of single molecule conductance of 1 using STM-BJ methods, and support the growing evidence that the pyridyl group is an efficient and effective anchoring group in sandwiched metal-monolayer-metal junctions prepared under a number of different conditions. © 2015 Osorio et al; licensee Beilstein-Institut.


Marques-Gonzalez S.,Durham University | Yufit D.S.,Durham University | Howard J.A.K.,Durham University | Martin S.,University of Zaragoza | And 8 more authors.
Dalton Transactions | Year: 2013

Conductance across a metal|molecule|metal junction is strongly influenced by the molecule-substrate contacts, and for a given molecular structure, multiple conductance values are frequently observed and ascribed to distinct binding modes of the contact at each of the molecular termini. Conjugated molecules containing a trimethylsilylethynyl terminus, -C≡CSiMe 3 give exclusively a single conductance value in I(s) measurements on gold substrates, the value of which is similar to that observed for the same molecular backbone with thiol and amine based contacting groups when bound to under-coordinated surface sites. © 2013 The Royal Society of Chemistry.


Mazario E.,Autonomous University of Madrid | Sanchez-Marcos J.,Autonomous University of Madrid | Menendez N.,Autonomous University of Madrid | Canete M.,Autonomous University of Madrid | And 6 more authors.
Journal of Physical Chemistry C | Year: 2015

Superparamagnetic iron oxide-based nanoparticles (SPIONS) have attracted an enormous amount of attention for their potential use in biomedical applications, due to their good biocompatibility and low toxicity. The current study considers citric acid-conjugated manganese ferrite and its synergy to be used in MRI and in hyperthermia treatment, thus showing theragnostic applications. High colloidal stability was obtained with this functionalization. SPIONS with superparamagnetic behavior of crystal sizes of approximately 20 nm were obtained via an electrochemical synthesis method. One of the highest specific absorption rate (SAR) values was achieved in this work (1661 W g-1), under a magnetic field of 30 mT at 717 kHz frequency, compared with other magnetic ferrites in the literature. These nanoparticles dissipate heat through Néel relaxation and, together with the high SAR value obtained, indicate an excellent material for hyperthermia treatment of cancer. In addition, these nanoparticles exhibit transverse relaxivity behavior, with an r2 value of 394 mM-1 s-1, i.e., at least two times higher than the value of a commercial magnetic contrast agent based on iron oxides. Finally, no toxicity effects of these nanoparticles are evidenced; as a result, these nanoparticles are appropriate for in vivo application. © 2015 American Chemical Society.


Ballesteros L.M.,University of Zaragoza | Ballesteros L.M.,Industrial University of Santander | Martin S.,University of Zaragoza | Martin S.,Laboratorio Of Microscopias Avanzadas Lma | And 8 more authors.
Journal of Physical Chemistry C | Year: 2015

Monomolecular films of an oligo(phenylene)ethynylene, OPE, derivative [2-isocyano-1,3-dimethylbenzene][4-(4′-aminophenylethynyl)phenylethynyl]gold, 1, containing a gold atom in the molecule backbone have been prepared by the Langmuir-Blodgett (LB) method in order to study how the electrical properties can be modulated in monolayers of OPEs by incorporation of a gold center in their structures. UV-vis reflection spectra of Langmuir monolayers of 1 at the air-water interface reveal strong aurophilic interactions between neighboring molecules that increase upon compression. Monolayer Langmuir-Blodgett (LB) films were readily fabricated by the transfer of Langmuir films of 1 onto solid substrates. Quartz crystal microbalance (QCM) experiments conclusively demonstrate formation of monolayer LB films with a high surface coverage. The morphology of these films was analyzed by atomic force microscopy (AFM), revealing formation of homogeneous layers with an optimum surface pressure of transference of 6 mN·m-1. Film homogeneity and integrity was confirmed by cyclic voltammetry, with efficient blocking of gold electrodes by these well-formed monolayers of 1. The electrical properties of LB films of 1 were investigated by scanning tunneling microscopy (STM) using a tip-to-contact method. Characteristic shape for a tunneling junction (Simmons type behavior) I-V curves were observed, with analysis of the pseudolinear (ohmic) region giving a conductance value G = 3.9 × 10-5 G0, which is relatively high for an OPE derivative and may indicate a beneficial role of metal atom incorporation within the wire-like system. © 2014 American Chemical Society.


Ballesteros L.M.,University of Zaragoza | Martin S.,University of Zaragoza | Martin S.,Laboratorio Of Microscopias Avanzadas Lma | Momblona C.,University of Zaragoza | And 7 more authors.
Journal of Physical Chemistry C | Year: 2012

Langmuir and Langmuir-Blodgett films have been fabricated from an acetylene-terminated phenylene-ethynylene oligomer, namely 4-((4-((4- ethynylphenyl)ethynyl)phenyl)ethynyl)benzoic acid (HOPEA). Characterization of the Langmuir film by surface pressure vs area per molecule isotherms and Brewster angle microscopy reveals the formation of a high quality monolayer at the air-water interface. One layer Langmuir-Blodgett (LB) films were readily fabricated by the transfer of HOPEA Langmuir films onto solid substrates by the withdrawal of the substrate. The deposition mode was Z-type. Quartz crystal microbalance (QCM) experiments confirm the formation of directionally oriented, monolayer LB films, in which the HOPEA molecules are linked to the gold substrate by attachment through the acid group. The morphology of these films was analyzed by atomic force microscopy (AFM), which revealed an optimum transference surface pressure of 18 mN m -1 for the formation of homogeneous films. Cyclic voltammetry also showed a significant blockage of gold electrodes covered by HOPEA monolayers. Electrical properties of HOPEA monolayers sandwiched between a bottom gold electrode and a gold STM (scanning tunneling microscope) tip have been recorded, revealing that the acetylene group is an efficient linker for electron transport. In addition, the STM experiments indicate a nonresonant tunneling mechanism of charge transport through these metal-molecule-metal junctions. © 2012 American Chemical Society.


Rivero M.,Autonomous University of Madrid | Del Campo A.,CSIC - Institute of Ceramics and Glass | Mayoral A.,Laboratorio Of Microscopias Avanzadas Lma | Mayoral A.,University of Zaragoza | And 3 more authors.
RSC Advances | Year: 2016

A series of zinc ferrite nanoparticles were synthesized following a single-step electrochemical method in aqueous medium. This strategy allowed the control of both the size and chemical composition of the nanoparticles in an easy and reproducible manner by simply varying the intensity of the applied current. The obtained nanoparticles were morphologically and structurally characterized as a function of the particle size and the Zn content in the sample by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma emission spectroscopy (ICP) and Raman microscopy. The formation of ZnxFe(3-x)O4 (x = 0.18-0.93) ferrite nanoparticles with crystal sizes in the range of 9 to 18 nm and with a homogeneous distribution of the Zn2+ cation in the crystalline structure was observed. However, following a thermal treatment, a migration of zinc cations was detected that led to the formation of two different crystalline phases, stoichiometric zinc ferrite and hematite. Raman microscopy revealed the formation of segregated micro-domains enriched within these crystalline phases. The study of the magnetic properties of the electro-synthesized ferrite nanoparticles with a homogeneous incorporation of Zn in the structure shows that the saturation magnetization and the coercively values are highly dependent on the chemical composition and crystal size. © The Royal Society of Chemistry 2016.


Ballesteros L.M.,University of Zaragoza | Martin S.,University of Zaragoza | Martin S.,Laboratorio Of Microscopias Avanzadas Lma | Cortes J.,University of Zaragoza | And 6 more authors.
Chemistry - A European Journal | Year: 2013

The preparation, characterization and electrical properties of Langmuir-Blodgett (LB) films composed of a symmetrically substituted oligomeric phenylene ethynylene derivative, namely, 4,4′-[1,4-phenylenebis(ethyne-2, 1-diyl)]dibenzoic acid (OPE2A), are described. Analysis of the surface pressure versus area per molecule isotherms and Brewster angle microscopy reveal that good-quality Langmuir (L) films can be formed both on pure water and a basic subphase. Monolayer L films were transferred onto solid substrates with a transfer ratio of unity to obtain LB films. Both L and LB films prepared on or from a pure water subphase show a red shift in the UV/Vis spectrum of about 14 nm, in contrast to L and LB films prepared from a basic subphase, which show a hypsochromic shift of 15 nm. This result, together with X-ray photoelectron spectroscopic and quartz crystal microbalance experiments, conclusively demonstrate formation of one-layer LB films in which OPE2A molecules are chemisorbed onto gold substrates and consequently -COO-Au junctions are formed. In LB films prepared on a basic subphase the other terminal acid group is also deprotonated and associates with an Na+ counterion. In contrast, LB films prepared from a pure water subphase preserve the protonated acid group, and lateral H-bonds with neighbouring molecules give rise to a supramolecular structure. STM-based conductance studies revealed that films prepared from a basic subphase are more conductive than the analogous films prepared from pure water, and the electrical conductance of the deprotonated films also coincides more closely with single-molecule conductance measurements. This result was interpreted not only in terms of better electron transmission in -COO-Au molecular junctions, but also in terms of the presence of lateral H-bonds in the films formed from pure water, which lead to reduced conductance of the molecular junctions. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Loading Laboratorio Of Microscopias Avanzadas Lma collaborators
Loading Laboratorio Of Microscopias Avanzadas Lma collaborators