Jaime Colchero

University of Murcia | UM · Department of Physics

Nanoparticles (NPs) of conjugated polymers in intimate contact with sheets of graphene oxide (GO) constitute a promising class of water-dispersible nanohybrid materials of increased interest for the design of sustainable and improved optoelectronic thin-film devices, revealing properties exclusively pre-established upon their liquid-phase synthesis...

Conductive polymers have fundamental relevance as well as novel technological applications in the organic optoelectronics field. Their photophysical and transport properties strongly depend on the molecular arrangement, and nanoscale characterization is needed to fully understand the optoelectronic processes taking place in organic devices. In this...

Hace décadas que expertos en ciencia de materiales de todo el mundo tratan de dar respuesta a un bellísimo fenómeno de la naturaleza: el modo en que las esféricas gotitas de rocío se adhieren a los pétalos de la flor más popular del mundo, y no se caen, aunque pongamos la flor boca abajo. Este fenómeno recibe el nombre de efecto pétalo de rosa. Enc...

Graphene oxide (GO) is widely used as a component in thin film optoelectronic device structures for practical reasons because its electronic and optical properties can be controlled. Progress critically depends on elucidating the nanoscale electronic structure of GO. However, direct experimental access is challenging because of its disordered and n...

Rose petals can involve high water contact angles together with drop adhesion which are antagonistic wetting properties. Petal surfaces have a cuticle, a layer that is generally considered a continuous, hydrophobic lipid coating. The peculiar properties of rose petals are not fully understood and have only been associated with high surface roughnes...

We present a study of the effect of gold nanoparticles (Au NPs) on TiO2 on charge generation and trapping during illumination with photons of energy larger than the substrate band gap. We used a novel characterization technique, photoassisted Kelvin probe force microscopy, to study the process at the single Au NP level. We found that the photoinduc...

Two-dimensional materials, in particular graphene, exhibit a low friction coefficient and good wear properties. However, the tribological properties of these materials strongly depend on faint differences at the atomic level, and the coexistence of different type of atomic defects in studied samples up to date led to experimental results difficult...

Computational electrodynamics modelling plays an important role in understanding and designing new photonic devices. The results offered by these simulations are usually close-range field distributions or angular power emission plots. We describe a procedure to compute the optical microscopy image from simulated far-field scattering data using thre...

The performance of organic thin film optoelectronic devices strongly relies on the nanoscale aggregate structure of the employed conjugated polymer. Their impact on electronic interface interactions with adjacent layers of graphene, widely reported to improve the device characteristics, yet remains an open issue, which needs to be addressed by an a...

Under ambient conditions, surfaces are rapidly modified and contaminated by absorbance of molecules and a variety of nanoparticles that drastically change their chemical and physical properties. The atomic force microscope tip–sample system can be considered a model system for investigating a variety of nanoscale phenomena. In the present work we u...

Sequence stretches localized in the 5′-UTR or ORF1 of carmovirus genomes with complementarity to their 3′-CITEs.

Nucleotide sequence conservation of the 5′-end and 3′-CITE of MNSV genomes. (A) Sequence alignment of the 5′-end sequences of MNSV isolates using ClustalW. (B). Sequence alignment of the 3′-CITE sequences of MNSV isolates using ClustalW. The GenBank accession numbers of MNSV sequences included in the alignments are Mα5 (MNSV-Mα5)-AY122286, Ma71-EU5...

Prediction of RNA interactions between the 5′-end and 3′-UTR of MNSV genomes. Bioinformatic prediction of possible functional interactions between the ends of MNSV genomes (Transat) (Wiebe and Meyer, 2010). Aligned sequences of 13 MNSV genomes (GenBank accession numbers in Supplementary Figure S1) including the first 150 nt and the 3′-UTR sequence,...

Viral 5′-end secondary structure models. Schematic representation of the secondary structure prediction obtained with Mfold of the 5′-ends (between 180 and 240 nt) of the viral genomes (A) with I-shaped 3′-CITEs; (B) of the other carmoviruses apart from MNSV with proposed or identified 3′-CITEs; (C) of the tombusvirus CIRV. The arrows indicate the...

Importance of sequence complementarity for translation controlled by Ma5TE. In vivo cap-independent translation efficiency obtained in melon protoplasts of constructs with only the Ma5TE (45 nt) instead of the 3′-UTR flanking the 3′-end of the luciferase gene. A structure-stabilizing G-C clamp (+K) as described by Miras et al. (2017b) was added to...

Prediction of RNA interactions between the 5′-end and 3′-UTR of CarMV genomes. Bioinformatic prediction of possible functional interactions between the ends of MNSV genomes (Transat). Aligned sequences of all known CarMV genomes available in GenBank including the first 150 nt and the 3′-UTR sequence, separated by 10 adenosines. Color of arched line...

Secondary structure prediction of the 5′-end of the MNSV genome. Prediction of the secondary structure using RNAalifold generated by structural alignment of the (A) 5′-UTRs and (B) 5′-ends (150 nt) of the MNSV genome sequences available in GenBank. Structure drawing with conservation annotation. Positions of nucleotide variations in the 5′-end sequ...

Sequence stretches of the 5′-UTR or ORF1 with complementarity to I-shaped 3′-CITEs.

In eukaryotes, the formation of a 5′-cap and 3′-poly(A) dependent protein–protein bridge is required for translation of its mRNAs. In contrast, several plant virus RNA genomes lack both of these mRNA features, but instead have a 3′-CITE (for cap-independent translation enhancer), a RNA element present in their 3′-untranslated region that recruits t...

Atomic force microscopy is based on tip sample interaction, which is determined by the properties of tip and sample. Unfortunately, in particular in ambient conditions the tip as well as the sample are contaminated, and it is not clear how this contamination may affect data in Atomic Force Microscopy (AFM) applications. In the present work we propo...

We have used the Scanning Kelvin probe microscopy technique to monitor the charging process of highly resistive granular thin films. The sample is connected to two leads and is separated by an insulator layer from a gate electrode. When a gate voltage is applied, charges enter from the leads and rearrange across the sample. We find very slow proces...

The present work analyses how the tip-sample interaction signals critically determine the operation of an Atomic Force Microscope (AFM) set-up immersed in liquid. On heterogeneous samples, the conservative tip-sample interaction may vary significantly from point to point - in particular from attractive to repulsive - rendering correct feedback very...

In this work, we propose an intuitive and easily implementable approach to model and interpret scanning Kelvin probe microscopy images of insulating samples with localized charges. The method, based on the image charges method, has been validated by a systematic comparison of its predictions with experimental measurements performed on charge domain...

Here we present the Mendeleev-Meyer Force Project which aims at tabulating all materials and substances in a fashion similar to the periodic table. The goal is to group and tabulate substances using nanoscale force footprints rather than atomic number or electronic configuration as in the periodic table. The process is divided into: (1) acquiring n...

Kelvin probe force microscopy in darkness and under illumination is reported in order to provide nanoscale-resolved surface photovoltage maps of hybrid materials. In particular, nanoscale charge injection and charge recombination mechanisms occurring in ZnO polycrystalline surfaces functionalized with Protoporphyrin IX (H2PPIX) are analyzed. Local...

The surface potential of conducting polymers has been studied with scanning Kelvin probe microscopy. The results show that this technique can become an excellent tool to really ‘see’ interesting surface charge interaction effects at the nanoscale. The electron glass model, which assumes that charges are localized by the disorder and that interactio...

In this work we demonstrate the capabilities of atomic force microscopies (AFMs) for the non-destructive determination of the polarity of GaN nanowires (NWs). Three complementary AFMs are analyzed here: Kelvin probe force microscopy (KPFM), light-assisted KPFM, and piezo-force microscopy (PFM). These techniques allow to assess the polarity of indiv...

The growth selectivity and structural quality of GaN nanowires obtained by plasma-assisted molecular beam epitaxy on pre-patterned GaN(0001) templates are investigated by means of non-destructive techniques. Optimum control over the nanowire arrangement and size requires a pitch between the mask apertures below twice the diffusion length of Ga atom...

We experimentally investigate the influence of AlN buffer growth on the nucleation and the polarity of a self-organized assembly of GaN nanowires (NWs) grown on Si. Two complementary growth mechanisms for AlN buffer deposited on Si are demonstrated. Both emphasize the aggregation of Si on the AlN surface and the growth of large cubic crystallites,...

Summary: Scanning Probe Microscopy (SPM) is already a relevant tool in biological research at the nanoscale. We present “Flatten plus”, a recent and helpful implementation in the well-known WSxM free software package. “Flatten plus” allows reducing low frequency noise in SPM images in a semi-automated way preventing the appearance of typical artifa...

A systematic study on the thin film morphology of heteroacenic derivatives such as indolo[2,3-a]carbazole and 11,12-dioctylindolo[2,3-a]carbazole has been carried out using scanning force microscopy and optical microscopy techniques. The investigation has comprised the preparation of a series of thin films by combining different solvents (dimethylf...

In this work the weathering phenomenon of building stones has been studied on the nanoscale. Red Quipar limestone samples have been exposed to ultraviolet (UV) radiation and acid attack and have been analysed by Scanning Force Microscopy (SFM) as well as optical measurements. The morphology of the samples along each step of the process has been cha...

In this work, we report a Kelvin probe microscopy investigation on the structural and electronic properties of gold and aluminum thin films evaporated on poly(3-octyl-thiophene) films. Our experimental setup allows us to perform scanning force microscopy (SFM) studies of the same area even if the sample is taken out of the SFM system for different...

The electro-optical properties of Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) thin films have been studied while the sample is illuminated with blue light. By combining Kelvin probe microscopy with classical optical techniques it has been possible to monitor the evolution of the nanoscale contact potential, the surface photo...

Scanning force microscopy and near-edge X-ray absorption spectroscopy are used to study the attachment of Protoporphyrin IX dye molecules to the low-index single-crystal faces of ZnO, namely, the polar (0001̅) face and the nonpolar (101̅0) face. We found that surface etching depends on the crystal face for various dye immobilization procedures: whe...

The changes in morphology and electronic properties of Poly-3-octyl-thiophene (P3OT) thin films produced by UV/ozone exposure have been studied using Scanning Force Microscopy techniques. The layered structures associated to crystalline P3OT domains on the polymer film show a better resilience to the degradation than the amorphous polymer backgroun...

A method to precisely calibrate the oscillation amplitude in dynamic scanning force microscopy is described. It is shown that the typical electronics used to process the dynamic motion of the cantilever can be adjusted to transfer the thermal noise of the cantilever motion from its resonance frequency to a much lower frequency within the typical ba...

In this work we describe two simple and compact submicrometer-precision sample holders that are easily integrated into a Scanning Force Microscopy (SFM) system. The designs are based on a traditional kinematic mounting or on self-adjustment of the sample holder and the upper piece of the piezoelectric scanner. With these sample holders the sample p...

Scanning Probe Microscopy allows for extreme resolution down to the atomic scale. Unfortunately, total scanning range is rather limited, therefore finding a specific position on the sample is tedious. This is an important limitation of many Scanning Probe Microscopes, in particular when the sample has to be removed for some kind of treatment and th...

The wavelength dependence of the nanoscale light induced processes taking place in MEH-PPV/TCBM blended thin film samples has been studied by means of Kelvin probe microscopy implemented with controlled external sample illumination. First, both materials have been characterized individually and then these results have been used to explain the behav...

In this study, we show that the correct determination of surface morphology using scanning force microscopy (SFM) imaging and power spectral density (PSD) analysis of the surface roughness is an extremely demanding task that is easily affected by experimental parameters such as scan speed and feedback parameters. We present examples were the measur...

A study of the molecular structure of regio-regular bulk poly-3-octyl-thiophene (P3OT) and poly-3-hexyl-thiophene (P3HT) and the phase transitions during heating and cooling scans in a temperature range of –158–773 °C has been performed by means of calorimetry of bulk samples and grazing incidence X-ray diffraction from synchrotron radiation. Addit...

This paper describes a new strategy to obtain PEDOT/Au-nanorods nanocomposites with different PEDOT: Au ratio. A polymeric ionic liquid (PIL) was used as stabilizer during the chemical synthesis of PEDOT dispersions. PEDOT/Au-nanorods dispersions in organic media were obtained. Electrochemical characterization of PEDOT/Au-nanorods nanocomposites re...

Kelvin probe microscopy implemented with controlled sample illumination is used to study nanoscale surface photovoltage effects. With this objective a two trace method, where each scanning line is measured with and without external illumination, is proposed. This methodology allows a direct comparison of the contact potential images acquired in dar...

In this work variable temperature scanning force microscopy techniques have been used to study poly(3-octylthiophene) (P3OT) thin film samples. Topography images in combination with scanning force spectroscopy have been applied to characterize the morphology and mechanical properties of the P3OT surface. It has been found that at room temperature l...

The modification of the nanoscale morphology and electronic behavior as well as the mesoscopic optical properties of thin films of poly-3-octyl-thiophene (P3OT) has been studied as these films are irradiated by ultraviolet light (UV). Films of about 100nm thickness were prepared by spin-casting a P3OT solution in toluene on glass substrates. The sa...

The use of conducting polymers in optoelectronic devices is subject to the understanding of the electro-optical processes that take place at the nanoscale. One of the photo-induced processes that limit their application is the photodegradation, which reduces the device working life. In this work the photodegradation of poly(3-octylthiophene) thin f...

The modification of the conductivity as well as the nanoscale morphology and electrostatic properties of poly-3-octyl-thiophene (P3OT) thin films have been studied as these films are irradiated by ultraviolet light (UV). Films of about 100 nm thickness were prepared by spin-coating a P3OT solution in toluene on glass substrates. The samples were ch...

Thermal fluctuation of the cantilever position sets a fundamental limit for the precision of any scanning force microscope. In the present work we analyze how these fluctuations limit the determination of the resonance frequency of the tip-sample system. The basic principles of frequency detection in dynamic scanning force microscopy are revised an...

Thermal fluctuation of the cantilever position sets a fundamental limit for the precision of any Scanning Force Microscope. In the present work we analyse how these fluctuations limit the determination of the resonance frequency of the tip-sample system. The basic principles of frequency detection in Dynamic Scanning Force Microscopy are revised an...

The present work proves that when non-contact Dynamic Scanning Force Microscopy (DSFM) is performed in ambient conditions wrong height measurements of heterogeneous samples can be obtained. In some extreme cases even contrast inversion can be observed. Alkanethiol islands on Au (111) have been used as model system, where contrast inversion is obser...

ZnO thin films grown by metal–organic vapor phase epitaxy along the nonpolar direction and exhibiting semipolar facets have been chemically etched with HCl. In order to get an insight into the influence of the ZnO wurtzite structure in the chemical reactivity of the material, Kelvin probe microscopy and convergent beam electron diffraction have bee...

Frequency modulation dynamic scanning force microscopy has been implemented in ambient conditions using low oscillation amplitudes (<1 nm) to simultaneously record not only topographic but also additional channels of information, in particular contact potential images. The performance of this mode as compared to the conventional amplitude modulatio...

The morphology and mechanical properties of poly-(3-octylthiophene) P3OT films thin has been studied by scanning force microscopy techniques. On these films we find self-assembled layered structures that appear regardless of the preparation conditions, that is, spin-coating or drop-casting, of the solvent concentration or of the type of substrate....

In this work the electrostatic properties of poly(3-octylthiophene) thin films have been studied on a nanometer scale by means of electrostatic force microscopy and Kelvin probe microscopy (KPM). The KPM images reveal that different surface contact potential domains coexist on the polymer surface. This result, together with additional capacitance m...

In this paper, the electrical transport and mechanical properties of Pt/ZnO Schottky nanocontacts have been studied simultaneously during the formation and rupture of the nanocontacts. By combining multidimensional conducting scanning force spectroscopy with appropriated data processing, the physical relevant parameters (the ideality factor, the Sc...

In this paper scanning force microscopy is combined with simple but powerful data processing to determine quantitatively, on a sub-micrometer scale, the orientation of surface facets present on crystalline materials. A high-quality scanning force topography image is used to determine an angular histogram of the surface normal at each image point. I...

We have studied blends of poly-(3-octylthiophene) (P3OT) and graphitic nanoparticles by macroscopic transport measurements, Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Scanning Force Microscopy (SFM) techniques. Their morphology as well as their mechanical and electrical properties have been characterized on a nanometer scal...

In this work we briefly describe the most relevant features of WSXM, a freeware scanning probe microscopy software based on MS-Windows. The article is structured in three different sections: The introduction is a perspective on the importance of software on scanning probe microscopy. The second section is devoted to describe the general structure o...

Scanning force microscopy related techniques are applied to study surface nanoscale properties. We show that nanogoniometry can be combined with local electrostatic measurements – electrostatic force microscopy and Kelvin probe microscopy – to identify surface planes families and to study their local electrical properties. The scanning force micros...

Quantitative characterization of tip–sample interaction in scanning force microscopy is fundamental for optimum image acquisition as well as data interpretation. In this work we discuss how to characterize the electrostatic and van der Waals contribution to tip–sample interaction in non-contact scanning force microscopy precisely. The spectroscopic...

Mixtures of poly(3-octylthiophene) (P3OT) with graphite nanoparticles have been investigated by scanning force microscopy (SFM) techniques. The morphology as well as the mechanical and electrical properties of the blends has been characterized at the nanoscale level as a function of the carbon nanoparticle content in the blend. An increase in the c...

ZnO thin films have been grown along the nonpolar [10 1 0] direction by metal organic vapor phase epitaxy. The ZnO (10 1 0) surface develops well defined facets. The orientation of the topographic normals reveals that the inclination angle of the facets increases as thicker films are considered, attaining a maximum value of about 28.4°. This angle...

The surface electrical properties of ZnO thin films grown along the nonpolar [1120] direction have been investigated by Kelvin probe microscopy on a nanometer scale. Two different charge domains, with a 75 meV work function difference, coexist within the ZnO surface, which is covered by rhombohedral pyramids whose sidewalls are shown to be {1011}-t...

Locally resolved electrostatic force spectroscopy is combined with Kelvin force microscopy to compare the results obtained using either the force or the frequency as signal source for tip-sample interaction. A two-component locally heterogeneous sample-islands of octadecanethiol molecules self-assembled on Au(111)-is used as a nanometer scale model...