Papers by José L. Costa-Krämer
Nanowires, 1997
When a scanning tunnelling microscope (STM) tip is driven into a metallic sample surface a nanome... more When a scanning tunnelling microscope (STM) tip is driven into a metallic sample surface a nanometer sized wire (nanowire) is formed during the subsequent retraction. The electrical conduction measured during this retraction process shows signs of quantized conductance in units of 2e 2 h. Due to the inherent non-reproducibility of the measured conductance curves a standard technique is to build histograms from a large number of curves. Such histograms, built with conductance experiments on gold nanowires at room temperature, show 3-4 peaks at integer values of 2e 2 h, while in a low temperature mechanically controlled break junction study only the first peak is reported. In this work, histograms made up of thousands of consecutive curves at 4K are presented, showing up to 5 conductance peaks. An explanation for this discrepancy could be a higher nanowire temperature resulting from the higher retraction speed used in our measurements. However, a simple estimation, where we used macroscopic heat transport theory, resulted in a very low temperature increase, less than 1 µK, ruling out this possibility. Thus, no significant difference with previous room temperature studies were observed, pointing to a conductance quantization that is the same at room and low temperature.
Quantized Conductance in Bismuth Nanowires at 4K
Nanowires, 1997
... Rev. B, 55,(7); Costa-Kramer JL, Garcia N. and Olin H., Conductance Quantization Histograms o... more ... Rev. B, 55,(7); Costa-Kramer JL, Garcia N. and Olin H., Conductance Quantization Histograms of Gold Nanowires at 4K, Phys. Rev. ... Rev. Lett. 60, 848; Wharam D. A., Pepper M., Ahmed H.,Frost JEF, Hasko DG, Peacok D. C, Ritchie DA, and Jones G AC (1988) J. Phys. ...
Low Voltage Nonlinear Conductance of Gold Nanowires: Room Temperature Coulomb Blockade Effect?
Nanoscale Science and Technology, 1998
ABSTRACT. We present and analyze theoretically measurements of the room temperature IV characteri... more ABSTRACT. We present and analyze theoretically measurements of the room temperature IV characteristics of gold nanowires whose zero current conductance is quantized in units of 2e2/h. A faster than linear increase of current was observed at low voltages beginning from Vc~ 0.1 V. We analyze the nonlinear behavior using a Luttinger liquid approach and show that it can be understood in terms of a dynamic Coulomb blockade effect.
Simple Model for Force Fluctuations in Nanowires
Nanoscale Science and Technology, 1998
Abstract. When two metal electrodes are separated, a nanometer sized wire (nanowire) is formed ju... more Abstract. When two metal electrodes are separated, a nanometer sized wire (nanowire) is formed just before the contact breaks. The electrical conduction measured during this retraction process shows signs of quantized conductance in units of GO= 2e2/h. Recent experiments show that the force acting on the wire during separation fluctuate, which is interpreted as due to atomic rearrangements. In this report we use a simple free electron model and show that the electronic contribution to the force fluctuations are comparable to ...
Conductance Quantization in Metallic Nanocontacts: Experimental Results and Novel Theoretical Aspects
Atomic and Molecular Wires, 1997
ABSTRACT In this paper we present results showing the main features of the conductance quantizati... more ABSTRACT In this paper we present results showing the main features of the conductance quantization in metallic contacts under uncontrolled and controlled conditions. We present histograms formed by thousands of single STM measurements, revealing the universality and reproducibility of this phenomenon. The analysis of such histograms reveals some interesting features, explained by tight-binding calculation in terms of the presence of disorder within the nanowire. We have determined the possible chaotic distribution of the electronic states within the nanocontact by studying the distribution of elapsed times in a given conductance level. We also present new results showing the existence of light emission from the nanocontact.
Conductance Quantization in Metallic Nanowires
Mesoscopic Electron Transport, 1997
ABSTRACT Recent investigations carried out in our group concerning the conductance quantization o... more ABSTRACT Recent investigations carried out in our group concerning the conductance quantization of metallic nanowires are reviewed. These include: i) The formation of metallic nanowires between macroscopic electrodes, including liquid metals, demonstrating that at the last stages of the contact breakage, a nanowire exists, independently of the initial contact size. ii) A statistical study of the conductance using thousands of consecutive contact breakage experiments, both at room and at liquid helium temperatures. These histograms, totally reproducible, present clear peaks close to integer values of the quantum of conductance G(0)=2e(2)/h for diamagnetic metals like Gold, Silver, Copper, Sodium, Platinum.... Ferromagnetic metals, Iron, Cobalt and Nickel, exhibit a flat conductance histogram. This effect is attributed to the combination of the lifting of the spin degeneracy in the ferromagnetic nanowires and the effect of geometry and disorder. The measured conductance histograms are basically independent of the temperature, iii) A discussion of the position and width of the observed peaks. Just geometrical effects can not explain the large conductance peak shifts observed experimentally, and disorder, behaving as a residual resistance, has to be invoked to explain them. iv) First realization of conductance quantization in Bi at 4K. Conductance plateaus lasting 20-100 nm electrode separation are presented; the histogram displays also clear peaks. v) A statistical study of the conductance plateau duration, demonstrating a broad distribution of this duration, 0.05-0.4 nm, with an average value that decreases as conductance increases. vi) A discussion of force and energy quantization within a resonant energy model of two reservoirs connected by a ballistic channel. vii) Experiments performed in ultra high vacuum, where we manage to stabilize the nanowires for hours and study switching and current voltage characteristics for different quantum conductance channels with remarkable accuracy. viii) Visualization inside scanning and transmission electron microscopes of the metallic contact between two macroscopic electrodes at the micron and nanometer scales. These experiments provide experimental evidence of the formation of a connective neck between the electrodes. ix) Experiments on light emission from breaking nanowires. A plausible explanation for this phenomenon is presented.
Metallic Nanowires: Conductance Statistics, Stability, IV Curves, and Magnetism
Nanowires, 1997
ABSTRACT Conductance quantization (CQ) in three dimensional nanowires is a phenomenon with fundam... more ABSTRACT Conductance quantization (CQ) in three dimensional nanowires is a phenomenon with fundamental and technological significance, particularly in the area of miniaturized electronic devices. Up to date, even with carefull controlled conditions, it has not been possible to reproduce exactly the current evolution on breaking a metallic nanocontact. This is due to the deformation mechanisms;of the nanocontact. It has been argued that in order to prove CQ, a statistical study including several conductance experiments has to be performed. However, some criteria has been always used to select the conductance curves with which the nanowire conductance histogram is built. To prove the quantized nature of the conductance in these nanostructures at room temperature (RT) we have performed a statistical study using tens of thousands of consecutive nanocontact breaking conductance curves to build the conductance histogram for different metallic junctions. This is at least 100 times more samples than any previous study, and without sample selection. The experiment is performed at RT and ambient conditions in a Scanning Tunneling Microscope (STM), where: a "tip" is crashed repeteadly into the surface, measuring the conductance of the breaking contact and building its histogram in real time. The remarkable reproducibility of the CQ histograms obtained this way allows the study of the effect of applied bias, electrode separation speed, etc. on the histograms. Notably, clear conductance peaks are observed in these "massive" histograms for gold, silver, copper, sodium and, platinum nanocontacts at RT, with the first peak centered always at a slightly lower value than 1G(0)=2e(2)/h. The small deviations of the CQ peaks from the value nG(0)=n2e(2)/h (corresponding to a perfectly ordered nanowire) in these diamagnetic nanowires are: attributed to disorder, behaving effectively for Au like a resistance in series with the contact. Experimental and theoretical results supporting this view are presented. The same experiment with ferromagnetic electrodes produces no peaks in the histogram, even though the measured conductance curves exhibit a stepped behaviour. This observation is most probably due to the lifting of the spin degenaracy due to the ferromagnetic character of the electrodes. In addition, we have studied the stability of gold nanocontacts in an Ultra High Vacuum (UHV) environment, finding remarkable stability and using this fact to measure the current-voltage characteristics (IV) with high accuracy. A positive non-linear contribution to the conductance is found in the IV characteristics. This contribution is roughly independent of the quantum conductance channel and its origin is not clear yet.
Surface Science, 2010
Hydrogen adsorption in gold nanocontact electrodes in electrochemical solution is experimentally ... more Hydrogen adsorption in gold nanocontact electrodes in electrochemical solution is experimentally discerned. This is performed with gold nanocontact conductance histograms in an electrochemical environment in which both the electrochemical potential and the electrolyte type are varied. Different salts, acids, and hydrogen peroxide electrolytes are studied. Salts and acids exhibit at negative electrochemical potentials different fractional quantum conductance histograms peaks associated to extra stable structures due to H adsorption while these peaks do not appear for H O 2 where electron transfer between solution and electrodes occurs without hydrogen formation or hydrogen adsorption on the gold electrode..
Physical Review B, 2006
A theoretical formalism that allows analysis of the magneto-optical response of nanocorrugated fe... more A theoretical formalism that allows analysis of the magneto-optical response of nanocorrugated ferromagnetic surfaces is presented and its validity checked with measurements in expressly fabricated structures. The formalism uses conventional scattering theory to find the expressions that account for the power scattered per unit area, and finds that for particular light-scattering directions and incidence polarizations the topographic and the magnetic contributions to the scattered light can be separated. By comparing theoretical and experimental results the magnetic state of the surfaces and its field evolution can be extracted.
physica status solidi c, 2010
Controlling electrochemical parameters (setting the bias voltage and monitoring the current) duri... more Controlling electrochemical parameters (setting the bias voltage and monitoring the current) during immobilization of thiolated single stranded DNA (SH‐ssDNA) on gold coated cantilevers allows tailoring the reaction kinetics. In particular, the immobilization time can be reduced more than 40 times when compared with conventional passive immobilization (cantilever electrically floated during the process). Besides the kinetics, the surface stress induced during the immobilization process can be also controlled and maximized. The combination of an electrochemically monitored immobilization with in‐situ profile measurements provides a powerful tool to optimize DNA immobilization and increase the nanomechanical response. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Journal of Magnetism and Magnetic Materials, 2001
Arrays of single crystalline Fe (0 0 1) squares separated by submicrometric distances have been f... more Arrays of single crystalline Fe (0 0 1) squares separated by submicrometric distances have been fabricated by electron beam lithography and ion beam etching to study the in#uence of size reduction on the magnetic anisotropy properties. This magnetic behaviour has been analysed by in-plane magneto-optical hysteresis loops. For large square sizes, the angular dependence of the remanence is consistent with the Fe cubic magnetic anisotropy. On the other hand, a dramatic change is found for square sizes smaller than 3 m, where an uniaxial magnetic behaviour is observed.
Partial versus total conductance histograms: A tool to identify magnetic effects in nanocontacs
Journal of Magnetism and Magnetic Materials, 2006
Conductance histograms, a powerful tool to study transport properties of metallic nanocontacs, ar... more Conductance histograms, a powerful tool to study transport properties of metallic nanocontacs, are analyzed from a new point of view. For Ni and Cu nanocontacs at room temperature, histograms obtained with no curve selection criteria are basically unaffected by the presence of a magnetic field. On the other hand, selection of particular sets of conductance curves indicates that conductance quantization could occur in steps of 12G0=e2/h and G0=2e2/h in Ni as well as in Cu in the presence or absence of a magnetic field. For Ni, the number of curves which exhibit plateaus at just G0 almost disappears with the applied field, indicating that magnetic fields are noticeable. On the contrary, for Cu nanocontacts, the analysis of partial conductance histograms reveals that the presence of an applied magnetic field keeps the ratio of curves that present plateaus at 12G0 with respect those presenting G0 plateaus unchanged. This would imply that the origin of the fractional quantization is not related to the presence of an intrinsic magnetic behavior of the Cu nanocontacs.
Journal of Applied Physics, 2002
Magneto-optic (MO) studies are performed on regular arrays of Fe(100) micrometric squares, where ... more Magneto-optic (MO) studies are performed on regular arrays of Fe(100) micrometric squares, where the elements are patterned with different sizes (2.5–10 μm) and separations (0.2–0.6 μm). When a laser beam is focused inside the patterned structure a Bragg diffraction pattern is produced allowing MO studies on both reflected and diffracted spots. The magnetic anisotropy has been analyzed by in-plane MO hysteresis loops finding that, for square sizes below 2.5 μm, it is not consistent with the Fe crystalline cubic anisotropy, presenting a uniaxial-like behavior. The magnitude of the corresponding anisotropy constants has been determined by analyzing the array response (on reflected and diffracted spots) to a rotational magnetic field in a magneto-optical torque setup. For square sizes of 10 μm the anisotropy induced by patterning is negligible whereas for the small squares (2.5 μm) the uniaxial magnetic constant has been found to be roughly 0.2 times the Fe cubic anisotropy constant.
IEEE Transactions on Magnetics, 2005
The fabrication of a periodic domain structure in a ferromagnetic thin film is reported. This per... more The fabrication of a periodic domain structure in a ferromagnetic thin film is reported. This periodic domain structure is formed in a thin continuous magnetic film by coupling it to a periodic array of magnetic elements grown on top. When the array and the continuous film are exchange decoupled, magnetostatic interactions produce in the continuous layer a domain structure replica of the topographic pattern at selected field values. The present work reports a direct confirmation of this periodic domain structure in the flat continuous film by Kerr microscopy, which is responsible for the pure magnetooptic diffraction. The effect on the magnetization processes of one-and two-dimensional structures with different periodicities and dimensions is studied in detail and compared with micromagnetic simulations, for Co and Fe films.
Applied Physics Letters, 2009
An actuation mode is presented to drive the mechanical oscillation of cantilevers for dynamic ato... more An actuation mode is presented to drive the mechanical oscillation of cantilevers for dynamic atomic force microscopy. The method is based on direct mechanical excitation of the cantilevers coated with amorphous Fe–B–N thin films, by means of the film magnetostriction, i.e., the dimensional change in the film when magnetized. These amorphous magnetostrictive Fe–B–N thin films exhibit soft magnetic properties, excellent corrosion resistance in liquid environments, nearly zero accumulated stress when properly deposited, and good chemical stability. We present low noise and high resolution topographic images acquired in liquid environment to demonstrate the method capability.
Structural study of nanocrystallized Cu83Co17 ribbons by scanning friction force microscopy
Applied Physics Letters, 1996
Nanocrystallized cobalt clusters embedded in a copper matrix exhibiting giant magnetoresistance h... more Nanocrystallized cobalt clusters embedded in a copper matrix exhibiting giant magnetoresistance have been revealed by scanning force and friction microscopy. The microscopic images reported here should be important to understand the magnetic properties of these novel systems.
Applied Physics Letters, 2002
Magneto-optic (MO) experimental and computational studies are reported on arrays of epitaxial Fe(... more Magneto-optic (MO) experimental and computational studies are reported on arrays of epitaxial Fe(001) microsquares. Measuring the transverse Kerr signal, in both reflected and diffracted spots, when the array is exposed to a rotating magnetic field allows the quantification of the magnetization inhomogeneties within the microsquares. The MO signal at diffracted spots is extremely sensitive to magnetization inhomogeneities, while working at a large constant field amplitude eliminates uncertainties due to domain-wall movements. The presence of anomalous peaks at the diffracted MO response is unambiguously assigned to the matching of inhomogeneities of the magnetization distribution to the corresponding pattern periodicity. Interaction between microsquares appears as a second-order effect.
Characterization of Dna Immobilization and Hybridization Combining Nanomechanical and Electrochemical Biosensors
ABSTRACT The development of highly sensitivity and inexpensive DNA biosensors is of great interes... more ABSTRACT The development of highly sensitivity and inexpensive DNA biosensors is of great interest for medical analysis, forensics, genomics etc. While conventional methods achieve most of the requirements, sample labelling has some disadvantages: it is time-consuming, there is interference with the molecular recognition process and an unspecific background signal. On the other hand, nanomechanical 1,2 and electrochemical 3,4 biosensors are label free detection schemes that can be combined to characterize the mechanisms involved in the immobilization of thiolated ss-DNA onto gold surfaces. The sensitivity of a DNA biosensor depends on the hybridization efficiency, which is in turn related to the DNA orientation and the surface coverage, and on the detection signal. Local measurements of the displacement along the cantilever position give information about the homogeneity of the DNA adsorption and about the surface stress induced by DNA adsorption and hybridization. The electrochemical measurements give information about the electron transfer through the monolayers. This is relevant to accurately determine the molecule sites involved in the interaction with the gold surface and with other molecules:5thiolated end, the phosphate backbone (negative charge) or the amines on the bases (positive charges). The dynamics of the absorption mechanism and the resulting coverage pattern depend on the chemical environment, the deposited species, and presumably on the charge state of the metallic surface on which the DNA strands deposit. Cantilever deflexion measurements show a clear relation between the gold surface charge and the mechanism of DNA adsorption and intermolecular interactions at the nanometer scale. The experiments show how the cantilever bending is modified drastically depending on the initial surface charge state. Remarkably, the cantilever bends downward or upwards after DNA immobilization (figure 1) depending on the initial charge state. This is probably related to differential population of DNA strands standing up and laying down on the gold surface.. (Further support of this assumption comes from white light reflectivity measurements that show a different DNA apparent thickness depending on the surface charge. In situ measurements of the electric currents during both immobilization and hybridization processes in an electrochemical cell allow to optimize the conditions for nanomechanical translation of hybridization events. Moreover it allows a deeper understanding of the mechanism of surface stress generation under self-assembly of DNA on gold and subsequent hybridization.
Monte Carlo calculations on the magnetization profile and domain wall structure in bulk systems and nanoconstricitons
... Seleccionar todos Título: Monte Carlo calculations on the magnetization profile and domain wa... more ... Seleccionar todos Título: Monte Carlo calculations on the magnetization profile and domain wall structure in bulk systems and nanoconstricitons Autores: Serena, PA; Costa-Krämer, JL Revista: Revista Mexicana de Física, 2001 MAR; 47 Suplemento 1 Página(s): 72-82 ISSN ...
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Papers by José L. Costa-Krämer