Raul C. Munoz

Bio: Raul C. Munoz is an academic researcher from University of Chile. The author has contributed to research in topics: Scattering & Electrical resistivity and conductivity. The author has an hindex of 15, co-authored 29 publications receiving 477 citations.

Size effects and charge transport in metals: Quantum theory of the resistivity of nanometric metallic structures arising from electron scattering by grain boundaries and by rough surfaces

Abstract: We discuss recent progress regarding size effects and their incidence upon the coefficients describing charge transport (resistivity, magnetoresistance, and Hall effect) induced by electron scattering from disordered grain boundaries and from rough surfaces on metallic nanostructures; we review recent measurements of the magneto transport coefficients that elucidate the electron scattering mechanisms at work. We review as well theoretical developments regarding quantum transport theories that allow calculating the increase in resistivity induced by electron-rough surface scattering (in the absence of grain boundaries) from first principles—from the parameters that describe the surface roughness that can be measured with a Scanning Tunnelling Microscope (STM). We evaluate the predicting power of the quantum version of the Fuchs-Sondheimer theory and of the model proposed by Calecki, abandoning the method of parameter fitting used for decades, but comparing instead theoretical predictions with resistivity m...

Surface roughness and surface-induced resistivity of gold films on mica: Application of quantitative scanning tunneling microscopy

Abstract: We report measurements of the resistivity $\ensuremath{\rho}(T)$ of a gold film 70 nm thick deposited on mica preheated to 300 \ifmmode^\circ\else\textdegree\fi{}C in UHV, performed between 4 and 300 K, and measurements of the surface topography of the same film performed with a scanning tunneling microscope (STM). From the roughness measured with the STM we determine the parameters \ensuremath{\delta} (rms amplitude) and \ensuremath{\xi} (lateral correlation length) corresponding to a Gaussian representation of the average height-height autocorrelation function (ACF). We use the parameters \ensuremath{\delta} and \ensuremath{\xi} to calculate the quantum reflectivity R and the increase in resistivity induced by electron-surface scattering on this film, according to a modified version of the theory of Sheng, Xing, and Wang (mSXW) [Munoz et al., J. Phys.: Condens. Matter 11, L299 (1999)]. The mSXW theory is able to select the appropriate scale of distance over which corrugations take place, leading to $R\ensuremath{\approx}1$ for corrugations taking place over scales of distances that are long when compared to a few Fermi wavelength ${\ensuremath{\lambda}}_{F},$ and $Rl1$ for corrugations taking place over scales of distances that are comparable to ${\ensuremath{\lambda}}_{F}$ (to within an order of magnitude). The reflectivity R determined by corrugations ocurring over a scale of distances comparable to ${\ensuremath{\lambda}}_{F}$ approaches zero for a certain angle. The resistivity $\ensuremath{\rho}(T)$ of the film increases by roughly a factor of 4 between 4 and 300 K, and so does the bulk resistivity ${\ensuremath{\rho}}_{0}(T)$ predicted by mSXW theory. With the parameters \ensuremath{\delta} and \ensuremath{\xi} measured on our 70-nm film, we reproduced approximately the thickness and temperature dependence of the resistivity (between 4 and 300 K) of several gold films on mica reported by Sambles, Elsom, and Jarvis [Philos. Trans. R. Soc. London, Ser. A 304, 365 (1982)], without using any adjustable parameters. The results of this paper suggest that the relevant quantities controlling electron-surface scattering in continuous gold films of arbitrary thickness, are the parameters \ensuremath{\delta} and \ensuremath{\xi} describing the average ACF that characterizes the surface of the sample on a nanoscopic scale, in agreement with the accepted view regarding the conductivity of ultrathin films.

Electron grain boundary scattering and the resistivity of nanometric metallic structures

Abstract: The resistivity of metallic structures depends on both electron-grain boundary scattering and electron-surface scattering. By tuning the grain size, we have been able to separate the contribution to the resistivity originating in electron-grain boundary scattering, from that arising in electron-surface scattering, on gold films approximately 54 nm thick deposited onto mica substrates under high vacuum. Surprisingly, the resistivity measured between 4 and 300 K can be described by Drude's model; it can be described as well by Mayadas's theory using the grain boundary reflectivity $R$ as the only adjustable parameter.

Surface-induced resistivity of thin metallic films bounded by a rough fractal surface

Abstract: We have extended the modified formalism of Sheng, Xing, and Wang@J. Phys.: Condens. Matter11 L299 ~1999!# to allow the calculation of the conductivity of a thin metallic film bounded by a rough fractal surface. We utilized the so-called k-correlation model proposed by Palasantzas and Barnas @Phys. Rev. B 48, 14 472 ~1993!; 56, 7726 ~1997!#, to describe the height-height autocorrelation function corresponding to a self-affine roughness. This extension permits the calculation of the conductivity of the film as a function of the r.m.s. roughness amplitude d, of the lateral correlation length j, of the mean free path in the bulk l, and of the roughness exponent H. We found that the degree of surface irregularity, represented by the roughness exponent H characterizing the surface, does influence the conductivity of the film, as first discovered by Palasantzas and Barnas. However, this influence manifests itself for large bulk mean free paths l’1000 nm and for large correlation lengths j’5 nm, in which case the conductivity of the film for H51 exceeds by about 30% the conductivity for H50.2, an effect which is smaller than that reported by Palasantzas and Barnas. For correlation lengths j below 1 nm and mean free paths l’100 nm, the influence of the roughness exponent H on the conductivity is reduced to below 10%, and for smaller mean free paths and correlation lengths the conductivity becomes insensitive to H. We also found that Mathiessen’s rule is severily violated in the case of thin metallic films. The resistivity of the film coincides roughly with the surface-limited resistivity only in the case of ultrathin films t,5 nm. For thicker films 100 nm.t.5 nm, the resistivity of the film exceeds by some 20 to 30 % the value dictated by Mathiessen’s rule. And conversely, the apparent surface-induced resistivity estimated assuming the validity of Mathiessen’s rule, exceeds by nearly one order of magnitude the true surfaceinduced resistivity, except in the case of ultrathin films t, 5n m.

Art of electronics

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High power pulsed magnetron sputtering: A review on scientific and engineering state of the art

Abstract: High power pulsed magnetron sputtering (HPPMS) is an emerging technology that has gained substantial interest among academics and industrials alike. HPPMS, also known as HIPIMS (high power impulse ...

Quantitative study of the spin Hall magnetoresistance in ferromagnetic insulator/normal metal hybrids

Abstract: We experimentally investigate and quantitatively analyze the spin Hall magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic insulator/nonferromagnetic metal/platinum hybrid structures. For the ferromagnetic insulator, we use either yttrium iron garnet, nickel ferrite, or magnetite and for the nonferromagnet, copper or gold. The spin Hall magnetoresistance effect is theoretically ascribed to the combined action of spin Hall and inverse spin Hall effect in the platinum metal top layer. It therefore should characteristically depend upon the orientation of the magnetization in the adjacent ferromagnet and prevail even if an additional, nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our experimental data corroborate these theoretical conjectures. Using the spin Hall magnetoresistance theory to analyze our data, we extract the spin Hall angle and the spin diffusion length in platinum. For a spin-mixing conductance of 4×1014 ??1m?2, we obtain a spin Hall angle of 0.11±0.08 and a spin diffusion length of (1.5±0.5) nm for Pt in our thin-film samples