Surface roughness and surface-induced resistivity of gold films on mica: Application of quantitative scanning tunneling microscopy (original) (raw)
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Journal of Physics: Condensed Matter, 2000
We report measurements of the resistivity (T) of a gold film 70 nm thick deposited on mica preheated to 300°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 ͑STM͒. From the roughness measured with the STM we determine the parameters ␦ ͑rms amplitude͒ and ͑lateral correlation length͒ corresponding to a Gaussian representation of the average height-height autocorrelation function ͑ACF͒. We use the parameters ␦ and 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 ͑mSXW͒ ͓Munoz et al., J. Phys.: Condens. Matter 11, L299 ͑1999͔͒. The mSXW theory is able to select the appropriate scale of distance over which corrugations take place, leading to RϷ1 for corrugations taking place over scales of distances that are long when compared to a few Fermi wavelength F , and RϽ1 for corrugations taking place over scales of distances that are comparable to F ͑to within an order of magnitude͒. The reflectivity R determined by corrugations ocurring over a scale of distances comparable to F approaches zero for a certain angle. The resistivity (T) of the film increases by roughly a factor of 4 between 4 and 300 K, and so does the bulk resistivity 0 (T) predicted by mSXW theory. With the parameters ␦ and measured on our 70-nm film, we reproduced approximately the thickness and temperature dependence of the resistivity ͑between 4 and 300 K͒ of several gold films on mica reported by Sambles, Elsom, and Jarvis ͓Philos. Trans. R. Soc. London, Ser. A 304, 365 ͑1982͔͒, 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 ␦ and 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.
Journal of Physics-condensed Matter, 2000
We analyse the thickness and temperature dependence of the resistivity for several gold films on mica reported by Sambles, Elsom and Jarvis (SEJ: Sambles J R, Elsom K C and Jarvis J D 1982 Phil. Trans. R. Soc. A 304 365). Data analysis proceeds according to an iteration procedure proposed recently (Munoz R C, Concha A, Mora F, Espejo R, Vidal G, Mulsow M, Arenas C, Kremer G, Moraga L, Esparza R and Haberle P 2000 Phys. Rev. B 61 4514; Munoz R C, Vidal G, Kremer G, Moraga L, Arenas C and Concha A 2000 J. Phys.: Condens. Matter 12 2903), that permits the calculation of the temperature-dependent bulk conductivity σ0(T) from the parameters δ (r.m.s. roughness amplitude) and ξ (lateral correlation length) that describe the surface roughness. To assess the influence of the theoretical modelling of the electron-surface scattering, we use the theory of Tesanovic, Jaric and Maekawa (TJM), the theory of Trivedi and Aschroft (TA) and the modified theory of Sheng, Xing and Wang (mSXW). With the parameters δ and ξ measured for a 70 nm gold film deposited on mica, under similar conditions of evaporation, all three models reproduce approximately the thickness and temperature dependence of the resistivity (between 4 K and 300 K) of the SEJ films without using any adjustable parameter. Agreement between theory and experiment improves according to the sequence TJM, TA, mSXW.
Journal of Physics-condensed Matter, 2000
We report measurements of the temperature dependent resistivity icons/Journals/Common/rho" ALT="rho" ALIGN="TOP"/> (T ) of a gold film 70 nm thick deposited on mica preheated to 300 °C in UHV, performed between 4 K and 300 K, and measurements of the surface topography of the same film performed with a scanning tunnelling microscope (STM). From the roughness measured with the STM we determine the parameters icons/Journals/Common/delta" ALT="delta" ALIGN="TOP"/> (r.m.s. amplitude) and icons/Journals/Common/xi" ALT="xi" ALIGN="TOP"/> (lateral correlation length) corresponding to a Gaussian and to an exponential representation of the average autocorrelation function (ACF). We use the parameters icons/Journals/Common/delta" ALT="delta" ALIGN="TOP"/> and icons/Journals/Common/xi" ALT="xi" ALIGN="TOP"/> determined via STM measurements to calculate the quantum reflectivity R , and the temperature dependence of both the bulk resistivity icons/Journals/Common/rho" ALT="rho" ALIGN="TOP"/> 0 (T ) and of the increase in resistivity icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> icons/Journals/Common/rho" ALT="rho" ALIGN="TOP"/> (T ) = icons/Journals/Common/rho" ALT="rho" ALIGN="TOP"/> (T ) - icons/Journals/Common/rho" ALT="rho" ALIGN="TOP"/> 0 (T ) induced by electron-surface scattering on this film, according to a modified version of the theory of Sheng, Xing and Wang recently proposed (Munoz et al 1999 J. Phys.: Condens. Matter 11 L299). The resistivity icons/Journals/Common/rho" ALT="rho" ALIGN="TOP"/> 0 in the absence of surface scattering predicted for a Gaussian representation of the ACF is systematically smaller than that predicted for an exponential representation of the ACF at all temperatures. The increase in resistivity icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> icons/Journals/Common/rho" ALT="rho" ALIGN="TOP"/> induced by electron-surface scattering predicted for a Gaussian representation of the average ACF data is about 25% larger than the increase in resistivity predicted for an exponential representation of the ACF data.
Surface roughness and size effects of thin gold films on mica
Physical Review B, 2000
We report measurements of the topography of a gold film deposited on a mica substrate using scanning tunneling microscope ͑STM͒, and measurements of the conductivity of the film performed between 4 and 300 K. From images obtained with the STM running in air in the constant current mode of a gold sample 70-nm-thick deposited under UHV on a mica substrate preheated to 300°C, we compute the average autocorrelation function ͑ACF͒ that characterizes the surface of the film in the scale of 10ϫ10 nm 2 , and determine by least-squares fitting the parameters ␦ ͑rms. amplitude͒ and ͑lateral correlation length͒ corresponding to an exponential that best describes the average ACF data. Using an exponential representation of the ACF, the parameters ␦ and determined from STM measurements, and a modified version of the theory of Sheng, Xing, and Wang recently proposed ͓R. C. Munoz et al., J. Phys.: Condens. Matter 11, L299 ͑1999͔͒, we calculate the temperature dependence of the bulk resistivity 0 (T) and of the increase in resistivity ⌬(T)ϭ(T)Ϫ 0 (T) induced by electron-surface scattering on this film. The result is that 1Ϫ/ 0 ϭ1Ϫ 0 /ϭ⌬/ amounts to about 2.6% at 300 K, and increases linearly with increasing mean free path, to about 10.5% at 4 K. The increase in resitivity ⌬ turns out to be weakly temperature dependent.
Physical Review B, 2006
We contrast the numerical solution of the transport theory published by Calecki ͓D. Calecki, Phys. Rev. B 42, 6906 ͑1990͔͒, with transport data published recently ͓R. C. Munoz et al., J. Phys.: Condens. Matter 18, 3401 ͑2006͒; Phys. Rev. Lett. 96, 206803 ͑2006͔͒. We use the resistivity, transverse magnetoresistance, and Hall voltage data of thin gold films deposited on mica substrates measured under high magnetic fields B ͑1.5 T ഛ B ഛ 9 T͒ at low temperatures T ͑4 Kഛ T ഛ 50 K͒, as well as the surface roughness measured on each sample with a scanning tunneling microscope. The surprising result is that theory does provide an accurate description of the temperature dependence of the resistivity, a less accurate description of the Hall voltage observed at 4 K, but predicts a magnetoresistance at 4 K that turns out to be several orders of magnitude smaller than observed.
Electron scattering at surfaces and grain boundaries in thin Au films
Applied Surface Science, 2013
The electron scattering at surfaces and grain boundaries is investigated using polycrystalline Au films deposited onto mica substrates. We vary the three length scales associated with: (i) electron scattering in the bulk, that at temperature T is characterized by the electronic mean free path in the bulk 0 (T ); (ii) electron-surface scattering, that is characterized by the film thickness t; (iii) electron-grain boundary scattering, that is characterized by the mean grain diameter D. We varied independently the film thickness from approximately 50 nm to about 100 nm, and the typical grain size making up the samples from 12 nm to 160 nm. We also varied the scale of length associated with electron scattering in the bulk by measuring the resistivity of each specimen at temperatures T, 4 K < T < 300 K. Cooling the samples to 4 K increases 0 (T ) by approximately 2 orders of magnitude. Detailed measurements of the grain size distribution as well as surface roughness of each sample were performed with a Scanning Tunnelling Microscope (STM). We compare, for the first time, theoretical predictions with resistivity data employing the two theories available that incorporate the effect of both electron-surface as well as electron-grain boundary scattering acting simultaneously: the theory of A.F. Mayadas and M. Shatzkes, Phys. Rev. 1 1382 (1970) (MS), and that of G. Palasantzas, Phys. Rev. B 58 9685 (1998). We eliminate adjustable parameters from the resistivity data analysis, by using as input the grain size distribution as well as the surface roughness measured with the STM on each sample. The outcome is that both theories provide a fair representation of both the temperature as well as the thickness dependence of the resistivity data, but yet there are marked differences between the resistivity predicted by these theories. In the case of the MS theory, when the average grain diameter D is significantly smaller than 0 (300) = 37 nm, the electron mean free path in the bulk at 300 K, the effect of electron-grain boundary scattering dominates the increase in resistivity of the film over the bulk, and the electronic mean free path, D (4), computed from Drude's model at 4 K, is similar to the grain diameter D. The increase in resistivity attributable to electron-grain boundary scattering can be as large as 220 at low temperatures, for samples made out of 12 nm grains. On the contrary, when D is significantly larger than 0 (300), then electron-surface scattering dominates the increase in resistivity. When D is comparable to 0 (300), there is a cross over where both electron-surface and electron-grain boundary scattering do contribute to increasing the resistivity of the film over that of the bulk. These predictions are in sharp contrast with those based upon the theory of Palasantzas, that predicts an increase in resistivity-attributable to electron-grain boundary/surface scattering-that turns out to be essentially unity regardless of the size of the grains making up the sample. (R.C. Munoz). last decade within the semiconductor industry . Current interest is growing rapidly, as illustrated by several experiments concerning this problem published over the last three years . However, after more than a century of research, the understanding of size effects in thin metallic films today still seems fragmentary and incomplete.
Morphological and electrical study of gold ultrathin films on mica
Thin Solid Films, 2013
We present a topographical study of the formation of thin films of gold on muscovite mica. The characterization of the samples was done with scanning tunneling microscopy, atomic force microscopy as well as electric measurements. We performed our study on two groups of samples: first group of samples, evaporated at room temperature for thickness ranging from 1.5 up to 97 nm; second group of samples, for two different thicknesses of 3 nm and 50 nm evaporated at different substrate temperatures, between 110 and 530 K. The gold films show a Volmer-Weber growth. The complete films are obtained from samples with a nominal thickness of 8 nm deposited. The average grain diameter is constant, with nominal thicknesses of 18.5 nm, up to 8 nm and increases with the thickness for higher deposition. The average grain diameter is similar regardless of the temperature of the substrate for samples of 3 nm thickness, but changes for samples of 50 nm thickness. The resistivity is inversely dependent on nominal thickness and the mean free path is lineally dependent on nominal thickness.