Heat Transfer and Thermoelectric Voltage at Metallic Point Contacts

1993 ◽  
Vol 115 (3) ◽  
pp. 757-762 ◽  
Author(s):  
P. E. Phelan ◽  
O. Nakabeppu ◽  
K. Ito ◽  
K. Hijikata ◽  
T. Ohmori ◽  
...  
Keyword(s):  
Temperature Drop ◽  
Point Contact ◽  
Thermal Characteristics ◽  
Mean Free Path ◽  
Contact Radius ◽  
Point Contacts ◽  
Plate Temperature ◽  
Thermoelectric Voltage ◽  
The Mean ◽  
Electron Mean Free Path

Metallic point contacts have been extensively studied from the viewpoint of their interesting, and often nonlinear, electrical properties. Their thermal characteristics, however, have largely been ignored, even though they show great potential as microscale temperature sensors. It has been previously demonstrated that when a temperature drop exists across a point contact consisting of two identical metals, a thermoelectric voltage can be generated, provided the mean contact radius is comparable in size to the electron mean free path. In the present experimental study, a point contact is formed by pressing a sharply etched Ag whisker against either an Ag or a Cu flat plate. In addition to confirming the previous results, the feasibility of using such a point contact is demonstrated by calibrating the voltage output against the nondimensionalized plate temperature. Furthermore, the thermoelectric voltage at an Ag–Cu point contact is also presented, showing that a point contact made from dissimiliar metals is even more promising than one made from identical materials. Finally, the point-contact thermal resistance is shown to depend nonlinearly on the electrical resistance, or contact area, and on the temperature drop.

Interplay Between Thermoelectric and Thermionic Effects in Heterostructures

2000 ◽  
Author(s):  
Taofang Zeng ◽  
Gang Chen
Keyword(s):  
Film Thickness ◽  
Free Path ◽  
Thermionic Emission ◽  
Approximate Solutions ◽  
Mean Free Path ◽  
Boltzmann Transport ◽  
Thermoelectric Effects ◽  
Double Heterojunction ◽  
The Mean ◽  
Electron Mean Free Path

Abstract When electrons sweep through a double-heterojunction structure, there exist thermionic effects at the junctions and thermoelectric effects in the film. While both thermoelectric and thermionic effects have been studied for refrigeration and power generation applications separately, their interplay in heterostructures is not understood. This paper establishes a unified model including both thermionic and thermoelectric processes based on the Boltzmann transport equation for electrons, and the nonequilibrium interaction between electrons and phonons. Approximate solutions are obtained, leading to the electron temperature and Fermi level distributions inside heterostructures and discontinuities at the interfaces as a consequence of the highly nonequilibrium transport when the film thickness is much smaller than the electron mean free path. It is found that when the film thickness is smaller than the mean free path of electrons, the transport of electrons is controlled by thermionic emission. The coexistence of thermoelectric and thermionic effects may increase the power factor when the electron mean free path is comparable to the film thickness.

scholarly journals Evidence of weak Anderson localization revealed by the resistivity, transverse magnetoresistance and Hall effect measured on thin Cu films deposited on mica

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Eva Díaz ◽  
Guillermo Herrera ◽  
Simón Oyarzún ◽  
Raul C. Munoz
Keyword(s):  
Integrated Circuits ◽  
Hall Effect ◽  
Electron Scattering ◽  
Anderson Localization ◽  
Mean Free Path ◽  
Negative Magnetoresistance ◽  
Cu Films ◽  
Transverse Magnetoresistance ◽  
The Mean ◽  
Electron Mean Free Path

AbstractWe report the resistivity of 5 Cu films approximately 65 nm thick, measured between 5 and 290 K, and the transverse magnetoresistance and Hall effect measured at temperatures 5 K < T < 50 K. The mean grain diameters are D = (8.9, 9.8, 20.2, 31.5, 34.7) nm, respectively. The magnetoresistance signal is positive in samples where D > L/2 (where L = 39 nm is the electron mean free path in the bulk at room temperature), and negative in samples where D < L/2. The sample where D = 20.2 nm exhibits a negative magnetoresistance at B < 2 Tesla and a positive magnetoresistance at B > 3 Tesla. A negative magnetoresistance in Cu films has been considered evidence of charge transport involving weak Anderson localization. These experiments reveal that electron scattering by disordered grain boundaries found along L leads to weak Anderson localization, confirming the localization phenomenon predicted by the quantum theory of resistivity of nanometric metallic connectors. Anderson localization becomes a severe obstacle for the successful development of the circuit miniaturization effort pursued by the electronic industry, for it leads to a steep rise in the resistivity of nanometric metallic connectors with decreasing wire dimensions (D < L/2) employed in the design of Integrated Circuits.

Thermoelectric Voltage at Metallic Point Contacts From Nonequilibrium Effects

1995 ◽  
Vol 117 (4) ◽  
pp. 822-827 ◽  
Author(s):  
K. Ito ◽  
K. Hijikata ◽  
K. Torikoshi ◽  
P. E. Phelan
Keyword(s):  
Large Scale ◽  
Point Contact ◽  
Nonequilibrium State ◽  
Open Circuit ◽  
Point Contacts ◽  
Thermoelectric Voltage ◽  
Nonequilibrium Effect ◽  
Gold Silver ◽  
Large Scale Integration ◽  
Scale Integration

This paper presents results for thermoelectric voltage experiments carried out with metallic point contacts. The motivation for this work is the fundamental understanding of the nonequilibrium state between electrons and phonons, and for applying this phenomenon to a point temperature measurement of small heating elements like an LSI (Large-Scale Integration) electronic chip. The experiments were carried out by using gold, silver, copper, and tungsten point contacts under cryogenic conditions, and a heat flux through the point contact was applied via a temperature difference across the contact. In this condition, thermoelectric voltages appeared even when the entire open circuit consisted of only one material. This phenomenon was explained theoretically by considering the nonequilibrium effect between the phonon and electron temperatures, and the geometric effect at the point contact. Good agreement was found between the theory and the experiment.

scholarly journals Depth Resolution Dependence on Sample Thickness and Incident Energy in On-Axis Transmission Kikuchi Diffraction in Scanning Electron Microscope (SEM)

2017 ◽  
Vol 23 (6) ◽  
pp. 1096-1106 ◽  
Author(s):  
Etienne Brodu ◽  
Emmanuel Bouzy
Keyword(s):  
Incident Energy ◽  
Depth Resolution ◽  
Mean Free Path ◽  
Total Sample ◽  
Sample Thickness ◽  
Crystal Sample ◽  
Continuous Absorption ◽  
Orientation Maps ◽  
The Mean ◽  
Electron Mean Free Path

AbstractTransmission Kikuchi diffraction is an emerging technique aimed at producing orientation maps of the structure of materials with a nanometric lateral resolution. This study investigates experimentally the depth resolution of the on-axis configuration, via a twinned silicon bi-crystal sample specifically designed and fabricated. The measured depth resolution varies from 30 to 65 nm in the range 10–30 keV, with a close to linear dependence with incident energy and no dependence with the total sample thickness. The depth resolution is explained in terms of two mechanisms acting concomitantly: generation of Kikuchi diffraction all along the thickness of the sample, associated with continuous absorption on the way out. A model based on the electron mean free path is used to account for the dependence with incident energy of the depth resolution. In addition, based on the results in silicon, the use of the mean absorption coefficient is proposed to predict the depth resolution for any atomic number and incident energy.

Perpendicular Resistance of Co/Cu Multilayers Prepared by Molecular Beam Epitaxy

1995 ◽  
Vol 384 ◽  
Author(s):  
N.J. List ◽  
W.P. Pratt ◽  
M.A. Howson ◽  
J. Xu ◽  
M.J. Walker ◽  
...  
Keyword(s):  
Free Path ◽  
Spin Diffusion ◽  
Mean Free Path ◽  
Ferromagnetic Structure ◽  
Order Of Magnitude ◽  
The Mean ◽  
Electron Mean Free Path ◽  
Determining Factor ◽  
Second Peak ◽  
Key Parameter

ABSTRACTResults are presented of the magnetoresistance of MBE-grown (111) Co/Cu multilayers measured with the current perpendicular to the plane of the layers (CPP). Although for measurements made with the more common geometry of current in the plane of the layers (CIP) there are large differences between the results on samples made by sputtering and those prepared by MBE, for these new CPP data the results on samples made by the two techniques are very much alike. For copper layers with thicknesses between 0.9nm to 6nm the magnetoresistance shows oscillations with copper thickness that were almost non-existent in the earlier CIP data. At the second peak the magnetoresistance in the CPP geometry is an order of magnitude greater than that in the CIP configuration. Although the interfaces in these samples have been shown to be very sharp, they appear to form a mosaic structure with the antiferromagnetic regions embedded in a ferromagnetic structure. It is argued that for CIP measurements the GMR is greatly reduced by these ferromagnetic correlations over lengthscales long compared to the electron mean free path. For CPP measurements, on the other hand, it is the spin diffusion length that is the determining factor with the mean free path no longer a key parameter and with values of the GMR virtually independent of the growth process.

Transverse magnetoresistance, Hall mobility and Hall constant of thin Cu films deposited onto cleaved mica: Evidence of weak Anderson localization.

2021 ◽  
Author(s):  
Eva Díaz ◽  
Guillermo Herrera ◽  
Simón Oyarzún ◽  
Raul Munoz
Keyword(s):  
Integrated Circuits ◽  
Electron Scattering ◽  
Anderson Localization ◽  
Mean Free Path ◽  
Negative Magnetoresistance ◽  
Hall Constant ◽  
Cu Films ◽  
Transverse Magnetoresistance ◽  
The Mean ◽  
Electron Mean Free Path

Abstract We report the resistivity of 5 Cu films approximately 65 nm thick, measured between 5 K and 290 K, and the transverse magnetoresistance and Hall effect measured at temperatures 5 K< T<50 K. The mean grain diameters are D=(8.9, 9.8, 20.2, 31.5, 34.7) nm, respectively. The magnetoresistance signal is positive in samples where D>L/2 (where L=39 nm is the electron mean free path in the bulk at room temperature), and negative in samples where D<L/2. The sample where D=20.2 nm exhibits a negative magnetoresistance at B < 2 Tesla and a positive magnetoresistance at B > 2 Tesla. A negative magnetoresistance in Cu films has been considered evidence of charge transport involving weak Anderson localization. These experiments reveal that electron scattering by disordered grain boundaries found along L leads to weak Anderson localization, confirming the localization phenomena predicted by the quantum theory of resistivity of nanometric metallic connectors. Anderson localization becomes a severe obstacle for the successful development of the circuit miniaturization effort pursued by the electronic industry, for it leads to a steep rise in the resistivity of nanometric metallic connector with decreasing wire dimensions (D<L/2) employed in the design of Integrated Circuits.

scholarly journals Ballistic Heat Transport in Nanocomposite: The Role of the Shape and Interconnection of Nanoinclusions

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1982
Author(s):  
Paul Desmarchelier ◽  
Alice Carré ◽  
Konstantinos Termentzidis ◽  
Anne Tanguy
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Free Path ◽  
Mean Free Path ◽  
Strong Increase ◽  
Moderate Increase ◽  
Energy Propagation ◽  
The Mean ◽  
Dynamics Simulations

In this article, the effect on the vibrational and thermal properties of gradually interconnected nanoinclusions embedded in an amorphous silicon matrix is studied using molecular dynamics simulations. The nanoinclusion arrangement ranges from an aligned sphere array to an interconnected mesh of nanowires. Wave-packet simulations scanning different polarizations and frequencies reveal that the interconnection of the nanoinclusions at constant volume fraction induces a strong increase of the mean free path of high frequency phonons, but does not affect the energy diffusivity. The mean free path and energy diffusivity are then used to estimate the thermal conductivity, showing an enhancement of the effective thermal conductivity due to the existence of crystalline structural interconnections. This enhancement is dominated by the ballistic transport of phonons. Equilibrium molecular dynamics simulations confirm the tendency, although less markedly. This leads to the observation that coherent energy propagation with a moderate increase of the thermal conductivity is possible. These findings could be useful for energy harvesting applications, thermal management or for mechanical information processing.

Sputtering pressure dependence of hydrogen-sensing effect of palladium films

2009 ◽  
Vol 24 (6) ◽  
pp. 1919-1927 ◽  
Author(s):  
Chung Wo Ong ◽  
Yu Ming Tang
Keyword(s):  
Electrical Resistivity ◽  
Magnetron Sputtering ◽  
Mean Free Path ◽  
Induced Response ◽  
Resistivity Ratio ◽  
Hydrogen Sensing ◽  
The Mean ◽  
Sputtering Pressure ◽  
Specific Volumes ◽  
Hydride Phases

The electrical resistivity ρ of palladium (Pd) films prepared by using magnetron sputtering at different pressures φ ranging from 2 to 15 mTorr showed very different hydrogen (H)-induced response. This reaction is because the mean free path of the particles in vacuum changes substantially with φ, such that the structure of the deposits is altered accordingly. A film prepared at a moderate φ value of 6 mTorr has a moderate strength. After a few hydrogenation-dehydrogenation cycles, some cracks are generated because of the great difference in the specific volumes of the metal and hydride phases. Breathing of the cracks in subsequent switching cycles occurred, which led to the response gain of ρ, defined as the resistivity ratio of the dehydrogenated-to-hydrogenated states during a cycle, to increase to 17. This result demonstrates the attractiveness of using the Pd films in H2 detection application. The H-induced resistive response of the films prepared at other φ values was found to be much smaller.

scholarly journals Electromigration-induced directional steps towards the formation of single atomic Ag contacts

2020 ◽  
Vol 11 ◽  
pp. 680-687
Author(s):  
Atasi Chatterjee ◽  
Christoph Tegenkamp ◽  
Herbert Pfnür
Keyword(s):  
Fourier Transforms ◽  
Single Point ◽  
Point Contact ◽  
Single Atom ◽  
Point Contacts ◽  
Cross Sectional ◽  
Shell Effects ◽  
Theoretical Approaches ◽  
Average Grain Size ◽  
Thinning Process

Even though there have been many experimental attempts and theoretical approaches to understand the process of electromigration (EM), it has not been quantitatively understood for ultrathin structures and at grain boundaries. Nevertheless, we showed recently that it can be used reliably for the formation of single atomic point contacts after careful pre-structuring of the initial Ag nanostructures. The process of formation of nanocontacts by EM down to a single-atom point contact was investigated for ultrathin (5 nm) Ag structures at 100 K by measuring the conductance as a function of the time during EM. In this paper, we compare the process of thinning by EM of structures with constrictions below the average grain size of Ag layers (15 nm) with that of structures with much larger initial constrictions of around 150 nm having multiple grains at the centre constriction prior to the formation of a point contact. Even though clear morphological differences exist between both types of structures, quantized conductance plateaus showing the formation of single point contacts have been observed for both. Here we put emphasis on the thinning process by EM, just before a point contact is formed. To understand this thinning process, the semi-classical regime before the contact reaches the quantum regime was analyzed in detail. For this purpose, we used experimental conductance histograms in the range between 2G 0 and 15G 0 and their corresponding Fourier transforms (FTs). The FT analysis of the conductance histograms exhibits a clear preference for thinning along the [100] direction. Using well-established models, both atom-by-atom steps and ranges of stability, presumably caused by electronic shell effects, can be discriminated. Although the directional motion of atoms during EM leads to specific properties such as the instabilities mentioned, similarities to mechanically opened contacts with respect to cross-sectional stability were found.

Sign in / Sign up

Export Citation Format

Share Document