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Related Concept Videos

Current Density01:21

Current Density

The total amount of current flowing through one unit value of a cross-sectional area is referred to as current density. If the current flow is uniform, the amount of current flowing through a conductor is the same at all points along the conductor, even if the conductor area varies. The current density consists of the local magnitude and direction of the charge flow, which varies from point to point. Current density is measured in amperes per meter square, and direction is defined as the net...
Carrier Transport01:21

Carrier Transport

The generation of electrical current in semiconductors is fundamentally driven by two mechanisms: drift and diffusion. These processes are essential for the functionality and performance of semiconductor-based devices.
Drift Current:
The drift of charge carriers is started by an external electric field (E). Charged particles, such as electrons and holes, experience an acceleration between collisions with lattice atoms. For electrons, this results in a drift velocity (vd) given by:
Boundary Conditions for Current Density01:25

Boundary Conditions for Current Density

Current density becomes discontinuous across an interface of materials with different electrical conductivities. The normal component of the current density is continuous across the boundary.
Maxwell's Thermodynamic Relations01:23

Maxwell's Thermodynamic Relations

Maxwell's thermodynamic relations are very useful in solving problems in thermodynamics. Each of Maxwell's relations relates a partial differential between quantities that can be hard to measure experimentally to a partial differential between quantities that can be easily measured. These relations are a set of equations derivable from the symmetry of the second derivatives and the thermodynamic potentials.
All thermodynamic potentials are exact differentials. Therefore, their second-order...
Thermodynamic Potentials01:26

Thermodynamic Potentials

Thermodynamic potentials are state functions that are extremely useful in analyzing a thermodynamic system. They have dimensions of energy. The four important thermodynamic potentials are internal energy, enthalpy, Helmholtz free energy, and Gibbs free energy. These thermodynamic potentials can be expressed using two of the following variables: pressure, volume, temperature, and entropy. These two variables are expressed as the rate of change of the thermodynamic potential with respect to other...
Continuity Equation01:20

Continuity Equation

The total amount of current flowing per unit cross-sectional area is called the current density. Hence, the current passing through a cross-sectional area can be written as the surface integral of the current density.

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Related Experiment Video

Updated: May 10, 2026

Characterization of Thermal Transport in One-dimensional Solid Materials
05:20

Characterization of Thermal Transport in One-dimensional Solid Materials

Published on: January 26, 2014

Thermionic current densities from first principles.

Johannes Voss1, Aleksandra Vojvodic, Sharon H Chou

  • 1Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA. vossj@stanford.edu

The Journal of Chemical Physics
|June 8, 2013
PubMed
Summary
This summary is machine-generated.

This study introduces a new computational method for calculating thermionic emission currents. The approach offers accurate predictions for adsorbate-coated surfaces, aiding in the design of new electrode materials.

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Area of Science:

  • Computational materials science
  • Surface science
  • Quantum mechanics

Background:

  • Thermionic emission is crucial for vacuum electronics and energy conversion.
  • Existing methods rely on approximations, limiting accuracy for complex surfaces.
  • Accurate modeling of electron emission from coated cathodes is challenging.

Purpose of the Study:

  • To develop a first-principles method for calculating thermionic emission currents.
  • To provide quantitative predictions for adsorbate-coated surfaces without semi-classical approximations.
  • To enable the computational design of advanced electrode materials.

Main Methods:

  • Density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) formalism.
  • Calculation of thermionic emission currents from cathode surfaces into vacuum.
  • Avoidance of semi-classical approximations and simplified electronic structures.

Main Results:

  • Quantitative predictions of thermionic emission currents for adsorbate-coated surfaces.
  • Excellent agreement between calculated and experimental temperature-dependent current densities.
  • Demonstration of a method free from common approximations.

Conclusions:

  • The DFT-NEGF approach provides accurate thermionic emission calculations.
  • This method overcomes limitations of previous computational techniques.
  • Enables computational design and optimization of composite electrode materials for enhanced performance.