TEMs

TEMs is a plural form used for several concepts in science and engineering. Two of the most common meanings are Transmission Electron Microscopy and Transverse ElectroMagnetic modes.

Transmission Electron Microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through an ultra-thin specimen. The interactions between the electrons and the sample form an image or diffraction pattern that can be used to study structure at the atomic scale. TEM requires high accelerating voltages (typically 60-300 keV) and very thin samples. TEM images and electron-diffraction data can reveal crystallography, defects, and morphology, while energy-dispersive X-ray spectroscopy (EDS) attached to TEM can provide elemental composition. TEM has variants like high-resolution TEM, tomography, and scanning TEM (STEM). Limitations include sample damage from electron irradiation, vacuum requirements, and the need for extensive sample preparation. TEM is widely used in materials science, chemistry, physics, and biology.

Transverse ElectroMagnetic modes (TEM) are electromagnetic waves or field configurations in which both the electric and magnetic fields are entirely transverse to the direction of propagation. TEM modes occur in two-conductor transmission lines, such as coaxial cables and two-wire lines, and are characterized by a nonzero E field between conductors and a magnetic field encircling the conductors. They have no cutoff frequency and a phase velocity near the speed of light in the line’s dielectric. The characteristic impedance Z0 of a TEM line is determined by its inductance and capacitance per unit length, Z0 = sqrt(L/C). TEM modes are not supported in hollow single-conductor waveguides or most traditional waveguides, where only TE or TM modes exist. They are fundamental to RF and telecommunications, enabling broadband, low-dispersion transmission on coaxial and microstrip lines, among others.

See also transmission line, coaxial cable, electron microscopy.