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A backscattered electron is a primary beam electron redirected out through the incident side of a specimen after scattering. Backscattered signals commonly retain much more of the incident kinetic energy than emitted low-energy secondary electrons.^[ref]

In a scanning electron microscope, collecting these electrons can provide backscattered-electron atomic-number contrast, but specimen tilt, collection geometry and crystallographic electron channeling also change brightness. Comparing detector directions or tilting the specimen tests some of those contributions. A bright region is therefore not uniquely a region of greater atomic number.

Crystallographic electron channeling is orientation-dependent propagation of electrons in a crystal, where the spatially ordered electrostatic potential changes how the beam travels relative to atomic planes or columns. Changing crystal orientation can therefore change the collected signal even without changing chemical composition.

A small specimen tilt at fixed beam energy is a useful test: brightness changes correlated with orientation suggest a channeling or electron diffraction contribution. This matters when interpreting backscattered-electron atomic-number contrast or atomic-scale chemical maps. A bright region is not by itself proof of a different atomic number.

Atomic force microscopy senses tip–sample interactions through a compliant cantilever. Contact deflection, oscillation amplitude, phase or resonance frequency can be converted into a feedback signal. Chemical bonding and short-range repulsion, van der Waals forces, electrostatic forces and, where relevant, magnetic or capillary interactions produce contrast. Apparent height at a fixed force or frequency setpoint can therefore contain interaction contrast as well as geometry. Lateral resolution depends on the effective tip apex and interaction range; finite tip radius broadens features. Vertical sensitivity also depends on thermal and detector noise, cantilever calibration, vibration, drift and feedback bandwidth. Strongly localized short-range forces favor atomic resolution, whereas extended interactions average over more of the tip and surface.

For small oscillations about equilibrium separation $z_0$, write $z=z_0+x$ and linearize $F(z)=F(z_0)+F^{\prime }(z_0)x$. The constant force is absorbed into the equilibrium displacement. The cantilever equation becomesConsequently the small-amplitude AFM frequency shift isThe linear expression is the small-force-gradient approximation, $|F^{\prime }|\ll c$, in addition to the small-oscillation assumption. For an attractive force $F=-C/z^2$, $F^{\prime }>0$ and the resonance softens. A finite oscillation amplitude samples a weighted range of forces rather than only the gradient at one separation, and $F^{\prime }\ge c$ destroys local stability in this simple static model.

In a scanning electron microscope, a focused electron beam scans the surface and a detector records an emitted signal at each beam position. Low-energy secondary electrons escape from near the surface; changes in local slope, edges and detector-facing geometry give strong secondary-electron topographic contrast. Backscattered electrons result from elastic deflection of primary electrons and generally have a larger yield for higher atomic number. Their backscattered-electron atomic-number contrast therefore helps separate compositional regions. Detector geometry, crystal orientation and topography can also affect this signal, so brightness is not a unique elemental identification.

An environmental scanning electron microscope admits gas around the specimen while pressure-limiting apertures and differential pumping preserve the electron-optical column's vacuum. Electron collisions ionize the gas. Positive ions can neutralize negative charging of a poorly conducting specimen, enabling observation without a conductive coating. A gaseous secondary electron detector uses gas amplification to collect secondary-electron signals under these conditions. Gas pressure, path length and scattering must be controlled because they also affect the probe and background.^[ref]

Finally, acquire an energy-dispersive X-ray spectroscopy spectrum at each pixel to add elemental specificity. The beam creates inner-shell vacancies, and characteristic X-rays emitted as they fill identify chemical elements. Selecting fitted characteristic-line intensities yields elemental maps that can be compared with the electron image. Peak overlap, detector response, absorption and the X-ray-generating interaction volume limit identification, quantification and spatial resolution. This gives chemical-element contrast; resolving different bonds or oxidation states generally needs more detailed spectral information than one broad elemental map.