---
title: "PEEM: Thresholds & Magnetic Domains Interactive Lab | Sandbox Physics"
description: "Can PEEM tell magnetic contrast apart from brightness caused by uneven illumination? Yes, once each image is corrected for the incoming flux."
canonical_url: "https://sandboxphysics.com/labs/peem-surface/"
language: "en"
page_type: "lab"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/labs/peem-surface/"
last_modified: "2026-10-27"
---

E58 · Surface spectromicroscopy

# PEEM: Thresholds & Magnetic Domains

**Can PEEM tell magnetic contrast apart from brightness caused by uneven illumination?** Yes, once each image is corrected for the incoming flux. A region can also look bright because of its chemistry or work function. Normalize every image to its monitored flux, then compare images taken with opposite circular polarization. Only contrast that reverses when the polarization flips is magnetic.

Light the whole field of a synthetic surface. Compare UV work-function thresholds, absorption spectra and images taken with opposite helicities. Pull spectra out of the stored image stacks, and correct for the incident flux before you interpret any magnetic contrast.

> Interactive simulation: open this page in a web browser to change the parameters and run the model.

Model assumptions

This is a teaching model of UV-PEEM and of secondary-yield XAS/XMCD-PEEM, with an ideal 18 keV cathode image relay. The Lab does not do energy-filtered core-level XPS. The 8 micrometre square surface has two invented absorption resonances and work functions, and two opposite magnetic projections. A collection-yield ridge shared by both phases imitates topographic brightness. The UV yield follows a quadratic threshold at zero temperature. The X-ray spectra are assumed Gaussian resonances, not computed atomic cross sections. Both helicity stacks hold sampled detector counts after a Gaussian spatial blur, and their flux monitors read exact teaching values. Drift of the negative-helicity image misregisters the two images. Changing the region or the normalization reuses the stored counts. Gray pixels in the asymmetry map have fewer than five weighted counts. Each image has its own logarithmic color scale; the asymmetry scale is linear. The 0.2 micrometre pixels limit spatial sampling. The Lab does not solve the electrostatic field and does not include material calibration, damage, space charge or reconstruction of the magnetic vector.

Physics tutorial

## PEEM: Thresholds & Magnetic Domains

**Background** Light falls on the whole field of a synthetic surface at once. You compare UV work-function thresholds, absorption spectra and images taken with opposite helicities, pull spectra out of the stored image stacks and correct for the incident flux before interpreting any magnetic contrast.

**Why it matters** The task is to measure the magnetic contrast of one domain. Use XMCD mode with monitor normalization at the phase-A resonance, and keep the selected region inside the upper-left domain without crossing an edge. Hold the image displacement to 0.05 micrometre or less and the image width to 0.3 micrometre or less, collect more than 1,000 counts in the region and bring the counting error below 0.035. Align the magnetization with the photon projection. Flux correction cannot repair drift.

Start with the essentials

- **Focus question**: Can PEEM tell magnetic contrast apart from brightness caused by uneven illumination?
- **One-sentence intuition**: Chemical, threshold and magnetic contrast each depend on different experimental settings. Correct for flux and look at local spectra before you decide why a region is bright.

### Core mathematical model

#### Photoemission yield near the UV threshold

$$
Y_{UV}\propto(h\nu-\Phi)_+^2
$$

This near-threshold yield assumes zero temperature. Image brightness also depends on how well the electrons are collected.

#### Intensities divided by the flux monitor

$$
I_\pm=\frac{C_\pm}{F_\pm}
$$

Dividing the counts by the incident exposure removes the flux imbalance. The two images still have unequal counting precision.

#### Asymmetry between the two helicities

$$
A=\frac{I_+-I_-}{I_++I_-}
$$

Under the assumed response, this ratio measures the dichroism along the beam projection. It does not give the full magnetic vector.

### Common difficulties

#### Brightness needs a model

**Typical misconception** If a region looks bright, I can tell directly what makes it bright.

**Better mental model** Chemical, threshold and magnetic contrast each depend on different experimental settings. Correct for flux and inspect the local spectra before you assign a bright region to a physical cause.

### Run the experiment

1. 01

   #### Predict the false contrast

   Look at the unequal-flux preset, then turn on monitor normalization.

   **What to observe:** Unequal illumination shifts the raw ratio. After normalization, the upper and lower domains show opposite signs again.

2. 02

   #### Separate chemistry from threshold

   Compare the absorption and UV presets. Move the region across the chemical boundary.

   **What to observe:** The two phases have different resonance positions and emission thresholds. The bright ridge they share is not a map of chemical concentration.

3. 03

   #### Test the magnetic interpretation

   Try low counts, drift and transverse magnetization before checking the target.

   **What to observe:** Noise, misregistered images or a small projection on the beam can each make the target fail.

Physical conclusion

Before you blame a bright region on chemistry, work function or magnetism, correct the flux and check its local spectrum.

Fields & matter · Starter path

## From a field to an electron microscope

Map an electric field and steer a charged particle. Then find the electron's wavelength and use electron beams to see a crystal and a surface.

[Start here → **Make an Electric Field Visible** Move the probe around a dipole and check that the field always points downhill on the potential landscape. Observe · 8 min](https://sandboxphysics.com/labs/electric-field/)

1. [1 Make an Electric Field Visible](https://sandboxphysics.com/labs/electric-field/)
2. [2 A Charge Bending through Fields](https://sandboxphysics.com/labs/charged-particle/)
3. [3 Electron Wavelength & Voltage](https://sandboxphysics.com/labs/electron-wavelength/)
4. [4 Electron Diffraction & Reciprocal Space](https://sandboxphysics.com/labs/electron-diffraction/)
5. [5 TEM Bright Field, Dark Field & SAED](https://sandboxphysics.com/labs/tem-mode-selector/)
6. [6 SEM Secondary-Electron Topography](https://sandboxphysics.com/labs/sem-topography/)

[View the full path →](https://sandboxphysics.com/topics/fields-and-matter/#starter-path)