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Sandbox Physics

E23 · Frozen specimen workflow

Cryo-SEM: Preserve Before You Observe

Commit freezing, fracture, sublimation, coating, transfer and acquisition, then trace each artifact back to its cause.

Interactive modelCryo-SEM: Preserve Before You Observe
Assigned freezing preservation—\text{—}
Preparation structural retention—\text{—}
Remaining masking surface ice—\text{—}
Sublimated equivalent ice depth—\text{—}
Transfer frost depth—\text{—}
Committed coating thickness—\text{—}
Accumulated acquired dose—\text{—}
Assigned beam retention—\text{—}
Negative specimen potential—\text{—}
Accumulated recorded exposure—\text{—}
Selected-cell expected collected electrons—\text{—}
Experiment target—\text{—}

Physics tutorial

Cryo-SEM: Preserve Before You Observe

BackgroundCommit freezing, fracture, sublimation, coating, transfer and acquisition, then trace each artifact back to its cause.

Why it mattersCan you distinguish freezing damage, frost, charging and beam damage?

Start with the essentials

Focus question
Can you distinguish freezing damage, frost, charging and beam damage?
One-sentence intuition
The history of preparation is part of the image.

Core mathematical model

Freeze without inventing a guarantee

Pf=exp⁡ ⁣[−(tsℓf)4]P_f=\exp\!\left[-\left(\frac{t_s}{\ell_f}\right)^4\right]

Assigned preservation depth: 10 micrometres for plunge, 200 for high pressure. This surrogate is not a probability or a vitrification guarantee.

Surface ice exchange

h˙=1ρimw2πkB×[pwTg−psat,i(Ts)Ts]\begin{aligned}\dot h&=\frac{1}{\rho_i}\sqrt{\frac{m_w}{2\pi k_B}}\\&\quad\times\left[\frac{p_w}{\sqrt{T_g}}-\frac{p_{\rm sat,i}(T_s)}{\sqrt{T_s}}\right]\end{aligned}

Positive thickness means frost deposition; negative means sublimation. Gas and specimen temperatures are distinct. Reservoirs stay fixed.

Acquisition leaves a record

Dtotal=∑jDjB=exp⁡(−Dtotal/Dc)\begin{aligned}D_{\rm total}&=\sum_j D_j\\B&=\exp(-D_{\rm total}/D_c)\end{aligned}

Every acquisition adds dose. Assigned characteristic damage dose is ten electrons per square nanometre; display gain does not change it.

Common difficulties

Model boundaries

Typical misconceptionA passed task is a calibrated instrument recipe.

Better mental modelTeaching workflow, not a preparation protocol or measured micrograph. Freezing preservation, coating conductivity and beam damage are assigned proxies. Ice exchange uses a flat-interface, unit-accommodation reservoir law and Murphy–Koop saturation; no heat transfer, nucleation, fracture mechanics, deposition microstructure or calibrated kinetics. Each step records its settings; later controls cannot repair prior damage. Dimensions and hardware are schematic.

Run the experiment

  1. 01

    Freeze and fracture

    Reset, select a freezing method and thickness, then commit freeze and fracture.

    What to observe: Changing method after freezing cannot repair ice crystal damage.
  2. 02

    Reveal and coat

    Choose sublimation temperature and time, commit etching, then coat the exposed face.

    What to observe: Too little ice removal hides detail; too much loses structure.
  3. 03

    Protect the transfer

    Set cold-stage temperature, residual water pressure and transfer time, then commit transfer.

    What to observe: Frost contamination is distinct from crystals created during freezing.
  4. 04

    Acquire sparingly

    Acquire, check the target, then acquire again or change display gain.

    What to observe: A new image adds irreversible dose; display gain does not.