Surface Barrier 1953 Cool and Inspect Crystal

# Cool and Inspect the Crystal: Two Independent Gates, Now Guarding Two Multiplied Specs Instead of One

This step still runs the same two-part gate the alloy-junction route already established — survive the cooldown mechanically, then measure what the pull actually delivered electrically — and the second gate now carries the weight step two attached to it three steps ago. A crystal that passes both checks here is not just cleared for one downstream resistance target; it is cleared against the pair of multiplied specs, base body resistance and base-spreading resistance, that this process's later etching step will read out of the same resistivity number.

## 1. Thermal Stress Still Threatens the Crystal Before Any Electrical Question Is Even Asked

$$\sigma_{\text{th}}(x) = E\, \alpha_{\text{th}}\, \left.\frac{dT}{dx}\right|_x$$

As in the alloy-junction route, uneven cooling across the rod's cross-section generates real mechanical stress $\sigma_{\text{th}}$ from thermal gradient $dT/dx$ alone, with no electrical cause whatsoever. A crystal that cracks or over-accumulates dislocations during cooldown fails this gate regardless of whether step three's resistivity drift stayed inside its tolerance band — a purely mechanical outcome, unchanged by anything specific to surface-barrier processing, because cooldown physics does not know yet that this crystal will later be etched rather than alloyed.

## 2. Real Diagram: The Same Two Gates, a Heavier Second One

Mechanical Survival, Then a Measurement That Decides Two Specs identical two-gate sequence to the alloy-junction route — the second gate's stakes are what changed gate one — mechanical, during cooldown crack or reject — identical to alloy-junction's gate gate two — electrical, four-point probe measures ρ(g), feeds body R AND spreading R one measurement, doubled downstream consequence same probe sweep, same tolerance band — the number it checks now guards two specs instead of one

## 3. The Probe Sweep Still Measures the Band, But Now Against a Doubled Downstream Risk

$$\rho_{\text{meas}}(g) \overset{?}{\in} \left[\rho_0(1-\delta_{\text{tol}}),\ \rho_0(1+\delta_{\text{tol}})\right]$$

A four-point probe sweep converts step three's predicted drift into the same kind of measured $\rho_{\text{meas}}(g)$ curve the alloy-junction route produces, checked against the identical tolerance band. What differs is only what a flagged section now threatens: in the alloy-junction route, an out-of-band section costs one spec if used anyway; here, it costs two — base body resistance and, once a later step's etch geometry multiplies it, base-spreading resistance as well. This step still does not decide what to keep, exactly as in the alloy-junction route; it only produces the measured data the next step will act on, now carrying a sharper penalty for any section let through at the edge of the band.

Measured Resistivity, Now Read Against a Doubled Stake the same probe data as the alloy-junction route, carrying a sharper penalty at the margins position along rod → measured resistivity tolerance band from step three flagged — costs body R and spreading R together step five draws the usable/unusable cutoff from this same curve, now against a sharper margin

## Cool and Inspect the Crystal's Place in the Process Lineage

Cooling and inspecting the crystal is step four of Philco's surface-barrier process, immediately after the single crystal has been grown and before any section of it is selected for use — procedurally identical to the equivalent step in this project's alloy-junction series. The structural gate is unchanged; the electrical gate still produces the same kind of measured resistivity curve. What this step hands forward differs only in weight: step five, selecting usable crystal sections, now draws its usable/unusable cutoff knowing that any section let through at the edge of the band pays twice downstream rather than once.

Take surface barrier 1953 cool and inspect crystal further

Ask the copilot about this term, or have our engineers assess it against your process.

Ask CFSGPT about this → Request a technical assessment → Open the CFS app