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_th(x) = E alpha_th (dT)/(dx)|_x

As in the alloy-junction route, uneven cooling across the rod's cross-section generates real mechanical stress sigma_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_meas(g) overset(?)(in) [rho_0(1-delta_tol), rho_0(1+delta_tol)]

A four-point probe sweep converts step three's predicted drift into the same kind of measured rho_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.

Go deeper with CFSGPT

Get AI-powered deep-dives, save terms, and run advanced simulations — free account.

Create Free Account