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Original Articles

Formation and Properties of Sub-Image and Latent-Image Silver Specks. Part I: Thermodynamics of Silver Speck FormationFootnote

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Pages 12-17 | Received 14 Aug 1976, Published online: 22 Jul 2016
 

Abstract

The formation of latent image specks has been discussed so far as a sequence of steps (Ag1,→Ag2 -→Ag3-→ .) which allegedly leads from precursors (Ag1, Ag2,...) finally to full image centres. This reaction scheme demands that a continuous growth of silver specks by electron capture regardless of the size of the specks takes place as the result of exposure. Sub-image specks obtained by a weak pre-exposure, or reduction sensitization specks are believed to be such precursors of latent image. If silver speck formation is treated as a process of phase formation, calculations suggest that such a continuous growth does not take place: Very small specks (e.g.Ag1, Ag2,) tend to capture holes and are thus destroyed by exposure. Growth by electron capture requires a minimum size of the silver specks which depends on the value of the exposure-induced supersaturation in the crystal.

resume

La formation des germes d'image latente a été envisagée jusqu'à présent comme une suite d’étapes (Ag,-> Ag2-> Ag3-s-. ..) qui, prétendument conduit des précurseurs (Aglf Ag. . . .) aux centres complets. Ce schéma réactionnel implique qu'indépendamment de leurs dimensions, les germes argentiques croissent de façon continue par capture d'électrons lors de l’exposition. Les sous-germes provenant d'une préexposilion faible et les germes obtenus par sensibilisation par réduction sont considérés être les précurseurs de l’image latente.

Ën fait, le calcul assimilant la formation des germes à un processus de formation de phase suggère qu’une telle croissance continue ne peut avoir lieu, car les très petits germes (par exemple Ag,, Ag2) ont tendance à piéger les trous positifs et, de ce fait, à disparaître au cours de l’exposition. La croissance par capture d’électrons ne peut avoir lieu que si les germes d’argent ont une taille minimale qui dépend de la valeur de la sursaturation induite dans le cristal par l’exposition.

Zusammenfassung

Die Bildung von Latentbildkeimen ist bisher als eine Folge von Schritten (Ag, -> Ag2 Ag3 diskutiert

worden, die über angebliche Vorläufer wie Ag,, Ag2, schließlich zum Latentbildkeim führen sollen. Dieses Schema setzt voraus, daß alle Keime, unabhängig von ihrer Größe, bei Belichtung durch Elektroneneinfang monoton wachsen können. Durch unterschwellige Belichtung oder durch Reduktionsreifung erzeugte Subkeime wären demnach solche Vorstufen. Wenn die Silberkeimbildung als ein Prozess der Phasenbildung behandelt wird, ergeben die Berechnungen, daß ein monotones Wachstum nicht stattfinden kann: Die kleinsten Silberkeime (Ag,, Ag.,) reagieren mit Defektelektronen und werden infolgedessen bei der Belichtung abgebaut. Um durch Elektroneneinfang wachsen zu können, müssen die Silberkeime eine Mindestgröße besitzen, die von der durch die Belichtung bewirkten Übersättigung im Kristall abhängt.

Riassunto

La formazione dei germi di immagine latente è stata finora descritta come una successione di stadi (Ag,-* Ag, * Ag3 > .. .) che porta presumibilmente dai precursori (Ag,, Ag2 . . .) allo stadio finale completo dei centri di immagine.

Questo schema di reazione richiede che, come conseguenza dell’esposizione, abbia luogo una crescita continua per cattura di elettroni dei germi di argento indipendentemente dalla dimensione del germe.

Se la formazione del germe di argento viene trattata come un processo di formazione di fase, i calcoli suggeriscono che tale crescita continua non ha luogo.

I germi molto piccoli (p. es. Ag,, Ag2) tendono a catturare buche e conseguentemente vengono distrutti nel corso dell'esposizione.

La crescita per cattura di elettroni richiede una dimensione minima dei germi di argento la quale dipende dal valore della supersaturazione nel cristallo prodotta dall'esposizione.

Notes

Here and throughout the series of these communications-unless otherwise stated-the charge of silver aggregates refers to an isolated particle whereby the influence of the surrounding lattice is neglected. So e.g. a neutral silver atom on a lattice site which here is denoted Ag has actually a negative charge related to the lattice. The same silver atom in an interstitial position however would actually have the charge zero related to the lattice.

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