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Sublimation Growth of Organic Charge Transfer Salt Crystal Films and Bulk Crystals

IP.com Disclosure Number: IPCOM000081552D
Original Publication Date: 1974-Jun-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 56K

Publishing Venue

IBM

Related People

Braccini, RB: AUTHOR [+4]

Abstract

Preparatory techniques for organic charge transfer salt (OCTS) crystals have largely been confined to solution growth methods. Experience has shown that in most cases solution growth of OCTS crystals proceeds under conditions of extreme supersaturation, resulting in small, highly defective crystals with dendritic-like growth habits.

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Sublimation Growth of Organic Charge Transfer Salt Crystal Films and Bulk Crystals

Preparatory techniques for organic charge transfer salt (OCTS) crystals have largely been confined to solution growth methods. Experience has shown that in most cases solution growth of OCTS crystals proceeds under conditions of extreme supersaturation, resulting in small, highly defective crystals with dendritic-like growth habits.

A growth technique for substance-supported OCTS epitaxial single crystals, as well as bulk crystals, under conditions of controlled supersaturation from the vapor phase is herein shown. This method appears to have wide application to the production of OCTS epitaxial films and crystals for experimental purposes, as well as possible technological applications. The technique has been applied to the growth of (TTF)(TCNQ)* and (ATTF)(TCNQ)*, two OCTS which are currently of intense interest as possible model systems for the synthesis of high- temperature superconductors.

The experimental arrangement is shown in the figure. The OCTS 2 is contained in an evacuated tube 2 which encloses a metal block substrate holder 3, which can be cooled by a N(2) flow. The apparatus is heated to the sublimation temperature of the OCTS 1 at typically 10/-4/ - 10/-5/ mm Hg pressure. Soon after the sample 1 and substrate 4 have equilibrated at the bath temperature (approx. 100 degrees C for (TTF) (TCNQ) and (ATTF)(TCN2)), a thin deposit 5 of the OCTS can be observed on the cold section of the inner tube 6 at a level above the surface of the bath fluid 7.

It should be noted that this arrangement is the critical feature of the method being used - it is a hot wall sublimation epitaxy technique, in which the equilibrium vapor pressure of the OCTS is maintained throughout the chamber (with the exception of the top). Thus, a controlled degree of supersaturation at the substrate surface is achieved, by adjusting the flow rate (and/or temperature) of the cooling gas impinging upon the metal block substrate holder 3.

In this manner, single crystal films of (TTF) (TCNQ) and double-positioned epitaxial films of (ATTF)(TCNO) have been grown on (211) and (100) NaCl substrates at temperatures between 70-95 degrees
C. These films are typically approx. 1 cm/2/ x 1-20 mu thick with the <010> (high conductivity) axis of these salts lying along <110> NaCl. Epitaxy was confirmed by SEM, electron microsco...