Ordered arrays of ∼4.5 nm diameter silver nanocrystals passivated with dodecanethiol show remarkable thermal stability at temperatures up to 975 K. Defects in the ordered-assembly were the first areas to show signs of melting while much of the structure remained intact. The mechanism for their stability is attributed to the unusually strong inter-nanocrystal bond formed by the interpenetration of thiol chains between neighboring nanocrystals within the nanocrystal superlattice. Individually dispersed nanocrystals show stability up to 800 K while some persist until 975 K.The potential application of nanoscale materials in fields ranging from biology to electronics has spurred remarkable interest and investigation into the preparation and characterization of identical, isolated, nanometer-scale entities composed of materials such as metals, 1,2 semiconductors, 3 magnetic materials, 4 and a wide variety of others. 5,6 Applications in catalysis and biological tagging 7 and the possibility of nanometer-sized magnetic domains for ultrahigh-density recording media 4 are just a few of their many possible uses. The subsequent organization of identical passivated nanometer-scale objects into micron-scale ordered arrays gives encouragement to the use of these novel materials particularly in regards to their collective nonlinear optical properties where stability at high temperatures is necessary. 8 The studies of nanometer-sized crystallites over the past twenty years and more recently their composite structures have been numerous. 9,10 Various methods are being used to produce these materials in such abundance as to allow their characterization by means of well-known chemical and physical techniques. 6,11,12 The solution phase, gas (aerosol) phase, and reverse-micelle methods have been the most popular nanocrystal production techniques lately.An important factor in the production of nanocrystals is the ability to keep them physically isolated from one another. Many different types of systems have been used for nanocrystal passivation as well as exchange of one surfactant for another. 3,7,13 Factors such as the binding energy of the headgroups to the nanocrystal surface, 14 how the exposed tails affect the solubility and reactivity of the passivated nanocrystal (i.e., its functionality), 10 the effect of the passivation agent on the electronic and optical properties of the nanocrystal core, the electronic properties of the surfactant material itself, 15 and, further, the agent's ability to bind or link nanocrystals together both structurally and electronically [16][17][18] are all very important conditions placed on a material that will allow the nanocrystal to be stable and isolated yet not affect its core material's properties. Here we present an in-situ temperature analysis of the aforementioned nanocrystals and their superlattices and show that not only do individual passivated silver nanocrystals supported on an amorphous carbon film remain stable at temperatures near 800 K, but also that the silver nanocrystal superc...