Sublimation Of Materials Research Articles

Modifications in the microscopic structure of Ru and Pb phthalocyanine films by intermolecular interactions

Ruthenium and lead phthalocyanine (RuPc, PbPc) thin films were characterized by photoelectron spectroscopies (XPS and UPS), optical spectroscopies (UV-Vis and photocurrent) and were prepared by mass-spectrometer-controlled sublimation of ultrapure materials using Ag substrates. Phthalocyanine molecules can be sublimed without fragmentation in the gas phase. However, there are strong intermolecular interactions in Knudsen-deposited films even for substrate temperatures of 300 K which cause the formation of dimers and excess metal atoms. This results in specific changes of the ideal stoichiometric composition, the electronic structure and the interaction with oxygen.

Radiation enhanced sublimation of carbon and carbon related materials

Radiation enhanced sublimation of carbon and carbon related materials

Radiation enhanced sublimation of carbon and carbon related materials

Above 1200 K ion bombardment of carbon materials results in an anomalous emission of carbon atoms. The present experimental basis of this effect, called Radiation Enhanced Sublimation (RES), is described. The current model attributes the RES of carbon materials to the diffusion of radiation produced interstitials to the graphite surface from where they evaporate easily. The basic features of this model are presented and compared with experimental observations. The present knowledge on the influence of doping carbon materials with metals on the RES emission of carbon atoms is shown.

Radiation-Enhanced Sublimation of Graphite Materials due to Hydrogen Ions

For isotropic graphite, C/C composite and pyrolytic graphite, yields of Radiation-Enhanced Sublimation (RES) due to hydrogen ion bombardment were measured in the temperature range up to 2000K by weight loss method. Graphite samples were irradiated by H3+ ions with the energy of 4.5keV and fluences from 1019H/cm2 to 1020H/cm2. The RES yields measured showed no clear differences among these three types of isotropic graphite and the pyrolytic carbon. Namely, the RES did not depend on physical properties and/or structure of graphite. The activation energy corresponding to the RES was approximately 0.8eV for the isotropic graphites. The angular dependences of sputtering at various temperature were also examined. The result showed that the physical sputtering yield increased with ion-incident angle, but the chemical sputtering and RES yields were approximately independent of the incident angle.Raman spectra of the samples as-received and irradiated in RES regime were examined. While R-number (=I1360/I1585) before irradiation varied with the kind of graphite samples, the value became almost the same for every graphite sample irradiated at elevated temperature. In the RES regime, the sample irradiated at higher temperature showed better crystallinity than that at lower temperature. The change of surface morphology due to irradiation was also examined by Scanning Electron Microscopy.

Optical Material Problems of Interplanetary Space

The successful flights of Mariners II and IV demonstrated that optical systems can survive and operate after months of exposure to interplanetary space. Special considerations must be taken in designing for deep space. The phenomena of sublimation and deterioration of solid materials in deep-space vacuum influence the selection of all materials used in the optical system including metals and organic compounds. Three basically different approaches of thermal design are available to the designer. Each method is capable of maintaining focus throughout large temperature excursions. Micrometeoroid and radiation damage are not major problems. The material selection for and thermal design of the Mariner IV television camera optical system is described.