1,721,044 research outputs found
Thermal model of Knudsen cells for organic molecular beam deposition
No full textKnudsen cells used for molecular beam deposition of organic materials are usually derived from the ones employed for conventional epitaxy of inorganic semiconductors. However, organic molecular materials need rather low evaporation temperatures and a very precise temperature control in the
range from 100 to 400 °C. Therefore, a thermal model of the cell is needed, which, taking into account the peculiarity of organic molecular beam deposition, gives the thermal dynamics of the cell
and can be used for developing accurate algorithms for thermal programming and control. In this article such a model is developed and fully assessed through a comparison with experimental results; on this basis, all information necessary for precisely controlling and programming Knudsen
cells for organics is obtained
Measurement of carrier transport and injection in metal-free tetraphenylporphyrin
No full textSubmitted t
Incommensurate epitaxy of tetrathiophene on potassium hydrogen phthalate: insights from molecular simulation
No full textBoron accumulation at epi-substrate silicon interface during epitaxial growth
No full textsilicio epitassiale, impurezze, assorbimento otticoBoron accumulation was observed close to the interface between an epitaxially grown silicon layer and a silicon substrate wafer and then analyzed. It was concluded that boron contamination interacting with the surface oxide on wafers led to boron accumulation close to the interface. Such accumulation is shown to occur for epilayers of standard thickness (approximately 10 μm), with boron being electrically unactive
Experimental assessment of nonergodicity in tetracene single crystals
No full textDielectric spectroscopy is applied to the study of phase transitions in the range from room temperature down to 12 K in single crystals of tetracene (TEN), a well-known material which, like most organic semiconductors, shows polymorphism. The present analysis, through proper experimental procedures, permits us to identify the wide range (T > 150 K) of instabilities and of strong hysteresis effects as clear evidence of a nonergodic state and then also to clarify some open questions, first of all the role of the sample thermal history, including the temperature variation rate and some apparent sample dependence of the results. Furthermore evidence is obtained of two transitions at 144 and 45 K
Electrical characterization of organic semiconductors by transient current methods
No full textThis paper presents a method for characterizing the transport properties of organic semiconductors by means of large-signal electrical transients. For validating the method, poly(phenylene-vinylene) (PPV) was chosen as a test material, thanks to its widely investigated properties. Large voltage steps are applied to Au/PPV/Au test structures and, from the resulting current transient, the carrier mobility is measured. Transient phenomena are shown to give insight on the physical properties of the material and on the technological characteristics of the device, while requiring a simpler test system in comparison to other methods, like impedance spectroscopy and time-of-flight measurements
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