Structural, optical and nanomechanical properties of (111) oriented nanocrystalline ZnTe thin films
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- Published on 17 June 2010
Structural, optical and nanomechanical properties of nanocrystalline Zinc Telluride (ZnTe) films of thickness upto 10 microns deposited at room temperature on borosilicate glass substrates are reported. X-ray diffraction patterns reveal that the films were preferentially oriented along the (1 1 1) direction. The maximum refractive index of the films was 2.74 at a wavelength of 2000 nm. The optical band gap showed strong thickness dependence. The average film hardness and Young's modulus obtained from load-displacement curves and analyzed by Oliver-Pharr method were 4 and 70 GPa respectively. Hardness of (1 1 1) oriented ZnTe thin films exhibited almost 5 times higher value than bulk. The studies show clearly that the hardness increases with decreasing indentation size, for indents between 30 and 300 nm in depth indicating the existence of indentation size effect. The coefficient of friction for these films as obtained from the nanoscratch test was ~0.4.
Structural, optical and nanomechanical properties of (111) oriented nanocrystalline ZnTe thin films, M.S.R.N. Kiran, S. Kshirsagar, M.G. Krishna and S.P. Tewari (2010), Eur. Phys. J. Appl. Phys. DOI 10.1051/epjap/2010071
Photoinduced Switching of Charge Carrier Mobility in Conjugated Polymers
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- Published on 26 June 2009
In this paper we investigate theoretically a mode of heating thick layers using a laser beam where the temperature of the layer propagates in a steady-state self sustained fashion from the bottom of the layer towards the surface and may exhibit a very steep front. The propagation of the thermal front happens at a constant speed, related to the intensity of the power flux. To achieve this heating mode the absorption coefficient of the layer has to remain low in weak temperatures and increase rapidly as a function of temperature in higher temperatures. Additionally, a significant temperature increase must be generated to trigger this propagation mode, for example through the presence of a strongly absorbing layer beneath the transparent layer. The mode is well suited to semiconductors, especially silicon . The theoretical approach is confirmed by a simulation in the case of a low doped silicon layer 150 micrometers thick above a highly doped substrate ; the low doped silicon is heated homogeneously at 1476 K by a 2E6Wcm-2 CO2 laser beam throughought the entire thickness in a timescale of 20µS.
Photoinduced Switching of Charge Carrier Mobility in Conjugated Polymers, M. Weiter, J. Navrátil, M. Vala and P. Toman (2009), Eur. Phys. J. Appl. Phys. DOI 10.1051/epjap/2009112
Evaluation of organic sub-monolayers by X-ray based measurements under gracing incident conditions
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- Published on 28 March 2009
The structural investigations of model organic systems like pentacene in the monolayer regime is very important for fundamental understanding of the initial nucleation process together with the electronic performance of transistor devices. The fact that the transistor performance saturates after deposition of some monolayers of the active organic material motivates a basic investigation of the submonolayer and monolayer regime in more detail. In this paper a method for the evaluation of the island formation and the island growth within the first monolayer is introduced. The method is based on X-ray scattering under grazing incident condition by means of specular X-ray reflectivity and off-specular X-ray scattering. From the specular reflectivity the electron density can be obtained which is directly correlated with the coverage of a submonolayer. Within the presented experiment coverages ranging from 7% up to 97% could be identified and are in excellent agreement with atomic force microscope results. Lateral information on the islands is obtained by rocking curve and detector scan measurements under grazing incident condition. The observed correlation peaks are evaluated by using Distorted Wave Born approximation, whereby mean island sizes ranging from 300nm to 1.5µm and mean island separation of about 2µm could be determined for the various samples. The obtained results encourages the use of this type of investigation for in-situ growth experiments to obtain a better understanding of the first monolayer formation.
Evaluation of organic sub-monolayers by X-ray based measurements under gracing incident conditions, O. Werzer, B. Satdlober, A. Haase, H.-G. Flesch and R. Resel (2009), Eur. Phys. J. Appl. Phys., DOI 10.1051/epjap/2009038
Laser heating of thick layers through a backwards, self-sustained propagation of a steep, steady state thermal front
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- Published on 05 January 2009
Presented paper reports on switching device based on reversible modulation of charge carrier mobility by photochromic additive distributed in polymer matrix. The light induced photochromic conversion of the additive is accompanied by significant increase of its dipole moment. The presence of the dipole moment induces change of electrostatic potential in its vicinity and shifts the site energies of individual polymer repeating units. Since the position and orientation of the photochromic additive with respect to the polymer chain are essentially random the effect results in broadening of the distribution of the transport states and consequently in the lowering of the charge carriers mobility. These notions suggested by quantum chemistry modeling are proved by experimental characterization of the optical and electrical switching properties of the suggested switch. The observed current-voltage characteristics showed reversible decrease of the currents after the photochromic switching of the additive to its metastable state with high dipole moment. This behaviour was explained on the basis of charge carrier mobility decrease due to the presence of charge traps. Impedance spectroscopy revealed a drop of the bulk conductivity when the polar state of the photochromic molecules was present. The induced conductivity decrease is proportional to the drop observed by current-voltage characterization.
Laser heating of thick layers through a backwards, self-sustained propagation of a steep, steady state thermal front, Michel Bruel (2009), Eur. Phys. J. Appl. Phys. DOI 10.1051/epjap:2008190
