| 1. |
- Abom, A.E., et al.
(författare)
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Influence of gate metal film growth parameters on the properties of gas sensitive field-effect devices
- 2002
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 409:2, s. 233-242
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of Pt have been grown as gate metals on the oxide surface of gas sensitive field-effect devices. Both electron beam evaporation and dc magnetron sputtering has been used. The energy of the impinging Pt atoms, the substrate temperature and the thickness of the Pt film were used as parameters in this study. The influence of the growth parameters on the gas response has been investigated and compared with the properties of the films, studied by transmission electron microscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The conditions during growth of the Pt film are found to have a large impact on the properties of the device. As expected, crystallinity, morphology and the metal/substrate interfacial structure are also affected by processing parameters. Three different growth processes stand out as the most promising from gas sensor considerations, namely room temperature evaporation, sputtering at high pressures and sputtering at high temperatures. The correlation between gas responses and properties of the gas sensitive layer is discussed. © 2002 Elsevier Science B.V. All rights reserved.
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| 2. |
- Almer, J, et al.
(författare)
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Microstructure, stress and mechanical properties of arc-evaporated Cr-C-N coatings
- 2001
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 385:1-2, s. 190-197
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Tidskriftsartikel (refereegranskat)abstract
- The relationships between coating microstructure and properties in the Cr-C-N system have been investigated as a function of composition and post-deposition annealing. Coatings of varying compositions were grown using arc-evaporation, by varying the reactive gas flow ratio fR = f(C2H4)/f(N2) from 0 to 0.2, and were found to consist primarily of the cubic d-Cr(C,N) phase. Changes in both the unstressed lattice parameter, ao, and X-ray diffraction background intensity indicate that both the carbon concentration within the d-phase and amorphous/crystalline content increases with fR. Increasing fR also decreases the magnitude of the compressive biaxial residual stress, from approximately 6 to 1 GPa, while increasing both the inhomogeneous stress and thermal stability. The elastic modulus and hardness of as-deposited coatings were determined from nanoindentation to be 320 and 23 GPa, respectively, for moderate carbon concentrations (fR=0.05). Concurrent variations in microstructure and hardness with post-deposition annealing indicate that the as-deposited hardness is significantly enhanced by the microstructure, primarily by lattice defects and related stresses (microstresses) rather than average stresses (macrostresses).
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| 3. |
- Arias, A.C., et al.
(författare)
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Use of tin oxide thin films as a transparent electrode in PPV based light-emitting diodes
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 371:1, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- Tin oxide (TO) thin films, nominally undoped, have been used as electrodes in poly(p-phenylene vinylene) (PPV) based organic electroluminescent devices. The evolution of the crystallinity and the electrical resistance of TO films submitted to the PPV thermal conversion conditions, have been investigated. It has been found that the electrical resistance is decreased whereas the crystallinity of the film is increased. It is shown in this work, that the photoluminescence of PPV converted on top of TO substrates is not as quenched as it is when converted on top of indium-tin oxide (ITO) substrates. The quantum efficiency of light-emitting diode is 0.07% at 17 V forward bias. It is also shown that the work function of TO films is very stable to different cleaning procedures, in contrast with previous results obtained for ITO films.
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| 4. |
- Arwin, Hans
(författare)
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Ellipsometry on thin organic layers of biological interest : Characterization and applications
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 377-378, s. 48-56
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Tidskriftsartikel (refereegranskat)abstract
- The thickness resolution and in situ advantage of ellipsometry make this optical technique particularly suitable for studies of thin organic layers of biological interest. Early ellipsometric studies in this area mainly provided thickness quantification, often expressed in terms of surface mass. However, today it is possible to perform monolayer spectroscopy, e.g. of a protein layer at a solid/liquid interface, and also to resolve details in the kinetics of layer formation. Furthermore, complicated microstructures, like porous silicon layers, can be modeled and protein adsorption can be monitored in such layers providing information about pore filling and penetration depths of protein molecules of different size and type. Quantification of adsorption and microstructural parameters of thin organic layers on planar surfaces and in porous layers is of high interest, especially in areas like biomaterials and surface-based biointeraction. Furthermore, by combining ellipsometric readout and biospecificity, possibilities to develop biosensor concepts are emerging. In this report we review the use of ellipsometry in various forms for studies of organic layers with special emphasis on biologically-related issues including in situ monitoring of protein adsorption on planar surfaces and in porous layers, protein monolayer spectroscopy and ellipsometric imaging for determination of thickness distributions. Included is also a discussion about recent developments of biosensor systems and possibilities for in situ monitoring of engineering of multilayer systems based on macromolecules.
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| 5. |
- Baudin, M., et al.
(författare)
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Molecular dynamics simulations of an Al2O3(0001 +/-, 0-10(II))/CeO2 (011 +/-,01-1(II)) interface system
- 2001
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 401:02-jan, s. 159-164
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Tidskriftsartikel (refereegranskat)abstract
- Constant stress, constant temperature (10 K, 300 K) molecular dynamics simulations were carried out with shell-model potentials for an infinite composite ceria-alumina slab with two free surfaces [alpha -Al2O3 (0001) and CeO2(011) and their opposite counterparts]. The interface introduces considerable structural and dynamical changes, both at the slab surfaces and in the center of the slab. Structurally, both oxide surfaces become effectively oxygen-terminated and the surface structures become disordered close to the interface. Dynamically, in the region near the 'alumina surface/ceria surface/alumina-ceria interface' 3-phase junction the ionic motion is considerably enhanced. Thus, in the interface region, the ionic mean-square displacements increase 2-3 times compared to the pure slabs. Moreover, the ions at the interface participate in a new kind of motion, not present in the pure oxide slabs: large occasional, but frequently reoccurring, back-and-forth ionic motions take place with square-amplitudes as large as similar to0.70 Angstrom (2).
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| 6. |
- Chen, Weimin
(författare)
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Applications of optically detected magnetic resonance in semiconductor layered structures
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 364:1, s. 45-52
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Tidskriftsartikel (refereegranskat)abstract
- A short introduction is given on the physics, method, capabilities and limitations of the optically detected magnetic resonance (ODMR) technique. The advantages of the optical detection method in terms of sensitivity and of its direct probe in recombination processes, as compared with the traditional spin resonance technique, will be demonstrated. The importance of these advantages for the ODMR applications in semiconductor layered and quantum structures will be emphasized. The ability of the ODMR technique to provide important information on physical properties of semiconductor layered structures will be highlighted. These include chemical identification, electronic and geometric structure of both radiative and non-radiative defects, carrier recombination mechanism, electronic excitation, etc. Representative cases from CVD-SiC and MBE-Si/SiGe based layered structures will be discussed as examples. The most recent progress, on-going efforts and prospects in achieving unprecedentedly high spectral, time and spatial resolution of the ODMR technique will also be outlined.
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| 7. |
- Chirita, Valeriu, et al.
(författare)
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Cluster diffusion and surface morphological transitions on Pt (111) via reptation and concerted motion
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 370:1, s. 179-185
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Tidskriftsartikel (refereegranskat)abstract
- Embedded-atom molecular dynamics simulations were used to follow the diffusion dynamics of compact Pt clusters with up to 19 atoms on Pt (111) surfaces. The results reveal a novel cluster diffusion mechanism, involving successive shear translations of adjacent subcluster regions, which give rise to reptation, a snake-like gliding motion. We show that for compact clusters with 4 to 6 atoms, this mechanism competes energetically with that of island diffusion through concerted motion. However, as the cluster size increases from > 7 to ? 20 atoms, reptation becomes the energetically favored diffusion mechanism. The concerted shear motion of subcluster regions, leading to reptation, is also shown to play a significant role in dendritic-to-compact morphological transitions of Pt island.
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| 8. |
- Cobet, C., et al.
(författare)
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Optical properties of SiC investigated by spectroscopic ellipsometry from 3.5 to 10 eV
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 364:1, s. 111-113
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Tidskriftsartikel (refereegranskat)abstract
- In this work we present the dielectric function of hexagonal 4H- and 6H-SiC polytypes as well as the cubic 3C-SiC polytype in the energy range from 3.5 to 10 eV measured by spectroscopic ellipsometry. We operated with synchrotron radiation at the Berlin electron storage ring BESSY I. Additionally the samples were investigated by atomic force microscopy to correct the measured dielectric function for the influence of surface roughness. The experimental results are compared to theoretical calculations.
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| 9. |
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| 10. |
- Donchev, V., et al.
(författare)
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Photoluminescence study of AlAs/GaAs superlattices containing enlarged wells
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 364:1, s. 224-227
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence (PL) spectra of MBE grown short-period AlAs/GaAs superlattices with one or two enlarged wells (5 and 12 nm) have been measured at 2 K. Sharp PL peaks corresponding to excitonic transitions between the lowest electron and heavy-hole states in the enlarged wells are observed. The excitonic transition energies are calculated by means of an envelope function based model, taking into account the exciton binding energies. The model incorporates a smooth potential at the interfaces, which is represented by a diffusion potential, the diffusion length being a parameter. The calculated and experimentally observed excitonic transition energies agree well if diffusion lengths of 3.5 and 4.5 monolayers are considered in the samples with and without a buffer layer, respectively. These values are consistent with the complicated nature of the growth kinetics and mechanisms of quantum heterostructures. The PL spectra reveal also complicated structures connected with the superlattice. Their qualitative discussion confirms the smooth potential model. Thus, an attempt is made to extend the analysis of complicated AlAs/GaAs heterostructures towards real interfaces, which is essential for advanced device fabrication.
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