Ján Ivančo

Increased thermal stability of Au/GaAs metal‐insulator‐semiconductor Schottky diodes with silicon nitride interfacial layer deposited by remote plasma‐enhanced chemical vapor deposition

The effect of the ultrathin interfacial layer of silicon nitride deposited by remote plasma‐enhanced chemical vapor deposition technique on the Schottky barrier characteristics of Au/n‐GaAs contacts is investigated. The changes of both capacitance‐voltage and current‐voltage characteristics, in dependence on the interfacial layer thicknesses are discussed and explained on the basis of the surface passivation. The influence of thermal annealing on the structure and electrical properties is also presented. In contrast to the very poor stability of the electrical characteristics of reference Au/GaAs contacts, structures with silicon nitride interfacial layers show much improved thermal stability with the minimum ideality factor for the silicon nitride interfacial layer being 9 A thick and annealed at 450u2009°C. The effect of silicon nitride interlayer as a diffusion barrier is confirmed by Auger electron spectroscopy analysis of both reference and silicon nitride containing structures.

Morphological and Electrical Properties of Stretched Nanoparticle Layers

To examine perspectives of nanoparticle films in the role of active elements in strain sensors, morphological and electrical properties of self-assembled Au nanoparticle monolayer prepared by modified Langmuir-Schaefer technique onto supporting Mylar foil were studied under elongation. Along the probing of electrical response (characterized by the gauge factor of about 60), the small-angle x-ray scattering (SAXS) characterization assessed an average interparticle distance change, which was shown to vary proportionally to the substrate elongation. The approach allowed to unambiguously address the mechanism of the deformation-resistivity transduction.

A study of Al/Si3N4/ultrathin Si/GaAs structures by DLTS and C-V measurements

Abstract We present a study on electrical properties of Al/Si3N4/Si/GaAs structure studied by deep level transient spectroscopy and capacitance–voltage technique. Here, the Si means an ultrathin silicon layer with thickness of approximately 2 nm. We have modelled the presented structure, while emissions from deep levels at Si/GaAs interface, traps in the bulk of GaAs and from a quantum well (QW) possibly formed by the Si interlayer, were taken into the account. Four deep traps were identified in the structure with the following thermal activation energies: 0.04, 0.19, 0.40 and 0.68 eV. The energy levels 0.4 and 0.68 are related with As defects, while the energy levels 0.04 and 0.19 are associated with the presence of the Si interlayer. Based on the emission behaviour, an existence of the QW is not probable (can be excluded). Rather, parameters of the Si-related energy levels suggest the levels are induced by δ-doping of GaAs.

Low-energy particle treatment of GaAs surface

Abstract Modification of high-doped GaAs surface by the interaction with RF plasma and a monoenergetic beam of similar chemical composition (Ar with a low content of H 2 ) was investigated via the evolution of optical, electrical and structural properties. A reduction in the free charge concentration in the GaAs surface region of ∼100 nm in thickness is concluded from Raman spectroscopy. In the processed samples, the surface electric field strength induced by a laser beam (photoreflectance technique) continually decreases with both the energy and fluence of impinging particles. The same results were obtained by evaluation of quasistatic C – V curves of corresponding MOS structures. They confirmed that longer exposure caused the formation of ∼100-nm-thick modified near-surface region with a decreased donor concentration. After the plasma irradiation, an ∼10-nm-thick outermost insulating layer was created in situ. The formation of textured polycrystalline grains with (100) orientation in the surface region was observed by X-ray diffraction.

Sensitivity and long-term stability of γ-Fe 2 O 3 and CoFe 2 O 4 nanoparticle gas sensors for NO 2 , CO and acetone sensing — A comparative study

Gas sensors based on γ-Fe₂O₃ and CoFe₂O₄ nanoparticles (NPs) were prepared by Langmuir-Schaeffer deposition onto Al₂O₃ and auxilliary Si substrates. NPs with the size of 6.4 nm (Fe₂O₃) and 7.6 nm (CoFe₂O₄) and polydispersity of 9 % were fabricated by chemical route. NP arrays were analyzed by GIXRD, SEM, TEM, DLS and ellipsometry. Fe₂O₃ sensors show high response of 38 for 500 ppb of strongly oxidizing NO₂. The response of CoFe₂O₄ sensors is 10 at 5 ppm of NO₂. Sensitivities are lower with reducing CO and acetone gases. After one year storage at room temperature, a 6 % decrease of response was found. The sensor sensitivities are discussed comparing with the best published results so far.

Control of interparticle distance of ordered iron-oxide nanoparticle assemblies by means of surfactant design

Effect of the nanoparticle effective size on interparticle distance in ordered nanoparticle films was investigated. To obtain different interparticle distance, the iron oxide nanoparticles (IONPs) with the size of 6.5u2005nm were functionalized by three kinds of surfactants: mixture of oleic acid/oleylamine, polybutylacrylate and polystyrene. Both hydrodynamic diameter and size distribution of nanoparticles in colloidal solution were measured by dynamic light scattering (DLS) in range from 8 to 17u2005nm. The ordering and homogeneity of the prepared Langmuir monolayers on solid surface was studied by scanning electron microscope (SEM) and atomic force microscopy (AFM). Method of pair correlation function was used for calculation of interparticle distance ensuing from SEM images. The distances from center to center of particles varied in the range from 6.75 to 11.75u2005nm. From the results it follows that we are able to change of interparticle distance on a solid substrate using of nanoparticles with different surfactant size.Effect of the nanoparticle effective size on interparticle distance in ordered nanoparticle films was investigated. To obtain different interparticle distance, the iron oxide nanoparticles (IONPs) with the size of 6.5u2005nm were functionalized by three kinds of surfactants: mixture of oleic acid/oleylamine, polybutylacrylate and polystyrene. Both hydrodynamic diameter and size distribution of nanoparticles in colloidal solution were measured by dynamic light scattering (DLS) in range from 8 to 17u2005nm. The ordering and homogeneity of the prepared Langmuir monolayers on solid surface was studied by scanning electron microscope (SEM) and atomic force microscopy (AFM). Method of pair correlation function was used for calculation of interparticle distance ensuing from SEM images. The distances from center to center of particles varied in the range from 6.75 to 11.75u2005nm. From the results it follows that we are able to change of interparticle distance on a solid substrate using of nanoparticles with different surfac...

Thermal stability of γ-Fe2O3 nanoparticles and their employment for sensing of acetone vapours

Stability of γ-Fe2O3 nanoparticles-based films upon an isochronal annealing in air was investigated by x-ray diffraction, differential scanning calorimetry, and thermogravimetry. The γ-α transformation temperature increased owing to the nanoscaling of Fe2O3; the higher stability of the γ phase was explained on the ground of the surface free energy of nanoparticles (with the size of about 6.4 nm). Further, chemiresistors based on the Fe2O3 nanoparticle bilayer prepared by the Langmuir-Schaefer method were fabricated and examined in terms of their sensitivity to acetone vapours down to 500 ppb concentration in air.

Cyclopean gauge factor of the strain-resistance transduction of indium oxide films

The resistance of indium-oxide covered polyethylene terephthalate foils (IO-PET) shows an extreme sensitivity to tensile strain. In terms of the deformation-resistance transduction, the gauge factor as high as about 60 000 was recorded upon the relative elongation up to 1%. Except the onset of deformation, the nearly exponential dependence of the resistance on strain suggests that the conductivity of the strained films is governed by tunnelling mechanism; this notion is supported by the formation of scattered cracks in the IO- PET film. The cracks are oriented perpendicularly to the strain vector and are characterized by a rather similar and uniform width. Appropriateness of the standard definition of the gauge factor for strain sensors, which are governed by tunnelling conductance, is critically discussed.

Nitrogen Dioxide and Acetone Sensors Based on Iron Oxide Nanoparticles

The Fe2O3 and CoFe2O4 nanoparticle-based Langmuir-Blodgett lms for sensingof nitrogen dioxide (NO2) and acetone vapours have been explored. Both the sensitivity of thechemiresistors and dynamic properties, such as the response/recovery time, have been probed independence of the number of nanoparticle monolayers and working temperatures. The responseof 23 at the NO2 concentration of 1 ppm has been monitored suggesting the pertinent sensitivityin the deep sub-ppm range, i.e. approaching the canine detection limit, and likewise implyingthe supposable detection of nitrate-based explosives.

Gas sensing properties and electrical resistance of Langmuir-Blodgett iron oxide nanoparticle arrays

Nanoparticle (NP) sensors are prepared by Langmuir-Blodgett deposition of colloid Fe₂O₃ or CoFe₂O₄ NPs onto alumina substrates. The thickness of the deposit is 1, 2, 4 or 7 NP monolayers (ML). NP arrays are analysed by GIXRD, SEM, SAXS, DLS and XANES. The average NP diameters are 6.4 nm and 7.6 nm for Fe₂O₃ and CoFe₂O₄, respectively. The response current of the sensor is measured at ≈ 400 °C in the mixtures of dry air with the monitored CO and NO₂ gases. The best relative response is 38 for 500 ppb of NO₂. The resistance of NP arrays was studied between 250 and 500 °C. With 2 ML Fe₂O₃ deposit the sheet resistance decreases with increasing temperature from 10¹¹ to 10⁹ Ω. Activation energy of the semiconductor type conductivity is 0.75 eV. High gas monitoring sensitivity of NP sensors is due to the big effective surface of Fe₂O₃ and CoFe₂O₄ NP arrays.