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1
Content available remote

Elastic Vibrations of Planar and Deterministic Rough Surfaces

100%
Djafari Rouhani B., Khelif A., El Boudouti E., Akjouj A., Dobrzynski L.
Acta Physica Polonica A
|
1996
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vol. 89
|
issue 2
129-137
EN
We present a few recent or new theoretical results about surface acoustic localized and resonant modes associated with planar or deterministic rough surfaces. The following composite systems are considered: one or two adlayers deposited on a semi-infinite substrate and wires or grooves integrated near a planar surface. The surface modes can be obtained as well-defined features of the density of states resulting from a calculation of the Green functions in these heterostructures. In this work, the materials are described in the framework of the elasticity theory.
2
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Surface True and Leaky Waves in Subsonic and Supersonic Regions. Explicit Solution of a Simple Model

100%
Trzupek D., Zieliński P.
Acta Physica Polonica A
|
2010
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vol. 117
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issue 4
570-573
EN
A simple model of a surface of a 2D continuum is shown to exhibit subsonic and supersonic surface resonances (leaky waves, pseudosurface waves), i.e. finite-lived excitations, along with usual surface waves (true subsonic surface waves). The physical meaning, controversial in the existing literature, of the surface leaky waves in both regions is discussed by a thought experiment in which a stimulus adjusted to the resonance parameters is applied to the surface. The infinite displacement-stimulus ratio in the long-time limit then is shown to be in power in all the cases of surface states and a finite amplitude of the leaky waves is demonstrated despite an apparent divergence suggested by their algebraic form.
3
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Applicability of Different SAW Oscillators' Topologies for High Frequency Gas Sensors Construction

100%
Pasternak M.
Acta Physica Polonica A
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2010
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vol. 118
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issue 6
1232-1234
EN
In general, there are three possible kinds of surface acoustic wave devices that may be applied for high frequency gas sensor construction: delay lines, one- and two-port resonators. Choice among them depends on individual preferences and sometimes it is the matter of chance. In the paper the key differences among the surface acoustic wave devices important from the gas sensors technology point of view are described.
4
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Pre-Melting in Cubic Structure with Relaxation

100%
Gwizdałła T., Czerbniak J.
Acta Physica Polonica A
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1998
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vol. 94
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issue 5-6
785-793
EN
We study the effect of melting of well-defined crystal surface within the frame of theory of atomic vibrations in harmonic approximation. We find that for two types of cubic crystal lattice: face centered cubic and body centered cubic, we may expect the existence of pre-melting. It is also shown that the occurrence or absence of surface melting depends strongly on the relaxation of lattice constant.
5
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Impulse and Resonant Response in Systems Showing Secular and Leaky Excitations

80%
Sobieszczyk P., Gałązka M., Trzupek D., Zieliński P.
Acta Physica Polonica A
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2013
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vol. 124
|
issue 6
1020-1024
EN
A model consisting of a string embedded in an elastic medium and terminated by a harmonic oscillator has been studied in the frequency and time domains to elucidate the physical effects of supersonic and subsonic leaky waves as well as that of true surface waves. A supersonic leaky wave manifests itself by a resonant maximum of the local density of states within the band of bulk waves and by an anomalous dispersion of the real part of the frequency dependent response function. The time domain impulse response then contains mainly resonant contribution from the poles of the response function in analogy to ordinary resonances. True surface waves show generally analogous behaviour. Here, however, the phenomenon is governed by dissipation mechanisms different from the radiation into the bulk. An important difference is that the impulse response contains equilibrated contributions due to the poles and due to the stop frequency gap in the case of true surface waves. The main manifestation of a subsonic leaky wave, i.e. a surface resonance with the frequency situated in the stop gap, is a sharp peak of the real part of the frequency-dependent response function just at the bottom of the bulk waves band. This is in certain analogy with a large reactive power in electric circuits. A strong destructive interference of the resonant part of the impulse response with the part due to the gap makes the time domain response fast attenuated.
6
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An Analytical Solution of Rayleigh Wave Propagation Problem on Elastic Substrate with Nonconductive Viscoelastic Layer

80%
Pasternak M.
Acta Physica Polonica A
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2009
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vol. 116
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issue 3
371-374
EN
The Rayleigh wave propagation problem in the elastic substrate-viscoelastic layer interface was analysed in the paper. The fundamental solution of the problem has been found in the Fourier-Laplace space using Biot viscoelastic solid model with Maxwell relaxation time. The space-time form of the solution was obtained using Cagniard-deHoop method. The solution presented in the paper seems to be applicable to surface acoustic waves gas sensors with polymeric (viscoelastic) layer.
7
Content available remote

A New System for Acoustoelectronic Gas Sensors Analysis

80%
Jasek K., Miluski W., Pasternak M.
Acta Physica Polonica A
|
2013
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vol. 124
|
issue 3
445-447
EN
Typical approach to the surface acoustic waves sensors response analysis is based on the use of self-oscillating circuits with surface acoustic wave device working inside positive feedback loop of an amplifier. Such kind of parametric measurement allows to track the center frequency of the sensor changes in particular. The method is widely used mainly due to their relative simplicity. Unfortunately, it has many disadvantages like frequency (phase) instability, sensitivity to unwanted factors, surface acoustic wave substrate mass-load limit etc. A new system to the analysis of surface acoustic wave gas sensors response as well as an exemplary measurement results are described in the paper. The presented system make the first step to the more complex conception realization.
8
Content available remote

Influence of Humidity on SAW Sensor Response

80%
Jasek K., Pasternak M.
Acta Physica Polonica A
|
2013
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vol. 124
|
issue 3
448-450
EN
In the surface acoustic wave sensors response analysis the influence of different factors on acoustic wave propagation velocity and resonant frequency of the surface acoustic wave device plays an important role. Because the resonant frequency is commonly assumed to be a sensor response, knowing the magnitude of this influence and its mechanisms is very important. The factors which interfere the most with the surface acoustic wave sensor response include: temperature, pressure, and humidity. The influence of humidity is almost impossible to eliminate because of phenomena connected with water adsorption at the surface of the substrate as well as the electrodes of the device.
9
Content available remote

New Approach to SAW Gas Sensors Array Response Measurement

80%
Jasek K., Miluski W., Pasternak M.
Acta Physica Polonica A
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2011
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vol. 120
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issue 4
639-641
EN
Majority papers concerning surface acoustic wave sensors technology is devoted to the analysis of self-oscillating circuits with surface acoustic wave device and its basic frequency changes in particular. Such circuits are widely used mainly due to their relative simplicity. Unfortunately the price of the simplicity is such drawbacks like frequency instability, sensitivity to unwanted factors, surface acoustic wave surface load limit etc. A new approach to the analysis of surface acoustic wave gas sensors response is proposed in the paper. The approach significantly eliminates the disadvantages of commonly used so far methods of analysis.
10
Content available remote

Photo-Induced Structural Changes at a Surface οf Organic Single Crystals Observed by Vibrational Sum Frequency Generation Spectroscopy

80%
Fukumoto K., Fukazawa N., Ishikawa T., Koshihara S., Yamamoto H., Kato R., Onda K.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
313-315
EN
Phase transitions from insulator to metal induced by thermal excitation and by photo-irradiation at the surface of β'-(BEDT-TTF)(TCNQ) are investigated using vibrational sum frequency generation spectroscopy. The results are compared with linear reflectivity measurements which detect the information mainly from bulk. IR absorption spectra of a_{g} vibrational modes of TCNQ induced by the dimerization are observed using vibrational sum frequency generation spectroscopy, and its intensity is found to become smaller by thermal excitation indicating the transition to the metal phase. Time-dependent degree of dimerization is also observed by pump-probe experiments with almost the same statistics as the static measurements. On the other hand, in the reflectivity experiments, the reduction of dimerization is also observed by elevating the temperature, however, the spectral shapes are deformed for the time-resolved measurements. These results imply that the different dynamics occur at the surface and in the bulk.
11
Content available remote

Surface Dynamics and Phononic Properties of 2D Field Tunable Auxetic Crystal

80%
Twaróg D., Trzupek D., Zieliński P.
Acta Physica Polonica A
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2009
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vol. 115
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issue 2
579-582
EN
The lattice in-plane dynamics is studied as a function of external field in a model of auxetic crystal consisting of rigid polar rods and of elastic springs. The phase speed of the transverse acoustic wave propagating parallel to the polar rods is shown to be higher than the speed of the longitudinal wave at strong fields. An absolute stop band for the lattice waves opens in the whole Brillouin zone with increasing field. The surface waves and resonances at a surface parallel to the rods are studied. Infinitely narrow resonances called exceptional surface waves are found within bulk bands at certain specific values of the parameters characterizing the surface. Generally, the surface layer should be significantly heavier and stiffer than the substrate for the phenomenon to occur.
12
Content available remote

SAW Sensor for Mercury Vapour Detection

80%
Jasek K., Neffe S., Pasternak M.
Acta Physica Polonica A
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2012
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vol. 122
|
issue 5
825-828
EN
Mercury is the element commonly applied in industry. Because of poisoning properties the monitoring of the mercury vapour concentration in the environment is very important. Mercury forms amalgams in connection with gold that causes a change in the electrical resistance and mass of the gold specimens. This effect was applied to measure mercury vapour concentration in the environment using surface acoustic wave technology. Two kinds of surface acoustic wave mercury sensors have been described in the paper. First one utilizes a thin film of gold deposited between aluminium interdigital transducers and reflectors of two-port surface acoustic wave resonator, and the second one golden interdigital transducers and reflectors without any sensitive film between them.
13
Content available remote

Stress Induced Phononic Properties and Surface Waves in 2D Model of Auxetic Crystal

80%
Trzupek D., Twaróg D., Zieliński P.
Acta Physica Polonica A
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2009
|
vol. 115
|
issue 2
576-578
EN
Elastic stiffness parameters are determined in a 2D model system of rigid rods interacting by harmonic force constants. Any positive ("normal" crystal) or negative (auxetic crystal) Poisson ratio can be obtained in this model as a function of the external stress. Conditions for opening an absolute stop band (phononic crystal) and for various kinds of surface waves are obtained.
14
Content available remote

Vibrations and Some Electronic Excitations of Adsorbed Alkali Metal Monolayers

70%
Hamawi A., Lindgren S., Svensson C., Wallden L.
Acta Physica Polonica A
|
1992
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vol. 81
|
issue 1
7-18
EN
We discuss briefly data obtained for adsorbed alkali metal monolayers with three different techniques (HREELS, UPS and SHG). The vibrational spectra provide support for the traditional picture of a fractionally charged adsorbate at low coverage and a neutral one at high coverage. We ascribe a vibrational overtone reported in previous work to contamination due to residual water vapour. UPS, uncharacteristically, gives little information of interest for low coverages except for substrates with a band gap and with a surface state in the gap. For Na on Si(100) we monitor the metallization of the surface region in the monolayer coverage range and observe metal induced gap states at higher coverages. For Cs on Cu(111) the optical second harmonic generation (SHG) shows a strong monolayer coverage dependence which we ascribe to optical transitions between surface bands and to surface barrier photoabsorption indicating the potential of SHG as a probe of the details of the surface electronic structure.
15
Content available remote

Mass-transport driven by surface instabilities in metals under reactive plasma/ion beam treatment at moderate temperature

51%
Pranevičius L., Milčius D., Pranevičius L., Širvinskaitë V., Nomgaudyte J., Rivier J.-P., Templier C.
Open Physics
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2004
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vol. 2
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issue 1
67-89
EN
This paper presents a generalized approach to the mechanisms of oxidation, hydrogenation and nitriding of metals under ion irradiation with reactive particles at elevated temperatures. Experimental results on the plasma oxidation of bilayered Y/Zr films, the plasma hydrogenation of Mg films and the ion beam (1.2 keV N2+) nitriding of stainless steel are presented and discussed. We make special emphasis on the analysis of surface effects and their role in the initiation of mixing of bilayered films, the ingress of reactive species in the bulk and the restructuring of the surface layers. It is suggested that primary processes driving reactive atoms from the surface into the bulk are surface instabilities induced by thermal and ballistic surface atom relocations under reactive adsorption and ion irradiation, respectively. The diffusion of adatoms and vacancies, at temperature when they become mobile, provide the means to relax the surface energy. It is recognized that the stabilizing effect of surface adatom diffusion is significant at temperatures below 300–350°C. As the temperature increases, the role of surface adatom diffusion decreases and processes in the bulk become dominant. The atoms of subsurface monolayers occupy energetically favorable sites on the surface, and result in reduced surface energy.
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