Elements for Nanoelectromechanics
Elements for Micro- and Nanoelectromechanics Based on the Whiskers of Quasi One-Dimensional Conductors and HTSCs
Tech Area / Field
- INS-MEA/Measuring Instruments/Instrumentation
- MAN-MAT/Engineering Materials/Manufacturing Technology
8 Project completed
Senior Project Manager
Safronova O N
Russian Academy of Sciences / Institute of Radioengineering and Electronics, Russia, Moscow
- Institute of General Physics named after A.M. Prokhorov RAS / Natural Sciences Center, Russia, Moscow
- TU Delft / Kavli Institute of Nanoscience, The Netherlands, Delft\nCNRS / Universite Joseph Fourier / Instutit National Politechnique de Grenoble / Centre de Recherches sur les Tres Basses Temperatures, France, Grenoble
Project summaryNanomechanics, as well as micromechanics, is the thriving direction of modern applied physics. The interest to this area is associated with the prospects of fabricating of integrated nanostructures, such as micro-mirror systems for digital projectors, and of inpidual micro- and nanodevices, e.g. diagnostic and micro-operating devices penetrating into a human, or new types of probes in scanning microscopes, such as scanning tunneling microscope (STM), or high-frequency vibration generators with enormous quality factor, etc.
Decrease of the dimensions of an object modifies the principles of its driving. With approaching the micron scale one has to switch from electromagnetic motors to electrostatic-force mechanical actuators. However, for submicron dimensions the electrical capacity and, correspondingly, the electrostatic force appears too small for the performance of actuators. In the nanometer scale one can expect progress with turning to principally new driving forces. One of the directions could be application of piezoelectricity, though in this case it is difficult to avoid large electric voltages.
The central goal of the Proposal is elaboration of elements of electromechanical devices with submicron dimensions. We shall make use of the high sensitivity of the dimensions of the Peierls conductors to electric field (an analogue of piezoeffect) and of the original technique for the study of deformation of needle-like objects.
The main direction of the research planned is application of the unique properties of quasi one-dimensional conductors with charge-density waves (CDW) for development of electric-field driven actuators of small displacements. The underlying operation principle of these devices is the interaction of the CDW with the pristine crystalline lattice. The CDW can be deformed by an electric field like a spring, or, other words, as an electronic crystal. The CDW deformation results in the deformation of a sample – typically a needle-like crystal, i.e. a whisker. Outwardly this phenomenon resembles piezoelectric effect, the piezoelectric constant being 2-3 orders of magnitude higher than that of the conventional piezocrystals. However, the effect has another physical origin and can exhibit itself in a somewhat another way. E.g., if one tries to detect the displacement of the middle of a sample with respect to its ends, he would expect an effect an order of magnitude higher than the total-length change.
Within the present project we intend to study these properties of the samples and apply them for elaboration of mechanical motion actuators, including resonance vibrators. The group members shall use the advantages of the needle-like (thread-like) form and small dimensions of the samples in the construction of the transducers. In particular, a sample will be arranged so that its ends will be fixed, while the middle will slightly sag. With this geometry we have succeeded to study thermal expansion (TE) of the quasi one-dimensional conductor TaS3. In the heart of the technique is measurement of the vertical (i.e. in the sagging plane) displacement of the sample middle, which by 2-3 orders of magnitude exceeds the sample expansion (dilatation). By means of the optical interference method we are able to detect relative expansion as small as L/L ~5*10-7. We should also mark such an effect as the drop of the Young modulus (up to 5%) and of the shear modulus (up to 30% (!!!)) with passing CDW current through the samples, which could be utilized, e.g., for the variation of resonant frequency of the vibration generators. We also expect to find effects in the high-Tc superconducting whiskers, which could also be exploited in actuators. These expectations are based on the enormous high sensitivity of the dimensions of the high- Tc superconductor Bi2S2CaCu20y to magnetic field – magnetostriction, and on the room-temperature elastic anomaly observed in the whiskers of this compound.
Apart from the optical one, we shall develop the methods of tunnel and atomic-force microscopy for the study of the profiles of submicron sample and detection of their displacement, including the cryogenic techniques. This approach will increase the sensitivity of the dilation studies by at least 2 orders of magnitude. We also plan studies of whiskers of ordinary piezoelectrics using the advantages of their geometry for our technique. Finally, our method of TE studies will be applied towards needle-like and film-like microsamples of various compounds, such as high-Tc whiskers, carbon nanotubes, Si3N4 films, polymeric (polyimide) films, and even spider silk.
Up to now metastable length states have been observed only for TaS3 – the compound with the Peierls transition temperature TP=2200K. In the framework of the Project CDW materials with TP close to the room temperature - NbS3, (TaSe4)2I, (NbSe4)10I3, (NbSe4)3I will be studied. Some of these samples will be synthesized in IRE, others will be provided by the Collaborators. At the same time, two STMs and an atomic-force microscope (AFM) working at cryogenic temperatures will be elaborated. This will allow us to perform also measurements at low temperatures.
Some of the principal directions and stages of the studies are as follows:
- Preliminary arrangement of the technique of the study of small displacements by means of the room temperature STM/AFM.
- Search and study of the CDW-lattice interaction in “high-TP” materials - NbS3, (TaSe4)2I, (NbSe4)10I3, (NbSe4)3I;
- Studies of needle-like piezoelectric crystals.
- Search and studies of an anomaly of the TE of the high-Tc Bi2S2CaCu20y (BSCCO (2212)) whiskers expected near the room temperature.
- Elaboration of the low-temperature AFM and STMs.
- Search and studies of anomalies of longitudinal ”electrodeformation”, i.e. shift of the middle of the sample with respect to the contacts.
- Study of the response of the quasi one-dimensional conductors to the AC electric field and search for the mechanical resonance.
- Study of the Peierls conductors with piezoelectric properties, such as (TaSe4)2I.
- Application of our techniques to different whisker-like materials.
These directions of studies could be promising for the fundamental science, e.g. for comprehending of the interaction of the CDW with the pristine lattice, but also have an obvious applied orientation: to use the unique properties of the CDW and HTSCs, as well as the experimental techniques at our disposal, for elaboration of elements for nanomechanics. In particular, these could be electric-field controlled devices, analogues of piezoelements, high-frequency and high-Q generators of vibrations controlled with AC electric field.
The participants of the Project are qualified specialists having many-year experience of studies of quasi one-dimensional conductors and HTSCs, including the experience of work with submicron-sized samples. Among the participants there are specialists in synthesis of crystals with CDW and HTSCs, as well as experienced specialists in elaboration of STMs and AFMs working at cryogenic temperatures. We have also the experience of studies of the CDW wavelength-scale structure by means of a cryogenic STM.
The Russian group will be in permanent contact with the collaborators, the results will be discussed. P. Monceau (Grenoble) is one of the pioneers of the CDW physics. Unique Peierls compounds are synthesized in his Scientific Center in Grenoble, including high-TP compounds and compounds with piezoelectric properties. We shall study the samples synthesized in Grenoble. Visits to Grenoble and work with the unique equipment are also planned, partly supported from other common grants. In the group of H. van der Zant (Delft) quasi one-dimensional conductors are also studied, including submicron structures; works on nanomechanics are also in process. From this the necessity of collaboration is obvious. Visits to Delft are also planned, partly supported from the INTAS grant.
Collaboration with these groups, as well as with the group of R.E. Thorne (Cornell University), lasts for many years, there are numerous joint publications in the leading scientific journals. R.E. Thorne is one of the leading specialists in the CDW, especially in the size effects. Collaboration with J.W. Brill (Ithaca University), T. Tritt and M. Skove (University of Clemson) is predetermined by our common interest towards the physics of interaction of the CDW with the crystalline lattice. It was J.W. Brill who has observed the drop of Young and shear moduli on the CDW depinning. These results were the first indication of the strong elastic interaction of the CDW with the lattice. This interaction has been also studied by Tritt and Skove by another method. The strain-stress device from their group will be delivered to IRE for the work within the Project. Besides, in the Tritt-Skove group BSCCO (2212) whiskers demonstrating anomalous elastic properties are synthesized, and it would be very appealing to compare the properties of the whiskers grown in Moscow and in USA. All the above makes the joint work with the collaborators of big mutual interest.
The enumerated research directions are exclusively peaceful. In prospect, they can find application in the scanning microscopy, fabrication of micro- and nano-manipulators, generators of mechanical oscillations, in measurement technique. We cannot see prospects of military application of the research proposed. Realization of the presented project will permit most of the participants from IRE to reorient their activity from weapon to peaceful sphere Collaboration with numerous laboratories from different countries will promote better understanding between countries. The applied direction of the research will promote partial switching of the science in Russia to the market relations. Thus, the activities within the Project proposed doubtlessly answer the goals and objectives of ISTC.