Dr. Victor Shelukhin page
Field of interest
My past and current research efforts focus on the field of experimental solid state physics, with particular emphasis on two topics: investigation of strongly correlated systems (superconductivity, ferromagnetism) and systematic study of ceramics materials (properties and effects in pyroelectric, SOFC materials and other ceramics). At first sight, being so different these two systems meet each other either in layered systems, where ceramics used as interfaces (substrate) for superconductor contained junctions (films), or in the class of samples where the ferromagnetic films and ceramics influences can by used ( for example, in detectors or spintronic system). Over the last eight years of PhD and post-doctoral research, I have specialized in samples microfabrication, cryogenic temperature measurement, wide range methods of film characterizations (scanning electronic microscopy, including EDS, X-ray diffraction analysis, ellipsometry and so on), detailed study of preparation processes and finding practical ways to receive quality samples and exclude interfaces influence for clarifying a physical origin of observed effects. Here I present the guidelines of my current and future research.
1. Strongly correlated systems
[Attachment B:1-5,8; Attachment C:1-4,6]
During my PhD studies I have performed the experimental investigations of the direct and the inverse proximity effects in superconductor-ferromagnet (SF) structures. The direct proximity effect was investigated by measurements of both critical temperature (Tc) and critical current (Ic) variations upon the thickness of the ferromagnetic layer and in superconductor-ferromagnet bi- and multi-layered samples. Measurements were focused on π –phase shifts observed in the experiments and similarity of the Tc and Ic behavior in our experiments, such as the same periods of oscillations that correspond to equal magnetic lengths in ferromagnetic layers. One of the main findings in my work was the observation of the strong oscillations of the critical superconductor current and critical temperature with the period different from previously reported experiments. The determination of the correct period was enabled due to fabrication of the samples with a fine variation of the ferromagnets thicknesses as opposed to a course one in the previous experiments. The inverse proximity effect in SF structures I measured by detecting the induced ferromagnetic order in the superconductor. One of the most important results of these experiments is the experimental observation of the "spin screening effect" which is intimately related to the formation of the triplet component in the superconductor condensate function. I prepared the heterostructures by evaporation and sputter technique on GaAs and Si substrates. I used the standard photolithographic process for sample fabrication. I performed the measurements in He4 and He3 cryogenic systems in the temperature range down to 300mK at the magnetic fields ranging from 0 to 7T. I investigated the critical currents in SNFNS (Nb-Cu(Au)-Ni-Cu(Au)-Nb) junctions and critical temperature in bilayers and pentalayers, inverse proximity effect in SF structures (Pb/Ni and Al/Co-Pd) by transport and optical methods. For this purpose, we have fabricated a variety of structures using both standard micro photolithography and more advanced e-beam lithography methods. Different deposition methods, namely sputtering and e-gun vacuum evaporation were employed in the process of fabrication of the structures. In the SNFNS junction, the oscillations and the decay of the critical current in the junction were observed with the increase of the thickness of the Ni layer. A reasonable agreement was found with a recent theoretical calculation in the appropriate limit. I have demonstrated that both the critical Josephson current and the critical temperature of Nb-Ni multilayer’s vary with the Ni thickness with approximately the same period, 16±1 Å. We deduce from the period a magnetic length LM = 10 Å, corresponding to an exchange energy of Eex=200 meV. By measuring Tc in Ni-Nb pentalayers, we have observed a 0→ π transition at a thickness for the central Ni layer consistent with the theoretical prediction using Usadel theory. For higher thicknesses, we see further π →0 and 0→ π transitions in the critical Josephson current, consistent with the period in our Tc measurements and with the predictions of theory. My results demonstrate the feasibility of using strong ferromagnetic materials in the design of Josephson devices for future applications. The data presented in both transport and optical studies of the inverse proximity effect in my thesis have strong indication that the signals (rotation of the polarization angle of light and hysteresis) arise from previously unobserved spin induced magnetization. The increase of the Kerr angle as the temperature is lowered through the superconductor transition temperature follows the theoretically predicted curve and therefore should be considered as the new direct experimental evidence for the phenomenon called "spin screening" due to proximity effect in S/F bilayers.
2. Ceramics properties
2.1. Qualitative pyroelectric SrTiO3 films (preparation and measurements)[B:6,7,9;C:5]
The existence of non-crystalline thin films of BaTiO3, SrTiO3 and BaZrO3 which demonstrate both pyro- and piezoelectricity has been reported recently. When an amorphous 30-250 nm thick film of BaTiO3, SrTiO3 or BaZrO3 prepared by sputtering, is pulled through a relatively steep temperature gradient, such a film does not crystallize but rather as it is found to exhibit room temperature pyro- and piezo-electricity. I innovated a procedure of metal covered SrTiO3 quasiamorphous pyroelectric thin film preparation based on this experience. Producing of these systems is important for understanding pyroelectric origin of mentioned films response to pulsed heating. These films are very sensitive to preparation conditions. The 306 Edward sputtering system after my modifications allows reproducible procedure of perovskite thin films preparation, which was difficult to achieve before. The method of preparation, which was presented in my work, was developed with a special attention to the quality of films. I found conditions for reproducible preparation quality SrTiO3 films during sputtering process. I will stressed that the both sides covered by equal metal SrTiO3 system producing is critical for explanation that measured electric response to heating has pyroelectric origin I checked the crystallinity of thin films was by XRD (X-ray Diffraction), SEM (scanning electron microscope) with EDS (Energy Dispersive Spectroscopy). Modulated IR radiation (Infrared LDCU5 ThorLab 1310 nm, 30 mW Laser or Infrared DPSS 1342nm, 800 mW Laser) causes periodic heating and cooling of the films. Periodic temperature change generates a pyroelectric current, the direction of which alternates with cooling and heating. I performed measurements of the pyroelectric response for Cr/SrTiO3/Cr and W/SrTiO3/W samples. I registered the time-dependent pyroelectric signal, which is generated in response to laser switch. In was no difference between response from these samples and from SrTiO3 film placed on Si. Thus I proved that contact potential difference didn't play a role in our measurements. Therefore I obtained that the origin of measured signal is pyro effect and different conditions of the metal layers preparation do not affect it. I will mention that our measurement results were reproducible in more than 20 samples and this fact approved reproducibility of the pyroelectric films preparation process.
2.2 Properties of the gadolinium doped ceria free standing membranes [B:10,11; C:7,8]
In the past decades the gadolinium doped ceria has been intensively investigated because it is used as solid ionic solution for fuel sell formation. On the other hand there exist several articles which describe the mechanical properties of this material in stress-strain-relaxation language. Since many properties of these films remain unclear I carried out investigation of these ceramic membranes behavior at low temperature. Central objects of my study were Ce0.8Gd0.2O1.9 free standing films placed between two metallic contacts. The choice of membrane as object for study is explained by the fact, that I want to investigate properties of Ce0.8Gd0.2O1.9 itself, excluding influence of substrates or induced stresses. As was found before, these membranes exhibit geometric deformation due to stress dissipation under preparation treatments. Previous electrical measurements were done at 300- 10000K. At these temperatures information about internal properties of CeGdO2 wasn't obtain due to thermal vibrations camouflage. As I found, the temperature for clearance of membranes properties is much lower than room temperature. I prepared the samples on thermally oxidized Si wafers with help of chemical wet etched wells in SiO2, followed sputtering of GDC and Si removing in the plasma etches in fluorine atmosphere.
My results were obtained in several types of experiments.
First of all I found, that after heating to 4400K semicircle impedance picture was obtained since unheated samples exhibited unstable and asymmetric picture due to the presence of surface oxygen and water. All my experiments in vacuum were started with this heating procedure, and after samples were cooled. I carried out all measurements with selected frequency. I found that at low temperature frequency used for measurement practically doesn't influence on results, but at high temperature we will use only high frequency measurements. In all experiments presented below I used only 0.4-1.0 MHz frequencies for our measurements. From my experiments it was found that at 90-1200K ("critical temperature") the dielectric constant as a function from temperature exhibits interesting unexpected behavior, it means unstable region at all measured membrane contained samples (more than 8 pixels) and in all temperature sweepings. In comparison I have not see this behavior on supported films. Interesting result I obtained in observation of heating process. The heating curves reverse at one temperature to cooling curve after low temperature bias treatment, which causes 1.5-2 times reducing of dielectric constant. Above this temperature dielectric constant is bias independent. In front of this results bias treatment below critical region (experiments were done at 25, 30, 50, 70 and 900K, at 5, 103 and 106 Hz) Cp is bias depended. I hadn't found this type bias dependence for supported films. After cooling membranes kept information about bias treatment up to 1200K or more. Picture of response to applied bias is different in range of temperatures; "memory" effect exists only below "critical temperature", while asymmetry in Cp under bias treatment can exists at higher temperatures which are different for different samples. In general I found the unexpected behavior at critical temperature about 1200K and described low temperature behavior of the dielectric constant with focus on bias treatment. I presented the "Memory" effect, which exists only below critical temperature. I proposed an explanation of all free standing film properties include asymmetry of films. I assume that Ce0.8Gd0.2O1.9 membranes properties before and after "transition temperature" are different due to vacancies association/dissociation and its rearrangement under applied bias. Based in the experience mentioned above, I can single out the existing problems and methods to solve then in the future.
One of general problems in all described experiments is the processing influence on the resulting quality of samples. My approach is based on the detailed study of the preparation processes and on finding practical ways to receive quality samples and to exclude the interfaces influence on the measurements for clarifying a physical origin of observed effects. My weapon is complex approach to the investigation that includes the results of different methods for building a general picture of the physical process. The methods that I used, include electric and magnetic measurements, which has been conducted in vacuum and at low temperature, as well as different type of film characterization using X-ray, SEM and optical systems, and etc. Current focus of my work is low dimensional and granular superconducting systems, include ceramics based subjects, high challenge is to find a light stimulated superconductivity at the enough high temperatures for using in the industry.
Second subject of my current studies is the face transitions in the advanced ceramics. It looks as the problem contained great chemical and physical challenges [C:10,14]. In the future I planed several interesting direction of investigation:
1. I propose experiments to observe directly the long range proximity effect in the superconductor-ferromagnet junctions, indirect evidences of the existing of this effect were obtained in the my PhD work (Physics, the field of strong correlated system only).
2. I plan to investigate the granular systems (include ferromagnet-superconductor systems) to search a new properties, include high temperature superconductivity under lighting. (Optics, strongly correlated systems)
3. I will continue to study low temperature ceramics properties using methods of impedance spectroscopy. Here I think about wide range of ceramics and about applying additional methods of investigation (Raman spectroscopy) and high intensity X-ray influence leads immediately to crystallization of ceramics films. (Ceramics, Material Science).
4. In respect to the last made work, first- I hope experimentally to find condition for carbon layers deposition from fluoride-contained plasma from one side; second – I will introduce in the common used ceramics preparation procedures innovation related to preparation of metalized ceramics on soft metal substrates, which will chemically dissolved.(Material Science, Chemistry)
5. I will perform number of experiments with spintronic samples using as interfaces ceramics elements with high vacancies concentration. I think that these experiments will show interesting effects to clarify ceramics behavior at low temperatures at one side and to build spintronic elements with slow electron injection (with using of ceramics as medium with changing properties). Special attention will be paid to topological structures as topological insulator and superconducting two-dimensional electron gas interfaces.(Solid State Physics; strongly correlated systems)
6. I think about ceramics detectors, which will work at low temperature with superconductive elements. It will be made long superconductive junctions, where properties will be limited by number of carriers and defects in the ceramics and ceramics polarization. It is important here to take in the account the interface processes (Interdisciplinary Science and Techniques) and other options for superconductivity medias instead of phonons.
Be’er Ya’akov, HaGolan 30b, Israel, 70300
Phone – 08-9247873, 054-6391225
E-mail: Victor.Shelukhin@gmail.com, email@example.com
Date and place of birth: 11.02.1964 Russia, Saint-Petersburg
Date of immigration: 12.07.2004 to Israel
Marital status: Married
Fields of interest: superconductivity: thin films and layered junctions, proximity effect; ferromagnetism – superconductivity interplay, include granular systems; ceramics: electric and dielectric properties of advanced ceramics, low temperature face transitions in these ceramics, carbon coatings; memristor like effects; molecular photonics: polariton-based long-range superconducting medias for high temperatures; pump-probe as universal research instrument; Raman spectroscopy; nanofabrication: multi-layered samples, granular systems, thin films, sputtering upgrades, co-evaporation, clean room facilities; low temperature measurements.
2004 – 2009 Tel Aviv University, Israel, Ph. D. in Physics Supervisor: Prof. Alexander Palevski
2003 – 2004 Tel Aviv University, Israel, confirmation of M.Sc. From Leningrad State University, Supervisor: Prof. Alexander Palevski
1981 – 1986 Leningrad State University (Russia), Department of Physics, B.Sc and M.Sc. in Physics (Photonics).
15.10.12 – present Tel-Aviv University, research scientist
01.04.2012- 14.10.12 Bar Ilan University, postdoctorant, supervisor: Prof. Yaakov R. Tischler
2009 – 31.03. 2012 Weizmann institute of science, postdoctorant, supervisor: Prof. Igor Lubomirsky
2001 – 2003 Tel-Aviv University, "RAMOT", researcher
1994 – 2000 Various positions related to working in engineering and trade companies
1990 – 1993 NKF "Foton" start-up company, Head of Laboratory for Nonlinear Optics
1986 – 1990 Leningrad Electro-Technical Institute of Communication, Research Centre of High Current process, junior scientist
Practical experience in micro-fabrication techniques Vacuum deposition techniques: electron beam and thermal evaporation of metals, RF and DC magnetron sputtering of metals and dielectrics. Sputtering on hot substrates; Photolithography including back side alignment and fine alignment Wire bonding to various metals; Practical experience with F-based Plasma Etching – ICP; Various wet etching technique for Si and GaAs and SiO2; Film thickness monitoring with various types of surface profilers; Automatic and manual ellipsometry, including ellipsometry of multi-layers. Design, construction and maintenance of vacuum equipment Practical skills in design of vacuum cryogenic equipment and deposition equipments; Practical skills in maintenance of vacuum equipment. Electrical characterization techniques (with emphasis on microfabrication) Conductivity measurements, four points and high-current; AC electrical measurements with Lock-in amplifiers, spectrum analyzers; Impedance spectroscopy. Other techniques Cryogenic measurements including measurements in helium dilution; SEM-based techniques, including EDS; Basic XRD analysis; X-Ray Reflectivity analysis; Pyroelectric coefficient measurements; Ellipsometry; Liquid nitrogen and liquid helium producing processing (Leningrad Electro-Technical Institute of Communication); High energy electric pulses generators (Leningrad Electro-Technical Institute of Communication); Molecular Bond Energy analyzers (S.Pb. University); Usage of high powerful lasers for holography making (NKF "Foton"); Sagnac interferometer for Polar Kerr Effect measurements (Tel-Aviv University with collaboration with Stanford University)
1987-1988 – Teacher of Physics in High School # 209, Sankt-Petersburg 2008 and 2009 – Children Guide in Summer school for schoolchildren in the Tel-Aviv University (two one month terms) 2001-2011 -Practical experience in guiding M.Sc. students and “technological support” 1996
List of selected publications
1. Y.Blum, M.Karpovski, V.Shelukhin, A.Palevski, A.Tsukernik in: Future Trends in Microelectronics: The Nano, the Giga, and the Ultra, eds.: S.Luryi, J.M.Xu, A.Zaslavsky, New York: Wiley Interscience/IEEE Press, 270, (2004)
2. I.Sternfeld, V.Shelukhin, A.Tsukernik, M.Karpovski, A.Gerber, A.Palevski, “Proximity effect in granular superconductor-normal metal structures”, Physical Review B-Condensed Matter, 71, pp. 064515, (2005)
3. V.Shelukhin, A.Tsukernik, M.Karpovski, Y.Blum, K.Efetov, A.Volkov, T.Champel, M.Eschrig, T.Lofwander, G.Schon, A.Palevski, “Observation of periodic pi-phase shifts in ferromagnet-superconductor multilayers”, Physical Review B 73, p. 174506, (2006)
4. J.Xia, V.Shelukhin, M.Karpovski, A.Kapitulnik, A.Palevski, “Inverse proximity effect in superconductor-ferromagnet bilayer structures”, Physical Review Letters 102, 087004, (2009)
5. V.Shelukhin, M.Karpovski, A.Palevski, J.Xia, A.Kapitulnik, A.Tsukernik, “Spin Screening of Magnetization Due to Inverse Proximity Effect in Superconducting/Ferromagnetic Bilayers”, in: Future Trends in Microelectronics: From Nanophotonics to Sensors and Energy, eds.: S. Luryi, J.M. Xu, A.Zaslavsky, New York: Wiley Interscience/IEEE Press, 273, (2010)
6. A.Yoffe, V.Shelukhin, “Modification of 306 Edwards sputtering system for reproducible making of sensitive thin films”, Material Science-Poland, 28, 4, 833, (2010)
7. V.Shelukhin, D.Ehre, E.Lavert, E.Wachtel, Y.Feldman, A.Tagantsev and I.Lubomirsky, “Structural Determinants of the Sign of the Pyroelectric Effect in Quasi-Amorphous SrTiO3 Films”, Advanced Function Material, 21, 8, 1403-1410, (2011)
8. V. Shelukhin, “Superconductivity and ferromagnetism interplay in layered junctions”, book, Lambert Academic Publishing, ISBN 978-3-8443-2830-1, (2011)
9. A.Yoffe, H.Cohen and V.Shelukhin, “High quality metal covered SrTiO3 pyroelectric film preparation”, Technical Physics, 57, 1, 134-136, (2012), Original Russian Text © A. Yoffe, H. Cohen, V. Shelukhin, 2012, published in Zhurnal Tekhnicheskoi Fiziki, 2012, Vol. 82, No. 1, pp. 136–138.
10. V.Shelukhin, I.Zon, E.Wachtel, Y.Feldman and I.Lubomirsky, “Low temperature dielectric properties of Ce0.8Gd0.2O1.9 films”, Solid State Ionics, 211, 12-19, (2012)
11. I.Zon, V.Shelukhin, “Anomalies in the gadolinium doped ceria resistance below 90K”, Materials Chemistry and Physics, 134 (2012) 219– 223, (2012)
Conferences, presentations, thanks and publications under submission
1. Y.Blum, A.Tsukernik, M.Karpovski, V.Shelukhin, A.Palevski, “Critical current and magnetic properties of Nb-Cu-Ni-Cu-Nb junctions”, Proceeding of FTM-4 Workshop, Corsica, 2003
2. I.Sternfeld, V.Shelukhin, M.Karpovski, A.Palevski, “Proximity effect in granular superconductor-normal metal structures”, Tel Aviv University Nanoscience and Nanotechnology Workshop, Kfar Blum, 2004
3. V.Shelukhin, Y.Blum, A.Tsukernik, M.Karpovski, A.Palevski, “Proximity effect in SFS and SNS junctions”, Tel Aviv University Nanoscience and Nanotechnology Workshop, Kfar Blum, 2004
4. V.Shelukhin, J.Xia, A.Tsukernik, M.Karpovski, A.Kapitulnik and A.Palevski, “Induced magnetization due to inverse proximity effect in S/F bilayers”, The 54th Annual Meeting of the Israel Physical Society , Beer Sheva, 2008
5. V.Shelukhin, I. Lubomirsky, “Undoubted detection of pyroelectric signal from quasi-amorphus SrTiO3 films”, IMEC-2009, P2-3, Israel, 2009
6. Thanks in D.Rosenblatt, M.Karpovsky and A.Gerber, “Reversal of the extraordinary Hall effect polarity in thin Co/Pd multilayers”, Applied Physics letter 96, 022512, (2010)
7. V.Shelukhin, I.Zon, I.Lubomirsky, “Dielectric anomalies in Gd-doped ceria below 130 K”, P-4-295, ACIN-2011, Belgium, 2011
8. V.Shelukhin, I.Zon and I.Lubomirsky, “Properties of the gadolinium doped ceria self-supported films at the low temperature”, MRS Symposium “Fall Meeting and Exhibits”, USA, 2011
9. V.Shelukhin , presentation in: University of California, Santa-Barbara, USA, 2011
10. I.Zon, O.Bitton, I.Feldman, V.Shelukhin and I.Lubomirsky, “Control over Carbon-Fluoride ratio in thin amorphous films deposited from C4F8 /N2/Ar plasma”, IMEC15, Israel, 2012
11. V.Shelukhin , presentation in: Ariel University, Israel, 2012
12. V.Shelukhin, I.Zon, I.Lubomirsky, “Dielectric anomalies in nanocrystalline membranes of Gd-doped ceria”, NanoIsrael 2012, Israel, 2012
13. V.Shelukhin, presentation in: Saint-Petersburg State University, Russia, 2012
14., A.Ioffe, I.Zon, I.Feldman and V.Shelukhin, “Amorphous carbon films with controlled fluoridation: making and characterization”, prepared for submission to “Materials letters” (2013)
15. I.Zon, I.Feldman, V.Shelukhin, “Giant Super-lattice in vacancies rich ceramics: experimental evidences”, prepared for submitting to "Material Science Letters" (2013)