Spectroscopy of atomic and molecular cryocondensates
Main research areas
- Excitonic states and processes of exciton self-trapping;
- Mechanisms of electron-stimulated defect formation and desorption;
- Radiation effects, relaxation channels of electronic excitations and post-irradiation phenomena;
- Charge carriers in atomic and molecular cryocondensates – formation and stabilization of charge centers, reactions involving charge centers, relaxation processes;
- Charge accumulation conditions and “frozen plasma” formation.
- New methods of charge states investigation in insulators;
Main investigation methods – optical and current spectroscopy
- Cathodoluminescence spectroscopy in a wide spectral range – from near infrared to vacuum ultraviolet;
- Correlated in time registration of thermoluminescence, electron emission and own particle emission;
- Correlated in time registration of optically-stimulated luminescence, electron emission and particle emission;
- Nonstationary luminescence;
- Matrix isolation;
- Low temperature radiation-induced absorption.
In rare gas solids doped with oxygen О- ions are formed under electron beam. Ions are neutralized by laser light. Thermally stimulated diffusion of oxygen atoms and their recombination lead to formation of excited molecules О2* emitting photons. This internal light source stimulates relaxation processes: luminescence of matrix, electron emission from the crystal surface and desorption of own particles.
A new channel of relaxation processes stimulated by chemiluminescent reactions is revealed
Thermoluminescence of solid nitrogen under step-wise heating
A new phenomenon of anomalous low temperature emission of own particles from preliminary irradiated atomic and molecular cryocondensates is found. Its mechanism is based on conversion of electronic excitations energy into the kinetic energy of particles in course of neutralization reactions observed at temperatures much lower than the characteristic sublimation temperature.
N3+ + e- -> N*(2D) + N2 (1Σg+) + hv1+ ∆Е
N4+ + e- -> N2*(1Σu-) + N2(1Σg+) + hv2+ ∆Е
Anomalous low-temperature post-irradiation desorption of own particles from solid N2
Comparison of desorption yields from preliminary irradiated and non-irradiated samples.
The same threshold for the yields of electrons thermoluminescence and desorption.
Holes self-trapping in solid nitrogen with formation of N4+ centers is detected
Detection of products of electron-hole dissociative recombination reaction in the yields of nonstationary luminescence, thermoluminescence and photoluminescence is a proof of holes self-trapping, e.g., formation of N4+.
N4+ + e- -> N2* (a‘) + N2* (a‘)+ +ΔE1 -> N2 + N2 + 2hv + ΔE2
Comparison of relaxation emissions: thermoluminescence, exoelectron emission and nonstationary luminescence of solid nitrogen.
Photo-stimulated luminescence and exoelectron emission from solid nitrogen.
Possibility of “frozen plasma” creation in pre-irradiated cryocondesates of atomic and molecular gases is demonstrated for the first time. The concentration of charge centers reaches 1016 cm-3
An ultra high concentration of negative charge is achieved in dielectric films of solid nitrogen. Participation of N3- centers in the formation of electrostatic charge was revealed. It was shown that these centers play an important role in post-desorption, e.g., emission of particles from the surface of irradiated nitrogen films.
This effect has to be taken into account to ensure trouble-free operation of various vacuum devices under conditions of exposure to ionizing radiation, as well as elements of space equipment. This result also opens the possibility of creating a new type of charge accumulators and a wide range of high-tech applications.
Yield of thermally stimulated exoelectron emission with different extracting potentials.
Partial sample discharge and photon-stimulated detachment of electrons from N3- centers.
We have developed a new approach - the method of nonstationary luminescence, for the study of charge centers in irradiated solids. This original two-stage technique is based on controlled "injection" of electrons by their release from the traps under the action of sample heating. The investigated ion centers are first generated by an intense electron beam. Then, the formed centers are studied by recombination luminescence under the influence of a beam of low intensity in order to minimize the creation of new charge centers. The spectra of nonstationary luminescence are recorded with a constant heating of the irradiated sample to successively release electrons from ever deeper traps and their subsequent recombination with positively charged centers.
A new method of charge states investigation – nonstationary luminescence is developed
Nonstationary luminescence spectrum of solid nitrogen.
E. Savchenko, I. Khyzhniy, S. Uyutnov, M. Bludov, G. Gumenchuk and V. Bondybey. Defect-induced electrostatic charging of nitrogen films, Phys. Stat. Solidi B, 253, No. 11, 2115 (2016).
E. V. Savchenko, I. V. Khyzhniy, S. A. Uyutnov, A. P. Barabashov, G. B. Gumenchuk, M. K. Beyer, A. N. Ponomaryov, and V. E. Bondybey. Radiation effects in solid nitrogen and nitrogen-containing matrices: Fingerprints of N4+ species, J. Phys. Chem. A 119, No. 11, 2475 (2015).
E. Savchenko, I. Khyzhniy, S. Uyutnov, A. Barabashov, G. Gumenchuk, A. Ponomaryov and V. Bondybey. Charged defects and defect-induced processes in nitrogen films, Phys. Stat. Solidi C, 12, No 1-2 , 49 (2015).
E.V. Savchenko, I.V. Khyzhniy, S.A. Uyutnov, A.N. Ponomaryov, G.B. Gumenchuk and V.E. Bondybey. Anomalous low-temperature “post-desorption” from solid nitrogen, FNT 39, 574-579 (2013) [Low Temp. Phys. 39, 446-450 (2013)].
E. V. Savchenko, I. V. Khyzhniy, S. A. Uyutnov, G. B. Gumenchuk, A. N. Ponomaryov, M. K. Beyer, V. E. Bondybey. Charging effects in an electron bombarded Ar matrix and the role of chemiluminescence-driven relaxation, J. Phys. Chem. A 115, No. 25, 7258 (2011).
E.V. Savchenko and Yu.A. Dmitriev. “New Aspects of Relaxation Processes in Cryogenic Solids”, in Applied Physics in the 21st Century (Horizons in World Physics. Volume 269) Ed. Raymond P. Valencia, Nova Science Publishers New York, 2010, p. 113-162
I.V. Khyzhniy, E.V. Savchenko, S.A. Uyutnov, G.B. Gumenchuk, A.N. Ponomaryov, V.E. Bondybey. Exoelectron emission from solid nitrogen, Radiation Measurements 45, No. 3-6, 353 (2010).
E.V. Savchenko, G. Zimmerer, V.E. Bondybey. Electronically induced modification of atomic solids and their relaxation probed by luminescence methods, J. Luminesc. 129, 1866 (2009).
I.V. Khyzhniy, S. A. Uyutnov, E.V. Savchenko, G.B. Gumenchuk, A.N. Ponomaryov, V.E. Bondybey. Electron traps in solid Xe, FNT 35, №. 4, 433 (2009) [Low Temp. Phys. 35, No. 4, 335 (2009)].
H. Tanskanen, L. Khriachtchev, A. Lignell, M. Räsänen, S. Johansson, I.V. Khyzhniy, E.V. Savchenko. Formation of noble-gas hydrides and decay of solvated protons revisited: diffusion-controlled reactions and hydrogen atom losses in solid noble gases, Phys. Chem. Chem. Phys., 10, 692 (2008).
I.V. Khyzhniy, O. N. Grigorashchenko, A.N. Ponomaryov, E.V. Savchenko, V.E. Bondybey. Thermally stimulated exoelectron emission from solid Xe, FNT 33, No. 6-7, 701 (2007) [Low Temp. Phys. 33, No. 6, 529 (2007)].
E.V. Savchenko, A.N. Ogurtsov, I.V. Khyzhniy, G. Stryganyuk, G. Zimmerer. Creation of permanent lattice defects via exciton self-trapping into molecular states in Xe matrix. Phys. Chem. Chem. Phys. 7, 785 (2005).
E.V. Savchenko, G.B. Gumenchuk, E.M. Yurtaeva, A.G. Belov, I.V. Khyzhniy, M. Frankowski, M.K. Beyer, A.M. Smith-Gicklhorn, A.N. Ponomaryov, V.E. Bondybey. Anomalous low temperature desorption from preirradiated rare gas solids, J. Luminesc. 112, 101 (2005).