|2019 Fall Graduate Colloquium Series|
Electron Diffraction Study of Crystal Structures of (Sr1−xBax)2Nb2O7
Selected-area electron diffraction and convergent-beam electron diffraction (CBED) techniques are used to reveal the Ba doping effect on the crystal structure of (Sr1−xBax )2Nb 2 O7 [SBN(x)] in the temperature range from 293 to 693 K. Ba doping of Sr2Nb2O7 (SN) causes weakening of the incommensurate modulation and deviation from the C-centered lattice. On the other hand, symmetries of fundamental reflections in CBED patterns of SBN(x) are seen to be the same as those of SN, showing a small structural deviation from Cmc21. Crystal symmetries above and below the temperature of a relax or like dielectric anomaly in SBN (x = 0.32) at 465 K remain unchanged. CBED experiments with a nanometer-sized electron probe do not show any indication of the presence of a nanodomain around this temperature. However, the presence of a few-micron-sized polar-inversion domains is found at around 573 K in SBN (x = 0.32). The origin of the reported relaxorlike dielectric anomaly in SBN (x = 0.32) is discussed based on the experimental results of CBED.
,center>Md Kazi Rokunuzzaman
High-Harmonic Generation from an Epsilon-Near-Zero
Attosecond (10-18s) physics is very essential to explore more insights into the dynamics of electrons in molecules. For the development of Attosecond physics, the research of non-linear optics is getting more attention. One of the most fundamental goals of non-linear optics to produce high-harmonic generation from a range of solid-state systems including dielectrics, semiconductors and emerging two-dimensional materials thus opening up new avenues for solid-state attosecond spectroscopy with the additional advantage of producing stable light waveforms in the deep ultraviolet regime with a compact set-up. However, strong above-bandgap absorption restricts the observed solid-state HHG process to a very thin layer of the material (typically tens of nanometres in thickness), significantly limiting the generation efficiency with the solution of this problem In recent days materials which exhibit real part of permittivity vanished in certain spectral ranges have been found to exhibit unique nonlinear optical properties. In this research Y. Yang, J.Liau et.al have showed harmonic generation up to the ninth order directly from an ENZ material: In-doped CdO. The sample is formed from a 75-nm-thick In-doped CdO layer epitaxially grown on a (100)-oriented MgO substrate by high power impulse magnetron sputtering. They found the carrier density and an electron mobility of In-doped CdO film are 2.8 × 1020 cm-3 and 300 cm2v-1s-1 respectively.
Reference: Y. Yang, J. .Liau et.al “High-harmonic generation from an epsilon-near-zero (ENZ) material”, Nature Physics https://doi.org/10.1038/s41567-019-0584-7 (October, 2019)
For more information contact: Dr. Kenneth Park, 254-710-2282