Browsing by Author "Apte, Amey"

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    High-K dielectric sulfur-selenium alloys
    (AAAS, 2019) Susarla, Sandhya; Tsafack, Thierry; Owuor, Peter Samora; Puthirath, Anand B.; Hachtel, Jordan A.; Babu, Ganguli; Apte, Amey; Jawdat, BenMaan I.; Hilario, Martin S.; Lerma, Albert; Calderon, Hector A.; Hernandez, Francisco C. Robles; Tam, David W.; Li, Tong; Lupini, Andrew R.; Idrobo, Juan Carlos; Lou, Jun; Wei, Bingqing; Dai, Pengcheng; Tiwary, Chandra Sekhar; Ajayan, Pulickel M.
    Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications.
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    Ultrafast non-radiative dynamics of atomically thin MoSe2
    (Springer Nature, 2017) Lin, Ming-Fu; Kochat, Vidya; Krishnamoorthy, Aravind; Bassman, Lindsay; Weninger, Clemens; Zheng, Qiang; Zhang, Xiang; Apte, Amey; Tiwary, Chandra Sekhar; Shen, Xiaozhe; Li, Renkai; Kalia, Rajiv; Ajayan, Pulickel; Nakano, Aiichiro; Vashishta, Priya; Shimojo, Fuyuki; Wang, Xijie; Fritz, David M.; Bergmann, Uwe
    Photo-induced non-radiative energy dissipation is a potential pathway to induce structural-phase transitions in two-dimensional materials. For advancing this field, a quantitative understanding of real-time atomic motion and lattice temperature is required. However, this understanding has been incomplete due to a lack of suitable experimental techniques. Here, we use ultrafast electron diffraction to directly probe the subpicosecond conversion of photoenergy to lattice vibrations in a model bilayered semiconductor, molybdenum diselenide. We find that when creating a high charge carrier density, the energy is efficiently transferred to the lattice within one picosecond. First-principles nonadiabatic quantum molecular dynamics simulations reproduce the observed ultrafast increase in lattice temperature and the corresponding conversion of photoenergy to lattice vibrations. Nonadiabatic quantum simulations further suggest that a softening of vibrational modes in the excited state is involved in efficient and rapid energy transfer between the electronic system and the lattice.