Controlling Three Laser-Excited Coherent Phonon Modes in Boron Nitride Nanotubes To Produce Ultrashort Shaped Terahertz Pulses: Implications for Memory Devices

Abstract

The excitation of lattice vibrations by ultrafast laser pulses provides a tool to steer atomic-scale motions beyond usual thermodynamic limitations. We simulate this process in armchair, chiral, and zigzag boron nitride nanotubes (BNNTs). In particular, for ultrathin zigzag-type tubes we show that three vibrational modes can be displacively excited. Since the boron nitride bonds are polar, the three coherent phonon oscillations emit terahertz (THz) radiation. In this work we focus on the (5,0) zigzag BNNT, which is the thinnest stable one, and demonstrate, by means of ab initio molecular dynamics simulations and optimization algorithms, that the relative amplitudes of the three phonon modes and therefore the corresponding shape of the emitted THz short pulse can be controlled by laser-pulse trains. Our work could serve as a basis for experimental studies using the coherent vibrations of BNNTs as optical memory devices in nanophononics, since information could be written in the phononic system by several femtosecond laser pulses and could be read out by measuring the produced THz emission.

Universal behavior of the band gap as a function of the atomic mean-square displacement in laser-excited silicon

“…Only at very low peak intensities, a small mismatch occurs. Equation (14) indicates that Bragg peaks related to a bigger scattering vector q hkl decay faster with increasing atomic MSD and, consequently, decay faster to zero, which can also be seen in the top panel of Figure 3. Now, we study the influence of a fs-laser excitation on the indirect electronic band gap.…”

“…We perform ab-initio simulation of laser-excited solids by using the T e -dependent DFT code CHIVES [14][15][16][17][18], which was developed in our group. We implemented the local density approximation (LDA) in CHIVES.…”

“…In the top panel of Figure 3, we show the time-dependent relative intensities of the (111), ( 220), (311) and (400) Bragg peaks directly calculated from the atomic coordinates using Eq. ( 12) averaged over 12 runs at T e = 25262 K. The dashed curves indicate the time behavior of these Bragg peaks obtained from the atomic MSD using the Debye-Waller theory (14). In the bottom panel of Figure 3, we show the time-dependent intensity of the (111) Bragg peak at all studied T e s averaged over 12 runs.…”

Synthesis and characterization of iridium-doped multi-walled carbon nanotubes

“…Boron and nitrogen doping is used to create electrocatalysts for oxygen reduction reactions, hydrogen evolution, biological reactions and gas sensing [3][4][5][6][7][8]. B-doped CNTs show the best sensitivity to ethylene, while N-doped CNTs show the best sensitivity to nitrogen dioxide and carbon monoxide [9][10][11][12][13]. These modifications open up prospects for the use of CNTs in transistors, sensors, solar cells, optoelectronic and thermoelectric devices, charge-storage and fuel-storage devices [14][15][16][17].…”