Search

For terahertz (THz) wave applications, tunable and rapid modulation is highly required. When studied by means of optical pump-terahertz probe spectroscopy, single-walled carbon nanotubes (SWCNTs) thin films demonstrated ultrafast carrier recombination lifetimes with a high relative change in the signal under optical excitation, making them promising candidates for high-speed modulators. Here, combination of SWCNTthin films and stretchable substrates facilitated studies of the SWCNT mechanical properties under strain,and enabled the development of a new type of an opto-mechanical modulator. By applying a certain strain to the SWCNT films, the effective sheet conductance and therefore modulation depth can be fine-tuned to optimize the designed modulator. Modulators exhibited a photoconductivity change of 3-4 orders of magnitude under the strain due to the structural modification in the SWCNT network. Stretching was used to control the THz signal with a modulation depth of around 100 % without strain and 65 % at a high strainoperation of 40 %. The sensitivity of modulators to beam polarisation is also shown, which might also come in handy for the design of a stretchable polariser. Our results give a fundamental grounding for the design of high-sensitivity stretchable devices based on SWCNT films.

Fabrication of nanostructured metasurfaces poses a significant technological and fundamental challenge. Despite developing novel systems that support reversible elongation and distortion, their nanoscale patterning and control of optical properties remain an open problem. Herein we report the atomic force microscope lithography (AFML) application for nanoscale patterning of single-walled carbon nanotube films and the associated reflection coefficient tuning. We present models of bundling reorganization, formed-pattern stability, and energy distribution describing mechanical behavior with mesoscopic distinct element method (MDEM). All observed and calculated phenomena support each other and present a platform for developing AFML patterned optical devices using meshy nanostructured matter.

Eumelanin is a widespread biomacromolecule pigment in the biosphere and is intensively tested in numerous bioelectronics and energetic applications. Many of these applications depend on eumelanin's ability to conduct proton current at various levels of hydration. The origin of this behaviour is connected with a comproportionation reaction between oxidized and reduced monomer moieties and water. However, neither this reaction nor the formation of the aqueous proton species have ever been directly observed. Presented here is a hydration dependent FTIR spectroscopic study on eumelanin, which allows for the first time to track the comproportionation reaction via the gradual decrease of the carbonyl group concentration (1725 $cm^{-1}$ band) versus hydration. Furthermore, we detect two types of interfacial water (3253 $cm^{-1}$ and 3473 $cm^{-1}$ bands). Finally, the feature detected at the 3600 $cm^{-1}$ band is assigned to the formation of the Zundel cation, $H_5O_2^+$, an observation and suggestion not previously made. We suggests, due to the behaviour of the hydration dependent feature at 3600 $cm^{-1}$ that the formation of the $H_5O_2^+$ cation potentially functions as a trap for mobile proton species, partially explaining the complex hydration dependent conductivity of eumelanin., Comment: Main text: 22 pages, 7 figures, plus ESI containing 8 pages, 5 figures and 1 table

Encapsulation of a single water molecule in fullerene-C60 via chemical surgery provides a unique opportunity to study the distinct rotational dynamics of the water spin isomers at cryogenic temperatures. Here, we employ single-cycle terahertz (THz) pulses to coherently excite the low-frequency rotational motion of ortho- and para-water, encapsulated in fullerene-C60. The THz pulse slightly orients the water electric dipole moments along the field polarization leading to the subsequent emission of electromagnetic waves, which we resolve via the field-free electro-optic sampling technique. At temperatures above ~100 K, the rotation of water in its cage is overdamped and no emission is resolved. At lower temperatures, the water rotation gains a long coherence decay time, allowing observation of the coherent emission for 10-15 ps after the initial excitation. We observe the real-time change of the emission pattern after cooling to 4 K, corresponding to the conversion of a mixture of ortho-water to para-water over the course of 10 hours.