Long-Range Energy Transfer in Strongly Coupled Donor-Acceptor Phototransistors.

Strong light-matter coupling offers a way to tailor the optoelectronic properties of materials. Energy transfer between strongly coupled donor-acceptor pairs shows remarkable efficiency beyond the Förster distance via coupling through a confined photon. This long-range energy transfer is facilitated through the collective nature of polaritonic states. Here, the cooperative, strong coupling of a donor (MoS2 monolayer) and an acceptor (BRK) generates mixed polaritonic states. The photocurrent spectrum of the MoS2 monolayer is measured in a field effect transistor while coupling the two oscillators to the confined cavity mode. The strongly coupled system shows efficient energy transfer, which is observed through the photoresponsivity even the donor and acceptor are physically separated by 500 Å. These studies are further correlated with the Hopfield coefficients and the overlap integral of the lower polaritonic and uncoupled/dark states. Cavity detuning and distance-dependent studies support the above evidence. These observations open new avenues for using long-range interaction of polaritonic states in optoelectronic devices.

Characteristics of surface plasmon-polariton waves excited on 2D periodically patterned columnar thin films of silver.

Periodically patterned thin films of slanted silver nanocolumns were deposited by directing a collimated vapor flux of silver toward square and hexagonal gratings of photoresist on glass substrates. Angle-resolved specular-transmittance measurements in the visible and near-infrared wavelength bands on these periodically patterned columnar thin films (CTFs) were carried out to investigate the excitation of surface plasmon-polariton (SPP) waves bound tightly to either the air/CTF or the photoresist/CTF interfaces. The orientation of the propagation vector of the incident p-polarized plane wave with respect to the morphologically significant plane of the CTFs was varied to reveal asymmetric (unidirectional) coupling of Floquet modes to SPP waves. The asymmetric coupling is maximal when the propagation vector of the incident plane wave lies wholly in the morphologically significant plane. Theoretical understanding based on the Bruggeman formalism to homogenize the silver CTFs into hyperbolic biaxial continua is able to explain the experimental observations very well.

Reconfiguring gratings of slanted plasmonic nanocolumns by ion beam irradiation.

Gratings with slanted plasmonic nanocolumns of silver (Ag) on top fabricated by physical vapor deposition at large oblique angles on predefined gratings show unique plasmonic properties. These aligned nanocolumns with high-aspect ratios can be uniformly re-oriented to any desired angle of slant by ion beam irradiation. A focused ion beam (FIB) has been used as the ion source here. The plastic deformation of the nanocolumns arises due to defect formation caused by the energetic ions and can enable the complete tuning of the photonic and plasmonic properties of the grating through the slant angle. The reorientation can be uniformly carried over large areas of 0.2 mm(2) with the FIB and the diffraction patterns from the reoriented grating show large changes in the diffraction efficiencies. Electromagnetic simulations of the grating structures reveal large changes in the photonic properties with the slant angle such as diffraction efficiencies and the electromagnetic near fields.

Fingerprint visualization enhancement by deposition of columnar thin films and fluorescent dye treatment.

Enhanced visualization of latent fingerprints on two non-porous surfaces, smooth glass slides and highly reflecting rough aluminum sheets, is obtained by depositing columnar thin films (CTFs) of calcium fluoride (CaF2) and silica (SiO2) by physical vapor deposition at large oblique angles. Due to the vapor flux getting shadowed by the physical residues in the fingerprints, the CTFs are deposited only on the upraised ridges, resulting in highly enhancing the visibility of the fingerprint. The visualization of these fingerprints with deposited CTFs is further enhanced by subsequently treating them with a fluorescent dye and fluorescence imaging. A specific amino-acid reagent (1,2-indanedione) and non-specific laser dye (Rhodamine 6G), both allowed enhanced visualization of the CTFs grown on the fingerprints, due to the localization and entrenchment of the dye within the CTF regions.