AuAg@CdS double-walled nanotubes: synthesis and nonlinear absorption properties

Theoretical simulation of nonlinear regulation of wall thickness dependent longitudinal surface plasmon in pentagonal gold nanotubes

In this paper, the longitudinal plasmon mode optical properties and localized electric field distribution of a single pentagonal gold nanotube are investigated for the first time by the discrete dipole approximation. It is found that pentagonal gold nanotube has stronger electric field distribution compared with circular gold nanotubes when the incident wavelength is located at the plasmon resonance peak. Additionally, we observed that the longitudinal plasmon resonance peak can blue shift nonlinearly with increasing wall thickness, but red shifts linearly with the increase of the length of the pentagonal gold nanotube. The localized electric field analysis reveals that the longitudinal plasmon peak of the pentagonal gold nanotube originates from the dipole resonance mode. The local electric field intensity is controlled by the wall thickness and length. Notably, the effect of wall thickness on the longitudinal plasmon resonance and electric field enhancement can be attributed to the change of the plasmon coupling position and intensity. This work has enriched the theoretical research of pentagonal gold nanotubes and provided ideas for the preparation of high sensitivity nanoprobes biosensors.

Selective controlling transverse plasmon spectrum of pentagonal gold nanotube: from visible to near-infrared region

In this paper, the optical properties and local electric field distribution of transverse plasmon mode of a single pentagonal gold nanotube are studied for the first time by the discrete dipole approximation (DDA). We find that the transverse plasmon peaks can nonlinearly red shift from visible to infrared region via controlling the inner diameter. In addition, the transverse plasmon peak firstly blue shifts and then red shifts in the visible region with the increase of outer diameter. Further analysis shows that the spectra red shift with the increase of outer diameters when scattering is dominant. Local electric field analysis reveals that transverse plasmon resonance peaks of gold nanotube mainly come from dipole resonance. When the tube wall is thin enough, multi-polar plasmon resonance mode will be generated, and the number of peaks will be increased. The surface charges of inner and outer tube walls are changed by tuning the inner diameter and outer diameter parameters of pentagonal gold nanotube. The selective controlling transverse plasmon spectra of gold nanotube are realized, which is of great significance to the study of optical properties of gold nanotube and the application of molecular detection and biological imaging.

Gold nanotubes: synthesis, properties and biomedical applications

This review (with 106 references) summarizes the latest progress in the synthesis, properties and biomedical applications of gold nanotubes (AuNTs). Following an introduction into the field, a first large section covers two popular AuNTs synthesis methods. The hard template method introduces anodic alumina oxide template (AAO) and track-etched membranes (TeMs), while the sacrificial template method based on galvanic replacement introduces bimetallic, trimetallic AuNTs and AuNT-semiconductor hybrid materials. Then, the factors affecting the morphology of AuNTs are discussed. The next section covers their unique surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS) and their catalytic properties. This is followed by overviews on the applications of AuNTs in biosensors, protein transportation, photothermal therapy and imaging. Several tables are presented that give an overview on the wealth of synthetic methods, morphology factors and biological application. A concluding section summarizes the current status, addresses current challenges and gives an outlook on potential applications of AuNTs in biochemical detection and drug delivery.Graphical abstract.

Highly tunable nonlinear response of Au@WS2 hybrids with plasmon resonance and anti-Stokes effect

We synthesize Au@WS2 hybrid nanobelts and investigate their third-order nonlinear responses mediated by a strong anti-Stokes effect. By using the femtosecond Z-scan technique and tuning the excitation photon energy (Eexc), we find the sign reversals of both nonlinear absorption coefficient β and nonlinear refractive index γ to be around 1.60 eV, which is prominently higher than the bandgap (1.35 eV) of WS2 bulk owing to the strong anti-Stokes processes around the bandgap of the indirect semiconductors. The saturable absorption and self-defocusing of the WS2 nanobelts are significantly enhanced by the plasmon resonance of the Au nanoparticles when Eexc > 1.60 eV. But the excited state absorption assisted by the anti-Stokes processes and the self-focusing observed at Eexc < 1.60 eV are suppressed by the surface plasmon. Furthermore, by using population rate equations, we theoretically analyze the sign reversals of both β and γ and reveal the physical mechanism of the unique nonlinear responses of the hybrids with the plasmon resonance and anti-Stokes effect. These observations enrich the understanding of the nonlinear processes and interactions between the plasmon and exciton and are helpful for developing nonlinear optical nanodevices.

Controlled growth and optical response of a semi-hollow plasmonic nanocavity and ultrathin sulfide nanosheets on Au/Ag platelets

Herein, we report a strategy to construct a semi-hollow plasmonic nanocavity and grow ultrathin sulfide nanosheets inside. The competition and cooperation of Au deposition with Ag etching based on flat Ag nanoplates are proposed. For the establishment of the semi-hollow nanocavity, Au shells are grown on Ag nanoplates, which serve as a stable frame, followed by partial etching of the Ag nanoplates. By controlling the thickness of the initial Ag nanoplates or the injected amount of etchant, the nanocavity size is fine-tuned. Significantly, the remaining unetched Ag layers provide a flat platform for the growth of 2D ultrathin sulfides of Ag₂S and CdS inside the semi-hollow plasmonic nanocavity. Strong plasmon resonance and large local field enhancement are exhibited inside the plasmonic cavity where the ultrathin semiconductor sulfides are grown, indicating strong plasmon-exciton interactions in the hybrids. Furthermore, this synthetic approach is extended to grow other metal sulfides such as Bi₂S₃ and PbS. The combination of a flat plasmonic cavity with ultrathin semiconductor nanosheets in this study provides a new strategy for the development of unique plasmon-based hybrids with excellent optical properties.