Hybrid metal-insulator-metal structures on Si nanowires array for surface enhanced Raman scattering

Surface enhanced Raman scattering(SERS)is an efficient technique to detect low concentration molecules.In this work,periodical silicon nanowires(Si NWs)integrated with metal-insulator-metal(MIM)layers are employed as SERS substrates.Laser interference lithography(LIL)combined with reactive ion etching(RIE)is used to fabricate large-area periodic nanostructures,followed by decorating the MIM layers.Compared to MIM disks array on Si surface,the SERS enhancement factor(EF)of the MIM structures on the Si NWs array can be increased up to 5 times,which is attributed to the enhanced electric field at the boundary of the MIM disks.Furthermore,high density of nanoparticles and nanogaps serving as hot spots on sidewall surfaces also contribute to the enhanced SERS signals.Via changing the thickness of the insulator layer,the plasmonic resonance can be tuned,which provides a new localized surface plasmon resonance(LSPR)characteristic for SERS applications.

Controlled fabrication of nanoscale wrinkle structure by fluorocarbon plasma for highly transparent triboelectric nanogenerator

In this paper,we report a novel nanoscale wrinkle-structure fabrication process using fluorocarbon plasma on poly(dimethylsiloxane)(PDMS)and Solaris membranes.Wrinkles with wavelengths of hundreds of nanometers were obtained on these two materials,showing that the fabrication process was universally applicable.By varying the plasma-treating time,the wavelength of the wrinkle structure could be controlled.Highly transparent membranes with wrinkle patterns were obtained when the plasmatreating time was o125 s.The transmittances of these membranes were 490%in the visible region,making it difficult to distinguish them from a flat membrane.The deposited fluorocarbon polymer also dramatically reduced the surface energy,which allowed us to replicate the wrinkle pattern with high precision onto other membranes without any surfactant coating.The combined advantages of high electron affinity and high transparency enabled the fabricated membrane to improve the performance of a triboelectric nanogenerator.This nanoscale,single-step,and universal wrinkle-pattern fabrication process,with the functionality of high transparency and ultra-low surface energy,shows an attractive potential for future applications in microand nanodevices,especially in transparent energy harvesters.

Development of new classes of plasmon active nano-structures and their application in bio-sensing and energy guiding

Metal nanostructures exhibit special optical resonance modes originating fronl tile subwavelengt.h confinement of conductive electrons in the material. These resonance modes represent a strong research focus due to their application potential in optics and sensing application, in this short review recent achievements of our group in this field are highlighted. A wet-chemistry approach synthesis of advanced metallic nanostruetures will be introduced and their exact positioning and manipulation by electric field is shown. Next. the application of these nanostructures for a detection of small molecules will be described in several examples. Also, it will be shown that inetal nanostruetures can be used for sub-wavelength light focusing and for efficient energy coupling into polymer chains.

Single crystal erbium compound nanowires as high gain material for on-chip light source applications

Integrated photonics requires high gain optical materials in the telecom wavelength range for optical amplifiers and coherent light sources. Erbium （Er） containing materials are ideal candidates due to the 1.5 μm emission from Era＋ ions. However, the Er density in typical Er-doped materials is less than 10^20 cm-3, thus limiting the maximum optical gain to a few dB/cm, too small to be useful for integrated photonic applications. Er compounds could potentially solve this problem since they contain much higher Era＋ density. So far the existing Er compounds suffer from short lifetime and strong upconversion effects, mainly due to poor crystal qualities. Recently, we explore a new Er compound： erbium chloride silicate （ECS, Er3（SiO4）2C1） in the form of nanowire, which facilitates the growth of high quality single crystal with relatively large Era＋ density 0.62 ×10^22 cm^-3）. Previous optical results show that the high crystal quality of ECS material leads to a long lifetime up to 1 ms. The Er lifetime-density product was found to be the largest among all the Er containing materials. Pump-probe experiments demonstrated a 644 dB/cm signal enhancement and 30 dB/cm net gain per unit length from a single ECS wire. As a result, such high-gain ECS nanowires can be potentially fabricated into ultra-compact lasers. Even though a single ECS nanowire naturally serves as good wavegnide, additional feedback mechanism is needed to form an ultra-compact laser. In this work, we demonstrate the direct fabrication of 1D photonic crystal （PhC） air hole array structure on a single ECS nanowire using focused ion beam （FIB）. Transmission measurement shows polarization-dependent stop-band behavior. For transverse electric （TE） polarization, we observed stop-band suppression as much as 12 dB with a 9 μm long airholed structure. Through numerical simulation, we showed that Ω-factor as high as 11000 can be achieved at 1.53 μm for a 1D PhC micro-cavity on an ECS nanowire. Such a high Q cavity combined with the high material gain of ECS nanowires provides an attractive solution for ultra-compact lasers, an important goal of this research.