Au Nanoislands Research Articles

The influence of ultrafast laser processing on morphology and optical properties of Au-GaAs composite structure

The results of direct femtosecond laser structuring of GaAs wafer coated with continuous semitransparent gold (Au) film are presented. The obtained structures demonstrate a combination of different features, namely laser-induced periodic surface structures (LIPSS) on semiconductor and metal film, nanoparticles, Au islands, and fragments of exfoliated Au film. The properties of Au-GaAs samples are studied with scanning electron microscopy (SEM), Raman scattering, and photoluminescence (PL) spectroscopy. The behaviour of phonon modes and enhancement of band-edge PL of Au-GaAs composite sample are discussed. The Raman spectra of Au-GaAs sample processed at different levels of irradiation pulse energy reveal forbidden TO and allowed LO phonon modes for selected geometry of experiment, as well as the manifestation of GaAs surface oxidation and amorphization. A 12-fold increase of PL intensity for Au-GaAs sample with LIPSS compared to initial GaAs surface is observed. The detected PL enhancement is caused by an increase of absorption in GaAs due to the light field enhancement near the Au nanoislands and a decrease of nonradiative surface recombination. The blue shift of PL band is caused by the quantum size effect in GaAs nano-sized features at laser processed surface. The combination of GaAs substrate with surface micro- and nanostructures with Au nanoparticles can be useful for photovoltaic and sensorics applications.

Tunable Nanoislands Decorated Tapered Optical Fibers Reveal Concurrent Contributions in Through-Fiber SERS Detection.

Creating plasmonic nanoparticles on a tapered optical fiber (TF) tip enables a remote surface-enhanced Raman scattering (SERS) sensing probe, ideal for challenging sampling scenarios like biological tissues, site-specific cells, on-site environmental monitoring, and deep brain structures. However, nanoparticle patterns fabricated from current bottom-up methods are mostly random, making geometry control difficult. Uneven statistical distribution, clustering, and multilayer deposition introduce uncertainty in correlating device performance with morphology. Ultimately, this limits the design of the best-performance remote SERS sensing probe. Here we employ a tunable solid-state dewetting method to create densely packed monolayer Au nanoislands with varied geometric parameters in direct contact with the silica TF surface. These patterns exhibit analyzable nanoparticle sizes, densities, and uniform distribution across the entire taper surface, enabling a systematic investigation of particle size, density, and analyte effects on the SERS performance of the through-fiber detection system. The study is focused on the SERS response of a widely employed benchmark molecule, rhodamine 6G (R6G), and serotonin, a highly relevant neurotransmitter for the neuroscience field. The numerical simulations and limit of detection (LOD) experiments on R6G show that the increase of the total near-field enhancement volume promotes the SERS sensitivity of the probe. However, we observed a different behavior for serotonin linked to its interaction with the nanoparticle's surface. The obtained LOD is as low as 10-7 M, a value not achieved so far in a through-fiber detection scheme. Therefore, our work offers a strategy to design nanoparticle-based remote SERS sensing probes and provides new clues to discover and understand intricate plasmonic-driven chemical reactions.

(Invited) Changes in Electric Double-Layer Structures Under Localized Surface Plasmon Excitation

For the visible light energy conversion, the localized surface plasmon resonance (LSPR), which is the collective oscillations of free electrons, should be promising. With the excitation of LSPR, the highly localized electric field generates in the vicinity of metal nanostructures. It is interesting that various unique photo-response properties, such as chemical reactions or molecular excitations, can be observed due to the enhancement of light-matter interaction.[1] To understand and control such mediated chemical reactions or electrochemical reactions, the precise understanding about the electrified interfaces of plasmonic nanostructures should be required.Especially in the electrochemical system, the electric double layer is formed due to the difference in electrochemical potential between the metal interface and solution. The study of the surface potential is important for the design of chemical reactions because the surface potential at the liquid-solid interface is dependent on the physical properties of the systems. The zeta potential which is the potential of the slipping surface near the Stern layer of the diffusion layer could provide such information. From this point of view, in this study, we investigated the electric double-layer structures through the examination of the zeta potential under LSPR excitation condition. To obtain the zeta potential, we have performed the streaming potential method using Au nanoisland structures under visible light illuminations to excite the LSPR. It was interesting that the zeta potential was drastically changes under the visible light illumination conditions. This zeta potential change indicates the changes in the electric double layer structures through the excitation of LSPR. Through the investigations of incident wavelength dependence or the substrate dependences, the effects for the LSPR excitations on the electric double layer structure have been revealed. The present work would provide the fundamental knowledge about the effect on the LSPR excitation at solid-liquid interfaces.[1] H. Minamimoto et al., Acc. Chem. Res., 2022, 55(6), 809.

Electrochemically deposited Au nano-island on laser-scribed graphene substrates as EC-SERS biochips for uremic toxins detection

BackgroundChronic kidney disease (CKD) leads to uremic toxin buildup, requiring early detection for better management. Existing methods lack sensitivity, speed, or affordability for point-of-care diagnosis. This work addresses this by creating a novel sensor for rapid, sensitive uremic toxin detection. MethodsThe sensor leverages the combined effects of surface-enhanced Raman scattering (SERS) and electrochemistry (EC) for superior detection. The LIG substrate provides a stable platform for AuNPs, facilitating interaction with target molecules. Additionally, electrochemical deposition optimizes the sensor's sensitivity by amplifying the local electromagnetic field around AuNPs and offering specific binding sites for uremic toxins. Significant findingsThe developed sensor demonstrates exceptional performance in detecting uremic toxins. It achieves remarkably low detection limits (10-3 M for creatinine/uric acid, 10-4 M for urea) and offers distinct, concentration-dependent responses for different toxins in cyclic voltammetry (CV) measurements. Furthermore, characteristic oxidation peaks at specific potentials allow for direct identification and quantification of the toxins. These findings highlight the immense potential of this cost-effective and scalable sensor for point-of-care diagnostics and remote monitoring of kidney function. This advancement can significantly improve patient care by facilitating early detection of kidney problems and enabling timely intervention.

Mass Transport Limitations in Plasmonic Photocatalysis.

The interpretation of mechanisms governing hot carrier reactivity on metallic nanostructures is critical, yet elusive, for advancing plasmonic photocatalysis. In this work, we explored the influence of the diffusion of molecules on the hot carrier extraction rate at the solid-liquid interface, which is of fundamental interest for increasing the efficiency of photodevices. Through a spatially defined scanning photoelectrochemical microscopy investigation, we identified a diffusion-controlled regime hindering the plasmon-driven photochemical activity of metallic nanostructures. Using low-power monochromatic illumination (<2 W cm-2), we unveiled the hidden influence of mass transport on the quantum efficiency of plasmonic photocatalysts. The availability of molecules at the solid-liquid interface directly limits the extraction of hot holes, according to their nature and energy, at the reactive spots in Au nanoislands on an ultrathin TiO2 substrate. An intriguing question arises: does the mass transport enhancement caused by thermal effects unlock the reactivity of nonthermal carriers under steady state?

Laser pulse shape transformation in hybrid LC cells containing gold nano-island films

A nano-structured surface containing an Au nano-island film is used to fabricate hybrid liquid crystal (HLC) cells. HLCs are characterized by faster response times. The dynamic holographic technique is applied to make the conversion of the laser pulse shape by using HLCs. From a comparative analysis of experimental results with theoretical modeling of a dynamic process, the time constants of the dynamic grating recording and relaxation have been determined.

Au-Pt alloy nanoislands for highly sensitive localized surface plasmon resonance sensing of antimony(III) ions

Alloy nanomaterials exhibit superior plasmonic properties that can exceed traditional single-metal nanomaterials. Hence, they hold great potential for developing highly sensitive sensors capable of detecting small analytes in nanoscale. The self-assembly Au-Pt alloy nanoislands structure is used, for the first time, for localized surface plasmon resonance sensing. Its nanostructure has been studied and characterized by using various microscopy and spectroscopy techniques. It was found that Au0.94-Pt0.06 was the optimum composition with the best sensitivity toward the change of refractive index over various concentrations of NaCl solution and double the sensitivity than that of pure Au nanoislands. The Au-Pt chip with its surface functionalized with nitrotyrosine was successfully developed for highly sensitive detection of antimony (III) ion, the electronic properties of the interaction between nitrotyrosine and Sb during the biosensing was explored using density functional theory simulation to explain their strong adsorption to make nitrotyrosine a successful receptor. The sensor achieved a limit of detection of 0.0504 ppb, which is the best ever value among all those reported for Sb(III) ions sensing. With its high selectivity tested among 14 other common elements, the present Sb(III) ion LSPR sensor also possesses attributes of label-free, easy to fabricate and simple to operate.

Gold-Deposited Graphene Nanosheets for Self-Cleaning Graphene Surface-Enhanced Raman Spectroscopy with Superior Charge-Transfer Contribution.

The interaction of graphene with metals initiates charge-transfer interaction-induced chemical enhancements, which critically depend on the doping effect from deposited metallic configurations. In this paper, we have explored the gold nanoparticle-decorated monolayer graphene nanosheets for the large graphene-induced Raman enhancement of adsorbed analytes, indicating the surface-enhanced Raman spectroscopy (SERS) capabilities of metal-doped graphene (G-SERS). Here, the systematically sputtered Au thickness optimization procedure revealed noticeable modifications in the graphene Raman spectra and photoluminescence (PL) background quenching, which indicated favorable charge transfer through n-type doping of chemical vapor deposition-grown graphene nanosheets. The highly consistent, individually distributed morphology of the gold nanoislands over graphene nanosheets depicted a reproducibly uniform G-SERS signal with excellent relative standard deviation values (<5%), resulting in the strongest Raman intensity enhancement factors of ∼108 (MB) (methylene blue) and 107 (DPA) (2,6-pyridinedicarboxylic acid) composed of the weakest PL background. The combined charge-transfer-induced chemical enhancement and electromagnetic enhancement from individual Au nanoislands result in a lowering of detectability down to 10-16 M (MB) and 10-11 M (DPA) concentrations with efficient time-dependent signal stability. Additionally, the GAu demonstrated its effective (∼94.4%) photocatalytic degradation capabilities by decomposing MB dye molecules from a concentration of 1 μM to 2.52 fM within 60 min. Therefore, the prominent charge-transfer contribution through controlled Au decoration over graphene nanosheets provides a potential strategy for fabricating superior SERS sensors and photocatalysts exhibiting adequate signal consistency, stability, and photodegradation efficiency through overcoming the limitations of the traditional sensing platforms.

Facile and Low-Cost Fabrication of SiO2-Covered Au Nanoislands for Combined Plasmonic Enhanced Fluorescence Microscopy and SERS.

An easy and low-cost way to fabricate monometallic Au nanoislands for plasmonic enhanced spectroscopy is presented. The method is based on direct thermal evaporation of Au on glass substrates to form nanoislands, with thicknesses between 2 and 15 nm, which are subsequently covered by a thin layer of silicon dioxide. We have used HR-SEM and AFM to characterize the nanoislands, and their optical transmission reveals strong plasmon resonances in the visible. The plasmonic performance of the fabricated substrates has been tested in fluorescence and Raman scattering measurements of two probe materials. Enhancement factors up to 1.8 and 9×104 are reported for confocal fluorescence and Raman microscopies, respectively, which are comparable to others obtained by more elaborated fabrication procedures.

Electric field-stimulated Raman scattering enhancing biochips fabricated by Au nano-islands deposited on laser-scribed 3D graphene for uremic toxins detection

BackgroundThe detection of uremic toxins is important for early-stage diagnosis of chronic kidney disease. However, Raman spectroscopy is shortcoming of the sensitivity for detecting the trace analytes. The electric field-induced chemical surface-enhanced Raman scattering (SERS) enhancement (EC-SERS) detection is great way to solve and investigates uremic toxins. MethodsIn this work, various thickness (5–25 nm) of Au nano-islands were deposited on the 3D laser-scribed graphene (LSG) substrate for increasing the sensitivity and reproducibility of SERS detection. Particularly, applying the electric-field stimulus in Au-LSG SERS substrate allows to further amplify the SERS signals, and measure the EC-SERS signals of biomolecules. Significant findingsThe results show that 20 nm of Au nano-islands coated on LSG substrate obtains the highest SERS enhancement effects, and successfully detects the dye molecules (rhodamine 6G, R6G) and uremic toxins (urea and creatinine). The EC-SERS signals of R6G would enhance 17 times at the potential of −1.3 V, compared to SERS signals without applying an electric field. Moreover, the urea also displays 4 times higher at the potential of −0.2 V. The detecting molecules could be selected to enhance SERS signals by different voltages, showing the capability of selectively detecting biomolecules, which can solve the problem of complex sample pretreatment.

Highly Efficient On-Chip Photothermal Cell Lysis for Nucleic Acid Extraction Using Localized Plasmonic Heating of Strongly Absorbing Au Nanoislands.

Cell lysis serves as an essential role in the sample preparation for intracellular material extraction in lab-on-a-chip applications. However, recent microfluidic-based cell lysis chips still face several technical challenges such as reagent removal, complex design, and high fabrication cost. Here, we report highly efficient on-chip photothermal cell lysis for nucleic acid extraction using strongly absorbed plasmonic Au nanoislands (SAP-AuNIs). The highly efficient photothermal cell lysis chip (HEPCL chip) consists of a PDMS microfluidic chamber and densely distributed SAP-AuNIs with large diameters and small nanogaps, allowing for broad-spectrum light absorption. The SAP-AuNIs induce photothermal heat, resulting in a uniform temperature distribution within the chamber and rapidly reaching the target temperature for cell lysis within 30 s. Furthermore, the localized plasmonic heating of SAP-AuNIs expeditiously triggers phase transition and photoporation in the directly contacted lipid bilayer of the cell membrane, resulting in rapid and highly efficient cell lysis. The HEPCL chip successfully lysed 93% of PC9 cells at 90 °C for 90 s without nucleic acid degradation. This on-chip cell lysis offers a new sample preparation platform for integrated point-of-care molecular diagnostics.

Laser-induced controllable crystallization of organic-inorganic hybrid perovskites assisted by gold nanoislands

Organic-inorganic hybrid perovskites have attracted great interest in recent years because of their excellent luminescence properties. However, the controllable and reversible growth of such perovskites by using a simple method remains a big challenge although it is highly desirable. Here, we demonstrate the controllable and reversible crystallization of MAPbBr3 in a thin liquid film on top of densely-packed gold (Au) nanoislands deposited on a silica substrate. The formation of MAPbBr3 crystal is induced by irradiating densely-packed Au nanoislands with femtosecond laser light. MAPbBr3 crystals with diameters of ∼10 µm can be stably created around the focal point of the laser beam and they will disappear rapidly after switching off the laser light. The threshold laser power for creating stable MAPbBr3 crystal depends strongly on the morphology of Au nanoislands, which can be modified by changing the sputtering time. By increasing the concentration of the precursors in the liquid film, high-quality MAPbBr3 microrods can be obtained after switching off the laser light. Our findings indicate a simple but effective method to induce perovskites with a controllable manner and pave the way for developing photonic devices based on organic-inorganic perovskites.

Atomic-scale characterization of contact interfaces between thermally self-assembled Au islands and few-layer MoS2 surfaces on SiO2

The interaction between metallic nanoparticles and transition metal chalcogenides (TMDs) can realize new functionalities in thriving technologies such as optoelectronics and nanoengineering. Here we have investigated the self-assembly of triangular-shaped crystalline Au nanoislands on MoS2 flakes mechanically exfoliated or grown by chemical vapor deposition (CVD). The density and size of the islands are determined by substrate temperature, deposition flux, and subsurface morphology. The thickness of the MoS2 layers is measured by Raman spectroscopy, which also enables the evaluation of the strain and doping distributions induced by the Au islands. Top and cross-sectional images of the Au-MoS2 interface are obtained by scanning electron microscopy (SEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Sub-nanometer resolution of the Au, Mo and S layers reveals that the MoS2 flakes follow the corrugation of the SiO2 substrate, with flattening and wrinkling effects induced by the growth of the Au islands on top.

Observation of Multi-Directional Energy Transfer in a Hybrid Plasmonic-Excitonic Nanostructure.

Hybrid plasmonic devices involve a nanostructured metal supporting localized surface plasmons to amplify light-matter interaction, and a non-plasmonic material to functionalize charge excitations. Application-relevant epitaxial heterostructures, however, give rise to ballistic ultrafast dynamics that challenge the conventional semiclassical understanding of unidirectional nanometal-to-substrate energy transfer. Epitaxial Au nanoislands are studied on WSe2 with time- and angle-resolved photoemission spectroscopy and femtosecond electron diffraction: this combination of techniques resolves material, energy, and momentum of charge-carriers and phonons excited in the heterostructure. A strong non-linear plasmon-exciton interaction that transfers the energy of sub-bandgap photons very efficiently to the semiconductor is observed, leaving the metal cold until non-radiative exciton recombination heats the nanoparticles on hundreds of femtoseconds timescales. The results resolve a multi-directional energy exchange on timescales shorter than the electronic thermalization of the nanometal. Electron-phonon coupling and diffusive charge-transfer determine the subsequent energy flow. This complex dynamics opens perspectives for optoelectronic and photocatalytic applications, while providing a constraining experimental testbed for state-of-the-artmodelling.

High-performance photodetectors based on Au nanoislands decorated CdSSe nanobelt

Ternary alloy CdS&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Se&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; has the physical properties of CdS and CdSe, and its band gap can be adjusted by changing the component ratio of the elements. The alloy has excellent photoelectric properties and has potential application in optoelectronic devices. Although one has made some research progress of the CdSSe-based photodetectors, their performances are still far from the commercial requirements, so how to improve the performance of the device is the focus of current research. In this work, a single crystal CdS&lt;sub&gt;0.42&lt;/sub&gt;Se&lt;sub&gt;0.58&lt;/sub&gt; nanobelt device is first prepared by thermal evaporation. Under 550 nm illumination and 1 V bias, the ratio of photocurrent to dark current of the device is 1.24×10&lt;sup&gt;3&lt;/sup&gt;, the responsivity arrives at 60.1 A/W, and the external quantum efficiency reaches 1.36×10&lt;sup&gt;4&lt;/sup&gt;%, and the detectivity is 2.16×10&lt;sup&gt;11&lt;/sup&gt; Jones. Its rise time and fall time are about 41.1/41.5 ms, respectively. Secondly, after the CdSSe nanobelt is decorated by Au nanoislands, the optoelectronic performance of the device is significantly improved. Under 550 nm illumination and 1 V bias, the &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt;/&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;d&lt;/sub&gt; ratio, responsivity, external quantum efficiency and detectivity of the device are increased by 5.4, 11.8, 11.8 and 10.6 times, respectively, and the rise time and fall time are both reduced to half of counterparts of single CdSSe nanobelt. Finally, the microscopic physical mechanism of the enhanced optoelectronic performance of the device is explained based on localized surface plasmon resonance of Au nanoislands. After the combination of gold nanoislands and CdSSe nanobelt, the difference in Fermi level between them results in the transfer of electrons from CdSSe nanobelt to Au nanoislands, thus forming an internal electric field at the interface, which is directed from CdSSe nanobelt to Au nanoislands. Under illumination, the electrons in the Au nanoislands acquire enough energy to jump over the Schottky barrier because of localized surface plasmon resonance. These photoexcited hot electrons are trapped and stored in extra energy levels above the conduction band minimum, and then are cooled down to the band edge, thus realizing the transfer of electrons from Au nanoislands to CdSSe nanobelt. Moreover, the internal electric field also greatly promotes the transfer of hot electrons from Au nanoislands to CdSSe nanobelt, and inhibits the recombination of carriers at the interface, resulting in large photocurrent. Our work provides an effective strategy for fabricating high-performance photodetectors without increasing the device area.

Synergy between plasmonic nanocavities and random lasing modes: a tool to dequench plasmon quenched fluorophore emission.

Metal nanoparticles (NPs) can be employed to modify the emission level of a dye emitter by tailoring the spectral overlap of the optical gain and localized surface plasmon resonance (LSPR). In the case of plasmonic random lasers, tuning the spectral overlap by manipulating metal NPs changes the scattering properties of the system, which is crucial in random lasers (RLs). In order to overcome this drawback, the emitter gain spectrum across the LSPR is tuned by appropriately choosing various dye emitters. A system with Au nanoislands (NIs) randomly distributed on the surface of vertically aligned ZnO nanorods on a glass substrate coated with three different dye emitters has been employed to study the metal-gain interaction as a function of spectral overlap. It is observed that the photoluminescence is quenched in the presence of Au NIs for all the three dye emitters; however, the degree of quenching is found to be directly proportional to the extent of spectral overlap of the LSPR and the fluorophore emission spectrum, with the resonantly coupled systems exhibiting higher random lasing thresholds. However, a dequenching of the emission is observed under spectrally off-resonant conditions, leading to a lower threshold RL. The effect of tailoring of the metal-gain interaction on the coherent and incoherent intensity components of RL emission is studied to elucidate the contrasting results of photoluminescence and RL emission. As the optical gain shifts away from the LSPR peak, the RL emission is dominated by the coherent intensity. The speckle-like field distributions of the RL modes couple to the plasmonic nanocavities along with a reduced absorption loss for the off-resonant case, leading to an enhanced stimulated emission. Hence, a synergy between random laser modes, plasmonic nanocavities and optimum spectral overlap has been utilized as a tool to dequench the plasmon quenched fluorophore emission.

A Self-Referenced Refractive Index Sensor Based on Gold Nanoislands.

We report on a self-referenced refractive index optical sensor based on Au nanoislands. The device consists of a random distribution of Au nanoislands formed by dewetting on a planar SiO2/metal Fabry-Pérot cavity. Experimental and theoretical studies of the reflectance of this configuration reveal that its spectral response results from a combination of two resonances: a localized surface plasmon resonance (LSPR) associated to the Au nanoislands and the lowest-order anti-symmetric resonance of the Fabry-Pérot cavity. When the device is immersed in different fluids, the LSPR contribution provides high sensitivity to refractive index variations of the fluid, whereas those refractive index changes have little impact on the Fabry-Pérot resonance wavelength, allowing its use as a reference signal. The self-referenced sensor exhibits a spectral sensitivity of 212 nm/RIU (RIU: refractive index unit), which is larger than those of similar structures, and an intensity sensitivity of 4.9 RIU-1. The proposed chip-based architecture and the low cost and simplicity of the Au nanoisland synthesis procedure make the demonstrated sensor a promising self-referenced plasmonic sensor for compact biosensing optical platforms based on reflection mode operation.

Highly Adsorptive Au-TiO2 Nanocomposites for the SERS Face Mask Allow the Machine-Learning-Based Quantitative Assay of SARS-CoV-2 in Artificial Breath Aerosols.

Human respiratory aerosols contain diverse potential biomarkers for early disease diagnosis. Here, we report the direct and label-free detection of SARS-CoV-2 in respiratory aerosols using a highly adsorptive Au-TiO2 nanocomposite SERS face mask and an ablation-assisted autoencoder. The Au-TiO2 SERS face mask continuously preconcentrates and efficiently captures the oronasal aerosols, which substantially enhances the SERS signal intensities by 47% compared to simple Au nanoislands. The ultrasensitive Au-TiO2 nanocomposites also demonstrate the successful detection of SARS-CoV-2 spike proteins in artificial respiratory aerosols at a 100 pM concentration level. The deep learning-based autoencoder, followed by the partial ablation of nondiscriminant SERS features of spike proteins, allows a quantitative assay of the 101-104 pfu/mL SARS-CoV-2 lysates (comparable to 19-29 PCR cyclic threshold from COVID-19 patients) in aerosols with an accuracy of over 98%. The Au-TiO2 SERS face mask provides a platform for breath biopsy for the detection of various biomarkers in respiratory aerosols.

Mechanisms of Quasi van der Waals Epitaxy of Three-Dimensional Metallic Nanoislands on Suspended Two-Dimensional Materials.

Understanding structure at the interface between two-dimensional (2D) materials and 3D metals is crucial for designing novel 2D/3D heterostructures and improving the performance of many 2D material devices. Here, we quantify and discuss the 2D/3D interface structure and the 3D morphology in several materials systems. We first deposit faceted Au nanoislands on graphene and transition metal dichalcogenides, using measurements of the equilibrium island shape to determine values for the 2D/Au interface energy and examining the role of surface reconstructions, chemical identity, and defects on the grown structures. We then deposit the technologically relevant metals Ti and Nb under conditions where kinetic rather than thermodynamic factors govern growth. We describe a transition from dendritic to faceted islands as a function of growth temperature and discuss the factors determining island shape in these materials systems. Finally, we show that suspended 2D materials enable the fabrication of a novel type of 3D/2D/3D heterostructure and discuss the growth mechanism. We suggest that emerging nanodevices will utilize versatile fabrication of 2D/3D heterostructures with well-characterized interfaces and morphologies.

Plasmon effect on Pd/Au for optical sensing

In this study, gold nanoislands thin films were fabricated by pulsed laser deposition (PLD) method on quartz substrates at different substrate temperatures of 25, 300, 450, and 600 °C. A thin (4-5 nm) Pd film, as hydrogen catalyst over-layer, was sputter deposited on Au films. PLD at 25 and 300 °C led to semi-continuous surface morphology consisting of very fine-grained aggregates, and at 450 and 600 °C to spherical Au NPs. UV-Vis spectrometry showed localized surface plasmon resonance (LSPR) absorption at 732, 606, 586, and 560 nm for room temperature (R.T.), 300, 450, and 600 °C, respectively. FESEM revealed that hydrogen (10%) exposure induces surface stress leading to Au nanoislands separation. UV-Vis spectrophotometry showed a spectral blue-shift for the LSPR peak attributed to the plasmon coupling effect. Results showed that at various hydrogen concentration of 0 to 10%, films deposited at R.T. provides the most LSPR shift. Overall, we showed that plasmon coupling of PLD derived gold thin films is a suitable tool for accurate detection of hydrogen gas.