Modulation of Morphology and Optical Property of Multi-Metallic PdAuAg and PdAg Alloy Nanostructures

Pandey, Puran,Kunwar, Sundar,Sui, Mao,Bastola, Sushil,Lee, Jihoon Springer US 2018 NANOSCALE RESEARCH LETTERS Vol.13 No.1

<P>In this work, the evolution of PdAg and PdAuAg alloy nanostructures is demonstrated on sapphire (0001) via the solid-state dewetting of multi-metallic thin films. Various surface configurations, size, and arrangements of bi- and tri-metallic alloy nanostructures are fabricated as a function of annealing temperature, annealing duration, film thickness, and deposition arrangements such as bi-layers (Pd/Ag), tri-layers (Pd/Au/Ag), and multi-layers (Pd/Au/Ag × 5). Specifically, the tri-layers film shows the gradual evolution of over-grown NPs, voids, wiggly nanostructures, and isolated PdAuAg alloy nanoparticles (NPs) along with the increased annealing temperature. In contrast, the multi-layers film with same thickness show the enhanced dewetting rate, which results in the formation of voids at relatively lower temperature, wider spacing, and structural regularity of alloy NPs at higher temperature. The dewetting enhancement is attributed to the increased number of interfaces and reduced individual layer thickness, which aid the inter-diffusion process at the initial stage. In addition, the time evolution of the Pd<SUB>150 nm</SUB>/Ag<SUB>80 nm</SUB> bi-layer films at constant temperature show the wiggly-connected and isolated PdAg alloy NPs. The overall evolution of alloy NPs is discussed based on the solid-state dewetting mechanism in conjunction with the diffusion, inter-diffusion, alloying, sublimation, Rayleigh instability, and surface energy minimization. Depending upon their surface morphologies, the bi- and tri-metallic alloy nanostructures exhibit the dynamic reflectance spectra, which show the formation of dipolar (above 700 nm) and quadrupolar resonance peaks (~ 380 nm) and wide dips in the visible region as correlated to the localized surface plasmon resonance (LSPR) effect. An absorption dip is readily shifted from ~ 510 to ~ 475 nm along with the decreased average size of alloy nanostructures.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (10.1186/s11671-018-2551-0) contains supplementary material, which is available to authorized users.</P>

Fabrication of Ag nanostructures by the systematic control of annealing temperature and duration on GaN (0001) via the solid state dewetting : Fabrication of Ag nanostructures

Pandey, Puran,Kunwar, Sundar,Sui, Mao,Li, Ming-Yu,Zhang, Quanzhen,Lee, Jihoon Wiley (John WileySons) 2017 Physica status solidi. PSS. A, Applications and ma Vol.214 No.3

Effect of Annealing Temperature on Morphological and Optical Transition of Silver Nanoparticles on c-Plane Sapphire

Pandey, Puran,Kunwar, Sundar,Sui, Mao,Li, Ming-Yu,Zhang, Quanzhen,Lee, Jihoon American Scientific Publishers 2018 Journal of nanoscience and nanotechnology Vol.18 No.5

<P>As a promising candidate for the improved performance, silver nanoparticles (Ag NPs) have been successfully adapted in various applications such as photovoltaics, light emitting diodes (LEDs), sensors and catalysis by taking the advantage of their controllable plasmonic properties. In this paper, the control on the morphologies and optical properties of Ag NPs on c-plane sapphire (0001) is demonstrated by the systematic control of annealing temperature (between 200 and 950 degrees C) with 20 and 6 nm thick Ag films through the solid state dewetting. With the relatively thicker film of 20 nm, various configuration and size of Ag NPs are fabricated such as irregular, round dome-shaped and tiny Ag NPs depending on the annealing temperature. In a shrill contrast, the 6 nm Ag set exhibits a sharp distinction with the formation of densely packed small NPs and ultra-highly dense tiny Ag NPs due to the higher dewetting rate. While, the surface diffusion assumes the main driving force in the evolution process of Ag NP morphologies up to 550 degrees C, the sublimation of Ag atoms has played a significant role on top on the surface diffusion between 600 and 950 degrees C. The reflectance spectra of Ag NPs exhibit the quadrupolar resonance and dipolar resonance peaks, and the evolution of peaks, shift and average reflectance were discussed based on the Ag NPs size and surface coverage. In particular, the dipolar resonance peak in the reflectance spectra red shifts from similar to 475 to similar to 570 nm due to the size increment of Ag NPs (38.31 to 74.68 nm). The wide surface coverage of Ag NPs exhibits the highest average reflectance (similar to 27%) and the lowest Raman intensity.</P>

Role of Annealing Temperature, Time, and Composition on the Fabrication of Aux Pd1−x Nanostructures on c-Plane Sapphire by the Solid-State Dewetting of Bimetallic Thin Films

Pandey, Puran,Kunwar, Sundar,Sui, Mao,Bastola, Sushil,Lee, Jihoon IEEE 2018 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol. No.

<P>Bimetallic nanostructures (BNSs) are important components in various applications due to their elemental composition and morphology dependent catalytic, electronic and optical properties. In this paper, the systematic evolution of Au <I><SUB>x</SUB></I>Pd<SUB>1−</SUB><I><SUB>x</SUB></I> (gold–palladium) BNSs on sapphire (0001) is studied via the solid-state dewetting of sequentially deposited Au–Pd bilayers along with the systematic control of elemental composition, annealing temperature, and time. Through the annealing of Au<I><SUB> x</SUB></I>Pd<SUB>1−</SUB><I><SUB>x</SUB></I> bilayers at various temperatures between 400 and 900 °C, the fabrication of nanoparticles (NPs) on bilayer, voids, and Au–Pd BNSs are observed with various compositions (Au<SUB>0.25</SUB>Pd<SUB>0.75</SUB>, Au<SUB>0.5</SUB>Pd<SUB>0.5</SUB>, and Au<SUB>0.75</SUB>Pd <SUB>0.25</SUB>). The evolution process of Au<I><SUB>x</SUB></I>Pd<SUB>1−</SUB><I><SUB>x</SUB> </I> BNSs is systematically analyzed based on the interdiffusion of Au and Pd and surface energy minimization mechanism. Along with the increased Au composition, the rate of dewetting is enhanced, which resulted in the significantly larger layer- top bimetallic NPs, voids, and BNSs. Furthermore, with the control of annealing time between 0 and 3600 s, the shape of Au–Pd BNSs is transform from the elongated to the round NPs due to the gradually enhanced diffusion. The reflectance (UV–VIS–NIR) spectra show the tight correlation with the surface morphology of Au<I><SUB>x</SUB></I>Pd<SUB>1−</SUB><I><SUB>x</SUB></I> BNSs and the average reflectance is gradually decreased along with the increased annealing temperature and time. The dipolar resonance peaks in the NIR region reveal a gradual blue-shift along with the increased annealing time due to the NP size reduction.</P>

Morphological and Optical Evolution of Silver Nanoparticles on Sapphire (0001) Along With the Concurrent Influence of Diffusion, Ostwald's Ripening, and Sublimation

Pandey, Puran,Kunwar, Sundar,Sui, Mao,Zhang, Quanzhen,Li, Ming-Yu,Lee, Jihoon IEEE 2017 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol. No.

<P>Silver nanoparticles (Ag NPs) have found a number of applications in various fields such as optoelectronics, sensors, and catalysts, and the optical, physical, and chemical properties of Ag NPs can be modified by the control of size, density, and configuration as well as their spacing. Therefore, in this paper, we demonstrate the size, shape, and spacing control of Ag NPs by the systematic control of annealing duration between 0 and 3600 s on sapphire (0001) (Al2O3). The Ag NPs show a sharp distinction in morphology along with the controlled duration at 20 and 14 nm thickness, and the evolution trend is systematically discussed based on the concurrent influence of surface diffusion, Ostwald's ripening, and sublimation. With the relatively thicker film of 20 nm, the fabrication of irregular and round NPs is demonstrated along with the gradually reduced size up on the annealing at 750 degrees C for the duration between 0 and 900 s. Between 1800 and 3600 s, tiny grain-like particles result as a consequence of an extensive sublimation. Meanwhile, with the film thickness of 14 nm at 400 degrees C, densely packed small NPs are resulted between 0 and 3600 s due to the limited surface diffusion. At the same time, the optical characterizations such as Raman and reflectance spectroscopy show a distinctive trend of spectra, i.e., intensity, peak position, and FWHM, based on the evolution of Ag NPs and are discussed in conjunction with the specific morphology and surface coverage of the Ag NPs.</P>

Evolution of morphological and optical properties of various Au_xPd_1−x bimetallic nanostructures by the systematic control of composition

Pandey, Puran,Kunwar, Sundar,Sui, Mao,Lee, Jihoon Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.450 No.-

<P><B>Abstract</B></P> <P>Bimetallic nanostructures (BMNSs) have gained significant attention because of their multi-functionality, site-specific response and electronic heterogeneity along with the additional opportunities to tune physical and optical properties. In this paper, the systematic evolution of Au<SUB>x</SUB>Pd<SUB>1−x</SUB> BMNS is thoroughly investigated in terms of morphological and optical properties through the solid state dewetting on <I>c</I>-plane sapphire. The bilayer composition and deposition order change are coherently tested along with the conventional growth parameter control. By the systematic control of annealing temperature, annealing duration and deposition thickness, the formation of various BMNSs demonstrate sharp distinctions at different Au<SUB>x</SUB>Pd<SUB>1−x</SUB> compositions (x = 0.25, 0.50 and 0.75). In specific, the high Au percentage in the Au<SUB>x</SUB>Pd<SUB>1−x</SUB> bilayers shows an enhanced dewetting due to the higher diffusivity and lower surface energy of Au atoms as compared to the Pd. Furthermore, the deposition order also induces a significant alteration on the dewetting process. Upon annealing, the evolution of BMNSs relies on the combination of atomic diffusion, inter-diffusion, alloying, surface and interface energy minimization and Rayleigh-like instability. Furthermore, the analysis of reflectance spectra demonstrates the development of the quadrupolar and dipolar resonance peaks, absorption band and their shift, induced by the localized surface plasmon resonance (LSPR) of various Au<SUB>x</SUB>Pd<SUB>1−x</SUB> BMNSs. Specifically, the quadrupolar resonance peak is consistent ∼380 nm whereas the dipolar resonance peak and absorption dip are readily blue-shifted and narrowed along with the evolution of isolated and uniform BMNSs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabrication of binary Au<SUB>x</SUB>Pd<SUB>1-x</SUB> alloy NPs with various alloy compositions. </LI> <LI> Demonstration of individual nanoparticles with bi-metallic alloy composite. </LI> <LI> Characterizations of binary alloy NPs by AFM, SEM, EDS and UV-VIS-NIR reflectance. </LI> <LI> Demonstration of LSPR resonance peaks, peak shift and absorption band evolution. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Modified Solid State Dewetting of Plasmonic Pt NPs by Using In-Pt Bi-Layer System: Improvement on the Surface Morphology and LSPR Properties of Pt NPs

Pandey, Puran,Sui, Mao,Kunwar, Sundar,Pandit, Sanchaya,Lee, Jihoon IEEE 2019 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol.18 No.-

<P>The solid state dewetting (SSD) is a useful synthesis technique to fabricate arrays of metallic nanostructures with the diverse size, density, and inter-particle spacing utilizing the solid-state diffusion of atoms below the melting point of elements. However, this technique is limited when the elements utilized possess very low diffusivity such as platinum (Pt), generally yielding poor surface morphologies even at high annealing temperature of 800 °C. In this paper, a clever approach of Pt NP fabrication is demonstrated based on the utilization of sacrificial In layer on sapphire (0001), namely, the modified SSD of In/Pt bilayer system. This approach offers much improved control on the surface morphology of Pt NPs and improved LSPR response. Upon annealing, In atoms can inter-mix with the Pt atoms, consequently yielding the In-Pt alloy and thus can significantly enhance the overall dewetting by increasing the diffusivity. The result is well defined surface morphology of Pt NPs with an improved control at much lower temperature. Subsequently, the desorption of In atoms from the NP matrix occurs through the sublimation, generating nearly pure Pt NPs. These plasmonic Pt NPs exhibit strong absorption bands at the visible region due to the dipolar resonance with the relatively small NPs and along with the gradually improved NP uniformity, the width of extinction peak gradually becomes narrower. The larger Pt NPs demonstrate a slightly broader extinction band in the visible wavelength with the multipolar resonance mode. The significant improvement in the configuration and uniformity of Pt NPs are coherently discussed with the enhanced diffusion, sublimation, Rayleigh-like instability, energy minimization, and equilibrium configuration. The conventional limitation of SDD with the low diffusivity elements can be simply overcome by introducing an intermediate layer with the low surface energy and melting point, which can significantly enhance the dewetting of target system.</P>

Tunable localized surface plasmon resonance by self-assembly of trimetallic and bimetallic alloy nanoparticles via Ag sublimation from Ag/Au/Pt tri-layers

Kunwar, Sundar,Pandey, Puran,Pandit, Sanchaya,Sui, Mao,Lee, Jihoon Elsevier 2020 APPLIED SURFACE SCIENCE - Vol.504 No.-

<P><B>Abstract</B></P> <P>In this work, various configurations, size, density and composition of AgAuPt and AuPt alloy NPs are demonstrated via the solid-state dewetting (SSD) of Ag/Au/Pt tri-layers on the transparent c-plane sapphire (0001) and the corresponding LSPR characteristics are thoroughly investigated along with the FDTD simulation. The SSD is adapted to convert the sputtered Ag/Au/Pt tri-layers into the definite alloy NPs based on the diffusion, interdiffusion and energy minimization process. The resulting AgAuPt and AuPt NPs demonstrate much stronger plasmonic characteristics as compared to their counterparts with the tunable LSPR bands in the UV and VIS regions along with the various plasmon resonance modes such as dipolar (DR), quadrupolar (QR), multipolar (MR) and higher order (HO). Furthermore, the Ag atom sublimation demonstrates a significant role in the dewetting process, which significantly alters the size, shape and composition of alloy NPs, giving a rise to the development of AuPt NPs. In specific, the LSPR response attenuates with the sublimation, however, as the AuPt NPs in this study are significantly improved in terms of composition and configuration, i.e. shape, size and spacing, the LSPR responses are much stronger and dynamic as compared to the pure Pt NPs on sapphire in the previous studies.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabrication of AgAuPt and AuPt NPs by the solid-state dewetting of Ag/Au/Pt tri-layers of various thickness. </LI> <LI> Demonstration of individual nanoparticles of tri and bi-metallic alloy composite. </LI> <LI> Demonstration of various LSPR bands, peak shift and absorption band evolution. </LI> <LI> Demonstration of finite-difference time domain (FDTD) simulations for various ternary AgAuPt and binary AuPt NPs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Evolution of Self-Assembled Au NPs by Controlling Annealing Temperature and Dwelling Time on Sapphire (0001)

Lee, Jihoon,Pandey, Puran,Sui, Mao,Li, Ming-Yu,Zhang, Quanzhen,Kunwar, Sundar Springer US 2015 Nanoscale research letters Vol.10 No.1

<P>Au nanoparticles (NPs) have been utilized in a wide range of device applications as well as catalysts for the fabrication of nanopores and nanowires, in which the performance of the associated devices and morphology of nanopores and nanowires are strongly dependent on the size, density, and configuration of the Au NPs. In this paper, the evolution of the self-assembled Au nanostructures and NPs on sapphire (0001) is systematically investigated with the variation of annealing temperature (AT) and dwelling time (DT). At the low-temperature range between 300 and 600 °C, three distinct regimes of the Au nanostructure configuration are observed, i.e., the vermiform-like Au piles, irregular Au nano-mounds, and Au islands. Subsequently, being provided with relatively high thermal energy between 700 and 900 °C, the round dome-shaped Au NPs are fabricated based on the Volmer-Weber growth model. With the increased AT, the size of the Au NPs is gradually increased due to a more favorable surface diffusion while the density is gradually decreased as a compensation. On the other hand, with the increased DT, the size and density of Au NPs decrease due to the evaporation of Au at relatively high annealing temperature at 950 °C.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s11671-015-1200-0) contains supplementary material, which is available to authorized users.</P>

Effect of Systematic Control of Pd Thickness and Annealing Temperature on the Fabrication and Evolution of Palladium Nanostructures on Si (111) via the Solid State Dewetting

Kunwar, Sundar,Pandey, Puran,Sui, Mao,Zhang, Quanzhen,Li, Ming-Yu,Lee, Jihoon SPRINGER SCIENCE + BUSINESS MEDIA 2017 NANOSCALE RESEARCH LETTERS Vol.12 No.1

<P>Si-based optoelectronic devices embedded with metallic nanoparticles (NPs) have demonstrated the NP shape, size, spacing, and crystallinity dependent on light absorption and emission induced by the localized surface plasmon resonance. In this work, we demonstrate various sizes and configurations of palladium (Pd) nanostructures on Si (111) by the systematic thermal annealing with the variation of Pd thickness and annealing temperature. The evolution of Pd nanostructures are systematically controlled by the dewetting of thin film by means of the surface diffusion in conjunction with the surface and interface energy minimization and Volmer-Weber growth model. Depending on the control of deposition amount ranging between 0.5 and 100 nm at various annealing temperatures, four distinctive regimes of Pd nanostructures are demonstrated: (i) small pits and grain formation, (ii) nucleation and growth of NPs, (iii) lateral evolution of NPs, and (iv) merged nanostructures. In addition, by the control of annealing between 300 and 800 °C, the Pd nanostructures show the evolution of small pits and grains, isolated NPs, and finally, Pd NP-assisted nanohole formation along with the Si decomposition and Pd-Si inter-diffusion. The Raman analysis showed the discrepancies on phonon modes of Si (111) such that the decreased peak intensity with left shift after the fabrication of Pd nanostructures. Furthermore, the UV-VIS-NIR reflectance spectra revealed the existence of surface morphology dependent on absorption, scattering, and reflectance properties.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s11671-017-2138-1) contains supplementary material, which is available to authorized users.</P>