Effect of the TiO2 Nanoparticles on the Growth Behavior of Intermetallics in Sn/Cu Solder Joints

Shengyan Shang,Anil Kunwar,Jinye Yao,Yanfeng Wang,Haitao Ma,Yunpeng Wang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.2

In order to investigate the effect of TiO2 nanoparticles on growth behavior of interfacial Cu6Sn5 intermetallics compounds(IMCs) in Pb-free Sn/Cu system, the solder joints are fabricated by using flux doped with different content (0.0–2.0 wt% offlux) and particle diameter (5 nm and 50 nm) of TiO2 . In context of isothermal reflow soldering at 250 °C and subsequentair cooling, the increase in reflow duration from 10 to 120 s was characterized with an increment in IMC layer thicknessand grain size, due to the enhancement of Cu flux contribution for Ostwald ripening during constant temperature reflow andprecipitation kinetics during cooling. The increased proportion of TiO2 nanoparticles in flux was found to reduce the growthof IMC layer and grain size. The suppression effect on IMC was more pronounced for 5 nm particles as compared to the 50nm TiO2 . The TiO2 nanoparticles, adsorbed on IMC plane can retard the growth of the latter. Presence of sufficient amountof a given sized TiO2 nanoparticles among IMCs, by increasing the effective stress at the localized interfaces, and causingthe breaking of brittle Cu6Sn5 during growth stage; can help in the inhibition of IMC whisker formation. Particle diameterand mass proportion of TiO2 nanoparticles are important for soldering materials design.

Preparation of Y3Al5O12 Nanocrystals by a Glycol Route

Kunwar Singh Bartwal,Sujan Kar,Nanda Kaithwas,Monica Deshmukh,Mangla Dave,Hojin Ryu 한국세라믹학회 2007 한국세라믹학회지 Vol.44 No.5

Yttrium aluminum garnet, Y3Al5O12 (YAG) is an extensively used solid-state laser host material. YAG nanocrystals were synthesized using low-temperature glycol method, a modified sol–gel method performed at low temperature that consists of a mixture of salts that are mostly nitrates in an aqueous media. Single-phase nanocrystalline YAG was obtained at 850oC, which is a much lower temperature than with other techniques such as a wet-chemical technique. The structural characterization is done by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A crystallite size range of 20-50 nm was observed for the materials prepared at 850-950oC.

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>

Morphological and optical properties of Pd _x Ag _1-x alloy nanoparticles

Kunwar, Sundar,Pandey, Puran,Sui, Mao,Bastola, Sushil,Lee, Jihoon unknown 2018 SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS Vol.19 No.1

<P><B>Abstract</B></P><P>Alloy nanoparticles (NPs) can offer a wide range of opportunities for various applications due to their composition and structure dependent properties such as multifunctionality, electronic heterogeneity, site-specific response, and multiple plasmon resonance bands. In this work, the fabrication of self-assembled Pd<SUB>x</SUB>Ag<SUB>1-x</SUB> NPs alloy nanostructures with distinct size, density, shape, and composition is demonstrated via the solid-state dewetting of sputtered Pd/Ag thin films on c-plane sapphire. The initial stage of bilayer dewetting exhibits the nucleation of voids, followed by the expansion of voids and cluster breakdown and finally shape transformation along with the temperature control. Bilayer composition shows a substantial influence on the dewetting such that the overall dewetting is enhanced along with the increased Ag composition, i.e. Pd<SUB>0.25</SUB>Ag<SUB>0.75</SUB> > Pd<SUB>0.5</SUB>Ag<SUB>0.5</SUB> > Pd<SUB>0.75</SUB>Ag<SUB>0.25</SUB>. On the other hand, the size and density of NPs can be efficiently controlled by varying the initial thickness of bilayers. Reflectance peaks in UV and near-infrared (NIR) regions and a wide absorption band in the visible region arisen from the surface plasmon resonance are observed in reflectance spectra. The peak intensity depends on the composition of Pd<SUB>x</SUB>Ag<SUB>1-x</SUB> NPs and the NIR peaks gradually blue-shift with the size decrement.</P>

Fabrication of Ternary AgPdAu Alloy Nanoparticles on c-Plane Sapphire by the Systematical Control of Film Thickness and Deposition Sequence

Kunwar, Sundar,Pandey, Puran,Sui, Mao,Bastola, Sushil,Lee, Jihoon Springer New York 2018 Metallurgical and Materials Transactions A - Physi Vol.49 No.6

Determination of growth regimes of Pd nanostructures on c-plane sapphire by the control of deposition amount at different annealing temperatures

Kunwar, S.,Sui, M.,Pandey, P.,Zhang, Q.,Li, M. Y.,Bhandari, H.,Lee, J. Royal Society of Chemistry 2017 Physical chemistry chemical physics Vol.19 No.23

<P>Metallic nanoparticles (NPs) with tunable physical, optical and catalytic properties have a wide range of applications including various optoelectronics, sensors and fuel cells. In this paper, we demonstrate the evolution of various physical properties, configurations, size and density of palladium (Pd) nanostructures on sapphire(Al2O3) (0001) by the systematic control of deposition amount (DA) at distinct annealing temperatures. The transformation of the deposited thin films into various Pd NPs is achieved by the dewetting of the thin film by means of surface diffusion, nucleation, Volmer-Weber growth and surface energy minimization mechanism. Depending on the evolution of size, density and configuration, five distinctive regimes of Pd nanostructures are demonstrated: (i) nucleation and evolution of small NPs between 1 and 3 nm, (ii) medium NPs with the dominating vertical growth between 5 and 20 nm, (iii) laterally expanded large NPs between 30 and 40 nm, (iv) irregular coalesced Pd NPs between 50 and 80 nm and (v) voids evolution between 100 and 200 nm. Initial film thickness and annealing temperature play major roles on the dewetting process and the resulting Pd nanostructures are notably distinguished. The fabricated Pd nanostructures influence the lattice vibration modes of sapphire(0001) such as gradual decrement in the intensity and left-shift of the peak position with increased surface coverage. In addition, the optical properties are studied by UV-VIS-NIR (300-1100 nm) reflectance spectra, which shows the reflectance, absorption and scattering over the wavelength and are closely related to the morphology evolution of Pd nanostructures.</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>

Coming Out of the Traditional Trap

KUNWAR, Pashupati 이화여자대학교 아시아여성학센터 2013 Asian Journal of Women's Studies(AJWS) Vol.19 No.4

Samabikas Nepal is an organization based in the western part of Nepal that is doing social awareness-raising against the century old tradition of chhaupadi, a local practice of isolating women during menstruation. In this region women are discriminated against during their menstrual periods; they are not given good food and cannot participate in normal social activities as they are sent away from their homes for about a week. Samabikas has mobilized social, political and religious leaders, rights workers, teachers, students, young adolescent boys and girls, women’s groups and their networks, and mothers’ cooperatives to campaign against this practice. In three districts, women have started to abandon the chhaupadi practice. Samabikas has been continuously engaged in empowering women and young girls. In the course of the campaign, three parts of Achham district are already declared as chhaupadi-free areas. The chhaupadi huts have been dismantled and more women and girls have been enabled to share in power. Vigilance committees have become active and alert for rescuing women who are vulnerable to discrimination and gender-based violence. The campaign is gaining momentum and spreading in neighboring districts, but resentment remains. The government has issued a directive that prohibits any sort of practice that discriminates against women such as chhaupadi. However, its implementation remains weak and unmonitored. As a survivor myself, I have come a long way in the peaceful struggle against this tradition.

Palladium Nanostructures on GaN (0001): Evolution of Pd Hillocks, Voids, Nanoclusters and Nanoholes via Systematic Control of Annealing Temperature at Various Pd Thickness

Kunwar, Sundar,Sui, Mao,Zhang, Quanzhen,Pandey, Puran,Li, Ming-Yu,Lee, Jihoon American Scientific Publishers 2018 Journal of nanoelectronics and optoelectronics Vol.13 No.6

<P>Controllable synthesis of metallic nanostructures is of great importance in electronic, optical, catalytic, sensing and medical applications, in which the various corresponding properties can be directly tuned by the control of configuration, dimension and density of nanostructures. Here, the fabrication of self-assembled Pd nanostructures and porous GaN (0001) is demonstrated by the systematic control of annealing temperature and thickness of Pd thin films. The evolution of various Pd nanostructures is systematically presented and discussed in correlation with the diffusion of Pd adatoms, void nucleation and growth, Volmer-Weber growth model and surface and interface energy minimization mechanism. Depending on the systematic temperature control, the Pd nanostructures exhibit three distinctive growth regimes: tiny pits and hillocks along with void nucleation and growth (regime-I) between 400 and 600 degrees C, expanded void to the isolated nanoclusters (regime-II) between 650 to 750 degrees C and finally Pd nanoclusters assisted nanohole (NH) formation along with a GaN decomposition (regime-III) between 800 and 850 degrees C. Under an identical growth condition, the growth regimes shift along with the variation of Pd thickness due to the alteration in the required diffusion energy: that is the dewetting process occurs at relatively lower temperature for thinner initial Pd film and vice-versa. In addition, the evolution of the Pd nanostructures on GaN (0001) is closely associated with the optical characteristics such that photoluminescence (PL) and Raman intensity is high for low surface coverage whereas the average optical reflectance holds the reverse relationship.</P>

Plasmonic Pt Nanocrystals by Using a Sacrificial In Component via the Enhanced Dewetting on Sapphire (0001): Improvement on Morphological and Localized Surface Plasmon Resonance Properties

Kunwar, Sundar,Pandey, Puran,Sui, Mao,Pandit, Sanchaya,Gu, Zenan,Lee, Jihoon American Chemical Society 2019 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.123 No.4

<P>Modulation of functional metallic nanoparticles (NPs) in terms of their size, configuration, and dimension can offer a promising route to control the optical, catalytic, magnetic, and sensing properties for a wide range of applications. Herein, the platinum (Pt) nanostructures of improved morphological and localized surface plasmon resonance properties are demonstrated via the enhanced solid-state dewetting by using a sacrificial indium (In) layer on sapphire (0001). Upon annealing, the concurrent occurrence of intermixing between In and Pt atoms, formation of In-Pt alloy and sublimation of In atoms plays major roles in accelerating the dewetting process, which results in the formation of definite Pt nanostructures. The alteration in the In and Pt ratio readily varies the shape, size, and areal density of the resulting Pt NPs. The optical characteristics reveal that the localized surface plasmon resonance (LSPR) response is sensitively affected by the resulting surface morphology of Pt NPs. Specifically, the LSPR peak is dynamically tunable in the visible region over the range of wavelength 450 nm < λ < 520 nm on the basis of the variation of the surface morphologies of Pt NPs. In contrast to the conventional dewetting of pure Pt films, this approach signifies the advantages such as improved configuration, uniformity, and isolation of Pt NPs under similar growth conditions. The growth characteristics and structures of the resulting Pt NPs are discussed on the basis of the enhanced diffusion, energy minimization, and equilibrium configuration mechanism.</P> [FIG OMISSION]</BR>