Silver disposition and dynamics during electroless metal thin film synthesis

Ongoing advancements in the design and fabrication of semiconductor devices have prompted the exploration of chemical approaches for the metallization of titanium nitride (TiN), a uniquely conductive ceramic material, as alternatives to conventional, high-cost, physical-based deposition techniques. Although direct electrolytic deposition of thin metallic films onto TiN surfaces remains industrially impractical, electroless metallization using an amine-terminated seed layer presents a promising solution. In this study, a copolymer of 4-nitrophenyl and 4-vinylpyridine (a PVP-like film) is successfully electrografted onto the TiN surface via diazonium chemistry. The interaction between the resulting amine-terminated PVP-like seed layer and a PdCl2/HCl activator is throughout investigated to provide insight into the autocatalytic mechanism underlying the electroless nickel plating process. This process facilitates the formation of a compact, continuous nickel–boron (Ni–B) thin film. The electrolessly deposited Ni–B layer serves as a robust base for subsequent electrolytic copper deposition, enabling the effective filling of serpentine structures in silicon microdevices. Thus, this work introduces a fully aqueous metallization approach suitable for microelectromechanical systems (MEMS). More importantly, covalent bonding of the electrografted polymer, as confirmed by X-ray photoelectron spectroscopy (XPS), is discussed to elucidate the strong adhesion properties of the PVP-like/Ni–B/Cu multilayer stack on the TiN surface.

A new methodology was developed to probe glass transition temperatures (Tgs) of polymer thin films supported on gold (Au) substrates and confined between two solid (silica and silver) surfaces based on the surface plasmon polariton (SFPP) signals generated by sum frequency generation (SFG) spectroscopy. The measured Tgs for polymer (poly(methyl methacrylate), poly(benzyl methacrylate) and poly(ethyl methacrylate)) thin films supported on Au substrates showed similar thickness-dependent trend, that is, the Tg decreased as the thin film thickness decreased due to the free surface effect. However, the measured Tg of the (poly(methyl methacrylate)) thin films confined between two solid surfaces increased significantly with respect to the bulk value, indicating the strong interfacial effect when the free surface was replaced by a buried interface. This method to measure the Tg can be applied to study different polymer thin films supported on metal surfaces or confined between two solid surfaces with different surface chemistries. More importantly, SFG has the unique selectivity and sensitivity to study surfaces and interfaces, providing the feasibility to develop SFG into a powerful tool to detect surface, interfacial, and bulk Tgs of a polymer thin film simultaneously in the future.

Cr films of controlled thickness deposited on glass substrates were irradiated by a high number of low-intensity femtosecond laser pulses below the Cr single-pulse damage threshold, producing periodic surface structures (LIPSS) of very high regularity via metal oxidation. To address the multiplicity of electromagnetic modes allowed for thin films, a rigorous numerical approach for modeling surface plasmon polaritons (SPP) in thin-film geometry has been developed. Three types of modes are predicted: the classical SPP with periodicities Λ ~ λ (λ is laser wavelength) at air-film interface, and Λ ~ λ/n at film-substrate interface (n is refractive index of substrate), and a propagation mode Λ ~ λ/nCr where nCr is refractive index of film material. Experimentally observed LIPSS periods match well the predicted modes for the extreme cases, Λ ~ λ/n at film thickness h ≤ 30 nm and Λ ~ λ at h ≥ 200 nm, indicating respectively the dominance of SPP excited at the film-substrate interface and at the metal surface. For 30 nm < h < 200 nm, decreasing of the film thickness results in transition from the pure surface mode to its coupling with and finally domination of the electromagnetic wave excited at the film-substrate interface, providing evidence of the SPP mechanism of LIPSS formation under laser irradiation of thin metallic films.

The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220–250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.

Ultrafast interactions of surface plasmon-polaritons (SPPs) in systems with multiple coherently excited SPP and light beams are studied. SPPs on thin metallic films are excited by local scattering of the laser light on surface nanostructures consisting of polymeric or metallic ridges [1] and grooves. SPP interaction and scattering effects are investigated by leakage radiation microscopy (LRM) [2]. The interference of SPPs inside dielectrically-loaded SPP waveguides [3] as well as the interference of SPPs with additional light fields is used for tracking the propagation of ultrashort SPP pulses excited by 60 fs laser pulses at a central wavelength of 800 nm. We present results on SPP autocorrelation, allowing the SPP dispersion and pulse durations to be measured. An example of a LRM image of an interference pattern of two counter-propagating SPPs inside a dielectrically-loaded waveguide is shown in Fig. 1. Furthermore, we demonstrate ultrafast scattering of propagating SPPs on regions of metal films pumped by additional laser pulses. In a time-delay pump-probe experiment it is shown that this SPP scattering occurs on the time scale of the pulse duration. Applications of this effect as ultrafast SPP switches are discussed.

Electromagnetic surface waves are known to propagate along metal-dielectric interfaces (surface plasmon-polaritons) as well as along dielectric-dielectric interfaces (Dyakonov waves) if the two dielectrics have different spatial symmetries. Columnar and sculptured thin films, which are optically biaxial nanomaterials, may be grown on either metallic or dielectric substrates. Both surface plasmon-polaritons and Dyakonov waves can exist at the interface of a thin film and an appropriate substrate. The direction of propagation relative to the thin-film morphology is, in general, limited, and depends on the material and the vapor deposition angle used during fabrication. At the interface of a chiral sculptured thin film and an isotropic dielectric substrate, surface-wave propagation occurs over a much wider angular range and may allow for the first experimental observation of a Dyakonov wave. The characteristic properties of the surface wave, such as phase speed and decay rate, are dependant on the direction of propagation and the vapor deposition angle. As engineered nanomaterials, thin films offer a controllable medium for surface-wave propagation which may be tailored to exhibit specific characteristics. The porosity of the thin films may also offer certain technological advantages.

Periodical concentration of surface plasmon polaritons by wave interference in metallic film with nanocavity array

Silver localization on polyimide using microcontact printing and electroless metallization

Ambient pressure X-ray photoelectron spectroscopy (APXPS) combined with the dip-and-pull method can be used for operando studies of electrochemical systems. A complete coupling between the spectroscopic and the electrochemical measurements is generally challenging due to an inherent difference between the meniscus and the bulk electrolyte - the mass transport. This work investigates meniscus mass transport and its effect on the meniscus electrochemical processes by simultaneously conducting time-resolved APXPS and chronoamperometry for two types of electrochemical processes: capacitive and faradaic. Additionally, experiments are complemented with simulations based on a purposefully constructed transmission line model. In the investigated system, based on a gold electrode and carbonate electrolyte, the meniscus resistance is shown to be over 1000 times larger than the bulk electrolyte resistance. Consequently, during faradaic processes, considerable iR drop in the meniscus results in two to three orders of magnitude slower rate of charge transfer in the meniscus than in the bulk electrolyte. Using the acquired understanding of the meniscus mass transport, we suggest an experimental practice to quantify the iR drop and propose possible remedies for experiments where any impact of the iR drop must be avoided.

Using synchrotron radiation, the adsorption and decomposition of propene (C3H6) on the Ni(100) surface has been investigated in situ by time-resolved and temperature-programmed x-ray photoelectron spectroscopy. At 105 K, high-resolution C 1s spectra indicate precursor mediated occupation of a single adsorption state from submonolayer to monolayer coverage with evidence of adsorbate–adsorbate interactions and dispersed phase growth. High exposures lead to the formation of multilayers which desorb above 105 K leaving a chemisorbed monolayer. Between 105 and 150 K, a shift of the binding energies in the C 1s spectra is attributed to the transition from π- to di-σ-bonded propene. An abrupt change in the photoemission spectra occurs at 200 K due to the conversion of di-σ-bonded propene to a C3 intermediate containing a methyl group. Formation of this C2HxCH3 surface species is complete at 300 K and is immediately proceeded by dehydrogenation to carbidic carbon which is the final decomposition product above 370 K.

Luminescent color modulation of Zn/BaAl2O4:0.2%Eu phosphors for LED application

We present a novel noncontact, photothermal technique, based on the focus error signal of a commercial CD pickup head that allows direct determination of absorption in thin films. Combined with extinction methods, this technique yields the scattering contribution to the losses. Surface plasmon polaritons are excited using the Kretschmann configuration in thin Au films of varying thickness. By measuring the extinction and absorption simultaneously, it is shown that dielectric constants and thickness retrieval leads to inconsistencies if the model does not account for scattering.

In this study, a flexible strain sensor is devised using corrugated bilayer thin films consisting of poly(3-hexylthiophene) (P3HT) and poly(3,4-ethylenedioxythiophene)-polystyrene(sulfonate) (PEDOT:PSS). In previous studies, the P3HT-based photoactive non-corrugated thin film was shown to generate direct current (DC) under broadband light, and the generated DC voltage varied with applied tensile strain. Yet, the mechanical resiliency and strain sensing range of the P3HT-based thin film strain sensor were limited due to brittle non-corrugated thin film constituents. To address this issue, it is aimed to design a mechanically resilient strain sensor using corrugated thin film constituents. Buckling is induced to form corrugation in the thin films by applying pre-strain to the substrate, where the thin films are deposited, and releasing the pre-strain afterwards. It is known that corrugated thin film constituents exhibit different optical and electronic properties from non-corrugated ones. Therefore, to design the flexible strain sensor, it was studied to understand how the applied pre-strain and thickness of the PEDOT:PSS conductive thin film affects the optical and electrical properties. In addition, strain effect was investigated on the optical and electrical properties of the corrugated thin film constituents. Finally, flexible strain sensors are fabricated by following the design guideline, which is suggested from the studies on the corrugated thin film constituents, and the DC voltage strain sensing capability of the flexible strain sensors was validated. As a result, the flexible strain sensor exhibited a tensile strain sensing range up to 5% at a frequency up to 15 Hz with a maximum gauge factor ~7.

Surface modification of polyethylene naphthalate substrates by ultraviolet light-irradiation and assembling multilayers and their application in electroless deposition: The chemical and physical properties of the stratified structure

Si thin films are attracted as materials for ultra-large-scale solar cell systems at relatively low cost. Electrodeposition is expected as one fabrication method of Si thin films due to its advantages such as relatively simplicity process, precision control of nanostructure and continuous deposition in large area. Si thin films have been electrodeposited in non-aqueous solvents owing to their large electrochemical windows which allows for the study of Si electrodeposition [1-3]. Among various non-aqueous solvents, organic solvents and ionic liquids, which can be used under low temperature, have been used as electrolytes for the electrodeposition of Si thin films in our laboratory. We have previously succeeded to electrodeposit Si thin films in organic solvents and ionic liquids [4-6]. However, there is a problem for applications to solar cells that some impurities (mainly carbon and oxygen) are incorporated in thin films. We have reported the carbon content can be reduced by annealing treatment [7]. On the other hand, the decrease of oxygen content is still required. Thus, we evaluate the composition of Si thin films electrodeposited in an organic solvent and an ionic liquid without oxygen atoms in order to analysis the effect of bath conditions on the composition of thin films (especially, where the oxygen incorporated in Si thin films comes from). Si thin films were electrodeposited with 3 electrode cell (W.E. : Au, R.E. : Ag/Ag+, C.E. : Pt) in acetonitrile, 0.3 M tetrabutylammonium chloride and 0.5 M SiCl4 was used as an organic solvent, and 1-butyl-3-methylimidazolium hexafluorophosphate and 0.5 M SiCl4 as an ionic liquid. The composition of Si thin films were evaluated by X-ray photoelectron spectroscopy. As a result, the oxygen content in Si thin films were decreased by using the solvents without oxygen atoms in both organic solvent and ionic liquid cases. This results suggest that the reason the oxygen inclusion is derived from the incorporation of solvents themselves in films during electrodeposition, and propose us the way to obtain films with low impurities. In addition, the rotating disk electrode was used in the organic solvent case in order to promote the convection. The usage of this rotating disk electrode showed the decrease of impurities in Si thin films. Therefore, it is indicated that the stable supply of SiCl4 to the electrode surface is important factor to obtain films with low impurities. This study reveals that bath condition significantly affects to the composition of Si thin films, and could help us to fabricate films for applications to solar cells. This study was financially supported in part by the Japan Science and Technology Agency (JST) CREST program, and Y. T. acknowledges the Leading Graduate Program in Science and Engineering, Waseda University, from MEXT, Japan. [1] S. Zein El Abedin, N. Borrissenko, F. Endres, Electrochem. Comm., 6 (2004) 510. [2] T. Munisamy, A. J. Bard, Electrochim. Acta, 55 (2010) 3797. [3] M. Bechelany, J. Elias, P. Brodard, J. Michler, L. Philippe, Thin Solid Films 520 (2012) 1895. [4] Y. Nishimura and Y. Fukunaka, Electrochim. Acta, 53 (2007) 111. [5] T. Homma, J. Komadina, Y. Nakano, T. Ouchi, T. Akiyoshi, Y. Ishibashi, Y. Nishimura, T. Nishida, and Y. Fukunaka, Electrochem. Soc. Trans., 41 (2012) 9. [6] J. Komadina, T. Akiyoshi, Y. Ishibashi, Y. Fukunaka, T. Homma, Electrochim. Acta, 100 (2013) 236. [7] Y. Tsuyuki, A. Pham, J. Komadina, Y. Fukunaka, T. Homma, Electrochim. Acta, 183 (2015) 49.