The electroless plating of metals and their alloys, oxides, and chalcogenides represents a critically important technology for the automotive, aerospace, machine tools, and, especially, the electronics industries. Since the initial efforts involving the plating of industrially important metals, such as Ni, Co, Cu, Ag, and Au, in the mid-20th century, the process has evolved to encompass a growing number of elements. At the same time, this expansion in the palette of accessible metals has enabled progress in these industries and evoked new nonconventional applications. In this review, we collect and survey available electroless processes in aqueous and organic solvent systems for each element organized according to position in the Periodic Table as a resource for the reader. Examples illustrating progress in the field are presented and are described in sufficient detail to be useful and understandable for both the expert and nonexpert. Given the historical importance of electronics as a driver for development of electroless processes, examples are electronics-related where possible. However, we strive to also include examples of applications in nontraditional fields to provide the reader with a sense of generality available for electroless methods. The review closes with an outlook for the field and a challenge to scientists and engineers to adapt electroless processes for new applications to continue the growth of the field.

The strong CO ligand vibrations of an octahedral complex, fac-[Re (CO)3(bpy)(CH3CN)]+, in acetonitrile are observed at 2040 and 1932 cm-1. Facial rhenium tricarbonyl systems offer very strong and isolated CO vibrations with the potential for interactions between these vibrations. This work first identifies the dominant ion-pair species using attenuated total reflection infrared (ATR-IR) absorption spectra on a dilution series and then determines the strength of these CO ligand vibrations (as isolated vibrations) with a combination of ATR-IR and etalon-based measurements that determine the absolute complex index of refraction of the solution. Finally, the etalon experiments are modeled to study the interaction between vibrations, which is a property not embedded in the solution's complex index of refraction. The ATR-IR spectra are accomplished on a dilution series as well as a larger set of spectra as these solutions evaporated. The A'(1) CO ligand band at 2040 cm-1 is fit with a sum of three Lorentzian functions characterizing the distribution of free, solvent-separated, and contact ion pairs of this octahedral complex vs concentration. The other CO ligand band at 1932 cm-1 is broader and complicated by the dynamics of vibrational interactions, the unresolved splitting of the A'(2) and A″ CO vibrations, and ion-pair speciation. The etalon transmission measurements vs angle were on a 0.029 M solution, and Rabi splittings of 19 and 38 cm-1 were observed for the A'(1) CO vibration and the unresolved A'(2) + A″ CO vibrations, respectively. The great strength of the CO ligand vibrations is evident despite the use of a dilute solution. Integrated band intensities are reported in comparison to hybrid density functional calculations for isolated vibrations. Then, the observed Rabi splittings are modeled to obtain the coupling strength of the CO ligand vibration with etalon cavity modes and with each other. In summary, this work develops a method to determine the concentration of these solutions from the ATR-IR spectrum, characterizes the ion-pairing, shows that the index of refraction is not constant in the IR spectral region of interest, and develops an interaction Hamiltonian that characterizes cavity-vibration and vibration-vibration coupling.

A new method is established using an etalon cavity to assist in the determination of the wavelength-dependent complex index of refraction of a solution throughout the mid-infrared range. The results are used to study the cavity-vibration polaritons of PF6- in acetonitrile. Mixed states are formed by placing solution inside a pair of parallel plate mirrors with a wavelength-scale spacing, i.e., within an etalon, such that there are cavity states that are angle-tuned into resonance with the strong P-F vibrations. The dominant ν3 vibrations of PF6- consist of nearly triply degenerate oscillations of the partial-positively charged phosphorous against antisymmetric concerted motions of different sets of fluorine atoms with partial negative charges. These vibrations are dominant even though the solute is 29 times less concentrated than the solvent on a molar basis. The first part of the paper describes the method of determining the complex index of refraction of the solution from a combination of etalon transmission maxima and the attenuated total reflection (ATR) absorption spectrum of the solution. The results are presented as an analytical function including a sum of 37 vibrational contributions. Absolute integrated isolated band intensities were determined to be 463 ± 4, 462 ± 7, and 266 ± 4 km/mol for the three ν3 PF6- vibrations at 841.4, 847.4, and 854.0 cm-1, respectively, which sum to 1191 ± 9 km/mol for the ν3 band. Then, the results are used to simulate the measured etalon transmission using the transfer matrix (TM) method with and without the ν3 target vibrations. The etalon transmission simulations reconstruct the position of cavity modes in the absence of target vibrations. They provide input data for the testing of simple quantum mechanical models for the interaction of vibrations with cavity modes and the interactions of vibrations with other vibrations within the molecule and between solute and solvent. The model shows that the nearly degenerate ν3 vibrations interact with each other with a vibration-vibration coupling of 33 ± 5 cm-1. This is comparable to the cavity-vibration coupling of 30.4 ± 2.9 cm-1 of the two strongest vibrations of PF6-.

Metallic nanoscale 3D architectures concentrate electromagnetic energy at precise spatial locations to enable sensing and photocatalysis applications. We have developed solution-based methods to reproducibly fabricate 3D gold nanostructures useful as efficient surface-enhanced Raman spectroscopy (SERS) biosensors. Virus capsids were recruited as templates to assemble gold nanoparticles on their surfaces at well-defined locations to prepare the nanoscale 3D structures. Cowpea mosaic virus (CPMV) and its variants were selected as specific templates due to their high symmetry, scalability, and stability, which have proven useful in materials science applications. While the methods described herein were optimized for the CPMV capsids, they also provide a useful starting point for researchers who are working toward the nanoassembly of metal nanoparticles on other protein scaffolds.

Steady-state and ultrafast vibrational spectroscopy can help to elucidate the interactions between small anions and their environment because the anions’ infrared absorption frequencies and vibrational energy relaxation (VER) times depend strongly on those interactions. Their strong infrared absorptions also make many of these anions promising candidates for strong coupling to optical fields. Here, we report the vibrational energy relaxation of dicyanamide (DCA) in H2O and D2O and find that the so-called solvent isotope effect on VER is not as pronounced as for other anions. In addition, we report the infrared spectroscopy and VER lifetimes of DCA, N3−, and NCS− embedded in a polyelectrolyte polymer. We find that the polymer matrix accelerates VER in a similar fashion to H2O, but the detailed mechanism of this acceleration remains unclear.

We describe the use of a paper-based probe impregnated with a vanadium-containing polyoxometalate anion, [PMo11VO40]5−, on screen-printed carbon electrodes for the electrochemical determination of chlorate. Cyclic voltammetry (CV) and chronocoulometry were used to characterize the ClO3− response in a pH = 2.5 solution of 100 mM sodium acetate. A linear CV current response was observed between 0.156 and 1.25 mg/mL with a detection limit of 0.083 mg/mL (S/N > 3). This performance was reproducible using [PMo11VO40]5−-impregnated filter paper stored under ambient conditions for as long as 8 months prior to use. At high concentration of chlorate, an additional catalytic cathodic peak was seen in the reverse scan of the CVs, which was digitally simulated using a simple model. For chronocoulometry, the charge measured after 5 min gave a linear response from 0.625 to 2.5 mg/mL with a detection limit of 0.31 mg/mL (S/N > 3). In addition, the slope of charge vs. time also gave a linear response. In this case the linear range was from 0.312 to 2.5 mg/mL with a detection limit of 0.15 mg/mL (S/N > 3). Simple assays were conducted using three types of soil, and recovery measurements reported.

We describe the use and characterization of a multilayer film, prepared via layer-by-layer deposition of cationic para-rosaniline acetate dye (i.e., PR) and the vanadium-containing Keggin-type polyoxometalate anion, [PMo11VO40](5-) (i.e., PVMo11), on indium tin oxide (ITO) as an electrode for determination of chlorate. A linear cyclic voltammetry (CV) current response was observed for the 0 mu M <= [ClO3-] <= 1000 mu M range with a detection limit of similar to 220 mu M ClO3- (S/N > 3) in a pH = 2.5 solution of 100 mM sodium acetate. Electrode response was insensitive to interference by oxygen and nitrogen-based explosives like TNT, a prerequisite for use in the field. A Taguchi L16 array was used to investigate the performance of the electrode as functions of number of PVMo11/PR bilayers (L; 3-6 bilayers), solution pH (H; pH similar to 1.32-2.85), solution [ClO3-] (C; 250-1000 mu M), CV scan rate (S; 50-200 mV s(-1)), and film age (A; 1-8 weeks). Maximum current response was obtained for a 1 week old 5 bilayer film immersed in a pH 2.85 0.10 M NaCl (aq) solution containing 1000 mu M ClO3-. However, current response fell as films aged, requiring aging of films for approximately 8 weeks prior to use to obtain reproducible analyses. A two-level full factorial design using films aged 8 weeks identified the variables S, L, H, and C and variable interactions LS and HS as statistically significant contributors to the film current response and provided a model describing film performance. Published by Elsevier B.V.

fac-(bpy)Re(CO)3CF3SO3 reacts with sodium dicyanamide in THF/MeOH/H2O to give fac-(bpy)Re(CO)3N(CN)2 (1) in 81% yield. Complex 1 was characterized spectroscopically and electrochemically using NMR, IR, UV–Vis, fluorescence and cyclic voltammetry. Complex 1 crystallizes in the P21/c space group with a=7.2004(3) Å, b=12.9547(5) Å, c=16.8523(6) Å, β=101.989(1) °, and Z=4. Photophysical measurements indicate the π-acceptor ability of N(CN)2− as equivalent to that of the 4-N,N-dimethylaminopyridine ligand. Strong luminescence is observed in solution at room temperature and in 4:1 ethanol:methanol matrices at 77K attributed to the 3MLCT state.

We will focus on approaches which make use of light-matter interactions to alter the chemical behavior of a target molecular species. This is done through cavity coupling to a molecular vibration. Coupling vibrational transitions to resonant optical modes creates vibrational polaritons shifted from the uncoupled molecular resonances and provides a convenient way to modify the energetics of molecular vibrations. This approach is a viable method to explore controlling chemical reactivity and energy relaxation. Here, we demonstrate frequency domain results for vibrational bands strongly coupled to optical cavities. We experimentally and numerically describe strong coupling between a Fabry-Pérot cavity and several molecular species (e.g., poly-methylmethacrylate, thiocyanate, hexamethyl diisocyanate). We investigate strong and weak coupling regimes through examination of cavities loaded with varying concentrations of a urethane monomer. Rabi splittings are in excellent agreement with an analytical description using no fitting parameters. We show that coupling strength is a function of molecule/cavity mode overlap by systematically altering the position of a molecular slab throughout a first order cavity with results agreeing well with analytical and transfer matrix predictions. Further, remote molecule-molecule interaction will be explored by placing discrete and separated molecular layers throughout a cavity. In addition to establishing that coupling to an optical cavity modifies the energy levels accessible to the coupled molecules, this work points out the possibility of systematic and predictive modification of the excited-state kinetics of vibration-cavity polariton systems. Opening the field of polaritonic coupling to vibrational species promises to be a rich arena amenable to a wide variety of infrared-active bonds that can be studied in steady state and dynamically.

Self-healing materials, which enable an autonomous repair response to damage, are highly desirable for the long-term reliability of woven or nonwoven textiles. Polyelectrolyte layer-by-layer (LbL) films are of considerable interest as self-healing coatings due to the mobility of the components comprising the film. In this work mechanically stable self-healing films were fabricated through construction of a polyelectrolyte LbL film containing squid ring teeth (SRT) proteins. SRTs are structural proteins with unique self-healing properties and high elastic modulus in both dry and wet conditions (>2 GPa) due to their semicrystalline architecture. We demonstrate LbL construction of multilayers containing native and recombinant SRT proteins capable of self-healing defects. Additionally, we show these films are capable of utilizing functional biomolecules by incorporating an enzyme into the SRT multilayer. Urease was chosen as a model enzyme of interest to test its activity via fluorescence assay. Successful construction of the SRT films demonstrates the use of mechanically stable self-healing coatings, which can incorporate biomolecules for more complex protective functionalities for advanced functional fabrics.

Fabrication of nanoscale structures with localized surface plasmons allows for substantial increase in sensitivity of chem/bio sensors. The main challenge for realizing complex nanoplasmonic structures in solution is the high level of precision required at the nanoscale to position metal nanoparticles in 3D. In this study, we report a virus-like particle (VLP) for building a 3D plasmonic nanostructure in solution in which gold nanoparticles are precisely positioned on the VLP by directed self-assembly techniques. These structures allow for concentration of electromagnetic fields in the desired locations between the gold nanoparticles or "hot spots". We measure the efficiency of the optical field spatial concentration for the first time, which results in a ten-fold enhancement of the capsid Raman peaks. Our experimental results agree with our 3D finite element simulations. Furthermore, we demonstrate as a proof-of-principle that the plasmonic nanostructures can be utilized in DNA detection down to 0.25 ng/μl (lowest concentration tested), while the protein peaks from the interior of the nanoplasmonic structures, potentially, can serve as an internal tracer for the biosensors.

Designing coupled vibrational-cavity polariton systems to modify chemical reaction rates and paths requires an understanding of how this coupling depends on system parameters (i.e., absorber strength, modal distribution, and vibrational absorber and cavity line widths). Here, we evaluate the impact of absorption coefficient and cavity design on normal mode coupling between a Fabry-Perot cavity and a molecular vibration. For a vibrational band of urethane in a polymer matrix, the coupling strength increases with its concentration so that the system spans the weak and strong coupling regimes. The experimentally determined Rabi splitting values are in excellent agreement with an analytical expression derived for classical coupled oscillators that includes no fitting parameters. Also, the cavity mode profile is altered through choice of mirror type, with metal mirrors resulting in stronger confinement and thus coupling, while dielectric stack mirrors provide higher transmission for a given cavity quality factor and decreased coupling due to greater mode penetration into the dielectric mirror. In addition to polymers, the cavities can couple to molecular vibrational bands of dissolved species in solution, which greatly expands the range of systems that can be explored. Finally, longer path length cavities are used to demonstrate the path length independence of the coupling strength. The ability to adjust the cavity line width, through the use of higher order modes, represents a route to match the cavity dephasing time to that of the molecular vibration and may be applied to a range of molecular systems. Understanding the roles of cavity design and validating empirical and analytical descriptions of absorber properties on coupling strength will facilitate application of these strong coupling effects to enable currently unreachable chemistries.

Coherent coupling between an optical-transition and confined optical mode, when sufficiently strong, gives rise to new modes separated by the vacuum Rabi splitting. Such systems have been investigated for electronic-state transitions, however, only very recently have vibrational transitions been considered. Here, we bring strong polaritonic-coupling in cavities from the visible into the infrared where a new range of static and dynamic vibrational processes await investigation. First, we experimentally and numerically describe coupling between a Fabry-Perot cavity and carbonyl stretch (~1730 cm 1) in poly-methylmethacrylate. As is requisite for “strong coupling”, the measured vacuum Rabi splitting of 132 cm 1 is much larger than the full width of the cavity (34 cm-1) and the inhomogeneously broadened carbonyl-stretch (24 cm-1). Agreement with classical theories providea evidence that the mixed-states are relatively immune to inhomogeneous broadening. Next, we investigate strong and weak coupling regimes through examination of cavities loaded with varying concentrations of urethane. Rabi splittings increases from 0 to ~104 cm-1 with concentrations from 0-20 vol% and are in excellent agreement to an analytical description using no fitting parameters. Ultra-fast pump-probe measurements reveal transient absorption signals over a frequency range well-separated from the vibrational band as well as modifications of energy relaxation times. Finally, we demonstrate coupling to liquids using the C-O stretching band (~1985 cm-1) of Mo(CO)6 in an aqueous solution. Opening the field of polaritonic coupling to vibrational species promises to be a rich arena amenable to a wide variety of infrared-active bonds that can be studied statically and dynamically.

Polyelectrolyte multilayer films were fabricated via layer-by-layer deposition using polyallylamine hydrochloride lightly functionalized (∼1%) with a covalently bound polypyridyl Ru(II) chromophore dye (RuPAH) and polystyrenesulfonate (PSS). Absorbance oscillations were noted in the UV–visible spectra of these films as functions of the number of PSS/RuPAH bilayers and identified as optical interference effects. The interference effects were modeled according to a Fabry-Pérot cavity and a powerful conversion methodology was developed capable of correcting many spectra from relatively few fits. It is recommended that this method be applied as a standard to enable accurate analysis of absorbance spectra in thin films containing chromophores.

We present a method of Cu(In,Ga)S2 (CIGS) thin film formation via conversion of layer-by-layer (LbL) assembled Cu-In-Ga oxide (CIGO) nanoparticles and polyelectrolytes. CIGO nanoparticles were created via a novel flame-spray pyrolysis method using metal nitrate precursors, subsequently coated with polyallylamine (PAH), and dispersed in aqueous solution. Multilayer films were assembled by alternately dipping quartz, Si, and/or Mo substrates into a solution of either polydopamine (PDA) or polystyrenesulfonate (PSS) and then in the CIGO-PAH dispersion to fabricate films as thick as 1-2 microns. PSS/CIGO-PAH films were found to be inadequate due to weak adhesion to the Si and Mo substrates, excessive particle diffusion during sulfurization, and mechanical softness ill-suited to further processing. PDA/CIGO-PAH films, in contrast, were more mechanically robust and more tolerant of high temperature processing. After LbL deposition, films were oxidized to remove polymer and sulfurized at high temperature under flowing hydrogen sulfide to convert CIGO to CIGS. Complete film conversion from the oxide to the sulfide is confirmed by X-ray diffraction characterization.