This work was sponsored by the Army Research Laboratory and was accomplished under USARL Cooperative Agreement Number W911NF&#8208;17&#8208;2&#8208;0057 awarded to G.T.F. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.

1. Allocation of Au nanorods
NOTE: Cetyltrimethylammonium bromide (CTAB)-covered AuNR may be synthesized by wet-chemistry (step 1.1) or purchased commercially (step 1.2) according to the reader&#8217;s preference, with each yielding similar results. Results in this work were based on commercially-sourced, AuNR with penta-twinned crystal structure. Impact of AuNR seed crystal structure (i.e., monocrystalline vs. penta-twinned) on ultimate morphology of the secondary metal shell remains unclear within the scope of plasmonic photodeposition, but has been of keen interest in both wet-14,15 and similar photo-chemical12 syntheses. Alternative surfactants to CTAB may be employed so long as Zeta-potential is positive, although final Pd morphology could change.
<ol>
	<li>Synthesis Techniques: Synthesize aqueously-dispersed AuNR at 0.5 mM Au using the silver-assisted method by Nikoobakht et al.16,17 (yielding monocrystalline structure) or the surfactant-assisted method by Murphy et al.18,19 (yielding penta-twinned crystal structure). Wash the AuNR via centrifugation20,21 to remove excess, free CTAB to a final concentration of 1-10 mM.</li>
	<li>Commercial Sources: Purchase aqueous AuNR dispersions at 0.5 mM Au with the following specifications: 40 nm diameter, 808 nm LSPR, and CTAB ligand (5 mM concentration) in DI water. Wash the AuNR via centrifugation20,21 to remove excess, free CTAB if the CTAB concentration exceeds 1-10 mM upon receipt. 
	NOTE: Aqueous AuNR dispersions with CTAB surfactant at a variety of sizes, aspect ratios, and particle number densities may be purchased from many commercial vendors and used successfully in this protocol.</li>
</ol>
2. Plasmonic photodeposition of Pd onto Au nanorods
<ol>
	<li>Preparation of Pd precursor
	<ol>
		<li>Prepare a 20 mM HCl solution. First, make 0.1 M HCl by diluting 830 &#956;L of stock concentrated HCl (37%, 12 M) with water to 100 mL. Second, make 0.02 M HCl by diluting 4 mL of 0.1 M HCl with water to 20 mL.</li>
		<li>Pipette 10 mL of 20 mM HCl into appropriate glassware and place in a bath sonicator (no sonication) with water temperature set to 60 &#176;C.</li>
		<li>Add 0.0177 g of PdCl2 into the 10 mL of 20 mM HCl and mix via sonication until all PdCl2 is dissolved. The resultant 10 mM H2PdCl4 solution should exhibit a dark orange color.</li>
	</ol>
	</li>
	<li>Preparation of photodeposition reaction mixture 
	NOTE: The procedure described assumes a 3 mL total volume for use in a cuvette to allow real-time feedback into plasmonic photodeposition process. The cited masses/volumes were selected for compatibility with typical chemicals/materials/reagents while allowing facile washing/recovery of the Pd-decorated AuNR. It is anticipated that similar results may be achieved if scaled to other volumes and/or alternative reaction vessels are used (e.g., glass beaker).
	<ol>
		<li>Degas stock AuNR solution and methanol (MeOH) in a bath sonicator for 30 min.</li>
		<li>Pipette 2.5 mL of aqueously-suspended AuNR (from step 2.2.1) into a 1 cm path length, macrovolume cuvette with a magnetic stir bar. Place the cuvette on a stir plate. 
		NOTE: Typical volume of a macrovolume cuvette is 3.5 mL. Quartz may be substituted with UV-transparent plastics.</li>
		<li>Pipette 475 &#956;L of degassed MeOH (from step 2.2.1) into the cuvette while gently stirring for approximately 15-30 min. Periodically remove any bubbles by gently tapping the bottom of the cuvette against a rigid surface as needed; removing solvated gasses can prolong the stability of the metal halide salt.</li>
		<li>Pipette 5 &#956;L of stock concentrated HCl (37%, 12 M) into the cuvette and let mix for 15 min. 
		NOTE: Tuning concentration of HCl support could influence final morphology/rate of Pd deposition, but concentrations less than 20 mM in the reaction mixture will allow H2PdCl4 to progressively hydrolyze and oxolate, leading to eventual PdOx formation after ~3 h.</li>
	</ol>
	</li>
	<li>Plasmonic photoreduction of [PdCl4]2- onto AuNR1,13
	<ol>
		<li>Inject 25 &#956;L of 10 mM H2PdCl4 into the reaction mixture for a 1:5 Pd:Au atomic ratio. Let the solution complex in dark for 1 h while stirring. 
		NOTE: This quantity may be adjusted according the desired Pd:Au ratio as the expense of altering the final molarities of Au, [PdCl4]2-, HCl, and MeOH of the reaction mixture. Reference22 illustrates example Pt-AuNR morphologies at different Pt:Au ratios- similar results can be expected with Pd.</li>
		<li>Irradiate the reaction mixture with an un-polarized, 715 nm long-pass filtered tungsten-halogen lamp at 35 mW/cm2 intensity for 24 h. 
		NOTE: Different light filters (or sources, e.g., laser) may be chosen according to unique LSPR wavelength for different Au nanostructure seeds. For example, a 420 nm long-pass filter may be used for plasmonic seed structures exhibiting LSPR at 450 nm. Light intensity may be decreased with neutral density filtration at the expense of a slower [PdCl4]2- reduction rate, leading to a longer total reaction time. Light intensity may be increased to reduce reaction time at the expense of potential for thermal reduction of [PdCl4]2- (onset is ~360 &#176;C via Reference23). An appropriate intensity can be calculated a priori to mitigate thermal reduction via calculation of nanoparticle surface temperature in isolation and/or collective ensembles24. Effects on ultimate Pd-AuNR morphology from varying irradiation intensity have not been explored.</li>
		<li>Wash the residual chemicals/reagents from the Pd-AuNR two times, each by: centrifugation at 9,000 x g, removing the supernatant with a pipette, re-suspending the Pd-AuNR pellet in water, and immersing the vial into a bath sonicator for 1-2 min to disperse20,21.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

Monitoring changes in optical absorbance using transmission UV-vis spectroscopy is useful to assess status of the photocatalytic reaction, with particular attention to the LMCT features of H2PdCl4. Wavelength maxima of LMCT features after injection of H2PdCl4 at step 2.3.1 (going from solid black to solid blue in Figure 1) provide insights into the local &#8220;environment&#8221; of the [PdCl4]2- molecules1</...

Guiding metal deposition onto plasmonic substrates via plasmonic hot carriers generated from a resonant external field could support 2-step formation of heterometallic, anisotropic nanostructures at ambient conditions with new degrees-of-freedom1,2,3. Conventional redox chemistry, vapor deposition, and/or electrodeposition approaches are ill-suited for high-volume processing. This is primarily due to excess/sacrificial reagent waste, low throughput 5+ step lithography processes, and energy intensive environments (0.01-10 Torr and/or 400-1000 &#176;C temperatures) with little or no direct control over resultant material characteristics. Immersion of a plasmonic substrate (e.g., Au nanoparticle/seed) into a precursor environment (e.g., aqueous Pd salt solution) under illumination at the localized surface plasmon resonance (SPR) initiates externally-tunable (i.e., field polarization and intensity) photochemical deposition of the precursor via plasmonic hot electrons and/or photothermal gradients3,4. For example, protocol parameters/requirements for plasmonically-driven photothermal decomposition of Au, Cu, Pb, and Ti organometallics and Ge hydrides onto nanostructured Ag and Au substrates have been detailed5,6,7,8,9. However, utilization of femtosecond plasmonic hot electrons to directly photoreduce metal salts at a metal-solution interface remains largely undeveloped, absent processes employing citrate or poly(vinylpyrrolidone) ligands acting as intermediary charge relays to direct nucleation/growth of the secondary metal2,10,11,12. Anisotropic Pt-decoration of Au nanorods (AuNR) under longitudinal SPR (LSPR) excitation was recently reported1,13 where the Pt distribution coincided with the dipole polarity (i.e., the assumed spatial distribution of hot carriers).
The protocol herein expands upon recent Pt-AuNR work to include Pd and highlights key synthesis metrics that can be observed in real-time, showing the reductive plasmonic photodeposition technique is applicable toward other metal halide salts (Ag, Ni, Ir, etc.).

<table>
	<tbody>
		<tr>
			<td>Aspheric Condenser Lens w/ Diffuser</td>
			<td>Thorlabs</td>
			<td>ACL5040U-DG15</td>
			<td>f=40 mm, NA=0.60, 1500 grit, uncoated</td>
		</tr>
		<tr>
			<td>Deuterium + Tungsten-Halogen Lightsource</td>
			<td>StellarNet</td>
			<td>SL5</td>
			<td></td>
		</tr>
		<tr>
			<td>Gold Nanorods, AuNR</td>
			<td>NanoPartz</td>
			<td>A12-40-808-CTAB</td>
			<td>CTAB surfactant, 808 nm LSPR, 40 nm diameter</td>
		</tr>
		<tr>
			<td>Ground Glass Diffuser</td>
			<td>Thorlabs</td>
			<td>DG20-1500</td>
			<td>1500 grit, N-BK7</td>
		</tr>
		<tr>
			<td>Hydrochloric acid, HCl</td>
			<td>J.T. Baker</td>
			<td>9539-03</td>
			<td>concentrated, 37%</td>
		</tr>
		<tr>
			<td>Low Profile Magnetic Stirrer</td>
			<td>VWR</td>
			<td>10153-690</td>
			<td></td>
		</tr>
		<tr>
			<td>Macro Disposable Cuvettes, UV Plastic</td>
			<td>FireFlySci</td>
			<td>1PUV</td>
			<td>10 mm path length</td>
		</tr>
		<tr>
			<td>Methanol, MeOH</td>
			<td>J.T. Baker</td>
			<td>9073-05</td>
			<td>&#8805;99.9%</td>
		</tr>
		<tr>
			<td>Palladium (II) chloride, PdCl2</td>
			<td>Sigma Aldrich</td>
			<td>520659</td>
			<td>&#8805;99.9%</td>
		</tr>
		<tr>
			<td>Plano-Convex Lens</td>
			<td>Thorlabs</td>
			<td>LA1145</td>
			<td>f=75 mm, N-BK7, uncoated</td>
		</tr>
		<tr>
			<td>Quartz Tungsten-Halogen Lamp</td>
			<td>Thorlabs</td>
			<td>QTH10</td>
			<td></td>
		</tr>
		<tr>
			<td>UV-vis Spectrometer</td>
			<td>Avantes</td>
			<td>ULS2048L-USB2-UA-RS</td>
			<td>AvaSpec-ULS2048L</td>
		</tr>
	</tbody>
</table>

photodeposition of pd onto colloidal au nanorods by surface plasmon excitation

A protocol is described to photocatalytically guide Pd deposition onto Au nanorods (AuNR) using surface plasmon resonance (SPR). Excited plasmonic hot electrons upon SPR irradiation drive reductive deposition of Pd on colloidal AuNR in the presence of [PdCl4]2-. Plasmon-driven reduction of secondary metals potentiates covalent, sub-wavelength deposition at targeted locations coinciding with electric field &#8220;hot-spots&#8221; of the plasmonic substrate using an external field (e.g., laser). The process described herein details a solution-phase deposition of a catalytically-active noble metal (Pd) from a transition metal halide salt (H2PdCl4) onto aqueously-suspended, anisotropic plasmonic structures (AuNR). The solution-phase process is amenable to making other bimetallic architectures. Transmission UV-vis monitoring of the photochemical reaction, coupled with ex situ XPS and statistical TEM analysis, provide immediate experimental feedback to evaluate properties of the bimetallic structures as they evolve during the photocatalytic reaction. Resonant plasmon irradiation of AuNR in the presence of [PdCl4]2- creates a thin, covalently-bound Pd0 shell without any significant dampening effect on its plasmonic behavior in this representative experiment/batch. Overall, plasmonic photodeposition offers an alternative route for high-volume, economical synthesis of optoelectronic materials with sub-5 nm features (e.g., heterometallic photocatalysts or optoelectronic interconnects).

Transmission UV-vis spectra, X-ray photoelectron spectroscopy (XPS) data, and transmission electron microscopy (TEM) images were acquired for the CTAB-covered AuNR in the presence/absence of H2PdCl4 in dark and under resonant irradiation at their longitudinal SPR (LSPR) to catalyze nucleation/growth of Pd. Transmission UV-vis spectra in Figure 1 and Figure 2 provide insights into the reaction dynamics according to changes in: (a) precursor ...

Watch this Scientific Journal Video about Photodeposition of Pd onto Colloidal Au Nanorods by Surface Plasmon Excitation at JoVE.com

Photodeposition of Pd onto Colloidal Au Nanorods by Surface Plasmon Excitation

A protocol for anisotropic photodeposition of Pd onto aqueously-suspended Au nanorods via localized surface plasmon excitation is presented.

A protocol is described to photocatalytically guide Pd deposition onto Au nanorods (AuNR) using surface plasmon resonance (SPR). Excited plasmonic hot ...

photodeposition-pd-onto-colloidal-au-nanorods-surface-plasmon

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JoVE Journal

Chemistry

7.4K Views.  U.S. Army Research Laboratory. A protocol for anisotropic photodeposition of Pd onto aqueously-suspended Au nanorods via localized surface plasmon excitation is presented.

Video: Photodeposition of Pd onto Colloidal Au Nanorods by Surface Plasmon Excitation

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date back to the early 1980s the focus of these early papers primarily characterized the changes to the structures under extremely harsh conditions (pH or temperature)1-3. It is also known that paramagnetic molecular oxygen undergoes a Heisenberg spin exchange interaction with stable radicals that extremely broadens the EPR signal4-6. Recently, we reported interesting results where this interaction of molecular oxygen with a certain part of the existing stable radical structure can be reversibly affected simply by flowing a diamagnetic gas through the carbon samples at STP7. As flows of He, CO2, and N2 had a similar effect these interactions occur at the surface area of the macropore system.
This manuscript highlights the experimental techniques, work-up, and analysis towards affecting the existing stable radical nature in the carbon structures. It is hoped that it will help towards further development and understanding of these interactions in the community at large.

Stable radicals that are present in carbon substrates interact with paramagnetic oxygen through a Heisenberg spin exchange. This interaction can be significantly reduced under STP conditions by flowing a diamagnetic gas over the carbon system. This manuscript describes a simple method to characterize the nature of those radicals.

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date ...

Quantitative and Qualitative Examination of Particle-particle Interactions Using Colloidal Probe Nanoscopy

Colloidal Probe Nanoscopy (CPN), the study of the nano-scale interactive forces between a specifically prepared colloidal probe and any chosen substrate using the Atomic Force Microscope (AFM), can provide key insights into physical interactions present within colloidal systems. Colloidal systems are widely existent in several applications including, pharmaceuticals, foods, paints, paper, soil and minerals, detergents, printing and much more.1-3 Furthermore, colloids can exist in many states such as emulsions, foams and suspensions. Using colloidal probe nanoscopy one can obtain key information on the adhesive properties, binding energies and even gain insight into the physical stability and coagulation kinetics of the colloids present within. Additionally, colloidal probe nanoscopy can be used with biological cells to aid in drug discovery and formulation development. In this paper we describe a method for conducting colloidal probe nanoscopy, discuss key factors that are important to consider during the measurement, and show that both quantitative and qualitative data that can be obtained from such measurements.

Colloidal probe nanoscopy can be used within a variety of fields to gain insight into the physical stability and coagulation kinetics of colloidal systems and aid in drug discovery and formulation sciences using biological systems. The method described within provides a quantitative and qualitative means to study such systems.

Colloidal Probe Nanoscopy (CPN), the study of the nano-scale interactive forces between a specifically prepared colloidal probe and any chosen substrate ...

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and engineers. Growth of such anisotropic nanocrystals through a simple chemical method is a challenging task. In this study, we fabricate discotic nanodisks of zirconium phosphate [Zr(HPO4)2&#183;H2O] as a model material using hydrothermal, reflux and microwave-assisted methods. Growth of crystals is controlled by duration time, temperature, and concentration of reacting species. The novelty of the adopted methods is that discotic crystals of size ranging from hundred nanometers to few micrometers can be obtained while keeping the polydispersity well within control. The layered discotic crystals are converted to monolayers by exfoliation with tetra-(n)-butyl ammonium hydroxide [(C4H9)4NOH, TBAOH]. Exfoliated disks show isotropic and nematic liquid crystal phases. Size and polydispersity of disk suspensions is highly important in deciding their phase behavior.

A two dimensional model material of discotic zirconium phosphate was developed. The inorganic crystal with lamellar structure was synthesized by hydrothermal, reflux, and microwave-assisted methods. On exfoliation with organic molecules, layered crystals can be converted to monolayers, and nematic liquid crystal phase was formed at sufficient concentration of monolayers.

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and ...

Photochemical Oxidative Growth of Iridium Oxide Nanoparticles on CdSe@CdS Nanorods

We demonstrate a procedure for the photochemical oxidative growth of iridium oxide catalysts on the surface of seeded cadmium selenide-cadmium sulfide (CdSe@CdS) nanorod photocatalysts. Seeded rods are grown using a colloidal hot-injection method and then moved to an aqueous medium by ligand exchange. CdSe@CdS nanorods, an iridium precursor and other salts are mixed and illuminated. The deposition process is initiated by absorption of photons by the semiconductor particle, which results with formation of charge carriers that are used to promote redox reactions. To insure photochemical oxidative growth we used an electron scavenger. The photogenerated holes oxidize the iridium precursor, apparently in a mediated oxidative pathway. This results in the growth of high quality crystalline iridium oxide particles, ranging from 0.5 nm to about 3 nm, along the surface of the rod. Iridium oxide grown on CdSe@CdS heterostructures was studied by a variety of characterization methods, in order to evaluate its characteristics and quality. We explored means for control over particle size, crystallinity, deposition location on the CdS rod, and composition. Illumination time and excitation wavelength were found to be key parameters for such control. The influence of different growth conditions and the characterization of these heterostructures are described alongside a detailed description of their synthesis. Of significance is the fact that the addition of iridium oxide afforded the rods astounding photochemical stability under prolonged illumination in pure water (alleviating the requirement for hole scavengers).

A protocol for the photochemical oxidative growth of small crystalline iridium oxide nanoparticles on the surface of CdSe@CdS seeded rod nanoparticles is presented.

We demonstrate a procedure for the photochemical oxidative growth of iridium oxide catalysts on the surface of seeded cadmium selenide-cadmium sulfide ...

Hydroquinone Based Synthesis of Gold Nanorods

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the synthetic methods for the preparation of gold nanorods are still not fully optimized. In this paper we describe a new, highly efficient, two-step protocol based on the use of hydroquinone as a mild reducing agent. Our approach allows the preparation of nanorods with a good control of size and aspect ratio (AR) simply by varying the amount of hexadecyl trimethylammonium bromide (CTAB) and silver ions (Ag+) present in the "growth solution". By using this method, it is possible to markedly reduce the amount of CTAB, an expensive and cytotoxic reagent, necessary to obtain the elongated shape. Gold nanorods with an aspect ratio of about 3 can be obtained in the presence of just 50 mM of CTAB (versus 100 mM used in the standard protocol based on the use of ascorbic acid), while shorter gold nanorods are obtained using a concentration as low as 10 mM.

This paper describes a protocol for the synthesis of gold nanorods, based on the use of hydroquinone as reducing agent, plus the different mechanisms for controlling their size and aspect ratio.

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the ...

Capillary Electrophoresis to Monitor Peptide Grafting onto Chitosan Films in Real Time

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. Compared to other analytical separation techniques, such as chromatography, CE is cheap, robust and effectively requires no sample preparation (for a number of complex natural matrices or polymeric samples). CE is fast and can be used to follow the evolution of mixtures in real time (e.g., chemical reaction kinetics), as the signals observed for the separated compounds are directly proportional to their quantity in solution.
Here, the efficiency of CE is demonstrated for monitoring the covalent grafting of peptides onto chitosan films for subsequent biomedical applications. Chitosan&#39;s antimicrobial and biocompatible properties make it an attractive material for biomedical applications such as cell growth substrates. Covalently grafting the peptide RGDS (arginine - glycine - aspartic acid - serine) onto the surface of chitosan films aims at improving cell attachment. Historically, chromatography and amino acid analysis have been used to provide a direct measurement of the amount of grafted peptide. However, the fast separation and absence of sample preparation provided by CE enables equally accurate yet real-time monitoring of the peptide grafting process. CE is able to separate and quantify the different components of the reaction mixture: the (non-grafted) peptide and the chemical coupling agents. In this way the use of CE results in improved films for downstream applications.
The chitosan films were characterized through solid-state NMR (nuclear magnetic resonance) spectroscopy. This technique is more time-consuming and cannot be applied in real time, but yields a direct measurement of the peptide and thus validates the CE technique.

Free solution capillary electrophoresis is a fast, cheap and robust analytical method that enables the quantitative monitoring of chemical reactions in real time. Its utility for rapid, convenient and precise analysis is demonstrated here through analysis of covalent peptide grafting onto chitosan films for improved cell adhesion.

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. ...

Facet-to-facet Linking of Shape-anisotropic Colloidal Cadmium Chalcogenide Nanostructures

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be covalently and site-specifically linked via their end facets, resulting in polymer-like linear or branched chains. The linking procedure begins with a cation-exchange process in which the end facets of the cadmium chalcogenide NCs are first converted to silver chalcogenide. This is followed by the selective removal of ligands at their surface. This results in cadmium chalcogenide NCs with highly reactive silver chalcogenide end facets that spontaneously fuse upon contact with each other, thereby establishing an interparticle facet-to-facet attachment. Through the judicious choice of precursor concentrations, an extensive network of linked NCs can be produced. Structural characterization of the linked NCs is carried out via low- and high-resolution transmission electron microscopy (TEM), as well as energy-dispersive X-ray spectroscopy, which confirm the presence of silver chalcogenide domains between chains of cadmium chalcogenide NCs.

A protocol detailing how shape-anisotropic colloidal cadmium chalcogenide nanocrystals can be covalently linked via their end facets is presented here.

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be ...

Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a challenge, as it requires asymmetric growth of symmetric crystals. Here, we report a distinctive synthesis of substrate-bound Au nanowires. This template-free synthesis employs thiolated ligands and substrate adsorption to achieve the continuous asymmetric deposition of Au in solution at ambient conditions. The thiolated ligand prevented the Au deposition on the exposed surface of the seeds, so the Au deposition only occurs at the interface between the Au seeds and the substrate. The side of the newly deposited Au nanowires is immediately covered with the thiolated ligand, while the bottom facing the substrate remains ligand-free and active for the next round of Au deposition. We further demonstrate that this Au nanowire growth can be induced on various substrates, and different thiolated ligands can be used to regulate the surface chemistry of the nanowires. The diameter of the nanowires can also be controlled with mixed ligands, in which another &#34;bad&#34; ligand could turn on the lateral growth. With the understanding of the mechanism, Au nanowire-based nanostructures can be designed and synthesized.

We report a solution-based method to synthesize substrate-bound Au nanowires. By tuning the molecular ligands used during the synthesis, the Au nanowires can be grown from various substrates with different surface properties. Au nanowire-based nanostructures can also be synthesized by adjusting the reaction parameters.

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...