We have produced passivating coatings on 80-nm aluminum particles by plasma-enhanced chemical vapor deposition (PECVD). Three organic precursors--isopropyl alcohol, toluene, and perfluorodecalin--were used to fabricate thin films with thicknesses ranging from 5 nm to 30 nm. The coated samples and one untreated sample were exposed to 85% humidity at 25 °C for two months, and the active Al content was determined by thermogravimetric analysis (TGA) in the presence of oxygen. The results were compared with an uncoated sample stored in a glovebox under argon for the same period. We find that all three coatings provide protection against humidity, compared to the control, and their efficacy ranks in the following order: isopropyl alcohol < toluene < perfluorodecalin. This order also correlates with increasing water contact angle of the three solid coatings. The amount of heat released in the oxidation, measured by differential scanning calorimetry (DSC), was found to increase in the same order. Perfluorodecalin resulted in providing the best protection, and it produced the maximum enthalpy of combustion, ΔH = 4.65 kJ/g. This value is higher than that of uncoated aluminum stored in the glovebox, indicating that the coatings promote more complete oxidation of the core. Overall, we conclude that the plasma polymer coatings of this study are suitable passivating thin film for aluminum nanoparticles by providing protection against oxidation while facilitating the complete oxidation of the metallic core at elevated temperature.

A dry process for tailoring nanoparticle wetting characteristics using plasma enhanced chemical vapor deposition technique is established. The “plasma polymer” coating imparts the properties of the precursors used in the plasma technique, without the requirement for nanoparticle surface preparation. For a range of chosen precursors, the water contact angle of a sessile droplet on coated copper oxide nanoparticles was shown to vary from 54° to 76°, 92° to 108°. Stable suspensions of coated nanoparticles were demonstrated.

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A method for generating charge-induced plasmonic shifts, using argon plasma to charge nanoparticle arrays, is presented. Particles develop a negative charge, due to enhanced collisions with high-temperature electrons, in low-temperature plasmas. The negative charge generated causes a blue shift in the localized surface plasmon resonance. The dynamics of the shift were recorded and discussed. This effect could be used as a real-time method for studying the dynamics for charging in plasma. Plasmonics deals with optically excited, oscillations of electrons at the interface between a metal and a dielectric, 1 and this phenomenon has driven the development of many optical devices. 2-9 Surface plasmons excited in metal structures, confined at the nanoscale in three dimensions (i.e., nanoparticles, nanodisks, etc.), are known as localized surface plasmons. At certain wavelengths, maximum coupling from electromagnetic waves to localized surface plasmons can be achieved and these are known as the localized surface plasmon resonances (LSPRs) of the structure. LSPRs of metal nanostructures depend on properties such as the size, 10,11 shape, 12-14 metal material, 15 surrounding dielectric material, [16][17][18][19][20][21][22] and the charge of the metal. [23][24][25][26][27][28][29][30] Active plasmonic devices can be realized by externally tuning the LSPR of nanostructures. Previously, chemical/electrochemical charging was used to actively tune the LSPR of arrays of both silver 24,25,30 and gold 23,26,27,29 nanostructures; however, this process is relatively slow. In this study, a rapid shift in the LSPR of an array of gold nanodisks was induced by surrounding the particles with a low-temperature argon plasma. This shift can be explained by the charging effect of the plasma. [31][32][33][34] Charging by the plasma takes place in only seconds, where chemical/electrochemical charging can take several minutes 24 to hours. 27 This method allows real-time monitoring of the charging effect induced by low-pressure plasmas and could be utilized for photonics applications based on the LSPR shift.In the experiment, the optical extinction spectrum of an array of gold nanodisks was measured while generating plasma. An array of gold nanodisks (diameters of 120 nm, thicknesses of 30 nm, and a periodicity of 300 nm) was fabricated on glass via electron-beam lithography. 35 A custom vacuum chamber was designed to include two flat, parallel windows to allow transmission of a probe light (Fig. 1(a)). The nanodisk array was placed inside the vacuum chamber where it was attached to one of the flat windows. The probe light, ejected from the input optical fiber and collimated by a lens, traveled through the vacuum chamber and the sample. The output light was collected by the output lens/optical fiber and delivered to an optical spectrometer. A vacuum system was used to evacuate the chamber to a base pressure of 150 mTorr. Argon was introduced into the chamber using a mass flow controller. The argon gas was introduced at a flow rate of 6 SCCM ...

We calculate the collision cross section of a charged finite cylinder (nanowire) with a beam of ions and electrons in collisionless plasma. We find that, while the shape and area of the cross section has complex dependence on the charge and orientation of the nanowire relative to the charged beam, its orientational average has a remarkably simple form: for attractive interactions, it is a linear function of the electrostatic ratio qjqpe2/4πϵ0L0kT, where qje is the charge of the ions/electrons, qpe is the charge on the cylinder, L0 is the half-length of the nanowire, T is the temperature of the charged species, and ϵ0 is the permittivity of free space. This linearity persists into the repulsive regime up until the cross sectional area is reduced to about 5% of its value for neutral collisions. We calculate the corresponding charging currents and show that the charging behavior of the nanowire in Maxwellian plasma is described by an equivalent sphere whose radius depends only on the aspect ratio of the nanowire. For small aspect ratios, the equivalent sphere has the same surface area as the nanowire.