We propose a generalized ellipsometric technique using a rotating sample. The ellipsometer consists of a polarizer, a rotatable sample holder, an analyzer, and a detector. Fourier coefficients are measured and used to extract the system’s dielectric tensors and film thicknesses. The main advantage of the technique is that all parts of the ellipsometer are fixed except the sample, whose azimuth angle can be modulated. We show calculated responses to isotropic and anisotropic materials as well as superlattices. Potential applications for characterizations of anisotropic nanostructures are discussed.

DNA was used as a scaffold for the binding of gold nanoparticles using a standard chemical technique. A DNA template was designed with amino-modified thymines located every 3.7 nm, which would allow the attachment of the carboxylic acid functionalized gold nanoparticles. The gold particles were covalently bound to the amino groups on the DNA using standard 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) chemistry in the presence of a competitor to block excess gold binding sites. The products were analyzed by transmission electron microscopy (TEM) and atomic force microscopy (AFM).

Anisotropic, noble metal nanoparticles have been synthesized using a template synthesis strategy. In short, metallic salts are reduced in the nanometer scale pores of either an alumina or polycarbonate membrane. The particles can then been released from the template to form suspensions of anisotropic nanoparticles. These nanoparticles have been modified with deoxyribonucleic acid (DNA) oligomers of varying length using several different attachment chemistries. The thermodynamics and kinetics of modifying these particles with DNA has been explored. DNA has also been used to assemble the particles on planar Au surfaces as well as lithographically defined Au pads on Si wafers. In addition to surface assembly, DNA has been used to assemble the nanowires into simple, yet deterministic structures in solution.

We present here an electrical transport property study of Te-doped Bi nanowires, and Bi1−xSbx alloy nanowires embedded in a dielectric matrix. The crystal structure of the nanowires were characterized by X-ray diffraction measurements, indicating that the nanowires possess the same lattice structure as bulk Bi in the presence of a small amount of Te or Sb atoms. The resistance measurements of 40-nm Te-doped Bi nanowires were performed over a wide range of temperature (2 K≤ T ≤ 300 K), and the results are consistent with theoretical predictions. The 1D-to-3D localization transition and the boundary scattering effect are both observed in magneto-resistance measurements of Bi1−xSbx alloy nanowires at low temperatures (T < 4 K).

The use of low pressure radio-frequency (rf) plasma for nanoparticle formation and the deposition of thin film on particulate substrates are reported. Plasma polymer particles are synthesized in a capacitively-coupled Ar/monomer discharge at rf power of 15-30 W. A variety of particle structures are observed, including monodispersed nanospheres and liquid-like viscous nano-droplets. Styrene in particular is observed to produce hollow nanospheres. By manipulating the process parameters, films of plasma polymers can be deposited onto suspended submicron particles. We take advantage of the electrostatic trapping of “dusty plasma” to suspend small particles in plasma for extended periods of time until the desired coating thickness is achieved. Sub-micron silica particles introduced into a low pressure rf Ar/monomer plasma are coated with film of thickness ranging from 2 to 70 nm.

The stacking sequence of several layers of self-assembled semiconducting CdSe nanoparticles has been investigated using transmission electron microscopy. FCC, HCP, saddle sites occupation and ring structures were found coexisting in the supercrystals formed by CdSe nanoparticles.

Polymers provide a useful tool for the controlled assembly of colloidal nanoparticles. We have developed a bricks and mortar strategy in which colloidal gold particles functionalized with recognition elements serve as the bricks and polymers bearing complementary functionality serve as mortar to hold together the nanoparticles. In this methodology, the conformational flexibility of the polymer compensates for irregularities in the size and shape of the aggregate structure. We have used this method to create discrete micrometer-scale spherical assemblies based on 2 nm gold nanoparticles. Both the size and shape of these assemblies can be controlled, providing spherical assemblies ranging from 50 nm to 1500 nm, as well as network structures.

Large arrays of perpendicularly oriented anisotropic nanoparticles of ferric oxyhydroxide (Akaganeite, β-FeOOH) and oxide (Hematite, α-Fe2O3) of typically 3-5 nm in diameter, self-assembled as bundles of about 50 nm in diameter and of up to 1 μm in length have been successfully grown onto polycrystalline substrates without template and/or surfactant by heteronucleation from an aqueous solution of ferric salts and their optical and electronic properties investigated.

Our study describes the synthesis of novel nanoscale Pd cage and wires whose sizes and shapes are templated by mesoporous matrices. The templates used are cubic phase MCM-48 and hexagonal phase CnMCM-41 (n = 16, and 22), SBA-15, which have pore diameters of ∼3, ∼3.8, ∼4.7, and ∼9 nm, respectively. For Pd@MCM-48, the Pd metal forms spherical domains (∼38 nm) consisting of three dimensionally interconnected into Pd arrays; for Pd@SBA-15 and Pd@MCM-41, the Pd metal forms of one-dimensional wires. Etching out the matrix produces porous Pd cages (pore sizes of ∼1.5 - 2.0 nm) with retaining original domain sizes of ∼38 nm; similarly Pd@SBA-15 and Pd@MCM-41 afford freestanding Pd nanowires. All the materials are examined by TEM, XRD, BET, and EDAX analysis. Furthermore, the thermal behavior of Pd nanowire is briefly described.

We present a dynamical effective medium theory (EMT) of the dielectric properties of nanoparticle aggregates formed from DNA-linked gold nanoparticles. Experimental measurements show that such aggregateshave reduced UV extinction and plasmon bands that are considerably red-shifted and broadened relative to the plasmon absorption feature observed in spectra of dispersed colloid. The EMT, which can be used to reproduce the observed spectral changes, is tested by comparing aggregate spectra calculated using the EMT dielectric function with spectra from explicit coupled particle calculations, and good agreement is found. The EMT dielectric function is used as well in discrete dipole calculations to calculate extinction spectra for a variety of aggregate shapes not amenable to analytic solution, and the sensitivity of the spectra to aggregate shape is examined. We find that the spectra are only weakly sensitive to aggregate shape, and conclude that, when calculating extinction of the DNA-linked aggregates for comparison with experiment, spherical shapes can be assumed.

Early work with size-tunable periodic particle arrays (PPAs) fabricated by nanospherelithography (NSL) demonstrated that the localized surface plasmon resonance (LSPR) could be tuned throughout the visible region of the spectrum. The LSPR is sensitive to changes in nanoparticle aspect ratio and local dielectric environment. This property has recently been exploited to develop a novel method of measuring surface-enhanced Raman scattering (SERS) excitation profiles. Single layer PPAs consist of size-tunable anisotropic nanoparticles that can be modified to exhibit anisotropic surface chemistry. This work demonstrates multiple schemes for PPA modification using self-assembled monolayers and colloid decoration. Nanoparticle anisotropy can be further exploited with the recent combination of NSL and reactive ion etching (RIE); this extends the two-dimensional PPA structure into the third dimension.