### Equipment

UV-visible absorption measurements were conducted using an Agilent Spectrophotometer model 8453 (Biodirect, Inc., Taunton, MA, USA). A quartz cuvette with an optical path of 0.25 cm was used for the optical absorption measurements. Scanning tunneling microscopy (STM) measurements were performed in a NanoSurf Easy Scan E-STM (Nanosurf Inc., Boston, MA, USA), version 2.1, using a Pt/Ir tip. The STM was calibrated with measurements performed on a commercial gold ruler. Measurements performed on longitudinal features of dry deposits of submonolayer quantities of C_{12}-SH and C_{10}-SH alkyl thiols coincided with the expected molecular lengths of these molecules. A drop of the silver/SWCNT dispersion was deposited on a highly oriented graphite attached to a magnetic holder and allowed to dry prior to the measurements. TEM measurements were performed with a JEOL 2010 electron microscope (JEOL USA, Inc., Peabody, MA, USA). The samples were outgassed at 10^{-3} Torr for several days prior to placement in the TEM sample compartment. TEM measurements were performed with an acceleration voltage of 120 kV. Negatives of the micrographs were processed using standard techniques and scanned with an EPSON Perfection V750 PRO scanner (Epson, Long Beach, CA, USA) and stored in a PC computer for further analysis. Scanning electron microscopy measurements were performed with a JEOL 6460 LV SEM instrument (JEOL USA, Inc., Peabody, MA, USA) equipped with an X-ray detector for energy dispersive X-ray spectroscopy (EDAX) measurements.

### Computer simulations

Simulations of the optical absorption spectra of silver spheres are based on Mie theory. The wavelength-dependent absorbance (

*A*) of light by a substance is given by:

$A=n\gamma {I}_{\mathsf{\text{o}}}\u2215ln10$

(1)

where

*n* represents the number of absorbers,

*γ* is the absorption cross section, and

*I*
_{o} is the incident light intensity. For spheres smaller than the wavelength of the incident light, the absorption cross section may be estimated by calculating the dipole contribution to the absorption spectra as:

$\gamma =9{{\epsilon}_{\alpha}}^{3\u22152}V\left(\omega \u2215c\right){\epsilon}_{2}\u2215\left\{{\left[{\epsilon}_{1}+2{\epsilon}_{2}\right]}^{2}+{{\epsilon}_{2}}^{2}\right\}$

(2)

where

*ε*
_{
α
}is the dielectric constant of the medium,

*ω* is the frequency of the incoming radiation,

*c* is the speed of light, and

*ε*
_{1} and

*ε*
_{2} represent the real and imaginary parts of the particle's dielectric constant (

*ε*). In the case of silver, the real and imaginary parts of the dielectric constants have contributions from interband transitions (IB) and the excitation of the plasmon (P):

$\begin{array}{cc}\hfill {\epsilon}_{\mathsf{\text{1}}}={\epsilon}_{\mathsf{\text{1IB}}}+{\epsilon}_{\mathsf{\text{1}},\mathsf{\text{P}}}\hfill & \hfill {\epsilon}_{\mathsf{\text{2}}}={\epsilon}_{\mathsf{\text{2IB}}}+{\epsilon}_{2\mathsf{\text{P}}}\hfill \end{array}$

(3)

The plasmon contributions to the components of the dielectric constant are calculated as:

$\begin{array}{cc}\hfill {\epsilon}_{1}=1-{{\omega}_{\mathsf{\text{P}}}}^{2}\u2215\left({\omega}^{2}+{{\omega}_{\mathsf{\text{o}}}}^{2}\right)\hfill & \hfill {\epsilon}_{2}={{\omega}_{\mathsf{\text{p}}}}^{2}{\omega}_{\mathsf{\text{o}}}\u2215\left[\omega \left({\omega}^{2}+{{\omega}_{\mathsf{\text{o}}}}^{2}\right)\right]\hfill \end{array}$

(4)

where

*ω*
_{P} and

*ω* represent the frequencies corresponding to the bulk plasmon and incident light, and

*ω*
_{o} is the size-dependent surface scattering rate estimated as:

${\omega}_{\mathsf{\text{o}}}=A{v}_{\mathsf{\text{F}}}\u2215r$

(5)

where *A* is proportionality factor, *v*
_{F} is the Fermi velocity, and *r* is the particle radii.

The simulations of the absorption spectra of the one-dimensional structures are based on the Gans treatment of Mie theory. The absorption cross section within the dipole approximation is calculated as:

$\frac{\gamma}{{N}_{P}V}=\frac{2\Pi {\in}_{\alpha}^{1/2}}{3\lambda}{\displaystyle \sum}_{j}\frac{\left(\frac{1}{{P}_{j}^{2}}\right){\in}_{2}}{{\left[{\in}_{1}+\left(\frac{1-{P}_{j}}{{P}_{j}}\right){\in}_{\alpha}\right]}^{2}+{\in}_{2}^{2}}$

(6)

where *N*
_{P} and *V* represent particle concentration and volume, respectively, and *λ* is the incident light wavelength. The contributions of the real (*ε*
_{1}) and imaginary (*ε*
_{2}) components of the refractive index are obtained from Harris et al. [10]. In the equation, *P*
_{
j
} represents a geometric factor related to the coordinates of an elliptical particle [12]. The letters used in the *P*
_{
j
} represent the longitudinal axis "A" and transverse axes "B" and "C." In elongated ellipsoids, B and C are equal and represent the diameter (*d*) of the ellipsoid.