HAuCl4(aq), AgNO3(aq), the freshly prepared L-ascorbic acid (L-AA)(aq), and the seed solution were added to the surfactant mixture (Experimental Section). Figure shows the structure of the GNB. By changing the amount of L-AA, the UV/VIS/NIR spectra (Figure ) and TEM images of the nanomaterials also changed (Figure ). At a lower concentration of L-AA, the UV/VIS/NIR spectrum exhibited a strong absorbance peak (at the NIR region) and another relatively weak peak at the visible area derived from the plasmon on nanomaterial surfaces. This is a typical characteristic of the GNR spectrum. At an appropriate concentration of L-AA, the UV/VIS/NIR peaks displayed two distinguished peaks at around 550 nm and 650 nm. Both peaks exhibited the same intensity, and this represents a characteristic of GNBs.