**1. Introduction**

[22] Asher, B. J., Ross, MS, & Wong, C. S. (2012). Tracking chiral polychlorinated biphenyl sources near a hazardous waste incinerator : Fresh emmissions or weathered revola‐

[23] Holoubek, I., Adamec, V., Bartoš, M., Černá, M., Čupr, P., Bláha, K., Bláha, L., Dem‐ nerová, K., Drápal, J., Hajšlová, J., Holoubková, I., Jech, L., Klánová, J., Kohoutek, J., Kužílek, V., Machálek, P., Matějů, V., Matoušek, J., Matoušek, M., Mejstřík, V., No‐ vák, J., Ocelka, T., Pekárek, V., Petira, O., Punčochář, M., Rieder, M., Ruprich, J., Sáň‐ ka, M., Vácha, R., & Zbíral, J. (2003). National stocktaking of Persistent organic pollutants in the Czech Republic. *Project GF/CEH/01/003 Enabling activities to facilitate early action on the implementation of the Stockholm Convention on Persistent organic pollu‐ tants (POPs) in the Czech Republic. TOCOEN REPORT* [249], http://www.genasis.cz/ stockholm-stockholmska\_umluva-inventura\_pops\_2007/, accessed 22 August 2012.

tilization? *Environmnetal Toxicology and Chemistry*, 31(7), 1453-1460.

28 Organic Pollutants - Monitoring, Risk and Treatment

In the modern world, environmental problems have attracted more and more attention, for environmental pollutants are extremely harmful to human beings' health. Environmental pollutants, such as persistent organic pollutants, are widely separated in the environment and difficult to detect at trace level.Within persistent organic pollutants, polychlorinated bi‐ phenyls (PCBs), due to their excellent dielectric properties, had been widely used since the 1920s in transformers, heat transfers, capacitors, etc., and had polluted nearly everywhere in the world [1]. In recent years, however, they have been found to be very harmful to human beings. They may cause serious diseases, such as cancers and gene distortion, when exceed‐ ing the critical dose in human bodies, and more seriously, PCBs can be accumulated in plants and animals from the environment and yield higher doses in human bodies, making PCBs very dangerous to human beings even in trace amounts [1-3]. Therefore, the detection of PCBs in trace amounts is crucial. Currently, the mostly applied detection technique for PCBs is the combination of high-resolution gas chromatography and mass spectrometry. It requires, however, very sophisticated devices, standard samples, complicated pretreatments of samples, favourable experimental environments and experienced operators [4-7]. Thus, new methods are demanded especially for the rapid detection of trace amounts of PCBs.

Surface-enhanced Raman scattering (SERS) has been proven to be an effective way to detect some organics [8]. With the great progress of nanoscale technology in recent years, SERS has attracted enormous attention due to its excellent performance and potential applications in the detection of molecules in trace amounts, even single molecule detection.

Among the approaches so far available to prepare nanostructure as SERS substrate, the glancing angle deposition (GLAD) technique is a simple but powerful means which is capa‐ ble of producing thin films with pre-designed nanostructures. These nanostructures can be

used in the field of SERS. For instance, using Ag nanorods as SERS substrates,Rhodamine 6G with concentration of 10-14 M (dissolved in water) was detected [9]; with the aluminamodified AgFON substrates, bacillus subtilis spores were detected to 10-14 M [10, 11]; Vo-Dinh reported even the detection of specific nucleic acid sequences by the SERS technique [12-14]. In spite of the numerous studies on the application as a chemical and biological sen‐ sor [15-17], the SERS technique has not yet been employed to detect PCBs as they are hardly dissolved in water.

positing rate of 0.5 nm/s, with the thickness monitored by a quartz crystal microbalance. To produce films of aligned Ag nanorods, the incident beam of Ag flux was set at ~ 85 o from the normal of the silicon substrate, at different substrate temperatures. The morphology and structure of the thin Ag films was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and high-resolution TEM, selected area diffraction (SAD) and X-ray diffraction (XRD), respectively. The performance of the nanostructured Ag films as SERS substrates was evaluated with a micro-Raman spectrometer using R6G as the

The Detection of Organic Pollutants at Trace Level by Variable Kinds of Silver Film with Novel Morphology

http://dx.doi.org/10.5772/53602

31

It is well known that the major factors influencing the growth morphology of the films by GLAD are the incident direction of the depositing beam flux, the temperature and the move‐ ment of the substrate, and the deposition rate, etc. When fixing the incident Ag flux at ~85 o from the normal of the substrate and the deposition rate at ~0.5 nm/s, the growth morpholo‐ gy of the Ag films was greatly dependent on the temperature and movement of the sub‐ strate. Fig 1 shows the growth morphology of thin Ag films versus the temperature and movement of the substrate. The SEM micrographs were taken by a FEI SEM (QUANTA

Fig 1(a) and (b) shows typical SEM images of the surface morphology of thin Ag films

0.2 rpm, respectively. One sees from the images that at this temperature, Ag nanorods formed in two films with a length of 500 nm, yet they were not well separated - most nanorods were joined together. A major difference between the two is the growth direc‐ tion of the joined nanorods, i.e. without rotation the nanorods grew at a glancing angle on the substrate, while with substrate rotation the nanorods grew vertically aligned. An‐ other difference noticeable is the size of the nanorods, i.e. nanorods grown with substrate

Fig 1(c) and (d) shows respectively the surface morphology of thin Ag films deposited at -40

C, without substrate rotation and with rotation at a speed of 0.2 rpm. Comparing with Figs 1(a) and (b), it can be seen that the decrease in the deposition temperature led to the separa‐ tion of Ag nanorods in the two films, while the rotation of the substrate also determined the growth direction and diameter of the nanorods, as observed from Figs 1(a) and 1(b). The Ag nanorods grown at this temperature are 20-30 nm in diameter, ~ 800 nm in length and are well separated. Therefore, through adjusting the temperature and movement of the sub‐ strate one can grow well separated and aligned Ag nanorods on planar silicon substrates.

Fig 1(e) and 1(f) shows respectively a bright-field TEM and a HRTEM image of Ag nanorods shown by Fig 1(c); inset of Fig 1(f) is the corresponding SAD pattern. The images and the SAD pattern were taken with a JEM-2011F working at 200 kV. One sees from the Figs that the Ag nanorod is ~ 30 nm in diameter and its micro-structure is single crystalline. By index‐ ing the SAD pattern it is noticed that during the growth process the {111} plane of the nano‐ rod was parallel to the substrate surface, with its axis along the <110> direction. This was confirmed by XRD analysis. Fig 2 shows a XRD pattern of the Ag nanorods shown by Fig 1(c). The pattern was taken with a Rigaku X-ray diffractometer using the Cu k line, work‐ ing at the θ-2θ coupled scan mode. From the Fig, a very strong (111) texture is observed,

C, without substrate rotation and with substrate rotation at a speed of

model molecule.

200FEG) working at 20 kV.

rotation have a slightly larger diameter.

deposited at 120 o

o
