Plasmons are collective excitations of free electrons in metals, such as Au, Ag or Cu, that, when stimulated by an energy source, such as sunlight, or a laser. A harmonic oscillation of the surface charges is induced with a wave-like behavior. In the process, they scatter light that can be read by a spectrometer, which captures and categorizes light according to its wavelength .
Silver deposition porocesses are very reproducible because the silver nanoparticle size distribution under identical deposition conditions is rather similar, to the benefit of potential industrial applications . Ultrathin layers deposited on PMP could select and amplify specific wavelengths in order to enhance the electrical outcome of the photo-piezo-electric systems designed in the frame of PULSE-COM project.
For the purpose of this study, different silver depositions have been made on three kind of substrates: thick PET (PET), thin PET (PETs) and on BK7 type optical glass (OG). The Ag film thickness had been varied from 1 to 9 nm with a 2 nm step.
The atomic force microscope (AFM) used is a XE100 model from Park System, model XE100. It has the capability to scan the samples in contact mode, non-contact mode and intermittent contact mode to provide information of local roughness. The maximum horizontal scan range is about 50×50 μm2 and the maximum vertical movement is 8 μm. A lateral resolution of tens of nano-meters can be achieved. The maximum image (data) resolution is 1024×1024 pixels. Images of samples of 1 and 5 nm thick Ag deposition on optical glass are presented below.
AFM images of samples of 1 (left) and 5 nm (rigth)thick Ag deposition on optical glass
A scanning electron microscope (FEI QUANTA INSPECT S) was used to observe the structures and morphology of the samples. A thin layer of gold was sputtered onto the samples prior to imaging. Images of samples of 1(left) and 5 nm (right) thickness on OG are presented below.
SEM images of samples of 1 (left) and 5 nm (right) thick Ag deposition on OG
The transmittance, reflectance and absorption were measured with an UV-Vis Lambda 35 (PerkinElmer) Spectrophotometer, Range: 190 – 1100 nm, Bandwidth: 0.5 – 4 nm (our samples were analysed with a 1 nm slit), Absorbance range (linearity 0.99 r2): 3.2 A, working temperature: 15°C, 35°C, Relative humidity: 20%, 80%, Precision: up to 0.1 nm, Scanning rate: 60 – 2,880 nm/min (our samples – 240 nm/min). Transmittance of the samples of 1, 5 and 9 nm thickness on PET (left) and OG (right) is presented below.
Transmittance of the samples of 1, 5 and 9 nm thick Ag deposition on PET (left) and OG (right)
The refraction index (n) and k factor, important for the optical behaviour of the designed systems were calculated using data collected with a Spectro-ellipsometer VVASE with a spectral range of 250-1700 nm at three angles of incidence: 60°, 65° and 70°. From measurement of amplitude ratio Ψ and the phase difference Δ at each wavelength and at different angle of incidents, optical models are generated by WVASE32 software and the n, k parameters and roughness are measured.
The refraction index of the samples of 7 and 9 nm thickness on PET (left) and OG (right) is presented below
The refraction index of the samples of 7 and 9 nm thick Ag deposition on PET (left) and OG (right)
Ultrathin Ag films of 1, 3, 5, 7 and 9 nm thickness were deposited by RF Magnetron Sputtering onto glass and PET substrates.
Samples were morphologically analysed by AFM showing roughness of up to 3 nm.
The films’ refractive index was obtained by means of spectroscopic ellipsometry data using Drude and General Oscillator models-based technique by minimizing the difference between the measured spectrum of the ellipsometric parameters and the values calculated from the model.
The calculated refractive index n present 0.1-0.6 values in the 345-1200 nm region.
The transmittance and reflection of the samples, investigated using UV-Vis-NIR spectroscopy, show a transmission maximum specific to Ag and a transmittance minimum at about 500 nm, which depends on the thickness of the deposited film, showing the appearance of surface plasmon resonance at low thickness of films, meaning 1, 3 and 5 nm.
The film of 3 nm thick was chosen to be deposited on PMP to increase the electrical response and to induce a wavelength selection to designed materials.
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