Microstructure and optical absorption of Au-MgF2 nanoparticle cermet films

The microstructure and optical absorption of Au-MgF2 nanoparticle cermet films with different Au contents are studied. The microstructural analysis shows that the films are mainly composed of the amorphous MgF2 matrix with embedded fcc Au nanoparticles with a mean size of 9.8-21.4nm. Spectral analysis suggests that the surface plasma resonance （SPR） absorption peak of Au particles appears at λ=492-537nm. With increasing Au content, absorption peak intensity increases, profile narrows and location redshifts. Theoretical absorption spectra are calculated based on Maxwell-Garnett theory and compared with experimental spectra.     

Multilayer Au/TiO2Composite Films with Ultrafast Third-Order Nonlinear Optical Properties

We report on the ultrafast third-order optical nonlinearity in multilayer Au/TiO2 composite films fabricated on quartz substrates by pulsed laser deposition technique. The linear optical properties of the films are determined and optical absorption peaks due to surface plasmon resonance of Au particles are observed at about 590hm. The third-order optical nonlinearities of the films are investigated by z-scan method using a femtosecond laser （50 fs） at the wavelength of 800 nm. The sample showed fast nonlinear optical responses with nonlinear absorption coefficient and nonlinear refractive index being -3.66 × 10^-10 m/W and -2.95 × 10^-17 m^2/W, respectively. The results also show that the nonlinear optical effects increase with the increasing Au concentration in the composite films.     

Linear and nonlinear optical properties of Au/SiO2 nanocomposite prepared by P123

Mesoporous silica thin films loaded with gold nanoparticles are synthesized in the presence of EO20PO70EO20（P123）.Transmission electron microscope images show that the matrix of the nanocomposite is an ordered porous structure with a two-dimensional hexagonal phase.The wide-angle X-ray diffraction pattern implies that the nanocomposite contains gold crystals.These metallic nanoparticleembedded solid thin films show some linear and nonlinear optical properties due to their special structure and composition.Gold nanoparticles bring about surface plasmon resonance,and an absorption peak stemming from this effect has been observed.The linear absorption property is analyzed by a quantum mechanism,and the results show that it is influenced by the size and volume fraction of gold nanoparticles. Furthermore,it shows an obviously clear nonlinear optical property measured by the z-scan technique.The magnitude of the nonlinear refractive index of the nanocomposite is estimated to be about 10？ 10 cm 2 /W.     

Large Third-Order Optical Nonlinearity of Cadmium Sulphide Nanoparticles Embedded in Polymer Thin Films

A simple method for synthesis of well dispersed cadmium sulphide nanoparticles embedded in a polyethylene glycol matrix （PEG 400） in thin film form is presented. The large blue shift of the band gap energy of the CdS nanoparticles compared to the bulk semiconductors is observed via UV-vis absorption spectra. Photoluminescence spectra of CdS nanocomposite films show that the emission peaks shift towards the longer wavelength with the increase of annealing temperature. Transmission electron microscopic images as well as Raman scattering studies confirm the CdS nanometer size particle formation within the polymer matrix. The particle size is about 8 nm. Selected area electron diffraction （SAED） shows the cubic zinc blende polycrystalline rings. Third-order optical nonlinearity of the CdS nanopartieles embedded in polymer thin films is studied with the Z-scan technique under 1064 nm excitation. The results show that the CdS nanocomposite film exhibits negative nonlinear refraction index and positive absorption coefficient. The film shows large optical nonlinearity, and the magnitude of the third-order nonlinear susceptibility of the film is calculated to be 1.73 × 10^-9 esu. The corresponding mechanism is discussed.     

Optical Constants of Palladium Phthalocyanine Derivative Thin Films

Ellipsometric parameters of a series of spin-coated thin films of palladium phthalocyanine derivatives with broine and tetraalkoxyl substitutes(PdPc(OC8H17)4Brm,m=0,2,3,4)are determined from a rotating analyserpolarizer type of scanning ellipsometer.The optical,dielectric constants and absorption coefficients of the films in the 500-800nm wavelength region are reported.The results show that refractive index N(N=n-k),dielectric constant ε（ε=ε1-ε2)and absorption coefficient α in the region 500-800nm are influenced by bromine atom substituted on the conjugated phthalocyanine ring regularly.It is found that there is approximately a linear relationship between the resonance absorption wavelengths of the films and the number of bromine atoms substituted on the phthalocyanine ring.     

Spectral features and antibacterial properties of Cu-doped ZnO nanoparticles prepared by sol-gel method

Zn_(1-x)Cu_x O(x=0.00, 0.01, 0.03, and 0.05) nanoparticles are synthesized via the sol-gel technique using gelatin and nitrate precursors. The impact of copper concentration on the structural, optical, and antibacterial properties of these nanoparticles is demonstrated. Powder x-ray diffraction investigations have illustrated the organized Cu doping into ZnO nanoparticles up to Cu concentration of 5%(x = 0.05). However, the peak corresponding to CuO for x= 0.01 is not distinguishable. The images of field emission scanning electron microscopy demonstrate the existence of a nearly spherical shape with a size in the range of 30–52 nm. Doping Cu creates the Cu–O–Zn on the surface and results in a decrease in the crystallite size. Photoluminescence and absorption spectra display that doping Cu causes an increment in the energy band gap. The antibacterial activities of the nanoparticles are examined against Escherichia coli(Gram negative bacteria)cultures using optical density at 600 nm and a comparison of the size of inhibition zone diameter. It is found that both pure and doped ZnO nanoparticles indicate appropriate antibacterial activity which rises with Cu doping.     

Spectroscopy and Optical Properties of Novel Metal（Ⅱ）-Azo Complex Films in Blue-Violet Light Region

A novel azo derivative,α-（2-azoxyisoxazole)-β-diketone derivative (ADD),and its copper (Ⅱ） and nickel （Ⅱ） complex (CuADD and NiADD) films have been prepared respectively by spin-coated method.The absorption spectra of the films on a K9 glass substrate in the 300-800 nm wavelength region have been measured.The optical constants (complex refractive index N=n iκ） and thickness of the complex films on a single-crystal silicon substrate in the 300-600nm wavelength region have been investigated on an improved rotating analyser-polariser (RAP) type of scanning ellipsometer,and the dielectric constants ε（ε=ε1 iε2),absorption coefficients α as well as reflectance R of the films were calculated.It is found that the absorption maxima of the ADD,CuADD and NiADD films are at 324nm,372nm and 385nm,respectively,and small absorption values and steep absorption band edges of the CuADD and NiADD films are observed at the 405nm side;The CuADD and NiADD films give high n values of 2.08 and 1.98,and low κ values of 0.2 and 0.28,respectively,at 405nm,and their thicknesses are in the range of 130-150nm;the high reflectivity of 58.5% and 45.5% of the CuADD and NiADD films with Ag as a reflective layer were obtained at the film thicknesses of 70 nm and 80nm respectively.These results show that the novel CuADD and NiADD films seem to be a very promising organic recording material for the next generation of high density digital versatile disc-recordable (HD-DVD-R) systems that use a high numerical aperture of 0.85 at 405nm wavelength.     

Linear and nonlinear optical properties of Sb-doped GeSe_2 thin films

Sb-doped Ge Se2 chalcogenide thin films are prepared by the magnetron co-sputtering method.The linear optical properties of as-deposited films are derived by analyzing transmission spectra.The refractive index rises and the optical band gap decreases from 2.08 e V to 1.41 e V with increasing the Sb content.X-ray photoelectron spectra further confirm the formation of a covalent Sb–Se bond.The third-order nonlinear optical properties of thin films are investigated under femtosecond laser excitation at 800 nm.The results show that the third-order nonlinear optical properties are enhanced with increasing the concentration of Sb.The nonlinear refraction indices of these thin films are measured to be on the order of 10-18m2/W with a positive sign and the nonlinear absorption coefficients are obtained to be on the order of 10-10m/W.These excellent properties indicate that Sb-doped Ge–Se films have a good prospect in the applications of nonlinear optical devices.     

Nonlinear optical properties of Au/PVP composite thin films

Colloidal Au and poly（vinylpyrrolidone） （PVP） composite thin films are fabricated by spin-coating method. Linear optical absorption measurements of the Au/PVP composite films indicate an absorption peak around 530 nm due to the surface plasmon resonance of gold nanoparticles. Nonlinear optical properties are studied using standard Z-scan technique, and experimental results show large optical nonlinearities of the Au/PVP composite films. A large value of χ^（3）/α up to 0.56× 10-^10esu·cm is obtained, which is comparable to the best values reported in metal/oxlde composite films.     

Spectroscopic Ellipsometry Study on Surface Roughness and Optical Property of AZO Films Prepared by Direct-Current Magnetron Reactive Sputtering Method

All as-deposited AZO films by direct current magnetron reactive sputtering （DC-MS） exhibit ZnO characteristic （002） and （103） diffraction peaks. Especially, AZO films prepared at 200℃ show a strongest （002） c-axis pref- erential orientation due to the minimum stress along the （002） orientation. The results show that larger stress easily induces a rougher surface. The film real and imaginary parts of dielectric constants show a sharp changes near the optical absorption edge due to the interband direct transition. The film blue and red shifts of the optical absorption edge can be explained in terms of the change of Free-electron concentration in as-deposited AZO films.     

Optical absorption properties of Ge-Sb-Te films

The optical properties of monolayer Ge2Sb2Te5 thin films with three different thicknesses prepared by dc magnetron sputtering method at the range of 400-800 nm were studied. The optical absorption coefficients and the optical energy gap (Eg) were calculated, The results gave values for the absorption coefficients in the range of (1.3-7.5)×105 cm-1 which were in the high absorption wavelength region of     

Study on third-order nonlinear optical properties of a soluble poly(p-phenylene vinylene) derivative

A soluble poly(2-methoxyo5-decoxy)-p-phenylene vinylene (PMODOPV) was synthesized via dehydrochlorination reaction and characterized by UV-visible absorption spectrum. The results showed that PMODOPV had a broad optical absorption band in the range of 450-550 nm and the optical band gap was calculated to be around 2.12 eV. The third-order nonlinear optical susceptibilities (χ(3)) of PMODOPV films implanted by 30-kev N+ ions in the dose range of 3.8 × 1015-9.6 × 1016 ions/cm2 were measured by degenerate four-wave mixing (DFWM) technique. The results demonstrated that the resonant and offresonant χ(3) values were all enhanced significantly by means of ion implantation. The maximum resonant χ(3) value of 9.67 × 10-9 esu at 532 nm and off-resonant χ(3) value of 2.49 × 10-10 esu at 1.064μm were obtained when the ion dose was 3.8 × 1016 ions/cm2.     

Optical properties of hexagonal boron nitride thin films deposited by radio frequency bias magnetron sputtering

The optical properties of hexagonal boron nitride (h-BN) thin films were studied in this paper. The films were characterized by Fourier transform infrared spectroscopy, UV--visible transmittance and reflection spectra. h-BN thin films with a wide optical band gap E_g (5.86 eV for the as-deposited film and 5.97 eV for the annealed film) approaching h-BN single crystal were successfully prepared by radio frequency (RF) bias magnetron sputtering and post-deposition annealing at 970~K. The optical absorption behaviour of h-BN films accords with the typical optical absorption characteristics of amorphous materials when fitting is made by the Urbach tail model. The annealed film shows satisfactory structure stability. However, high temperature still has a significant effect on the optical absorption properties, refractive index n, and optical conductivity σ of h-BN thin films. The blue-shift of the optical absorption edge and the increase of E_g probably result from stress relaxation in the film under high temperatures. In addition, it is found that the refractive index clearly exhibits different trends in the visible and ultraviolet regions. Previous calculational results of optical conductivity of h-BN films are confirmed in our experimental results.     

Microstructure and Raman spectra of Ag-MgF_2 cermet films

Ag-MgF2 cermet films with different Ag fractions were prepared by vacuum evaporation. The micfostruc-ture of the films was examined by Raman scattering technique. The surface-enhanced Raman spectrum for MgF2 molecules in the cermet film strongly suggests the existence of Ag nanoparticles dispersed in MgFa matrix. The intensities of the Raman spectra of Ag-MgF2 cermet films increase with Ag fraction. The enhancement of Raman scattering disappears when Ag content reaches wt.20%. The analyses with the transmission electron microscopy showed that Ag-MgF2 cermet films are mainly composed of amorphous MgF2 matrix with embedded faced-center-cubic Ag nanoparticles. It suggests that the percolation threshold should be around wt.20% of Ag content.     

Advantages of using gold hollow nanoshells in cancer photothermal therapy

Lots of studies have been conducted on the optical properties of gold nanoparticles in the first region of near infrared(650 nm–950 nm), however new findings show that the second region of near-infrared(1000 nm–1350 nm) penetrates to the deeper tissues of the human body. Therefore, using the above-mentioned region in photo-thermal therapy(PTT) of cancer will be more appropriate. In this paper, absorption efficiency is calculated for gold spherical and rod-shaped nanoshells by the finite element method(FEM). The results show that the surface plasmon frequency of these nanostructures is highly dependent on the dimension and thickness of shell and it can be adjusted to the second region of near-infrared. Thus, due to their optical tunability and their high absorption efficiency the hollow nanoshells are the most appropriate options for eradicating cancer tissues.     

Enhanced Optical Absorption of Amorphous Silicon Films by Ag Nanostructures

The optical absorption of amorphous silicon （α-Si） films is enhanced by silver （Ag） nanostructures deposited on the films. The reflection at the long wavelength side of localized plasmon polaritons （LPPs） resonance originated from Ag nanostructures is significantly decreased, i.e. the optical absorption is enhanced. The results show that the average reflection value of the amorphous silicon films in the wavelength range of 900-1200 nm could be decreased by 11.4%. Moreover, the reduction of the reflection is found to be mainly dependent on the size of the Ag nanostructures, which is related to the island sizes, i.e. the LPP＇s resonance peak position.     

Effect of annealing on the damage threshold and optical properties of HfO_2/Ta_2O_5/SiO_2 high-reflection film

The effect of thermal annealing on the optical properties, microstructure, and laser-induced damage threshold(LIDT) of HfO_2/Ta_2O_5/SiO_2 HR films has been investigated. The transmission spectra shift to a short wavelength and the X-ray diffraction peaks of monoclinic structure HfO_2 are enhanced after thermal annealing. The calculated results of the m(-111) diffraction peak show that the HfO_2 grain size is increased, which is conducive to increasing the thermal conductivity. Thermal annealing also reduces the laser absorption of high-reflection films. The improvement of thermal conductivity and the decrease of laser absorption both contribute to the improvement of LIDT. The experimental results show that the highest LIDT of 22.4 J/cm~2 is obtained at300°C annealing temperature. With the further increase of annealing temperature, the damage changes from thermal stress damage to thermal explosion damage, resulting in the decrease of LIDT.     

Local structure and optical absorption characteristic investigation on Fe doped TiO2 nanoparticles

The local structures and optical absorption characteristics of Fe doped Ti O2 nanoparticles synthesized by the sol-gel method were characterized by X-ray diffraction(XRD), X-ray absorption fine structure spectroscopy(XAFS) and ultraviolet-visible absorption spectroscopy(UV-Vis). XRD patterns show that all Fe-doped Ti O2 samples have the characteristic anatase structure. Accurate Fe and Ti K-edge EXAFS analysis further reveal that all Fe atoms replace Ti atoms in the anatase lattice. The analysis of UV-Vis data shows a red shift to the visible range. According to the above results, we claim that substitutional Fe atoms lead to the formation of structural defects and new intermediate energy levels appear, narrowing the band gap and extending the optical absorption edge towards the visible region.     

Electronic and optical properties of CdS/CdZnS nanocrystals

Cd1-x ZnxS nanocrystals are prepared by a co-precipitation method with different atomic fractions of Zn.The texture,structural transformation and optical properties with increasing x value in Cd1-x ZnxS are studied with scanning electron microscopy,electron diffraction patterning,and absorption spectra respectively.Quantum confinement in a strained CdS/Cd1-xZnxS related nanodot with various Zn content values is investigated theoretically.Binding energies on exciton bound CdS/CdxZn1-xS quantum dot are computed,with consideration of the internal electric field induced by the spontaneous and piezoelectric polarizations,and thereby the interband emission energy is calculated as a function of the dot radius.The optical band gap from the UV absorption spectrum is compared with the interband emission energy computed theoretically.Our results show that the average diameter of composite nanoparticles ranges from 3 nm to 6 nm.The X-ray diffraction pattern shows that all the peaks shift towards the higher diffracting angles with an increase in Zn content.The lattice constant gradually decreases as the Zn content increases.The strong absorption edge shifts towards the lower wavelength region and hence the band gap of the films increases as the Zn content increases.The values of the absorption edge are found to shift towards the shorter wave length region and hence the direct band gap energy varies from 2.5 eV for the CdS film and 3.5 eV for the ZnS film.Our numerical results are in good agreement with the experimental results.     

Absorption Spectra and Refractive Index Changes of an Exciton in a Core/Shell Quantum Dot

The absorption spectra and the refractive index changes are calculated theoretically for an exciton in a core/shell quantum dot. The advantage of our methodology is that one can investigate the influence of the repulsive core by varying two parameters in the confinement potential. The dimensionality effect of exciton quantum dots on the optical absorptions has been studied. It has been found that in the same regime, the optical absorption intensities of excitons are much smaller for the core/shell quantum dots than for the two-dimensional quantum rings. The linear and the nonlinear optical absorption coefficients and refractive index changes have been examined with the change of the confinement potential. The results show that the optical absorptions and the refractive index changes are strongly affected by the repulsive core of core/shell quantum dots. Moreover, the calculated results also reveal that as the inner radius increases, the peak values of the absorption coefficients and the refractive index changes of an exciton will show the optical Aharonov–Bohm oscillation in core/shell quantum dots.