Laser Irradiation Of Thin Films Research Articles

Discrimination of different amorphous carbon by low fluence laser irradiation

Carbon thin film depositions were carried out with femtosecond laser ablation from two different sp 2 -bonded carbon targets, namely highly oriented pyrolytic graphite (HOPG) and glassy carbon (GC). Femtosecond laser deposition is generally known as a means of generating nanoparticles. To our knowledge, Raman spectroscopy is not able to directly discriminate the as-deposited amorphous films which may contain different sp 2 carbon nanoclusters while still showing similar Raman spectra. Moreover, these films are not easily distinguishable from each other by transmission electron microscopy observation due to their amorphous structure. In this work, we show that controlled laser irradiation of thin films at low fluence is an interesting approach to reveal the existence of structural differences for amorphous films deposited from sp 2 carbon targets (HOPG and GC).

Intensity enhancement of LIBS of glass by using Au thin films and nanoparticles

We investigate the features of Au nanoparticles (NPs) formation by laser irradiation of thin films and its application in Nanoparticle Enhancement Laser Induced Breakdown Spectroscopy (NELIBS). Ns laser pulsed irradiation of Au thin films previously deposited on glass, allowed simultaneously the modification of the surface morphology of the metal film and the enhancement of the LIBS signal of the glass. Our results demonstrate that the presence of Au either as thin film or NPs favors the formation of a plasma composed by Au and the elements of underlying substrate. Thus, it is possible observing the optical emission of the glass at much lower irradiance than in conventional LIBS. The effect of the thickness of the starting film, laser fluence and number of pulses on the nanostructuration of the surface and the enhancement of the emission signal were analyzed. Under the studied conditions, the first pulse produces the formation of Au NPs and a LIBS spectrum with dominant emission of Au lines over the lines from the substrate. The subsequent pulses modify the NPs morphology and decrease the amount of Au on the substrate, thus the emission of the glass elements dominates the spectrum. After a certain number of pulses, the NPs are removed leaving an apparently clean surface after the analysis.

Photoacoustic transients generated by laser irradiation of thin films

Irradiation of an optically thin layer immersed in a transparent fluid with pulsed laser radiation can generate photoacoustic waves through two mechanisms. The first of these is the conventional optical heating of the layer followed by thermal expansion, in which the mechanical motion of the expansion launches a pair of oppositely directed sound waves. A second, recently reported mechanism, is operative when heat is conducted to the transparent medium raising its temperature, while at the same time reducing the temperature in the absorbing body. The latter mechanism has been shown to result in compressive transients at the leading edges of the photoacoustic waveforms. Here the photoacoustic effect produced by irradiating thin metal films which undergo negligible thermal expansion under optical irradiation, but which generate sound solely by the heat transfer mechanism is investigated. Solution to the wave equation for the photoacoustic effect from the heat transfer mechanism is given and compared with the results of experiments using nanosecond laser pulses to irradiate thin metal films.

Effect of laser irradiation on structural and optical properties of thermally evaporated thin films of amorphous Cd5Se95−xZnx

Thin films of Cd5Se95−xZnx (x = 0, 2, 4) were deposited by a thermal evaporation technique on glass substrates. These films were irradiated by pulsed laser at different durations of time. Laser irradiation of Cd5Se95−xZnx (x = 0, 2, 4) was accompanied structural changes which in turn leads to the change in optical properties of the material. The X-ray diffraction pattern of Cd5Se95−xZnx (x = 0, 2, 4) shows that the grain size increases due to the addition of Zn and decreases after laser irradiation. It was also found that the value of dislocation density increases after laser irradiation. The surface morphology of laser-irradiated thin films of Cd5Se95−xZnx (x = 0, 2, 4) shows that the disorderness or defects are produced due to laser irradiation. Energy dispersive X-ray spectroscopy confirms the elemental composition of the ternary alloy of Cd5Se95−xZnx (x = 0, 2, 4). The optical constants of Cd5Se95−xZnx (x = 0, 2, 4) were calculated from optical transmission spectra. The value of optical band gap increases after laser irradiation and decreases due to the addition of Zn.

Properties of an Indium Tin Oxide Electrode Modified by a Laser Nanostructured Thin Au Film for Biosensing

AbstractStructural, optical, and electrochemical characteristics of the indium tin oxide (ITO) electrode modified by Au nanoparticle (NPs) produced by pulsed UV laser irradiation of thin films are investigated in this work. Properties of the NP arrays depend on the film thickness and parameters of the laser interaction. Semi‐regular structures characterized by broad size distributions of mean values ca. 62–92 nm are observed in the SEM images. In absorbance spectra the plasmon resonance peaks located around 544 nm reveal an IR shift and an increase of damping of the plasmonic enhancement with increasing NP size. Despite the broad size distribution and negative effect of damping that results in plasmon decay times of below 3.2 fs, the ITO electrode modified by Au NP arrays shows marked improvement of the electrochemical activity towards the Fe2+/Fe3+ redox couple and also glucose. Results obtained for non‐enzymatic glucose detection indicate the potential for cost‐effective solutions in the area of biosensing.

Structural and optical properties of Te doped Ge–Se phase-change thin films: A material for optical storage

Amorphous Ge25Se75−xTex chalcogenide thin films of thickness 400nm were prepared by thermal evaporation technique. Thin films were crystallized by transversely-excited atmospheric-pressure nitrogen laser for different time intervals. As-prepared and laser-irradiated thin films were characterized by X-ray diffraction, field emission scanning electron microscopy and UV/VIS/NIR spectroscopy. X-ray diffraction results show that the as-deposited films are of amorphous nature while the laser-irradiated films are of polycrystalline nature. The optical absorption spectra of these films were measured in the wavelength range of 400–1100nm in order to drive the extinction and absorption coefficient of these films. It was found that the mechanism of the optical absorption follows the rule of the allowed non-direct transition. The optical band gap is found to decrease by increasing the laser-irradiation time. It is due to the crystallization of amorphous films. As the phase of the films changes from amorphous to crystalline, a non sharp change of the band gap is observed. The decrease in optical band gap by laser-irradiation is an interesting behavior for a material to be used in optical storage. The optical gap has been observed to increase with the increase of Te content in Ge–Se system.

Laser irradiation of thin films: Effect of energy transformation

AbstractThe irradiation of thin films by intensive subpicosecond laser pulses with nanosecond prepulse is accompanied by a number of various physical processes. The laser beam transmissions through the film as well as the re-emission flux on both sides of the film plasma have been evaluated by simulation for Al and CH2 materials. It has been demonstrated that the thickness of the film can be chosen to cut off the long nanosecond prepulse whereas the main pulse is transmitted through the plasma. Thus, thin films can be useful for the laser contrast improvement in experiments with different targets.Nevertheless, the laser energy transformation into the soft X-ray radiation on the back side of the shielding film plasma can reach up to 7% of the incident intensity for the Al film and result in strong preheating of the target. At the same time the re-emission flux produced by a CH2 film is an order lower than that in the case of Al film. The shielding of an Ag bulk target by Al and CH2 films is simulated and discussed.

Role of thermal stresses on pulsed laser irradiation of thin films under conditions of microbump formation and nonvaporization forward transfer

This paper presents a theoretical analysis of the processes in thin solid films irradiated by short and ultrashort laser pulses in the regimes of film structuring and laser-induced forward transfer. The regimes are considered at which vaporization of the film materials is insignificant and film dynamics is governed mainly by mechanical processes. Thermoelastoplastic modeling has been performed for a model film in one- and two-dimensional geometries. A method has been proposed to estimate the height of microbumps produced by nanosecond laser irradiation of solid films. Contrary to femtosecond laser pulses, in nanosecond pulse regimes, stress waves across the film are weak and cannot induce film damage. The main role in laser-induced dynamics of irradiated films is played by radial thermal stresses which lead to the formation of a bending wave propagating along the film and drawing the film matter to the center of the irradiation spot. The bending wave dynamics depends on the hardness of the substrate underlying the film. The causes of the receiver substrate damage sometimes observed upon laser-induced forward transfer in the scheme of the direct contact between the film and the receiver are discussed.

Influence of laser-irradiation on structural and optical properties of phase change Ga25Se75−xTex thin films

Ga25Se75−xTex chalcogenide thin films of thickness 400nm were deposited by thermal vacuum evaporation technique. These films were irradiated by transversely-excited atmospheric-pressure (TEA) nitrogen laser for 15min. As-prepared and laser-irradiated thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV/VIS/NIR spectroscopy. The XRD results revealed the amorphous nature of as-prepared films whereas, the laser-irradiated thin films showed the polycrystalline nature. The results were discussed in terms of the structural change, i.e. amorphous to polycrystalline phase change after laser irradiation. These structural changes were associated with the interaction of the incident photon and the lone-pair electrons, which affects the band gap of the Ga25Se75−xTex thin films. It was observed that the optical band gap decreases whereas, the absorption coefficient increases with increasing Te concentration and also inducing laser-irradiation. This decrease in the optical band gap was explained on the basis of changes in the structural behavior of films, i.e. from amorphous to polycrystalline state.

Optical properties of Au nanostructures obtained by pulsed UV laser irradiation of thin films

Optical properties of Au nanostructures obtained by pulsed UV laser irradiation of thin films

Optical Properties of Thin Films of Ga<SUB>15</SUB>Se<SUB>75</SUB>Ag<SUB>10</SUB> Chalcogenide Glasses Before and After Laser Irradiation

Thin films of chalcogenide glasses of Ga15Se75Ag10 with thickness 4000 A were prepared by thermal evaporation technique. The amorphous nature of Ga15Se75Ag10 glasses and thin films was verified by Differential Scanning Calorimeter (DSC) and X-ray diffractometer. The surface microstructure of amorphous and laser irradiated thin films w re examin d by scanning electron microscope (SEM). The changes in optical properties due to the influence of laser radiation on amorphous thin films of Ga15Se75Ag10 glassy alloy were calculated from absorbance spectra as a function of photon energy in the wave length region 300–900 nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It has been observed that laser-irradiation of the films leads to a decrease in optical band gap while increase in absorption coefficient and extinction coefficient. The decrease in the optical band gap is explained on the basis of change in nature of films, from amorphous to polycrystalline state.

Annealing and laser irradiation effects on optical constants of Ga 15Se 85 and Ga 15Se 83In 2 chalcogenide thin films

Chalcogenide thin films finds extensive applications in optical imaging, optical recording, integrated optics, optical communications and microelectronics. Optical constants (absorption coefficient, refractive index and extinction coefficient) of amorphous, thermally annealed and laser irradiated Ga 15Se 85 and Ga 15Se 83In 2 thin films deposited by thermal evaporation onto chemically cleaned glass substrate, were calculated from absorbance and reflectance spectra as a function of photon energy in the wavelength region 400–900 nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It has been found that the absorption coefficient increasing with increasing the exposure time of laser irradiation and also by increasing photon energy. The optical band gap decreases with increasing annealing temperatures. The refractive index (n) decreases, while the extinction coefficient (k) increases with increasing annealing temperature. The laser irradiated thin films showed a decrease in optical band gap and absorption coefficient with increasing exposure time of laser irradiation. The values of refractive index (n) increases and extinction coefficient (k) decreases with increasing exposure time of laser irradiation. The results have been analyzed on the bases of thermal annealing and laser irradiation effects in the chalcogenide thin films.

Influence of laser-irradiation on the optical constants Se 75S 25 − xCd x thin films

Amorphous thin films of glassy alloys of Se 75S 25 − x Cd x ( x = 2, 4 and 6) were prepared by thermal evaporation onto chemically cleaned glass substrates. Optical absorption and reflection measurements were carried out on as-deposited and laser-irradiated thin films in the wavelength region of 500–1000 nm. Analysis of the optical absorption data shows that the rule of no-direct transitions predominates. The laser-irradiated Se 75S 25 − x Cd x films showed an increase in the optical band gap and absorption coefficient with increasing the time of laser-irradiation. The results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level. The value of refractive index increases decreases with increasing photon energy and also by increasing the time of laser-irradiation. With the large absorption coefficient and change in the optical band gap and refractive index by the influence of laser-irradiation, these materials may be suitable for optical disc application.

Photochemical Oxygenation and Cross-Linking of Poly(4-trimethylsilylmethylstyrene) Thin Film by UV Irradiation

KrF laser irradiation of thin films of poly(4-trimethylsilylmethylstyrene) (PTMSMS) under atmospheric conditions induced oxygenation at the film surface and cross-linking inside the film. The irradiated film surface became hydrophilic owing to the formation of carboxylic acid group, and the photo-cross-linking caused the insolubilization of the film inside. Similar irradiation of poly(4-methylstyrene) (P4MS) and polystyrene (PS) films, on the other hand, induced oxidative degradation of the polymer main chain. Selectivity in the bond cleavage involved in their photoreactions would lead to the contrast results. Selective cleavage of the benzylic C−Si bond of PTMSMS gives benzyl-type radicals, which react with oxygen, leading to the formation of carboxylic acid groups at the surface, or couple with each other, giving the cross-linked structure inside the film. Cleavage of the C−H bond of the main chain in P4MS and PS would be involved in the oxidative degradation of the polymer main chain. Since the cross-l...

Image analysis of structural changes in laser irradiated thin films of photodeposited a-Se

Write and erase features by the photodeposition effect have been accomplished in recent investigations. Quantitative analysis of the surface grains size and structure in the laser affected areas of the deposited thin films is of importance to the understanding of the material surface redistribution phenomena. Fractal dimensionality and 2D-Fourier spectral analyses have been employed as the most straightforward quantitative approaches connecting the change of grain size distribution with the driving forces involved in the formation of the grain shapes. These approaches have been used since the irregular spatial shapes of the grains cannot be approximated by simple or regular geometrical shapes of definite size. Hence, we use these two topological analysis methods for classifying the surface morphology in the various zones of the laser beam written thin film.

Influence of the substrate on the temperature induced by pulsed laser irradiation of thin films

When the thickness of thin films compares with the light absorption length and the diffusion length of heat during pulsed laser irradiation, the thermal properties of the substrate influence the temperature in the film. In order to understand these phenomena, numerical simulation of temperature of thin film-substrate systems are performed. The influence of the nature of the substrate and of the thickness of the film is studied.

Through-thickness mark length variations in laser-irradiated thin films

Low-conductivity, laser-irradiated thin films such as the chalcogenides employed for optical data storage can display manifestations of significant through-thickness thermal gradients. A combined Laplacetra nsform, Fou rier-i nteg ral method was used to derive the tern peratu re distributions in such films, and the results were used to examine the effects of some marking parameters on through-thickness thermal gradients. The results were in good qualitative agreement with experimental observations.

Thermocapillary Effects in Laser Direct-Write Metallization

AbstractA model describing melting and thermocapillary (or Marangoni) flow in laser irradiated thin films is presented. The free surface formulation leads to predictions of surface profiles that are in qualitative agreement with experimental observations. Additional experimental results for direct-writing of palladium from palladium acetate films demonstrate the influence of thermocapillary effects on the dynamics of the process.

A model for laser induced diffusion

A model for laser induced diffusion is proposed, assuming the melting of Si surface under pulsed laser irradiation and the diffusion, in liquid phase, of a thin film deposited impurity. Depending on the thickness of the film, it results in a dopant distribution profile with a surface disordered layer induced either by segregation effects or precipitation of the dopant in excess of the solubility limit achieved by laser annealing. Experimental results obtained for a ruby laser irradiation of thin films of various dopants such as Sb, Ga, Bi, and In deposited on Si substrates are in good agreement with the model.

Substrate Latent Heat Effects in The Calculations for Pulsed Laser Irradiated Thin Films

ABSTRACTWe present a numerical model for the calculation of the temperature rise caused by pulsed laser irradiation of a thin film/substrate structure. This model includes phase changes in both the thin film and the substrate. The inclusion of phase changes results in more complex thermal behavior and significantly affects melt durations. This model was applied to the AuGe/GaAs system. Morphological observation using the scanning electron microscope and SIMS profiles provides experimental verification for the numerical calculations.