Laser Irradiation Of Films Research Articles

Ablation threshold, structural modification, and sensing of graphene oxide thin film induced by UV nanosecond laser

Reduction of graphene oxide by laser irradiation is crucial for developing conductive thin films. This study investigates the ablation threshold, reduction of graphene oxide, and high-precision patterning by UV nanosecond laser irradiation of graphene oxide films on flexible substrates. The ablation threshold of graphene oxide thin film was evaluated by examining the relationship between micropore diameters and laser pulse energy density. The single pulse ablation threshold was 2.29 J/cm², indicating that the UV nanosecond laser energy density is sufficient for the ablation of graphene oxide. Based on ablation threshold evaluation, graphene oxide was reduced by UV nanosecond laser irradiation, and laser-irradiated graphene oxide-based flexible thin film with four different line widths was fabricated. UV nanosecond laser irradiation graphene oxide-based grid structure patterns on the flexible substrates were fabricated by analyzing these different line widths. In addition, laser-irradiated graphene oxide-based grid structure flexible electrode were used to monitor human hand motion and finger press sensing. This study underscores the significance of laser irradiation of graphene oxide, a controllable strategy, and highlights the novelty and practical applications for fabricating flexible graphene oxide-based electronics.

Characterization of graphene oxide by pulsed UV nanosecond laser irradiation for flexible electrodes

This article focused on the fabrication of a thin film of rGO through pulsed Ultraviolet nanosecond laser irradiation. With the influence of laser power energy, the thickness of the fabricated thin film decreased, the contents of Carbon increased, Oxygen contents decreased, electrical resistance decreased, and a normalized specific surface area increased. When the thin film of GO was exposed to laser-irradiation, leads to the reduction of oxygen and the restoration of sp2 hybridization, resulting in a material with reduced electrical resistance and improved specific surface area. As a result, at 125 mW of laser power energy and 200 mm/s scanning speed of pulsed UV nanosecond laser, the contents of Carbon increased up to 81.6%, Oxygen contents decreased to 11.3%, and normalized specific surface area of 0.97 m2/g with good electrical conductivity was obtained. Therefore, its good electrical properties offer prospects for fabricating flexible electrodes and the practical application of pulsed laser-irradiated rGO substrate films for flexible electronics applications.

Two-temperature model for ultrafast melting of Au-based bimetallic films interacting with single-pulse femtosecond laser: Theoretical study of damage threshold

Ultrashort-pulse laser excitation and associated thermal damage of single-layer metallic films have been extensively studied both theoretically as well as experimentally. However, study of ultrafast heat transfer mechanism in bimetallic films, a topic of immense current interest for designing next-generation optical components with better thermal resilience, is limited to a low fluence regime. Moreover, available results for damage threshold (DT) of bimetallic films have several ambiguities. The current work is an attempt towards development of comprehensive theory for the DT of Au-based bimetallic films, analyzing its dependence on associated physical parameters and bridging the gap in existing literature. This has been achieved by developing fully implicit two-temperature model-based Python code. Excellent agreement of the predicted temperature profiles with recently reported [E. L. Gurevich, Y. Levy, S. V. Gurevich, and N. M. Bulgakova, Phys. Rev. B 95, 054305 (2017)] femtosecond laser irradiated Au film validates the code. Subsequently, the code is utilized to investigate the influence of different metallic substrates, $M$ ($M$ = Ni, Cr, Cu) on ultrafast melting damage of $\mathrm{Au}\text{/}M$ films excited by single-pulse femtosecond laser. Simulations carried out for increasing Au layer thickness revealed a nonmonotonic variation of DT for all substrates. This study also brought out an important observation that for every substrate metal, there exists an optimum Au thickness for maximizing the incipient and the complete melting threshold. Maximum achievable enhancement for $\mathrm{Au}\text{/}M$ films over pure Au are found to be 30%, 22%, and 14% with Cu, Ni, and Cr substrates, respectively. The observed distinction in maximum DT among three different $\mathrm{Au}\text{/}M$ targets is explained by developing appropriate thermophysical models. Finally, an empirical function is proposed here for expressing nonmonotonic variation of two-layer DTs. Very good agreement between the substrate-specific peak positions predicted by the proposed function and effective electron diffusion length arising from thermophysical analysis makes the modeling robust and applicable for a wide range of laser wavelengths as well as arbitrary combinations of bimetallic films.

Time-dependent laser irradiation-induced kinetics of changes in linear–nonlinear optical properties of Bi15In20Se65 thin films for IR applications

The current research depicts the laser irradiation-induced effect on the optoelectrical and structural properties of thermally evaporated Bi15In20Se65 thin films with different exposure durations (0, 10, 20, 30, 60, and 90 min). The illumination effect under different lasing times leads to the retention of amorphous nature, indicating the short-range ordering inside the matrix. An improvement in the homogeneous and smooth texture of the film surface even after irradiation has been observed. However, significant optical changes have been noticed with different exposure durations. Transparency decreased with the exposure time, whereas an increment in the absorption coefficient with red shifting in the absorption edge was observed. Broad transparency and less absorption over the infrared region make these films promising for infrared optics such as temperature detection, energy management, monitoring, night vision, etc. Laser illumination allowed bond rearrangements that led to an increase in defect states over the forbidden gap regime and reduced the bandgap from 1.02 to 0.94 eV, confirming the photodarkening nature. This consequently enhanced the Urbach energy and electron–phonon interactions. Both extinction coefficient and refractive index enhanced with lasing duration, indicating an increment in the scattering centers with the lasing duration. The increase in the lasing time results in the increase of interband transitions, which might be due to the increase of carrier concentrations in the system. The non-linear susceptibility (χ(3)) and refractive indices showed enhancement with exposure duration. The observed non-linear refractive index (SI) is 20–30 times greater than silica. This reduction of Eg and enhancement in non-linearity improves the occurrence of two-photon absorption, signifying the potentiality for photonic devices. The hydrophilic nature of laser-irradiated films makes them suitable for applications such as self-cleaning, antifouling, and antifogging as coating materials.

Order-disorder control of Si nanoparticles in laser-irradiated amorphous-Si thin film

Ordering of Si nanoparticles formed on an amorphous-Si thin film via laser irradiations was examined in terms of laser fluences, incident angles, and polarizations. The Si nanoparticles were created through two-dimensional scans of an ultraviolet nanosecond laser with a Gaussian beam. The arrangements of the nanoparticles varied significantly depending on the polarization at off-normal incidence. To perform quantitative analysis, an edge detection algorithm (the Hough transform method) was used to extract the nanoparticle size and position data from secondary electron microscopy images, and the nanoparticle distribution and ordering were estimated through the pair-correlation function. At normal incident angle, the Si nanoparticles were well ordered along the polarization direction, whereas for off-normal incidence at 30°, the Si nanoparticles were significantly disordered at polarization angles below 90° (out-of-plane) but ordered at the polarization angle of 90°. These features were interpreted in terms of the Rayleigh anomaly condition and competition between two wave vectors at off-normal incidence. The features can be applied to control the device performance in substrates for electronic or photovoltaic devices via nanoparticle ordering.

Effect of Atomic-Temperature Dependence of the Electron-Phonon Coupling in Two-Temperature Model.

Ultrafast laser irradiation of metals can often be described theoretically with the two-temperature model. The energy exchange between the excited electronic system and the atomic one is governed by the electron–phonon coupling parameter. The electron–phonon coupling depends on both, the electronic and the atomic temperature. We analyze the effect of the dependence of the electron–phonon coupling parameter on the atomic temperature in ruthenium, gold, and palladium. It is shown that the dependence on the atomic temperature induces nonlinear behavior, in which a higher initial electronic temperature leads to faster electron–phonon equilibration. Analysis of the experimental measurements of the transient thermoreflectance of the laser-irradiated ruthenium thin film allows us to draw some, albeit indirect, conclusions about the limits of the applicability of the different coupling parametrizations.

High-Density Nanowells Formation in Ultrafast Laser-Irradiated Thin Film Metallic Glass

HighlightsUltrafast laser-induced nano-topography modifications: generation of highly concentrated 20 nm diameter nanowells on the surface with expected applications for storage of chemical and biological active species and for blocking crack propagation.Ultrafast laser-induced structural modifications: turning of a metallic glass to a composite material of monoclinic zirconia crystallites embedded inside amorphous metallic glass.A flexible one-step laser irradiation process without direct mechanical contact for thin film metallic glasses surface functionalization.

Structural and optical properties of tin sulfide nanostructures

This paper presents modification of tin sulfide (SnS) thin films by pulsed laser irradiation. Tin sulfide films of 1 µm thickness were prepared using chemical bath deposition (CBD) technique. The chemical bath contained 5 ml acetone, 12 ml of triethanolamine, 8 ml of 1 M thioacetamide, 10 ml of 4 M ammonium hydroxide and 65 ml of distilled water. The chemical bath was kept at a constant temperature of 60 °C for 6 h which resulted in SnS films with 500 nm thickness. By double deposition, the final thick- ness of SnS thin films obtained was 1 µm. Laser processing was conducted to modify the structure, morphology and physical properties of the SnS thin films. The laser specifications were pulsed Nd:YAG laser with 532 nm wavelength, 300 mJ pulse energy and 10 ns pulse width. Properties of the laser-irradiated SnS thin films were compared with the as- prepared SnS thin films. The changes in structure, morphology, optical and electrical properties of the laser-irradiated SnS thin films were described.

Effect of 532 nm Nd:YAG laser irradiation on the optical properties of Ge1Se2.5 glass film

Ge1Se2 .5 alloy was prepared using the melt quenching method and the film was deposited by the thermal evaporation method. The as-prepared film was irradiated with Nd:YAG laser at 532 nm wavelength for different durations. The structural and morphological characterization indicates that the film has nanoparticles of different shapes with sizes varying from 80 to 300 nm and the structure becomes more crystalline on laser irradiation. The refractive index of the film increases, while the band gap decreases on laser irradiation. The dispersion behaviour of refractive index was studied using the WDD model. The decrease in band gap is attributed to the increase of laser-induced defects, which consequently narrows the energy gap. The non-linear optical parameters were found to increase with an increase in laser irradiation time. The increase in these parameters and transformation from the amorphous to the polycrystalline phase make laser-irradiated films suitable for non-linear optical devices and optical recording media.

CrSb2Te thin film as a dry resist and its etching mechanism for lithography application

Lithography has important applications in chip manufacturing, micro-electro-mechanical system, nanostructure fabrication et al. Photoresist is a key factor for the lithography. However, current organic resists suffer from poor line-edge roughness, environmentally unfriendly et al. In parallel, conventional wet development can readily cause the undercut of photoresist due to its isotropic etching. In this work, CrSb2Te thin film, as an inorganic resist, was prepared and its etching characteristics were investigated via dry development with CHF3/O2 mixed gases. It is found that superior etching selectivity can be realized in the CrSb2Te thin film. In order to elucidate the lithography characteristics, XRD, EDS, XPS, and Raman spectra are obtained. The results indicate that laser irradiation leads to the generation of Sb crystals and CrSb2Te3 phase. According to dry etching, Sb crystals of the laser-irradiation film can be readily broken. On the other hand, the as-deposited thin film possesses higher etching resistance owing to the uniform distribution of Cr in Sb2Te along with the formation of Cr-Sb and Cr-Te bonds. Therefore, CrSb2Te thin film may be utilized as a superior inorganic resist for the field of lithography.

Nanostructuration of Thin Metal Films by Pulsed Laser Irradiations: A Review.

Metal nanostructures are, nowadays, extensively used in applications such as catalysis, electronics, sensing, optoelectronics and others. These applications require the possibility to design and fabricate metal nanostructures directly on functional substrates, with specifically controlled shapes, sizes, structures and reduced costs. A promising route towards the controlled fabrication of surface-supported metal nanostructures is the processing of substrate-deposited thin metal films by fast and ultrafast pulsed lasers. In fact, the processes occurring for laser-irradiated metal films (melting, ablation, deformation) can be exploited and controlled on the nanoscale to produce metal nanostructures with the desired shape, size, and surface order. The present paper aims to overview the results concerning the use of fast and ultrafast laser-based fabrication methodologies to obtain metal nanostructures on surfaces from the processing of deposited metal films. The paper aims to focus on the correlation between the process parameter, physical parameters and the morphological/structural properties of the obtained nanostructures. We begin with a review of the basic concepts on the laser-metal films interaction to clarify the main laser, metal film, and substrate parameters governing the metal film evolution under the laser irradiation. The review then aims to provide a comprehensive schematization of some notable classes of metal nanostructures which can be fabricated and establishes general frameworks connecting the processes parameters to the characteristics of the nanostructures. To simplify the discussion, the laser types under considerations are classified into three classes on the basis of the range of the pulse duration: nanosecond-, picosecond-, femtosecond-pulsed lasers. These lasers induce different structuring mechanisms for an irradiated metal film. By discussing these mechanisms, the basic formation processes of micro- and nano-structures is illustrated and justified. A short discussion on the notable applications for the produced metal nanostructures is carried out so as to outline the strengths of the laser-based fabrication processes. Finally, the review shows the innovative contributions that can be proposed in this research field by illustrating the challenges and perspectives.

Aging Processes in Implanted Fluorine Ions and Laser Irradiated Films of LaGa:YIG

Based on the results of X-ray structural analysis, changes in the crystalline structure during natural aging and laser annealing, which occurred in near-surface layers of epitaxial films of LaGa-substituted Iron-Yttrium Garnet, implanted by F+ ions, were studied. The processes that occur during the ion implantation by F+ in ferrite-garnet films, and the processes that accompany the low-temperature aging of ion-implanted films are considered. From the experimental rocking curves, obtained immediately after ion implantation, after the laser irradiation and after several years, strain profiles were determined. Two stages in the changes of the crystalline structure of the nearsurface disturbed layer over time are revealed. During the first of them, the maximum deformation in the ionimplanted layer increased slightly, and on the second it decreased. It was established that the results of laser annealing and natural aging of near-surface layers implanted by F+ ions and laser irradiated LaGa:YIG films depend on the direction from which laser irradiation occurred. However, the result of their total exposure does not depend on the side of laser irradiation.

Chromium oxide formation on nanosecond and femtosecond laser irradiated thin chromium films

Thin coatings of Cr2O3 have been used for numerous applications. Selective oxidation of chromium will be beneficial for integrated device fabrications. Thin coatings of pure chromium were vacuum deposited on a glass substrate using hot electrons from tungsten filament. These coatings were then treated with nanosecond and femtosecond laser in ambient conditions. The microstructure, morphology and the color of the coatings treated with laser sources were modified and there was a formation of an oxide layer due to the heat dissipation on the chromium coating from the energetic photons. High-resolution scanning electron microscope studies showed the morphological evolution, which is directly correlated with the laser fluence of both the nanosecond and femtosecond lasers. This morphological evolution was accompanied by the microstructural change as observed from the X-ray diffraction patterns. The chromaticity response of the coating was studied by UV–Vis spectroscopy and the response of the coating in the visible region evolved with the laser fluences. The divergence in chromaticity of these two laser treatments, is due to the difference in morphology as the result of the varied pulse duration. It could be concluded that the morphology had effect on the chromaticity of the films. Futhermore, Rutherford backscattering depth profiling of the laser treated coatings revealed the diffusion of oxygen atoms in the coating as a result of laser treatment fluence. We have analyzed both the optical and material properties of the laser induced oxidation and demonstrated laser writing as a promising tool to selectively oxidize Chromium for integrated device applications.

Reduced Graphene Oxide/Amorphous Carbon P-N Junctions: Nanosecond Laser Patterning.

The device integration of graphene and reduced graphene oxide (rGO) is impeded by scalability and high temperature (>2000 K) treatment required for effective reduction into high-quality rGO. In this article, we present a novel approach for direct laser writing of heavily reduced graphene oxide films by nanosecond laser melting of amorphous carbon on silicon (001) substrates under ambient conditions. Ultrafast quenching from the undercooled melt state above the melting threshold energy density (Ed) of 0.4 J/cm2 leads to the formation of large-area rGO films. The first-order phase transformation of liquid carbon into graphene is triggered by low undercooling at the C melt/silicon interface. The laser-irradiated rGO films exhibit electron mobility of 12.56 cm2/V s and charge carrier concentration of -1.2 × 1021/cm3 at 300 K. Temperature-dependent electrical measurements and Raman spectroscopic investigations suggest low disorder and charge transport via 2D Mott variable range hopping between the graphene islands for rGO films. The localization length corresponding to the size of these graphitic domains is 3 nm. The ultrafast regrowth of rGO creates an atomically sharp interface between n-type rGO and p-type amorphous carbon, resulting in p-n junction heterojunction diodes with a turn-on voltage of 0.3 V, rectification ratio of 110@±1.5 V, and activation energy of 0.13 eV under reverse bias. This unique laser processing method solves the problems of traps and defects associated with equilibrium-based rGO fabrication methods, enabling high conductivity and mobility, providing insights into the fundamental mechanism driving laser writing of graphene-based materials on silicon.

Effect of ArF excimer laser annealing on morphology and surface plasmon resonance properties of Ag nanoparticles

Ag nanoparticles were obtained in AZO/Ag and AZO/Ag/AZO films by magnetron sputtering method at room temperature. These as-deposited films are then annealed by ArF excimer laser system operated at λ = 193 nm. The effect of two different laser annealing processes on surface plasmon resonance (SPR) of Ag particles and photoelectric properties of these films can be discussed detailedly. AZO film substrates where the thermally active surface diffusion of Ag occurs play an important role in determining the morphologies of Ag particles. Ag films irradiated directly by laser annealing in AZO/Ag films tend to form spherical particles, while Ag films deposited on laser-irradiated AZO film substrates are likely to form irregular long particles. The results show that irregular long Ag particles can be obtained on AZO films with small and dense grains as nucleation centers induced by high laser energy densities, which can exhibit redshift of SPR peaks and optimize photoelectric properties. The SPR peak of irregular long Ag particles based on laser-irradiated AZO substrate can reach to 750 nm with an optical average transmittance of 83% and a $$ R_{\text{S}} $$ value of 16 Ω/sq at a laser energy density of 250 mJ/cm2.

High performance flexible solid-state symmetric supercapacitors based on laser induced porous reduced graphene oxide-graphene oxide hybrid nanostructure devices

Materials with a porous structure and high surface area have gained tremendous research interests in the design of advanced high energy density supercapacitors because of their great capacitance and chemical stability. Herein, an effective method is introduced to achieve a large-scale production of porous graphene network by laser irradiation of graphene oxide films with a short span of time. Interestingly, this method introduces a porous structure, high surface area and promising electrochemical properties which significantly enhances the reversible capacitance behaviour. Notably, laser irradiated graphene oxide films electrodes show excellent areal capacitance of 149.7 mF cm−2 at 3 mV s−1 with a maximum energy density of 7.5 mWhcm−3. Also, these electrodes demonstrate an outstanding cycling stability, which retains above 85% capacitance of its initial capacitance after 5000 charge-discharge cycles shows a significant enhancement over other values reported in the literature. Furthermore, the bending tests confirms that the superior flexible performance of the laser irradiated graphene oxide electrodes holds a great potential for the development of wearable electronic devices.

Shortening Nucleation Time to Enable Ultrafast Phase Transition in Zn1Sb7Te12 Pseudo-Binary Alloy.

Zn1Sb7Te12 thin films have been deposited by magnetron co-sputtering of ZnTe and Sb2Te3 targets. The microstructure, phase-change speed, optical cycling stability, and crystallization kinetics have been investigated during thermal annealing and laser irradiation. The thermal-annealed and laser-irradiated films give a clear evidence of the coexistence of trigonal Sb2Te3 and cubic ZnTe phases, which are homogeneously distributed in a single alloy as confirmed by advanced scanning transmission electron microscopy. The formation of both phases increases the initial nucleation sites, leading to the rapid phase-change speed in the Zn1Sb7Te12 film. The film has a minimum crystallization time of ∼3 ns at 70 mW with almost no incubation period for the formation of critical nuclei compared to Ge2Sb2Te5 and other Zn-based films. Moreover, the complete crystallization of Zn1Sb7Te12 thin films is achieved within 10 ns. The ultrafast two-dimensional nucleation and crystal growth speed in Zn1Sb7Te12 obtained from the laser-irradiated system is almost 7 times faster compared to that in Ge2Sb2Te5 film. Controlling the crystallization process through doping ZnTe into Sb2Te3 is thus promising for the development of high-speed optical switching technology.

Controlled slicing of single walled carbon nanotubes under continuous flow

Single walled carbon nanotubes (SWCNTs) are sliced with control over their length distribution within a laser irradiated dynamic thin film in a vortex fluidic device (VFD) operating under continuous flow conditions. Length control depends on the laser pulse energy, the flow rate of the liquid entering the device, the speed of the rapidly rotating tube and its tilt angle, choice of solvent and concentration of the as received SWCNTs. The induced mechanoenergy in the thin film while being simultaneously irradiated with a Nd:YAG pulsed laser operating at 1064 nm wavelength results in the slicing, with laser pulse energies of 250, 400 and 600 mJ affording 700, 300 and 80 nm length distributions of SWCNTs respectively. The processing avoids the need for using any other reagents, is scalable under continuous flow conditions, and does not introduce defects into the side walls of the SWCNTs.

Atomic diffusion in laser irradiated Ge rich GeSbTe thin films for phase change memory applications

The atomic diffusion and compositional variations upon melting have been studied by transmission electron microscopy and electron energy loss spectroscopy in Ge rich GeSbTe films, with a composition optimized for memory applications. Melting and quenching has been achieved by laser pulses, in order to study pure thermal diffusion without electric field induced electromigration. The effect of different laser energy densities has been investigated. The diffusion of Ge atoms in the molten phase is found to be a prominent mechanism and, by employing finite elements computational analysis, a diffusion coefficient of Ge on the order of 5 × 10−5 cm2 s−1 has been estimated.

Properties of Al- and Ga-doped thin zinc oxide films treated with UV laser radiation

This paper reports the Nd:YAG laser irradiation treated modified properties of aluminum (Al) and gallium (Ga) co-doped zinc oxide (ZnO) (AGZO) films prepared on Si-substrate via combined sol–gel and spin-coating method. The impact of varying laser energy (150–200 mJ) on the structure, morphology, electrical and optical properties of such AGZO films were determined. Laser-treated samples were characterized using various analytical tools. Present techniques could achieve a high-quality polycrystalline films compared with those produced via conventional high temperature processing. AGZO films irradiated with third harmonics UV radiation (355 nm) from Nd:YAG laser source revealed very low resistivity of 4.02 × 10− 3 Ω cm. The structural properties grain size was calculated firm the X-ray diffraction spectra using the Scherrer equation that increased from 12.7 to 22.5 nm as the annealing laser energy increased from (150–200) mJ. The differences in crystallinity and orientation are explained in terms of the thermal effect caused by laser irradiation. (FESEM) images have been demonstrated that Nd:YAG laser annealing can significantly improve the crystallinity level, densification, and surface flatness of sol–gel derived AGZO thin films that occurred as a result of laser processing. Synthesized AGZO films displayed favorable growth orientation along (101) lattice direction. AGZO films with energy band gap of 3.37–3.41 eV were obtained. Results on the crystallinity, surface morphology, roughness, bonding vibration, absorption, photoluminescence, and resistivity of the laser-irradiated films were analyzed and discussed.