Increasing Laser Fluence Research Articles

Utilizing the 2nd harmonic Nd: YAG laser ablation in liquid for the production of copper oxide quantum dots: Influence of laser fluence and ablation duration

One environmentally friendly technique for creating colloids of nanoparticles is pulsed laser ablation in liquid, which stands out for its ability to create nanoparticles free of contamination without the use of hazardous chemicals. In the present work, A Q-Switched Nanosecond Nd: YAG laser was utilized to precisely produce colloidal copper oxide nanoparticles (CuONPs) through the laser ablation of a copper target immersed in distilled water. The impact of the laser fluence and laser ablation time on the size, morphology, and concentration of the generated CuONPs was investigated experimentally. The UV–visible absorption spectra of CuONPs display surface plasmonic resonance peaks in the UV region, which are attributed to interband transitions. The energy band gaps of the colloidal CuONPs were determined using UV–visible spectroscopy, and they ranged between 3.45 and 3.72 eV at various ablation times and laser fluences. The TEM micrographs were used to assess the size and morphology of the CuONPs, while the concentration and elemental composition were determined using ICP and EDXA spectroscopy. The TEM images of the CuONPs indicate a spherical shape at various laser ablation times and laser fluences. The average size of the CuONPs decreased to the quantum size range. The experimental results show that increasing laser fluence from 28.6 to 51.5 × 103 J/cm2 while keeping laser ablation time fixed for 30 min resulted in a reduction in the average size of the nanoparticles from 8.5 to 4.6 nm, respectively. Moreover, increasing laser ablation time from 10 to 50 min at a constant incident laser fluence of 34.3 × 103 J/cm2 decreased the average size of the CuONPs from 6.8 to 4.3 nm, respectively. The concentration of the synthesized CuONPs increased as laser fluence and laser ablation time increased.

A comparative study of laser fluence effect on surface modification and hardness profile of austempered ductile iron

The impact of laser transformation hardening (LSH) and Laser surface melting (LSM) on an austempered ductile iron (ADI) alloy was investigated. Various laser fluences (J mm−2) were irradiated on the ADI specimens, obtained by different beam powers and scanning speeds to reach the optimum parameters to attain a surface with a good combination of high hardness and deep hardened depth, together with obtaining minimal distortion and crack-free surface. ADI surfaces were treated by means of high-power Nd:YAG laser in continuous wave mode. A detailed investigation of the obtained microstructure was characterized via optical and scanning electron microscopy attached to an EDX analyzer as well as X-ray diffraction analysis. Such a wide laser fluence range has a considerable effect on the achieved microstructure. A process parameter map was established which indicated that three different laser treatments were induced under such values of laser fluences: a laser transformation hardening, a partial laser melting, and a complete laser melting. The results revealed that to produce a hardened microstructure, specimens have to be operated within a very small range of laser fluence from 9.6 up to 29 J mm−2, achieving surface hardness values around 900 HV0.1 and depths of approximately 184–700 μm, respectively. Meanwhile, partial melting of the treated layer took place at a medium energy density range from 37 to 112 J mm−2, by a further increase in laser fluence (120–360 J mm−2), complete melting occurred which resulted in a deeper treated layer that reached 3.5 mm with an increase in microhardness value to almost 1100 HV0.1 at 360 J mm−2. The obtained microstructure in case of low laser fluence consisted of an austenite dendritic structure with undissolved graphite nodules, however, at medium and high laser fluence, the microstructure contains large cementite plates, iron-silicon carbides, a small area of ledeburite structure, and some retained austenite. The quantitative amounts of such phases directly depend on the applied laser fluence. Such phases were identified by means of EDX analysis.

Application of pulsed laser ablation thermal model in nanosecond pulsed laser removal of the epoxy resin paint film

The effect of laser surface paint removal depends on the mechanism of paint removal. The mechanism of nanosecond laser removal of epoxy resin paint film on aluminum alloy surfaces was studied theoretically and experimentally. Firstly, a laser thermal paint removal model was established based on the heat conduction equation, Hertz-Knudsen equation, and Hooke's law. The adsorption relationship between the paint film and the aluminum alloy substrate molecules and the adsorption force between the paint film and the substrate were analyzed and calculated. A laser thermal paint removal model was solved using COMSOL finite element software. By analyzing the changes in temperature and thermal stress with laser fluence, we obtained the theoretical threshold for laser paint removal. Subsequently, experimental research was conducted on laser paint removal. Through theoretical and experimental studies, it was found that the paint removal threshold of nanosecond pulse laser is 0.47 J/cm2. The primary mechanism of nanosecond laser paint removal is thermal stress stripping. When the laser fluence is low, the nanosecond pulse laser can only ablate the paint on the surface, and the thermal stress between the paint film and the substrate makes it difficult to remove the paint film. As the laser fluence increases, the nanosecond laser will ablate the surface paint film, and the thermal stress between the paint film and the substrate will cause the stripping of the underlying paint film and the substrate. The primary mechanism of laser paint removal is stripping.

193 nm laser annealing on p-GaN with enhanced hole concentration and wall-plug-efficiency in deep ultraviolet LED

The high acceptor ionization energy and, thus, low carrier concentration in p-type III-nitride have widely been recognized as the bottleneck preventing the development of high-efficiency light-emitting-diodes (LEDs). In this contribution, the influences of 193 nm pulsed laser annealing on the structure, electrical, and optical properties of p-type GaN were systematically analyzed. The hole concentration of p-GaN first increases and then decreases with increasing laser fluence, regardless of post-growth thermal annealing. The effective dopant activation due to laser annealing can be attributed to the dissociation of Mg–H complexes during the treatment. Laser-annealed p-GaN was utilized in a 280 nm deep ultraviolet LED. A maximum of 1.47 times higher wall-plug-efficiency enhancement factor was obtained compared to that without laser annealing, demonstrating that 193 nm laser annealing plays a decisive role in the boosting of quantum efficiency of optoelectronic devices.

A Systematic Study on the Processing Strategy in Femtosecond Laser Scribing via a Two-Temperature Model.

Balancing quality and productivity, especially deciding on the optimal matching strategy for multiple process parameters, is challenging in ultrashort laser processing. In this paper, an economical and new processing strategy was studied based on the laser scribing case. To reveal the temperature evolution under the combination of multiple process parameters in the laser scribing process, a two-temperature model involving a moving laser source was developed. The results indicated that the peak thermal equilibrium temperature between the electron and lattice increased with the increase in the laser fluence, and the temperature evolution at the initial position, influenced by subsequent pulses, was strongly associated with the overlap ratio. The thermal ablation effect was strongly enhanced with the increase in laser fluence. The groove morphology was controllable by selecting the overlap ratio at the same laser fluence. The removal volume per joule (i.e., energy utilization efficiency) and the removal volume per second (i.e., ablation efficiency) were introduced to analyze the ablation characteristics influenced by multiple process parameters. The law derived from statistical analysis is as follows; at the same laser fluence with the same overlap ratio, the energy utilization efficiency is insensitive to changes in the repetition rate, and the ablation efficiency increases as the repetition rate increases. As a result, a decision-making strategy for balancing quality and productivity was created.

Analysis of the microscopic characteristics of periodic structure arrays on silicon carbide fabricated by femtosecond laser

The fabrication of large dimension structures (800 μm × 800 μm) featuring fine and coarse ripple patterns, nano particle structures, and V-shaped grooves was achieved on silicon carbide (SiC) through the use of femtosecond laser. The X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy (Raman) were performed on sample surface to investigate the atomic bond, residual stress and lattice disorder. XPS analysis revealed that an increase in laser fluence resulted in an increase in the content of C=O bond, while the content of O–C=O bond decreased. The C–C (sp2) bond was destroyed, while the unstable C–C (sp3) bond increased. Additionally, there was a decrease in the content of Si–Si bond and Si–C bond, and an increase in the content of Si–O bond. The resulting oxide layer contributed to an improvement in the fracture toughness of the periodic array. XRD analysis results indicate that the technique is not sensitive to structural defects in SiC and surface contaminants caused by laser ablation. On the (0008) crystal plane, an increase in fluence resulted in an initial increase in lattice spacing, strain, and residual stress, followed by a plateau. The laser-modified area corresponded to a region of tensile stress, with the maximum tensile stress being 179.464 MPa. On the (0004) crystal plane, an increase in fluence resulted in varying degrees of increase in lattice spacing, strain, and residual stress. The residual tensile stress at the fine ripple and groove bottom was 0 and 14.623 MPa, respectively, while the residual tensile stress at the coarse ripple and nano particle structure was 277.847 MPa. The residual tensile stress increased with an increase in scanning interval. Raman analysis showed that the overall disorder increased with an increase in laser fluence, with a maximum degree of disorder being 0.548.

Removal mechanism of Hydroides fouling on high-strength steel in the marine environment during nanosecond pulsed laser cleaning

The surface of metal materials will be contaminated by marine organisms when serving in the marine environment, which seriously affects the service life of the materials, and must be cleaned regularly. The Hydroides fouling on the surface of 30Cr3 high-strength steel was taken as the object to be cleaned; the cleaning quality at different laser fluences was studied; the desorption behavior and the characteristics of spectral and acoustic signals during laser cleaning were analyzed; and the removal mechanism of Hydroides fouling on the surface of high-strength steel was summarized. The results show that the cleaning effect of nanosecond pulsed laser on Hydroides fouling increases with the increase of laser fluence, and the laser fluence of 9.95 J/cm2 can be used to clean the Hydroides fouling with the maximum diameter of 1.62 mm completely with little damage to the substrate. The removal mechanism of Hydroides fouling is the inverse bremsstrahlung mechanism. In the process of cleaning, the surface fouling is partially vaporized and ionized into high-temperature plasma under the action of pulsed laser. The laser energy is absorbed through inverse bremsstrahlung absorption to form shock waves to compress the surface, which leads to cracks on Hydroides fouling. When the surface compressive stress is released, the Hydroides fouling is removed from the surface, and the removal effect increases with the increase of laser fluence.

Excimer laser processing of nanostructured SnO2 thin films and its impact on LPG sensing

KrF excimer laser (λ = 248 nm) has been employed to anneal nanocrystalline Tin oxide (SnO2) films deposited at 200 °C using spray pyrolysis. With the increase of irradiation laser fluence, the film crystallinity has been improved while the matrix stress decreased along all the crystal planes except (110) and (301), for an energy density of 150 mJ/cm2 as compared to non-irradiated films. The maximum liquid petroleum gas (LPG) response observed for a fluence 150 mJ/cm2 is 92.6% at 350 °C whereas a response is 4% at the onset sensing temperature of 100 °C. Moreover, the response and recovery times have also improved by the laser processing and the cross sensitivity for NH3 and NO2 gases are in a desirable range. FESEM images of irradiated films show polygonal shaped distributions of aggregated nanocrystalline particle-clusters with grain boundaries and nanovoids. XPS shows oxygen deficient lattice besides surface and/or pore-bound oxygen contributions. Raman analyses confirm the sub-stoichiometric SnO2-x phases and a high concentration of defects such as oxygen vacancies (OVs) on surface sites. Based on these observations, the gas sensing mechanism is discussed in brief.

Rapid laser-induced low temperature crystallization of thermochromic VO2 sol-gel thin films

The thermochromic properties of vanadium dioxide (VO2) offer great advantages for energy-saving smart windows, memory devices, and transistors. However, the crystallization of solution-based thin films at temperatures lower than 400°C remains a challenge. Photonic annealing has recently been exploited to crystallize metal oxides, with minimal thermal damage to the substrate and reduced manufacturing time. Here, VO2 thin films, obtained via a green sol–gel process, were crystallized by pulsed excimer laser annealing. The influence of increasing laser fluence and pulse number on the film properties was systematically studied through optical, structural, morphological, and chemical characterizations. From temperature profile simulations, the temperature rise was confirmed to be confined within the film during the laser pulses, with negligible substrate heating. Threshold laser parameters to induce VO2 crystallization without surface melting were found. With respect to furnace annealing, both the crystallization temperature and the annealing time were substantially reduced, with VO2 crystallization being achieved within only 60 s of laser exposure. The laser processing was performed at room temperature in air, without the need of a controlled atmosphere. The thermochromic properties of the lasered thin films were comparable with the reference furnace-treated samples.

A new method for predicting the morphology and surface roughness of micro grooves in aluminum alloy ablated by pulsed laser

It is challenging to predict the morphology of the grooves ablated by pulsed laser. To predict the morphology and surface roughness of aluminum alloy grooves at low laser fluence (ranging from 17.68 J/cm2–28.29 J/cm2), a method which combines analytical and simulation approaches is proposed in this research. The proposed method takes into account the evaporation and redeposition behavior, examines the impact of pulse interactions through simulations, and focuses on the influence of molten pool flow on surface roughness. Firstly, the level set method is employed to accurately track the vapor-liquid interface and predict the ablative morphology of a single pulse. Secondly, the influence of molten pool flow on surface morphology in the case of pulse interaction is quantitatively described by comparing the morphology of a two-pulse ablation simulation with scanning speed in the heat source to the morphology obtained by simple superposition of a single pulse, the resulting morphological error is attributed to flow. Finally, the flow deviation of the ablated groove is compensated for applying an analytical method, and the three-dimensional morphology of the ablated groove is calculated by using the proposed expression. The computational analysis using the new method is compared with the experimental results, demonstrating that the average prediction error for contour is less than 7 %, and the error for roughness prediction is less than 10 %. By analyzing the melt flow using the new method, it is discovered that as the laser fluence increases, the range of melt flow expands and the amplitude of vertical flow increases, which results in the increase of surface roughness. Notably, the scanning speed does not directly affect the roughness by influencing the melt flow.

Femtosecond Laser‐Induced Hydrophobic Surface of NiTi Shape Memory Alloy and its Blood Compatibility

The study of nickel–titanium shape memory alloy (NiTi SMA) surface wettability is important to improve the blood compatibility of medical implant materials. Herein, a femtosecond laser with a wavelength of 1030 nm is used to process the hydrophobic surface of NiTi SMA. A scanning electron microscope, an X‐ray photoelectron spectrometer, a surface profiler, and a contact angle meter are used to measure the microstructure, the chemical composition, the surface roughness, and the surface contact angle of NiTi SMA. The influence of the laser fluence on the NiTi SMA surface wettability is analyzed using the Wenzel–Cassie composite model. The results show that as the laser fluence increases, the surface roughness gradually increases and then fluctuates. Moreover, a rapid increase followed by a gradual rise is observed in the surface contact angle. The blood compatibility of NiTi SMA surface increases with the increase in the surface contact angle. Specifically, the superhydrophobic surface with high contact angle and low rolling angle can significantly improve hemolysis and coagulation while reducing platelet adhesion and deformation. The study of the superhydrophobic microstructure of NiTi SMA surface will provide a new approach for improving the blood compatibility of medical implant materials.

Understanding non-stochiometric deposition of multi-principal elemental NiCoCr thin films

Multi-principal elemental NiCoCr thin films with compositional flexibility have potential applications as a thermal barrier, corrosion-resistant coatings, and functional energy materials. In this study, the non-stochiometric multi-principal element alloy thin film formation behavior from an equiatomic ablation target of NiCoCr using pulsed laser deposition has been reported. Here, the effect of varying laser fluence on compositions of constituent elements in the NiCoCr thin films is systematically investigated. The increase in laser fluence typically increases the likelihood of acquiring undesirable particulates in thin films. Therefore, to maintain the film quality the laser fluences are adjusted within the range of 1.3–3.3 J·cm−2, while the film thicknesses are kept constant at ∼30 nm. Results show that the constituent elements are well-distributed in the formed NiCoCr thin films, however, having average atomic percentages of Ni and Cr twice as high as Co irrespective of the equiatomic composition of individual elements in the ablation target. This stochiometric alteration in the as-deposited thin films is governed by the rate of ablation and subsequent evaporation of each element, which is facilitated by the optical properties and vapor pressure of individual constituent elements. Additionally, electron energy-loss spectroscopy and x-ray absorption spectroscopy analysis reveal that the thin films have partially oxidized, with the Cr oxidation contributing the most to the O-K edge in comparison to Ni and Co. This study presents a laser-assisted pathway for fabricating compositionally flexible NiCoCr thin films and develops an understanding of the non-equilibrium laser-material interactions and how the intrinsic properties of constituent elements affect the stoichiometric flow of materials from the target to the final film deposition.

Creation of NV centers over a millimeter-sized region by intense single-shot ultrashort laser irradiation

Recently, ultrashort laser processing has attracted attention for creating nitrogen-vacancy (NV) centers because this method can create single NV centers in spatially-controlled positions, which is an advantage for quantum information devices. On the other hand, creating high-density NV centers in a wide region is also important for quantum sensing because the sensitivity is directly enhanced by increasing the number of NV centers. A recent study demonstrated the creation of high-density NV centers by irradiating femtosecond laser pulses, but the created region was limited to micrometer size, and this technique required many laser pulses to avoid graphitization of diamond. Here, we demonstrate the creation of NV centers in a wide region using only an intense single femtosecond laser pulse irradiation. We irradiated a diamond sample with a femtosecond laser with a focal spot size of 41 µm and a laser fluence of up to 54 J/cm2, which is much higher than the typical graphitization threshold in multi-pulse processing. We found that single-pulse irradiation created NV centers without post-annealing for a laser fluence higher than 1.8 J/cm2, and the region containing NV centers expanded with increasing laser fluence. The diameter of the area was larger than the focal spot size and reached over 100 µm at a fluence of 54 J/cm2. Furthermore, we demonstrated the NV centers’ creation in a millimeter-sized region by a single-shot defocused laser pulse over 1100 µm with a fluence of 33 J/cm2. The demonstrated technique will bring interest in the fundamentals and applications of fabricating ultrahigh-sensitivity quantum sensors.

Stoichiometry, Orbital Configuration, and Metal-to-Insulator Transition in Nd0.8Sr0.2NiO3 Films

The discovery of superconductivity in the infinite-layer nickelate Nd0.8Sr0.2NiO2 has motivated tremendous efforts for its significance toward the understanding of high-temperature superconductivity. However, the synthesis of infinite-layer nickelates is instable and has become a hindrance to experimental progress. Optimizing the growth of precursor Nd0.8Sr0.2NiO3 by pulsed laser deposition is crucial for obtaining infinite-layer nickelates. By systematically investigating the growth of Nd0.8Sr0.2NiO3 with wide range of conditions, we found that the laser fluence plays a critical role in determining the stoichiometry, lattice structure, and electronic properties. A higher Ni deficiency and larger c-axis lattice constant appeared with the lower laser fluence. At 0.6 J/cm2, the Ni deficiency is as large as 25%. According to X-ray absorption spectra and X-ray linear dichroism, we further find that (i) there are no obvious changes of the Ni valence and (ii) the energy level of the dx2-y2 orbital gradually increases relative to the d3z2-r2 orbital with increasing Ni deficiency. What is more, the onset temperature and magnitude of the resistivity change at the metal-to-insulator transitions (MITs) also are found to decrease with increasing laser fluence during the growth.

Effect of laser surface modification on the tensile properties of ultra-thin titanium sheet

Laser scanning irradiation (LSI) was a promising method to improve the surface hemo-compatibility of vascular stent (VS). This paper firstly studied the effect of LSI on the tensile properties of ultra-thin Ti sheet, the thickness of which was close to that of VS’s wall. Meanwhile, the influence of plastic deformation on the hydrophilicity of LSI sheets and the hydrophobicity of the ones modified with fluorosilane was evaluated. The results indicated that the tensile properties of Ti sheets gradually declined with increasing laser fluence (Fp) and decreasing scanning speed (v). As using laser gentle ablation (LGA) with Fp = 1.1 ∼ 2.9 J/cm2, the declination degree of tensile properties was relative slight, but it was obviously sharper as using laser strong ablation (LSA) with Fp = 4.0 ∼ 6.6 J/cm2. In addition, the tensile and yield strengths of LSA samples using v = 42 mm/s were much smaller than those using higher v of 126 ∼ 630 mm/s, owning to the much larger laser-ablated depth in the surfaces. All of the LSA surfaces exhibited superhydrophilicity, and after fluorination they rapidly turned to be superhydrophobic with low adhesion to water. Interestingly, plastic deformation within the tensile fracture point slightly improved the super-hydrophilicity or superhydrophobicity of these LSA surfaces rather than destroyed it. Therefore, LSA with v = 126 ∼ 630 mm/s was more suitable to be applied in the stent, which could not only obtain super-hydrophilicity/hydrophobic surfaces with hierarchical microtextures but just slightly affect the stent’s tensile properties.

Mechanism of surface corrosion resistance of 304 stainless steel processed by nanosecond laser pulses

AbstractA nanosecond pulsed fiber laser was used to modify the surface of 304 stainless steel. The compactness, microstructure, chemical composition, and corrosion resistance of the stainless steel passive film were observed by the blue dot detection method, scanning electron microscopy, x‐ray photoelectron spectroscopy, and electrochemical methods. The influence of different laser fluences on the stability and corrosion resistance of the stainless steel passive film was studied. The results show that with increasing laser fluence, the discoloration reaction time of the stainless steel surface increases first and then decreases, while the surface roughness decreases first and then increases. When the laser fluence is lower than 11.19 J/cm2, a compact and uniform passive film is formed. When the laser fluence is larger than this value, the stainless steel substrate is prone to secondary corrosion. Chromium oxides are enriched in the passive film, and the anodic dissolution rate decreases, which promotes a positive shift in the corrosion potential of the stainless steel, decreases the corrosion current density and increases the polarization resistance and the corrosion resistance. The surface corrosion resistance is thus significantly improved.

Facile strategy for advanced selectivity and sensitivity of SnO2 nanowire-based gas sensor using chemical affinity and femtosecond laser irradiation

This study proposes an effective strategy to improve the selectivity and response of SnO2 nanowire (NW)-based gas sensors. Self-assembled monolayer (SAM) functionalization of SnO2 NWs enhances the gas selectivity by tuning the surface chemical states. Different chemical moieties with alkyl and fluoroalkyl of the SAM molecules are adopted for the chemical affinities toward the corresponding target gas molecules. The alkyl and fluoroalkyl moieties show excellent selectivity toward CH4 and C3F8, respectively, owing to the strong chemical affinity between the moieties and gases. Post-treatment femtosecond (FS) laser irradiation with different laser fluences is applied to the SAM-functionalized SnO2 NW-based gas sensor. The FS laser-irradiated SnO2 NWs show an enhanced sensor response with higher resistance values and shorter response and recovery times compared to those of the pristine SnO2 NWs. Transmission electron microscopy analysis reveals that the FS laser irradiation induces the formation of embossing surface on the SnO2 NW, creating additional gas adsorption sites. Moreover, twin structures develop on the SnO2 NWs with increasing laser fluences. Electron energy loss spectroscopy analysis supports that the FS laser irradiation creates non-stoichiometric SnO and SnOx phases, providing O vacancies and improved response.

Laser based surface treatment of bioactive glass: Dependence on pulsed laser ablation

Experimental results and theoretical simulation of material ablation on nanosecond Nd:YAG laser irradiation of bioactive glass targets, is presented. The process of pulsed laser ablation critically affects both, laser based surface modification and pulsed laser deposition (PLD) of bioactive glass (BG). A thermal model based theoretical simulation has been carried out describing heat-transport, melting and vaporization of a laser irradiated BG target under near-threshold ablation conditions. Calculated mass ablation rate per laser pulse has been compared with our experimental observations over the average laser fluence of 0.5J/cm2 to 6J/cm2. With increasing laser fluence, possibility of material ablation approaching phase explosion has been discussed by comparing the calculated maximum temperature reached by the laser irradiated target and the estimated thermodynamic critical temperature for BG. Our investigations indicate that with average laser fluence restricted to ∼5 J/cm2 material ablation occurs largely via normal vaporization ensuring deposition of an uniform, homogeneous BG coating through PLD. Target surface temperatures estimated from our calculations also suggest that laser based surface modification of BG can be reproducibly carried out without causing target crystallization and surface damage through crater formation for irradiating laser fluence in the region of ∼ 5J/cm2.

Colloidal synthesis of cesium iodide nanocrystals for visible-enhanced photodetection applications

In this study, cesium iodide (CsI) nanoparticles were synthesized for the first time by pulsed laser ablation in ethanol at various laser fluences . The structural and optical properties of the CsI nanoparticles were studied as a function of laser fluence. The x-ray diffraction (XRD) results confirm the formation of crystalline CsI with a cubic structure along (110) plane. The optical absorbance spectra showed two absorption peaks at 291 and 363 nm. The optical energy gap of CsI NPs decreases as laser fluence increases. Transmission electron microscope studies show that the synthesized nanoparticles have a spherical shape and the mean particle size prepared at 22.9, 33.1 and 43.3 J/cm 2 was 23, 25, and 28 nm, respectively. Scanning electron microscope results reveal the formation of nanosized spherical CsI nanoparticles. The fluorescence emission data of CsI shows two main bands centered at 339 nm and 387 nm. Raman spectra show three Raman peaks located at 15, 26 and 44 cm −1 . The zeta potential results confirm that the CsI NPs prepared at 33.1 J/cm 2 have good stability. The current-voltage characteristics of CsI/Si heterojunctions show rectification properties, and the illuminated current-voltage shows that the maximum photocurrent was found for a photodetector fabricated at 33.1 J/cm 2 . The maximum responsivity and detectivity of the photodetector are 1.66 A/W and 5.5 × 1012 Jones at 400 nm, respectively, for a photodetector prepared at 33.1 J/cm 2 . A quantum efficiency of 5.16 × 10 2 % at 400 nm is reached for a photodetector prepared at 33.1 J/cm 2 . The Hall effect shows that the synthesized CsI NPs are p-type and the highest hole mobility was found for a sample prepared at 33.1 J/cm 2 . • Colloidal Cesium iodide nanoparticles were synthesized by laser ablation in liquid. • The effect of laser fluence on the properties of CsI was investigated. • Different morphologies of CsI nanocrystals were obtained. • High performance CsI nanostructure/Si photodetector was fabricated.

Texture evolution mechanism of pulsed laser deposited in-doped Ga2O3 film affected by laser fluence and its application in solar-blind photodetector

This work explored the crystal structural, optical bandgap, and morphological texture evolution of pulsed laser deposited In-doped Ga2O3 films grown on sapphire substrate at different laser fluence from 1.0 to 2.6 J/cm2. The in situ optical emission spectroscopy was carried out to monitor the plasma radicals generated during the deposition. All the deposited films were crystallized and some clusters were formed because of high deposition temperature and rapid surface diffusion of indium (In). The growth rate and the crystallinity of the film increased and then declined with increasing laser fluence. The texture evolution mechanism of the films has been proposed firstly. The rapid diffusion of In, the sputtering and reflection effect of plasma species exist in whole films’ deposition process, which has a significant impact on the texture characteristics of the films. The clusters emerging on film surface were the crystallized In-rich InGaOx nanoparticles consisting of β-Ga2O3 and cubic In2O3 phases. Metal-semiconductor-metal solar-blind photodetectors were also fabricated and analyzed to illustrate the effect of laser fluence. The elaboration of texture evolution mechanism and effect of laser fluence on the properties of the In-doped Ga2O3 films and photodetectors is very beneficial for its application in high performance photoelectric devices.