Laser Ablation Of Silicon Research Articles

Multigram-Scale Production of Hybrid Au-Si Nanomaterial by Laser Ablation in Liquid (LAL) for Temperature-Feedback Optical Nanosensing, Light-to-Heat Conversion, and Anticounterfeit Labeling.

Recent progress in hybrid optical nanomaterials composed of dissimilar constituents permitted an improvement in the performance and functionality of novel devices developed for optoelectronics, catalysis, medical diagnostics, and sensing. However, the rational combination of contrasting materials such as noble metals and semiconductors within individual hybrid nanostructures via a ready-to-use and lithography-free fabrication approach is still a challenge. Here, we report on a two-step synthesis of hybrid Au-Si microspheres generated by laser ablation of silicon in isopropanol followed by laser irradiation of the produced Si nanoparticles in the presence of HAuCl4. Thermal reduction of [AuCl4]- species to a metallic gold phase, along with its subsequent mixing with silicon under laser irradiation, creates a nanostructured material with a unique composition and morphology, as revealed by electron microscopy, tomography, and elemental analysis. A combination of basic plasmonic and nanophotonic materials such as gold and silicon within a single microsphere allows for efficient light-to-heat conversion, as well as single-particle SERS sensing with temperature-feedback modality and expanded functionality. Moreover, the characteristic Raman signal and hot-electron-induced nonlinear photoluminescence coexisting within the novel Au-Si hybrids, as well as the commonly criticized randomness of the nanomaterials prepared by laser ablation in liquid, were proved to be useful for the realization of anticounterfeiting labels based on a physically unclonable function approach.

Resistivity dependence on nanostructure formation in picosecond ablation of silicon and SERS-based sensing applications

We report on the influence of resistivity in picosecond (ps) laser ablation of silicon (Si) leading to the formation of diverse surface micro- and nanostructures. Subsequently, we investigated their potential in sensing applications based on the surface enhanced Raman scattering (SERS) technique. The varying resistivity (ρ 1: 1–10 Ω cm, ρ 2: 0.01–0.02 Ω cm, ρ 3: 0.001–0.005 Ω cm) Si wafers were subjected to cross patterned ps laser ablation in ambient air. Ladder-like microstructures embedded with numerous nano growths were formed on low resistivity Si (ρ 3) while similar micro- and nanostructures were observed on higher resistivity Si (ρ 2 < ρ 1). The structures were non-plasmonic and anti-reflecting in nature with an optical reflectance of <6% over a broad range of wavelengths (350–1200 nm). Non-plasmonic Si microstructures were subsequently transformed to plasmonic by means of deposition of a thin layer of gold (Au). Additionally, the effect of annealing on the evolution of nanostructures was also investigated. We employed these hybrid substrates for the trace detection of an explosive molecule, ammonium nitrate, and dye, malachite green. Our detailed SERS studies have demonstrated a superior enhancement in the trace detection of analytes for low resistivity Si substrate. However, the annealed hybrid substrates have demonstrated further improvement in the SERS signal (by at least one order of magnitude). These detailed SERS investigations provide us a proof of the sensitivity of different resistivity Si nano/microstructures.

Low surface damage laser processing of silicon by laser-induced plasma etching (LIPE)

The precise surface machining of silicon by pulsed laser processing is challenging. Laser ablation enables direct patterning but causes numerous modifications of the surface and sub-surface region. Due to the increasing demand of precisely structured silicon surfaces in various fields, such as optics and micro-electronics and micro-fluidics, new laser-based ultra-precise surface machining techniques are required. Therefore, the recently developed laser-induced plasma etching process (LIPE) was studied in relation to chemical as well as structural modifications after the etching of single-crystalline silicon. For the studies, a fs-laser (775 nm, 150 fs, 1 kHz) with a pulse energy of maximum 750 µJ was focused to a CF4/O2 gas mixture at atmospheric pressure igniting a laser-induced plasma in front of the 〈100〉 Si sample. For comparison, a silicon surface was also structured by direct laser ablation.The LIP etched surface, that is characterized by SEM, TEM, XPS- and Raman-spectroscopy, shows no melting features, no structural surface or subsurface defects and almost no chemical contamination from etching besides a 2 nm thick silicon oxyfluoride on top of the atomically ordered silicon. The comparison shows clearly that the severe structural and chemical modifications at laser ablation of silicon can be avoided enabling ultraprecise surface machining.

Laser ablation of silicon with THz bursts of femtosecond pulses

In this work, we performed an experimental investigation supported by a theoretical analysis, to improve knowledge on the laser ablation of silicon with THz bursts of femtosecond laser pulses. Laser ablated craters have been created using 200 fs pulses at a wavelength of 1030 nm on silicon samples systematically varying the burst features and comparing to the normal pulse mode (NPM). Using bursts in general allowed reducing the thermal load to the material, however, at the expense of the ablation rate. The higher the number of pulses in the bursts and the lower the intra-burst frequency, the lower is the specific ablation rate. However, bursts at 2 THz led to a higher specific ablation rate compared to NPM, in a narrow window of parameters. Theoretical investigations based on the numerical solution of the density-dependent two temperature model revealed that lower lattice temperatures are reached with more pulses and lower intra-burst frequencies, thus supporting the experimental evidence of the lower thermal load in burst mode (BM). This is ascribed to the weaker transient drop of reflectivity, which suggests that with bursts less energy is transferred from the laser to the material. This also explains the trends of the specific ablation rates. Moreover, we found that two-photon absorption plays a fundamental role during BM processing in the THz frequency range.

Silicon and Silver Nanoparticles Obtained by Laser Ablation in Liquid

The obtained colloidal solutions of nanoparticles are studied during laser ablation of silicon and silver in ethanol. It is shown that silver nanoparticles are present in the form of both polycrystals and single crystals and have two polymorphic modifications with a cubic and a hexagonal structure. Silicon nanoparticles are mainly amorphous; there are also silicon nanoparticles with a single-crystal structure.

Laser ablation of silicon in water at different temperatures

Underwater laser machining process is an alternative method to cut materials with less thermal damage due to the water cooling of workpiece during the ablation. However, the rapid cooling induced by water can instantly solidify the laser-molten material rather than expel it to form a cut. To understand the roles of processing temperature on ablation performance in water, this paper presents the influences of water temperature on cut width, depth, and surface morphology in the underwater laser grooving of silicon. The effects of laser power, laser traverse speed, and number of laser passes on the groove characteristics were also examined in this work. The results revealed that using high water temperature can increase the groove aspect ratio, particularly when high laser power, slow traverse speed, and multiple laser passes were employed. However, debris deposition and oxides were found on the laser-ablated surface when processing at high water temperature. The implication of this study could enhance the ablation rate for the underwater laser as well as low-power laser cutting systems.

Studies on laser ablation of silicon using near IR picosecond and deep UV nanosecond lasers

Micromachining and other processing of different materials using lasers have been the focus of a large number of investigations in recent years. In this study, we investigate the interactions of two different lasers with crystalline silicon in air. The first laser is a solid state Ti:sapphire laser that has a pulse width of ∼110 ps and emits radiation of a wavelength in the near infrared (IR) region of 785 nm. The second laser is an excimer laser that emits radiation in the deep ultraviolet region (DUV) at a wavelength of 193 nm and has a pulse width of ∼ 4 ns. The excimer laser has a flat-top beam profile while the picosecond laser has a Gaussian beam profile. A series of craters was produced on a crystalline silicon wafer at different fluence, repetition rate, and number of pulses, and the resultant craters were characterized offline for surface morphology and ablation rate using optical and scanning electron microscopy. At low fluence, ablation with the excimer laser produced clean craters with minimal ejection of molten material. Increasing the fluence increased the amount of molten material deposited around the ablation crater, as well as the crater depth. Particles of different shapes and sizes with distributions depending on the number of laser pulses and laser fluence were observed around the ablation craters. Ablation rate was found to be dependent on the repetition rate of the excimer laser. Craters produced by picosecond laser pulses showed surface morphology and ablation rate differences from those of craters produced by excimer laser pulses. The differences in crater morphology, ablation rate, and ablation threshold observed using the two different types of laser can be attributed to differences in the properties of the two laser beams.

Green synthesis of silver/silica nanocomposite in seconds at room temperature using reducing agents obtained from silicon nanoparticles

In this work, we present a single step, highly stable, energy efficient, green and economically scalable room temperature method for the synthesis of silver/silica (Ag/SiO2) nanocomposite. The Ag/SiO2 nanocomposites are synthesized from silver nitrate solution using extracts of silicon nanoparticles. The silicon nanoparticles, which are prepared through the laser ablation of silicon in ethanol with polyvinylpyrrolidone,are used as the reducing agent. The nanocomposites have been characterized by ultraviolet–visible spectroscopy, x-ray diffraction pattern and Fourier transform infrared spectrum. The ultraviolet–visible absorption spectrum of the colloidal nanocomposites shows a surface plasmon peak at 424 nm. The x-ray diffraction pattern of Ag/SiO2 nanocomposite powder only contains silver structures, and thus SiO2 nanoparticles are amorphous. The nonlinear properties of Ag/SiO2 colloidal nanocomposite solution are studied using the Z-scan method. The value of the nonlinear absorption is measured as 17 × 10−3 cm W−1 with a positive sign, which illustrates the two photon absorption phenomena. The Ag/SiO2 nanocomposite shows a large nonlinear absorption near the surface plasmon resonance frequency of Ag nanoparticles.

Laser micromachining of silicon in air and ice layer

Thermal damage is an important drawback of laser micromachining process, and several techniques have been developed to control and limit heat induced by laser during the ablation. A novel method presented in this study is to perform the laser micromachining in ice, where the ablation take places while a workpiece is cooled in a thin ice layer. This technique is expected to limit the excessive heat conducting toward the workpiece material and also to prevent the cut debris depositing in the work surface as usually found in the dry laser ablation. Silicon wafer was used as a work sample to be cut in this study. The effects of ice temperature, ice layer thickness and average laser power on cut dimensions were experimentally investigated, and the predictive models for cut width and depth based on energy balance theorem were also formulated in this paper. Although some optical disturbances due to ice-water-vapor transitions limited the cut depth obtained, a clean and narrow cut with small taper angle was achievable when silicon was cut in ice layer. According to the findings of this study, the ice-assisted laser micromachining process could be a promising method for minimizing thermal damage in the laser ablation of silicon. In addition, this technique could also be of high potential for processing other heat-sensitive materials for micro-manufacturing applications.

A continuous-profile diffractive focuser for terahertz radiation fabricated by laser ablation of silicon

A method of high-frequency laser ablation using a two-coordinate beam scanner for the fabrication of a diffractive element of terahertz range with a continuous profile has been developed and successfully applied. Results of the characterization of the fabricated microrelief of a silicon focuser of a Gaussian beam into a square region are presented.

Dynamic features of bubble induced by a nanosecond pulse laser in still and flowing water

Underwater laser ablation techniques have been developed and employed to synthesis nanoparticles, to texture workpiece surface and to assist the material removal in laser machining process. However, the understanding of laser-material-water interactions, bubble formation and effects of water flow on ablation performance has still been very limited. This paper thus aims at exploring the formation and collapse of bubbles during the laser ablation of silicon in water. The effects of water flow rate on bubble formation and its consequences to the laser disturbance and cut features obtained in silicon were observed by using a high speed camera. A nanosecond pulse laser emitting the laser pulse energy of 0.2–0.5 mJ was employed in the experiment. The results showed that the bubble size was found to increase with the laser pulse energy. The use of high water flow rate can importantly facilitate the ejection of ablated particles from the workpiece surface, hence resulting in less deposition to the work surface and minimizing any disturbance to the laser beam during the ablation in water. Furthermore, a clean micro-groove in silicon wafer can successfully be produced when the process was performed in the high water flow rate condition. The findings of this study could provide an essential guideline for process selection, control and improvement in the laser micro-/submicro-fabrication using the underwater technique.

Broadening and shift of the spectral lines of hydrogen atoms and silicon ions in laser plasma

We report an experimental investigation of the broadening and shift of discrete lines in the plasma spectrum produced in the laser ablation of silicon in a broad pressure range of the ambient gas . The broadening and line shifts are measured in relation to the distance from the target and initial gas pressure. The threshold nature of the resulting dependences is found to be related to the formation of virtual percolation clusters proceeding in the hot dense plasma.

Laser ablation of silicon in water under different flow rates

Underwater laser ablation is typically used to scribe a silicon wafer with low thermal damage and less redeposition of cut debris on the workpiece surface. However, the hydrodynamic characteristics of water and some particles suspending in water are able to disturb the laser beam during the ablation. As such, the overall laser cutting performance in water and cut results can become poor or even unacceptable in some ablating conditions. This study thus aims at enhancing the underwater laser ablation process by controlling the water flow rate and flow direction in a closed water chamber setup. A single-crystalline silicon wafer selected as a work sample in this study was grooved by a nanosecond pulse laser under different water flow rates in order to carry the excessive heat and cut debris away from the workpiece. According to the experimental findings, a deeper groove and less redeposition can be obtained when the ablation was performed in a higher water flow rate. By processing silicon in the flowing water, the significant disturbances of air bubbles, water waves, and cut debris to the laser beam can be minimized, hence gaining a better ablating performance than the laser ablation in still water. Furthermore, the plastic deformation of silicon was evident as per the presence of slip bands on the cut surface, where the band size was found to decrease with the increased water flow rate.

From single pulse to double pulse ns laser ablation of silicon in water: photoluminescence enhancement of silicon nanocrystals

In this paper we introduce a comparative approach for studying the emission properties of silicon nanocrystal (Si-nc) colloids prepared by single pulse and double pulse laser ablation processes of a silicon wafer in distilled water. Experiments were conducted to investigate the luminescence properties of the colloids considering the size distributions and surface characteristics of the synthesized Si-ncs. The results indicated that single pulse and double pulse laser ablation processes under similar experimental conditions can lead to the preparation of Si-nc colloids with almost the same size distributions and different surface chemistry. The results show that double pulse laser processing with an inter-pulse delay time of ~5 ns can produce Si-nc colloids with a much greater emission intensity (about fivefold to tenfold) in the orange–red region (550–700 nm) of the visible spectrum. Based on the detailed analysis of the Si-nc size distribution and surface characteristics, the observed prominent orange–red emission is possibly due to a different type of Si–OH surface termination that protects the nanocrystal core upon inward oxidation.

真空条件下不同波长固体激光烧蚀单晶硅的实验研究

Lasers with wavelengths of 532 nm,355 nm and 266 nm are obtained using harmonic generation of a Nd∶ YAG solid-state laser by nonlinear optical crystal. The relationship between the absorption of single crystal silicon and the laser wavelength and ablation characteristics of single crystal silicon by 3 different wavelength lasers under vacuum condition are studied. The results show that single crystal silicon has a good absorption of ultraviolet laser in the wavelength range of 100- 370 nm,and under the same conditions,the minimum single pulse energy for 532 nm laser ablation of silicon is 30 μJ and the minimum single pulse energy for 355 nm or 266 nm laser ablation of silicon is 15 μJ. The ablation threshold values of 532 nm,355 nm and 266 nm laser ablation of silicon are different,which become smaller with the decrease of wavelength.

Thermodynamic Investigations on the Laser Ablation Rate of Silicon over Five Fluence Decades

Laser ablation of silicon is investigated with a large set of laser parameters to determine the ablation rate over five laser fluence decades. A thermodynamic model approach for the ablation of silicon has been derived. This simplified model determines the achievable ablation depth per pulse as a function of the applied laser fluence ranging from femtosecond to microsecond laser pulse duration. Furthermore different laser wavelengths from near-infrared to ultra-violet are investigated to determine the dependence on the optical penetration depth and on the ablation efficiency. The measured ablation depth per pulse is in agreement to the models predictions with the restrictions made.

Large Scale Molecular Dynamics Simulation of Femtosecond Laser Ablation of Silicon Using Sensing-VISICOM

Silicon is widely used as substrate material for the fabrication of micro-electro and micromechanical components. Since silicon is very brittle, how to cut it into complex shapes remains a hot topic. Thanks to the small spot diameter, laser cutting is a promising alternative. However, during laser cutting, different kinds of defects can be generated depending on the beam-material interaction phenomena (ablation, melting, etc). Molecular Dynamics simulation is an effective way to study the beam-material interaction phenomena. Lots of work has been done to develop MD models of laser ablation of silicon. However, due to lack of support from high performance parallel simulation platform, the scale of the molecular systems is limited. This paper presents a component-based parallel simulation platform Sensing-VISICOM, for large scale molecular dynamics simulation. To test its runtime performance, a molecular system of femtosecond laser ablation of silicon is designed and implemented under Sensing-VISICOM. The results of the simulation show the platform can scales well to millions of atoms.

Laser ablation of silicon using a Bessel-like beam generated by a subwavelength annular aperture structure

Using a femtosecond laser incident to an oxide-metal-oxide film engraved with a subwavelength annular aperture (SAA) structure, we generated a Bessel-like beam to ablate silicon. Experimental results show that the silicon can be ablated with a 0.05 J/cm(2) input ablation threshold at 120 fs pulse duration. We obtained a surface hole possessing a diameter less than 1 μm. Optical performance, including depth-of-focus and focal spot of the SAA structure, were simulated using finite-different time-domain calculations. We found that a far-field laser beam propagating through a SAA structure possesses a submicrometer focal spot and high focus intensity. Our method can be easily adopted for surface machining in microfabrication applications.

Synthesis of nanofiber-filled polydimethylsiloxane using ultrafast laser irradiation

In this article, we report the filling of polydimethylsilioxane (PDMS) with nanofibers using femtosecond laser of MHz pulse frequency under ambient conditions. Nanoscale fibrous structure was created by femtosecond laser ablation of silicon. The generated silicon nanofiber was dispersed into PDMS resin. A site-specific curing of PDMS induced by direct laser irradiation results in nanofiber-reinforced polymer. The proposed technique permits single-step curing and is capable of fabricating microscale structures. No additives are used in developing the polymer nanocomposite. Scanning electron microscopy was used to investigate the dispersion of filler (nanofiber) in PDMS matrix.

INFRARED NANOSECOND LASER ABLATION OF SILICON: THE SPATIAL MULTI-PULSE ENHANCEMENT EFFECT AND ITS DEPENDENCE ON LASER PULSE DURATION – TECHNICAL COMMUNICATION

An experimental study has been performed for laser ablation of silicon at 1064 nm with variable pulse durations from 50 nanoseconds to 200 nanoseconds. A spatial multi-pulse enhancement effect has been revealed, which has been rarely reported in literature. The specific feature of this effect is that for multi-pulse laser ablation of silicon performed sequentially at a group of locations, the ablation efficiency and quality starting from the second location can be enhanced if the distance between adjacent locations is sufficiently small, and the ablation efficiency enhancement becomes more obvious as the distance decreases or the laser pulse duration increases. Further study is needed to understand the underlying physical mechanism. This effect, if well understood, can be utilized to significantly improve the quality and efficiency of infrared nanosecond laser silicon ablation. This will widen the practical applications of the low-cost and low-energy-consumption infrared nanosecond lasers and hence significantly decrease the manufacturing cost and energy consumption in many relevant areas.