Laser-assisted Etching Process Research Articles

Enhancing the temporal response of modified porous silicon-based CO gas sensor

In this paper, the role of gold nanoparticles on the temporal response of a porous silicon gas sensor has been studied. The porous layer was prepared by a laser-assisted etching process using 810 nm wavelength and 2 W infrared laser diode as an illumination photonics source. The experimental etching conditions involve 20 mA/cm2 current density and 10 min etching time. Gold nanoparticles were incorporated into porous silicon structures via the ion reduction process. The characteristics of sensors were studied comprehensively by SEM, XRD, and the electrical properties were investigated for the sensor before and after the gold nanoparticles incorporation process. The obtained results manifested that the decay time of the sensor was reduced by a factor almost greater than (50%) as compared with the bare porous silicon sensor. The results were discussed based on the role of gold nanoparticles that enhanced the thermal conductivity of porous silicon. A higher thermal conductivity of about (130 W/mK) due to the gold nanoparticles was achieved as compared with the bare porous silicon gas sensor.

Efficient, fast response, and low cost sensor for NH3 gas molecules based on SnO2: CuO/macroPSi nanocomposites

In the present study, a procedure of the inserting of SnO2:CuO nanoparticles with different CuO nanoparticles contents within a macroporous silicon layer (macroPSi) gas sensor was prepared and successfully investigated. The macroPSi was effectively fabricated by laser assisted etching process, and CuO nanoparticles loaded with SnO2 with a high value of surface area were successfully synthesized by the spray pyrolysis method. Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FE-SEM) manifested a novel morphology for CuO Bucky particles inside the pores and a nano nail like structure for SnO2 with a small average grain size of CuO Bucky particles with 30% content. This morphology of nanocomposites improved the sensing performance for NH3 gas. A higher sensitivity with a very swift response and recovery times of 4 s and 55 s, respectively, was obtained with 150 ppm of NH3 gas at the room temperature. This improvement in gas sensor performance is strongly related to the higher specific surface areas and smaller particle size with a higher surface roughness of SnO2 and CuO nanoparticles within the nanocomposites.

Modified laser-etched silicon covered with bimetallic Ag–Au Alloy nanoparticles for high-performance SERS: laser wavelength dependence

The effect of etching laser wavelength on the performance of bimetallic alloy Ag–Au nanoparticles (Ag–AuNPs) SERS-active substrate was investigated. Two kinds of macro-P-Si structures were synthesized by a laser-assisted etching process using two laser wavelengths 650 and 532 nm. Ag–AuNPs/macro-P-Si SERS-active substrate was made up via the ion reduction process. The SERS-active substrates were investigated by utilizing XRD, FE-SEM microscope, EDS analysis and Raman microscope. P-Si surface modification process by bimetallic alloy Ag–AuNPs was carried out to form efficient and nearly uniformly distributed Ag–AuNPs hot spot regions with ultra-high specific surface areas. The morphological features of the deposited Ag–AuNPs on the P-Si layer prepared by 650 nm exhibited that the nucleation process is mainly concerted on the pore boundaries with a low tendency for aggregation, while for 532 nm, the Ag–AuNPs layer is mostly well ordered of high-density semi-uniformly distributed spherical nanoparticles initiate over the macro-P-Si. The SERS results of Ag–AuNPs/macro-P-Si exposed a strong dependence on the hot spot regions among bimetallic nanoparticles. The enhancement factor of the Raman signal of Ag–AuNPs/macro-P-Si modified with 532 nm is four orders of magnitude greater than that of modified with 650 nm, which is about 2.1 × 1012 and 9.3 × 108, respectively.

Efficient SnO2/CuO/porous silicon nanocomposites structure for NH3 gas sensing by incorporating CuO nanoparticles

In this paper, a porous silicon (Psi) surface modification process, including the incorporating of pure and CuO mixed SnO2 within a Psi layer, was investigated. A Psi layer with a pore-like structure prepared via laser-assisted etching process with a laser illumination intensity of (40) mW/cm2 was employed as a substrate for materialization SnO2/CuO/Psi nanocomposites for gas sensing application. Pure SnO2 and SnO2:CuO nanoparticles were synthesized via a chemical spray pyrolysis process on the Psi surface at 350 °C. The materialization of SnO2:CuO/Psi nanocomposites were recognized through Field-Emission Scanning Electron Microscopy, X-ray Diffraction, Atomic Force Microscopy, and Energy-dispersive X-ray Analysis. The results displayed that the morphological properties of SnO2:CuO nanoparticles were definitely controlled by varying the CuO contents. Different shapes (nearly cubic shape and spherical shape) with various sizes of SnO2 and SnO2:CuO within the Psi surface were achieved by increasing the CuO content. SnO2:CuO/Psi nanocomposites, plans, grain size, average surface roughness, homogeneity and specific surface area of SnO2:CuO nanoparticles were considerably influenced by CuO content. The lower grain size and higher average surface roughness and specific surface area were attained when the percentage of CuO was about 30% within the structure of 70% SnO2:30% CuO, and the performance of the NH3 gas sensor revealed a short response time with a high sensitivity of (88%).

Accurate controlled deposition of silver nanoparticles on porous silicon by drifted ions in electrolytic solution

In this study, a low-cost, simple, single-step low-voltage operation and a well-controlled method for deposition of uniformed and unique size distributions of silver nanoparticles (AgNPs) on the porous silicon (PS) layer were achieved via controlling the drift velocity of electrons in an aqueous solution of AgNO3. The laser diode of 530 nm and 60 mW/cm2 laser wavelength and illumination power density was employed to prepare PS layer by a laser-assisted etching process. The PS layer was incorporated on the platinum disk cathode electrode, and a stainless steel plate as an anode was employed. Low applied operating voltage of about 3V DC at different drift currents of 10, 20, 30 and 40 mA for 2 min was applied to sustain the drift motion of Ag2+. Structural properties of AgNPs layer were examined via the field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) pattern. These measurements exposed that AgNPs were adjusted by controlling the drift current, and a uniform AgNPs with specific unique sizes were obtained. Grain size, specific surface area and nucleation sites of metallic AgNPs were intensely influenced by the drift current.

Optimizing of porous silicon alloying process with bimetallic nanoparticles

Bimetallic Ag–Au alloy nanoparticles with a tunable size and composition were synthesized by laser beam power density. A set of Psi substrates with different morphologies fabricated by laser-assisted etching process with laser power density from 10 to 40 mW/cm2 was explored as a substrate for materialization bimetallic Ag–Au alloy nanoparticles by a simple immersion plating process of Psi in a mixture of AgNO3 and HAuCl4 solutions. The materialization of alloy nanoparticles was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray analysis (EDS). The results showed that the sizes and distribution of Ag–Au alloy nanoparticle sizes were easily well-ordered by changing the surface morphologies of Psi layer. Pore-like structures with different pores shapes: ultra-fine pores, irregular (grotto form), circular, and star full pore shape (gambling pores) with different sizes were prepared by changing the irradiation laser power density. Bimetallic Ag–Au alloy nanoparticles, phases, crystalline size, specific surface area, and growth sites of Ag–Au alloy nanoparticles were significantly influenced by pore shape. The lower nanoparticle size with higher S.S.A was obtained when the laser power intensity was about 30 mW/cm2.

Illumination effects on the physical properties of porous silicon prepared by PECE

Laser-assisted etching process was used to prepare porous silicon on n-type silicon substrate of resistivity 10 Ω cm and orientation incubated in hydrofluoric acid of 25% concentration. The porous layers were prepared using laser diode of 645 nm wavelength illumination with different intensities of about 14 and 20 mW/cm2 and current density of 10 mA/cm2 for a fixed etching time (8 min). The morphology and optical characterization of porous silicon were evaluated. Scanning electron microscopy results demonstrated that the power density is a prominent parameter that controls the morphology of pores. The reflectivity decreased with increase in the highest power density to 0.66% and the peak position of PL results increased with increase in power density and moved toward the blue region. These phenomena were due to changing in the characteristics of the surface morphology the change of Si to nanostructures.

Room temperature CO2 gas sensors of AuNPs/mesoPSi hybrid structures

Mesoporous silicon (mesoPSi) layer prepared by a laser-assisted etching process in HF acid has been employed as CO2 gas sensors. The surface morphology of mesoPSi was modified by embedding gold nanoparticles AuNPs by simple and quick dipping process in different gold salts concentrations to form mesoPSi/AuNPs hybrid structures. Morphology of hybrid structures was investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrical characteristics of the prepared gas sensor were carried out at room temperature. It was found that the nanoparticles size, shape and the specific surface area of the nanoparticle strongly influence the current–voltage characteristics. Considerable improvement was noticed in sensitivity, response and recovery times of gas sensor with decreasing incorporated AuNPs into the mesoPSi matrix.

Fabrication of diffractive microlens array by femtosecond laser-assisted etching process

Graphical abstractDisplay Omitted Highlights? The diffractive microlens array is fabricated by the femtosecond laser and chemical etching process. ? The effect of micro-grating forming is studied upon laser power and etching ratio. ? The quasi-crystal diffraction patterns with the types of cross and octagon can be achieved. The study presents the fabrication of diffractive microlens array on glass substrate by using the femtosecond laser (FS-laser) and chemical etching process. Here, the laser is based on an all-in-one FS-laser system with the central wavelength of 517?2.5nm for fabricating the embedded grating structures inside glass substrate. The laser beam focused distance between the surface and sample is 25µm. The repetition rate and pulse duration of FS-laser are 100kHz and 350fs, respectively. The attenuated laser beam is directly into objective lens (20i?) with the numerical apertures (NA=0.4). Hence, the microstructures can be patterned by the routes of X-Y motion stage. The glass sample is then etched by hydrofluoric acid (HF) in an ultrasonic bath for 15min for developing structures. Finally, the results show a successful process for forming the microlens array of the diffractive patterns, in which two types of cross and octagon are obtained from the single and double diffraction, respectively.

Fabrication and characterization of InGaAlP∕InGaP semiconductor circular ring lasers

We report the fabrication of a semiconductor circular ring lasers based on an InGaAlP∕InGaP graded-index separate confinement heterostructure (GRIN-SCH) which attracted much attention for light sources in optical information processing systems such as a laser printer, compact disk player and optical link system. The dimensions of the circular ring cavity are 100μm–250μm in diameter, 5–10μm width of the ridge waveguide, and a Y junction output coupler of 250μm in length. An ultraviolet (UV) laser-assisted etching process and the two-layer photolithography process were developed for the fabrication of the circular ring cavity. The luminescence-current and spectrum characteristics of laser output showed a single-mode output operating at 698 nm and at threshold current about 60 mA. The reports showed that the pattern definition by the combination of UV laser-assisted etching, and the two-layer photolithography process was capable of complex optoelectronic integrated device processing.

Fabrication of CdTe strip detectors for imaging applications

p–i–n CdTe strip detectors were fabricated in a new and simple technique for their probable applications in astrophysics and medical imaging. The detector has an iodine-doped n-CdTe epitaxial layer followed by aluminum metallization on the Te-face of (1 1 1) oriented CdTe crystal, as an anode. The cathode consists of the p-type segmented regions formed on the crystal by the diffusion of dopant atoms from an alkaline metal compound through a patterned shadow mask using the excimer laser radiation. Afterward, the gold electrode is evaporated through the same shadow mask to make the strip cathodes. In a different way, we also studied the laser ablation process for the selective area etching by irradiating the laser through a mask. Details of these fabrication processes for making strip detectors and results on laser-assisted etching process will be presented.

Effects of a quartz beam-guide on high-precision laser-assisted etching of Al2O3 ceramics

Abstract Laser-assisted chemical etching of ceramic materials has been attracting continuous attention as a laser microfabrication technique with relatively low power levels. In this study, in order to improve the accuracy of etching depth and diameter, the application of a quartz beam-guide to the pulsed Nd:YAG laser-assisted etching process is proposed. By using this technique, possibilities of high-precision hole drilling with high aspect ratio and uniform surface etching in the radial direction of the beam using a beam-homogenizing effect of the beam-guide have been investigated for Al 2 O 3 ceramics immersed in H 3 PO 4 solution at room temperature. The results revealed that: (1) the distance between the beam-guide surface and the workpiece surface dominates the surface etching rate; (2) by using the beam-guide, the beam-homogenizing effect in the radial direction of the beam at the surface is confirmed; and (3) possibilities of uniform surface etching and high-precision hole drilling are demonstrated by applying the beam-homogenizing effects of the beam-guide.

Laser-Assisted Etching of Lithium Niobate

ABSTRACTLaser-assisted dry etching of lithium niobate, LiNbO3, as well as other electro-optic materials could be an industrially important process in the fabrication of optical waveguides. In this investigation, an excimer laser (ArF; 193nm) was used to conduct etching reactions using nitrogen trifluoride, NF3. Enhancement of etching was observed by comparing the etch rate for a gas assisted process with that of a purely photoablative process. Chemical analysis of the etched features via Auger electron spectroscopy and correlation of a simple rate equation with the experimental data revealed that lasersurface interactions are responsible for the laser-assisted etching process.

XeCl laser controlled chemical etching of aluminum in chlorine gas

The 308 nm XeCl laser assisted etching process of thin Al metal films on Si substrate in Cl2 gas was investigated. Etch rates were measured versus the laser fluence on the sample, the laser repetition rate, the Cl2 pressure and the sample temperature. Irradiation experiments under vacuum of films which were previously exposed to Cl2, and laser assisted etching in rare gases, nitrogen and air mixtures with Cl2 were also performed to elucidate the mechanism of the etching process. The surface morphology was investigated by scanning electron microscopy. The results show that a) Etch rates of up to about 1.5 μm per pulse are obtained which are strongly dependent on the Cl2 pressure and sample temperature. b) The etching mechanism is essentially a chemical chlorination of the Al in between the laser pulses which is followed by photo-ablation of the reaction products, c) AlCl3 evaporation and redeposition processes can explain the observed results. d) The Al films can be etched fully and cleanly without damage to the smooth Si substrate. e) Etching through adjacent or imaged mask on the Al film yielded relatively smooth and well defined Al walls with structures of the order of 1 μm.

Laser chemical etching of vias in GaAs

Rapid drilling of vias in thick wafers (381 µm) of GaAs has been achieved by a laser assisted etching process. The technique utilized a cw visible argon ion laser and an etchant gas of low pressure Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . Data on the dependence of the etch rate on the laser power, wavelength, and Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas pressure are presented.