Photoetching Technique Research Articles

Photomechanical crossroads - Comparing 19th-Century Chromocupography and Charles Eckstein’s method from a Printmaker’s Perspective

Chromocupography is a photo-etching technique developed in 19th-century Portugal under the supervision of chemist José Júlio Rodrigues (1843-1923). Very scarce literature is associated with the process, and it doesn’t seem to have been widely used after being made public. At the time, the technique was presented as a variant of Charles Eckstein’s (1840-1913) method, working in Hague, Holland. Eckstein’s technique consisted of hatching the lithograph stone with very fine delicate multiple-point needles to produce tone variations. Chromocupography substitutes the stone for a copper plate and the needles for a special coating with resin, thus creating a granular reservation protecting the metal from the etching bath.With this paper, we aim to present how the technical entanglements which are felt from a practical experience of the contemporary printmaker. We will be showing the various results we obtained conducting research following the descriptions found in literature around the subject of Portuguese process chromocupography, at the Faculty of Fine Arts of the University of Porto within the project of Pure Print Archaeology (i2ADS/FBAUP)

Structural properties of porous silicon obtained with laser photoetching assisted by computerized numeric control

This study presents the preparation of porous silicon (PS) using the photoetching technique. The light source was a laser with a 405 nm wavelength. Hydrofluoric acid, hydrogen peroxide, and ethanol were used in the process. An approach to forming PS in a selected area was also studied, in which a computational control of the laser movement was developed. A laser allows for the formation of PS in short period of time using n-type crystalline silicon (c-Si) as a substrate. Photosynthesized PS shows similar characteristics (physical and chemical) to anodized PS. Raman scattering showed a broadening of the peak centered at 525 cm−1, this behavior is related to the formation of PS. Micro-Fourier transform infrared spectroscopy showed bands related to Si-H wagging and SiH2 bending vibrations, these types of bonds were generated during the porosification process. The morphologic characteristics were defined by scanning electron microscopy (SEM) and revealed that the porous structures depend on the potency of the laser used. The topography of the surface confirms PS formation. SEM analysis demonstrated that pores with diameters of 60 and 300 nm can be obtained. Energy-dispersive x-ray spectroscopy showed an increase in oxygen in the PS due to the oxidation process following photoetching. The x-ray diffraction showed that this type of etching eliminates the induced tension in the c-Si grain edges due to PS formation.

Geometry-on-demand fabrication of conductive microstructures by photoetching and application in hemostasis assessment

Photo-corrosion is a common phenomenon observed in the photocatalytic semiconductor materials, which can seriously harm the photoelectric properties and performances in the energy applications. However, in this paper, we demonstrated that the photo-corrosion effects can be used for the microfabrication of conductive structures on a photocatalytic film like zinc oxide (ZnO), named as “photoetching”. Our results demonstrated that microstructures can be prepared within seconds with a precision at an order of tens of micrometers using our current devices. Different from the previous work, the etching process was achieved free of conducting layer under the ZnO film, avoiding the short-circuit of the conductive micro-patterns and enabling the use for the impedance sensing. We demonstrated the fabricated ZnO microelectrode pairs can work for the electrochemical impedance measurements like assessment of hemostasis integrated with a microfluidic chip. Compared to the noble metal microelectrodes, the ZnO conductive microelectrodes can be fabricated within seconds and the low costs make it possible as a disposable diagnostic device. Besides, the photoetching technique can be performed without a cleanroom reducing the technical barriers, possibly helpful for the low resources areas. We believe the simplicity of device, low costs and fast fabrication can be useful in the relevant fields such as biomedical and energy harvesting, especially for low resources areas.

Characterization of focusing performance of spiral zone plates with fractal structure**Project supported by the National Natural Science Foundation of China (Grant Nos. 11404290 and 61505178), the Major National Scientific Instruments Developing Special Project (Grant No. 2012YQ130125), the Postdoctoral Science Foundation of Henan Province, China (Grant No. 2013008), the Program for Science & Technology Innovation Talents in Universities of Henan Province,

We propose an efficient method of generating a vortex beam with multi-foci by using a fractal spiral zone plate (FSZP), which is designed by combining fractal structure with a spiral zone plate (SZP) in the squared radial coordinate. The theoretical analysis reveals that the number of foci that embed vortices is significantly increased as compared with that obtained by using a conventional SZP. Furthermore, the influence of topological charge on the intensity distribution in focal plane is also discussed in detail. For experimental investigation, an FSZP with topological charge p = 1 and 6.4 mm diameter is fabricated by using a photo-etching technique. The calibration indicates that the focusing performances of such a kind of zone plane (ZP) accord well with simulations, thereby providing its potential applications in multi-dimensional optical manipulation and optical imaging technology.

Experimental Investigation on Grinding Temperature of Ti–6Al–4 V Using Biomimetic Engineered Grinding Wheel

Ti–6Al–4 V is classed as difficult-to-process material due to its lower thermal conductivity and specific heat. Furthermore, the contact area between grinding wheel and workpiece is larger than other processing methods generally. Therefore, the process of grinding Ti–6Al–4 V is easier to generate high temperature. Most grinding fluid are used and wasted in usual grinding process to dissipate heat. Some green technologies are used to solve this issue in the aspect of fluid supply usually. This paper is to reduce grinding temperature from the other way–grinding wheel. In order to lower grinding temperature without increasing liquid coolant flow, an innovative grinding wheel inspired by phyllotaxis theory was manufactured using electroplating method and photo etching technique. Some contrastive experiments of grinding temperature for the alloy were conducted with the measured method of artificial thermocouple. The change rule of grinding temperature with the change of grinding parameters was found. The results shown that the grinding temperature of Ti–6Al–4 V with the biomimetic engineered grinding wheel was always the lowest in experiments due to less heat generation and more heat dissipation. Finally, the grinding temperature of the biomimetic engineered grinding wheels with different phyllotactic coefficient were investigated and discussed. A new point of view to lower grinding temperature was present and proved in this paper, which may become an important green technology for grinding in future.

Processing and doping of thick polymer active layers for flexible organic thermoelectric modules

While the majority of research on organic thermoelectric generators has focused on individual devices with organic films having thicknesses of several hundred nanometers (nano-films), films with micrometer-scale thicknesses (micro-films) provide a longer thermal conduction path that results in a larger temperature gradient and higher thermoelectric voltages in modules. In this study, the properties of solution-processed nano- and micro-films of the p-type semiconductor P3HT doped with two different dopants, F4-TCNQ and Fe3+-tos3·6H2O, were investigated. While doping with F4-TCNQ resulted in high electrical conductivity only in nano-films, doping with Fe3+-tos3·6H2O from a 25 mM solution yielded power factors of up to ∼30 μWm−1 K−2 with a conductivity of 55.4 Scm−1 in micro-films. Changes in the molecular packing were compared based on X-ray diffraction, and the best operational stability in air was found for the Fe3+-tos3·6H2O-doped micro-films. Using Fe3+-tos3·6H2O as dopant, flexible thermoelectric modules with solution-processed micro-films patterned by a photo-etching technique that does not require alignment and assembly of individual devices were demonstrated, exhibiting a maximum power output of 1.94 nWK−2 for a uni-leg module with 48 elements. Analysis of the flexible module performance showed that the performance is limited by the contact resistance, which must be taken into consideration when optimizing module structure.

Architectural transformation of the nanoparticle superstructures induced by ultraviolet light irradiation and their application in photoelectrochemical switch devices

The studies of the self-assembly processes of nanoparticles (NPs) will benefit the understanding of both the fundamental properties of nanomaterials and the bottom-up fabrication technologies at nanoscales. The NPs can self-assemble into complex microscale structures, which have been reported and attracted increasing attention in recent years. In this paper, a kind of bowknot-shaped structure formed from the individual (CdS)/CdTe NPs has been fabricated. Interestingly, the bowknot structure twists upon ultraviolet (UV) light irradiation. Special multiparticle assemblies of the double-flower-shaped structures are identified. The structural transformation process could be attributed to photocorrosion of CdS under the UV light. The bowknot-shaped topotactic structure is also important for the transformation of NP superstructures (NP-S). These results indicate that the photoetching technique could adjust the transformation among different NP superstructures, which offers a new method to fabricate novel NP-S. Both irradiated and unirradiated NP-S have been applied in photoelectrochemical devices to verify the photovoltaic effect.

Photoinduced Surface Oxidation and Its Effect on the Exciton Dynamics of CdSe Quantum Dots

With increased interest in semiconductor nanoparticles for use in quantum dot solar cells there comes a need to understand the long-term photostability of such materials. Colloidal CdSe quantum dots (QDs) were suspended in toluene and stored in combinations of light/dark and N2/O2 to simulate four possible benchtop storage environments. CdSe QDs stored in a dark, oxygen-free environment were observed to better retain their optical properties over the course of 90 days. The excited state lifetimes, determined through femtosecond transient absorption spectroscopy, of air-equilibrated samples exposed to light exhibit a decrease in average lifetime (0.81 ns) when compared to samples stored in a nitrogen/dark environment (8.3 ns). A photoetching technique commonly used for controlled reduction of QD size was found to induce energetic trap states to CdSe QDs and accelerate the rate of electron–hole recombination. X-ray absorption near edge structure (XANES) analysis confirms surface oxidation, the extent of whi...

Alcohol-assisted photoetching of silicon carbide with a femtosecond laser

Femtosecond lasers have proved to be effective tools for micromachining silicon carbide material. In the drilling process, however, when the debris around the hole was not removed efficiently, the depth of hole would not increase further. In this paper, alcohol-assisted photoetching of 6H silicon carbide was investigated using a femtosecond laser. Machining in the presence of alcohol was beneficial to the debris ejection from the hole. The alcohol flow and volatilization was also helpful to further carry away the ablation debris and reduce the ablated material redeposition. The experiment showed that photoetching assisted by alcohol produced cleaner ablation effect and deeper hole than in ambient air. Moreover, alcohol assistance would not produce additional thermal damage around the hole. Vias were formed in a 250 μm thick wafer with alcohol-assisted photoetching technique using a femtosecond laser, which demonstrated the potential for this processing technique.

Oriented growth and assembly of zeolite crystals on substrates

The aligned array and thin film of zeolites and molecular sieves possess a variety of potential applications in membrane separation and catalysis, chemical sensors, and microelectronic devices. There are two main synthesis methods for manufacturing the aligned arrays and thin films of zeolites and molecular sieves, i.e. in situ hydrothermal reaction and self-assembly of crystal grains on substrates. Both of them have attracted much attention in the scientific community worldwide. A series of significant progress has been made in recent years. By the in situ hydrothermal synthesis, the oriented nucleation and growth of zeolite and molecular sieve crystals can be achieved by modifying the surface properties of substrates or by changing the composition of synthesis solutions, leading to the formation of uniformly oriented multicrystal-aligned arrays or thin films. On the other hand, the crystal grains of zeolites and molecular sieves can be assembled onto the substrate surface in required orientation using different bondages, for instance, the microstructure in the array or thin film can be controlled. This review is going to summarize and comment the significant results and progress reported recently in manufacturing highly covered and uniformly aligned arrays or thin films of zeolites and molecular sieves. It involves (1) in situ growth of highly aligned zeolite arrays and thin films via embedding functional groups on the substrate surface, modifying the surface microstructure of substrates, as well as varying the composition of synthesis solutions; (2) assembly of zeolite and molecular sieve crystals on various substrates to form aligned arrays and thin films with full coverage by covalent, ionic, and intermolecular coupling interactions between crystals and substrates; (3) coupling surface assembly with microcontact printing or photoetching technique to produce patterned zeolite arrays and thin films. Finally, the functionality and applications of zeolite arrays and thin films are briefly introduced. Some critical issues are addressed for future studies.

Synthesis of metal–cadmium sulfide nanocomposites using jingle-bell-shaped core-shell photocatalyst particles

Photocatalytic deposition of gold (Au) and silver (Ag) nanoparticles was investigated using jingle-bell-shaped silica (SiO2)-coated cadmium sulfide (CdS) nanoparticles (SiO2/CdS), which each had a void space between the CdS core and SiO2 shell, as a photocatalyst. A size-selective photoetching technique was used to prepare the jingle bell nanostructure of SiO2/CdS. Nanoparticles of Au and Ag were deposited by irradiation of the photoetched SiO2/CdS in the presence of the corresponding metal complexes under deaerated conditions. Chemical etching of Au-deposited particles enabled the selective removal of CdS without any influence on the surface-plasmon absorption of Au. TEM analyses of the resulting particles suggested that some particles were encapsulated in hollow SiO2 particles, while other Au particles were deposited on the outer surface of the SiO2 shell. Emission spectra of the photoetched SiO2/CdS showed that the metal deposition developed a broad emission with a peak around 650 nm originating from surface defect sites, the degree being dependent on the kind of metal nanoparticles and their amount of deposition. This fact can be explained by the formation of metal–CdS binary nanoparticles having defect sites at the interface between metal and CdS.

Effects of the dark-exciton state on photoluminescence dynamics in surface-modified CdS quantum dots prepared by a colloidal method

We have investigated exciton dynamics in surface-modified CdS quantum dots (QDs) prepared by a colloidal method. The size- and surface-controlled CdS QDs have been successfully prepared by using a size-selective photoetching and surface modification technique. The decay profiles exhibit an unusual temperature dependence: increase of the decay time with increase in temperature. The temperature dependence of the decay profiles can be explained in terms of a three-level model including the exciton state with a triplet origin, the so-called dark-exciton state.

Preparation of novel silica-cadmium sulfide composite nanoparticles having adjustable void space by size-selective photoetching.

The size-selective photoetching technique was used to control the size of a CdS nanoparticle inside a silica shell. With monochromatic light irradiation, the diffuse reflectance spectra of silica-coated CdS nanoparticles were blue-shifted, and the size of the resulting CdS nanoparticles incorporated in the silica shells was adjustable by varying the wavelength of irradiated light. TEM observation revealed that the original CdS nanoparticle seemed to be in close contact with the amorphous silica shell to leave almost no clearance, while the monochromatic light irradiation caused the decrease in the size of CdS particles, resulting in the formation of a void space between the photoetched CdS core particle and the silica shell. The average void spaces available in the shells were calculated to be ca. 1.4 and 2.4 nm with the irradiation at 514 and 458 nm, respectively. These results indicated that the size-selective photoetching technique enables the regulation of void space formed in the core-shell structure by choosing the wavelength of irradiation light.

Characterization of Ultrasmall CdS Nanoparticles Prepared by the Size-Selective Photoetching Technique

Ultrasmall CdS nanoparticles were prepared by the size-selective photoetching technique. The smallest size of the CdS nanoparticles was obtained by the irradiation with the monochromatic light having the wavelength of 365 nm, while the absorbance of CdS nanoparticles monotonically decreased, for the whole wavelength, to null if the irradiation was performed using a wavelength less than 365 nm. The surface modification of CdS nanoparticles with thiophenol caused the red-shift of the absorption spectra due to the electric interaction between the bound thiophenol molecules and the CdS core, the degree being enhanced with a decrease in the particle size. 1H NMR signals of thiophenol bound on the surface of the smallest CdS nanoparticles prepared by 365-nm irradiation were shifted upfield compared to those obtained for the larger thiophenol-modified CdS nanoparticles prepared by the longer wavelength irradiation, and the signals appeared in positions similar to those of chemically synthesized CdS cluster molec...

A high performance ethanol sensor based on field-effect transistor using a LaFeO 3 nano-crystalline thin-film as a gate electrode

The LaFeO 3 nano-crystalline thin-film of perovskite-type composite-oxides is obtained by using a sol–gel coating technique, and the photo-etching technique is employed to etch and pattern the film. Combining this thin-film technology with the NMOS integrated circuit technology, we have developed an ethanol-sensitive field-effect transistor by using a LaFeO 3 nano-crystalline thin-film as a gate electrode of an ordinary n-channel MOSFET. The sensor has excellent selectivity, good sensitivity to ethanol, and a good stability. In order to improve the recovery transient of the sensor, the LaFeO 3 doped with strontium ions has been investigated.

Transdermal iontophoretic delivery of insulin using a photoetched microdevice

In order to develop practical iontophoretic devices for insulin delivery, five types of device, a square type, a square anode with a U-shaped inset cathode-type device (2 divided type), and three types with a square anode, with, respectively, 4, 9 and 16 small square inset cathodes (4, 9 and 16 divided types), were fabricated by a photoetching technique, and their effectiveness was examined in vitro by measuring the permeability of 6-carboxyfluorescein (6-CF) through the excised abdominal skin of a nude mouse. All four divided types enhanced the penetration rate of 6-CF more than 16-fold compared with passive diffusion. To test the transdermal iontophoretic delivery of insulin in normoglycemic control and diabetic rats, we selected the 2 divided type device, since this pattern was the easiest to fabricate. A significant reduction in blood glucose level (BGL) of 33% after 90 min of treatment, and a corresponding increase in immunoreactive insulin (IRI) concentration were observed in diabetic rats during cathodic direct current (DC) iontophoresis (IP) at a constant voltage of 1.5 V. The effectiveness of pulsed IP was also studied, but there was no significant difference between DC and pulsed IP in the decrease of BGL. The level of current during the initial 10 min was closely related to the hypoglycemic effect. These findings suggest that some cathodic reaction products may change the function of the stratum corneum or that these products may develop a shunt pathway and enhance the transdermal delivery of aggregated insulin molecules. Iontophoresis-induced skin damage was also evaluated by measuring impedance changes. It was shown that at constant-voltage IP of 1.5 V, IP could be carried out for up to 60 min without any marked effects on the skin.

Microscopic observation of the grain structure of photoetched CdSe xS 1 − x solid solution and CdSeCdS mixed crystal semiconductor electrodes

Grain structure of the polycrystalline CdSe x S 1− x solid solution and CdSeCdS mixed crystal semiconductor electrodes has been investigated by a photoelectrochemical etching (photoetching) technique. Photoetching produces a unique surface morphology on these electrode surfaces. After photoetching under ordinary anodic polarization, the grain boundary is selectively dissolve and characteristic etching patterns appear on each grain surface depending on the cyrstallographic orientations. Under weak anodic polarization the grain bulk is selectively dissolved and grain boundaries are left undissolved. This finding makes it possible to observe directly the grain boundaries as isolated specimens separated from the bulk. Chemical composition of the grain boundaries and the bulk of CdSe x S 1 − x solid solutions with various x values were examined by analyzing X-ray diffractograms and electron diffraction patterns. The results have shown that the grain boundary has almost the same composition of that of the grain bulk for each x of CdSe x S 1− x solid solutions, whereas grain boundaries between CdSe and CdS grains in the mixed crystal pellets consist mainly of CdSe and/or CdS and sometimes of CdSe x S 1− x solid solution.

MAJORITY CARRIER ASSESSMENT BY EBIC : DETERMINATION OF DOPANT CONCENTRATION AT COMPOSITION INHOMOGENEITIES

The EBIC mode of an SEM has generally been used to measure the minority carrier properties of semiconductors such as diffusion length L. However, also majority carrier properties, i. e. dopant concentration, can be quantitatively assessed by EBIC if due account is taken of the space charge region (SCR) associated with the Schottky or p-n junction used for charge collection /1/. If energy-dependent EBIC /2/ is used, the SCR width W is obtained by best fitting of the theoretical EBIC efficiency (dependent on L and W) to the experimental one. Dopant concentration is then inversely proportional to W squared. The greatest accuracy in the determination of W (hence in dopant concentration) is achieved when L is small (≤ 1 µm). For high values of L (> ~ 3 µm), EBIC efficiency is much less sensitive to W changes because the diffusion current of the electron-beam generated minority carriers is much greater than the drift current, which is mainly affected by W, so that W determination becomes less reliable. The method is, thus, very well suited for the evaluation of the majority carrier properties in low diffusion length semiconductors, like the bulk III-V compounds (GaAs, InP). Moreover, higher sensitivity is achieved for low doping levels (~1016 cm-3) than for high doping levels (>~ 1018 cm -3). EBIC measurements of dopant concentration at composition inhomogeneities (growth striations) have been carried out in GaAs crystals. Evaluation of dopant density obtained by EBIC has been checked by comparison with the average dopant density measured by capacitance-voltage characteristics in the EBIC Schottky diode, and by measurement of W as a function of reverse bias. Very good agreement has always been found. The method has also been used to calibrate the photoetching technique in n-type GaAs /3/. It has, thus, been possible to establish the etch rate dependence on dopant concentration which resulted to be exponential over about one decade of dopant density, smaller etching rates corresponding to higher dopant concentration. The latter result is explained as being due to changes in the width of the depletion layer associated with the band-bending at the etching solution-semiconductor interface. In fact, since six (photogenerated) holes are necessary to dissolve one GaAs molecule at the surface /4/, the fewer the available holes the lower is the etching rate. Therefore, low doped regions exhibit higher etching rates than the highly doped regions because the surface depletion layer (where the holes most likely do not recombine) is larger for the low doped regions than for the high doped ones.

Controlled degradation and ablation of polymer surfaces by ultraviolet laser radiation

When pulsed ultraviolet laser radiation falls on the surface of an organic polymer the material at the surface is spontaneously etched away to a depth of 0·1 to several microns. The process is characterized by the control which can be exercised over the depth of etching by controlling the temporal width of the laser pulse and its fluence (energy per unit surface area of the polymer) and by the lack of detectable thermal damage to the substrate. The material that is removed by etching consists of products ranging from atoms to small fragments of the polymer. They are ejected at supersonic velocities. This photoetching technique is useful in patterning polymer films since it requires no special sensitization of the polymer, no wet development step, and is potentially capable of as high a resolution as any wet patterning method.

Ablation of polymers and biological tissue by ultraviolet lasers.

When pulsed, ultraviolet laser radiation falls on the surface of an organic polymer or biological tissue, the material at the surface is spontaneously etched away to a depth of 0.1 to several micrometers. In the process, the depth of etching is controlled by the width of the pulse and the fluence of the laser, and there is no detectable thermal damage to the substrate. The material that is removed by etching consists of products ranging from atoms to small fragments of the polymer. They are ejected at supersonic velocities. This dry photoetching technique is useful in patterning polymer films. It is also under serious investigation in several areas in surgery.