Currently, methods of laser micromachining of various kinds of microsized structures are actively developed by scientists and engineers in a variety of fields. Particularly, laser micromachining allows for selective ablation of thin metal films on dielectric substrates in order to create planar conductive structures with rather complex patterns. Meander-like structures on dielectric substrates can serve as a slow-wave structure in perspective compact millimeter band vacuum electronic devices such as traveling-wave tubes. Thus, the aim of this work was to prepare conductive planar structures from thin metal coatings based on a copper-molybdenum alloy. Copper-molybdenum thin films were deposited onto dielectric substrates by magnetron co-sputtering. Then the coatings were micromachined using a nanosecond pulsed laser to form a series of planar structures in the shape of strips of varied width. Deposited coppermolybdenum thin films after laser micromachining suffer from lack of adhesion to the substrates. Possible way to overcome this issue is use of an adhesion sublayer such as titanium or chromium.
Using artificial materials such as electromagnetic bandgap structures can be one of the promising ways to improve the efficiency of compact miniaturized vacuum electronic devices such as millimeter-band traveling-wave tubes with 2D planar microstrip slow-wave structures on dielectric substrates. Precision micromachining of the microsized elements of the electromagnetic bandgap structures is challenging. Here we proposed and studied an approach for microfabrication of the electromagnetic bandgap structure with microsized patterns by pulsed laser ablation. The obtained results of the morphology studies by scanning electron microscopy and optical microscopy show that the proposed approach allows fabricating of the microsized pattern with suitable tolerance. Also, we showed several results of numerical simulations of the electromagnetic parameters of the meander-line slow-wave structure on a dielectric substrate with an incorporated electromagnetic bandgap structure.
Scalable and cost-effective microfabrication approaches are highly demanded for manufacturing of RF and millimeterwave circuits such as transmission structures for flexible electronic devices. Flexible electronics play a key role in wearable and wireless technologies applicable in personalized medicine, sensing, energy harvesting, and communication areas. Here we report the results of thin copper films patterns micromachining using nanosecond-pulsed laser on flexible dielectric substrates. Thin copper films were deposited by magnetron sputtering onto 100 μm thick polyimide films that were used as dielectric substrates. Then, patterns were created through film ablation using a CNC laser micromachining system with a 1064 nm ytterbium 8 ns pulse duration fiber laser to chisel away the superfluous material just as it have been done in sculputure for ages. Several regimes of laser micromachining were studied. The most important issue in the laser micromachining of the metal films on the flexible dielectric substrate is flexible substrate thermal damage due to overheating. Optimal regimes of laser micromachining were found that allow to prevent this. These regimes will be used in the future to fabricate flexible transmission lines for RF and millimeter-wave signals. The schematic and design of the transmission line are considered. Results of numerical simulations made by ANSYS HFSS are presented.
Traveling-wave tubes (TWT) with microstrip planar slow wave structures (SWS) have attracted an increasing interest thanks to low operating voltage and size of the tube, as well as compatibility with modern microfabrication technologies. In this work, we report the results of design, fabrication, and experimental cold-test study of planar meander-line SWSs for millimeter-band TWTs (V-, W-, and D-band). SWS samples have been fabricated using the technology based on magnetron sputtering and subsequent laser ablation.
Design and preliminary numerical simulations of D-band planar microstrip meander-line slow wave structure for lowvoltage tubes with sheet electron beam were carried out. An original approach based on magnetron sputtering and laser ablation methods was utilized for microstrip meander-line slow wave structure microfarication. An application of nanosecond and picosecond laser ablation for microfabrication of D-band (110-170 GHz) planar microstrip meander-line slow wave structure was considered. We have verified our original approach for planar slow wave structures microfabrication by using different CNC precision laser machines operating with different values of laser pulse duration (100 ns, 8 ns, 4 ns and 10 ps). Samples of slow wave structures were fabricated and characterized by scanning electron microscopy and profilometry methods. It was shown that each considered CNC precision laser machine allows fabricating D-band microstrip meander-line slow wave structure with required dimensions, but picosecond laser ablation has such advantages as the absence of ablation products (droplets, and etc.) on the slow wave structure surface. As the next step, we are going to study S-parameters of microfabricated D-band microstrip meander-line slow wave structure samples experimentally by using vector network analyzer with D-band frequency converters.
We consider the results of dielectric properties study in millimeter band of thin-films based on silicon nitride compositions. Silicon nitride thin-film coatings were deposited on a substrate by DC magnetron sputtering. As a substrate for silicon nitride thin-film coatings a quartz plate were utilized. The ratio of argon and nitrogen in the working gas mixture was chosen as the variable parameter to control the composition of the deposited thin-film coating. Several samples of silicon nitride thin-film coatings with about 1 um thickness were fabricated. Radiophysical and dielectric properties of the fabricated SiN-type thin-film coatings were studied in millimeter wave frequency band of 50-70 GHz (V-band) with help of free space measurement method. The obtained results have shown that by controlling the resistive thin-film coating composition one can only slightly vary the radiophysical and dielectric properties of coating in millimeter-band.
In this paper, we consider a short review of existing technologies of flexible antenna fabrication and propose our original approach for flexible antenna fabrication. Review of existing technologies of flexible antenna fabrication includes photolithography, screen printing, pad printing, gravure printing, inkjet printing, micro-dispensing, micro-jetting, and aerosol-jet technology. Advantages and disadvantages of each mentioned above technologies were noted. In the second part of this study, we consider our original technology for antenna fabrication on flexible substrates utilizing magnetron sputtering and laser ablation methods. Samples of flexible antennas are formed on a flexible dielectric substrate in a technology process comprising following basic stages: 1) deposition a conductive coating onto the dielectric substrate with help of magnetron sputtering, 2) formation the pattern of the antenna structure on the conductive coating by laser ablation. In the final stage, the substrate is divided into individual samples of specific sizes. A number of test flexible antennas fabricated by our original approach are shown.
We have propose an original approach for fabrication of flexible antennas for biomedical-related applications. The technology is based on magnetron sputtering and laser ablation methods. The magnetron sputtering method is used to deposit a thin layer of metal (copper) on a flexible substrate (polyimide film). Then laser ablation is utilized to remove excess copper thus forming an antenna pattern on the metal layer. ISM band flexible design with microstrip feeding structure was chosen for testing this technique. Results of numerical simulation are presented. A number of test flexible antennas were fabricated by our original approach. Similar flexible antennas were also fabricated via photolithography process. A comparison of the experimental results of return loss (S11) measurements of antennas with different fabrication approach was carried out. The obtained experimental data is in a good agreement with the numerical modeling results. Proposed technology has significant advantages in cost, speed, and flexibility over photolithography processes commonly utilized for such applications.
Encapsulation of various nanoparticles in nanofibers has become one of the most interesting topics in the field of electrospinning and SERS. Literature review shows that several main approaches can be distinguished for the preparation of electrospun nanofibers with embedded metal nanostructures. However, there is no information about the comparison of various methods of metal nanoparticles introduction into nanofiber-based SERS-platforms. Three main approaches were used here for preparation of SERS-platforms based on electrospun nanofibers with embedded silver nanoparticles: synthesis of metal nanostructures inside fibers prepared with incorporated precursor, metal nanostructures synthesis via their nucleation in prepared nanofibers and sorption of metal nanostructures onto ready-made nanofibers. SERS-platforms based on polyacrylonitrile nanofibers containing various concentrations of Ag nanoparticles were obtained using techniques described above and tested.
This study presents experimental results of the investigation of the diffusion behavior of commercially pure titanium when interacting with oxygen and hydrogen. To study the gas absorption, electron microscopy combined with energy-dispersive analysis and secondary ion mass spectrometry were used. It was shown that in the course of heat treatment with high-frequency currents in the temperature range from 600 to 1200 °C, an intensive absorption of oxygen by the surface of titanium was observed. At the same time, desorption of hydrogen from the near-surface layer of titanium occurred and there was a double decrease in hydrogen concentration during thermal treatment in this temperature range.
Microfabricated vacuum power amplifiers and oscillators operating at millimeter and submillimeter (THz) bands are of great interest for applications in high-speed communication, radar, security and military systems, electronic warfare, etc. In this work, we report the results of numerical simulation and cold-test measurements of electromagnetic parameters of the V-band (50-70 GHz) planar meander-line SWS. The microstrip meander-line SWS is suitable for using in a millimeter-band TWT amplifiers. Several samples of copper microstrip meander-line SWS on a quartz substrate consisting of 50 meander periods with input and output couplers were designed, microfabricated and optimized. The SWS was microfabricated by using magnetron sputtering and laser ablation processes. This technique is a more facile, flexible and lower cost as compared to photolithography method. Transmission and reflection of proposed SWS were measured experimentally and calculated numerically. The results of the experimental cold-test measurements are verified by numerical simulations. Electromagnetic parameters of the SWSs were simulated using the finite-element ANSYS HFSS and COMSOL Multiphysics software packages. The results obtained with these two codes are in excellent agreement with each other and good agreement between experimental and numerical results is also observed.
We consider the results of modern scientific literature review on the experience and possibilities of using resistive thinfilm layers in vacuum electron devices (resistive wall amplifier). Such thin-film layers can be used as analogue of conventional slow wave structures in vacuum microwave amplifiers. The disadvantages of conventional slow wave structures in millimeter and submillimeter wavelength ranges are discussed. The main advantages and features of resistive thin-film layers, which could be serve as slow wave structures in amplifying devices of vacuum microwave electronics of millimeter and submillimeter wavelength range, are revealed. The proposed review covers the period from 1953, when the idea of a resistive wall amplifier was first introduced, to 2018. It was shown that the majority of literature consist only theoretical results, only a few papers consider the experimental results. Also it is noted that the focus of modern study shifts to the using of metamaterials as a resistive thin-film layer, very promising theoretical results and some cold measurements were obtained only in the GHz region.
The treatment with high frequency currents (HFC) is traditionally used to improve the mechanical properties of metal products, in particular hardness and wear resistance. A new method of carburization of titanium samples in a solid carburizer using HFC is proposed in the work. The temperature of the carburization is characterized by a wide range from 1000 to 1400 °C. As a result of thermochemical treatment, a hard coating of TiC (H ≥ 20 GPa) with a microstructure (d = 7-14 μm) consisting of nanoparticles (d = 10-12 nm) is formed on the titanium surface. These coatings are widely used in friction pairs for various purposes, including machinery, instrumentation and medicine.
The aim of this report is detection of model compound, rhodamine 6G (R6G), in blood and urine samples using surfaceenhanced Raman spectroscopy (SERS) as a detection tool and liquid-liquid extraction (LLE) for improving quality of SERS analysis (SERS-LLE combination). SERS substrate is a plasmonic nanomaterial which possesses drastic increasing of Raman spectrum intensity (106‒108) of any molecule adsorbed onto its surface. Here we used citrate stabilized silver nanoparticles as SERS substrate and synthesized them applying wet chemical approach. Before SERS measurements, blood and urine samples were artificially contaminated with R6G using 50 and 500 ng/mL concentrations for both samples. In order to reduce detectable concentrations of R6G and improve signal-to-noise ratio, we applied LLE which allows us to separate R6G from the matrix mixture and increase the analyte concentration. Four different LLE protocols were used and the most efficient one was found. Obtained results showed usefulness of SERS-LLE combination for chemical analysis of body fluids with level of detectable concentration down to tens ng/mL.
The aim of this work was the fabrication of nanolabels (SERS-nanotags) which are used for chemical analysis by means of surface-enhanced Raman spectroscopy (SERS), and registration of their SERS spectra inside photonic crystal fibers (PCF). The SERS nanotags fabrication included synthesis of silver nanoparticles with subsequent deposition of Raman active layer (thiol-group contained aromatic compound) and protecting layer composed of silica shell. Finally, SERS spectra of the SERS nanotags were registered inside PCF in order to determine the value of fiber-enhancement of the Raman signal and to estimate analytical potential of this combination.
Control methods of temperature fields inside a tissue during laser photothermolysis are an important point to develop biomedical applications of thermal destructions of cancer. One of the most promising approaches to measure and to control of temperature is the application of luminescence nanothermometers such as CuInS2 nanoparticles. Temperature measurement can be carried out by determination of the maximum of the luminescence band. Thus, we have investigated the influence of exposure time and temperature on the position of the maximum of the luminescence band of CuInS2 nanoparticles.
Manuscript is devoted to the comparison of CdSe/ZnS and CuInS2/ZnS quantum dots thermosensitivity in the view of their applications as nanothermometers. It was found the luminescence spectrum of CuInS2/ZnS quantum dots consists of two components, which are described by Gauss type functions and connected with different types of defects into nanoparticles. The heat treatments provide different effects such as spectral shifts, FWHM and amplitude for these too components. CdSe/ZnS nanoparticles spectra shifted to the red region; the average speed of spectrum shift is 0.065 nm per degree.
New SERS-active materials were obtained by preparation of alumina with embedded silver nanoparticles and their application both as sorbents for pre-concentration and SERS platforms was studied. The influence of ionic strength on Ag NPs size, absorption spectra and SERS signal was investigated. Synthesized materials were examined by Raman spectroscopy, scanning electron microscopy, and UV-visible spectroscopy. The optimal conditions for SERSmeasurements were chosen. Synthesized materials were applied for pre-concentration of model analytes (Rhodamine 6G, folic acid and pyrene) and their SERS detection directly within the sorbent. It was shown that the recovery of analytes could be improved by alumina modification. The combination of surface-enhanced Raman spectroscopy with preconcentration is a promising instrument for analytical applications.
The temperature dependence of the fluorescent spectra of ZnCdS nanoparticles placed into a biological tissue has been
investigated. It is shown that the fluorescence peak of the nanoparticles is shifted towards longer wavelengths, and
fluorescence quenching is observed during heating the biological tissue until its denaturation. ZnCdS nanoparticles are
suitable for measuring the temperature of biological nanoobjects under photothermolysis.
The temperature sensitivity of the spectral characteristics of ZnCdS nanoparticles both stabilized and coated with polyacrylic acid is compared. It is shown that the luminescence of the nanoparticles has two temperature-dependent parameters, namely, the intensity and the peak position. Variations in these parameters are due to the distortion of the energy states of luminescent surface defects. Aggregation of the nanoparticles does not distort obtained dependencies. Temperature sensitivity is higher for the nanoparticles coated with a layer of polyacrylic acid.
KEYWORDS: 3D modeling, Crystals, Scanning electron microscopy, 3D visualizations, Crystallography, Bioalcohols, Electron microscopes, Data modeling, 3D applications, Visualization
Crystal formations were observed on the surface of etched dentine after it had been exposed to 95% ethanol in solution for 30 days at room temperature. 3D visualization of surface formations was carried out using a scanning electron microscope and Alicona 3D MeX software (Alicona GmbH). Metric characteristics of the mentioned above structures were evaluated and the nature of possible errors on the steps of model design was studied. It was shown that the shape of crystal models were likely to be approximated by ellipsoid segments.
Laboratory experiments conducted in Saratov State University in the first half of 2012 revealed crystal formations on the surface of etched dentine after it had been exposed to 95% ethanol in solution for 30 days at room temperature. It was discovered that the structures observed were calcium-phosphate crystals. The nature of crystal formation on rough dentine surface was described based on substance diffusion in solution, which resulted in dentine becoming spatially inhomogeneous over time. The crystal formation was established to be determined by the limited ion redistribution in dentine material.
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