This study addresses key challenges in gas sensing, particularly achieving high sensitivity at low operating temperatures. Tungsten disulfide (WS2) thin films were deposited by sputtering and sulfurized at 800 °C for 30 and 60 min on quartz and sapphire substrates. Raman spectroscopy confirmed multilayer WS2 formation, with characteristic modes at 349 and 417 cm-1. X-ray diffraction revealed that the films are polycrystalline with the formation of the hexagonal 2H-WS2 phase on both substrates. FESEM images showed clearly visible nanoparticles, but they were not evenly distributed and were differently oriented, with a hint of texturing. The WS2 films exhibited stable sensing performance at low operating temperatures from 30 to 150 °C and high sensitivity toward NH3 in the 10-200 ppm range. Experimental results indicate a limit of detection, highlighting the potential of WS2 films for low operating temperature ammonia sensing. A minimum value of the limit of detection of 0.6 ppm for an operating temperature of 150 °C was achieved for the WS2 sample sulfurized at 800 °C for 60 min on a quartz substrate.

This study presents the Raman spectral characteristics and selected electrical parameter measurements of WS2 films deposited by magnetron sputtering on sapphire and subsequently sulfurized. The analysis of the Raman spectra focuses on the positions and shifts of the E12g and A1g vibrational modes. The effects of different sputtering times on WS2 films and the corresponding activation energy values were also investigated. From both physical and experimental perspectives, the Raman spectral features of WS2 films were found to depend on the laser excitation wavelengths (532 nm and 632.8 nm) as well as on possible crystallographic defects and variations in the excitation point position. These defects have a significant influence on both the Raman spectra and the activation energies of the studied samples. The calculated activation energies (~ 0.15–0.19 eV) of the conduction charge carriers correlate with shallow defect-related energy levels indicated by the Raman characteristics.

In this contribution, our primary objective is to comprehensively examine the influence of sulfurization temperature on the optical properties of WS2 thin films deposited on quartz/sapphire substrates. We employed dc-magnetron sputtering for the deposition of WS2 thin films into the targeted substrates and then we prepared our samples at different sulfurization temperatures, 600 degrees C, 700 degrees C, and 800 degrees C. The characterization of the samples was performed using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and Raman spectroscopy. Additionally, optical transmittance measurements were employed to further analyze the optical properties of the samples, with the Tauc plot method being utilized to determine the bandgap of each sample. The samples consist of flakes and films ranging in size from less than 30 nm to over 3 mu m, with a uniform thickness of 10 nm. Raman spectroscopy revealed the presence of the characteristic vibrational modes E-12g and A(1g) at approximately 350 and 419 cm-1, respectively, confirming the formation of a layered structure in all samples. The bandgap values obtained for the samples were in the range of 1.87 to 1.95 eV. The experimental findings demonstrate that variations in sulfurization temperature and substrate choice significantly influence the size, morphology, and density of the films and flakes, thereby impacting the optical properties, particularly the bandgap.

We present experiments and simulations of the electron lithography process aimed at optimizing parameters for the lift-off technique, a critical step in creating metal patterns on a substrate using an electron beam. The study focused on a bilayer consisting of two PMMA resists with different molecular weights - 950,000 on the top and 495,000 on the bottom - corresponding to different sensitivities. The shape of the developed resist images, specifically in the case of a line grating (Line/Space 100/500 nm), was examined. The influence of the exposure dose on the sidewall geometry of the developed profiles in a 550 nm bilayer PMMA resist system was investigated both experimentally and theoretically to achieve nearly vertical profile sidewalls. Contour plots showing the half linewidths of the developed bilayer PMMA resist as a function of the exposure dose along the resist depth were obtained through simulation, allowing for the prediction of profile geometry for doses ranging from 440 μC/cm 2 to 760 μC/cm 2 .

Abstract The experimental investigation and simulation of electron beam lithography (EBL) for bilayer and trilayer resist systems have been carried out. Important parameters of the EBL process, such as dissolution rate, resolution, absorbed energy, and resist profile in the investigated bilayer resist systems, have been studied and discussed. Various combinations of resist layers with positive electron resist have been proposed to examine the effects of lithographic process parameters on the resist profile. The results of this work are intended for use in multilayer resist systems to produce high-frequency electronics, where the fabrication of a T-shaped gate is one of the most crucial processes.

This study presents different approaches to increase the sensing area of NiO based semiconducting metal oxide gas sensors. Micro- and nanopatterned laser induced periodic surface structures (LIPSS) are generated on silicon and Si/SiO2 substrates. The surface morphologies of the fabricated samples are examined by FE SEM. We select the silicon samples with an intermediate Si3N4 layer due to its superior isolation quality over the thermal oxide for evaluating the hydrogen and acetone sensitivity of a NiO based test sensor.

Semiconducting metal oxides are widely used for solar cells, photo-catalysis, bio-active materials and gas sensors. Besides the material properties of the semiconductor being used, the specific surface topology of the sensors determines device performance. This study presents different approaches for increasing the sensing area of semiconducting metal oxide gas sensors. Micro- and nanopatterned laser-induced periodic surface structures (LIPSSs) are generated on silicon, Si/SiO2 and glass substrates. The surface morphologies of the fabricated samples are examined by FE SEM. We selected the nanostructuring and characterization of nanostructured source Ni/Au and Ti/Au films prepared on glass using laser ablation as the most suitable of the investigated approaches. Surface structures produced on glass by backside ablation provide 100 nm features with a high surface area; they are also transparent and have high resistivity. The value of the hydrogen sensitivity in the range concentrations from 100 to 500 ppm was recorded using transmittance measurements to be twice as great for the nanostructured target TiO2/Au as compared to the NiO/Au. It was found that such transparent materials present additional possibilities for producing optical gas sensors.

One of the major functions of the larval salivary glands (SGs) of many Drosophila species is to produce a massive secretion during puparium formation. This so-called proteinaceous glue is exocytosed into the centrally located lumen, and subsequently expectorated, serving as an adhesive to attach the puparial case to a solid substrate during metamorphosis. Although this was first described almost 70 years ago, a detailed description of the morphology and mechanical properties of the glue is largely missing. Its main known physical property is that it is released as a watery liquid that quickly hardens into a solid cement. Here, we provide a detailed morphological and topological analysis of the solidified glue. We demonstrated that it forms a distinctive enamel-like plaque that is composed of a central fingerprint surrounded by a cascade of laterally layered terraces. The solidifying glue rapidly produces crystals of KCl on these alluvial-like terraces. Since the properties of the glue affect the adhesion of the puparium to its substrate, and so can influence the success of metamorphosis, we evaluated over 80 different materials for their ability to adhere to the glue to determine which properties favor strong adhesion. We found that the alkaline Sgs-glue adheres strongly to wettable and positively charged surfaces but not to neutral or negatively charged and hydrophobic surfaces. Puparia formed on unfavored materials can be removed easily without leaving fingerprints or cascading terraces. For successful adhesion of the Sgs-glue, the material surface must display a specific type of triboelectric charge. Interestingly, the expectorated glue can move upwards against gravity on the surface of freshly formed puparia via specific, unique and novel anatomical structures present in the puparial’s lateral abdominal segments that we have named bidentia.

This article presents experiments and simulation of the electron lithography process with the aim of finding optimal parameters for lift-off technique which is a crucial step in the process of creating metal patterns on a substrate utilizing an electron beam. A bilayer comprising two PMMA resists with different molecular weights 950,000 on the top and 495,000 on the bottom (different sensitivities accordingly) was studied. The shape of the obtained developed resist images in the case of a single line (500 nm) was studied and the influence of the exposure dose on the sidewall geometry of the developed profiles in 550 nm bilayer PMMA resist system was investigated experimentally and theoretically in order to achieve close to vertical profile sidewalls. Contour plots of the developed bilayer PMMA resist half linewidths depending on the exposure dose along the resist depth were obtained through simulation and allow the profile geometry to be predicted for doses in the range from 360 mu C/cm2 to 2120 mu C/cm2.

This paper focus on electron beam lithography (EBL) experimental investigation and simulation of single/multilayer resists for pattern transfer. Important EBL process parameters such as solubility rates, resolution, absorbed energy in the pattern concerning investigated single and trilayer PMMA and HSQ resist systems are studied and discussed. The novelty of the presented approach is in that the bottom layer of HSQ is not etched in plasma, however developed after the middle layer etching. The calculated energy deposition distribution in the top resist layers for single and trilayer PMMA and HSQ systems shows the advantage of the studied trilayer PMMA and HSQ systems due to the reduced contribution of the forward and backscattered electrons.

Experimental investigation of negative electron resist AR-N 7520 profiles using an electron beam lithography system ZBA23 (Raith) is performed at variation of the exposure doses and the exposure patterns. The form of the obtained after the exposure resist profiles is investigated and optimized. Artificial neural networks for the dependence of the overall geometry of the obtained resist profiles on process parameters are trained, tested and validated. Several overall geometry quality criteria for the shape of the developed resist profile cross-sections are defined. An approach, based on the defined overall quality characteristics and multicriterial parameter optimization, is proposed and implemented for fulfillment of the technological requirements for the produced resist profile dimensions.

In this work, four types of negative electron beam resists are investigated. Electron beam lithography (EBL) experiments were conducted using EBL system ZBA23 ( Raith ) with the variable-shaped electron beam cross-section at 40 keV electron energy. Important electron beam resist characteristics such as sensitivity, dissolution rate, aspect ratio and sidewall developed profiles in the chemically amplified resist (CAR) SU-8 2000, non-CARs ma-N 2410 and ARN-7520, and inorganic negative resist HSQ XR-1514 are studied and compared. This study was motivated by the selection of a suitable resist for practical use such as large area gratings fabrication for optoelectronics.

This paper deals with the performance of the AR-N7520 (Allresist) negative electron beam resist (EB resist) which was selected as an etch mask for the fabrication of gratings on GaAs substrates. The developed resist sidewall shape is crucial for this purpose. The required near-to-vertical sidewall shape can be achieved by optimizing the electron beam lithography (EBL) process based on experimental investigations and computer simulations. The sidewall shape dependence on the EBL parameters (exposure dose, resist pattern, etc.) and the proximity effect are studied.

We present structural, optical and electrical investigations of layered WS2 films prepared on tungsten. A two-step technique has been used to synthesize layered WS2 films using sulfurization of W films sputtered with thinner (1 and 2 nm) and thicker (14 and 28 nm) thicknesses at 800 degrees C. XRD analysis revealed that the examined films are polycrystalline with texture and have a 2H-WS2 hexagonal microstructure. Using Raman spectroscopy with the 532 nm laser excitation, the presence of E-2g(1), and A(1g) vibration modes was observed and the layered nature of WS2 was confirmed. FE SEM observations showed two different surface morphologies. The samples grown on thinner W films were not compact over the surface and agglomeration of nanosize grains in combination of triangles and flakes was visible. In another group the surface was lamellar and contained plenty of nanorods embedded vertically and/or inclined at different angles to the surface. Layered WS2 films exhibited a direct band gap in the range of 2.1-2.5 eV and they were n-type semiconductors with the sheet resistance in the order of several M Omega at room temperature.

Abstract We present results on very thin NiO films which are able to detect 3 ppm of acetone, toluene and n-butyl acetate in synthetic air and to operate at 300°C. NiO films with 25 and 50 nm thicknesses were prepared by dc reactive magnetron sputtering on alumina substrates previously coated by Pt layers as heater and as interdigitated electrodes. Annealed NiO films are indexed to the (fcc) crystalline structure of NiO and their calculated grain sizes are in the range from 22 to 27 nm. Surface morphology of the examined samples was influenced by a rough and compact granular structure of alumina substrate. Nanoporous NiO film is formed by an agglomeration of small grains with different shapes while they are created on every alumina grain.

The influence of electron beam lithography parameters (such as electron energy, resist thickness, the exposure dose) on the resist sidewall shape (profile) was studied for the PMMA (polymethyl-methaaylate) positive resist. The profile of the positive tone resist PMMA was investigated depending on varying exposure doses for the resist thicknesses 600 and 1300 nm, and electron energy 30 keV. Simulation results based on measurements along the resist profile depth are presented and discussed. The results obtained contribute to the knowledge on electron scattering in resist/substrate in electron beam lithography for the case of field emission cathode and Gaussian intensity distribution, and to the development and approval of models for the prediction and precise control of resist profiles in thick PMMA layers for 3D proximity effect simulation, the bilayer resist system, and the lift-off method.

The study reveals the influence of the electron-beam lithography parameters (such as the exposure dose, resist thickness, depth) on the resist profile shape in the case of the PMMA (polymethyl-methacrylate) positive resist. The experiments are performed using an Elphy Quantum ( Raith) e-beam lithography control system installed on an Inspect F50 (FEI) scanning electron microscope with a field emission cathode and a Gaussian intensity distribution. Profiles developed in the PMMA using the MIBK:IPA 1:3 developer and simulation results based on measurements along the resist profile depth for the case of 30-keV electron energy are presented and discussed. The results contribute to the knowledge on electron scattering in the resist/substrate in electron-beam lithography and assist in the development and approval of simulation tools for prediction and control of resist profiles in thick PMMA layers for lift-off nanopatterning.

Experimental and simulation results of the proximity effects study for the case of the high-resolution electron beam resist Hydrogen Silsesquioxane (HSQ) on TiO2 thin film at 40 keV electron energy are presented and discussed. The dependence of resist pillar size and shape on the exposure dose, resist thickness and resist patterns configuration is studied for thick HSQ. The influence of the proximity effects on the precision and limitations of electron beam lithography is discussed.