Substrate Distance Research Articles

Fabrication and Characterization of High-Crystalline Nanoporous ZnO Thin Films by Modified Thermal Evaporation System

The aim of this work is to fabricate high-crystalline nanoporous zinc oxide (ZnO) thin films by a modified thermal evaporation system. First, zinc thin films have been deposited on bare glass substrate by the modified thermal evaporation system with pressure of 0.05[Formula: see text]mbar, source–substrate distance of 3[Formula: see text]cm and source temperature 700[Formula: see text]C. Then, high-crystalline ZnO thin film is obtained by annealing at 500[Formula: see text]C for 2[Formula: see text]h in atmosphere. The prepared ZnO films are characterized with various deposition times of 10[Formula: see text]min and 20[Formula: see text]min. The structural property was investigated by X-ray diffractometer (XRD). The optical bandgap and absorbance/transmittance of these films are examined by ultraviolet/visible spectrophotometer. The surface morphological property has been observed by scanning electron microscope (SEM). ZnO films have showed uniform nanoporous surface with high-crystalline hexagonal wurtzite structure. The ZnO films prepared with 20[Formula: see text]min has excitation absorption-edge at 369[Formula: see text]nm, which is blueshifted with respect to the bulk absorption-edge appearing at 380[Formula: see text]nm. The gap energy of ZnO film is decreased from 3.14[Formula: see text]eV to 3.09[Formula: see text]eV with increase of the deposition time, which can enhance the excitation of ZnO films by the near visible light, and is suitable for the application of photocatalyst of waste water cleaning and polluted air purification.

Simulation of Suppression of Gamma Sensitivity of ‘Fission Electron-Collection’ Neutron Detector**Supported by the National Natural Science Foundation of China under Grant No 11205141, and the Science and Technology Foundation of China Academy of Engineering Physics under Grant No 2012B0103003.

The fission electron-collection neutron detector (FECND) is a current-type neutron detector. Based on the analysis of the generation process of the gamma signals of the FECND, a mechanism utilizing symmetrical structure is proposed and discussed to suppress the gamma signals. According to this mechanism, the electrons generated from the gamma rays can be well compensated for by the adjustment of the electrodes' thickness and distance. In this study, based on the Monte–Carlo simulation of the gamma signals of the FECND, the varying patterns are obtained between the gamma signals and the detector parameter settings. As indicated by the simulation results, the gamma electrons can be compensated for completely by simply adjusting the coated electrode substrate thickness and distance. Moreover, with a proposed optimal parameter setting, the gamma sensitivity can be as low as 3.39×10−23 C·cm2, while the signal-to-noise ratio can be higher than 200:1. The compensation results of the γ-rays in the FECND will be slightly affected by the manufacturing error or the assembly error.

Laser tailored nanoparticle arrays to detect molecules at dilute concentration

By nanosecond pulsed laser ablation in an ambient gas gold nanoparticles (NPs) were produced that self-assemble on a substrate resulting in increasingly elaborated architectures of growing thickness, from isolated NP arrays up to percolated films. NPs nucleate and grow in the plasma plume propagating through the gas. Process parameters including laser wavelength, laser energy density, target to substrate distance, nature and pressure of the gas affect plasma expansion, thus asymptotic NP size and kinetic energy. NP size, energy and mobility at landing determine film growth and morphology that affect the physico-chemical properties of the film. Keeping fixed the other process parameters, we discuss the sensitive dependence of film surface nanostructure on Ar pressure and on laser pulse number. The initial plume velocity and average ablated mass per pulse allow predicting the asymptotic NP size. The control of growth parameters favors fine-tuning of NP aggregation, relevant to plasmonics to get optimized substrates for surface enhanced Raman spectroscopy (SERS). Their behavior is discussed for testing conditions of interest for clinical application. Both in aqueous and in biological solutions we obtained good sensitivity and reproducibility of the SERS signals for the anti-Parkinson drug apomorphine, and for the anti-epilepsy drug carbamazepine.

Ellipsometry of TiO_x coatings deposited in a magnetron apparatus with an unbalanced magnetic system: effect of the oxygen concentration and the magnetron–substrate distance

The method of spectral modulation ellipsometry is used to investigate the structure and optical properties of thin TiOx coatings deposited by magnetron with various oxygen concentrations in the plasma, a working pressure of 0.28 Pa, and a discharge current of 5.6 A. It is established that, depending on the fraction of O2, three types of coatings are formed in the plasma: semitransparent three-layer coatings, transparent two-layer coatings, and transparent three-layer coatings. The last coatings have a dense contact layer up to 50 nm thick, whose optical characteristics correspond to crystalline anatase and/or rutile. A correlation is established between the roughness, the band gap, and the impurity concentration in the plasma. It is pointed out that, with 19 vol. % O2, coatings with a low refractive index (2.347), a small band gap (3.31 eV), and high roughness (16.8 nm) are deposited in the plasma, and this must increase the photocatalytic activity of the coatings.

Study of Impingement Types and Printing Quality during Laser Printing of Viscoelastic Alginate Solutions.

Laser-induced forward transfer-based laser printing has been being implemented as a promising orifice-free direct-write strategy for different printing applications. The printing quality during laser printing is largely affected by the jet and droplet formation process and subsequential impingement. The objective of this study is to investigate the impingement-based printing type and resulting printing quality during the laser printing of viscoelastic alginate solutions, which are representative inks for soft structure printing such as bioprinting. Three printing types are identified: droplet-impingement printing, jet-impingement printing with multiple breakups, and jet-impingement printing with a single breakup. Printing quality, in terms of printed droplet morphology and size, has been investigated as a function of alginate concentration, laser fluence, and direct-writing height based on a time-resolved imaging approach and microarrays of printed droplets. Of these, the best printing quality is achieved with single-breakup jet-impingement printing, followed by multiple-breakup jet-impingement printing, with droplet-impingement printing producing the lowest quality printing. The printing quality can be improved by using high-concentration alginate solutions. The increase of laser fluence may lead to a well-defined primary droplet for low-concentration alginate solutions; however, this can cause the droplet diameter to increase, which may not be desirable. The direct-writing height (i.e., ribbon coating-receiving substrate distance) also influences the print quality. For example, an increase in direct-writing height can cause the printing type to change from the ideal jet-impingement with a single breakup, to the jet-impingement with multiple breakups, and even the least desired droplet-impingement printing, with only slight variations in droplet diameter.

Thermoelectric nanocrystalline YbCoSb laser prepared layers

Filled thermoelectric YbxCo4Sb12 layers were prepared by pulsed laser deposition method. The Yb0.19Co4Sb12 target was fabricated by hot pressing. Various deposition conditions were tested: target—substrate distance dT–S (4 or 6 cm), ambient argon pressure (from 0.5 to 13 Pa), laser repetition rate (from 3 to 10 Hz), substrate temperature (from 250 to 400 °C) and laser fluence (in region from 0.8 to 5 J cm−2). Film roughness was determined by mechanical profilometer and by AFM. For dT–S = 4 cm we observed a deficit of Yb and surplus of Co. Sb was transferred from target to film roughly stoichiometrically (as measured by EDX). Films created at 0.8 J cm−2 exhibited generally poor stoichiometry and mechanical properties. Optimal conditions and stoichiometric transport were found for dT–S = 6 cm and 13 Pa of Ar. XRD shows that the films were nanocrystalline with CoSb3 structure. Grain size was in the range of ~50–80 nm. Temperature dependence of Seebeck coefficient and power factor was measured. Thermoelectric efficiency ZT ~ 0.04–0.05 was measured at room temperature using Harman method. In dependence on layers quality, we calculated thermal conductivity λ ~ 0.4–1.3 W K−1 m−1.

Alignment of One-Dimensional SnO2 Lines by Electrohydrodynamic Jet Printing.

One-dimensional (1-D) SnO2 line as a representative semiconducting oxide were formed by electro- hydrodynamic jet-printing (EHD) of tin chloride pentahydrate and polyvinylpyrrolidone (PVP, 1,200 k, Aldrich) solution ink. The 1-D polymer lines including Sn precursors were created by controlling the viscosity, that is, polymer/tin precursor ratio, and adjusting printing conditions such as tip to substrate distance, applying voltage, flow rate of ink and velocity. The printed lines were dried at 200 degrees C to get rid of solvent and finally heat-treated at 600 degrees C to burn out PVP and form tin oxide line. We found out that the linearity and shape of the aligned 1-D SnO2 could be controlled by adjusting various parameters such as the viscosity of a precursor solution, the ratio of Sn to PVP polymer in the solution, the shape of a cone, the size of a droplet, the applied voltages, the working distance, the flow rate on the glass slides and the Si wafers with a SiPO2 layer, respectively. It is found out that the heat-treatment for the removal of polymers should be tailored to produce continuous 1-D SnO2 lines due to the drastic volume reduction (>90%) of the aligned fibers in the annealing process. The electrical properties of the 1-D SnO2 aligned on the Si wafers with Au electrode patterns were evaluated.

Membrane patches as ion channel probes for scanning ion conductance microscopy.

We describe dual-barrel ion channel probes (ICPs), which consist of an open barrel and a barrel with a membrane patch directly excised from a donor cell. When incorporated with scanning ion conductance microscopy (SICM), the open barrel (SICM barrel) serves to measure the distance-dependent ion current for non-invasive imaging and positioning of the probe in the same fashion of traditional SICM. The second barrel with the membrane patch supports ion channels of interest and was used to investigate ion channel activities. To demonstrate robust probe control with the dual-barrel ICP-SICM probe and verify that the two barrels are independently addressable, current-distance characteristics (approach curves) were obtained with the SICM barrel and simultaneous, current-time (I-T) traces were recorded with the ICP barrel. To study the influence that the distance between ligand-gated ion channels (i.e., large conductance Ca2+-activated K+ channels/BK channels) and the ligand source (i.e., Ca2+ source) has on channel activations, ion channel activities were recorded at two fixed probe-substrate distances (Dps) with the ICP barrel. The two fixed positions were determined from approach curves acquired with the SICM barrel. One position was defined as the "In-control" position, where the probe was in close proximity to the ligand source; the second position was defined as the "Far" position, where the probe was retracted far away from the ligand source. Our results confirm that channel activities increased dramatically with respect to both open channel probability and single channel current when the probe was near the ligand source, as opposed to when the probe was far away from the ligand source.

Ultrahigh-throughput generation and characterization of cellular aggregates in laser-ablated microwells of poly(dimethylsiloxane)

Ultrahigh-throughput generation and characterization of cellular aggregates in laser-ablated microwells of poly(dimethylsiloxane)

Lipase immobilization for catalytic applications obtained using fumed silica deposited with MAPLE technique

Lipases are enzymes used for catalyzing reactions of acylglycerides in biodiesel production from lipids, where enzyme immobilization on a substrate is required.Silica nanoparticles in different morphologies and configurations are currently used in conjunction with biological molecules for drug delivery and catalysis applications, but up to date their use for triglycerides has been limited by the large size of long-chain lipid molecules.Matrix assisted pulsed laser evaporation (MAPLE), a laser deposition technique using a frozen solution/suspension as a target, is widely used for deposition of biomaterials and other delicate molecules. We have carried out a MAPLE deposition starting from a frozen mixture containing fumed silica and lipase in water. Deposition parameters were chosen in order to increase surface roughness and to promote the formation of complex structures. Both the target (a frozen thickened mixture of nanoparticles/catalyst in water) and the deposition configuration (a small target to substrate distance) are unusual and have been adopted in order to increase surface contact of catalyst and to facilitate access to long-chain molecules. The resulting innovative film morphology (fumed silica/lipase cluster level aggregation) and the lipase functionality (for catalytic biodiesel production) have been studied by FESEM, FTIR and transesterification tests.

Application of X-ray micro-CT for micro-structural characterization of APCVD deposited SiC coatings on graphite conduit

SiC coatings are commonly used as oxidation protective materials in high-temperature applications. The operational performance of the coating depends on its microstructure and uniformity. This study explores the feasibility of applying tabletop X-ray micro-CT for the micro-structural characterization of SiC coating. The coating is deposited over the internal surface of pipe structured graphite fuel tube, which is a prototype of potential components of compact high-temperature reactor (CHTR). The coating is deposited using atmospheric pressure chemical vapor deposition (APCVD) and properties such as morphology, porosity, thickness variation are evaluated. Micro-structural differences in the coating caused by substrate distance from precursor inlet in a CVD reactor are also studied. The study finds micro-CT a potential tool for characterization of SiC coating during its future course of engineering. We show that depletion of reactants at larger distances causes development of larger pores in the coating, which affects its morphology, density and thickness.

Material behavior under extreme domain constraint in laser-assisted surface nanostructuring

Using systematic atomistic modeling, the objective of this study is to explore the nanoscale tip-confinement effect in near-field surface nanostructuring. It is to provide important knowledge base for the understanding and design of tip-based manufacturing at the nanoscale. Our result reveals that the number of ablated-out atoms decreases significantly due to the tip-confinement. Tip apex oscillation occurs because of tip interaction with the substrate. The dynamic nanostructuring process and final surface structure are strongly affected by tip–substrate distance and laser fluence. When the tip–substrate distance is smaller, it takes a longer time for the substrate to cool down and solidify.

CrSi(O,N)-based cermet-like material for high-ohmic thin film resistor applications

The thin film material CrSi(O,N) has been investigated with the aim to realize resistive films with precision properties in the resistivity range between 2 and 20 mΩcm. The resistor layers were prepared by radio-frequency magnetron sputtering from cermet targets containing all functionally required film components. The influence of typical technological parameters as argon pressure, source power, and target–substrate distance on the film properties was studied. Depending on target composition, preparation conditions, and thermal treatment, the attainable resistivity limits of the precision parameters temperature coefficient of resistivity (TCR) and long time stability (ΔR/R) were determined. It could be shown that two of the studied target materials achieve the resistivity range 2 mΩcm < ρ < 20 mΩcm with the resistor parameters TCR of 10 ppm K−1 and ΔR/R of <0.2%.

Synthesis of Hexagonal Boron Nitride Monolayer: Control of Nucleation and Crystal Morphology

Monolayer hexagonal boron nitride (hBN) attracts significant attention due to the potential to be used as a complementary two-dimensional dielectric in fabrication of functional 2D heterostructures. Here we investigate the growth stages of the hBN single crystals and show that hBN crystals change their shape from triangular to truncated triangular and further to hexagonal depending on copper substrate distance from the precursor. We suggest that the observed hBN crystal shape variation is affected by the ratio of boron to nitrogen active species concentrations on the copper surface inside the CVD reactor. Strong temperature dependence reveals the activation energies for the hBN nucleation process of ∼5 eV and crystal growth of ∼3.5 eV. We also show that the resulting h-BN film morphology is strongly affected by the heating method of borazane precursor and the buffer gas. Elucidation of these details facilitated synthesis of high quality large area monolayer hexagonal boron nitride by atmospheric pressure ...

Manipulation of Superparamagnetic Beads on Patterned Exchange-Bias Layer Systems for Biosensing Applications.

A technology platform based on a remotely controlled and stepwise transport of an array arrangement of superparamagnetic beads (SPB) for efficient molecular uptake, delivery and accumulation in the context of highly specific and sensitive analyte molecule detection for the application in lab-on-a-chip devices is presented. The near-surface transport of SPBs is realized via the dynamic transformation of the SPBs’ magnetic potential energy landscape above a magnetically stripe patterned Exchange-Bias (EB) thin film layer systems due to the application of sub-mT external magnetic field pulses. In this concept, the SPB velocity is dramatically influenced by the magnitude and gradient of the magnetic field landscape (MFL) above the magnetically stripe patterned EB substrate, the SPB to substrate distance, the magnetic properties of both the SPBs and the EB layer system, respectively, as well as by the properties of the external magnetic field pulses and the surrounding fluid. The focus of this review is laid on the specific MFL design in EB layer systems via light-ion bombardment induced magnetic patterning (IBMP). A numerical approach is introduced for the theoretical description of the MFL in comparison to experimental characterization via scanning Hall probe microscopy. The SPB transport mechanism will be outlined in terms of the dynamic interplay between the EB substrate’s MFL and the pulse scheme of the external magnetic field.

Effect of the processes in the laser ablation plume on the resistivity and morphology of nanocrystalline ZnO films

The specific features of the formation of nanocrystalline ZnO films by pulsed laser deposition have been studied at different target–substrate distances. Expressions for estimating the temperature, particle concentration, and pressure in the laser ablation plume have been obtained. The effect of these parameters on electrical properties of nanocrystalline ZnO films grown by pulsed laser deposition has been estimated. The feasibility of the controlled growth of nanocrystalline ZnO films with a surface roughness of ~2–15 nm, grain diameters of 70–620 nm, and resistivities in the range of (1.75–5.3) × 10–3 Ω cm has been demonstrated.

Optimization of substrate-target distance for pulsed laser deposition of tungsten oxide thin films using Langmuir probe

The paper investigates the spatial and temporal variation of laser produced plasma of tungsten oxide using a Langmuir probe. The plasma was produced by laser ablation of tungsten oxide target using an Excimer laser of wavelength 248 nm. Our experimental studies confirmed that oxygen partial pressure (P) of 2× 10−2 mbar is sufficient enough to get stoichiometric tungsten oxide thin films and the plume dynamics was diagnosed for their spatial and temporal behaviour at the above optimised oxygen pressure. Spatial distribution was recorded with the target to substrate distance (D) ranging from the target position to a distance of 75 mm away from the target, whereas the temporal variation was taken in the range of 0–50 μ S with an interval of 0.5 μ S. The average electron densities were found to be maximum at 30 mm from the target position. However, ion density was constant beyond the probe distance of 45 mm from the target. The plasma current was found to be maximum at 28 μ S. The target to substrate distance was optimized for homogenous adherent good quality thin films using plasma parameters such as ion density and average electron density obtained at different oxygen pressure. The target distance and background gas pressure were correlated as PD scaling law and fitted as PD3 in the model.

Optimization of substrate-target distance for pulsed laser deposition of tungsten oxide thin films using Langmuir probe

The paper investigates the spatial and temporal variation of laser produced plasma of tungsten oxide using a Langmuir probe. The plasma was produced by laser ablation of tungsten oxide target using an Excimer laser of wavelength 248 nm. Our experimental studies confirmed that oxygen partial pressure (P) of 2× 10−2 mbar is sufficient enough to get stoichiometric tungsten oxide thin films and the plume dynamics was diagnosed for their spatial and temporal behaviour at the above optimised oxygen pressure. Spatial distribution was recorded with the target to substrate distance (D) ranging from the target position to a distance of 75 mm away from the target, whereas the temporal variation was taken in the range of 0–50 μ S with an interval of 0.5 μ S. The average electron densities were found to be maximum at 30 mm from the target position. However, ion density was constant beyond the probe distance of 45 mm from the target. The plasma current was found to be maximum at 28 μ S. The target to substrate distance was optimized for homogenous adherent good quality thin films using plasma parameters such as ion density and average electron density obtained at different oxygen pressure. The target distance and background gas pressure were correlated as PD scaling law and fitted as PD3 in the model.

Double glow plasma chromizing of Ti6Al4V alloys: Impact of working time, substrate–target distance, argon pressure and surface temperature of substrate

Surface chromizing of Ti6Al4V alloys was achieved by double glow plasma surface metallurgy technology. Effects of working time, substrate–target distance, argon pressure and surface temperature of substrate on chromium coating were investigated in detail. The results show that the structure of coating achieved by double glow plasma surface chromizing includes a complete structure of surface deposited layer, inter diffusion layer and sputtering-affected zone. Working time has a significant effect on the composition, morphology and structure of plasma chromium coating. An increasing number of β-Ti turned into α-Ti and TiCr2 phases precipitated in the inter diffusion layer with rising of surface temperature of Ti6Al4V and working time. Argon pressure and the substrate–target distance mainly affected the surface deposited layer of coating. A multilayered deposited structure appeared in the coating when working time was 5 h, which led to the degradation of coating.

Effect of target–substrate distance on the quality of AlN films grown on Si(110) substrates by pulsed laser deposition

Abstracts Effect of target–substrate distance on the quality of AlN films grown on Si(110) substrates by pulsed laser deposition (PLD) is carefully studied. It is found that the quality of AlN films is firstly improved and then is deteriorated as the target–substrate distance increases from 5 to 10 cm, and we find that 8 cm is the appropriate target–substrate distance for achieving high-quality AlN films on Si(110) substrates by PLD. The as-grown ~400 nm-thick AlN films show flat surface with a root-mean-square surface roughness of 1.8 nm. Meanwhile, there is no interfacial layer existing in the AlN/Si(110) interface. This work is paramount importance for the fabrication of AlN-based devices on Si(110) substrates by PLD.