Polycrystalline Zinc Research Articles

Impact of bias stress and endurance switching on electrical characteristics of polycrystalline ZnO-TFTs with Al2O3 gate dielectric

Abstract This study experimentally investigates electrical characteristics and degradation phenomena in polycrystalline zinc oxide thin-film transistors (ZnO-TFTs). ZnO-TFTs with Al2O3 gate dielectric, Al-doped ZnO (AZO) source–drain contacts, and AZO gate electrode are fabricated using remote plasma-enhanced atomic layer deposition at a maximum process temperature of 190 °C. We employ positive bias stress (PBS), negative bias stress (NBS), and endurance cycling measurements to evaluate the ZnO-TFT performance and examine carrier dynamics at the channel-dielectric interface and at grain boundaries in the polycrystalline channel. DC transfer measurements yield a threshold voltage of −5.95 V, a field-effect mobility of 53.5 cm2/(V∙s), a subthreshold swing of 136 mV dec−1, and an on-/off-current ratio above 109. PBS and NBS measurements, analysed using stretched-exponential fitting, reveal the dynamics of carrier trapping and de-trapping between the channel layer and the gate insulator. Carrier de-trapping time is 88 s under NBS at −15 V, compared to 1856 s trapping time under PBS at +15 V. Endurance tests across 109 cycles assess switching characteristics and temporal changes in ZnO-TFTs, focusing on threshold voltage and field-effect mobility. The threshold voltage shift observed during endurance cycling is similar to that of NBS due to the contrast in carrier trapping/de-trapping time. A measured mobility hysteresis of 19% between the forward and reverse measurement directions suggests grain boundary effects mediated by the applied gate bias. These findings underscore the electrical resilience of polycrystalline ZnO-TFTs and the aptitude for 3D heterogeneous integration applications.

Generation mechanism of optical surface in ultra-precision cutting polycrystalline zinc selenide

Despite having an excellent infrared optical property, efficient material removal of zinc selenide (ZnSe) is yet to be realized and its defect generation mechanisms during ultra-precision cutting are not fully elucidated. In this study, ultra-precision cutting experiments on polycrystalline ZnSe were conducted by considering various cutting parameters and utilising surface topography, chip morphology, cutting force, and X-ray diffraction data to investigate its surface generation mechanisms, which were further augmented by molecular dynamics simulations to analyse the generation and suppression of surface defects. The results revealed the presence of irregular microstructures on the surface of polycrystalline ZnSe, arising from variations in material rebound owing to differing grain orientations, as well as micron-sized craters located at grain boundaries and submicron-sized pits within individual grains. Increasing the cutting speed facilitated instantaneous grain fractures, thus preventing grain peeling and effectively suppressing the generation of micron-sized craters and material rebound. Although the use of a negative rake angle on the tool suppressed the generation of micron-sized craters, it introduced a proliferation of burrs that was detrimental to the surface finish. These findings provide valuable insights for optimising the ultra-precision machining process and enhancing the surface quality of brittle polycrystalline ZnSe.

Healing of discontinuities in metal by the strong electromagnetic field treatment

Abstract The results of a study microstructure of polycrystalline zinc specimens under by short pulses of the high-energy electromagnetic field treatment on them are presented. The aim is to study the possibility of healing micropores and microcracks inside the material during such treatment. The equipment used and the experimental technique are described, the analysis of the experimental data obtained is carried out. Metallographic studies of the zinc microstructure before and after HEEMF treatment confirm the assumption that in the process of such treatment, the decrease in its porosity may occur in the metal and, as a consequence, a significant increase in the ultimate plastic strain before fracture. Investigations of the polycrystalline structure of the metal have shown that the decrease in porosity is not the result of recrystallization.

Investigation of the Nonlinear Refractive Index of Polycrystalline Zinc Selenide by Single-Beam Z-Scan

Investigation of the Nonlinear Refractive Index of Polycrystalline Zinc Selenide by Single-Beam Z-Scan

Effect of different salt precursors on zinc ferrite synthesis and their photo-Fenton activity

Polycrystalline and mesocrystalline zinc ferrite were successfully fabricated via a solvo-thermal method using different salt precursors. This study found that when iron sulfate salt was used as a precursor, polycrystalline zinc ferrite was formed. Polycrystalline zinc ferrite is a well-dispersed 400-nm sphere solid particle. Primary nano-crystals have highly preferred orientations; however, defects exist among the particles. When iron chloride salt was used as a substitute as a prime material, mesocrystalline zinc ferrite was synthesised. The products are shaped as hollow-spheres with an average size of approximately 500 nm and are composed of nano-crystal sub-units aligned in a highly oriented crystallographic structure. Zinc ferrite mesocrystalline samples have many voids, and the inter-spaces of their structure indicate the high porosity hollow-sphere architecture of zinc ferrite. The experimental results show that specific adsorption of Cl− and SO42− ions on the surface plays a crucial role during the growth process of products with different morphologies and crystallographic structures. Cl− adsorption on the surface may promote the formation of mesocrystal hollow-sphere particles; whereas, SO42− gives rise to polycrystalline solid spheres. The use of the as-prepared products as catalysts for the photo-Fenton degradation of Rhodamine B (RhB) with an H2O2 oxidant under visible-light irradiation and the effects of reaction conditions, including pH, catalyst amount and H2O2 contratentation on the removal of RhB, were investigated. The reuse of the catalysts and a possible catalytic mechanism were also proposed. These results indicate that mesocrystalline hollow-sphere zinc ferrite is a favourable catalyst for dye degradation photo-Fenton processes.

Green Synthesis and Characterization of Zinc Oxide Using Carica papaya Leaf Extract

AbstractEnvironmental methodologies are gaining recognition in this modern world. Environmental nanotechnology plays a major role in improving modern fields of environmental engineering and science. Metal oxide nanoparticles have exceptional properties due to their small size, including quantum confinement, surface‐to‐volume ratio, plasmon excitation, high biocompatibility, and surface modifiability. The biosynthesis of nanoparticles using fungi, bacteria, and plants through various biotechnological techniques is currently a new paradigm for environmental protection. Synthesis of nanoparticles through plant extract is good because it eliminates the dangers of toxic chemicals, it is environmentally friendly, simpler, and safer as the reaction time is reduced and it can also be increased in size for higher operation. The present study is based on the development of zinc oxide nanoparticles from papaya leaf extract where zinc nitrate is used as a precursor. The biosynthesized nanoparticles are characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, electron microscopy, energy‐dispersive X‐ray analysis, UV‐visible spectroscopy, and dynamic light scattering analysis. The crystalline phase determination of the zinc oxide nanoparticles is analyzed by X‐ray diffraction and the formation of polycrystalline zinc oxide nanoparticles is confirmed. FT‐IR spectrum reveals the main functional groups and chemical information in zinc oxide nanostructures. Morphological analysis is performed using SEM at different magnification levels. EDAX analysis shows the purity of the composite samples. Optical characterization is performed using a UV–vis spectrophotometer. DLS analysis shows that the nanoparticles formed have a relatively well‐defined dimension.

Exploring physicochemical characteristics and antimicrobial efficacy of biosynthesized zinc oxide nanoparticles using Lantana Camara leaf extract

Polycrystalline Zinc oxide (ZnO) nanoparticles (NPs) were synthesized using an environmentally benign, and cost-effective way by using Lantana Camara leaf extract (LCLE). X-ray diffractogram of biosynthesized ZnO NPs depicted a wurtzite-type hexagonal crystal structure with P63mc space group as confirmed by the Rietveld refinement method. The phytochemicals such as saponins, flavonoids, and glycosides were detected in the Fourier transform infrared (FTIR) spectrum of LCLE@ZnO NPs. The characteristic hump positioned at 403 nm in the UV–Visible spectrum of biosynthesized ZnO NPs confirmed the formation of NPs. The thermal gravimetric and differential thermal analysis (TGA/DTA) was performed to check the stability of LCLE@ZnO NPs. The surface morphology of LCLE@ZnO NPs showed agglomeration with an average granular size of 24±0.49 nm as obtained from statistical analysis of the distribution of grain size. The antibacterial potential of LCLE@ZnO NPs was investigated in gram-positive bacteria: Staphylococcus aureus and Bacillus subtilis; gram-negative bacteria: Escherichia coli, and S. typhi strains, and it was observed that biosynthesized ZnO NPs exhibit maximum potency to inhibit the growth of harmful E. coli.

Investigation on the machinability of polycrystalline ZnSe by elliptical vibration diamond cutting.

Polycrystalline zinc selenide is widely used in advanced optical systems due to its superior optical properties. However, the soft and brittle properties bring a challenge for high-quality surface processing. In recent years, elliptical vibration cutting has been proven as a promising method for machining brittle materials. In the present research, a series of grooving and planning experiments were carried out to investigate the machinability of zinc selenide with elliptical vibration cutting. The removal mechanism was analyzed from fracture characteristics, chip morphology, and phase transformation. The results show that elliptical vibration cutting is effective in suppressing cleavage-induced craters. Reducing the nominal cutting speed is beneficial to inhibit the spring back-induced tearing of grains. A 94-time increase in the critical depth of cut was achieved by vibration trajectory optimization compared to ordinary cutting. Moreover, the influence mechanism of feed on the evolution of surface morphology was revealed. Finally, a zinc selenide microlens array was successfully fabricated. The performance was evaluated by geometric parameter measurements and a multiple imaging test. The findings provide a prospective method for ductile regime machining of zinc selenide.

Вивчення взаємодії інфрачервонопрозорих матеріалів ZnSe, ZnS, Si, Ge з розплавами металів

Wetting of infrared-transparent materials — selenide and sulfide zinc, germanium, and silicon by metal melts in a vacuum in a wide temperature range was studied by the sessile drop method using the method of capillary purification of the drop melt during the experiment. Pure metals In, Sn, Pb, Al, Fe, Ni, binary Al—Si, Ge—Si, In—Cu and multicomponent In—Sn—Cu—Ti alloys were used. When zinc chalcogenides are wetted with In—Sn—Cu—Ti melts, zinc selenide is wetted better than zinc sulfide. This is due to the lower thermodynamic stability of selenide. In systems where copper is present in melts, wetting is affected not only by the interaction of selenium or sulfur with titanium, but also by the interaction of copper and zinc (in the copper-zinc system, solid solutions of copper and zinc are formed and copper dissolves in solid zinc). This conclusion also confirms the wetting of the substrate by the In—Cu melt. The values of the contact angle at 650 C are equal to 32, which is less than for the In—Sn—Ti melt at the same temperature. It can be said that for such a system, the interaction of zinc with copper is very important, which is not inferior to the wetting effect of the interaction of chalcogens with titanium. The wetting of single crystals of germanium and silicon by metal melts improves with increasing temperature. Iron and nickel wet silicon (contact angles close to zero) at temperatures lower than their melting point. Contact melting also occurs when silicon substrates are wetted with aluminum melts (the eutectic in the Al—Si system has a temperature of 577 °C). Germanium is better wetted by tin than by indium and lead. Technological processes of soldering infrared transparent materials with metals were developed and soldered joints were obtained. Keywords: infrared transparent materials, polycrystalline zinc selenide and sulfide, single crystals of germanium and silicon, wetting, soldering.

Carrier–phonon interaction and anharmonic phonon decay in ZnS thin film studied by resonance Raman scattering

AbstractResonance Raman scattering was carried out on polycrystalline zinc sulfide (ZnS) thin film. The resonance Raman spectra revealed strong carrier–phonon interaction where longitudinal optical phonon (LO) with overtones up to the fourth order and its combination phonons with transverse acoustic (TA) phonons were observed, namely, nLO + mTA (where n and m are integers). The resonance Raman scattering processes were well explained within the framework of the cascade scattering model. The wavenumber of the LO phonon with increased temperature was dominated by anharmonic phonon decay. Detailed experimental data fittings showed that thermal expansion contribution to the nLO phonon overtones differed from the fundamental LO phonon due to the involvement of the scattering of the LO phonons at the Brillion zone edge. The negative value of the mode‐Grüneisen parameter for the TA phonon slowed down the wavenumber shift of the combination nLO + mTA phonon modes with increasing temperature compared to the nLO phonons. The anharmonic phonon decay of combination nLO + mTA phonons were dominated by anharmonic phonon decay of nLO phonons.

Microstructure Evolution of Polycrystalline Zinc during Tensile Testing at Room Temperature

Microstructure Evolution of Polycrystalline Zinc during Tensile Testing at Room Temperature

Extreme nonlinear optics in a long pulse regime: High harmonic generation of picosecond mid-IR pulses in polycrystalline zinc selenide.

High harmonic generation (HHG) in semiconductors has been extensively studied recently in the high-intensity limit using middle infrared (mid-IR) femtosecond laser pulses resulting in emission spectra of self-phase modulated harmonics resting on top of a broadband continuum. In this report, a different approach to HHG in polycrystalline zinc selenide (poly-ZnSe) was explored utilizing a relatively low power regime (1-40 GW/cm2) and much longer (30 ps) mid-IR laser pulses. Through a combination of low power, picosecond excitation, and narrowband (<10 nm full width at half maximum) mid-IR excitation, the nonlinear optical effects in poly-ZnSe could be isolated and studied independently. From the clearly distinguishable HHG peaks, harmonic conversion efficiencies of 10-4-10-12 for second to ninth harmonic in poly-ZnSe were measured, and the relationship between the Nth harmonic intensity and excitation intensity (I0) was found to follow a power law, I0x with x ≤ N/2, as a result of the random quasi-phase matching process.

Effective medium method in solution of the elastic and thermo-elastic homogenization problems for polycrystals with spheroidal transverse isotropic grains

Self-consistent effective medium method is used for determination of the effective elastic and thermo-elastic properties of polycrystalline materials with spheroidal transverse isotropic grains. The grains with arbitrary aspect ratios including very oblate (disks) and very prolate (fibers) spheroids are considered. The function of the Owens-March type is used for description of distribution of grains over orientations. The equations for the effective elastic stiffness tensor and the tensor of effective coefficients of thermo-expansion of polycrystals are derived using integral equations for elastic and thermo-elastic fields in heterogeneous media and the hypotheses of the effective medium method. The numerical algorithm of the method is described in detail. Numerical examples are presented for polycrystalline clay rock materials with strongly anisotropic grains and for polycrystalline zinc. Graphs of the dependences of the effective elastic constants and effective coefficients of thermo-expansion of the polycrystals on the parameters of the orientation distribution function and aspect ratios of grains are presented.

Mesoporous Zn2SnO4 for efficient sensing of ethylene glycol vapor

Within this study, mesoporous Zn2SnO4 nanostructures have been prepared by a facile and eco-friendly hydrothermal method. Through X-ray diffraction analysis, a polycrystalline zinc tin oxide structure is recognized with a cubic inverse spinel phase crystal structure. By Field emission scanning electron microscopy method, various morphologies based on the hydrothermal time ranging from the cubic-like morphology, irregular hexagonal plates, and large quantity of microspheres to the truncated octahedron have been observed. By the aid of Energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy analyses, the atomic ratio and characteristic vibration peaks of Zn2SnO4 have been evaluated. By the help of Brunauer–Emmett–Teller analysis, specific surface area, mean pore diameter, and total pore volume were measured. The nanostructured Zn2SnO4 prepared in 36 h hydrothermal treatment (as a selected sample) showed a higher BET specific surface area (9.10 m2/g) and total pore volume (0.078 cm3/g) than the other samples. The gas-sensing performance of the samples was investigated towards different vapors. The optimum operating temperature (270 °C), transient response, response/recovery times, and long-term stability (eight months) of the samples have been evaluated. For the selected sample, appreciable sensing response (92.92 toward 100 ppm ethylene glycol), the ultra-fast response time (1 s), excellent selectivity (about 6–23 times more than other tested vapors) and excellent long-term stability (the response decay of about 10% after eight months) has been perceived which makes it a promising gas sensor. It seems that the selected sample has shown relatively better performance for two reasons: Firstly, high crystalline quality (largest crystallite size and lowest strain value) which can affect the combination or separation of adsorbed oxygen species on the surface of the material. Secondly, the higher specific surface area and the relatively larger total pore volume can lead to more gas adsorption sites leading to further narrowing of the depletion layer and resulting in a high and very fast response.

Cyclic growth and tillering of layered polycrystalline zinc hydroxide sulfate and the resulting dendritic fractals

Two-dimensional dendritic fractals of layered zinc hydroxide sulfate (LZHS) were allowed to grow on a porous ZnO substrate-coated glass slide in an aqueous ZnSO4 solution through the dissolution-redeposition process. The generated LZHS seeds with polycrystalline structure gradually evolved into two-dimensional dendritic fractals with a diameter of 50∼100 μm through a plant-like growth mode involving tillering and the formation of layered tiller buds at branch ends. Such tiller mechanism is proposed to explain the evolution of LZHS fractals based on results obtained by the scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and energy dispersive X-ray detection. The synthesized polycrystalline LZHS fractals can be topologically converted into hierarchical nanostructured zinc oxide by thermal pyrolysis combined with an alkaline wash process. After the modification by octyltrimethoxysilane, the topological zinc oxide surfaces, corresponding to the immersion time of 2, 4 and 6 h, showed superhydrophobic property with a water contact angle of 153.4°, 157.6°, and 164.7°, respectively. The enhanced hydrophobicity of zinc oxide films compared with the porous ZnO substrate surface is mainly attributed to the topological fractal morphologies and hierarchical nanostructures.

Application of hot isostatic pressing to improve the optical performance of polycrystalline zinc sulfide

The hot isostatic pressing of zinc sulfide, obtained by chemical vapor deposition technology, are studied to improve its quality characteristics. As a result of the studies carried out in the visible and near IR regions of the spectrum, the transmission of the treated samples was increased by 6-7 times compared to the untreated ones. In the wavelength range of 3-10 μm, the light transmission of the treated samples reached the theoretical limit. Keywords: chalcogenides, zinc sulfide, chemical vapor deposition, hot isostatic pressing.

Surface hardness of pristine and laser-treated zinc as a function of indentation load and its correlation with crystallite size valued by Williamson-Hall analysis, size-strain plot, Halder-Wagner and Wagner-Aqua models

To get a range of crystallite size, 5 N pure polycrystalline zinc specimens were shined with 50–100 Nd:YAG laser shots. Williamson-Hall, Size-Strain Plot, Halder-Wagner, and Wagner-Aqua models were employed to evaluate the crystallite size and lattice strain of pristine and laser-treated specimens. Surface hardness of the specimens were measured under 0.2 and 0.3 kgf indentation loads for 10 s. In each case, the surface hardness followed inverse Hall – Petch Relation. For a fixed number of laser shots, the surface hardness was greater for 0.2 kgf indentation load than that for 0.3 kgf. The surface hardness of pristine zinc specimen increased on treatment with 50 laser shots. With further rise in laser shots up to 80, the surface hardness progressively decreased close to that of pristine specimen. Later, it again increased for 90 laser shots and then slightly decreased for 100 laser shots.

Random quasi-phase-matching for pulse characterization from the near to the long wavelength infrared.

Experiments requiring ultrafast laser pulses require a full characterization of the electric field to glean meaning from the experimental data. Such characterization typically requires a separate parametric optical process. As the central wavelength range of new sources continues to increase so too does the need for nonlinear crystals suited for characterizing these wavelengths. Here we report on the use of poly-crystalline zinc selenide as a universal nonlinear crystal in the frequency resolved optical gating characterization technique from the near to long-wavelength infrared. Due to its property of random quasi-phase-matching it's capable of phase matching second-harmonic and sum-frequency generation of ultra-broadband pulses in the near and long wavelength infrared, while being crystal orientation independent. With the majority of ultra-fast laser sources being in this span of wavelengths, this work demonstrates a greatly simplified approach towards ultra-fast pulse characterization spanning from the near to the long-wavelength infrared. To our knowledge there is no single optical technique capable of such flexible capabilities.

Effect of 4He2+ ion irradiation on the optical, electrical, morphological, and structural properties of ZnO thin films

A study of the effect of 2.5 MeV 4He2+ ion irradiation on the optical, electrical, morphological and structural properties of ZnO thin films is presented. Polycrystalline zinc oxide thin films were deposited on soda lime glass substrates using the spray pyrolysis technique. During the process, the substrates’ surfaces were kept at 400, 450 and 500 °C. The samples were analyzed by different techniques and the optical results showed a red shift in the energy band gap after irradiation. It was also confirmed that the wurtzite-type hexagonal structure of the ZnO films remained after irradiation, the crystallite size increased and the lattice parameters decreased due to He2+ irradiation. SEM micrographs revealed that ion irradiation favors the nucleation and the formation of grains in the films. Micrographs showed nanometric particles with spherical and flake-like forms, which depend on the deposition temperature. A decrement in the average particle size of the samples deposited at 400 and 450 °C was observed after irradiation; meanwhile, an increase in the particle size was detected in the film deposited at 500 °C. The resistivity values increased with He2+ ion irradiation.

Near infrared performance of a pile-of-plates polariser based on poly-crystalline Zinc Selenide

Zinc Selenide (ZnSe) has wide transparency from 0.6 μm–18 μm making it a desirable substrate for infrared (IR) optical applications. We present experimental results on the NIR transmission of a pile-of-plates polariser at 780 nm and 1.06 μm based on polycrystalline ZnSe plates tilted at Brewster's angle. Due to the high refractive index of ZnSe, n ∼2.5, the degree of polarisation (DOP, V) at λ = 780 nm and 1.06 μm reached V = 0.98 and 0.97 respectively with 4 plates and an extinction ratio E < 10−2 at 780 nm. The calculated DOP for 1–4 plates agree well with theory when allowance is made for internal surface reflections, as in the Airy expressions. While the DOP achieved with 4, 1 mm thick plates is relatively high, the absolute transmission for the P component (TP = 0.83, 0.84 respectively) is much lower than expected, based on the NIR extinction coefficients k < 10−6 (780 nm) and k ∼10−7 (1.06 μm), inferring TP > 0.96. The source of this absolute loss has been considered, including residual surface scatter, diffuse scatter from grain boundaries in the polycrystalline micro-structure and the likely effect of residual birefringence. This loss, we believe is primarily due to residual surface scatter in thin crystal lattice damage layers created during the polishing process and observed when using a hand-held near infrared (NIR) camera. This scatter is polarisation dependent as expected but much higher than scatter theory predicts, consistent with crystalline surface damage. A 6-plate assembly demonstrated an extinction ratio of 1/600 and transmission Tp ∼0.72 at 1.06 μm. The very low absorption and dispersion in ZnSe, particularly at longer wavelengths infer that this polariser would work well in the important MIR region.