Cross-sectional Scanning Electron Microscopy Research Articles

Impact of acetic acid exposure on metal contact degradation of different crystalline silicon solar cell technologies

Degradation due to acetic acid in photovoltaic (PV) modules has been a commonly observed phenomenon for both damp-heat exposure and outdoor operations. Acetic acid is a degradation byproduct of ethylene-vinyl acetate (EVA), a common module encapsulant. To address this issue, robust metallization pastes and cell technologies are being developed. However, it is important to assess how these technologies perform in an acetic acid environment and withstand degradation before they are implemented in the solar market. In this work, we investigate the impact of acetic acid exposure on four different cell groups: monofacial passivated emitter and rear contact (PERC) cells with advanced telluride-based front contact pastes, bifacial PERC cells with novel aluminum rear contact pastes, bifacial tunnel oxide passivated contacts (TOPCon) cells, and silicon heterojunction (SHJ) cells. These cells were exposed to acetic acid for different time increments. The recombination losses were characterized by Suns- V OC , and multi-variate regression analysis of intensity-dependent photoluminescence (PL) images with Griddler AI. Resistive losses were tracked with the transmission line method (TLM). Samples showing severe performance degradation were selected for further materials characterization to understand the root cause. Top-down and cross-sectional scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were performed to investigate the change in materials properties. Our study shows that the front contacts of the bifacial TOPCon cells and monofacial PERC cells were significantly affected by acetic acid exposure. The SHJ cells were found to be the most stable. • Effect of acetic acid on metallization pastes and cell technologies was investigated. • Front Ag-Al contacts for Bifacial TOPCon cells degrade the most due to acid exposure. • Monofacial PERC cells with Pb-free Te-O paste is the second group that is affected. • Bifacial PERC cells were stable with Al back contacts showing no signs degradation. • SHJ cells were the most stable group in this experiment.

Synthesis of a large area ReS2 thin film by CVD for in-depth investigation of resistive switching: effects of metal electrodes, channel width and noise behaviour.

The anisotropic crystal structure and layer independent electrical and optical properties of ReS2 make it unique among other two-dimensional materials (2DMs), emphasizing a special need for its synthesis. This work discusses the synthesis and in-depth characterization of a 1 × 1 cm2 large and few layered ReS2 film. Vibrational modes and excitonic peaks observed from the Raman and photoluminescence (PL) spectra corroborated the formation of a ReS2 film with a 1.26 eV bandgap. High resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) patterns inferred the polycrystalline nature of the film, while cross-sectional field emission scanning electron microscopy (FESEM) indicated planar growth with ∼10 nm thickness. The chemical composition of the film analysed through X-ray photoelectron spectroscopy (XPS) indicated the formation of a ReS2 film with a Re : S atomic ratio of 1 : 1.75, indicating a small amount of non-stoichiometric RexSy. Following the basic characterization studies, the ReS2 film was tested for resistive switching (RS) device application in which the effects of different metal electrodes (Pt/Au and Ag/Au) and different channel widths (200, 100, and 50 μm) were studied. The highest memory window equal to 108 was obtained for the Ag/Au electrode while Pt/Au showed a memory window of 102. RS for the former was ascribed to the formation of a conducting filament (CF) because of the migration of Ag+ ions, while defect mediated charge carrier transport led to switching in the Pt/Au electrode. Furthermore, the RHRS/RLRS ratio achieved in this work (108) is also of the highest magnitude reported thus far. Furthermore, a comparison of devices with Ag/Au electrodes but with different channel widths (50, 100 and 200 μm) gave insightful results on the existence of multiple resistance states, device endurance and retention. An inverse relationship between the retention time and the device's channel width was observed, where the device with a 50 μm channel width showed a retention time of 48 hours, and the one with a 200 μm width showed stability only up to 3000 s. Furthermore, low frequency noise measurements were performed to understand the effect of defects in the low resistance state (LRS) and the high resistance state (HRS). The HRS exhibited Lorentzian noise behaviour while the LRS exhibited Lorentzian only at low current bias which converged to 1/f noise at higher current bias.

A Study on Aging Fracture Behavior of Sintered Joint by Bi-Modal Cu Paste

Power semiconductors for automobiles were joined by high Pb soldering to joint properties at high temperatures during operations. However, this process is being replaced by low-temperature sintering. In the low-temperature sintering bonding method, Cu powder is low-cost and exhibits high-performance material and excellent bonding properties. In this study, the effect of high-temperature aging on Cu paste sintered joints and the failure mechanism of the shear test were investigated. Cu monomodal and bimodal pastes were manufactured, and electroless nickel immersion gold (ENIG) surface treatment was applied on the Cu chip side. In the ENIG-treated joints, a significant number of Kirkendall voids were observed at the interface under Au after 2,000 h at 200 °C, and Cu2O was also formed. This is attributed to the difference between the interdiffusion coefficients of Au and Cu, which decreases the shear strength of the junction and rapidly increases the electrical resistance. After the shear strength tests, the crack propagation pattern at the interface of the ENIG-treated joint was confirmed via cross-section scanning electron microscopy. Future studies on surface treatment are required to clarify the long-term stability of the joints.

Electroplating on Al6082 Aluminium: A New Green and Sustainable Approach

Aluminium and its alloys are interesting for many applications because they are very light, cheap, and unlimitedly recyclable. Despite being a promising base material for the fashion-jewellery sector, their tendency to form a passivating film makes them difficult to be galvanized, even more when recycled aluminium contains impurities of refractory elements. Indeed, the most common processes for galvanising aluminium are often expensive and not environmentally sustainable because they involve the use of cyanides. In this work we focussed on the pre-treatments and electroplating on Al6082 aluminium which is largely used for fashion-jewellery applications. The objective of the present study was to assess whether Al6082 series aluminium is suitable a as base material for the fashion market; therefore, we investigated the effectiveness of plating pre-treatments and the success of electroless zinc deposition using an innovative alkaline cyanide-free zincate solution. After the electroplating, adhesion between the deposited layers was evaluated both with cross-sectional scanning electron microscope (SEM) analysis as well as with an adhesion evaluation test (ISO2819:2018): no detachments confirmed the positive test outcomes and thereby highlighted that Al6082 can be exploited as base material in the fashion-jewellery market.

Relationship between Reflectivity, Chemical Composition and Mechanical Behaviour of Orthodontic Bonding Nanofiller Resin Materials: A Proposal of an Alternative Method of Investigation

Background: Relationships between reflectivity, hardness and chemical composition of the dispersed phase, included in orthodontic composites Transbond XTTM (Trans), Light-Cure Orthodontic Paste (Leone) and Bisco Ortho Bracket Paste LC (Bisco), were investigated in vitro to evaluate whether reflectivity results can be useful in internal material composition interpretation, thus obtaining information on mechanical behaviours. Methods: Light transmission through 36 resin discs was measured with a UV/Vis spectrophotometer, evaluating the spectral range from 190–1100 nm. To have a benchmark of material hardness and internal composition, Vickers measurements and Cross-Sectional Focus Ion Beam Scanning Electron Microscopy (FIB/SEM) analysis were provided. Results: Bisco has the highest reflectivity, Leone shows an absorption pattern in the UV region similar to Bisco and Transbond has the lowest reflectivity compared to the others. This trend is confirmed by FIB/SEM imaging, showing a more similar induced roughness and internal composition for Bisco and Leone, with respect to Transbond. Higher filler presence in the composition of Bisco and Leone justifies a higher hardness of these two materials, with respect to Transbond, as confirmed by Vickers measurements. Conclusions: Bisco and Leone show similar optical responses and similarities in mechanical performance. This statement is explained by the lower and similar filler content as confirmed also by FIB/SEM analysis. The inner composition of Bisco and Leone provides a higher value of microhardness, as demonstrated by Vickers measurements. Therefore, this study confirms that the UV-Vis analysis can also offer a significant overview on the internal material composition, thus indirectly providing information on the mechanical properties of orthodontic composites.

Conformal chemical vapor deposition of boron-rich boron carbide thin films from triethylboron

We report conformal chemical vapor deposition (CVD) of boron carbide (BxC) thin films on silicon substrates with 8:1 aspect-ratio morphologies, using triethylboron [B(C2H5)3] as a single source CVD precursor. Step coverage (SC) calculated from the cross-sectional scanning electron microscopy measurements shows that films deposited at ≤450 °C were highly conformal (SC = 1). We attribute this to the low reaction probability at low substrate temperatures enabling more gas phase diffusion into the features. The chemical state of the material, determined by x-ray photoelectron spectroscopy, shows as a carbide with B–B, B–C, C–B, and C–C chemical bonds. Quantitative analysis by time-of-flight elastic recoil detection analysis reveals that films deposited at 450 °C are boron-rich with around 82.5 at. % B, 15.6 at. % C, 1.3 at. % O, and 0.6 at. % H, i.e., about B5C. The film density as measured by x-ray reflectometry varies from 1.9 to 2.28 g/cm3 depending on deposition temperature.

Deep precision machining of SiC ceramics by picosecond laser ablation

Silicon carbide (SiC) ceramic is becoming widely used in multiple industrial applications, owing to its exceptional high-temperature properties. Yet it is still a challenge to machine SiC using traditional means without causing damage due to its high hardness and brittleness. In this study, a subtractive manufacturing technique based on the use of a fiber picosecond laser was employed to remove material from the reaction bonded SiC surface or create micro-patterns with the minimum damage to the surface, maximum surface quality and precision. Multiple laser processing parameters were investigated with the purpose of obtaining deep high-quality cuts with the minimum surface roughness and the minimum amount of the re-deposited material. The heat affected zone was analyzed by grazing angle X-ray diffractometry, cross-sectional scanning electron microscopy, energy dispersive and micro Raman spectroscopy techniques. The cut shape, depth, surface roughness as well as the kerf width and re-deposition height were assessed using a 3D laser scanning microscopy. The optimum values were established for the focal position, the laser power, linear speed, wobble frequency, wobble pattern, and number of passes. This study also identified the processing parameters for shallow and deep high-precision SiC cutting at a material removal rate of ∼2 mm3/min. The work demonstrated that the developed laser machining process is an efficient subtractive manufacturing tool that can be integrated into the automated precision cutting systems for machining hard ceramic materials such as SiC and alumina.

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Automated measurement method based on deep learning for cross-sectional SEM images of semiconductor devices

Feature length measurement in cross-sectional scanning electron microscopy images of modern semiconductor devices is time-consuming and laborious. We propose an automated measurement method based on deep learning technology and applied it to trench pattern images. The method combines two image-recognition tasks: (1) object detection for determining the coordinates of each unit of a pattern and (2) semantic segmentation for obtaining the boundaries of each area (mask, substrate, and background). By combining the results of these two tasks, typical feature lengths, such as width and depth, are precisely and immediately measured. The extraction speed of the proposed method is 240 times faster than manual measurement and provides measurement results independent of the engineer’s skills.

Mesogen-jacketed liquid crystal like block copolymers: synthesis and self-assembly to prepare 1D PC thin films

One dimensional photonic crystals (1D PCs) show great potential application in light control, sensors and functional displays. Self-assembly of block copolymer is a facile method to prepare 1D PCs in large area and easy processing. However, due to the low refractive index of polymer and the chain entanglement at very high molecular weight, it is difficult to prepare 1D PCs by self-assembly of linear block copolymers. In this work, mesogen-jacketed liquid crystals like block copolymers with two different lumbar connected benzene terephthalate derivatives and polynorbornene backbone are designed and synthesized. The big steric hindrance of the mesogenic benzene terephthalate derivatives extends the polymer backbone to be rigid, and the resultant block copolymers are rapidly self-assembled into lamellar structures with big domain spacing. The refractive indexes of the two blocks is differentiated by selecting the phenyl and decyl substitute group of benzene terephthalate derivatives. Hence, 1D PCs are prepared by self-assembly of mesogen-jacketed liquid crystals like block copolymers. The maximum reflectance is ranged from ultraviolet to near infrared by increasing the polymerization degree of the block copolymers from 400 to 1400 gradually. The lamellar structures are characterized by cross section scanning electron microscope and small angle X ray scattering. Mesogen-jacketed liquid crystal like block copolymer is favored in 1D PC preparation for its facile synthesis and flexible structure design.

Kinetic influences on void formation in epitaxially regrown GaAs-Based PCSELs

We report an investigation into the formation of crystallographic voids during the metalorganic vapour phase epitaxial regrowth of GaAs photonic crystal structures. We employ a combination of cross-sectional scanning electron microscopy and scanning transmission electron microscopy to study structures regrown with AlAs, AlGaAs and GaAs. The change in regrowth material allows the effect of adatom diffusion kinetics on the void structure to be assessed. Whilst complete grating infill is observed for GaAs, void formation is promoted for Al-containing materials, with void size increasing with Al mole fraction, in line with reduced adatom mobility. In the case of both AlAs and AlGaAs-regrown structures, a degree of asymmetry is observed in the shape of the voids within the plane of the photonic crystal. These differences are attributed to variations in group-III adatom surface mobility and the polarities of high-index crystal planes along orthogonal crystal directions. Two growth regimes of stable and dynamic faceting are observed in cross-sections containing crystal planes with A- and B-type polarities, respectively.

Hybrid carbon molecular sieve membranes having ordered Fe3O4@ZIF-8-derived microporous structure for gas separation

Carbon molecular sieve (CMS) membranes have great promise in CO2 capture. However, tortuous transport passageways restrict the enhancement in the permeability due to the presence of disordered porous structure and dead-end pore. Herein, the growth of ZIF-8 layer on the surface of Fe3O4 formed magnetic core-shell Fe3O4@ZIF-8 particles, which were fixed into 6FDA/ODA:DABA polyimides under magnetic field-induction to fabricate a precursor membrane with vertically oriented chain-like particles. It was then pyrolyzed to form hybrid carbon molecular sieve (HCMS) membranes with ordered microporous structure under high temperature conditions. The cross-section scanning electron microscopy images and N2 adsorption for resultant HCMS membranes indicate that Fe3O4@ZIF-8-derived carbons frameworks were vertically oriented to form the ordered microporous structure, which also had good compatibility with carbon matrix stemmed from 6FDA/ODA:DABA polyimides. The as-prepared HCMS membranes embedded with 5 wt% Fe3O4@ZIF-8 manifested a highest gas separation performance (permeability of 5130 Barrer; CO2/N2 selectivity of 29; CO2/CH4 selectivity of 48), outperforming the pristine CMS membranes, which were near and beyond 2019 CO2/N2 and CO2/CH4 upper bounds, separately. These good separation performances resulted from vertical chain-like microporous particles, which provided fast transport channels to accelerate CO2 diffusion rate. In addition, we supposed that Fe3O4 prevent ZIF-8 frameworks from destruction during the pyrolysis and promote the size screening capability. More importantly, this membrane exhibited excellent aging resistance over 30 days aging testing compared to pristine CMS membranes. Therefore, it affords a feasible way for carbon capture from flue gas and natural gas.

Thermally conductive 2D filler orientation control in polymer using thermophoresis

To achieve efficient heat dissipation using polymer composites, it is important to optimize the heat conduction pathway. Therefore, manipulating the orientation of thermally conductive and anisotropic fillers in composites represents a judicious strategy. So far, external fields have been applied to align fillers within the matrix. However, these processes are energy-intensive and require stimuli-responsive fillers through surface modification, further complicating the process and deteriorating filler thermal conductivity. Herein, to these ends, a facile method for manufacturing composite with an orientation-controlled model anisotropic filler, hexagonal boron nitride (h-BN), was proposed by harnessing thermophoresis. Thermophoresis causes movement and/or rotation of solid particles in a fluid with a steady temperature gradient. A suspension of UV-curable monomer with well-dispersed h-BN was subjected to a temperature gradient, inducing filler rotation via thermophoresis. A subsequent photo-curing yielded a solid composite with the frozen h-BN aligned in a direction agreed with expected for thermophoresis, as indicated by the anisotropic thermal conductivity measurement and cross-sectional scanning electron microscopy (SEM) observation. Additionally, the theoretically estimated Peclet number, induced by thermophoresis, was higher than the experimentally determined value required to align suspended h-BN. To our best knowledge, the current study is the first experimental demonstration of controlling anisotropic filler orientation using thermophoresis.

Quantifying the Relationship Between Microstructure and Performance in Gadolinium-Doped Ceria Infiltrated Ni/YSZ Symmetric Cells

Infiltration of mixed ionic/electronic conducting nanocatalysts into the anodes of solid oxide fuel cells allows the hydrogen oxidation reaction to occur at double-phase boundaries (DPBs) rather than being confined only to the triple-phase boundaries (TPBs). In this research, we use a combination of cross-sectional scanning electron microscopy, three-dimensional (3D) reconstruction, and electrochemical methods to characterize both baseline and gadolinium-doped ceria (GDC)-infiltrated symmetric cells, with the goal of establishing a comparison between the density of electrochemically active sites in uninfiltrated and GDC-infiltrated cells. Electrochemical impedance spectroscopy and distribution of relaxation times analysis showed GDC infiltration decreased the overall polarization of the anode by a factor of 8.78× and decreased the resistance associated with the reactions at the TPBs/DPBs by a factor of over 21×. By quantifying expected GDC deposition morphology in the Ni/YSZ anode, it is estimated that reactions occur in the baseline cell up to 84 nm from the active TPB lines.

Granulation of Bismuth Oxide by Alginate for Efficient Removal of Iodide in Water.

The granulation of bismuth oxide (BO) by alginate (Alg) and the iodide adsorption efficacy of Alg–BO for different initial iodide concentrations and contact time values were examined. The optimal conditions for Alg–BO granulation were identified by controlling the weight ratio between Alg and BO. According to the batch iodide adsorption experiment, the Alg:BO weight ratio of 1:20 was appropriate, as it yielded a uniform spherical shape. According to iodide adsorption isotherm experiments and isotherm model fitting, the maximum sorption capacity (qm) was calculated to be 111.8 mg/g based on the Langmuir isotherm, and this value did not plateau even at an initial iodide concentration of 1000 mg/L. Furthermore, iodide adsorption by Alg–BO occurred as monolayer adsorption by the chemical interaction and precipitation between bismuth and iodide, followed by physical multilayer adsorption at a very high concentration of iodide in solution. The iodide adsorption over time was fitted using the intraparticle diffusion model. The results indicated that iodide adsorption was proceeded by boundary layer diffusion during 480 min and reached the plateau from 1440 min to 5760 min by intraparticle diffusion. According to the images obtained using cross-section scanning electron microscopy assisted by energy-dispersive spectroscopy, the adsorbed iodide interacted with the BO in Alg–BO through Bi–O–I complexation. This research shows that Alg–BO is a promising iodide adsorbent owing to its high adsorption capacity, stability, convenience, and ability to prevent secondary pollution.

Few-Layer Graphene As an Electrode, Electrode Additive and an Interfacial Layer in Aqueous Supercapacitors

The intermittent nature of many renewable energy sources such as wind and solar, coupled with fluctuations in energy demand, creates a pressing need for efficient, low-cost energy storage technologies. Supercapacitors are promising candidates to play a role in next-generation energy storage systems. They have a higher power density and better cycle life (although lower energy density) than batteries making them ideal for rapid energy storage and deployment [1]. Activated carbon is a favoured electrode material due to high surface area, although low conductivity requires use of a conductive additive (often carbon black), reducing available surface area for charge storage. In contrast, the high conductivity and specific surface area of graphene has made it a promising material for electrochemical double layer supercapacitors (EDLCs) [2], however, performance is limited by restacking of the graphene sheets, reducing available surface area.In this work, high-shear exfoliated few layer graphene (FLG) [3] is investigated both as an electrode material and as a conductive additive/interfacial layer for EDLCs. FLG suspensions were produced under a variety of exfoliation conditions, with platelet thickness and linear dimension determined from Raman spectroscopy based on metrics developed by Backes et al. [4] and through scanning electron microscopy (SEM).The FLG suspensions were used in three ways: i) to create thin ‘graphene paper’ electrodes; ii) as a conductive additive, mixed into the activated carbon electrode material; iii) deposited onto the back of (and diffused within) activated carbon electrodes. These electrodes were investigated by Raman spectroscopy and Scanning Electron Microscopy, before being assembled into symmetric two-terminal aqueous cells then evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS), and their electrochemical performance related to structure and composition.As expected, pure FLG electrodes often showed excellent low series resistance values, however specific capacitance was low, due to restacking. Directly mixing 5% FLG into activated carbon as a conventional conductive additive led to a specific capacitance of 63 F/g (from CV at 10 mV/s), and a series resistance of 19 W (from GCD at 1 A/g) - markedly inferior to those with 5% carbon black as a conductive additive (95 F/g and 2 Ohm) and inferior even to electrodes with no conductive additive (87 F/g and 10 Ohm).However, post fabrication deposition/infusion of FLG offers comparable performance to carbon black (90 F/g and 1 Ohm) at 7% FLG by weight. As the quantity of FLG is increased the specific capacitance decreases sharply. This behaviour is attributed to FLG restacking on the rear of the electrode, so adding mass whilst providing limited additional capacitance, and compression of the electrode.Adding high-shear exfoliated FLG to activated carbon electrodes shows promise for obtaining the benefits of both materials. At present, FLG/activated carbon electrodes can match the performance of those produced from activated carbon with a carbon black conductive additive and, with further optimization, we expect will be able to exceed them.Figure: a) Cross sectional SEM image of activated carbon electrode with graphene interfacial layer; b) magnified cross sectional SEM image of graphene interfacial layer; c) cyclic voltammograms at 10 mV/s of the different electrodes mentioned in the abstract.

Fabrication of AAO-Based Four-Stack Thin Film Solid Oxide Fuel Cells for the Low-Temperature Operation Using Sputtering Method

Anodic Aluminium Oxide (AAO) based four thin-film solid oxide fuel cell (TF-SOFC) stack was fabricated. The fuel cell stack was tested and analyzed at the low-temperature window. Since the low-temperature operation has many advantages, such as lowering the system cost and widening the material selection, there has been much effort to reduce conductive resistance, mainly at the electrolyte, which is the most problematic issue in low-temperature operation. One of the solutions is TF-SOFC deposited on the various substrates or supporting materials. AAO, a non-conductive and nanoporous substrate, has been widely used in fabricating TF-SOFC as a substrate because of its uniformly arranged pores and highly developed manufacturing process.However, AAO is a poor template for stacking TF-SOFCs because it has lower mechanical strength than metal, has no electrical conductivity, and has a different coefficient of thermal expansion from metal. In this study, therefore, planarly stacked TF-SOFC were fabricated to expand its limits of use as a template for the stacked fuel cell. Nickel-based anode, yttria-stabilized zirconia (YSZ) electrolyte with functional layers, and platinum cathode and current collector were sequentially deposited using sputtering and atomic layer deposition methods. All thin-film components of four cells were deposited on the AAO at the same time, making good connections between each electrode. By effectively setting the deposition process, unnecessary pores of AAO were blocked, and current collecting layers were stably formed in between the structure of the cells with a step difference.Then, the stacked TF-SOFC were electrochemically analyzed, including the current density-voltage-power density curve (i-V-P curve) and electrochemical impedance spectroscopy (EIS) being compared to a single cell. The microstructure of the fuel cell and its electrically connected structures were observed by scanning electron microscopy (SEM) and focused ion beam (FIB) cross-sectional SEM analyses. The cell’s overall voltage was comparable to four times that of a single cell, and the power density was obtained. We revealed the correlation between the electrochemical performance and the microstructure of individual cells and the whole stack. The full stack achieved electrochemical and mechanical stability by forming a complete fuel cell structure and enhanced the applicability of the planar cell stack on the AAO substrate.

Thickness-Based Dispersion in Opal Photonic Crystals

Photonic crystals (PhCs) are types of colloidal crystals which demonstrate a host of exciting optical phenomena, the nature of which can lend insight into their structure and enable a range of potential applications in fields such as optics and optoelectronics,1 energy storage,2-6 and sensors for environmental monitoring, biomedicine and food preservation.7 Artificial opals8 are PhCs which can be formed easily using low-cost self-assembly methods and their structures are composed of highly ordered, close-packed, polymeric sphere arrays. While the optical behaviour of opals has received significant attention over the last number of decades, there is limited information on the effect of crystal thickness on the optical properties they display. Most studies focus their attention on the lattice parameters and refractive index contrast within the materials.9,10 Here, the relationship between volume fraction and crystal thickness using an evaporation-induced self-assembly (EISA) method of formation is established.11-13 The extent to which thickness can be used to manipulate the optical properties of the crystals is explored, focusing on the change in the photonic band gap (PBG). Specifically, the thickness-induced changes in the properties which define the PBG for a range of volume fractions. Through meticulous structural and optical characterization, primarily in the form of scanning electron microscopy (SEM) images and angle-resolved ultraviolet-visible (UV-Vis) spectroscopy, the quality of the crystals formed is examined, with thicknesses exceeding 40 layers grown from volume fractions below 0.15 %, for the first time, to our knowledge. Crystal structure is correlated to optical fingerprint, shown in the form of transmission spectra in the UV-Vis region.We expect this work to provide our colleagues in the scientific community with a direct correlation between crystal thickness and the optical fingerprint of opal PhCs. Our analysis also stands as a manual to aid any future attempts at the growth of ultra-thick colloidal crystals. Such research may act as a precursor to further developments in materials employed in the photonics, sensing, energy storage and related communities. References 1 M. I. Shalaev, W. Walasik, A. Tsukernik, Y. Xu, and N. M. Litchinitser, Nature Nanotechnology 14, 31 (2019). 2 D. McNulty, A. Lonergan, S. O'Hanlon, and C. O'Dwyer, Solid State Ionics 314, 195 (2018). 3 D. McNulty, H. Geaney, D. Buckley, and C. O'Dwyer, Nano Energy 43, 11 (2018). 4 D. McNulty, E. Carroll, and C. O'Dwyer, Advanced Energy Materials 7, 1602291 (2017). 5 E. Armstrong, D. McNulty, H. Geaney, and C. O’Dwyer, ACS Applied Materials & Interfaces 7, 27006 (2015). 6 D. McNulty, H. Geaney, Q. Ramasse, and C. O'Dwyer, Adv. Funct. Mater. 30, 2005073 (2020). 7 J. Hou, M. Li, and Y. Song, Nano Today 22, 132 (2018). 8 E. Armstrong and C. O'Dwyer, Journal of Materials Chemistry C 3, 6109 (2015). 9 D. R. Solli and J. M. Hickmann, Optical Materials 33, 523 (2011). 10 S. G. Romanov, Physics of the Solid State 59, 1356 (2017). 11 Q. Jiang, C. Li, S. Shi, D. Zhao, L. Xiong, H. Wei, and L. Yi, Journal of Non-Crystalline Solids 358, 1611 (2012). 12 J. Zhang, Y. Li, X. Zhang, and B. Yang, Advanced Materials 22, 4249 (2010). 13 A. Lonergan, C. Hu, and C. O'Dwyer, Phys. Rev. Materials 4, 065201 (2020). 14 S. O'Hanon, D. McNulty, R. Tian, J. Coleman, and C. O'Dwyer, J. Electrochem. Soc. 167, 140532 (2020). Figure 1. Optical and structural analysis for 350 nm PS opals formed by EISA. Analysis presented in the form of transmission spectra obtained for samples formed from a range of five volume fractions, labelled by their dilution factors (a,d,g), sample plan view SEM images (b,e,f), and sample cross-sectional SEM images (c,f,i). (a-c) correspond to regions of maximum opal thickness, (d-f) to regions of lesser thickness, (g-i) to regions of minimal thickness. Figure 1

Micro Raman analysis on the impact of light ion irradiation of hydride vapor-phase epitaxy grown gallium nitride epilayers

Gallium Nitride (GaN) epilayer grown by Hydride Vapor-Phase Epitaxy was irradiated with 100 MeV O7+ light ions for different fluences. The X-ray diffraction results confirmed that all the grown epilayers have wurtzite structure. The thickness of the pristine GaN is measured by cross-section scanning electron microscopy. From atomic force microscopy, the irradiated sample's surface morphology and root mean square values were analyzed. The stopping range of ions in the materials calculation provided the projected range for the irradiation ions. From Raman spectroscopy, Raman active mode of EH2 and A1(LO) vibration was observed. These Raman modes were fitted by the Lorentz fitting method for line-shape model identification to calculate the area under the curve, full-width half maximum, and peak shift position. The biaxial stress, carrier concentration, and phonon lifetime for both pristine and irradiated GaN epilayers were obtained from the Raman active mode. The results indicated that the carrier concentration increases for higher fluences due to the defect formations. The photoluminescence spectrum was measured for all the epilayers and defect-induced photoluminescence emission was obtained for these irradiation epilayers.

Long-Term Study on the Impact of Depth of Discharge, C-Rate, Voltage, and Temperature on the Lifetime of Single-Crystal NMC811/Artificial Graphite Pouch Cells

This work examined the impact of depth of discharge (DOD), C-rate, upper cut-off voltage (UCV), and temperature on the lifetime of single-crystal NMC811/Artificial Graphite (AG) cells. Cells were cycled at C/50, C/10, C/5, or C/3, and 25, 50, 75, or 100% DOD at room temperature (RT, 20 ± 2 °C) or 40.0 ± 0.1 °C. The UCVs were 4.06 or 4.20 V. After 12000 hr of cycling, experiments such as electrochemical impedance spectroscopy (EIS), Li-ion differential thermal analysis (DTA), ultrasonic mapping, X-ray fluorescence (XRF), differential capacity analysis, synchrotron computed tomography (CT) scans, and cross-section scanning electron microscopy (SEM) were carried out. We showed that capacity loss increased slightly with DOD and C-rate, and that cells with 4.06 V UCV have superior capacity retention and impedance control compared to 4.20 V. SEM, CT scans, and differential capacity analysis show that microcracking and positive electrode mass loss did not occur regardless of DOD, C-rate, or UCV. DTA and ultrasonic mapping showed no C-rate or DOD dependency for electrolyte changes or “unwetting.” Finally, a simple square-root time model was used to model SEI growth in 4.06 V UCV cells.