Mater Sci Research Articles

CALPHAD-Type Reassessment of Cu-Si and Full Assessment of the Al-Cu-Si Systems

The theoretical assessment of the Al-Cu-Si was carried out in this work based on recent experimental studies (Riani et al. in Intermetallics, 17:154-164, 2009; He et al. in CALPHAD, 33:200-210, 2009. http://dx.doi.org/10.1016/j.calphad.2008.07.015; Ponweiser N and Richter KW in J. of Alloys and Compd, 512:252-263, 2012; Hallstedt et al. in CALPHAD, 53:25-38, 2016; Zobac et al in J Mater Sci, 55:5322-15333, 2020). The reassessment of the Cu-Si system was also carried out in the scope of this work, as experimental data indicates reasonable solubility of Al in all intermetallic phases in the Cu-Si binary system, and the stoichiometric models used in previous assessments of the Cu-Si binary system are not fully suitable for the extension into the ternary system. Excellent agreement was reached for the reassessment of the Cu-Si system with previous works, and new original results were obtained during the assessment of the ternary system. The high solubility of Si in the β(bcc) phase at high temperatures was modelled to explain experimental inconsistencies in the Cu-rich corner between 600 and 800 °C, and this assumption was confirmed experimentally. All main features of the experimental Al-Cu-Si phase diagram were reproduced well by theoretical modelling.

(Invited) Mitigation of BPD Faulting Using H2 Etches for Pulsed Power Applications

Basal plane dislocations (BPDs) have been a concern for SiC high-voltage bipolar devices for many years as they source Shockley-type stacking faults in the presence of an electron-hole plasma and reduce minority carrier lifetimes [1]. There has been much focus on the reduction of BPD densities including pre-growth treatments [2], growth interrupts [3], and proton implantation [4]. It has been demonstrated that with sufficient carrier injection, BPDs from the highly doped buffer layer or substrate can expand and propagate into the drift layer [5], causing device failure. Therefore, a technique is needed to prevent BPD faulting during high carrier injection for high peak, pulsed power applications. In this paper, we use an in-situ H2 etch process to mitigate BPD faulting under high-power UV exposure at 12 kW/cm2, which is equivalent to ~1x1019 cm-3 carrier injection in the substrate. Intentionally doped (ID) n-type (~ 5x1015 cm-3) epitaxial layers were grown on 4° off-axis substrates in a horizontal hot-wall chemical vapor deposition reactor using the standard chemistry of silane (2% in H2) and propane. Growth was conducted at 1620 °C, 100 mbar, and a C/Si of 1.55. A 6 µm buffer layer (n-type ~ 2x1018 cm-3) was grown prior to the ID drift layer. A H2 etch was performed at different stages of the growth to determine its impact on BPD faulting. The etch was conducted at 1665 °C and 70 mbar for 50 min, either before the buffer layer (BL), after the BL, or both before and after the BL. A fourth sample was grown with a H2 etch prior to the BL and a growth interrupt after the BL. The growth interrupt consisted of reducing the temperature to 1000 °C in H2 and immediately ramping back to the growth temperature, after which the ID drift layer was grown. A control sample was grown without any etches or growth interrupt. Ultraviolet photoluminescence (UVPL) imaging was used to identify the BPD faulting behavior after epitaxial growth, and before and after UV stressing. When exposing the control sample to 300 W/cm2, the BPDs present in the BL faulted after 420 s of UV exposure and continued to propagate throughout the drift layer. For the sample with a H2 etch between the BL and ID drift layer, only the pre-existing BPDs in the drift layer faulted at 300 W/cm2, and no BPDs from the BL faulted after > 1240 s. Similar results were found for the sample grown with a H2 etch before and after the BL. When these two H2 etched samples (etched before and after the BL, and etched after the BL) were stressed at an increased UV exposure of 1 kW/cm2, again, no faulting of BL or substrate BPDs were observed after 1900 s. With 10X higher power density (12 kW/cm2), BPD faulting from the substrate occurred for both of the H2 etched samples. However, for the sample with just a single H2 etch between the BL and drift layer, the density of additional BPD faulting was ~ 200 BPDs/cm2, whereas when the H2 etch was performed before and after the BL, the density of newly faulted BPDs was only ~ 50 BPD/cm2. For the sample grown with a H2 etch before and a growth interrupt after the BL, BPDs did not expand at 12 kW/cm2. Carrier concentration was simulated as a function of epitaxial layer depth for the various UV laser powers. At the highest power density, the injected carrier concentration is higher than the doping of all the layers, which should lead to recombination induced BPD faulting in the substrate, BL and ID epilayer. We propose that H2 from the H2 etch and growth interrupt pin the BPDs and prevent them from expanding. This level of suppression of BPD expansion, to our knowledge, has not been demonstrated before at these power densities.[1] J.P. Bergman, et al., Mater. Sci. Forum Vol. 353-356, 299 (2001).[2] N.A. Mahadik et.al., Mater Sci Forum 858, 233 (2016).[3] R. E. Stahlbush, et al., Appl. Phys. Lett. 94, 041916 (2009).[4] M. Kato, et al., Sci. Rep., 12, 18790 (2022).[5] N.A. Mahadik, et. al., Appl. Phys. Lett., 100, 042102 (2012).

Ultrasonic Atomization of New Alloys for Powder-Based Anodes in Next-Generation Non-Lithium Batteries

Improved battery performance has led to significant advancements in anode materials, with powder-based anodes emerging as a promising alternative to traditional graphite anodes[1,2]. Next-Generation Non-Lithium Batteries, like potassium and magnesium–ion batteries require anodes tailored to the ion diffusivity and anode-electrolyte-cathode compatibility[3,4]. Candidates like bismuth, magnesium, and antimony-based anodes can maximize specific capacity and cycling stability. Passivation film formed on their surface causes large potential drop and energy loss[5]. The alloys with tailored chemical composition can improve the electrochemical behavior of the anodes and significantly promote film formation influencing the interface with electrolyte[6]. Current powder-based anodes preparation methods involve mechanical milling, which produces irregular particles and distorts the structure obtained by eutectic solidification, which can showcase outstanding electrochemical properties[7,8]. We propose a powder production method based on ultrasonic atomization technology[9]. This technology uses the vibrations to eject the particles from liquid metal. Plasma or induction heating can be used for melting, allowing a wide range of metals to be processed. Powders obtained by ultrasonic atomization possess high sphericity which can stabilize the dissolution rate of the anode during cyclic charging and facilitate obtaining uniform coating thickness. Thanks to vibrations instead of high-velocity gases the powder production unit is much smaller and suitable for research and alloy development.[1] J. Zhao, Z. Wei, N. Chen, F. Meng, R. Tian, Y. Zeng, F. Du, Energy Storage Mater 2024, 65, DOI 10.1016/j.ensm.2023.103127.[2] B. Fu, G. Liu, Y. Zhang, Z. Liu, X. Xie, G. Fang, S. Liang, ACS Energy Lett 2024, 3292.[3] Z. Zhao-Karger, Y. Xiu, Z. Li, A. Reupert, T. Smok, M. Fichtner, Nat Commun 2022, 13, DOI 10.1038/s41467-022-31261-z.[4] D. Gu, Y. Yuan, J. Liu, D. Li, W. Zhang, L. Wu, F. Cao, J. Wang, G. Huang, F. Pan, J Power Sources 2022, 548, DOI 10.1016/j.jpowsour.2022.232076.[5] F. Liu, G. Cao, J. Ban, H. Lei, Y. Zhang, G. Shao, A. Zhou, L. zhen Fan, J. Hu, Journal of Magnesium and Alloys 2022, 10, DOI 10.1016/j.jma.2022.09.004.[6] X. You, X. Zhang, C. Yu, Y. Chen, H. Li, Y. Hou, L. Tian, N. Yang, G. Xie, Journal of Rare Earths 2023, 41, DOI 10.1016/j.jre.2022.04.011.[7] S. B. Wang, Q. Ran, R. Q. Yao, H. Shi, Z. Wen, M. Zhao, X. Y. Lang, Q. Jiang, Nat Commun 2020, 11, DOI 10.1038/s41467-020-15478-4.[8] L. Cao, M. Zheng, G. Dong, J. Xu, R. Xiao, T. Huang, J Mater Sci Technol 2025, 211, 278.[9] A. Priyadarshi, S. Bin Shahrani, T. Choma, L. Zrodowski, L. Qin, C. L. A. Leung, S. J. Clark, K. Fezzaa, J. Mi, P. D. Lee, D. Eskin, I. Tzanakis, Addit Manuf 2024, 83, DOI 10.1016/j.addma.2024.104033.

A two-phase thin-film model for cell-induced gel contraction incorporating osmotic effects

We present a mathematical model of an experiment in which cells are cultured within a gel, which in turn floats freely within a liquid nutrient medium. Traction forces exerted by the cells on the gel cause it to contract over time, giving a measure of the strength of these forces. Building upon our previous work (Reoch et al. in J Math Biol 84(5):31, 2022), we exploit the fact that the gels used frequently have a thin geometry to obtain a reduced model for the behaviour of a thin, two-dimensional cell-seeded gel. We find that steady-state solutions of the reduced model require the cell density and volume fraction of polymer in the gel to be spatially uniform, while the gel height may vary spatially. If we further assume that all three of these variables are initially spatially uniform, this continues for all time and the thin film model can be further reduced to solving a single, non-linear ODE for gel height as a function of time. The thin film model is further investigated for both spatially-uniform and varying initial conditions, using a combination of analytical techniques and numerical simulations. We show that a number of qualitatively different behaviours are possible, depending on the composition of the gel (i.e., the chemical potentials) and the strength of the cell traction forces. However, unlike in the earlier one-dimensional model, we do not observe cases where the gel oscillates between swelling and contraction. For the case of initially uniform cell and gel density, our model predicts that the relative change in the gels’ height and length are equal, which justifies an assumption previously used in the work of Stevenson et al. (Biophys J 99(1):19–28, 2010). Conversely, however, even for non-uniform initial conditions, we do not observe cases where the length of the gel changes whilst its height remains constant, which have been reported in another model of osmotic swelling by Trinschek et al. (AIMS Mater Sci 3(3):1138–1159, 2016; Phys Rev Lett 119:078003, 2017).

Design, fabrication, and characterization of high-entropy alloys (HEAs) of the type TiVCrX (X = Al, Mn, Mo)

According to Zhang et al. (Prog Mater Sci 61:1, 2014, https://doi.org/10.1016/j.pmatsci.2013.10.001), High-Entropy Alloys (HEAs) are an emerging class of advanced materials that contain multiple elements in equiatomic or near equiatomic concentrations. In recent years, extensive efforts have been made to design HEAs with suitable microstructures and superior properties. This work reports the preliminary results of fabrication and characterization of three HEAs (TiVCrAl, TiVCrMn, TiVCrMo) with equiatomic compositions. These HEAs were designed with the purpose of producing a single-phase BCC, according to calculations with the HEAPS (Martin et al. in Comput Phys Commun 278:108398, 2022, https://doi.org/10.1016/j.cpc.2022.108398) and CALPHAD programs. Microstructures consisting of BCC + C14 Laves phases (Mn), a mixture of two cubic phases (Mo) and a single BCC phase, were found, basically consistent with CALPHAD predictions, although the phase volume fractions and compositions were not accurately predicted.Graphical abstract

Numerical treatment of reactive diffusion using the discontinuous Galerkin method

AbstractThis work presents a new finite element variational formulation for the numerical treatment of diffusional phase transformations using the discontinuous Galerkin method (DGM). Steep concentration and property gradients near phase boundaries require particular focus on a sound numerical treatment. There are different ways to tackle this problem ranging from (i) the well-known phase field method (PFM) (Biner et al. in Programming phase-field modeling, Springer, Berlin, 2017, Emmerich in The diffuse interface approach in materials science: thermodynamic concepts and applications of phase-field models, Springer, Berlin, 2003), where the interface is described continuously to (ii) methods that allow sharp transitions at phase boundaries, such as reactive diffusion models (Svoboda and Fischer in Comput Mater Sci 127:136–140, 2017, 78:39–46, 2013, Svoboda et al. in Comput Mater Sci 95:309–315, 2014). Phase transformation problems with continuous property changes can be implemented using the continuous Galerkin method (GM). Sharp interface models, however, lead to stability problems with the GM. A method that is able to treat the features of sharp interface models is the discontinuous Galerkin method. This method is well understood for regular diffusion problems (Cockburn in ZAMM J Appl Math Mech 83(11):731–754, 2003). As will be shown, it is also particularly well suited to model phase transformations. We discuss the thermodynamic background by review of a multi-phase, binary system. A new DGM formulation for the phase transformation problem with sharp interfaces is then introduced. Finally, the derived method is used in a 2D microstructural evolution simulation that features a binary, three-phase system that also takes the vacancy mechanism of solid body diffusion into account.

Comments on the paper on the Nd-doped BiFeO3 by S. R. Dhanya and Jyotirmayee Satapathy, and published in J Mater Sci: Mater Electron (2023) 34:434, and on the corresponding correction published in J Mater Sci: Mater Electron (2023) 34:1484

Comments on the paper on the Nd-doped BiFeO3 by S. R. Dhanya and Jyotirmayee Satapathy, and published in J Mater Sci: Mater Electron (2023) 34:434, and on the corresponding correction published in J Mater Sci: Mater Electron (2023) 34:1484

Electrochemical CO2 Reduction Using a Free-Standing Porous Cu Framework as Catalyst

Due to fossil fuel combustion, the CO2 concentration in the atmosphere has reached around 410 ppm, causing major climate change on our planet. It thus becomes increasingly important to limit CO2 emissions or even remove CO2 from our atmosphere. One promising pathway to transform CO2 into useful chemicals is electrochemical reduction. However, electrochemical CO2 reduction is a challenging process that requires robust, low cost and stable catalysts. Copper is a promising candidate, at which CO2 can be reduced to several types of hydrocarbons.In this contribution, CO2 reduction was performed with a free-standing porous copper catalyst that was prepared using an inexpensive hydrogen assisted electroplating process [1]. The porous copper framework has good mechanical stability and a large internal surface area. Furthermore, it can easily be manufactured on a large scale. Due to its porous nature with tunable pore sizes this copper framework is at the same time gas diffusion layer and catalyst. A porous sample with a 10 cm2 geometric surface area was assembled in a custom-made electrochemical cell consisting of an open cell anode compartment, a closed compact cell for the cathode, separated by a cation-exchange membrane. CO2 mixed with water vapor is transported to the free-standing porous Cu in the closed compact cell for the CO2 reduction process. The electrochemical cell is connected to a gas chromatograph (GC) for further gas phase product analysis. The experiments were performed in the potential range between -0.3 V vs RHE and -1.7 V vs RHE in 0.5 M KHCO3 as the anolyte. GC measurements show a considerable amount of methane (CH4), ethylene (C2H4), ethane (C2H6), and propane (C3H8) which indicates a successful reduction reaction of the CO2 on the porous copper framework surface.[1] M. Kurniawan, M. Stich, M. Marimon, M. Camargo, R. Peipmann, T. Hannappel, A. Bund: "Electrodeposition of cuprous oxide on a porous copper framework for an improved photoelectrochemical performance." J. Mater Sci. 56 (2021) 11866-11880

Chelating agents for the removal of calcareous deposits from archaeological ceramic materials. Compositional evaluation after immersion and physical gel application methods

The removal of calcareous deposits from archaeological ceramics is a very normal conservation-restoration treatment. Among the products used, chelating agents are quite common, including ethylenediaminetetraacetic acid salts (EDTA) (Berducou in La Conservation en archéologie: méthodes et pratique de la conservation-restauration des vestiges archéologiques, Masson, Paris, 1990; Buys and Oakley The conservation and restoration of ceramics, Butterworth-Heinemann, Oxford, 1993; Crisci et al. in Appl Phys A Mater Sci Process, 2010. https://doi.org/10.1155/2009/893528). Nevertheless, some studies have proved that they can cause damages on the ceramic pieces, regarding changes in their composition, such as dissolution of calcareous components and metallic oxides leaching (Gibson in Stud Conserv, 1971. https://doi.org/10.1155/2009/893528; Fernández and Seva Sautuola in Rev del Inst Prehist y Arqueol 9:471–982, 2003). As a consequence, their artistic values might also change. In spite of that, these products are nowadays still in use, meaning that the treatments might be changing the information that archaeological ceramics carry. However, from the 80 s onwards a more secure alternative to direct application methods based on thickening agents was developed. With the aim of analysing the degradation mechanisms that may take place after the cleaning treatments’ application, ceramic specimens with artificial calcareous deposits (Sáenz-Martínez et al. in Eur Phys J Plus 136:798, 2021) were treated with a low-concentrated solution of EDTA tetrasodium salt applied by immersion and thickened with xanthan gum powder (Vanzan® NF-C). Finally, the products from the cleaning treatments were neutralised, respectively, by immersion and by rinsing with deionized water. The composition of the ceramic samples was established before the growth of calcareous deposits and after the treatments, in order to determine their effectiveness and safety. According to the results, EDTA salt treatments, both by immersion and thickened, were effective regarding the removal of the calcareous deposits and did not modify the elemental and mineralogical original composition of the specimens (XRF, XRPD, TG-DSC). In addition, no gel residues were detected by FTIR-ATR.

Crystallinity and Stiffness of Spider Silk Govern the Migration of Schwann Cells

Introduction: Nerve guidance conduits are a promising alternative to autologous nerve transplantation and conduits filled with fibrous materials have shown great potential in bridging nerve gaps. The application of spider silk as a filament material has led to results comparable to nerve autograft.1 However, the use of spider silk has been phenomenological so far and the reasons for its success are still not identified. The aim of this study is to elucidate the material properties of spider silk leading to its unique medical performance. This knowledge enables a targeted production of synthetic alternatives such as recombinant silk. Materials and Methods: In this work, various silk types were investigated.2 Schwann cells were seeded on the spider silks and monitored by live cell imaging and immunofluorescent staining. In addition, the silk fibers were inspected with an electron microscopy, Raman spectroscopy wide angle X-ray scattering, and tensile tests to determine morphology, secondary protein structure, crystallinity and stiffness, respectively. Results: It was found that the secondary protein structure and specifically the high content of β-sheets in the direction of silk’s axis gives the fiber its ability to act as a guiding element for Schwann cells. In addition, the results show that the crystallinity of the silk does not affect the proliferation of Schwann cells, while the directed movement of cells is affected by this material property. Conclusion: This direct comparison demonstrated the crucial role of the secondary protein structures and crystallinity of spider silk for the guidance properties of fibers during nerve regeneration. The crystalline structure of silk affects its stiffness, which in turn influences the directed migration of Schwann cells. These results should be considered during the targeted production of synthetic fibrous materials for nerve regeneration. 1. Kornfeld T, Nessler J, Helmer C, et al. Spider silk nerve graft promotes axonal regeneration on long distance nerve defect in a sheep model. Biomaterials 2021;271:120692. 2. Naghilou A, Pöttschacher L, Millesi F, et al. Correlating the secondary protein structure of natural spider silk with its guiding properties for Schwann cells. Mater Sci Eng C. 2020;116:111219.

(Invited) Deep Level Defects in AlN Studied By UV-Visible Spectroscopy

The ultrawide-bandgap (UWBG) AlGaN alloy system is emerging as a promising material for next generation power semiconductor devices. The increase in bandgap as the alloy composition is varied from the binary endpoints GaN to AlN leads to an increase in the critical electric field, which is a key parameter determining the performance of power semiconductor devices. As development of GaN and SiC materials for high-frequency and high-power devices reaches a state of maturity, pursuit of improved device performance is generating interest in UWBG materials with larger bandgaps. High Al composition AlGaN alloys, in addition to offering increased critical electric fields, offer prospects for improved device performance in high temperature operation. Fundamental challenges to the development of AlGaN-based devices, such as controllable doping, electrical contacts, and effective passivation, remain, but a variety of power devices have already been demonstrated (1-3).Point defects strongly affect the material properties of semiconductors, with important consequences for device performance. In traditional semiconductors, such as Si, point defects have been studied extensively, and point defect engineering methods have been developed to enhance device performance. However, the properties of point defects in UWBG materials are not as well understood. Point defects may be introduced during device growth, fabrication, and operation. On the one hand, intentionally introduced impurities (dopants) are critical to the control of electrical transport, while on the other hand, unintentionally introduced impurities may act deleteriously as carrier traps or recombination centers. In AlGaN, compensation by deep level, native point defects or unintentionally incorporated impurities limits achievable free carrier concentrations in electronic devices, while defects and their complexes affect the optical properties in optoelectronic devices. Since point defects exert such a strong influence on material properties, and are often responsible for device degradation, knowledge of their formation mechanisms and material effects are essential to develop strategies for the required control of point defect concentrations (4).In this work, we studied the optical signatures of deep level defects in single crystal AlN substrates. AlN possesses a high thermal conductivity and a close lattice match to high Al composition alloys, which make it an excellent substrate choice for growth of AlGaN-based power electronic and optoelectronic devices. High-quality, 2-inch diameter AlN substrates with average threading dislocation densities below 103 cm-2 were recently demonstrated (5). However, high optical absorption in the ultraviolet-C (UV-C) region was observed in AlN substrates grown by physical vapor transport (PVT), due to a deep level absorption band related to the carbon impurity. This absorption band negatively impacts the efficiency of UV-C optoelectronic devices that require light propagation through the substrate. In order to reduce the unwanted UV-C absorption, we studied the optical properties of double-side polished, 2-inch, c-plane AlN substrates by ultraviolet-visible (UV-Vis) spectroscopy and developed strategies for point defect control. Spatially uniform absorption coefficients below 30 cm-1 at 265 nm were demonstrated across 2-inch substrates (6). In this talk, UV-Vis absorption, photoluminescence (PL) emission, and PL excitation spectra will be presented and correlated with measured impurity concentrations from secondary ion mass spectrometry (SIMS) data, in order to identify deep level defects in AlN. Finally, the mechanisms for reduction of UV-C absorption in PVT AlN will be discussed.References R. J. Kaplar, A. A. Allerman, A. M. Armstrong, M. H. Crawford, J. R. Dickerson, A. J. Fischer, A. G. Baca, and E. A. Douglas, ECS J. Sol. State Sci. and Technol. 6(2), Q3061 (2017).P. H. Carey IV, F. Ren, A. G. Baca, B. A. Klein, A. A. Allerman, A. M. Armstrong, E. A. Douglas, R. J. Kaplar, P. G. Kotula, and S. J. Pearton, IEEE Trans. Semicond. Manuf. 32(4), 473 (2019).A. G. Baca, A. M. Armstrong, B. A. Klein, A. A. Allerman, E. A. Douglas, and R. J. Kaplar, J. Vac. Sci. Technol. A 38, 20803 (2020).S. Washiyama, P. Reddy, B. Sarkar, M. H. Breckenridge, Q. Guo, P. Bagheri, A. Klump, R. Kirste, J. Tweedie, S. Mita, Z. Sitar, and R. Collazo, J. Appl. Phys. 127, 105702 (2020).R. Dalmau, J. Britt, H. Fang, B. Raghothamachar, M. Dudley, and R. Schlesser, Mater Sci. Forum 1004, 63 (2020).R. Dalmau, S. Kirby, J. Britt, and R. Schlesser, ECS Trans. 104(7), 49 (2021).

(Best Student Presentation Award) Reduced Pressure – Chemical Vapor Deposition of Monocrystalline and Polycrystalline Si(:B) and SiGe(:B) Layers on Blanket Wafers

Monocrystalline SiGe alloys can be used instead of monocrystalline Si in order to increase the performances of devices such as heterojunction bipolar transistors (HBTs) [1]. The epitaxial growth of blanket, monocrystalline SiGe layers on Si with a dichlorosilane + germane + hydrochloric acid chemistry was extensively investigated in the literature [2,3]. Similarly, a switch from polycrystalline Si to polycrystalline SiGe can be favorable, for instance, in Complementary-MOS (C-MOS) devices [4,5]. However, the blanket growth by Reduced-Pressure Vapor Deposition (RP-CVD) of polycrystalline Si and SiGe has not been systematically investigated. We have thus performed a one-to-one comparison in terms of growth kinetics and electrically active dopant incorporation between blanket monocrystalline and polycrystalline Si(:B) and SiGe(:B) layers.Epitaxies or depositions were performed, in 300 mm RP-CVD chambers, on two types of templates (Fig.1): i) N-type Si substrates (Fig.1(a)) and ii) poly-Si/oxide/ P-type Si substrates (Fig.1(b)). The poly-Si layer in stack 1.(b) was obtained thanks to amorphous Si deposition followed by annealing at 750 °C, resulting in a poly-Si film. SiH4+HCl+H2 (named Process 1) and SiH2Cl2 (DCS)+HCl+GeH4+H2 (named Process 2) chemistries were used to deposit Si and SiGe layers between 675-750 °C and 10-20 Torr.Monocrystalline and polycrystalline SiGe growth kinetics for two process conditions: i) 750 °C, 10 Torr with a HCl partial pressure of 0.05 Torr and ii) 725 °C, 10 Torr, with a HCl partial pressure of 0.06 Torr, were similar to that in the literature [1-3, 6-8]. As already shown for monocrystalline layers, there was an increase of the intrinsic SiGe growth with the germane partial pressure and the temperature. Meanwhile, it was reduced when adding HCl (Fig.2). Very similar growth rates and evolutions were however obtained whatever the crystalline state of the layers.When diborane was added the gaseous mixture, different behaviors were evidenced depending on i) the crystallinity and ii) the stoichiometry. The Si:B and SiGe:B growth rates increased with the B2H6 flow whatever the chemistry (Fig.3). This was due to a hydrogen desorption increase on boron surface sites [5,10-11]. Growth rates were otherwise higher for monocrystalline than for polycrystalline layers. The electrical resistivities of c-Si:B and c-SiGe:B layers were one decade lower than those of poly-Si:B and poly-SiGe:B layers, however (Fig.4). Resistivity values were otherwise higher for c-Si:B than for c-SiGe:B. This was likely due to i) a better incorporation of B atoms into SiGe than in Si [3,8,9] and ii) a better hole mobility in SiGe [10]. An opposite behavior was observed for polycrystalline layers, with higher resistivities for poly-SiGe:B than for poly-Si:B. We otherwise had similar resistivity evolutions as the partial pressure of diborane Pp(B2H6) increased for all types of layers. A decrease was observed first, followed by a resistivity plateau then some resistivity re-increase for really high diborane flows. Such a phenomenon was already observed for monocrystalline layers and was explained by a crystalline quality degradation [3,8,9] that reduced the hole mobility. A similar behavior was assumed for poly-layers, with a morphological transition to the amorphous phase [11,12]. Top-view Scanning Electron Microscopy (SEM) images (Fig. 5) confirmed the morphological evolution of c-Si:B, poly-Si:B, c-SiGe:B and poly-SiGe:B as the diborane partial pressure increased.New data points for c-SiGe and c-SiGe:B will also be provided for other process conditions. For intrinsic layers, we will show that Refs. [1,2] x2/(1-x) = n×(F(GeH4)/F(SiH2Cl2)) relationship between the Ge concentration x and the germane over dichlorosilane mass-flow ratio is also valid at 10 Torr, with n = 3 at 700 °C with a F(SiH2Cl2)/F(H2) Mass-Flow Ratio (MFR) of 0.005 and a F(HCl)/F(H2) MFR of 0.006. Various characterization techniques were also used to determine the concentration of substitutional Boron atoms in SiGe:B layers and the lattice contraction coefficient (β = 9.11×10-24 cm3). The value of the latter, which is most useful to assess the compressive strain compensation by small boron atoms in SiGe layers, will be compared to literature values.[1] J. Appl. Phys. 88 (2000) 4044[2] J. Crystal Growth 305 (2007) 113[3] J. Crystal Growth 310 (2008) 62[4] J. Microelec. Sys. 16 (2007) 68[5] International Electron Devices Meeting (1991) 567[6] Appl. Phys. Lett. 56 (1990) 1275.[7] S. Chang et al., ECS Proceedings 87–8 (1987) 122[8] J Mater Sci: Mater Electron (2007) 18:747[9] ECS Trans. 75, 8 (2016) 265[10] Mater. Sci. Eng. B 114–115 (2004) 318[11] Appl. Phys. Lett. 66 (1995) 195[12] ECS Trans. 35, 30 (2011) 45 Figure 1

Assessment and validation of SPH modeling for nano-indentation

Nano-indentation tests are important techniques in material science. Over the past two decades, many numerical approaches have been proposed to model and simulate the nano-indentation process. In this paper, the possibility of modeling the process using a meshless numerical technique, known as smooth particle hydrodynamics (SPH), is explored. In particular, the SPH modeling of nano-indentation is conducted using the ANSYS/LS-DYNA software using three different published studies as benchmarks. More specifically, SPH results reported by Guo et al. (J Semicond 36:083007, 2015) when nano-indenting a KPD crystal were used first to verify the validity of the SPH model established in this work. Following this, the outcomes of further SPH simulations were found to compare well against finite element modeling and experimental results reported in Dao et al. (Acta Mater 49:3899–3918, 2001) and Karimzadeh et al. (Comput Mater Sci 81:595–600, 2014) for both micro- and nano-indentation, respectively. These observations suggest that SPH is a technique with the potential to be considered more widely by researchers investigating high strain, or strain rate, deformation phenomena on the nanoscale. For example, the presented research on the development of a SPH-based nano-indentation model lays the foundations toward formulating a comprehensive model for the accurate simulation of nanoscale tool-based machining processes.

On the utility of hierarchical self-healing fiber bundle materials under different environments.

Bio-materials use a hierarchical structure to optimize their self-healing mechanical behavior. However, the utility may be restricted by different environments. In this paper, based on the previous work in Ji and Li (J Mater Sci 53:14858-14870, 2018) on the constitutive relation of hierarchical self-healing fiber bundle materials (FBMs), the stability is investigated for the mechanical-environmental interaction system established in Ji and Li (Int J Fract 212:105-112, 2018). With the principle of total potential, the stability criterion is proposed. The critical environment stiffness is derived and the system is therefore classified into the absolutely stable one and the conditionally stable one. For the conditionally stable system, the applied strain of FBMs reduces to be [0,[Formula: see text]], where [Formula: see text] is the cutoff strain. Finally, the toughness of hierarchical self-healing FBMs is studied for different interaction systems. The results show that in the absolutely stable system there exists a critical healing rate across which the toughness benefits from a hierarchical structure. In the conditionally stable system, the toughness is significantly affected by the environment stiffness, i.e., the toughness of a FBM increases with a rising hierarchical level, whereas it decreases with a rising healing rate. Moreover, the critical healing rate for toughness becomes greater compared to that in an absolutely stable system.

(Invited) Complex Relative Permittivity of UV-C Transparent AlN

Development of high-power switching and radio frequency (RF) devices based on the ultrawide-bandgap (UWBG) AlGaN alloy system is generating interest in high Al composition alloys. The increase in bandgap as the alloy composition is varied from GaN to AlN is associated with an increase in the critical electric field, and thus the achievable breakdown voltage, of power devices based on these materials. In addition to the higher critical electric field, the relative insensitivity of saturation velocity to alloy composition offers prospects for RF applications. Also, high Al composition AlGaN transistors offer improved performance at high temperatures. Basic challenges, associated with controllable doping, electrical contacts, and passivation, remain for implementation of high Al composition alloys in these applications, but the expected improvement in device performance drives investigation of their properties. To date, both lateral and quasi-vertical power switching device geometries have been demonstrated (1), and the research on UWBG AlGaN transistors in power and RF electronics was recently reviewed (2).High-quality native substrates enable epitaxial growth of device heterostructures with low densities of threading dislocations, due to the low lattice and thermal mismatches to epitaxial active layers. Single crystal AlN substrates possess a high thermal conductivity and a close lattice match to high Al composition alloys, which make them an excellent choice for growth of AlGaN-based power switching and RF devices. Physical vapor transport growth (PVT) of 2-inch diameter AlN substrates free of low angle grain boundaries and with average threading dislocation densities below 103 cm-2 was recently demonstrated (3). However, high below-bandgap optical absorption in the ultraviolet-C (UV-C) region was observed in AlN grown by PVT in carbon-containing atmospheres, due to a deep-level absorption band related to the carbon impurity. This absorption band negatively impacts the efficiency of optoelectronic devices, which have driven adoption of AlN substrates to date, and typically require light extraction through the substrate. In this work, we studied the optical properties of double-side polished, 2-inch, c-plane AlN substrates by UV-Vis spectroscopy. Absorption coefficients were calculated by accurately accounting for reflection losses (4). Spatially uniform absorption coefficients below 30 cm-1 at 265 nm were demonstrated across 2-inch substrates. Furthermore, the calculated absorption and reflection coefficients were used to determine the complex refractive index and relative permittivity for the E⊥ c polarization in the 250-700 nm range, showing good agreement with published data for nominally unstrained, UV-C transparent bulk crystals.Finally, reliable values for the high-frequency and static permittivities, which are needed in the design of high-power electronic devices, were obtained.References R. J. Kaplar, A. A. Allerman, A. M. Armstrong, M. H. Crawford, J. R. Dickerson, A. J. Fischer, A. G. Baca, and E. A. Douglas, ECS J. Sol. State Sci. and Technol. 6(2), Q3061 (2017).A. G. Baca, A. M. Armstrong, B. A. Klein, A. A. Allerman, E. A. Douglas, and R. J. Kaplar, J. Vac. Sci. Technol. 38, 20803 (2020).R. Dalmau, J. Britt, H. Fang, B. Raghothamachar, M. Dudley, and R. Schlesser, Mater Sci. Forum 1004, 63 (2020).R. Dalmau, J. Britt, and R. Schlesser, ECS Trans. 98(6), 3 (2020).

Perovskites Doped with Small Amounts of Noble Metals for IT-SOFCs

Solid oxide fuel cells (SOFCs) have a great potential among the emerging energy conversion technologies because they can efficiently convert various types of fuel (hydrogen, methane, CO, biogas) into electrical energy in the 750-850 °C temperature range. The choice of electrodes remains a challenge because most metal oxides suffer from low chemical stability and low electrocatalytic activity toward oxygen reduction reaction (ORR) in the intermediate temperatures (IT) range (500-700 °C) [1]. In this view, perovskite oxides (ABO3) have shown excellent properties in terms of thermal stability, compatibility with other cell components, low production cost and, most importantly, great flexibility [1]. La0.6Sr0.4FeO3-δ, (LSF) perovskite oxide have been widely investigated for the high electrical conductivity and the electrochemical properties [2]. However, the main drawback is the poor activity towards ORR in the IT range, as most iron-based perovskite oxides [3]. The B-site doping with noble metal catalysts can sensitively improve the properties and make the compounds suitable for electrode application.The addition of small amounts of Ru or Pt into LSF structure can be an effective approach to improve the electrocatalytic properties [4,5]. Specifically, we synthesized B-site doped LSF powders with very low amounts (<5%mol) of Ru and Pt by using solution combustion synthesis (SCS) method. The synthesized powders were calcined at quite low temperature (750 °C) to get as high as possible surface area (>15 m2/g). All compounds showed a single perovskite phase. As reported in Fig. (a), the addition of Ru and Pt in the structure causes a progressive shift of the XRD peaks to lower 2θ angles indicating the perovskite lattice expansion due to the substitution of Fe4+/ Fe3+ sites with larger Ru and Pt ions.To assess the electrocatalytic activity, the compounds were investigated in oxidizing conditions using electrochemical impedance spectroscopy (EIS) analysis. Fig. (b) shows the Arrhenius plot of area specific resistance (ASR) values of LSFRu and LSFPt perovskite oxides. The ASR values were measured on LSFM/La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM)/LSFM (M=Ru, Pt) symmetric cells in the temperature range 550-800 °C. The insertion of a very low amount (1%mol) of Pt or Ru significantly reduces the polarization resistance, confirming the beneficial effect of noble metal ions on ORR activity. All these features suggest that very low Pt and Ru doping positively affects the structural and electrocatalytic properties valuably for cathodic applications.[1] Hwang J, Rao R.R. (2017). Science 358:751-756[2] Hansen KK, Mogensen M (2008). ECS Trans 13:153–160[3] Chavan SV, Singh RN (2013). J Mater Sci 48:6597–6604[4] Fan W, Sun Z. (2016) RSC Adv 6:34564[5]Shaoli G., Hongjing Wu, (2015),Catalysts, 5, 366-391 Figure 1

Influence of exposure conditions on helium transport and bubble growth in tungsten

Helium diffusion, clustering and bubble nucleation and growth is modelled using the finite element method. The existing model from Faney et al. (Model Simul Mater Sci Eng 22:065010, 2018; Nucl Fusion 55:013014, 2015) is implemented with FEniCS and simplified in order to greatly reduce the number of equations. A parametric study is performed to investigate the influence of exposure conditions on helium inventory, bubbles density and size. Temperature is varied from 120 K to 1200 K and the implanted flux of 100 eV He is varied from 10^{17},{text{m}^{-2}, text{s}^{-1}} to 5 times 10^{21}, {text{m}^{-2}, text{s}^{-1}}. Bubble mean size increases as a power law of time whereas the bubble density reaches a maximum. The maximum He content in bubbles was approximately 4 times 10^{8} He at 5 times 10^{21},{text{m}^{-2}, text{s}^{-1}}. After 1 h of exposure, the helium inventory varies from 5 times 10^{16} ,{text{m}^{-2}} at low flux and high temperature to 10^{25} ,{text{m}^{-2}} at high flux and low temperature. The bubbles inventory varies from 5 times 10^{12} bubbles m^{-2} to 2 times 10^{19} bubbles m^{-2}. Comparison with experimental measurements is performed. The bubble density simulated by the model is in quantitative agreement with experiments.

Comments on “Investigation on synthesis, laser damage threshold, and NLO properties of l-asparagine thioacetamide single crystal for photonic device applications” [J Mater Sci: Mater Electron. 31, 13310–13320 (2020)

The authors of the title paper [J. Mater. Sci. Mater. Electron. 31, 13310–13320 (2020)] report to have grown a so-called l-asparagine thioacetamide (LATA) single crystal by slow evaporation of an aqueous solution containing l-asparagine monohydrate and thioacetamide in 1:1 ratio. The same research group has claimed in another paper [J. Mater. Sci. Mater. Electron. 31, 791–798 (2020)] to have grown a so-called NLO-active potassium hydrogen phthalate fumaric acid crystal (KHPF). In this comment we prove that LATA and KHPF are improperly characterized crystals and both papers are erroneous.

Corrigendum: System identification based PSO approach for networked DC servo motor (2021 IOP Conf. Ser.: Mater Sci Eng. 1090 012059)

Corrigendum: System identification based PSO approach for networked DC servo motor (2021 IOP Conf. Ser.: Mater Sci Eng. 1090 012059)

Semi-convertible Hydrogel Enabled Photoresponsive Lubrication

Summary A semi-convertible hydrogel with reversible photoresponsive supramolecular lubricating ability is demonstrated by integrating a responsive supramolecular system of α-cyclodextrins/polyethylene glycol (α-CD/PEG) and competitive guest 1-[p-(phenylazo)benzyl]pyridinium bromide (AzoPB) within a poly(vinyl alcohol) (PVA) and polyacrylamide (PAAm) framework. The competitive host-guest interaction between α-CD/PEG supramolecular network and AzoPB after UV and visible-light irradiation enables the appearance and disappearance of the sol-state layer on the hydrogel surface while the PVA and PAAm consistently keeps the framework. This semi-convertible process realizes the reversible photoresponsive lubricating ability and variable toughness. We envision that this finding will offer a possible way for fabricating novel smart devices far beyond lubrication, leading to an emerging branch of interdisciplinary materials science that integrates supramolecular chemistry, hydrogel, and surface science.