Impurity Incorporation Research Articles

Cu Pillar Electroplating Using a Synthetic Polyquaterntum Leveler and Its Coupling Effect on SAC305/Cu Solder Joint Voiding

With the advancement of high-integration and high-density interconnection in chip manufacturing and packaging, Cu bumping technology in wafer- and panel- level packaging is developed to micrometer-sized structures and pitches to accommodate increased I/O numbers on high-end integrated circuits. Driven by this industrial demand, significant efforts have been dedicated to Cu electroplating techniques for improved pillar shape control and solder joint reliability, which substantially depend on additive formulations and electroplating parameters that regulate the growth morphology, crystal structure, and impurity incorporation in the process of electrodeposition. It is necessary to investigate the effect of an additive on Cu pillar electrodeposition, and to explore the Kirkendall voids formed during the reflowing process, which may result from the additive-induced impurity in the electrodeposited Cu pillars. In this work, a self-synthesized polyquaterntum (PQ) was made out with dual suppressor and leveler effects, and was combined with prototypical accelerator bis- (sodium sulfopropyl)-disulfide (SPS) for patterned Cu pillar electroplating. Then, Sn96.5/Ag3.0/Cu0.5 (SAC305) solder paste were screen printed on electroplated Cu pillars and undergo reflow soldering. Kirkendall voids formed at the joint interfaces were observed and quantified by SEM. Finally, XRD, and EBSD were employed to characterize the microstructure under varying conditions. The results indicate that PQ exhibits significant suppressive and levelled properties with the new structure of both leveler and suppressor. However, its effectiveness is dependent on liquid convection. PQ and SPS work synergistically, influencing the polarization effect in various convective environments. Consequently, uneven adsorption occurs on the surface of the Cu pillars, which results in more Kirkendall voids at the corners than at the center along the Cu pillar surface.

Boosting the two-dimensional electron gas density of Al0.20Ga0.80N/GaN heterostructures by regrowth of an epitaxial Sc0.18Al0.82N layer

Sc-alloyed AlN epilayers were grown on commercial GaN/sapphire templates by molecular beam epitaxy (MBE) to validate the Sc composition of 18% and in-plane lattice matching with GaN. As-grown Sc0.18Al0.82N/GaN heterostructure exhibits a two-dimensional electron gas (2DEG) density of 3.58 × 1013 (2.96 × 1013) cm−2 and a mobility of 241 (295) cm2⋅V−1⋅s−1 at 300 (77) K, demonstrating the feasibility of employing its high spontaneous polarization toward high 2DEG density and highlighting detrimental impurity scattering due to the regrowth interface. Implementation of AlN impurity blocking layers boosts 2DEG mobility to 1290 (8730) cm2 V−1⋅s−1at 300 (77) K. In addition, we have engineered a surface-treatment strategy to selectively decompose the 2.5-nm-thick GaN cap layer of commercial GaN(2.5 nm)/Al0.20Ga0.80N(22 nm)/GaN heterostructure epi-wafers at high temperature prior to MBE regrowth of Sc0.18Al0.82N to eliminate impurity incorporation at the regrowth interface. Regrowth of a Sc0.18Al0.82N layer on the pristine Al0.20Ga0.80N surface increases 2DEG density from 7.89 × 1012 to 9.57 × 1012 cm−2, together with a slight reduction in mobility from 2160 to 1970 cm2⋅V−1⋅s−1 at 300 K, reducing the sheet resistance by 10%. Our calculation implies that it is practical to boost 2DEG density to over 2.0 × 1013 cm−2 by thinning Al0.20Ga0.80N down to 4 nm.

Electrical properties of completely compensated single-crystal Ge-on-GaAs films with two-dimension Coulomb disorder

We present electrical properties of heavily doped and completely compensated Ge films grown on semiinsulating GaAs(100) substrates by vacuum evaporation. The thin (∼100 nm) Ge films are single-crystal and characterized using temperature-dependent transport measurements, with anomalously large activation energy up to half the Ge bandgap, anisotropy of the transverse magnetoresistance, high resistivity (up to 140 Ω cm), low free charge carrier mobility (∼50 cm2/V·s), and concentration (∼1014–1015 cm−3). This behaviour is attributed to a completely compensated semiconductors arising from Ga and As impurity incorporation and large-scale potential fluctuations. Analysis suggests a two-dimensional percolative transport mechanism in Ge-on-GaAs heterostructures.

Advances in Nickel Hydroxide: Structures and Modern Applications (review)

This review article provides an overview of research conducted over the past few decades on nickel hydroxide, a crucial material in both physics and chemistry with notable engineering applications, particularly in batteries. It begins by outlining the structures of the two known polymorphs, α-Ni(OH)2 and β-Ni(OH)2. The article also explores various types of disorder commonly found in nickel hydroxide, such as hydration, stacking faults, mechanical stresses, and the incorporation of ionic impurities. Related materials, including intercalated α-derivatives and basic nickel salts, are also discussed. The review goes on to summarize several methods for synthesizing nickel hydroxide, such as chemical and electrochemical precipitation, sol–gel synthesis, chemical aging, hydrothermal and solvothermal synthesis, electrochemical oxidation, microwave-assisted synthesis, and sonochemical methods. Finally, the known physical properties of nickel hydroxide—magnetic, vibrational, optical, electrical, and mechanical—are examined. The concluding section offers a summary of the potentially valuable properties of these materials and techniques for identifying and characterizing unknown nickel hydroxide-based samples.

Growth of broken crystals tracked in 4D using X-ray computed tomography and its influence on impurity incorporation

Crystallization is a commonly used unit operation for separation and purification. During processing, crystals may break due to mechanical stress, e.g., intentionally by milling or unintentionally through collision with stirrers. This study investigates the growth of broken crystals in three dimensions using X-ray micro-computed tomography. The results show that damaged regions of crystals grow faster than faceted regions, and crystals become faceted through growth. Initially, this happens on a microscale, producing faceted but concave regions on the crystal surface. Eventually, crystals become convex. Shape-healing through growth incorporates inclusions in the crystals. These findings have important implications for designing and optimizing crystallization processes in the pharmaceutical, food, and chemical industries, as purity is often a critical quality criterion adversely affected by inclusions. In addition, the kinetics in crystallization processes are likely to be strongly affected by the growth of non-faceted and concave crystals.

A Lab-Scale Evaluation of Parameters Influencing the Mechanical Activation of Kaolin Using the Design of Experiments.

This research investigates the mechanical activation of kaolin as a supplementary cementitious material at the laboratory scale, aiming to optimize milling parameters using the response surface methodology. The study evaluated the effects of rotation speed and milling time on the amorphous phase content, the reduction in crystalline kaolinite, and impurity incorporation into the activated clay through the Rietveld method. The results demonstrated that adjusting milling parameters effectively enhanced clay activation, which is crucial for its use in low-carbon cements. High rotation speeds (300/350 rpm) and prolonged grinding times (90/120 min) in a planetary ball mill increased the pozzolanic activity by boosting the formation of amorphous phases from kaolinite and illite and reducing the particle size. However, the results evidenced that intermediate milling parameters are sufficient for reaching substantial degrees of amorphization and pozzolanic activity, avoiding the need for intensive grinding. Exceedingly aggressive milling introduced impurities like ZrO2 from the milling equipment wear, underscoring the need for a balanced approach to optimizing reactivity while minimizing impurities, energy consumption, and equipment wear. Achieving this balance is essential for efficient mechanical activation, ensuring the prepared clay's suitability as supplementary cementitious materials without excessive costs or compromised equipment integrity.

Integrated textural and geochemical analysis of igneous zircon by atom probe tomography

Mechanisms relating to growth and/or compositional modification of zircon occur at the atomic scale. For felsic igneous systems, processes responsible for growth patterns in zircon have previously remained elusive as the volume of material needed to analyze these compositional features using traditional in-situ methods is considerably larger than the typical sub-micron scale distribution of trace elements. To illuminate some of these driving forces, we characterize and quantify minor and trace element concentrations in igneous zircon grains by combining methods of cathodoluminescence (CL) imaging, electron microprobe microanalysis (EMPA) elemental maps for Hf, Y, Yb and U or Th, and atom probe tomography (APT). We focus on igneous zircon from the Chon Aike Silicic Large Igneous Province (Patagonia) that provide novel insights into (1) dissolution and re-crystallization during crustal anatexis, (2) crystallization to produce oscillatory zonation patterns that are typical of igneous zircons, and (3) the incorporation of trace element impurities (e.g., P, Be, and Al) at the nanoscale. Significantly, these APT volumes provide nanoscale sampling of boundaries between oscillatory growth zones in an igneous zircon to reveal compositional zoning of Y and, to a lesser extent P, which appear as high-angle, planar features. These concentration boundaries measured on the order of 10 to 12 nm are difficult to reconcile with proposed mechanisms for generating fine-scaled oscillations. Lastly, we fit diffusional profiles to measured Y concentrations to provide an estimate on the maximum timescales of zircon growth prior to eruption, as a function of the temperature at which diffusion occurred. When combined with known pressure-temperature-time paths for the magmatic system considered, these extremely short diffusion profiles that are resolvable by APT provide a powerful method to constrain timescales of crystal growth.

Selective conversion of spent cracking catalyst to faujasite-structured zeolites

Current recycling strategies for spent catalyst in Fluid Catalytic Cracking (FCC) focus on valuable rare-earth elements (REE) and sometimes include a reuse of spent materials by down-cycling, which hinders a circular economy. Herein, a new procedure for the selective conversion of spent FCC catalysts to FAU-type zeolite without secondary crystalline phases such as sodalite, zeolite P or zeolite A is reported. The steps include a leaching process of REE, followed by thermal activation with sodium hydroxide and acid treatment to get an aluminum-rich feed. The synthesis of FAU-type zeolites with varying Si/Al ratios uses the aluminum-rich catalyst feed and commercial water glass. The experiments show that incorporation of silicate from water glass into the zeolite structure is limited to zeolite products with Si/Al ratio ≤ 2.0. It indicates a flocculation of silicates in higher concentration in competition to the crystallization process of FAU-type zeolites. This is reinforced by the resulting crystals, covered and surrounded with small particles with morphology of silica. Moreover, a clear differentiation between zeolite Y and zeolite X is possible from materials properties with the definite evidence of a mixed phase. The kinetics of feed dissolution and incorporation of impurities, alumina and silica are controlled by the pre-treatment temperature, duration and silicon source. This enables flexible adjustment of the aluminum re-use from spent FCC catalyst, the amount of foreign elements (Fe, Ni, V), phase purity, Si/Al ratio, specific surface area and thermal stability of the final zeolite product. Structural and textural data of the resulting zeolites reveals high crystallinity > 80 %, Si/Al ratios of 1.6–2.0, and specific surface areas up to 780 m2/g.

Synthesis and structural analysis of graphene nanosheets via microwave atmospheric pressure plasma

This study reports the effective synthesis of multilayered graphene sheets via microwave atmospheric pressure plasma. This innovative approach streamlines and expedites graphene production and other carbon nanostructures, eliminating the need for catalysts, solvents, or complex processing conditions. Ethanol is directly injected into a microwave-generated argon plasma plume, leading to the formation of graphene. Raman spectroscopy revealed characteristic peaks (2D, G, and D bands) confirming graphene composition, with defects indicated by the D band. X-ray diffraction analysis supported these findings, indicating a broad peak at 25∘ corresponding to the (002) plane, affirming a multi-layered graphene structure. Scanning electron microscopy exhibited crumpled, randomly oriented graphene sheets, albeit with uneven structures suggesting impurity incorporation. The presence of defects was quantified through the intensity ratio of the D to G band (ID/IG) in Raman spectroscopy, revealing a value of 0.80, signifying the presence of defects in the synthesized graphene. The 2D to G band intensity ratio (I2D/IG) suggested the existence of 7–10 graphene layers, highlighting the need for further optimization for enhanced graphene quality and purity.

(Invited) Insights into Atomistic Processes at Electrified Solid/Liquid Interfaces from Ab Initio Calculations

Many of the challenges we face today towards achieving a greener economy focus on processes occurring at electrified solid/liquid interfaces. Understanding how the interactions between the solid, the liquid and dissolved species are affected by the applied potential will aid our ability to achieve rational design and targeted optimization of relevant processes. Hereby, ab initio molecular dynamic simulations including explicit modelling of the aqueous environment have proven an indispensable tool to gain insights into reaction mechanisms. More approximate choices to modelling the electrolyte, such as implicit solvent models, are however also popular. The talk will discuss the suitability of approximate models for the aqueous environment to study, e.g., the stability of surface phases in the Mg/H2O system and incorporation of impurities in nano-aerogels during synthesis [1,2], by coupling DFT calculations with thermodynamic models. Furthermore, insights into reaction mechanism at electrified solid/liquid interfaces enabled by our recent developments of a thermopotentiostat [3,4] will be presented, using the example of Pt[5].[1] S.-H. Kim, S.-H. Yoo, S. Shin, A. El-Zoka, O. Kasian, J. Lim, J. Jeong, C. Scheu, J. Neugebauer, H. Lee, M. Todorova, B. Gault, Adv. Mater. 34, 2203030 (2022)[2] S.-H. Kim, S.-H. Yoo, P. Chakraborty, J. Jeong, J. Lim, A. El-Zoka, L. Stephenson, T. Hickel, J. Neugebauer, C. Scheu, M. Todorova, B. Gault, J. Am. Chem. Soc. 144, 987 (2022)[3] S. Surendralal, M. Todorova, M. Finnis, and J. Neugebauer, Phys. Rev. Lett. 120, 246801 (2018)[4] F. Deißenbeck, C. Freysoldt, M. Todorova, J. Neugebauer, and S. Wippermann, Phys. Rev. Lett. 126, 136803 (2021)[5] S. Surendralal, M. Todorova, and J. Neugebauer, Phys. Rev. Lett. 126,166802 (2021)

(Invited) Development of Single Crystal Nbn Superconductor on Wide Bandgap GaN By Sputtering and Thermal Annealing

The field of quantum computing is rapidly evolving, and Niobium Nitride (NbN) superconductors have emerged as a pivotal component in the field of quantum computing due to their unique properties. NbN possesses relatively higher superconducting transition temperature (Tc = 15-17 K) as compared to traditional superconductors, making it a promising material for various applications, including superconductor quantum computers, single photon detectors, and hot electron bolometers [1]. The investigation of NbN's superconductivity has been a subject of extensive research over the past few decades. Given that the properties of NbN are intricately linked to its crystal structure, lattice constant, and nitrogen content, precise control of the structural and electrical characteristics of NbN films is essential for the realization of NbN based quantum devices. The (111) planes of δ-NbN exhibit relatively small lattice mismatches with group-III nitride semiconductors (~0.2% for AlN and ~2.7% for GaN) [2], suggesting the potential for integrating crystalline NbN superconductors with nitride semiconductors on a single wafer. Notably, N-polar AlGaN/GaN high electron mobility transistors have been successfully fabricated on NbN films, operating under Tc with a negative differential resistance [3], indicating that the integration of nitride semiconductors and superconductors can be harnessed to create Josephson junctions. To achieve high-quality all-nitride NbN/group-III nitride/NbN Josephson junctions, a comprehensive understanding of the NbN/GaN heterointerfaces is crucial. Despite limited reports on the epitaxial growth of NbN films on nitride semiconductors, little is known about the structural and transport properties of such NbN films. Previously, MBE growth of NbN films have been demonstrated on GaN substrate, showing superconducting critical temperatures exceeding 10 K [4]. In this presentation, our efforts on the development of single crystal NbN thin films on wide bandgap GaN substrate using cost efficient sputtering technique followed by a subsequent high-temperature annealing will be presented. Commercially available single-crystalline GaN (0001)/sapphire templates as well as differently oriented (c and a-planes) sapphire substrates are used as the substrates for the sputtered deposition of NbN films at 20 °C. After the deposition, a high temperature annealing was performed separately at 950 °C for 30 mins under Ar as well as N2 atmosphere. While the as-deposited NbN film on GaN did not exhibit a discernible peak in the high-resolution XRD measurement, a high-intensity, single crystal (111)-oriented NbN film emerged prominently after annealing in both N2 and Ar environments. This suggests a notable enhancement in the crystalline quality of the superconducting material attributable to the thermal annealing process. Although the crystallinity of the NbN layer improves post-annealing, there is an associated increase in grain size and surface roughness. Preliminary findings indicate a reduction in the critical temperature of the NbN film from 12.82 K to 8.69 K after high-temperature annealing, potentially linked to the incorporation of impurities and crystallographic defects during this process. Further investigations using atomic resolution transmission electron microscopy, secondary ion mass spectrometry and X-ray photoelectron spectroscopy will be performed to investigate the influence of annealing duration, temperature, and conditions on the critical temperature, impurity incorporation and defect formation in NbN films deposited with different thickness.In continuation of our recent exploration into depositing crystalline superconducting NbN films on III-nitride semiconductors, this presentation will also focus on our recent advancement of ultrawide bandgap semiconductor materials such as the growth of high-quality quality β-Ga2O3 films and its ternary (AlxGa1-x)2O3 alloys, using metalorganic (MOCVD) and low-pressure (LPCVD) chemical vapor deposition growth techniques. Ga2O3 and (AlxGa1-x)2O3 have emerged as a promising semiconductor material platform for applications in high-power electronics and ultraviolet optoelectronics due to their excellent chemical and thermal stability, as well as high breakdown field strengths. The structural and electrical characteristics of Si-doped β-Ga2O3 and (AlxGa1-x)2O3 thin films will be presented. Additionally, we will present recent findings on achieving phase-pure β-(AlxGa1-x)2O3 films with a record-high Al composition (< 99%) [5]. Our research efforts into understanding the orientation-dependent Al incorporation in β-(AlxGa1-x)2O3 thin films and the determination of band offsets at β-(AlxGa1-x)2O3/β-Ga2O3 heterostructures will be presented. Furthermore, the presentation will touch upon the heteroepitaxial development of other phases of Ga2O3 and (AlxGa1-x)2O3, including α, γ, and κ. Acknowledgment: Dr. Bhuiyan acknowledges the support and guidance of his PhD advisor- Dr. Hongping Zhao at The Ohio State University for the MOCVD growth and characterization of β-Ga2O3 and (AlxGa1-x)2O3 films conducted in Zhao's group. Reference: Yamashita et al., Phys. Rev. Appl. 8, 054028 (2017).Kobayashi et al., Appl. Phys. Express 13, 061006 (2020).Yan et al., Nature 555, 183 (2018).G. Wright et al., APL Mater. 10, 051103 (2022).Bhuiyan et. al, Phys. Status Solidi RRL 17, 2300224 (2023). Figure 1

Stemless InSb nanowire networks and nanoflakes grown on InP

Among the experimental realization of fault-tolerant topological circuits are interconnecting nanowires with minimal disorder. Out-of-plane indium antimonide (InSb) nanowire networks formed by merging are potential candidates. Yet, their growth requires a foreign material stem usually made of InP–InAs. This stem imposes limitations, which include restricting the size of the nanowire network, inducing disorder through grain boundaries and impurity incorporation. Here, we omit the stem allowing for the growth of stemless InSb nanowire networks on an InP substrate. To enable the growth without the stem, we show that a preconditioning step using arsine (AsH3) is required before InSb growth. High-yield of stemless nanowire growth is achieved by patterning the substrate with a selective-area mask with nanohole cavities, containing restricted gold droplets from which nanowires originate. Interestingly, these nanowires are bent, posing challenges for the synthesis of interconnecting nanowire networks due to merging failure. We attribute this bending to the non-homogeneous incorporation of arsenic impurities in the InSb nanowires and the interposed lattice-mismatch. By tuning the growth parameters, we can mitigate the bending, yielding large and single crystalline InSb nanowire networks and nanoflakes. The improved size and crystal quality of these nanostructures broaden the potential of this technique for fabricating advanced quantum devices.

Microstructure and optical properties of Au:N doped diamond-like carbon films: Effect of working pressure

In recent years, the incorporation of impurities (metallic or non-metallic) into diamond-like carbon films for industrial and biological applications has garnered considerable attention from researchers. In this study, gold nanoparticles and nitrogen impurities were introduced into diamond-like carbon using a co-deposition method involving Radio Frequency Plasma-Enhanced Chemical Vapor Deposition (RF-PECVD) and Radio Frequency Sputtering (RF-sputtering),modifying the working pressure from 14.5 to 19.5 mTorr. X-ray Diffraction (XRD) patterns confirmed the presence of gold nanocrystals in the samples. The surface morphology of the films was analyzed using images obtained from Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) subjected to statistical and fractal analyses. These investigations revealed non-symmetric Gaussian distributions of the grains, demonstrating a multifractal nature in all samples, as well as a complex relationship between film roughness and working pressure. Films prepared at working pressures of 16.5 and 18.5 mTorr exhibited the roughest and smoothest surfaces, respectively. Fast Fourier Infrared (FTIR) spectroscopy was used to identify functional groups and to estimate the sp2/sp3 ratio. Raman spectra show D and G bands associated with the disordered graphitic carbon of the DLC, with the intensity of the G band being higher than that of the D band, indicating a higher sp2 bonding content compared to sp3 bonding. Subsequently, the absorption UV–visible spectrum of the samples was examined, confirming the presence of gold nanoparticles in the films, as evidenced by the occurrence of a Localized Surface Plasmon Resonance peak, whose location dependent on the working pressure used during deposition. These observations are consistent with other microscopic and structural analyses.

Diffusion of Co and Ga in α-Ti

The diffusion of Co and Ga atoms in α-Ti has been studied using the projector augmented-wave method in combination with the transition state theory. The formation energies of the interstitial and substitutional defects and the corresponding migration and activation energies along two crystallographic directions within the interstitial and vacancy diffusion mechanisms have been calculated. It has been shown that the energetically preferred interstice for the incorporation of both impurities is crowdion. In the case of Co, the formation energy of this defect is only 0.7 eV higher than that of the substitutional defect, while for Ga this difference reaches 2.6 eV. Using the Landman method and the eight-frequency model, the diffusion coefficients of Co and Ga have been calculated within both interstitial and vacancy mechanisms. It has been shown that Co diffusion occurs faster through the interstitials, while Ga diffuses within the vacancy mechanism. The migration and activation energies as well as diffusion coefficients and their anisotropy obtained in these cases are consistent with experimental data.

Achieving High Substitutional Incorporation in Mn-Doped Graphene.

Despite its broad potential applications, substitution of carbon by transition metal atoms in graphene has so far been explored only to a limited extent. We report the realization of substitutional Mn doping of graphene to a record high atomic concentration of 0.5%, which was achieved using ultralow-energy ion implantation. By correlating the experimental data with the results of ab initio Born-Oppenheimer molecular dynamics calculations, we infer that direct substitution is the dominant mechanism of impurity incorporation. Thermal annealing in ultrahigh vacuum provides efficient removal of surface contaminants and additional implantation-induced disorder, resulting in Mn-doped graphene that, aside from the substitutional Mn impurities, is essentially as clean and defect-free as the as-grown layer. We further show that the Dirac character of graphene is preserved upon substitutional Mn doping, even in this high concentration regime, making this system ideal for studying the interaction between Dirac conduction electrons and localized magnetic moments. More generally, these results show that ultralow energy ion implantation can be used for controlled functionalization of graphene with substitutional transition-metal atoms, of relevance for a wide range of applications, from magnetism and spintronics to single-atom catalysis.

Performance tweaking of Co3O4 UV radiation detector via zirconium dopant microstructural and photo-electronic engineering

Incorporation of dopant impurities in semiconducting metal oxide nanostructures has been presumed to increase the pace at which photo-induced holes and electrons separate due to possible bandgap engineering and oxygen vacancy modulations. In this study, we have adopted an electrodeposition technique using a three-electrode configuration for the preparation of Co3O4 thin film samples and investigated the effect of Zr as a dopant ion on the UV radiation sensing performance of nanostructured Co3O4 host material via energy band engineering and microstructural modulation. Consistency in optical energy band gap measurements of the deposited Zr-doped Co3O4 (Zr@Co3O4) was unveiled with the aid of two models: Tauc’s and absorption spectrum fitting (ASF) methods. Ag/Zr@Co3O4/ITO/glass UV radiation detector was fabricated and a sample with 3 % Zr-dopant content demonstrated high UV-365 nm detector performance: detectivity, 1.2 ×1011 Jones, and responsivity, 1818 mA W−1, with high cycling stability, attributable to the host's dopant microstructural tailoring, and the enhancement in its electronic charge carrier number and their scattering potentials within the host's band structure, thanks to the synergistic impacts of dopant ion incorporation and UV irradiation.

Effect of growth rate on the incorporation of silicon impurity in single crystal diamond

In this paper, we systematically investigate the influence of growth rate on the incorporation of silicon in single crystal diamond. The intensity of SiV− center is significantly enhanced with the increase of methane flow rate. By analyzing the optical emission spectrum and photoluminescence spectrum of samples grown with different methane concentrations, the enhancement of SiV− intensity is not associated with the Si–C concentration in the precursor but with the higher growth rate. In addition, an increased oxygen flow rate significantly decreases the intensity of SiV− center, which is attributed to the formation of insoluble silicon oxide as well as the relatively lower growth rate. Finally, we propose a growth model to explain the effect of growth rate on the incorporation of silicon impurity.

Generation of out-of-plane ferroelectric behavior in a one-atom-thick monolayer

Ferroelectricity with out-of-plane polarization has so far been found in several two-dimensional (2D) materials, including monolayers comprising three to five planes of atoms, e.g. α-In2Se3 and MoTe2. Here, we explore the generation of out-of-plane polarization within a one-atom-thick monolayer material, namely hexagonal boron nitride. We performed density-functional-theory calculations to explore inducing ferroelectric-like distortions through incorporation of isovalent substitutional impurities that are larger than the host atoms. This disparity in bond lengths causes a buckling of the h-BN, either up or down, which amounts to a dipole with two equivalent energies and opposing orientations. We tested several impurities to explore the magnitude of the induced dipole and the switching energy barrier for dipole inversion. The effects of strain, dipole–dipole interactions, and vertical heterostructures with graphene are further explored. Our results suggest a highly-tunable system with ground state antiferroelectricity and metastable ferroelectricity. We expect that this work will help foster new ways to include functionality in layered 2D-material-based applications.

Estimation of the Shear Viscosity of Mixed-Polymer Materials for Screw Extrusion-Based Recycling Process Modeling.

The scope of this work is the development of a method to estimate the temperature and shear rate-dependent viscosity of mixtures composed of two polymers. The viscosity curve of polymer mixtures is crucial for the modeling and optimization of extrusion-based recycling, which is the most efficient way to recycle polymeric materials. The modeling and simulation of screw extruders requires detailed knowledge of the properties of the processed material, such as the thermodynamic properties, the density, and the rheological behavior. These properties are widely known for pure materials; however, the incorporation of impurities, like other polymers in recycled materials, alters the properties. In this work, miscible, immiscible, and compatibilized immiscible polymer mixtures are considered. A new method based on shear stress is proposed and compared to the shear rate-based method. Several mixing rules are evaluated for their accuracy in predicting mixture viscosity. The developed methods allow the prediction of the viscosity of a compatibilized immiscible mixture with deviations below 5% and that of miscible polymer mixtures with deviations below 3.5%.

Nanomolecularly-induced Effects at Titania/Organo-Diphosphonate Interfaces for Stable Hybrid Multilayers with Emergent Properties.

Nanoscale hybrid inorganic-organic multilayers are attractive for accessing emergent phenomena and properties through superposition of nanomolecularly-induced interface effects for diverse applications. Here, we demonstrate the effects of interfacial molecular nanolayers (MNLs) of organo-diphosphonates on the growth and stability of titania nanolayers during the synthesis of titania/MNL multilayers by sequential atomic layer deposition and single-cycle molecular layer deposition. Interfacial organo-diphosphonate MNLs result in ∼20-40% slower growth of amorphous titania nanolayers and inhibit anatase nanocrystal formation from them when compared to amorphous titania grown without MNLs. Both these effects are more pronounced in multilayers with aliphatic backbone-MNLs and likely related to impurity incorporation and incomplete reduction of the titania precursor indicated by our spectroscopic analyses. In contrast, both MNLs result in two-fold higher titania nanolayer roughness, suggesting that roughening is primarily due to MNL bonding chemistry. Such MNL-induced effects on inorganic nanolayer growth rate, roughening, and stability are germane to realizing high-interface-fraction hybrid nanolaminate multilayers.