What Puts the "Tribo" in Triboelectricity?

An enduring question in science has been why sliding plays a major role in the triboelectric generation of static electricity-the "tribo" in triboelectricity. We provide here a general explanation which is rooted in established science. When sliding is taking place, there is symmetry breaking due to elastic shear, so the front of the sliding body experiences different elastic strains from the back.

Flexoelectricity, Triboelectricity, and Free Interfacial Charges.

Triboelectricity has been a topic of some confusion for many years, probably because it is very diverse and some of the fundamental science has not been clear. This is now starting to change. A few years ago, the importance of flexoelectricity at asperities is pointed out.

Wet to Dry Controls Lanthanide Scandate Synthesis.

The choice of temperature and gas conditions used in a water pressure-controlled reactor is guided by density functional theory (DFT) to synthesize nearly phase-pure lanthanide scandate nanoparticles (LnScO, Ln = La, Nd, Sm, Gd). In this synthetic method, low water-vapor partial pressures, well below water's gas liquidus, inhibit particle growth, while an excess of water vapor results in undesired rare-earth hydroxide and oxyhydroxide secondary phases. The optimal humidity for high-purity LnScO particle synthesis is shown to vary with the lanthanide; DFT is used to calculate the thermodynamics of secondary phase formation for each lanthanide tested such that the role of water vapor may be quantified and used to maintain phase purity (greater than 96 mol %) across the series.

Change in Financial Stress and Relational Wellbeing During COVID-19: Exacerbating and Alleviating Influences.

Guided by the family adjustment and adaptation response (FAAR) model and using a panel survey of 1510 adults in the US administered during the summer of 2020 and a mixed methods approach, we explored associations between changes in financial stress related to COVID-19 and relational wellbeing. Regression analyses showed that, compared to those who maintained their levels of financial stress, those who reported increased financial stress reported increased conflict and those who reported decreased financial stress reported decreased conflict. However, decreased financial stress was also associated with decreases in emotional closeness and relationship happiness, suggesting that changes in financial stress can lead to both and in families.

When Flexoelectricity Drives Triboelectricity.

Triboelectricity has been known since antiquity, but the fundamental science underlying this phenomenon lacks consensus. We present a flexoelectric model for triboelectricity where contact deformation induced band bending at the nanoscale is the driving force for charge transfer. This framework is combined with first-principles and finite element calculations to explore charge transfer implications for different contact geometry and materials combinations.

Band Bending and Ratcheting Explain Triboelectricity in a Flexoelectric Contact Diode.

Triboelectricity was recognized millennia ago, but the fundamental mechanism of charge transfer is still not understood. We have recently proposed a model where flexoelectric band bending due to local asperity contacts drives triboelectric charge transfer in non-metals. While this ab initio model is consistent with a wide range of observed phenomena, to date there have been no quantitative analyses of the proposed band bending.

CO Adsorption and Disproportionation on Smooth and Defect-Rich Ir(111).

CO adsorption and dissociation on "perfect" and "defect-rich" Ir(111) surfaces were studied by a combination of surface-analytical techniques, including polarization-dependent (PPP and SSP) sum frequency generation (SFG) vibrational spectroscopy, low-energy electron diffraction (LEED), Auger electron spectroscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. CO was found to be ordered and tilted from the surface normal at high coverage on the "perfect" surface (e.g.

Predictive Mixing for Density Functional Theory (and Other Fixed-Point Problems).

Density functional theory calculations use a significant fraction of current supercomputing time. The resources required scale with the problem size, the internal workings of the code, and the number of iterations to convergence, with the latter being controlled by what is called "mixing". This paper describes a new approach to handling trust regions within these and other fixed-point problems.

Humility in family relationships: Exploring how humility influences relationships in religious families.

In this article, we explored how humility influences family relationships in religious families. We used a qualitative methodology and interviewed a religiously, ethnically, and geographically diverse sample of 198 highly religious families ( = 476). Family-level data were collected by using multiple informants through joint interviews with family members.

Perspectives from Highly Religious Families on Boundaries and Rules About Sex.

We investigated the intersection of religion and boundaries placed around sex using qualitative data from 198 highly religious Muslim, Christian, and Jewish families. Coding performed by two researchers resulted in six core themes that provide insight into the connection between these two domains. Frequency counts of the core themes, participant quotes, and implications are presented-including the benefits of practitioners inquiring into how clients' faith affects sexual behavior and scripts, how fidelity and vows might serve a protective function for the relationships of highly religious couples, and how religion may empower women in terms of sexual boundary setting.

WIEN2k: An APW+lo program for calculating the properties of solids.

The WIEN2k program is based on the augmented plane wave plus local orbitals (APW+lo) method to solve the Kohn-Sham equations of density functional theory. The APW+lo method, which considers all electrons (core and valence) self-consistently in a full-potential treatment, is implemented very efficiently in WIEN2k, since various types of parallelization are available and many optimized numerical libraries can be used. Many properties can be calculated, ranging from the basic ones, such as the electronic band structure or the optimized atomic structure, to more specialized ones such as the nuclear magnetic resonance shielding tensor or the electric polarization.

Direct Visualization of Independent Ta Centers Supported on Two-Dimensional TiO Nanosheets.

Highly dispersed, supported oxides are ubiquitous solid catalysts but can be challenging to characterize with atomic precision. Here, it is shown that crystalline anatase TiO nanosheets (∼5 nm thick) are ideal supports for imaging highly dispersed active sites. Ta cations were deposited by several routes, and high-resolution high angle annular dark-field scanning transmission electron microscopy was used to determine the location of Ta with respect to the TiO lattice and quantify Ta-Ta distances.

Does Flexoelectricity Drive Triboelectricity?

The triboelectric effect, charge transfer during sliding, is well established but the thermodynamic driver is not well understood. We hypothesize here that flexoelectric potential differences induced by inhomogeneous strains at nanoscale asperities drive tribocharge separation. Modeling single asperity elastic contacts suggests that nanoscale flexoelectric potential differences of ±1-10  V or larger arise during indentation and pull-off.

How heteroepitaxy occurs on strontium titanate.

In traditional models of heteroepitaxy, the substrate serves mainly as a crystalline template for the thin-film lattice, dictating the initial roughness of the film and the degree of coherent strain. Here, performing in situ surface x-ray diffraction during the heteroepitaxial growth of LaTiO on SrTiO (001), we find that a TiO adlayer composed of the 33.7° and 45.

Early-stage NiCrMo oxidation revealed by cryo-transmission electron microscopy.

Hydroxide formation at the surface of corroded alloys is critical for understanding early-stage oxidation of many corrosion-resistant alloys. Many hydroxides are unstable in an ambient environment and are electron-beam sensitive, limiting the use of conventionally-prepared specimens for transmission electron microscopy characterization of these alloy-water interfaces. In order to avoid sample dehydration, NiCrMo alloys corroded in a Cl-containing electrolyte solution were cryo-immobilized by plunge freezing.

Charging ain't all bad: Complex physics in DyScO.

Although charging is ubiquitous in electron microscopy, its effects are typically avoided or ignored. However, avoiding charging is not possible in some materials, e.g.

Nonequilibrium Solute Capture in Passivating Oxide Films.

We report experimental results on the composition and crystallography of oxides formed on NiCrMo alloys during both high-temperature oxidation and aqueous corrosion experiments. Detailed characterization using transmission electron microscopy and diffraction, aberration-corrected chemical analysis, and atom probe tomography shows unexpected combinations of composition and crystallography, far outside thermodynamic solubility limits. The results are explained using a theory for nonequilibrium solute capture that combines thermodynamic, kinetic, and density functional theory analyses.

Spirituality, Humor, and Resilience After Natural and Technological Disasters.

Purpose: Multiple exposures to disaster are associated with high levels of stress and with long-term consequences for survivors. However, little is known about coping and resilience in multiple disaster contexts. In this study, we focused on spiritual and secular coping resources and the roles they may play in postdisaster resilience.

Kinetic Growth Regimes of Hydrothermally Synthesized Potassium Tantalate Nanoparticles.

A general mathematical kinetic growth model is proposed on the basis of observed growth regimes of hydrothermally synthesized KTaO nanoparticles from electron microscopy studies on the surface morphology and surface chemistry. Secondary electron imaging demonstrated that there are two dominant growth mechanisms: terrace nucleation, where the surfaces are rough, and terrace growth, where surfaces are smooth. In the proposed model based upon standard step-flow growth, the rates of both mechanisms are established to be dependent on the chemical potential change of the growth environment-terrace nucleation dominates with larger negative chemical potential, and terrace growth dominates with smaller negative chemical potential.

"The family that prays together . . .": Relational processes associated with regular family prayer.

In the present article we explored how family prayer reportedly influenced family relationships. We conceptualized family prayer as a family ritual in religious families and used a qualitative methodology to interview a religiously, ethnically, and geographically diverse sample of 198 families ( = 476). Analysis of data revealed 7 related themes.

Direct Observation of Large Flexoelectric Bending at the Nanoscale in Lanthanide Scandates.

There is a growing interest in the flexoelectric effect, since at the nanoscale it is predicted to be very large. However, there have been no direct observations of flexoelectric bending consistent with current theoretical work that implies strains comparable to or exceeding the yield strains of typical materials. Here we show a direct observation of extraordinarily large, two-dimensional reversible bending at the nanoscale in dysprosium scandate due to the converse flexoelectric effect, with similar results for terbium and gadolinium scandate.

Development of a hybrid molecular beam epitaxy deposition system for in situ surface x-ray studies.

A portable metalorganic gas delivery system designed and constructed to interface with an existing molecular beam epitaxy chamber at beamline 33-ID-E of the Advanced Photon Source is described. This system offers the ability to perform in situ X-ray measurements of complex oxide growth via hybrid molecular beam epitaxy. The performance of the hybrid molecular beam epitaxy system while delivering metalorganic source materials is described.

Synthesis of Gadolinium Scandate from a Hydroxide Hydrogel.

Gadolinium scandate (GdScO) has been synthesized at 300 °C through the decomposition of a mixed cation hydroxide hydrogel in a humid environment. Increasing the reaction temperature produced larger particles that better adopted the Wulff shape. A lack of water vapor during the synthesis caused the solid network of the hydrogel to collapse upon heating so an amorphous xerogel was produced.

Layer-by-Layer Epitaxial Growth of Defect-Engineered Strontium Cobaltites.

Control over structure and composition of (ABO) perovskite oxides offers exciting opportunities since these materials possess unique, tunable properties. Perovskite oxides with cobalt B-site cations are particularly promising, as the range of the cation's stable oxidation states leads to many possible structural frameworks. Here, we report growth of strontium cobalt oxide thin films by molecular beam epitaxy, and conditions necessary to stabilize different defect concentration phases.