Surface Tensile Strain Research Articles

Multifaceted anchoring ligands for uniform orientation and enhanced cubic-phase stability of perovskite quantum dots

All-inorganic CsPbI3 perovskite quantum dots (PQDs) hold significant potential for next-generation photovoltaics due to their unique optoelectronic properties, and the surface-bound ligand playing a key role in the stability and functionality of CsPbI3 PQDs. Initially used long-chain ligands in PQDs synthesis stabilize the black phase but hinder charge transport when employed to solar cells, necessitating their replacement with shorter ones. However, this leads to the formation of surface defects and loss of tensile strain, resulting in the transition to the undesired orthorhombic phase (δ-phase) and compromising PQD solar cell performance. Therefore, developing a ligand exchange process that achieves the optimal balance between conductivity and stability in PQD solid films continues to be a significant challenge. To address these issues, we developed an efficient ligand-exchange process utilizing a multifaceted anchoring ligand, 2-thiophenemethylammonium iodide (ThMAI). The larger ionic size of ThMA+ compared to Cs+ facilitates the restoration of surface tensile strain in PQDs, while its thiophene and ammonium groups enable effective passivation of surface defects. Owing to these advantages, ThMAI-treated CsPbI3 PQD thin films exhibit improved carrier lifetime, uniform PQD orientation, and increased ambient stability. As a result, the ThMAI-treated CsPbI3 PQD solar cells demonstrate an improved power conversion efficiency (PCE) of 15.3 % and an enhanced device stability.

Failure mechanisms of multilayer TiN films based on mechanical properties of film and substrate

The poor adhesion, which is related to the mechanical properties of the substrate and film, leads to the film peeling off from the substrate and failure. In this study, TiN films with various structure were prepared on Ti6Al4V titanium alloy (TC4), 316L stainless steel (316L), 4Cr5MoSiV1 hot work die steel (H13), and W6Mo5Cr4V2 high-speed steel (W6) by adjusting the discharge currents using a hot-wire plasma-enhanced magnetron sputtering rig. The morphologies of the single-layer TiN films varied from loose to dense and ductile to brittle, and the nanohardness and elastic modulus increased as the hot-wire discharge current increased. The morphologies, nanohardnesses, and elastic moduli of the multilayer TiN films gradually approached those of the dense TiN single-layer films as the thicknesses of the top dense layers increased. The results, both by numerical simulation and experimental tests, revealed that the interfacial tensile stress and surface strain of a TiN/substrate system increased as the elastic modulus differences between TiN and its substrate increased, resulting in a serious TiN film elastic and plastic deformation asynchrony and poor film–substrate adhesion. The loose layer between the top dense TiN layer and its substrate acts as a buffer because the elastic modulus of the loose layer is in the middle, higher than that of the substrate but lower than that of the top dense layer. For TiN/TC4 or 316L with large differences in elastic moduli, loose/dense thickness ratios of 1:2 or 1:4 for the multilayer TiN films were sufficient to improve their adhesion. For TiN/H13 or W6, with small elastic modulus differences, a ratio of 1:4 was sufficiently large and may not be necessary.

Self-aligned, inkjet-printed resistors on flexible substrates with excellent mechanical stability, high yield, and low variance

Resistors are basic yet essential circuit components that must be fabricated with high precision at low cost if they are to be viable for flexible electronic applications. Inkjet printing is one of many additive fabrication techniques utilized to realize this goal. In this work, a process termed self-aligned capillarity-assisted lithography for electronics (SCALE) was used to fabricate inkjet-printed resistors on flexible substrates. Capillary channels and reservoirs imprinted onto flexible substrates enabled precise control of resistor geometry and straightforward alignment of materials. More than 300 devices were fabricated using poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as the resistive material and silver as the electrode material. By varying PEDOT:PSS ink formulation and resistor geometry, resistances spanning from 170 Ω to 3.8 MΩ were achieved. Over 98% of devices were functional and the relative standard deviation in resistance ranged from 3% to 18% depending on resistor length and ink composition. The resistors showed no significant change in resistance after 10 000 cycles of bend testing at 1.6% surface tensile strain. In summary, this work demonstrated a fully roll-to-roll compatible process for inkjet printing resistors with superior properties.

Enhancing the selectivity of CO2-to-HCOOH conversion by constructing tensile-strained Cu catalyst

Heterogeneous interface engineering endows catalyst with the possibility to enhance the activity and tune the selectivity of electrochemical CO2 reduction reaction (CO2RR) by induced surface strain and interfacial charges transfer. Herein, a novel In2O3/Cu heterojunction catalyst with 3D succulents-like morphology significantly enhance the selectivity and activity for electrochemical CO2-to-HCOOH conversion as compared to the In2O3 and Cu counterparts, achieving a maximum faraday efficiency (FE) of 87.5 % at −1.1 V vs RHE with corresponding formate partial current density of −70 mA cm−2 at −1.4 V vs RHE. The combined DFT calculation and experimental studies revealed that electrons transfer from interfacial In to Cu via O bridge preserves the metallic state of Cu, which facilitates the capture and activation of CO2 molecules. Furthermore, the surface tensile strain together with interfacial electronic interaction lowers the energy barrier for the formation of *HCOO intermediate, thus boosting the selectivity for HCOOH production. This work demonstrates a feasible strategy for advanced catalyst design by implanted heterogeneous interfaces to manipulate the lattice strain and electronic coupling.

Mechanistic-Empirical Pavement Design for Low-Volume Roads Impacted by Freeze–Thaw

Low-volume roads (LVRs) make up more than half the centerline mileage in the United States and most of these roads are not designed. Instead, a standard thickness is used for all roads or a rough catalog is used to determine the thickness of the pavement layers. The Cornell University Local Roads Program worked with local highway agencies in New York State to develop a mechanistic-empirical (ME) pavement design tool that overcomes the limitations of expertise and time of most LVR highway officials but takes advantage of their knowledge of the LVRs within their jurisdictions. The goal was to use existing information and apply it to the limited design related to LVRs. The tool developed, RoadPE: LHI, uses two common pavement-fatigue criteria—surface tensile strain and subgrade vertical strain—with simplified inputs and built-in trend analysis to determine the thickness of the asphalt layers for overlaid, mill and filled, rehabilitated, and reconstructed LVRs. An ME-based tool will allow highway managers to prepare better designs that account for real-world variations.

In-plane strain engineering in ultrathin noble metal nanosheets boosts the intrinsic electrocatalytic hydrogen evolution activity

Strain has been shown to modulate the electronic structure of noble metal nanomaterials and alter their catalytic performances. Since strain is spatially dependent, it is challenging to expose the active strained interfaces by structural engineering with atomic precision. Herein, we report a facile method to manipulate the planar strain in ultrathin noble metal nanosheets by constructing amorphous–crystalline phase boundaries that can expose the active strained interfaces. Geometric-phase analysis and electron diffraction profile demonstrate the in-plane amorphous–crystalline boundaries can induce about 4% surface tensile strain in the nanosheets. The strained Ir nanosheets display substantially enhanced intrinsic activity toward the hydrogen evolution reaction electrocatalysis with a turnover frequency value 4.5-fold higher than the benchmark Pt/C catalyst. Density functional theory calculations verify that the tensile strain optimizes the d-band states and hydrogen adsorption properties of the strained Ir nanosheets to improve catalysis. Furthermore, the in-plane strain engineering method is demonstrated to be a general approach to boost the hydrogen evolution performance of Ru and Rh nanosheets.

Reducing the interfacial voltage loss in tin halides perovskite solar cells

Tremendous attention has been given to tin halide perovskite solar cells (TPSCs) due to the lower toxicity and similar electronic configuration compared with the lead perovskites. Nevertheless, on account of the intrinsic low bandgap, high defect density and surface/interface non-radiative recombination, the open-circuit voltage loss (Vloss) of TPSCs is comparatively large in all semiconductor solar cells. Herein, a hydrophobic bulky molecule of 3-(trifluoromethyl) phenethylamine hydroiodide (CF3PEAI) was utilized to passivate the lead-free perovskite surface by post-deposition treatment. The Vloss of the corresponding PSC devices was significantly reduced to afford a high open-circuit voltage (Voc) up to 0.73 V with a power conversion efficiency (PCE) of 10.35% in conjunction with the broadly utilized (6,6)-Phenyl C61 butyric acid methyl ester (PC61BM). Additionally, the CF3PEAI interlayer expressively suppressed the interfacial non-radiative recombination accompanying with extending photoexcited carrier lifetime. The formation of oriented 2D Sn-based perovskite could also facilitate the vertical charge-carrier transportation and improve the efficiency of Sn-based PSCs. The density of defect states and the amount of mid-gap states required to be filled were both dramatically reduced. Meanwhile, the surface reconstruction can effectively relax the tensile surface strain with the phenethyl ammonium iodide ligands. Therefore, this surface passivation strategy contributes to the development of high-quality lead-free perovskite film with low internal defects and residual stress.

Dynamic Active Sites in Bi5O7I Promoted by Surface Tensile Strain Enable Selective Visible Light CO2 Photoreduction.

Surface defects with abundant localized electrons on bismuth oxyhalide catalysts are proved to have the capability to capture and activate CO2. However, bismuth oxyhalide materials are susceptible to photocorrosion, making the surface defects easily deactivated and therefore losing their function as active sites. Construction of deactivation-resistant surface defects on catalyst is essential for stable CO2 photoreduction, but is a universal challenge. In this work, the Bi5O7I nanotubes with surface tensile strain are synthesized, which are favorable for the visible light-induced dynamic I defects generation. The CO2 molecules absorbed on I defects are constantly reduced by the incoming photogenerated electrons from I-deficient Bi5O7I nanotubes and the successive protonation of CO2 molecules is thus highly promoted, realizing the selective CO2 conversion process via the route of CO2-COOH--CO. The efficient and stable photoreduction of CO2 into CO with 100% selectivity can be achieved even under visible light (λ >420 nm) irradiation benefited from the dynamic I defects as active sites. The results presented herein demonstrate the unique action mechanism of light-induced dynamic defects during CO2 photoreduction process and provide a new strategy into rational design of deactivation-resistant catalysts for selective CO2 photoreduction.

Experimental investigation on the concrete fracture process zone using electronic speckle pattern interferometry

AbstractIn order to advance the understanding of fracture failure mechanisms in concrete, a series of three‐point bend tests of pre‐notched specimens were conducted to study the characteristics of the fracture process zone. Electronic speckle pattern interferometry (ESPI) was used to determine the location and size of the cracks. The experimental results have shown that crack in the pre‐notched concrete beams will initiate when the load increases to 40% of the peak load (Pmax) and expands unstably after reaching the peak load. When the load drops to about 25% Pmax in the load drop section, a complete fracture process zone (FPZ) was developed, and the corresponding crack tip opening displacement is about 7.1 times to the critical crack tip opening displacement. The analysis of surface strain of concrete specimen showed that microcracks will initiate when the surface tensile strain of concrete reaches about 2 × 10−4; when the surface tensile strain value of concrete reaches 4 × 10−2, the FPZ will move forward; the length of the FPZ of concrete essentially remains the same in the entire fracture process, which is about 71% of the ligament height. The analysis of experimental data also shows that the size of the FPZ is not significantly affected by the cubic compressive strength of concrete. In addition, the tension‐softening curves of the specimens were finally determined by using the incremental displacement collocation method, and it is concluded that the critical width of the FPZ is related to the cubic compressive strength of the concrete.

Strain-Engineering of Bi12O17Br2 Nanotubes for Boosting Photocatalytic CO2 Reduction

The effect of surface tensile strain on the photocatalysis is an open question. In this work, strain engineering has been demonstrated to promote the performance of photocatalysis by curved 2D mate...

3D focused ion beam sectioning of zirconium oxides in Zircaloy-4 for the characterisation of cracking

Sequential 2D sectioning and imaging using a dual-beam focused ion beam and scanning electron microscope has been used to characterise the interconnectivity of cracks in oxide films on Zircaloy-4. Evidence of cracks perpendicular to the metal/oxide interface have been observed in multiple oxides of different thicknesses. Such vertical features are considered critical in the provision of a percolation path between the environment and innermost band of lateral cracks (closest to oxide/environment interface), in between the lateral bands of cracks and between the final band of lateral cracks and the metal/oxide interface. Given the limited occurrence of cracks perpendicular to the metal/oxide interface, localised tensile surface strains have been considered as a potential source of initiation of these cracks.

The influence of tensile strain on water adsorbed on Fe (100) surface: Surface chemistry aspect of stress corrosion cracking

The water adsorption on Fe (100) surface with and without surface tensile strain is studied by spin-polarized self-consistent density functional theory calculations to elaborate the influence of tensile strain on surface chemistry. We find that the surface tension not only enhances the interaction between water and surface but also lowers the energy barrier for water dissociation on the surface. The dissociated reactive OH fragment may further attack the iron surface and the dissociated reactive H fragment could transfer into iron lattice and cause H embrittlement. This study clearly shows that the stressed induced surface chemistry could be an important aspect of stress-corrosion cracking (SCC) in iron based materials.

Competitive adsorption of CO and H<sub>2</sub> on strained Fe(110) surface

In this work, the competitive adsorption behavior of H<sub>2</sub> and CO on strained Fe(110) are investigated by the first-principles method based on the spin-polarized density functional theory to study the hydrogen embrittlement of steels. The results show that the most stable adsorption site for CO is top site, and the orbital of CO molecule hybridizing with Fe 3p and 4s states illustrates a strong electronic interaction between them. The adsorption energy values of CO at the four calculated adsorption sites are more negative than those of H<sub>2</sub>, which favors the binding with Fe(110) surface. The potential energy variations for CO and H<sub>2</sub> molecules close to the surface are calculated. The attractive force of the Fe(110) surface acting on CO in 1.5–3 Å is greater than that acting on H<sub>2</sub>. The pre-adsorbed CO increases the dissociation energy barrier of H<sub>2</sub> from 0.08 eV to 0.13 eV but reduces the force between H<sub>2</sub> and surface. The surface tensile strain enhances the interaction between hydrogen and Fe(110), which, however, is reduced by the compressive strain. The opposite tendency is found in the adsorption of CO. The binding strength of CO is stronger than that of H<sub>2</sub> on the strained Fe(110) surface. The difference in adsorption energy between CO and H<sub>2</sub> decreases with tensile strain increasing. The effect of surface strain and partial pressure of CO gas phase on the surface coverage ratio of H atom are also calculated quantitatively based on thermodynamics at 298 K, with the partial pressure of H<sub>2</sub> set to be 10 MPa. The surface ratio of the H atom decreases with partial pressure of CO increasing. The hydrogen coverage drops nearly to zero when the partial pressure of CO reaches a certain value. This result reveals that CO can inhibit hydrogen adsorption on Fe surface. In the case where the surface ratio of hydrogen decreases to 1%, the corresponding CO partial pressures are 105 Pa, 1.1 × 10<sup>3</sup> Pa, 2.4 × 10<sup>5</sup> Pa on –2%, 0, 2% strained Fe(110) surface, respectively. High CO partial pressure is needed to suppress the hydrogen adsorption since the binding strength of CO is close to that of H<sub>2</sub> on the expanded surface.

Surface Strain Effects on the Adsorption of Au Adatoms on MgO(001) Surfaces with Surface O Vacancies

By employing ab-initio total-energy and electronic-structure calculations based on the density-functional theory, we studied the effects of surface strain es on the adsorption properties of a Au adatom on defective MgO(001) surfaces with surface oxygen vacancies (Fs centers). The formation energy of the Fs center on MgO(001) varied very slightly in the region of es from −6% to −4% and monotonically decreased with the increase in es, from −4% to +6%. As es increased, the adsorption energy ( $$E_{ads}^{{F_S}}$$ ) of Au on the es center of strained MgO(001) monotonically decreased and, in particular, showed a much larger decrease in $$E_{ads}^{{F_S}}$$ for a tensile surface strain of es > +4%. The surface strain dependence on the physical properties, such as the charge states, the spatial charge rearrangement, for Au on the Fs center of strained MgO(001) surfaces was also analyzed. These results provide important physical information on the effects of surface strain on the adsorption of Au on MgO(001) surfaces with Fs centers.

Atomic-Scale Core/Shell Structure Engineering Induces Precise Tensile Strain to Boost Hydrogen Evolution Catalysis.

Tuning surface strain is a new strategy for boosting catalytic activity to achieve sustainable energy supplies; however, correlating the surface strain with catalytic performance is scarce because such mechanistic studies strongly require the capability of tailoring surface strain on catalysts as precisely as possible. Herein, a conceptual strategy of precisely tuning tensile surface strain on Co9 S8 /MoS2 core/shell nanocrystals for boosting the hydrogen evolution reaction (HER) activity by controlling the MoS2 shell numbers is demonstrated. It is found that the tensile surface strain of Co9 S8 /MoS2 core/shell nanocrystals can be precisely tuned from 3.5% to 0% by changing the MoS2 shell layer from 5L to 1L, in which the strained Co9 S8 /1L MoS2 (3.5%) exhibits the best HER performance with an overpotential of only 97 mV (10 mA cm-2 ) and a Tafel slope of 71 mV dec-1 . The density functional theory calculation reveals that the Co9 S8 /1L MoS2 core/shell nanostructure yields the lowest hydrogen adsorption energy (∆EH ) of -1.03 eV and transition state energy barrier (∆E2H* ) of 0.29 eV (MoS2 , ∆EH = -0.86 eV and ∆E2H* = 0.49 eV), which are the key in boosting HER activity by stabilizing the HER intermediate, seizing H ions, and releasing H2 gas.

Investigation on the morphology and optical properties of self-assembled Ag Nanostructures on [formula omitted]-plane GaN by the control of annealing temperature and duration

In this paper, the systematic control of self-assembled Ag nanostructures (NSs) on c-plane GaN is demonstrated by the control of annealing temperature (AT) and annealing duration (AD) at diverse Ag film thicknesses based on the solid-state-dewetting. The Ag NSs evolve in four distinctive growth regimes in terms of size, density and configuration with the 10 nm initial film thickness such as (i) nano-voids and -mounds (ii) nanoclusters (iii) nanoparticles (NPs) and (iv) NPs with sublimation. However, only three growth regimes are observed with the 40 nm set with variant NSs morphology due to the suppression of dewetting and diffusion. Meanwhile, based on the AD control with 30 nm Ag film, the size of Ag NSs are exponentially decreased in terms of the RMS roughness (Rq) and surface area ratio (SAR) due to the extensive sublimation of Ag atoms. The formation of various Ag NSs is discussed based on the Volmer–Weber growth model under the influence of several diffusion condition and Ag sublimation. The optical properties of Ag NSs are studied by the reflectance, Raman and photoluminescence, and the spectral evolution including the peak intensity and shift are discussed in terms of the specific plasmon resonance absorption band and surface tensile strain in reference to the morphology evolution of Ag NSs. In specific, the dipolar resonance peak clearly demonstrates shifts depending on the evolution of Ag NSs.

Ligand-induced symmetry breaking, size and morphology in colloidal lead sulfide QDs: from classic to thiourea precursors

Colloidal lead chalcogenide quantum dots (CQDs) exhibit promising optoelectronic properties for applications in solar cell devices and as thermoelectrics. Herein, we report and discuss a ferroelectric structural distortion, at the picometer scale resolution, in PbS CQDs prepared using both classic and new synthetic pathways. The investigation was performed using synchrotron X-ray total scattering data and advanced methods of analysis that rely on a homo-core-shell model and evaluate the atomic arrangement, stoichiometry, size and morphology of nanocrystals. The CQDs show comparable size-dependent relative elongation, up to 0.7 % of one body diagonal of the cubic rock-salt structure, which corresponds to a rhombohedral lattice deformation. The findings suggest a joint role for the oleate ligands (which induce surface tensile strain) and the Pb(II) lone pair as the driving forces of the deformation. Pb displacements along the [111] direction, which provoke a ferrolectric distortion related to the lattice change, fall in the 0.0 – 0.1 Å. Overall, the findings suggest the local nature of the metal off-centering, leading to different average displacements which depend on the synthetic conditions.

Strain engineering of H/transition metal systems

The effects of both compressive and tensile surface strain on the hydrogenated low-index faces of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt and Au has been investigated using density functional theory (DFT). Changes in the preferred H binding site have been observed on the Pd, Ir and Pt surfaces when the surface lattice constant is strained by up to 2%, and on Fe, Rh, Ag and Os surfaces for larger strains of up to 5%. A complete discussion of the variance of the hydrogen binding energy, charge, density of states and local geometry with strain is presented. The exchange-correlation, electrostatic and kinetic contributions to the binding energy are delineated and their respective contributions are discussed. The mechanism which determines the preferred binding site for each system under strain is shown to be complex.

Pt-based catalysts with tensile surface strain to boost activity

A Chinese–US research collaboration has developed fuel cell catalysts comprising biaxially strained platinum–lead core/Pt shell ‘nanoplates’, that offer enhanced oxygen reduction with minimal decay in catalytic activity.

Surface strain effects on the adsorption and the diffusion of Au atoms on MgO(001) surfaces

The effects of surface strain on the adsorption and the diffusion properties of a Au adatom on MgO(001) surfaces are studied using first-principles electronic-structure calculations based on the density functional theory. The adsorption of Au on MgO(001) is found to become stronger with increasing surface strain. In addition, the adsorption site of Au changes from a site on top of a surface O atom of MgO(001) to a site near a surface O atom for tensile surface strains over +4 %. In the case of a tensile surface strain of +7 %, the adsorption energy changes from −0.87 eV for unstrained MgO(001) to −1.17 eV. The variation in the charge states of Au on MgO(001) with surface strain, based on a Bader charge analysis, is also presented. The Bader charges of Au are found to become more negative as the surface strain increases. For a tensile surface strain of +7 %, the Bader charge is −0.38 |e|, more negative than the value of −0.29 |e| for unstrained MgO(001). Contrary to the adsorption energies and the charge states of Au, the variation in the surface diffusion barriers of Au on MgO(001) is found to be very small, less than 0.03 eV.