The magnetic lanthanide $\left({\mathrm{Ln}}^{3+}\right)$ ions in the fergusonite and scheelite crystal structures form a distorted or stretched diamond lattice which is predicted to host exotic magnetic ground states. In this study, polycrystalline samples of the fergusonite orthotantalates $M\text{−}{\mathrm{LnTaO}}_4$ (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) were synthesized and then characterized using powder diffraction and bulk magnetometry and heat capacity. ${\mathrm{TbTaO}}_4$ orders antiferromagnetically at 2.25 K into a commensurate magnetic cell with $\vec{k}=0$, magnetic space group 14.77 $(P{2}_1^{\prime }/c)$, and Tb moments parallel to the $a$ axis. No magnetic order was observed in the other materials studied, leaving open the possibility of exotic magnetic states at $T<2$ K.

Magnetic nanostructures with nontrivial three-dimensional (3D) shapes enable complex magnetization configurations and a wide variety of new phenomena. To date predominantly magnetic metals have been considered for nontrivial 3D nanostructures, although the magnetic and electronic transport responses are intertwined in metals. Here we report the first successful fabrication of the magnetic insulator yttrium iron garnet $({\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}, \mathrm{YIG})$ via atomic layer deposition (ALD) and show that conformal coating of 3D objects is possible. We utilize a supercycle approach based on the combination of subnanometer thin layers of the binary systems ${\mathrm{Fe}}_2{\mathrm{O}}_3$ and ${\mathrm{Y}}_2{\mathrm{O}}_3$ in the correct atomic ratio with a subsequent annealing step for the fabrication of ALD-YIG films on ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ substrates. Our process is robust against typical growth-related deviations, ensuring a good reproducibility. The ALD-YIG thin films exhibit a high crystalline quality as well as magnetic properties comparable to samples obtained by other deposition techniques. We show that the ALD-YIG thin films are conformal. This enables the fabrication of 3D YIG nanostructures once appropriate nonmagnetic, 3D templates are developed. Such 3D YIG structures build the groundwork for the experimental investigation of curvature-induced changes on pure spin currents and magnon transport effects.

A phase variation of a pseudo-Roddlesden-Popper-type ferroelectric oxide ${\mathrm{Li}}_2{\mathrm{Sr}}_{1-x}{\mathrm{Ca}}_x{\left({\mathrm{Nb}}_{1-x}{\mathrm{Ta}}_x\right)}_2{\mathrm{O}}_7$ is systematically investigated using dielectric measurements, second harmonic generation, and x-ray diffraction experiments. We find an exotic $x$-T phase diagram, including paraelectric Cmcm, antiferroelectric Pmcn, and in-plane antiferroelectric and out-of-plane ferroelectric $P{2}_{1}cn$ phases. At low $x$, we observe large and divergent dielectric anomalies associated with phase transitions from Cmcm to $P{2}_{1}cn$, whereas these become small kinks at high $x$. Structural analyses reveal an internal distortion, and the rotation of octahedra strongly depends on $x$, which is consistent with the lattice dynamics obtained by a density functional theory calculation. These results demonstrate the great tunability of dielectric properties in layered perovskite-type oxides by tuning the chemical bonding state in the octahedron.

Understanding the complex connection between flow-processing history, fluid structure, and fluid properties represents a grand challenge for the engineering and fundamental study of nanostructured soft materials. To address this challenge, we report measurements using scanning small-angle x-ray scattering in a fluidic four-roll mill (FFoRM), which enables rapid nanostructural characterization of complex fluids under an unprecedentedly diverse range of flow histories. Combining this technique with analysis of the Lagrangian deformation history of fluid elements, we demonstrate rapid mapping of orientational ordering of fluids' nanostructure along diverse deformation trajectories that emulate those encountered in flow processing. Using demonstrative experiments on model rodlike nanoparticle dispersions, we show that differences in rod flexibility and rod-rod interactions play a significant role in determining the fluid's anisotropic structural response to similar flow histories. An analysis of the coupling between measured particle alignment and interparticle correlations reveals these differences to arise from the nature and strength of interparticle interactions in flow. These measurement and analysis techniques produce large datasets that hold promise toward advancing process-structure-property models and inverse design processes of flows that are tailored to produce targeted nanostructures.

Amorphous silicon films prepared by electron-beam evaporation have systematically and substantially greater atomic density for higher thickness, higher growth temperature, and slower deposition rate, reaching the density of crystalline Si when films of thickness greater than $\sim$300 nm are grown at 425 ${}^{\circ }$C and at $<$1 Å/s. A combination of spectroscopic techniques provide insight into atomic disorder, local strains, dangling bonds, and nanovoids. Electron diffraction shows that the short-range order of the amorphous silicon is similar at all growth temperatures, but fluctuation electron microscopy shows that films grown above room temperature show a form of medium-range order not previously observed in amorphous silicon. Atomic disorder and local strain obtained from Raman spectroscopy are reduced with increasing growth temperature and show a nonmonotonic dependence on thickness. Dangling bond density decreases with increasing growth temperature and is only mildly dependent on thickness. Positron annihilation Doppler broadening spectroscopy and electron energy loss spectroscopy show that nanovoids, and not density variations within the network, are responsible for reduced atomic density. Specific heat and mechanical loss measurements, which quantify the density of tunneling two-level systems, in combination with the structural data, suggest that two-level systems in amorphous silicon films are associated with nanovoids and their surroundings, which are in essence loosely bonded regions where atoms are less constrained.

The hydrogen-enhanced localized plasticity (HELP) mechanism is a leading candidate among proposed hydrogen embrittlement (HE) mechanisms. Transmission electron microscopy (TEM) measurements of an increased dislocation mobility on exposure to hydrogen have provided the most direct evidence for the HELP mechanism. However, it has been hypothesized that the observed dislocation behavior is not a consequence of the interaction between hydrogen atoms and dislocations but a systematic error due to the nature of in situ TEM. Specifically, the electron beam in TEM microscopes can dissociate hydrogen, leading to a hydrogen fugacity much greater than the applied pressure. Such high fugacity will generate a large concentration gradient between the surface and interior of a TEM sample. It has been proposed that the observed dislocation mobility is due only to stresses arising from this concentration gradient rather than an effect of the interaction with hydrogen. Here we calculate the expected stresses for H/Fe and H/Ni systems fugacities expected in an in situ TEM. We show the stresses to be an order of magnitude too low to impact dislocation mobility in the H/Fe system, and that the concentration gradient-induced stresses dissipate quickly in both H/Fe and H/Ni systems—well before observation by TEM would occur.

Recent experiments [Barbero et al. Phys. Rev. B 95, 094505 (2017)] have established that bulk superconductivity $\left(T_c\sim 8.3\text{–}8.7\mathrm{K}\right)$ can be induced in $\mathrm{Al}{\mathrm{B}}_2\text{−}\mathrm{type}\mathrm{Zr}{\mathrm{B}}_2$ and $\mathrm{Hf}{\mathrm{B}}_2$, highly covalent refractory ceramics, by vanadium (V) doping. These $\mathrm{Al}{\mathrm{B}}_2\text{−}\mathrm{structured}$ phases provide an alternative to earlier diamondlike or diamond-based superconducting and superhard materials. However, the underlying mechanism for doping-induced superconductivity in these materials is yet to be addressed. In this paper, we have used first-principles calculations to probe electronic structure, lattice dynamics, and electron-phonon coupling (EPC) in V-doped $\mathrm{Zr}{\mathrm{B}}_2$ and consequently examine the origin of the superconductivity. We find that, while doping-induced stress weakens the EPC, the concurrently induced charges strengthen it. The calculated critical transition temperature $\left(T_c\right)$ in electron (and V)-doped $\mathrm{Zr}{\mathrm{B}}_2$ is at least one order of magnitude lower than experiments, despite considering the weakest possible Coulomb repulsion between electrons in the Cooper pair, hinting a complex origin of superconductivity in it.

The observation of clean 2D superconductivity and bosonic Landau levels below 0.85 K in superlattice van der Waals material ${\mathrm{Ba}}_6{\mathrm{Nb}}_{11}{\mathrm{S}}_{28}$ have received much interest. Here we report the crystal structure, Hall resistivity, and 2D superconductivity of its sister compound, ${\mathrm{Ba}}_6{\mathrm{Nb}}_{11}{\mathrm{Se}}_{28}$. The atomic-resolution transmission electron microscopy images reveal an alternate stacking of $2H\text{−}{\mathrm{NbSe}}_2$ with a 3 × 3 commensurate block layer, which is isostructural to ${\mathrm{Ba}}_6{\mathrm{Nb}}_{11}{\mathrm{S}}_{28}$ and with a larger $\mathrm{Nb}{X}_2$ ($X=\mathrm{S}$, Se) interlayer distance (12.8 Å). Transport property measurements demonstrate a twofold enhancement in superconducting temperature $\left({T_{\mathrm{c}}}^0=2.2\mathrm{K}\right)$, meanwhile the anisotropy in resistivity and carrier mobility in ${\mathrm{Ba}}_6{\mathrm{Nb}}_{11}{\mathrm{Se}}_{28}$ decrease drastically compared to its sulfur counterpart, driving the superconductor towards the dirty limit. Further measurements of angular-dependent upper critical field suggest the superconductivity in ${\mathrm{Ba}}_6{\mathrm{Nb}}_{11}{\mathrm{Se}}_{28}$ be Pauli-limit breaking (2 times the ${\mu }_0{H}_P$), and can be well described by the 2D Tinkham form. Our findings offer a valuable platform to investigate 2D superconductivity in bulk superlattice materials based on the transition-metal dichalcogenides.

Void swelling can develop in materials under persistent irradiation when nonequilibrium vacancy and self-interstitial populations migrate under sufficiently asymmetric interaction biases. In conventional metals, the propensity is determined to the first approximation by comparing point-defect relaxation strains. We thus present DFT-based calculations of structures and formation energies and volumes of point defects in the $\alpha$ and the $\delta$ phases of plutonium. We discuss the pros and cons of various levels of electronic structure theory: spin polarization, spin-orbit coupling, and orbital polarization. Our results show that lattice defects in $\delta$-Pu, in contrast to most fcc metals, have surprisingly small formation volumes. Equally unexpected are the large defect formation volumes found in the low-symmetry $\alpha$-Pu phase. Both these unusual properties can be satisfactorily explained from defect-induced spin/orbital moment formation and destruction in the Pu phases. Surprisingly, the point defects in $\alpha$-Pu are found to induce far larger transformation of the local electronic structure than in $\delta$-Pu. When we use the calculated defect properties to estimate the classic void swelling bias in each of the phases, we find it to be unusually small in $\delta$-Pu but likely much larger in $\alpha$-Pu. Hence, swelling rates and mechanisms can diverge dramatically between the different phases of Pu. Especially in the transient regime before the formation of large defect clusters, the swelling rate of $\alpha$-Pu can reliably be expected to be much larger than $\delta$-Pu. However, accurate forecasts over longer times will require the conventional void-swelling theory to be modified to handle the complexities presented by the different Pu phases. As a case in point, we show the possible anomalous temperature dependence of vacancy properties in $\delta$-Pu, caused by entropic contributions from defect-induced spin-lattice fluctuations. Such complications may affect defect-defect interactions and thus alter the void swelling bias.

In materials science, it is often assumed that ground-state crystal structures predicted by density functional theory are the easiest polymorphs to synthesize. Ternary nitride materials, with many possible metastable polymorphs, provide a rich materials space to study what influences thermodynamic stability and polymorph synthesizability. For example, ${\mathrm{ZnZrN}}_2$ is theoretically predicted at zero Kelvin to have an unusual layered “wurtsalt” ground-state crystal structure with compelling optoelectronic properties, but it is unknown whether this structure can be realized experimentally under practical synthesis conditions. Here, we use combinatorial sputtering to synthesize hundreds of ${\mathrm{Zn}}_x{\mathrm{Zr}}_{1-x}{\mathrm{N}}_y$ thin-film samples, and find metastable rocksalt-derived or boron-nitride-derived structures rather than the predicted wurtsalt structure. Using a statistical polymorph sampler approach, it is demonstrated that although rocksalt is the least stable polymorph at zero Kelvin, it becomes the most stable polymorph at high effective temperatures similar to those achieved using this sputter deposition method, and thus corroborates experimental results. Additional calculations show that this destabilization of the wurtsalt polymorph is due to configurational entropic and enthalpic effects, and that vibrational contributions are negligible. Specifically, rocksalt- and boron-nitride-derived structures become the most stable polymorphs in the presence of disorder because of higher tolerances to cation cross substitution and off stoichiometry than the wurtsalt structure. This understanding of the role of disorder tolerance in the synthesis of competing polymorphs can enable more accurate predictions of synthesizable crystal structures and their achievable material properties.

A high-quality ${\mathrm{NiTe}}_2{\mathrm{O}}_5$ single crystal was grown via the flux method and characterized using synchrotron x-ray diffraction (XRD) and electron probe microscopy techniques. The dc magnetization $\left(M\right)$ confirms the antiferromagnetic long-range ordering temperature $\left(T_{\mathrm{N}}\right)$ at 28.5 K. An apparent domelike dielectric anomaly near $T_{\mathrm{N}}$, with scaling of magnetodielectric (MD) coupling with magnetization $(\mathrm{MD}\%\propto M^2)$, signifies higher-order magnetoelectric (ME) coupling. The critical finding is that magnetoelastic coupling plays a pivotal role in bridging the electrical and magnetic dipoles, which was further confirmed by temperature-dependent XRD. In addition, the theoretical charge density difference maps indicate that the emergence of electrical dipoles between the Ni and O atoms below $T_{\mathrm{N}}$ originates through $p\text{−}d$ hybridization. Thus, the $p\text{−}d$ hybridization-induced magnetoelastic coupling is considered a possible mechanism for the higher-order ME effect in this quasi-one-dimensional spin-chain ${\mathrm{NiTe}}_2{\mathrm{O}}_5$.

Recently, researchers at the University of Waterloo (Canada) and Oak Ridge National Laboratory (Oak Ridge, TN) reported a new family of lithium thioborate halide electrolytes with the composition ${\mathrm{Li}}_{7.5}{\mathrm{B}}_{10}{\mathrm{S}}_{18}{X}_{1.5}$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$ having very impressive ionic room-temperature conductivity of magnitude $\sigma =1 \mathrm{mS}/\mathrm{cm}$. The researchers characterized the structures of the three materials in terms of a well-defined thioborate framework with a void structure containing fractionally occupied Li and X sites. The space group of the materials was identified to be monoclinic ($C2/c$, No. 15). We report the results of first-principles simulations of these materials focusing on understanding the idealized ground-state structures, the mechanisms of Li ion migration, and the overall stability of the materials. A systematic search of many possible stoichiometric crystalline configurations found ordered ground-state realizations of the materials for each of the three halides, $X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I}$. Molecular dynamics simulations based on the initially ordered structures at various temperatures show significant Li ion hopping within the void channels of the structures at temperatures as low as T = 400 K. Simulations of possible decomposition products suggest that these electrolytes are also chemically stable. Overall, the simulations are consistent with the experimentally reported findings indicating that these materials are very promising solid electrolytes for possible use in solid-state Li ion batteries.

Flat electronic bands with tunable structures offer opportunities for the exploitation and manipulation of exotic interacting quantum states. Here, we present a controllable route to construct easily tunable flat bands in folded graphene by nano origami-controlled strain engineering, and we discover correlated states in this system. Via tearing and folding graphene monolayer at arbitrary step edges with scanning tunneling microscope manipulation, we create strain-induced pseudomagnetic fields as well as resulting flat electronic bands in the curved edges of folded graphene. We show that the intensity of the pseudomagnetic field can be readily tuned by changing the width of the folding edge due to the edge-width-dependent lattice deformation, leading to the well adjustability of the geometry of flat bands in folded graphene. Furthermore, by creating expected dispersionless flat bands using this technique, the correlation-induced splits of flat bands are successfully observed in the density of states when these bands are partially filled. Our experiment provides a feasible and effective pathway to engineer the system with tunable flat band structures, and it establishes a platform that can be used to realize devisable strain and interaction-induced quantum phases.

Mechanically induced crystallographic phase transformation that reflects dynamic stress responses of intrinsically stochastic nature is a pertinent yet much less well understood phenomenon. We focus on understanding the physical significance of stochasticity and how it can enable an inference of principles underlying a crystallographic phase transformation. For interpreting the mechanical responses, a statistical approach of mapping the transformation dynamics to a probabilistic escape of crystallographic states defined on a free-energy landscape is shown to reliably explain the patterns of response. We demonstrate that stochastic responses associated with a structural phase transformation can offer a reliable quantitative tool for unraveling the free-energy profile, intrinsic kinetics, and microscopic details of solid-to-solid crystallographic transitions.

Two-dimensional (2D) magnetic materials have attracted tremendous attention in the spintronics and nanoelectronics fields. However, intrinsic and robust 2D magnetism is hard to achieve. Using high-throughput first-principles calculations, herein we have explored 2D ternary compounds of a transition metal $(\mathrm{X}=\mathrm{Fe}, \mathrm{Mn}, \mathrm{Cr})$, Ge, and Te, with diverse stoichiometries and geometric configurations. We screened 34 ferromagnetic and 111 antiferromagnetic XGT monolayer structures, including metals, half-metals, and semiconductors, with high magnetic transition temperatures for practical uses. The coupling strength of ferromagnetism in XGT monolayers is related to the ratio of the transition metal element, while the band gap opening is affected by the occupancy of transition metal $d$ states and the Te content. Therefore, the electronic and magnetic structures of XGT monolayers can be manipulated by their stoichiometries. This work delivers a unique perspective for designing compound functional materials and enriches the family of 2D magnets for technological applications.

The ${\mathrm{Ba}M\mathrm{F}}_4$ $(M=\mathrm{Fe}, \mathrm{Co}, \mathrm{Ni}, \mathrm{and} \mathrm{Mn})$ family consists of typical multiferroic materials, having antiferromagnetism at around liquid nitrogen temperature. In this paper, polycrystalline ${\mathrm{BaFeF}}_4$ has been prepared by solid state reaction. The slight deficiency of Fe leads to the coexistence of valence states of + 2 and + 3, facilitating the electrons to hop between the neighboring ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ ions through the middle ${\mathrm{F}}^{-}$ ion, leading to the strong double exchange interaction with weak ferromagnetism above room temperature. A bifurcation at $\sim 170\mathrm{K}$ between the zero-field-cooled and field-cooled temperature-dependent magnetization curves indicates the onset of two-dimensional antiferromagnetism, which is completed at $\sim 125\mathrm{K}$ with the sudden drop of magnetization. Despite being a type-I multiferroic, its magnetoelectricity (ME) can be evidenced by the pyroelectric current, which shows a peak starting at $\sim 170\mathrm{K}$ and finishing at $\sim 125\mathrm{K}$. The saturated ferroelectric polarization change of $\sim 34$ $\mu \mathrm{C}/{\mathrm{m}}^2$ is observed, which is switchable by the reversed poling electric field, and decreases to $\sim 30$ $\mu \mathrm{C}/{\mathrm{m}}^2$ under a magnetic field of 90 kOe. This ME can be qualitatively reproduced by first-principles calculations. Our results represent substantial progress to search for high-temperature multiferroics in ferroelectric fluorides.

Once doped away from their parent Mott insulating state, the hole-doped cuprates enter into many varied and exotic phases. The onset temperature of each phase is then plotted versus $p$—the number of doped holes per copper atom—to form a representative phase diagram. Apart from differences in the absolute temperature scales among the various families, the resultant phase diagrams are strikingly similar. In particular, the $p$ values corresponding to optimal doping ($p^{\mathrm{opt}}\sim 0.16$) and to the end of the pseudogap phase $(p^{*}\sim 0.19–0.20)$ are essentially the same for all cuprate families bar one: the single-layer Bi-based cuprate ${\mathrm{Bi}}_{2+z-y}{\mathrm{Pb}}_y{\mathrm{Sr}}_{2-x-z}{\mathrm{La}}_x{\mathrm{CuO}}_{6+\delta }$ (Bi2201). This anomaly arises partly due to the complex stoichiometry of this material and also to the different $p$ values inferred from disparate (e.g., bulk or surface) measurements performed on samples with comparable superconducting transition temperatures $T_c$. Here, by combining measurements of the in-plane resistivity in zero and high magnetic fields with angle-resolved photoemission spectroscopy studies in the superconducting and normal state, we argue that the phase diagram of Bi2201 may in fact be similar to that realized in other families. This study therefore brings Bi2201 into the fold and supports the notion of universality of $p^{\mathrm{opt}}$ and $p^{*}$ in all hole-doped cuprates.

Yb-based magnets, with a perfect triangular lattice of pseudospin-$\frac{1}{2}{\mathrm{Yb}}^{3+}$ ions, have emerged as candidates for realizing a quantum spin-liquid state, with ${\mathrm{NaYbS}}_2$ being a prominent example. Here, we present the solid-solution series ${\mathrm{NaYb}}_{1-x}{\mathrm{Lu}}_x{\mathrm{S}}_2$ with well-defined single crystals over the entire substitution range $0\le x\le 1$. Chemical and structural analysis indicate a statistically homogeneous replacement of ${\mathrm{Yb}}^{3+}$ by ${\mathrm{Lu}}^{3+}$ ions. We magnetically characterize the relatively small single crystals using electron spin resonance (ESR). Below $30\mathrm{K}$, the ESR intensity can be well described by a Curie-Weiss function for all $x$, with a decreasing Weiss temperature with increasing Lu content. This reduction of the average magnetic interaction upon Lu substitution is also supported by magnetization measurements. Importantly, no signs of magnetic or spin-glass order are detected down to $2\mathrm{K}$ for any $x$. For $x>0.5$, the ESR linewidth strongly increases, indicating the breakup of the magnetic system into disconnected clusters, as expected from percolation physics. The experimental magnetization data are found to be in good agreement for all $x$ with results of classical Monte Carlo simulations for a triangular-lattice Heisenberg model, amended with a small second-neighbor interaction. Taken together, our results establish ${\mathrm{NaYb}}_{1-x}{\mathrm{Lu}}_x{\mathrm{S}}_2$ as a family of diluted triangular-lattice spin liquids.

We report unipolar hole transport through unintentionally doped (UID) c-plane Ga-polar InGaN heterostructures to investigate the impact of alloy disorder on vertical transport. Simulations and experimental investigations were conducted on unipolar InGaN double heterostructures (DHs) and quantum well (QW) test structures by varying thicknesses and the number of QWs. The structures were simulated using one-dimensional (1D) and three-dimensional (3D) algorithms, incorporating the effects of random alloy disorder in the 3D model using the newly developed Localization Landscape theory. The electrical polarization discontinuity between GaN and InGaN results in a significant barrier for vertical carrier transport. Band-diagram and current density-voltage simulations indicate asymmetric polarization barriers to the vertical hole transport for the InGaN DHs. For the QW structures, however, the simulations indicate a symmetric barrier to the hole transport in forward and reverse bias. In the case of the InGaN DH layers, the 3D simulation results indicate a smaller barrier to hole transport compared to 1D simulations. For QW simulations, the barriers were found to be the same in both 1D and 3D simulations. The simulation results are experimentally verified using unipolar p-type vertical transport structures, enabled by n-to-p tunnel junctions to facilitate the current spreading within the bulk material for the mesa structures grown by ammonia-molecular beam epitaxy. The results indicate that increasing the UID ${\mathrm{In}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{N}$ DH layer thickness from 15 to 30 nm increases the forward bias voltage drop (∼2 V at $500\mathrm{A}/\mathrm{c}{\mathrm{m}}^2$) more than the reverse bias voltage drop (∼0.2 V at $500\mathrm{A}/\mathrm{c}{\mathrm{m}}^2$). For the QW structures, increasing the number of QWs from one to three increases the voltage penalty similarly in forward and reverse directions (∼0.25 V per QW at $500\mathrm{A}/\mathrm{c}{\mathrm{m}}^2$). The results are beneficial in understanding the impact of alloy disorder on the transport properties of the III-nitride heterostructures.

We have studied the proximity-induced superconductivity in $(\sqrt{7}\times \sqrt{7})R19.1^{\text{o}}$ Ni nanoislands by combing scanning tunneling microscopy/spectroscopy (STM/STS) with density-functional theory calculation. Through depositing Ni onto Pb(111) substrate at 80 K, the monolayer Ni nanoislands with the $(\sqrt{7}\times \sqrt{7})R19.1^{\text{o}}$ surface structure have been fabricated, where the termination of Ni atoms at the hexagonal close-packed site is energetically preferred and the filling of $3d$ orbitals from the charge transfer leads to the vanishing magnetic moment of Ni atoms. The topographic $(\sqrt{7}\times \sqrt{7})R19.1^{\text{o}}$ lattice as well as the asymmetric height contrast in atomic unit cell have been further corroborated by the STM simulations. With high spatial and energy resolution, tunneling conductance ($dI/dU$) spectra have resolved an isotropic superconducting gap with ${\mathrm{\Delta }}_{Ni(\sqrt{7}\times \sqrt{7})}\approx 1.29$ meV, which is slightly larger than ${\mathrm{\Delta }}_{Pb}\approx 1.25$ meV. The temperature dependence of ${\mathrm{\Delta }}_{Ni(\sqrt{7}\times \sqrt{7})}$ supports the substrate-induced superconducting proximity effect according to the same transition temperature $T_c\approx 7.14$ K with the Pb(111). The line spectroscopy has spatially mapped out the small increase of ${\mathrm{\Delta }}_{Ni(\sqrt{7}\times \sqrt{7})}$, which could be explained by an enhanced electron-phonon interaction ($V_{ep}$) under the framework of Bardeen-Cooper-Schrieffer theory as a manifestation of the hole doping of Pb(111) from the surface Ni atoms.