Metallic Crystals Research Articles

Metallic mesoporous oxide single crystals delivering enhanced electrocatalytic performance

We grew PSC Fe2O3 and PSC Co3O4 catalysts and quantitatively engineered Pt clusters/metal oxide interfaces on the surfaces, which exhibit excellent electrocatalytic performance in the OER.

Prolonged stirring pelleting coagulation for the enhanced treatment of fresh leachate: Removal performance and floc characteristics

Conventional coagulation (CC) is a widely adopted method for the pre-treatment of fresh leachate for enhancing subsequent advanced treatment processes. However, the formation of fluffy flocs in the CC process often results in limited separation and removal efficiency. In this study, a continuous alkali dosing prolonged stirring pelleting coagulation (C-PPC) process was proposed for the pre-treatment of fresh leachate. The C-PPC process consisted of three stages: prolonged stirring, reaction, and pelleting, achieving higher suspended solid (SS), turbidity, and organic removal efficiency compared with both CC and PPC processes. At a prolonged stirring intensity of 1500 r/min (G = 4241 s−1) and a final pH of 12, with polyaluminum chloride (PAC) and polyacrylamide (PAM) dosages of 2000 mg/L and 25 mg/L, impressive removal efficiency of 93.7 % SS, 99.7 % turbidity, and 35.7 % organic were obtained. In the prolonged stirring stage, the primary particle size decreased from 16.848 μm to 6.755 μm due to intensive stirring for 30 min, facilitating the compact floc formation. In the subsequent reaction stage, PAC was dosed once while NaOH was continuously dosed to achieve a final pH of 12 within 10 min. The floc size initially decreased due to fragmentation and small metal crystal generation. Subsequently, the generated small metal crystals served as the nuclei for organic matter adsorption and were entrapped by generated flocs, resulting in a significant increase in floc size with higher sphericity. Furthermore, compact pellets were formed during the pelleting stage after the addition of PAM. Floc restructuring also occurred during the pelleting stage, leading to a decreased pore volume of mesopores, achieving final floc densification and superior separation performance.

Microwave Hall measurements using a circularly polarized dielectric cavity.

We have developed a circularly polarized dielectric rutile (TiO2) cavity with a high quality-factor that can generate circularly polarized microwaves from two orthogonal linearly polarized microwaves with a phase difference of ±π/2 using a hybrid coupler. Using this cavity, we have established a new methodology to measure the microwave Hall conductivity of a small single crystal of metal in the skin-depth region. Based on the cavity perturbation technique, we have shown that all components of the surface impedance tensor can be extracted under the application of a magnetic field by comparing the right- and left-handed circularly polarized modes. To verify the validity of the developed method, we performed test measurements on tiny Bi single crystals at low temperatures. As a result, we have successfully obtained the surface impedance tensor components and confirmed that the characteristic field dependence of the ac Hall angle in the microwave region is consistent with the expectation from the dc transport measurements. These results demonstrate a significant improvement in sensitivity compared to previous methods. Thus, our developed technique allows for more accurate microwave Hall measurements, opening the way for new approaches to explore novel topological quantum phenomena, such as time-reversal symmetry breaking in superconductors.

Modulating Electronic Properties through Synthesis of Single-Layer Metallic Janus Crystal NbSSe

Janus crystals represent a family of 2D materials with structures that feature a metal cation between two different atomic species on the top and bottom faces. This unique structure with its broken mirror and inversion symmetry enables a host of fascinating quantum effects including formation of an internal electric field at the monolayer-limit, unique topological phases, and colossal polarization field. In particular, the metallic Janus crystal NbSSe is predicted to be a stable 2D polar metal of the kind theorized by Anderson and Blount and offers possible applications in nanoscale ferroelectric devices. In this talk I will introduce advances in realizing synthesis of metallic 2D Janus crystal NbSSe at Arizona State University. NbSSe is experimentally demonstrated via a surface-limited technique of plasma-driven atomic replacement at the surface to convert parent TMD crystals 1H-NbSe2 and 1H-NbS2 into 1T-NbSSe. Microscopic, topographical, and spectroscopic techniques are carried out to elucidate the structural transformation, air- and photo-stability, and electronic properties attributed to metallic Janus NbSSe1-6.References Anderson PW, Blount EI. 1965. Symmetry considerations on martensitic transformations: “Ferroelectric” metals? Phys. Rev. Lett. 14(7):217–219 Y. Qin, M. Sayyad, A. R.-P. Montblanch, M. S. G. Feuer, D. Dey, M. Blei, R. Sailus, D. M. Kara, Y. Shen, S. Yang, A. S. Botana, M. Atature, S. Tongay, Reaching the Excitonic Limit in 2D Janus Monolayers by In Situ Deterministic Growth. Adv. Mater.2022, 34, 2106222. D. B. Trivedi, G. Turgut, Y. Qin, M. Y. Sayyad, D. Hajra, M. Howell, L. Liu, S. Yang, N. H. Patoary, H. Li, M. M. Petrić, M. Meyer, M. Kremser, M. Barbone, G. Soavi, A. V. Stier, K. Müller, S. Yang, I. S. Esqueda, H. Zhuang, J. J. Finley, S. Tongay, Room-Temperature Synthesis of 2D Janus Crystals and their Heterostructures. Adv. Mater.2020, 32, 2006320.Fei, Z., Zhao, W., Palomaki, T.A. et al.Ferroelectric switching of a two-dimensional metal. Nature 560, 336–339 (2018). https://doi.org/10.1038/s41586-018-0336-3Zhou, W. X. and Ariando Ariando. “Review on ferroelectric/polar metals.” Japanese Journal of Applied Physics 59 (2020).Yagmurcukardes, M.; Qin, Y.; Ozen, S.; Sayyad, M.; Peeters, F. M.; Tongay, S.; Sahin, H., Quantum properties and applications of 2D Janus crystals and their superlattices. Applied Physics Reviews 2020, 7 (1). Figure 1

Construction of a mathematical model of turbulent heat and mass transfer processes for the case of electron beam melting of titanium alloy casts

This paper describes a mathematical model built for turbulent heat and mass transfer processes in the case of electron beam melting of titanium alloy ingots. The object of research is the conditions that ensure the quality of ingots. The model makes it possible to calculate the distribution of hydrodynamic flows in the liquid metal and temperature fields in the ingot, to determine the profile of the metal crystallization front, taking into account the interphase transition zones. The model solves the problem of finding the necessary melting regimes of ingots by calculation, in contrast to high-cost natural experiments. The thermal and hydrodynamic processes during the melting of a cylindrical ingot with a diameter of 110 mm of the newest titanium alloy Ti-6Al-7Nb for medical use were calculated and its melting parameters were determined. The small diameter of the ingot significantly facilitates its further machining. The geometry of the two-phase zone of the liquidus-solidus transition, which determines the crystallization front of the metal, was calculated. The position and geometry of this front greatly affects the quality of ingot formation and the concentration of the distribution of alloying elements and the homogeneity of the metal across its volume. A sufficiently flat crystallization front has been obtained, under which the given conditions are ensured. It was found that heat transfer in the liquid phase of the metal is mainly caused by heat and mass transfer due to its movement, and heat and mass transfer significantly depends on the power of the electron beam and its distribution on the surface of the bath. According to the calculated regimes, at the Institute of Electric Welding named after E. O. Paton, the National Academy of Sciences of Ukraine, high-quality ingots for the needs of the medical industry were smelted. The castings are used for the manufacture of light and ultra-strong endoprostheses and implants, which are chemically neutral and biologically and biomechanically compatible with the human body and do not cause rejection.

Growth of copper single crystal using cone die Czochralski method

Copper (Cu) and other metal single crystals are useful as substrates for the deposition of atomic layer materials for many electronic applications, but the growth of large-sized single crystals is difficult to achieve. Characteristics of the metal material, namely seed elongation and intense cooling radiation at high temperatures during crystal growth, are the main challenges encountered when growing ingots with large diameters. These problems can be resolved by optimizing the crystal growth parameters. By adjusting the shoulder formation angle of the ingot shape to approximately 20° to 40°, we are able to grow a large (1-inch diameter, 30 mm length) single crystal of metal Cu using the Czochralski (CZ) method. However, the generation of suspended solids and film impurities such as reactants and precipitates and their nucleation, growth, and solidification, limited the further increase in size of the Cu crystal. Using the cone-shape die CZ (CD-CZ) method solves this problem and a 2-inch diameter Cu single crystal is successfully grown. This is the world’s largest single crystal metal grown using this method and it paves the way for the growth of other metal crystals.

Crystallization, structure-property evolution, and solidification of heavy metals of glass-ceramics based on copper tailing/coal slag/red mud

The Dexing copper tailing (DCT), Coal slag (CS) and Red mud (RM) were used to prepare a solid waste-derived glass-ceramics. The result shows that the stable base glass can be formed when DCT/CS/RM mass ration is 35/25/40. Different crystallization temperatures (780∼980 ℃) were implemented on the base glass, and found that the glass-ceramics with Ca(Mg0.5Al0.5)((Si1.5Al0.5)O6) as the main crystal phase can be synthesized, whose bulk density, water absorption, Vickers hardness, bending strength, acid/alkali-resistance are in the range of 2.747∼2.887 g/cm3, 0.010∼0.027 %, 6.65∼8.24 GPa, 33.89∼118.53 MPa, 67.77∼99.97/97.85∼99.98 %, respectively. Especially, the GC880 not only shows the best properties (bulk density: 2.87 g/cm3; water absorption: 0.018 %; Vickers hardness: 6.96 GPa; bending strength: 118.53 MPa; acid/alkali-resistance: 99.34/99.97 %), but also has an solidification effect on heavy metal ions (Cr3+/Mn2+/Fe3+/Cu2+/Ni2+), wherein the leaching concentration reduction rates of Mn2+ and Fe3+ are over 97 %, which has the potential to be applied in decorative glass-ceramics.

Polarization-sensitive mechanically-tunable microwave filter using metallic photonic crystals

A tunable, polarization-sensitive microwave filter based on a reconfigurable dual-layered two-dimensional metallic photonic crystal is presented. The filter consists of a metallic plate with periodic holes and metal pillars which are anchored in a substrate material. The diameter of the pillars is smaller than that of the holes and the lateral position of the pillars with respect to the holes is tunable. We study the transmission of the device for linearly polarized electromagnetic radiation, which is polarized parallel and perpendicular to the displacement of the movable membrane, respectively. The tuning range spans from 20.18 GHz to 26.58 GHz for perpendicular polarization and from 20.18 GHz to 18.42 GHz for parallel polarization. The 3 dB operation bandwidth varies between 3.82 GHz and 6.44 GHz for perpendicular polarization and between 3.42 GHz and 3.82 GHz for parallel polarization. Experimental data are in good agreement with finite element method (FEM) simulations. The proposed structure is scalable to other frequency ranges such as terahertz frequencies.

Modifications in Subsurface of Catalysts: Impact of Bringing in Electrophilicity on Catalytic Applications

AbstractSurface, interface, and subsurface in catalysts are broadly perceived as independent units in materials, relying on diverse bonding environments and are recurrently studied discretely because of experimental challenges in distinguishing the surface and subsurface effects. Metal crystals, isolated atoms, or metal nanoparticles in supported catalysts induce an electrophilic nature in subsurface, enhancing the catalysis efficiency. In this review, the influence of modification in subsurface of catalysts and their specific catalytic outputs are discussed. Key approaches and techniques for insertion of subsurface modifications and impact of electrophilicity upon catalysis upgradation are observed. A compilation of frequently used chemical reactions catalyzed by subsurface‐modified catalysts have been structured and thoroughly illustrated.

In Situ Closing the van der Waals Gap of Two-Dimensional Materials.

Self-intercalation in two-dimensional (2D) materials, converting 2D materials into ultrathin covalently bonded materials, presents great possibilities for studying a new family of quantum-confined materials with the potential to realize multifunctional behavior. However, understanding the mechanisms and associated in situ kinetics of synthesizing self-intercalated 2D (ic-2D) materials, particularly at the atomic scale, remains elusive, greatly hindering the practical applications of ic-2D crystals. Here, we successfully in situ synthesized ic-2D thin films via thermal annealing of their parental TMDCs inside an electron microscope. We atomically visualized the evolution from TaS2 and NbS2 into the corresponding ic-2D Ta1+xS2 and ic-2D Nb1+xS2, respectively, by in situ scanning transmission electron microscopy (STEM). The self-intercalation process in TaS2 is atomically realized by metal adatom edge adsorption and subsequent diffusion in an atom-by-atom manner. On the other hand, MoS2 and MoSe2 tend to coalesce into metal crystals under the same annealing conditions, suggesting that the self-intercalation process is predominantly controlled by thermodynamic factors as further verified by density functional theory (DFT). By varying the ramping rate and annealing temperature, the coverage and spatial arrangement of the filling sites can be precisely tuned, ranging from 2a × a, a × a, or Ta trimers, as predominantly gauged by kinetic factors. Our work sheds light on the thermodynamics and growth kinetics involved in ic-2D formation and paves the way for growing highly crystalline ic-2D materials with intercalation concentration and topology-dependent properties.

On the Binding Energy of Atoms in Crystals of Noble Gases and Metals and the Speed of Sound

The speed of sound depends on the structure and material properties of the crystal, such as density and Young’s modulus. On the other hand, from atomistic arguments it is possible to associate Young’s modulus with other material properties. These observations lead to a relationship between binding energy of atoms in a crystal (which is one of the parameters appearing in Mie-Lennard-Jones potential), speed of sound in the longitudinal direction and mass of one atom in the lattice. This subject was addressed by several authors, providing different implementations of this relation. A literature review on this topic is made and the mathematical derivation of the relation is carried out. Applications of this relationship to rare gases, some metals and some rare earths are presented and the results compared to others taken from literature.

Diverse kinetic pathways in shock-compressed phase transitions of a metallic single crystal

Substantial gaps in solid-solid phase boundaries under hydrostatic and uniaxial compression have recently garnered great attention, though the underlying physics remains unclear. In this study, through molecular dynamics simulations of shock-compressed fcc Cu single crystals, we report pronounced orientation-dependent fcc-to-bcc phase transition pressures following the trend [100] < [110] < [111] ≈ thermodynamic phase boundary. We uncover a fundamental crystallographic law that explains these phase boundary gaps, rooted in the classical orientational relationship of martensitic transformations: the degree of alignment between loading directions and the easiest atomic moving path plays a critical role in determining phase transition pathways. The complex, orientation-dependent phase transition pathways and the observed temperature equilibrium efficiency ranking [100] > [110] > [111] further support the validity of this crystallographic law. This law is broadly applicable to fcc crystals, indicating that phase composition can be controlled by the method of compression, providing a new framework for selective polymorph formation.

Tunable Plasmon Resonance in Silver Nanodisk-on-Mirror Structures and Scattering Enhancement by Annealing.

In this study, we evaluated the surface plasmon characteristics of periodic silver nanodisk structures fabricated on a dielectric thin-film spacer layer on a Ag mirror substrate (NanoDisk on Mirror: NDoM) through finite difference time domain (FDTD) simulations and experiments involving actual sample fabrication. Through FDTD simulations, it was confirmed that the NDoM structure exhibits two sharp peaks in the visible range, and by adjusting the thickness of the spacer layer and the size of the nanodisk structure, sharp peaks can be obtained across the entire visible range. Additionally, we fabricated the NDoM structure using electron beam lithography (EBL) and experimentally confirmed that the obtained peaks matched the simulation results. Furthermore, we discovered that applying annealing at an appropriate temperature to the fabricated structure enables the adjustment of the resonance peak wavelength and enhances the scattering intensity by approximately five times. This enhancement is believed to result from changes in the shape and size of the nanodisk structure, as well as a reduction in grain boundaries in the metal crystal due to annealing. These results have the potential to contribute to technological advancements in various application fields, such as optical sensing and emission enhancement.

Crack-Deflecting Lattice Metamaterials Inspired by Precipitation Hardening.

Lattice structures, comprising nodes and struts arranged in an array, are renowned for their lightweight and unique mechanical deformation characteristics. Previous studies on lattice structures have revealed that failure often originates from stress concentration points and spreads throughout the material. This results in collapse failure, similar to the accumulation of damage at defects in metallic crystals. Here the precipitation hardening mechanism found in crystalline materials is employed to deflect the initial failure path, through the strategic placement of strengthening units at stress concentration points using the finite element method. Both the mesostructure, inspired by the arrangement of crystals, and the inherent microstructure of the base materials have played crucial roles in shaping the mechanical properties of the macro-lattices. As a result, a groundbreaking multiscale hierarchical design methodology, offering a spectrum of design concepts for engineering materials with desired properties is introduced.

Energetics and Structural Transitions of Nonequivalent Polytypes for FCC and HCP Metals

AbstractAlthough metal nanomaterials with unconventional phases have attracted extensive attention, the lack of information on the characteristics of metal polytypes hinders the development of related research. In this work, the energetics of nonequivalent polytypes for bulk face‐centered cubic (Li, Al, Ca, Cu, Sr, Rh, Pd, Ag, Ir, Pt, Au, and Pb) and hexagonal close‐packed metals (Be, Na, Mg, Sc, Ti, Zn, Cd, Y, Zr, Tc, Ru, Hf, Re, Os, and Tl) is systematically reported. For each metal, the structural properties and energies for its polytypes with up to the periodic stacking length of L = 10 is obtained by DFT calculation. The variation tendency of the energy differences between 3C and 2H polytypes is summarized in the Periodic Table of Elements. Generally, the ratio c/(La) increases when metal crystals except Ir, Rh, Zn, and Cd leave away from their ground‐state structure. It is found that the energy difference between polytypes originates from various interactions between the two types of atomic layers: the k layer and the h layer. The work is helpful to understand not only the structural transitions in bulk metals, such as Li, Na, Sr, Ti, Al, Pb, Y, Re, and Tl, but also the evolutions of Au nanomaterials.

Learning chemistry of metals in the context of forging: An ethnographic case study of blacksmithing in Guji Oromo, Ethiopia

This study explores the art of blacksmithing in Guji Oromo to locate underlying chemistry concepts, knowledge, and ways of knowing. The ethnographic case study design was employed, in which 11 blacksmiths were engaged through observation and semi-structured interviews. The data from the interview and observation were separately analyzed and triangulated against each other thematically. As a result, it was found that the blacksmiths in Guji use three mechanisms to identify the quality and suitability of metals collected for redesigning: textual, mechanical, and sparking tests. Besides, blacksmiths with no or little schooling have a remarkable conception of the fundamentals of metals and metallic bonding, malleability and ductility as a measure of metal qualities, rusting as threats to the existence of metals and how to prevent, metallic crystal and micro crystal rearrangement and thermal conductivity of metals. Moreover, the setting and underlying ways of knowing were found to be so constructivist because novices are allowed to explore and learn their way with minimal involvement from the experienced ones. Concerning the origin of blacksmithing, two themes of hypothesis were found in this study. One is that the origination of the art is among the ancestors of Guji themselves, and the other is that the explorers and metallurgists from other communities in Kenya or southern Ethiopia introduced the art. Thus, the narratives are controversial which call for further study. In conclusion, the findings revealed that the blacksmithing practice in Guji has utilizable chemistry contents and concepts that could enhance learning of chemistry by creating familiar context.

Precise Calorimetry of Small Metal Samples Using Noise Thermometry

We describe a compact calorimeter that opens ultra-low-temperature heat capacity studies of small metal crystals in moderate magnetic fields. The performance is demonstrated on the canonical heavy fermion metal YbRh2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}Si2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}. Thermometry is provided by a fast current sensing noise thermometer. This single thermometer enables us to cover a wide temperature range of interest from 175 µK to 90 mK with temperature-independent relative precision. Temperatures are tied to the international temperature scale with a single-point calibration. A superconducting solenoid surrounding the cell provides the sample field for tuning its properties and operates a superconducting heat switch. Both adiabatic and relaxation calorimetry techniques, as well as magnetic field sweeps, are employed. The design of the calorimeter results in an addendum heat capacity which is negligible for the study reported. The keys to sample and thermometer thermalisation are the lack of dissipation in the temperature measurement and the steps taken to reduce the parasitic heat leak into the cell to the tens of fW level.

Exploring photocatalytic tetracycline removal performance under simulated sunlight irradiation: Milling time effect on metallic reduction of MnO/ZrO2 mixed oxide

In the present research, it is reported that ball milling technique can be applied to enhance the photocatalytic properties of MnO and ZrO2 metal oxide powders (MZOx) furthermore the fabricated photocatalyst can be used for the degradation of tetracycline (TTC). XRD analyses revealed that increasing the milling time resulted in the formation of a pure metallic Mn crystal phase, which boosted the antibiotic degradation rate. It was confirmed by SEM technique that the morphological structures of the particles were generally small and uniform. The band gap energy was calculated as 3.70 eV for the hybrid metal oxide. Additionally, the adsorptive and photoluminescence features were illuminated via DRS and PL analyses. The effect of milling time had a major impact on the photodegradation rate of TTC, and the 8 h milling sample (MZOx-8h) exhibited the highest catalytic degradation activity (79.4 %). Low photocatalytic activity was obtained at acidic pHs and increased at alkaline pHs. The presence of H2O2 sharply decreased photocatalytic process time (60 min) and 94.3 % of the TTC was degraded at 7.5 mM H2O2. The photocatalytic degradation process proceeded through superoxide radicals and was supported by holes. The stability of MZOx-8h almost remained constant (70.02 %) even after seven cycles. It was determined that the presence of oxalic acid positively affected the progress of TTC degradation reactions. Further, practical application areas were investigated and MZOx-8h doped on support materials was found to be suitable for such applications in proportion to the doping ratio. Finally, it was demonstrated that MZOx-8h exhibited remarkable performance in photocatalytic reactions of different types of organic pollutants. The synergistic nature of MnO and ZrO2 with the contribution of ball milling time effect resulted in high photocatalytic activity.

Resonance energy transfer aided detection of nitroaromatics in aqueous medium by a luminescent Mn based metal-organic framework

A light brown needle-like crystal of Mn-based metal–organic framework (MOF); [Mn2.5(µ3-OH)(DTDB)2], (DTDB = 2,2′-dithiodibenzoate), compound 1, was synthesized using hydrothermal technique. Compound 1 was systematically characterized by single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), and infrared spectroscopy (IR). Photoluminescence study of compound 1 in an aqueous medium showed intense blue emission centred at 395 nm upon excitation at 310 nm. This emissive property of compound 1 was utilized for selective and sensitive detection of 2,4,6- trinitrophenol (TNP), 2,4- dinitrophenol (DNP) and 4-nitrophenol (NP) in the aqueous medium through luminescence quenching mechanism. As indicated by the good overlap of the absorption spectra of the analytes and the emission spectrum of the compound 1, and manifested as the reduction in luminescence lifetimes, it can be concluded that the resonance energy transfer is the most significant factor for the selective detection of aromatic nitro-phenol compounds. The resonance energy transfer requires the proximity of the donor and acceptor, which was achieved by the molecular level interactions between the ‘S’ atom of the DTDB ligand and phenolic –OH groups of the nitrophenols through non-covalent type interactions like hydrogen bonding and dipolar type interactions. Detection limits for TNP, DNP, and NP with the values of 208 ppb, 156 ppb, and 556 ppb, respectively, were obtained in an aqueous medium. The studies indicate that compound 1 could be helpful for detecting nitrophenol derivatives in water.

On the Adhesive Interaction Between Metals in Atomistic Simulations of Friction and Wear

Atomistic simulations are performed to assess how the main characteristics of a pairwise interatomic potential function can affect the occurrence of wear. A Morse-like potential is tailored in its attractive part such as to vary independently the cut-off radius and the maximum value of the attractive (adhesive) force. An ideal numerical experiment is then performed where the interaction between a metal crystal and a probe changes, while their material properties are not affected, to isolate the behavior of the interface. Force functions with larger adhesive force can loosely be interpreted as describing dry contacts while those with smaller adhesive force can be interpreted as describing lubricated contacts. Results demonstrate that the occurrence of wear is strongly dependent on the shape of the interatomic force field, and more specifically on the combination of maximum adhesive force and effective length of the interatomic attraction. Wear can initiate also at small adhesive energy, provided that the maximum adhesive force between atoms is large. When the surface of the crystal is taken to be rough instead of flat, the effect of the interatomic potential function on friction and wear becomes smaller, as the atoms belonging to the roughness are weakly bound to the rest of the crystal and are easily dislodged with any of the force functions we used.