Structure Of Overlayers Research Articles

Unveiling Electric Field Induced Ultrafast Charge Transfer Dynamics and Photoresponse Enhancement in Gold‐Interlayered Bi2Se3

AbstractIn the realm of optoelectronic applications, the incorporation of a metal interlayer between layers of a topological material holds significant potential. The interlayer introduces benefits such as improved charge transfer efficiency, tunable band alignment, plasmonics effect, and enhanced light‐matter interactions, paving the way for more efficient and versatile optoelectronic devices. This work explores the incorporation of gold between Bi2Se3, resulting in an enhancement in the response time of photoresponse of interlayered systems (Bi2Se3‐Au‐Bi2Se3). The introduction of a gold interlayer between Bi2Se3 significantly influences the overlayer structure, crystallinity, crystallite size, and even phonon behavior. Moreover, the responsivity of the interlayered device at a bias (2 V) is found to have high responsivity with fast response and decay time (τr = 0.1 ms, and τd = 24 ms of interlayered systems) as compared to intrinsic Bi2Se3(τr = 0.6 ms, and τd = 28 ms). This change is attributed to the bandgap alteration of the Bi2Se3/Au interface, which is monitored through transient spectroscopy performed at different electric biases. This study suggests that incorporating a gold interlayer holds potential benefits for various optoelectronic applications.

Self-terminated electrodeposition of Pt group metal: principles, synthetic strategies, and applications

Hydrogen, characterized by its carbon-neutral attributes and high energy density, is gaining momentum as a promising energy source. Platinum group metal (PGM) catalysts have emerged as pivotal components in water electrolysis and fuel cell technologies. However, their constrained availability and high cost impede the advancement of energy conversion systems. To address these challenges, various strategies have been explored within the realm of PGM catalysts. Particularly noteworthy are catalysts that exhibit an overlayer structure, offering exceptional catalyst utilization efficiency, bimetallic synergies, and strain-induced enhancements. Self-terminated electrodeposition (SED) stands out as a technique that enables precise atomic layer electrodeposition within an aqueous electrolyte environment. It allows meticulous control of metal loading quantities and surface coverage while operating at low temperatures and without the need for vacuum conditions. Catalysts with tailored properties achieved through SED exhibit distinct electrochemical reactivity compared to bulk catalysts, showcasing exceptional electrocatalytic activity, particularly in terms of mass and specific activity. This comprehensive review provides insights into the SED phenomenon, elucidates methodologies for fabricating PGM electrocatalysts using SED, and highlights their applications in water electrolysis and fuel cells.

N-heterocyclic carbene adsorption states on Pt(111) and Ru(0001).

N-heterocyclic carbene ligands (NHCs) are increasingly used to tune the properties of metal surfaces. The generally greater chemical and thermal robustness of NHCs on gold, as compared to thiolate surface ligands, underscores their potential for a range of applications. While much is now known about the adsorption geometry, overlayer structure, dynamics, and stability of NHCs on coinage elements, especially gold and copper, much less is known about their interaction with the surfaces of Pt-group metals, despite the importance of such metals in catalysis and electrochemistry. In this study, reflection absorption infrared spectroscopy (RAIRS) is used to probe the structure of benzimidazolylidene NHC ligands on Pt(111) and Ru(0001). The experiments exploit the intense absorption peaks of a CF3 substituent on the phenyl ring of the NHC backbone to provide unprecedented insight into adsorption geometry and chemical stability. The results also permit comparison with literature data for NHC ligands on Au(111) and to DFT predictions for NHCs on Pt(111) and Ru(0001), thereby greatly extending the known surface chemistry of NHCs and providing much needed molecular information for the design of metal-organic hybrid materials involving strongly reactive metals.

Nanometric Metal Overlayer Catalysts: Fundamental Aspects and Applications

Nanometric metal overlayer catalysts have been developed as novel catalyst structures with high three-way catalytic performance for practical applications. The metal overlayer is prepared via a dry process using pulsed arc plasma deposition, unlike wet coating processes for conventional powder catalysts containing nanoparticles. The key point to achieving high performance is the extremely high turnover frequencies for specific chemical reactions catalyzed by a large two-dimensional surface compared with metal nanoparticles. This overview study presents the preparation, structure, performance, reaction mechanism, and thermal stability of metal overlayer catalysts, focusing on rhodium (Rh) and catalytic conversion of nitric oxide (NO). Rh plays a pivotal role in the reduction of NO to N2 in automotive three-way catalytic converters. The potential benefit of the overlayer structure is the minimum loading of precious metal, such as Rh, which is limited and expensive.

Surface Structure and Temperature‐Reversible Phase Transition of Sn on W(110) Surface

The growth of Sn overlayers on the W(110) surface is investigated using low‐energy electron diffraction analysis. The structural investigation reveals Sn adsorption sites on the W(110) for (1 × 3) and (1 × 4) structures. During the formation of the (1 × 3) structure, Sn atoms are only adsorbed on the threefold hollow sites. However, at higher coverages, Sn atoms are adsorbed on the fourfold hollow sites after the threefold hollow sites are filled up to form the (1 × 4) structure, resulting in a dense overlayer structure. Both structures are overlayer with no alloy formation at the interface. The (1 × 3) phase exhibits a temperature‐reversible phase transition below ≈270 K. At low temperatures, a phase with long‐range order is developed.

Roles of metal oxide overlayers on hydrotalcite-structured Ni-MgAlOx for dry reforming of CH4 with CO2

The thermal stability of Ni nanoparticles on the coprecipitated hydrotalcite-like Ni-MgAl2O4 (NiMgAl) was enhanced by simply introducing an overlayer coating method with four different metal oxides (M) such as CeO2, ZrO2, SiO2 and Al2O3 (NiMgAl@M) for a harsh dry reforming reaction of CH4 with CO2 (DRM). Among the catalysts, the superior catalytic properties on the NiMgAl@Al such as less sintering and coke deposition were originated from the much stronger metal support interaction (SMSI), which were originated from the formed spatially confined Ni nanoparticles on the MgAl2O4 frameworks through the possible exsolution phenomena with the help of the porous Al2O3 overlayers. The unmodified NiMgAl catalyst revealed a relatively lower catalytic activity due to the facile coke depositions, which was mainly caused by the selective formation of larger Ni nanoparticles above 25 nm with its heterogeneous size distribution. The much simpler overlayer coating method with the porous overlayer structures, especially for Al2O3 coating layer, was found to be an effective way to achieve a superior catalytic activity and stability by preserving the thermally stable smaller Ni nanoparticles on the hydrotalcite-like Ni-MgAl2O4 surfaces.

Controlling the Strong Metal-Support Interaction Overlayer Structure in Pt/TiO2 Catalysts Prevents Particle Evaporation.

Platinum nanoparticles (NPs) supported by titania exhibit a strong metal-support interaction (SMSI)[1] that can induce overlayer formation and encapsulation of the NP's with a thin layer of support material. This encapsulation modifies the catalyst's properties, such as increasing its chemoselectivity[2] and stabilizing it against sintering.[3] Encapsulation is typically induced during high-temperature reductive activation and can be reversed through oxidative treatments.[1] However, recent findings indicate that the overlayer can be stable in oxygen.[4, 5] Using in situ transmission electron microscopy, we investigated how the overlayer changes with varying conditions. We found that exposure to oxygen below 400 °C caused disorder and removal of the overlayer upon subsequent hydrogen treatment. In contrast, elevating the temperature to 900 °C while maintaining the oxygen atmosphere preserved the overlayer, preventing platinum evaporation when exposed to oxygen. Our findings demonstrate how different treatments can influence the stability of nanoparticles with or without titania overlayers. expanding the concept of SMSI and enabling noble metal catalysts to operate in harsh environments without evaporation associated losses during burn-off cycling.

Mechanochemistry-Induced Strong Metal–Support Interactions Construction toward Enhanced Hydrogenation

The construction of strong metal–support interactions (SMSIs) represented an attractive approach to producing supported noble metal nanocatalysts possessing enhanced stability by overlayer encapsulation. The development of facile approaches capable of achieving efficient, controllable, and extensive SMSI overlayer formation, particularly under neat and ambient conditions, is a long-standing challenge. In this work, a mechanochemistry-driven pathway was deployed for efficient and controllable SMSI construction under neat and ambient conditions to customize the capsulation degree and overlayer structures toward enhanced catalysis. The reducibility of the additives and the high interaction efficiency provided by the mechanochemical treatment could afford abundant active intermediates (e.g., Ti3+ species and oxygen defects) within a short time to induce and tune the overlayer encapsulation. This facile approach could be extensively deployed to TiO2-derived nanocatalysts with diverse phases, diverse reducible metal oxides-involved systems, and different supported noble metal nanoparticles. Enhanced hydrogenation activity was achieved by the as-afforded nanocatalysts upon SMSI construction and further tuned by the encapsulation degree.

Molecular Origins of Chiral Amplification on an Achiral Surface: 2D Monolayers of Aspartic Acid on Cu(111).

Recent experiments have demonstrated an intriguing phenomenon in which adsorption of a nonracemic mixture of aspartic acid (Asp) enantiomers onto an achiral Cu(111) metal surface leads to autoamplification of surface enantiomeric excess, ees, to values well above those of the impinging gas mixtures, eeg. This is particularly interesting because it demonstrates that a slightly nonracemic mixture of enantiomers can be further purified simply by adsorption onto an achiral surface. In this work, we seek a deeper understanding of this phenomena and apply scanning tunneling microscopy to image the overlayer structures formed by mixed monolayers of d- and l-Asp on Cu(111) over the full range of surface enantiomeric excess; ees = -1 (pure l-Asp) through ees = 0 (racemic dl-Asp) to ees = 1 (pure d-Asp). Both enantiomers of three chiral monolayer structures are observed. One is a conglomerate (enantiomerically pure), another is a racemate (equimolar mixture of d- and l-Asp); however, the third structure accommodates both enantiomers in a 2:1 ratio. Such solid phases of enantiomer mixtures with nonracemic composition are rare in 3D crystals of enantiomers. We argue that, in 2D, the formation of chiral defects in a lattice of one enantiomer is easier than in 3D, simply because the stress associated with the chiral defect in a 2D monolayer of the opposite enantiomer can be dissipated by strain into the space above the surface.

Effects of monolayer and bilayer silica films on Fe-Phthalocyanine adsorption properties

We explore the adsorption properties of Fe-Phthalocyanine (FePc) molecule at various configurations of silica films supported by Ru(0001) and report on the geometric, electronic and magnetic features of the energetically preferred structures to fully understand the influence of the silica films on the adsorption properties of the FePc molecule. The investigation is carried out with the use of density of functional theory calculations and the self-consistent inclusion of van der Waals interaction. In addition, Oxygen atoms are added to govern the atomic structure of the silica overlayers on the surface. Our results show that both FePc/silica thin film systems exhibit both physisorption and chemisorption simultaneously. In addition, the FePc molecule on each substrate undergoes a symmetry reduction driven by mismatch with the substrates' symmetry as well as the breakup of the degenerate orbitals of Fe.

Oxidic structures on copper-gold alloy nanofacets

Bimetallic alloy catalysts often display superior performance to their monometallic counterparts in numerous chemical reactions, whose reactivity and selectivity primarily depend on their surface structures and chemical compositions under reaction environments. Predicting the structure and composition of alloy surfaces under reaction conditions is still challenging. In this work, using density-functional theory with ab initio thermodynamics, we examine the surface structures of the Cu-Au alloy system under different preparation and oxidative environments. We analyze the stability of thin copper oxide layers on various substrates, ranging from clean Au(111) to Au3Cu and their mixtures, and Cu overlayer structures. Our results show that the stability of the oxide layer structures strongly depend on the atomic configurations of the substrate. We also explore the possibility of using computational surface characterization methods to capture the atomic configurations and electronic structure of different interfacial regions of these substrates. Our electronic structure analysis demonstrates that controlling the concentration of surface Cu allows one to fine tune the surface electronic structure, and modulating the growth conditions to express the desired surface oxide phase may achieve the same effect. By providing an atomic-scale account, this study aims to capture the atomic configurations and electronic structure of different interfacial regions of these complex oxidic Cu/Au nanoalloys for selective oxidation reactions.

CO adsorption on Co(0001) revisited: High-coverage CO superstructures on the close-packed surface of cobalt

The adsorbate overlayer structures formed by CO on highly covered Co(0001) were investigated using temperature programmed desorption, low energy electron diffraction, reflection absorption infrared spectroscopy and synchrotron-based x-ray photoemission spectroscopy, with the purpose to clarify some recent confusion on CO adsorption at high coverages. TPD shows that the coverage of the (2√3 × 2√3)R30o structure (abbreviated as 2√3 structure) is 7/12 (0.583) ML. Its unit cell contains one COtop and six CObridge species that form three ‘bridge dicarbonyls’ in which two CObridge adsorbates share the same cobalt surface atom. Between 0.58 and 0.63 ML the 2√3 structure breaks up into small 2D domains separated by antiphase domain boundaries that consist of ‘double bridge dicarbonyls’ in which three CObridge adsorbates share two cobalt surface atoms. A phase transition that occurs around 0.63 ML creates previously unknown c(8 × 2) and c(12 × 2) domain boundary structures which consist of high density strips with a (2 × 2)–3CO structure and top/hollow site occupation which are separated by antiphase domain boundaries with a lower local coverage. Up to 0.63 ML the structures found at low temperature in UHV are very similar to those observed by others using in-situ STM at 300 K under CO pressure. This changes above 0.63 ML, where STM shows that moiré structures form instead of the c(n × 2) domain boundary structures. We propose that the moiré and c(n × 2) structures have a very similar enthalpy of formation so that small variations of temperature and CO chemical potential can lead to different structures for the same CO coverage. We show that these high-density phases that exist above 0.5 ML do not form at the typical pressures and temperatures used in applied FTS, but they do need to be considered when CO adsorption at room temperature is used as a diagnostic tool to characterize the catalyst surface.

Controlling the metal work function through atomic-scale surface engineering

Adsorbate induced work function modification of Ni have been investigated by means of first-principles calculations. More specifically, the adsorption of Li, Na, Si, Zr, Pd, Pt, or Sn at various coverages on Ni low-index surface models have been considered. In the case of Sn, a more thorough investigation was performed comparing the adsorption as an overlayer structure with the case of surface alloy formation. Our calculations suggest that the most stable Sn@Ni configuration corresponds to a surface alloy, and here the Ni(100)c(2 × 2)-Sn, Ni(110)c(2 × 2)-Sn, and Ni(111)(3×3)R30∘-Sn surface alloys were found to display similar stability. Concerning the induced work function change, a different behaviour as a function of coverage was observed depending on the nature of the Sn@Ni surface model. Both overlayer adsorption and surface alloying were found to induce a work function decrease already at relatively low coverages (≈ 0.05 atom Å −2), regardless of the underlying surface orientation. However, while the work function obtained for stable surface alloys was found to monotonously decrease as the coverage increases, the work function for the stable overlayer structures goes through a minimum. For all investigated surface modifications, the change in work function was found to be consistent with the orientation of the charge transfer at the adsorbate–surface interface. The computed data in this work may serve as handles for experimental endeavours aiming to optimize properties of active materials through atomic-scale surface engineering.

Evidence of a Tetrahedrally Coordinated RuO4 Surface Complex on RuO2(100): Density Functional Theory and Beyond

RuO2(100), an efficient low-temperature oxidation model catalyst, is able to undergo a c(2 × 2) reconstruction with a so far unknown surface structure that is accompanied by the loss of its catalytic activity. Here, the surface structure of the c(2 × 2) reconstruction of RuO2(100) is predicted by ab initio molecular dynamics simulations and shown to be consistent with available surface science experiments from the literature, including scanning tunneling microscopy (STM) images, low-energy electron diffraction (LEED) intensity versus voltage experiments, and thermal desorption experiments of O2. Mechanistically, the c(2 × 2) reconstruction starts from a simple c(2 × 2) overlayer structure of on-top O on RuO2(100), where the remaining undercoordinated surface Ru centers shift laterally toward the on-top O position, thereby breaking two Ru–O back bonds to lattice oxygen and forming a new Ru–O bond with on-top O. This leads to the formation of a tetrahedrally coordinated surface species Ru4f, a process that is activated by 0.95 eV and that results in an energy stabilization of 0.66 eV. The c(2 × 2) surface structure can readily explain the lack of activity in catalytic CO oxidation. The CO molecule is much more weakly bound on RuO2(100)-c(2 × 2) reconstruction than on the RuO2(110) or the RuO2(100)-(1 × 1) surface, and in addition, the Ru4f centers are too far apart to allow for O2 activation. The identified Ru4f surface species is expected to play a prevailing role as precursor species in the missing thermal and electrochemical stability of RuO2 under oxidizing reaction conditions by forming volatile RuO4.

Neural-network-backed evolutionary search for SrTiO3(110) surface reconstructions.

The determination of atomic structures in surface reconstructions has typically relied on structural models derived from intuition and domain knowledge. Evolutionary algorithms have emerged as powerful tools for such structure searches. However, when density functional theory is used to evaluate the energy the computational cost of a thorough exploration of the potential energy landscape is prohibitive. Here, we drive the exploration of the rich phase diagram of TiO x overlayer structures on SrTiO3(110) by combining the covariance matrix adaptation evolution strategy (CMA-ES) and a neural-network force field (NNFF) as a surrogate energy model. By training solely on SrTiO3(110) 4×1 overlayer structures and performing CMA-ES runs on 3×1, 4×1 and 5×1 overlayers, we verify the transferability of the NNFF. The speedup due to the surrogate model allows taking advantage of the stochastic nature of the CMA-ES to perform exhaustive sets of explorations and identify both known and new low-energy reconstructions.

Tuning the Composition of Silicon Oxide Overlayers to Control the Performance of Platinum Electrocatalysts

Membrane coated electrocatalysts (MCECs) have shown to be an attractive approach for improving the activity, stability, and selectivity of various electrochemical reactions. However, little is known about how overlayer structure impacts different catalytic properties and ultimate performance. By analyzing the affect that overlayer composition has on the electrochemical behavior for various probe reactions, guiding relationships that correlate MCEC structure and performance can be derived. For a silicon oxide (SiOx)|Pt MCEC, limiting the conversion of polydimethyl-siloxane (PDMS) to SiOx during synthesis can result in varied concentrations of carbon in the overlayer film, allowing composition to be manipulated and studied directly. These changes in composition consequently affect the hydrophobicity, density, and silicon-oxygen coordination of the overlayer, which in turn influences the final transport behavior of the SiOx membrane. Specifically, platinum electrodes with partially converted SiOxCy overlayers demonstrate a decreased permeability for protons when studying the hydrogen evolution reaction (HER), compared to the less carbon rich, fully converted Pt|SiOx electrodes. Surprisingly, the opposite trend was observed for oxygen permeability during the acidic oxygen reduction reaction (ORR), where the fully cured overlayers free of carbon suppress the transport of oxygen to the buried interface. These contrasting trends in transport suppression present a unique opportunity for future designs to dial in specific, intermediate concentrations of common co-reactants like oxygen and protons, potentially allowing for increased selectivity, poisoning resistance, and stability of the underlying catalyst simply by altering the overlayer’s final composition. Collectively, these results demonstrate the broadened design space that MCEC-style electrocatalysts introduce for future electrochemical systems, and further extend their applicability and relevance to a broader range of reactions.

Corrosion and Hydrogen Permeation in H2S Environments with O2 Contamination, Part 3: The Impact of Acetate-Buffered Test Solution Chemistry

This paper highlights the importance of considering the magnitude of acetate (ethanoate) species concentration on corrosion and hydrogen permeation rates, important factors associated with cracking initiation in steels for sour service qualification. Materials selection relies on standards, such as NACE TM0177 and NACE TM0284, which stipulate that oxygen pollution should be avoided during testing in H2S-containing media. The 5% NaCl test solutions in current standards are buffered using acetic acid (CH3COOH)/sodium acetate (CH3COONa) to fix the solution pH over long periods. In this third paper, as part of a series of articles that evaluate how oxygen entry modifies the corrosion of (and hydrogen permeation across) low alloy steel membranes in H2S-containing solutions, the effect that changing the solution chemistry has through testing X65 steel in different concentrations of acetic acid and sodium acetate in H2S-saturated 5% NaCl solutions, i.e., Solutions A and B (NACE TM0177-2016) and the high-strength line pipe (HLP) solution of NACE TM 0284-2016, is investigated. Increasing the total acetic acid + acetate concentration encourages a higher average X65 corrosion rate and longer-sustained hydrogen charging flux, assigned to the cathodic reaction rate enhancement by acetic acid and the iron solubilizing effects of acetates. Introducing 300 ppb of dissolved oxygen does not push the solution pH outside of the permitted error range but increases average X65 corrosion rates and, again, helps sustain hydrogen permeation flux for longer. Through an evaluation of the surface structure and electrochemical data, this appears to be due to an increase in the permeability and protectiveness of the troilite FeStroilite dominant scale and a possible acetic acid buffering of local pH increase at surface cathodic sites during corrosion. The HLP solution (at pH 3.5), with the highest acetic acid and acetate concentration, is the most aggressive. In this electrolyte, an iron sulfide overlayer structure is attained with an oxygen-rich inner layer between the metal substrate and a thick iron sulfide film.

Nanometric Iridium Overlayer Catalysts for High-Turnover NH3 Oxidation with Suppressed N2O Formation

In the present study, we prepared a 12 nm thick Ir overlayer via pulsed cathodic arc plasma deposition on a 50 μm thick Fe–Cr–Al metal (SUS) foil. Using this thin-film catalyst made NH3–O2 reactions more environmentally benign due to a much lower selectivity for undesirable N2O (<5%) than that of a Pt overlayer (∼70%) at 225 °C. Despite its small surface area, Ir/SUS exhibited promising activity as an ammonia slip catalyst according to a turnover frequency (TOF) >70-fold greater than that observed with conventional Ir nanoparticle catalysts supported on γ-Al2O3. We found that the high-TOF NH3 oxidation was associated with the stability of the metallic Ir surface against oxidation by excess O2 present in simulated diesel exhaust. Additionally, we found that the Ir overlayer structure was thermally unstable at reaction temperatures ≥400 °C and at which point the Ir surface coverage dropped significantly; however, thermal deterioration was substantially mitigated by inserting a 250 nm thick Zr buffer layer between the Ir overlayer and the SUS foil substrate (Ir/Zr/SUS). Although N2O formation was suppressed by NH3 oxidation over Ir/Zr/SUS, other undesired byproducts (i.e., NO and NO2) were readily converted to N2 by coupling with a V2O5–WO3/TiO2 catalyst in a second reactor for selective catalytic reduction by NH3. These results demonstrated that this tandem reactor configuration converted NH3 to N2 with nearly complete selectivity at a range of 200–600 °C in the presence of excess O2 (8%) and H2O (10%).

Exploring the temperature rise under low-energy electron irradiation for various materials

Scanning electron microscope (SEM) is frequently-used in analysis for micro/nanoscale structural information. During SEM analysis, besides the widely-known charging effect, the temperature rise because of electron beam bombardment has become an issue due to it also can modify SEM results with the downsizing of specimen. In this work, a sophisticated Monte Carlo (MC) model which considered the cascade electron production was adopted to quantitatively study the temperature rise during SEM imaging. The rule of temperature profile was explored focusing on four different materials (semi-infinite beryllium (Be), magnesium (Mg), copper (Cu) and gold (Au) bulks) and primary electron (PE) beam energies. It was concluded that the temperature profile presents three main characteristics: a) increasing first at surface until its maximum is reached, then has a sharp reduction as a function of depth from the surface for all materials; b) being affected seriously by PE energy and atomic number. The temperature rise integral from high to low is Be > Cu > Au > Mg; c) various elements show different capabilities of heat transfer direction and speed. The mechanism behind these observations was explained in detail. In addition, the temperature rise was investigated briefly on two overlayer structures (Be/Au and Au/Be), showing discontinuous jumping at the interface for two types of materials. This work on the one hand, provides a better understanding and elucidation for physical mechanism of electron-beam-induced deposition, of which process control, performance and reliability would thus get greater improved based on this study, on the other hand, reveals a potential implication that some damages caused by the heat transfer under electron irradiation in a SEM operation might be effectively avoided or reduced through selecting appropriate materials according to their different heat transfer performances.

Structure of chalcogen overlayers on Au(111): Density functional theory and lattice-gas modeling.

Ordering of different chalcogens, S, Se, and Te, on Au(111) exhibit broad similarities but also some distinct features, which must reflect subtle differences in relative values of the long-range pair and many-body lateral interactions between adatoms. We develop lattice-gas (LG) models within a cluster expansion framework, which includes about 50 interaction parameters. These LG models are developed based on density functional theory (DFT) analysis of the energetics of key adlayer configurations in combination with the Monte Carlo (MC) simulation of the LG models to identify statistically relevant adlayer motifs, i.e., model development is based entirely on theoretical considerations. The MC simulation guides additional DFT analysis and iterative model refinement. Given their complexity, development of optimal models is also aided by strategies from supervised machine learning. The model for S successfully captures ordering motifs over a broader range of coverage than achieved by previous models, and models for Se and Te capture the features of ordering, which are distinct from those for S. More specifically, the modeling for all three chalcogens successfully explains the linear adatom rows (also subtle differences between them) observed at low coverages of ∼0.1 monolayer. The model for S also leads to a new possible explanation for the experimentally observed phase with a (5 × 5)-type low energy electron diffraction (LEED) pattern at 0.28 ML and to predictions for LEED patterns that would be observed with Se and Te at this coverage.