Monolayer Growth Research Articles

Correlative light and scanning electron microscopy (CLSEM) for analysis of bacterial infection of polarized epithelial cells

Infection of mammalian host cells by bacterial pathogens is a highly dynamic process and microscopy is instrumental to reveal the cellular and molecular details of host-pathogen interactions. Correlative light and electron microscopy (CLEM) combines the advantages of three-dimensional live cell imaging with ultrastructural analysis. The analyses of adhesion to, and invasion of polarized epithelial cells by pathogens often deploys scanning electron microscopy (SEM), since surface structures of the apical brush border can be analyzed in detail. Most available CLEM approaches focus on relocalization of separated single cells in different imaging modalities, but are not readily applicable to polarized epithelial cell monolayers, since orientation marks on substrate are overgrown during differentiation. To address this problem, we developed a simple and convenient workflow for correlative light and scanning electron microscopy (CLSEM), using gold mesh grids as carrier for growth of epithelial cell monolayers, and for imaging infection. The approach allows fast live cell imaging of bacterial infection of polarized cells with subsequent analyses by SEM. As examples for CLSEM applications, we investigated trigger invasion by Salmonella enterica, zipper invasion by Listeria monocytogenes, and the enterocyte attachment and effacement phenotype of enteropathogenic Escherichia coli. Our study demonstrates the versatile use of gold mesh grids for CLSEM of the interaction of bacterial pathogens with the apical side of polarized epithelial cells.

How to ‘train’ your CVD to grow large-area 2D materials

In recent years 2D materials like monolayer of transition metal dichalcogenides (TMDs) have caught enormous interest due to their potential applications in electronic, optoelectronic, spintronic, valleytronic and twistronic devices. To grow large-area monolayer of these materials, chemical vapor deposition (CVD) is one of the most widely used techniques. But the size and quality of the samples are critically dependent on the various growth conditions. As a result, the CVD parameters vary from lab to lab and often it is difficult to find a stable and reproducible growth condition. Here we have demonstrated a methodology for the quick and easy optimization of various growth parameters of 2D materials using CVD. We have taken MoS2 as a model 2D system and discussed the way to achieve an optimum recipe for the growth of large-area monolayer reproducibly. We have done thorough electrical and optoelectrical characterization to show the device performance of the samples grown in various conditions. The methodology will help to optimize the growth condition of any other 2D materials easily and quickly.

Atomistic mechanisms of seeding promoter-controlled growth of molybdenum disulphide

Seeding promoters facilitate the nucleation and growth of transition metal dichalcogenides in chemical vapor deposition (CVD). However, sophisticated roles of seeding promoter remain unclear. Here, adopting triangular-shaped crystal violet (CV) consisting of nonpolar and polar parts as the seeding promoter, we study the role of seeding promoter for the growth of molybdenum disulfide (MoS2). We systematically control the geometrical configuration of CV on SiO2/Si substrate by changing the solvent polarity and find that it strongly affects the growth of monolayer or multilayer MoS2 domains via CVD. Monolayer MoS2 domains were predominantly grown on randomly lying-down CV configurations on SiO2/Si substrate, whereas multilayer MoS2 domains are synthesized at concentrated polar parts in CV micelle on the substrate. Density functional theory calculations reveal that the initial nucleation step for the MoS2 growth is the adsorption of S on CV and the most favourable S adsorption site is the polar part in CV. Furthermore, it is found that the CV adsorption to SiO2 is mediated by the polar CV part and additionally strengthened in the lying-down CV configuration. Enhancing the thermal stability as well as hindering the re-aggregation of CV at high temperature, the lying down CV configuration allows the predominant growth of monolayer MoS2. This work provides a general framework to understand the growth of MoS2 from aromatic seeding promoters.

Anisotropy diffusion in monolayer growth of Au on Cu (110) by kinetic Monte Carlo method

Morphological and Structural transitions during epitaxial growth of surface and interface are an important nanoscal phenomena. Understanding the diffusion of adatom in anisotropic surface on the fcc (110), presents a challenge because of the various processes and energy activation of diffusion. During monolayer formation, adatoms could aggregate and forming islands. the stability of these latter is related the its shapes and adatom bonding. In this work, we used the Kinetic Monte Carlo method, implementing anisotropic bond-breaking model (ABBM) to simulate the evolution of anisotropic islands. In order to discuss the monolayer growing, many parameters are taken into account such as potential barriers, temperatures, deposition rates at fixed coverage of 10% monolayer.

1924P - Exosomes in NSCLC as a source of biomarkers

BackgroundExosomes are small membranous vesicles (around 40-130nm), that have been detected in different biological samples, that play a key role in NSCLC and being relevant in stem cell differentiation as well. The main objective of this study was to analyze the exosomes cargo from NSCLC cell cultures growth in monolayer (2D) and suspension conditions (3D, lung tumorespheres). MethodsCultures were established from NSCLC resected patients and cell lines. Exosomes isolation was performed by ultracentrifugation. Characterization was carried out by NTA, electron microscopy, immunoblot and flow cytometry. Mutational status of EGFR and RAS genes was analyzed by BEAMing dPCR. Transcriptomic analysis has been carried out from exosomal RNA with microarrays, (p≤0.01). Consequently, XAGE1B (significantly expressed gene in exosomes) was analyzed by RTqPCR in 189 paired fresh-frozen tumor and normal tissue samples of resected NSCLC. Prognostic value was assessed by Kaplan‐Meier curves (log rank‐test), considering significant p<0.05. ResultsExosomal characterization through NTA and electron microscopy showed an exosomes size from 108-125nm. Specific markers were detected by IB and FC. Mutational analysis of EGFR and RAS genes in exosomes shown the same pattern displayed by the origin cells. Transcriptomic analysis showed that the expression of mRNAs, miRNAs and precursors were significantly different between 3D and 2D-derived exosomes. A pathway enrichment was carried out to know in which processes (cancer-related) are involved. Significant differential expression was also found between ADC vs SCC–derived exosomes. Concretely, XAGE1B is overexpressed in ADC-derived exosomes (p=0.00003). This overexpression in ADC was validated in NSCLC cohort (p=0.002). Furthermore, it has revealed a significant association with patient prognosis for overall survival in the ADC group (n=74)(OS 49.8 vs. NR months, p=0.043). ConclusionsDifferences in exosomal cargo have been observed between: i) 3D vs. 2D cultures and ii) ADC vs. SCC. In addition, the same mutational pattern was detected in exosomes as compared with parental cells. Therefore, exosomes can be a useful source of biomarkers in NSCLC analysis. Supported by grant GV/2018/026, PI18/00266, & AECC Valencia. Legal entity responsible for the studyFundación de Investigación del Hospital General Universitario de Valencia. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.

Graphene-Induced in Situ Growth of Monolayer and Bilayer 2D SiC Crystals Toward High-Temperature Electronics.

A reproducible graphene-induced in situ process is demonstrated for the first time for growing large-scale monolayer and bilayer cubic silicon carbide (SiC) crystals on a liquid Cu surface by chemical vapor deposition (CVD) method. Precise control over the morphology of SiC crystals is further realized by modulating growth conditions, thus leading to the formation of several shaped SiC crystals ranging from triangular, rectangular, pentagonal, and even to hexagonal kind. Simulations based on density functional theory are carried out to elucidate the growth mechanism of SiC flakes with various morphologies, which are in striking consistency with experimental observations. In the liquid Cu-assisted CVD system, growth temperature (∼1100 °C) enables sublimation and deposition of silicon oxide (SiO2) derived from quartz tube, while liquid Cu facilitates preformation of graphene originated from methane. The SiO2 and graphene, grown and reacted in situ in the CVD process, are served as the silicon and carbon source for the cubic SiC crystals, respectively. Moreover, the gradual transformation process from SiO2 particles to SiC flakes is directly observed, with several middle stages clearly displayed. The direct in situ growth of SiC crystals offers a novel method for scaled production of SiC crystals and is beneficial to understand its growth mechanism, and thus push forward the way to develop high-temperature and high-frequency electronic devices.

Modeling the thickness distribution of silicon oxide thin films grown by reactive magnetron sputtering

Target poisoning in reactive sputtering is one of the biggest problems in the coatings industry. In this work, we use the co-sputtering simulation reactive mode software, Co-SS Rm, to present a different solution of the compound formation both on the target and on the substrate, based on the comparison of the simulations with the thickness measurements of the films deposited at different flows of reactive gas. In these simulations, the spatial distribution of the deposited thin films is determined by analysing the angular distribution of the atoms and/or compound ejected from the target, as well as its sputtering yield. Results indicate that the target surface poisoning suffers an evolution ejecting metallic atoms and silicon oxide until the whole racetrack area is covered by silicon oxide, but at the same time, there is a reduction in the racetrack area due to the growth of several monolayers of silicon oxide. Spectroscopic ellipsometry analysis showed the formation of SiO2 in the thin films in almost all the reactive gas flows. Simulation results were validated by thickness measurements of actual thin films and plasma optical emission spectroscopy by analysing emission transitions from the target species (Si).

Glass-assisted CVD growth of large-area MoS2, WS2 and MoSe2 monolayers on Si/SiO2 substrate

In the last few years, there has been much effort to overcome the challenge of growing large-area transition metal dichalcogenide (TMDC) monolayers with a high-coverage to allow for their wide-usage in practical devices and applications. In this study, we investigate effects of two different glass lamellas on the formation of different monolayer TMDCs, namely MoS2, WS2 and MoSe2 for the CVD process in a horizontal growth configuration. Our approach is different from the widely used techniques of placing the substrate on the top the precursors (face-down configuration, generally causing non-uniform growth) or growing monolayers directly on glass lamellas which generally requires transfer step of the flakes if relevant devices will be fabricated on Si/SiO2 substrates. We confirm that rather than the glass surface effect, the glass lamellas ingredients enable the formation of monolayer TMDCs. Moreover, the repeatability problem of growing large-size monolayer flakes with uniform distribution and high coverage is successfully surpassed. For a comparison of ingredient compositions, two different glass lamellas (Glass-1 and 2) are used where the amount of Na and other ingredients are different. Our results show that although the uniformity and flake sizes change with the composition of the glass lamellas, MoS2, WS2 and MoSe2 monolayer flakes have been grown successfully for both of the glass lamella types. Thus, the catalytic effect of using a glass lamella in the CVD process is verified for three different TMDCs. Our monolayer TMDCs also show long-term stability where no-crack formation is observed since their initial growth, which is more than a year.

Selective Oxidation of WS2 Defect Domain with Sub‐Monolayer Thickness Leads to Multifold Enhancement in Photoluminescence

AbstractStabilizing defective domains of sub‐monolayer thickness in 2D materials plays a significant role in tuning the electronic and optical properties. The chemical vapor deposition growth of WS2 monolayers with control over phase and uniformly nucleated defect domains is reported. Multifold photoluminescence (PL) enhancement (≈20‐fold) is achieved by stabilizing defect‐dominated domains toward design of nanoscale optical devices. While the observed luminescence variation in the form of alternating triangles arises from planar heterostructure (1H–1T′) formation, defect domain present at the center of WS2 heterophase monolayer causes 20‐fold enhancement in photoluminescence. The observed luminescence enhancement is correlated with sulfur defects and confirmed by site‐specific spatial X‐ray photoemission spectroscopy and in situ PL measurements at cryogenic temperatures. Detailed microstructural and spectroscopic observations indicate the partial stripping of monolayers by removal of sulfur and incorporation of oxygen leading to increased excitonic emissions. The demonstrated atomic‐scale manipulation to stabilize defect domains over large area with enhanced luminescence behavior is relevant for developing next‐generation nanoscale photonic devices.

Inhibition of UBE2N-dependent CDK6 protein degradation by miR-934 promotes human bladder cancer cell growth.

Because bladder cancer (BC) is one of the most common malignant cancers of the urinary system, identification of BC cell growth-associated effectors is of great significance. Cyclin-dependent kinase (CDK)6 is a member of the CDK family of cell cycle-related proteins and plays an important role in cancer cell growth. This is borne out by the fact that a CDK6 inhibitor had been approved to treat several types of cancers. Nevertheless, underlying molecular mechanisms concerning how to regulate CDK6 expression in BC remains unclear. In the present study, it was observed that miR-934 was much higher in human BCs and human BC cell lines as well. The results also revealed that miR-934 inhibition dramatically decreased human BC cell monolayer growth in vitro and xenograft tumor growth in vivo; the outcomes were accompanied by CDK6 protein down-regulation and G0-G1 cell cycle arrest. Moreover, overexpression of CDK6 reversed the inhibition of BC cell growth induced by miR-934. Further studies showed that miR-934 binds to a 3'-UTR of ubiquitin-conjugating enzyme 2N (ube2n) mRNA, down-regulated UBE2N protein expression; this, in turn, attenuated CDK6 protein degradation and led to CDK6 protein accumulation as well as the promotion of BC tumor growth. Collectively, this study not only establishes a novel regulatory axis of miR-934/UBE2N of CDK6 but also provides data suggesting that miR-934 and UBE2N may be potentially promising targets for therapeutic strategies against BC.-Yan, H., Ren, S., Lin, Q., Yu, Y., Chen, C., Hua, X., Jin, H., Lu, Y., Zhang, H., Xie, Q., Huang, C., Huang, H. Inhibition of UBE2N-dependent CDK6 protein degradation by miR-934 promotes human bladder cancer cell growth.

Folate can promote the methionine-dependent reprogramming of glioblastoma cells towards pluripotency

Methionine dependency of tumor growth, although not well-understood, is detectable by 11C-methionine positron emission tomography and may contribute to the aggressivity of glioblastomas (GBM) and meningiomas. Cytosolic folate cycle is required for methionine synthesis. Its dysregulation may influence cell reprogramming towards pluripotency. We evaluated methionine-dependent growth of monolayer (ML) cells and stem cell-like tumor spheres (TS) derived from 4 GBM (U251, U87, LN299, T98G) and 1 meningioma (IOMM-LEE) cell lines. Our data showed that for all cell lines studied, exogenous methionine is required for TS formation but not for ML cells proliferation. Furthermore, for GBM cell lines, regardless of the addition of folate cycle substrates (folic acid and formate), the level of 3 folate isoforms, 5-methytetrahydrofolate, 5,10-methenyltetrahydrofolate, and 10-formyltetrahydrofolate, were all downregulated in TS relative to ML cells. Unlike GBM cell lines, in IOMM-LEE cells, 5-methyltetrahydrofolate was actually more elevated in TS than ML, and only 5,10-methenyltetrahydrofolate and 10-formyltetrahydrofolate were downregulated. The functional significance of this variation in folate cycle repression was revealed by the finding that Folic Acid and 5-methyltetrahydrofolate promote the growth of U251 TS but not IOMM-LEE TS. Transcriptome-wide sequencing of U251 cells revealed that DHFR, SHMT1, and MTHFD1 were downregulated in TS vs ML, in concordance with the low activity cytosolic folate cycle observed in U251 TS. In conclusion, we found that a repressed cytosolic folate cycle underlies the methionine dependency of GBM and meningioma cell lines and that 5-methyltetrahydrofolate is a key metabolic switch for glioblastoma TS formation. The finding that folic acid facilitates TS formation, although requiring further validation in diseased human tissues, incites to investigate whether excessive folate intake could promote cancer stem cells formation in GBM patients.

Pulsed laser deposition of monolayer and bilayer graphene

The properties of graphene vary with the number of layers, thus determining its usefulness in different applications. Consequently, it is important to develop a method for precisely controlling the number of layers for various application demands. In this study, high quality monolayer graphene was successfully prepared using pulsed laser deposition. Meanwhile, the growth of monolayer and bilayer graphene can be controlled by adjusting the laser energy density. Raman spectra show that high quality monolayer films grew at a laser energy density of 5.66 J/cm2 and bilayer graphene films grew at a laser energy density of 8.49 J/cm2. X-ray photoelectron spectroscopy indicate that the main chemical state of carbon is the sp2 hybrid state, and the maximum atomic ratio of sp2 and sp3 results from the sample with laser energy density of 5.66 J/cm2. Scanning electron microscope images show that monolayer graphene is connected by small sheets with different sizes, and the largest graphene sheet reaches 20 μm. High resolution transmission electron microscope images and selected area electron diffraction patterns show that graphene samples are highly crystalline and yield significant layer information. UV–Vis spectra indicate that the transmittance through monolayer and bilayer graphene at 550 nm are 96.93% and 95.05%, respectively. Ultraviolet photoelectron spectroscopic measurements show that the work function of graphene ranges from 3.72 eV to 4.76 eV; the variation in the work function is related to growth defects. Finally, the relationship between the structure of the graphene films and laser energy density are investigated in detail, and these results indicate that the controllable growth of graphene can be achieved by adjusting the laser energy density. This means that a suitable laser energy density is conducive to defining an equilibrium between diffusion and condensation of carbon atoms, which is crucial to the growth of high-quality monolayer and bilayer graphene. It is expected that this study might be facilitate the preparation of graphene-based composite films and devices.

Well-Ordered Monolayer Growth of Crown-Ether Ring Molecules on Cu(111) in Ultra-High Vacuum: An STM, UPS, and DFT Study

Crown-ether (CR) ring molecules are known as host molecules for capturing guest species inside the ring. So far CR molecular films have only been grown by drop-casting a CR solution on an inert substrate in air which offers little control over the molecular structure. Here we report the successful growth of a well-ordered CR molecular array on an atomically flat and clean noble metal Cu(111) substrate at 300 K in ultra-high vacuum (UHV), using 4,4′,5,5′-tetrabromodibenzo[18] crown-6 ether (Br-CR). The adsorption, self-assembly, and electronic structures of Br-CR were studied by means of UHV low-temperature scanning tunneling microscopy and spectroscopy, low electron energy diffraction, and angle-resolved ultraviolet photoemission spectroscopy. We found that (1) the Br-CR ring, which is bent both in the crystal and gas phase, flattens upon adsorption on Cu(111). Density functional theory reveals that the two benzene groups of the molecule lie flat on the surface such as to maximize the substrate-molecule interaction. (2) The moderate molecule–substrate interaction allows thermal diffusion of the Br-CR molecules, resulting in the formation of self-assembled monolayer islands with 7 × 4 superstructure. (3) While the deposition of 0.05 ML Br-CR forms multidomain islands with disordered defects, a drastic improvement occurred at 0.25 ML, where only atomically flat single-domain islands were grown. This Br-CR flat ring cavity array could become a template for designing novel two-dimensional arrays of desired guest atoms, ions, or functionalized molecules.

Functional hybrid multilayered van der Waals heterostructures from graphene and self-assembled supramolecular 2D crystals

We demonstrate the soft realization of a new generation of functional hybrid van der Waals (vdW) heterostructures alternating two-dimensional (2D) materials and surface-confined supramolecular self-assemblies of porous crystals into three-dimensional (3D) stacks. We show that graphene can be transferred on top of a graphite-confined self-assembled 2D porous network, the cavities of which might be filled with functional guests. Subsequent growth of a new 2D host-guest self-assembled monolayer on top of this intermediate vdW heterostructure further extends it into the third dimension. Thus, this versatile approach, potentially not limited in the number of layers, allows creating on demand sequences by the careful choice of the 2D materials and of the presence or not and choice of guest molecules and permits to envisage innovative structures such as record-density bulk heterojunctions.

A "Phase Separation" Molecular Design Strategy Towards Large-Area 2D Molecular Crystals.

2D molecular crystals (2DMCs) have attracted considerable attention because of their unique optoelectronic properties and potential applications. Taking advantage of the solution processability of organic semiconductors, solution self-assembly is considered an effective way to grow large-area 2DMCs. However, this route is largely blocked because a precise molecular design towards 2DMCs is missing and little is known about the relationship between 2D solution self-assembly and molecular structure. A "phase separation" molecular design strategy towards 2DMCs is proposed and layer-by-layer growth of millimeter-sized monolayer or few-layer 2DMCs is realized. High-performance organic phototransistors are constructed based on the 2DMCs with unprecedented photosensitivity (2.58 × 107 ), high responsivity (1.91 × 104 A W-1 ), and high detectivity (4.93 × 1015 Jones). This "phase separation" molecular design strategy provides a guide for the design and synthesis of novel organic semiconductors that self-assemble into large-area 2DMCs for advanced organic (opto)electronics.

KLF4 as a rheostat of osteolysis and osteogenesis in prostate tumors in the bone.

We previously showed that KLF4, a gene highly expressed in murine prostate stem cells, blocks the progression of indolent intraepithelial prostatic lesions into aggressive and rapidly growing tumors. Here we show that the anti-tumorigenic effect of KLF4 extends to PC3 human prostate cancer cells growing in the bone. We compared KLF4 null cells to cells transduced with a DOX-inducible KLF4 expression system, and find KLF4 function inhibits PC3 growth in monolayer and soft agar cultures. Furthermore, KLF4 null cells proliferate rapidly, forming large, invasive and osteolytic tumors when injected into mouse femurs whereas KLF4 re-expression immediately after their intra-femoral inoculation blocks tumor development and preserves a normal bone architecture. KLF4 re-expression in established KLF4 null bone tumors inhibits their osteolytic effects, preventing bone fractures and inducing an osteogenic response with new bone formation. In addition to these profound biological changes, KLF4 also induces a transcriptional shift from an osteolytic program in KLF4 null cells to an osteogenic program. Importantly, bioinformatic analysis shows that genes regulated by KLF4 overlap significantly with those expressed in metastatic prostate cancer patients and in three individual cohorts with bone metastases, strengthening the clinical relevance of the findings in our xenograft model.

Kinetic Monte Carlo simulations of coverage effect on Ag and Au monolayers growth on Cu (1 1 0)

In this work, different coverages (1% ≤ coverage ≤ 20%) are studied during the growth of Ag and Au monolayers on the Cu (1 1 0) surface using kinetic Monte Carlo simulations (kMC). The results have shown that as coverage increases, the likelihood of an isolated adatom connecting to another adatom or island also increases. Thus, the phenomenon by which an adatom disintegrates from one island to another becomes significant. Molecular statics method is used to calculate the activation energy barriers of several diffusion processes in the framework of the Embedded-Atom method (EAM). These diffusion processes are implemented in the kinetic Monte Carlo (kMC) simulations under the Anisotropic Bond-Breaking Model (ABBM) model. The results show that as the coverage increases, 1D clusters are observed at 200 K. However, the transition from compact 1D (at 200 K) to 2D islands has been observed for relatively high temperatures (300 K and 400 K).

Molecular Beam Epitaxy Scalable Growth of Wafer-Scale Continuous Semiconducting Monolayer MoTe2 on Inert Amorphous Dielectrics.

Monolayer MoTe2 , with the narrowest direct bandgap of ≈1.1 eV among Mo- and W-based transition metal dichalcogenides, has attracted increasing attention as a promising candidate for applications in novel near-infrared electronics and optoelectronics. Realizing 2D lateral growth is an essential prerequisite for uniform thickness and property control over the large scale, while it is not successful yet. Here, layer-by-layer growth of 2 in. wafer-scale continuous monolayer 2H-MoTe2 films on inert SiO2 dielectrics by molecular beam epitaxy is reported. A single-step Mo-flux controlled nucleation and growth process is developed to suppress island growth. Atomically flat 2H-MoTe2 with 100% monolayer coverage is successfully grown on inert 2 in. SiO2 /Si wafer, which exhibits highly uniform in-plane structural continuity and excellent phonon-limited carrier transport behavior. The dynamics-controlled growth recipe is also extended to fabricate continuous monolayer 2H-MoTe2 on atomic-layer-deposited Al2 O3 dielectric. With the breakthrough in growth of wafer-scale continuous 2H-MoTe2 monolayers on device compatible dielectrics, batch fabrication of high-mobility monolayer 2H-MoTe2 field-effect transistors and the three-level integration of vertically stacked monolayer 2H-MoTe2 transistor arrays for 3D circuitry are successfully demonstrated. This work provides novel insights into the scalable synthesis of monolayer 2H-MoTe2 films on universal substrates and paves the way for the ultimate miniaturization of electronics.

ZnO-Controlled Growth of Monolayer WS2 through Chemical Vapor Deposition.

Monolayer tungsten disulfide (2D WS2) films have attracted tremendous interest due to their unique electronic and optoelectronic properties. However, the controlled growth of monolayer WS2 is still challenging. In this paper, we report a novel method to grow WS2 through chemical vapor deposition (CVD) with ZnO crystalline whisker as a growth promoter, where partially evaporated WS2 reacts with ZnO to form ZnWO4 by-product. As a result, a depletion region of W atoms and S-rich region is formed which is favorable for subsequent monolayer growth of WS2, selectively positioned on the silicon oxide substrate after the CVD growth.

Nickel Doping Enhances the Reactivity of Fe3O4(001) to Water

We studied how nickel doping affects water adsorption at the Fe3O4(001) surface to understand the enhanced performance of spinel ferrites for the water-gas shift and oxygen evolution reactions. Two different configurations were prepared: 2-fold-coordinated Ni adatoms on top of the surface and Ni atoms incorporated into the octahedral sites of the support. Using temperature-programmed desorption, X-ray photoemission spectroscopy, and scanning tunneling microscopy, we show that water is adsorbed and dissociated on the nickel adatoms at room temperature, resulting in Ni–OH species and surface hydroxyl groups. Nickel atoms incorporated into the support do not directly adsorb water but modify the electronic properties of the surface Fe, and water adsorbed on these sites has similar characteristics as that of water adsorbed on intrinsic surface defects. In both cases, the presence of Ni significantly alters the growth of the first water monolayer on Fe3O4(001).