Noble Metal Substrates Research Articles

A Controllable Synthesis of Pt-Based Electrocatalyst for the Oxygen Reduction Reaction of PEMFC with High Pt Utilization

Proton exchange membrane fuel cells (PEMFCs) are characterized with many advantages including high power density, low operating temperature (~80 oC), quick start-up and quick match to shifting demands for power, and regarded as a very promising technology for powering transportation and stationary applications1. However, the kinetics of the cathodic oxygen reduction reaction (ORR) in PEMFCs is sluggish and the most efficient material is platinum (Pt) that is rare on the earth and has a prohibitive cost. To make PEMFCs economically available, it is imperative to maximize the utilization of Pt or rather noble metal by improving catalyst layer’s mass transport of reactants and products, and by increasing noble-metal-mass activities toward the ORR in cathode. One of the strategies to improve mass transport in cathode is to thin the catalyst layer through developing high-content and high-dispersion Pt electrocatalysts. However, it is difficult to prepare Pt supported catalysts with a high Pt content because of the agglomeration of Pt nanoparticles. It was reported that the commercial Pt/VC catalysts had a particle size of 2.0 nm in Pt(10 wt%)/VC, 3.2 nm in Pt(30 wt%)/VC, and 8.8 nm in Pt(60 wt%)/VC2. Although great efforts have been made to improve traditional methods, such as impregnation method and colloidal method, it remains very challenging to find an economical and controllable way to synthesize Pt/VC electrocatalysts with a high Pt content for the ORR in PEMFCs. This can be attributed to several facts, including the poor size control, the contaminants from stabilizer residue, tedious procedures and so on. In this work, we propose a simple and controllable approach to deposit highly-dispersed Pt nanoparticles on Vulcan XC-72 carbon black. The as-synthesized Pt/VC possesses a high Pt content as well as high-dispersion Pt NPs via controlling the nucleation and growth process, and was investigated as the cathodic catalyst in PEMFC. Ideally highest Pt utilization with an extraordinary Pt-mass activity has been achieved by the Pt-monolayer-shell electrocatalysts which possess monoatomic thick Pt shells on noble-metal substrates3. However, the noble-metal-mass activities for these Pt-monolayer-shell electrocatalysts were also compromised, since the noble-metal substrates are quite essential for fabricating such electrocatalysts. In this regard, with the highest Pt utilization, improving the non-Pt noble-metal utilization in the substrates is critical for developing the Pt-monolayer-shell electrocatalysts. In this work, a surfactant-based, composition- and size-tunable method has been demonstrated to synthesize the monodispersed Pd-Ni as the substrates for fabricating the carbon-supported Pd-Ni@Pt nanospheres with Pt monolayer shells. And an excellent balance among activity, durability and noble-metal utilization was acquired. Acknowledgements This work was supported in part by National Natural Science Foundation of China (Grant No. 21373135 and 21533005) and Science Foundation of Ministry of Education of China ( Grant No. 413064). Reference 1. M.L. Perry, F.T. Fuller, J Electrochem Soc, 149 S59-S67 (2002). 2. B. L. Gratiet, H. Remita, G. Picq, M. Delcourt, J Catal, 164, 36 (1996). 3. (a) J. Zhang, M. B. Vukmirovic, Y. Xu, M. Mavrikakis, R. R. Adzic, Angewandte Chemie International Edition, 44 2132-2135, (2005); (b) M. Shao, K. Shoemaker, A. Peles, K. Kaneko, L. Protsailo, J Am Chem Soc, 132 9253-9255, (2010). (c) J. X. Wang, H. Inada, L. Wu, Y. Zhu, Y. Choi, P. Liu, W. P. Zhou, R. R. Adzic, J Am Chem Soc, 131,17298( 2009) .

Photo-induced enhanced Raman spectroscopy for universal ultra-trace detection of explosives, pollutants and biomolecules.

Surface-enhanced Raman spectroscopy is one of the most sensitive spectroscopic techniques available, with single-molecule detection possible on a range of noble-metal substrates. It is widely used to detect molecules that have a strong Raman response at very low concentrations. Here we present photo-induced-enhanced Raman spectroscopy, where the combination of plasmonic nanoparticles with a photo-activated substrate gives rise to large signal enhancement (an order of magnitude) for a wide range of small molecules, even those with a typically low Raman cross-section. We show that the induced chemical enhancement is due to increased electron density at the noble-metal nanoparticles, and demonstrate the universality of this system with explosives, biomolecules and organic dyes, at trace levels. Our substrates are also easy to fabricate, self-cleaning and reusable.

Ultrahigh Raman Enhancement on Monolayer MoS2

Surface-enhanced Raman scattering (SERS) is commonly associated with noble metal substrates. However, over the years modest Raman enhancements ( 3 × 105 enhancement in SERS signal from an organic molecule (4-mercaptopyridine) placed in the near field of a two-dimensional semiconductor molybdenum disulfide (MoS2) monolayer. This large enhancement in the SERS signal is attributed to the charge transfer (CT) state formed at the interface of the 2D semiconductor and organic molecule and is found to occur when the excitation source is chosen to be in resonance with the CT state. This approach provides a new strategy for carrying out SERS experiments on molecules with very weak Raman sig...

LEED and photoemission study of growth and structural evolution of Sn on Ag(001)

Growth of tin (Sn) on Ag(001) substrate has been studied at elevated temperatures using low energy electron diffraction (LEED), x-ray photoemission spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) measurements. A c(2 × 2) ordered surface is observed for very low coverages (0.1 ML) of Sn which subsequently transforms into a p(2 × 2) ordered surface for 0.25 ML Sn coverage, suggesting formation of a substitutionally ordered surface alloy. For higher coverages of Sn beyond 0.5 ML, no further structural evolution was observed with a constant p(1 × 1) LEED pattern. Our XPS results indicate diffusion of Ag atoms into Sn layers and forming Ag–Sn alloy film. Along with LEED and XPS, our ARPES results confirm the presence of an ordered Ag overlayer on the alloy film, suggesting a sandwich structure. Our studies are important in understanding the growth mechanism and electronic properties of Sn films on noble metal substrates.

Odd–Even Effects in the Structure and Stability of Azobenzene-Substituted Alkanethiolates on Au(111) and Ag(111) Substrates

Structural properties and stability of the self-assembled monolayers (SAMs) of two prototypical azobenzene-based alkanethiols (C6H5–N═N–C6H4–(CH2)n–SH) on Au(111) and Ag(111) substrates were studied in detail using a combination of complementary experimental techniques. The azobenzene moiety in these films was linked to the thiol headgroup via short aliphatic spacers of variable length, i.e., (CH2)3 or (CH2)4, corresponding to a different parity of n. For both Au(111) and Ag(111) substrates, a pronounced dependence of the packing density and molecular inclination on the parity of n was observed, with a higher packing density (by ∼14%) and smaller inclination (by ∼17°) of the azobenzene moieties for n = odd as compared to n = even on Au(111) and reversed, but somewhat reduced, behavior on Ag(111). This dependence was related to the well-known odd–even effects in molecular assembly on noble metal substrates, reported previously for a variety of oligophenyl-substituted alkanethiolate SAMs and observed now fo...

Synthesis of Lanthanum Telluride Thin Films By Electrodeposition from Ionic Liquids

Thermoelectric devices allow for conversion between electrical and thermal energy and have a great deal of potential as both cooling devices and alternative energy sources. Currently they are limited by their low efficiency, and so are only used in very specialized applications. Some potential materials for use in high temperature thermoelectric devices include rare earth telluride compounds. One such material is bulk lanthanum telluride, La3-xTe4, 0 ≤ x ≤ 1/3, which was found to have a ZT greater than unity at temperatures near 1000 C [1]. Lanthanum is already commonly used in many industrial applications, including as lanthanum hydride in the cathode of nickel metal hydride batteries [2]. Nanostructured materials have been shown to have a higher thermoelectric efficiency relative to bulk materials due to the enhancement of phonon scattering through quantum confinement [3]. This has generated a great deal of interest in low-dimensional and nanostructured thermoelectric devices. Since lanthanum telluride is usually made by ball milling, the creation of complex nanostructures or thin films with traditional methods is difficult. We have developed a technique to electrochemically deposit lanthanum telluride thin films from an ionic liquid at low temperatures (approximately 70 C). The films were deposited on noble metal substrates from 1-ethyl-3-methylimidazolium bromide ionic liquid based electrolytes containing to 0.05 M to 0.25 M lanthanum nitrate and 0.025M (HTeO2)+. The ratios of lanthanum to tellurium in the deposited films were determined by relative concentrations of the anions and cations in the electrolyte. The technique used for the deposition of these thin films could ultimately be used in the synthesis of nanostructured lanthanum telluride. This electrochemical method promises to be simpler, less expensive, and more efficient than current techniques. 1. A. May, J-P. Fleurial and G. J. Snyder, Phys. Rev. B, 78, 125205 (2008). 2. T. Sakai et al., J. Less-Common Met., 161, 193-202 (1990). 3. L. D. Hicks and M. S. Dresselhaus, Phys. Rev. B, 47, 12727 (1993).

Study of metal specific interaction, F-LUMO and VL shift to understand interface of CuPc thin films and noble metal surfaces

The performances of organic electronic devices are significantly associated with their energy level alignment at organic semiconductor/metal–electrode interfaces. The electronic character of an organic semiconducting molecular over-layer on a metal surface can vary from semiconducting to metallic, depending on the nature of the molecular orbitals with respect to the Fermi level of the electrode. The general tendency of extrapolating established models for single crystal substrates to ‘real’ device substrates is highly misleading. Hence, the importance of metal specific interaction, former lowest unoccupied molecular orbital (F-LUMO) and vacuum level (VL) shift have been investigated as a function of thickness of the deposited films by means of photoelectron spectroscopy (XPS and UPS) to understand the interface between CuPc and Cu, Ag, Pt and Au foils sequentially. The XPS data provides the signature of affectability of pyrrole sites of CuPc molecules for partial charge transfer from Cu and Ag substrates while a negligible effect on pyrrole cites resulted for Pt and Au substrates. Furthermore, the appearance of F-LUMO, a hybridized state close to the Fermi level gives confirmatory information about partial charge transfer. Contrary to the general belief that vacuum level shift caused by charge transfer can partially or totally cancel that for push back effect, our observation indicates that the partial charge transfer does not play significant role in the shift of vacuum level. The entire thickness dependent electronic energy level alignment of CuPc films on all noble metal substrates is explained in terms of a combined effect of partial charge transfer and photoemission final state relaxation energy. A systematic variation of HOMO-FWHM was observed with CuPc thickness due to continuous change in molecular orientation.

Natural Ceramic Nanotube Substrates for Surface-Enhanced Raman Spectroscopy

Natural halloysite clay nanotubes are cheap and available in large quantities, thus seem superior to the other nanotube-based materials. Halloysite nanotubes are used to form structured substrates for surface-enhanced Raman scattering (SERS). Specifically, layered aluminum-halloysite- (noble) metal substrates were prepared by deposition of halloysite nanotubes on aluminum foil, followed by thin metal film coatings via vacuum evaporation. The composite substrates required no capping agent on the metal surface and thus avoided background peaks in the Raman spectra, making them well suited for SERS studies. Gold-, silver-, and copper-coated substrates exhibited SERS for p-mercaptobenzoic acid, whereas uncoated and platinum-coated substrates did not. The SERS enhancement factors for the gold-, silver-, and copper-coated substrates were, by a conservative estimate, 1.4 × 105, 3.5 × 104, and 3.5 × 103, respectively. Interestingly enough, the SERS enhancement factors of substrates decrease in a row: Au > Ag > Cu, which differ from those for the corresponding metal nanoparticles.

H2-Evolution Assistd Pt-Thin Film Deposition on Non-Noble Metal Surfaces

At the moment, sustainable energy supply is one of the most important topics in society, industry and science. Therefore, there is great interest in the development of alternative power supply units, such as fuel cells [1]. Though platinum is the preferred catalyst for many of these systems, its comparably high price limits its widespread application [2]. To achieve catalysts with low noble metal content, platinum thin-films are promising due to their high specific activity and potentially high mass activity as well as expected long-term stability [3] compared to currently used Pt-nanoparticles supported on carbon [4]. In recent years, various methods were used to enhance 2D vs. 3D growth to produce Pt-thin films or -monolayers on noble metal substrates. Some include galvanic displacement of less noble metal adlayers [5], carbon monoxide poisoning [6] and hydrogen adsorption [7] on the depositing Pt. All have in common that Pt-deposition on already deposited Pt-sites is hindered compared to deposition on the substrate surface. In principle, this accounts as well for electrochemical deposition while the Hydrogen Evolution Reaction (HER) is taking place on Pt-sites but not (or at a lower rate) on the support. Utilizing this concept, we show a comparison between Pt electrodeposited on Au in the absence (Potential I in Fig. 1) and presence (Potential II in Fig. 1) of the HER on Pt, demonstrating the effect of HER on the morphology and layer thickness of the deposit. However, in order to develop thin layer catalysts for commercial applications, conductive oxide supports, such as antimony-doped tin oxide (ATO) are promising [8]. As proof of concept, the approach developed on Au was applied to a tin metal substrate that is usually covered with an oxide film and can therefore be considered a model system for an ATO support. Since Sn readily forms an oxide layer on its surface in oxidizing conditions (e.g., in ambient atmosphere), high interfacial energy between the Pt-deposit and substrate surface that strongly favors 3D- over 2D-growth is expected [9]. In Fig. 1 we experimentally showed that electrochemical deposition of Pt from slightly alkaline solution does not take place in measurable amount on the surface of Au (similar for Sn) while the oxide layer is present. In order to overcome this challenge, surface reduction of the Sn-electrode was carried out before the electrochemical deposition. The oxide reduction was achieved by applying the minimum overpotential needed for SnO2 reduction, but still high enough to cause instantaneous H2-evolution on the depositing Pt (from K2PtCl4). This in turn hinders further Pt deposition on Pt and directs it to take place mainly on the Sn surface. Furthermore, we will show the effect of deposition parameters (deposition time, potential, pH and K2PtCl4concentration) on the morphology of the electrochemically deposited Pt thin films on Sn surfaces and demonstrate the optimum conditions required for the deposition of Pt-thin films. Acknowledgments The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2013-2016) for the Fuel Cell and Hydrogen Joint Technology Initiative under grant agreement CATAPULT n°.325268. Special thanks to Katia Rodewald for the superb SEM images.

Ionic Liquid Structure in Thin Films

Understanding molecular structure and organization of a fluid’s surface layers is important to control many heterogeneous electrochemical processes. Ionic liquids present an exciting opportunity to examine surface confined thin fluid films and extended interfacial systems that may prove useful for electrochemical applications. This work explores the behavior of thin (1-20 nm) ionic liquid films and bulk IL interfaces in contact with air and noble metal substrates. Thin IL films are introduced by a highly controlled emersion process. Bulk interfaces are prepared by immersing the metal electrode into an IL solution. Data from ellipsometry, vibrational spectroscopy, contact angle, and electrochemical measurements are reported for the thin films and bulk solution / metal interfaces. Results correlate film and interfacial thickness and molecular structure with the chemical nature of the IL components and substrates. We will be particularly interested in future studies showing the effects of common 'contaminents' (i.e. water) on IL instrfacial structure. Descriptors will include chemical interactions i.e. hydrophobic forces, hydrogen bonding, van der Waals, electrostatics, etc. These studies inform work in IL electrochemistry, IL modified materials, and new fabrication methods for tailored surfaces which are urgently desired.

Structural Requirements for Surface-Induced Aromatic Stabilization

ABSTRACTSurface-induced aromatic stabilization (SIAS), a recently proposed mechanism leading to a formation of charge-transfer (CT) states at organic/metal (O/M) interfaces [G. Heimel, et al., Nat. Chem.5, 187 (2013)], was investigated for an aromatic hydrocarbon, diindenoperylene (DIP), by means of synchrotron radiation-based ultraviolet photoelectron spectroscopy (UPS). By employing DIP and noble metal substrates (Ag and Cu), we confirmed the formation of CT states, indicating that an inclusion of a specific functional group with a hetero-atom within adsorbate molecules as suggested before is not necessarily required for the formation of CT states mediated by the SIAS. With a comparison of the mother and analogue molecules, perylene and PTCDA, we discuss the structural requirement for the realization of the SIAS.

How Contacting Electrodes Affect Single π-Conjugated Molecular Electronic States: Local Density of States of Phthalocyanine Nanomolecules on MgO(001), Cu(111), Ag(001), Fe(001), and Mn(001)

Single molecules have attracted much interest as new materials for future spin electronic devices; however, many open questions still remain. One of them is how the electronic local density of states (LDOS) of single molecules is affected when they are in contact with electrodes. We show a systematic study of the LDOS of π-conjugated phthalocyanine (H2Pc) nanomolecules adsorbed on various electrodes, namely, (1) MgO(001) thin films grown on Ag(001), (2) noble metals of Cu(111) and Ag(001), and (3) 3d magnetic metals of Fe(001) and Mn(001), adupting scanning tunneling spectroscopy techniques with an ultrahigh-vacuum scanning tunneling microscopy setup at room temperature. Since MgO thin films cut the electronic coupling from the substrate Ag(001), we could observe H2Pc molecular states at -1.5 and +1.0 eV. H2Pc molecules on the noble metal substrates form a pattern with a square unit cell of about 1.5×1.5 nm2 and have similar LDOS peaks near the Fermi energy. Strong hybridizations between the substrate 3d spin-polarized states and the molecular π orbitals produce new molecular states of H2Pc molecules adsorbed on Fe(001) and Mn(001) near the energy positions of the Fe(001) minority spin state and the Mn(001) majority spin state, respectively.

Clean transfer of graphene on Pt foils mediated by a carbon monoxide intercalation process

Noble metals such as Pt are a perfect substrate for the catalytic growth of monolayer graphene. However, the requirements of the subsequent transfer process are not compatible with the traditional etching method. In this work, we find that the interaction of graphene with Pt foil can be weakened through the intercalation of carbon monoxide (CO) under ambient pressure. This intercalation process occurs on both hexagonal-shape graphene islands and irregular graphene patches on changing the CO partial pressure from 0 to 0.6 MPa, as observed by scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoemission spectroscopy. We demonstrate that, on a practical timescale, the intercalation ratio is proportional to the partial pressure of CO. Furthermore, we develop a clean transfer method of CO-intercalated graphene with water as a peeling agent. We show that this method enables the transfer of tens of micrometer-scale graphene patches onto SiO2/Si, which are free from metal or oxide particle contamination. This transfer method should be a significant step towards the clean transfer of graphene, as well as the recyclable use of noble metal substrates.

Competing Interactions in Surface Reticulation with a Prochiral Dicarbonitrile Linker

The organic and metal-directed assembly of a prochiral carbonitrile (CN) oligophenyl molecule on a smooth noble metal substrate was investigated by combined scanning tunneling microscopy and computational modeling. The molecule is functionalized with two CN groups in meta and para positions of the terminating phenyl rings of the p-terphenyl backbone. Upon deposition on a Ag(111) surface, we observe two different organic supramolecular networks, one of them reflecting a chiroselective assembly. After coevaporating small amounts of Co, a hybrid network comprising both CN–phenyl and metal coordination bond motifs could be observed. Intriguingly, the CN group in the para position is favored for the metal coordination, whereas the meta group remains in a CN–phenyl motif. Computational modeling suggest that the high stability of the meta CN–phenyl motif is causing this selective interaction. An increase of the metal adatom ratio eventually induces divergent assembly of a room-temperature stable 2D random metal–organic network.

Non-reciprocal photonic bands in a two-dimensional holey metal filled with a magnetoelectric material

We present an electromagnetic tight-binding formalism for the study of the photonic band structure of a two-dimensional lattice of magnetoelectric material infiltrated in a holey metallic host. We find, in particular, that one-way (non-reciprocal) frequency bands may arise in a slab geometry as a result of the explicit time-reversal symmetry breaking induced by the magnetoelectric material. Furthermore, time-reversal symmetry breaking introduces mode coalescence and exceptional points which both manifest the non-trivial topological nature of the frequency bands. For realizing the above lattice in the optical regime, a nematic liquid crystal can be infiltrated within the holes of a noble-metal substrate such as silver or gold.

Ethylene Irradiation: A New Route to Grow Graphene on Low Reactivity Metals

A novel technique for growing graphene on relatively inert metals, consisting in the thermal decomposition of low energy ethylene ions irradiated on hot metal surfaces in ultrahigh vacuum, is reported. By this route, we have grown graphene monolayers on Cu(111) and, for the first time, on Au(111) surfaces. For both noble metal substrates, but particularly for Au(111), our scanning tunneling microscopy and spectroscopy measurements provide sound evidence of a very weak graphene-metal interaction.

Surface-Enhanced Raman Scattering of 4-Aminobenzenethiol in Nanogaps between a Planar Ag Substrate and Pt Nanoparticles

To determine how effectively transition metal nanoparticles can couple with a noble metal substrate to induce higher electromagnetic fields, we examined the surface-enhanced Raman scattering (SERS) characteristics of 4-aminobenzenethiol (4-ABT) positioned in the gaps formed by a flat Ag substrate and 20–150 nm Pt nanoparticles. Initially, no Raman peaks of 4-ABT could be identified when 4-ABT was self-assembled on a polished flat Ag substrate; however, Raman peaks could be seen by attaching Pt nanoparticles onto the pendent amine groups. Conversely, a higher Raman signal was observed when larger Pt nanoparticles were attached onto 4-ABT, regardless of the excitation wavelength. Moreover, a higher Raman signal was measured in response to excitation at 488 nm, followed by excitation at 514.5, 568, and 632.8 nm. Very similar size and excitation wavelength dependences were found from the 3-dimensional finite-difference time-domain simulation. Accordingly, the highest enhancement was achieved using ∼150 nm Pt particles at 488 nm excitation with an enhancement factor (EF) of 3.5 × 104 per Pt particle. However, the electromagnetic field enhancement observed was not in conformity with the UV/vis absorbance of ∼150 nm Pt nanoparticles, which suggested that higher EFs would be measured in the order of excitations at 632.8 > 568 > 514.5 > 488 nm. This discrepancy was attributed to the structure of Pt nanoparticles in that the 150 nm Pt particles were actually composed of 7 nm seed particles; thus, the electromagnetic interactions of individual Pt seed particles with the underlying Ag substrate occurred collectively, being more effective at shorter excitation wavelengths.

Transfer doping of a metallic carbon nanotube and graphene on metal surfaces

In this paper we show the results of systematic investigations for the electronic-structure modifications of an armchair (10,10) single-walled carbon nanotube (SWNT) and graphene adsorbed on metal surfaces. The first-principles calculations based on the density-functional theory (DFT) were used to investigate transfer doping of these nanomaterials adsorbed on the fcc (111) surfaces of Al, noble metals (Ag, Cu, and Au), and transition metals (Rh, Pd, Ir, and Pt). We confirmed that the SWNT weakly interacts with the surfaces of Al and the noble metals (physisorption), while it strongly bonds to the transition-metal surfaces (chemisorption). The graphene adsorption on these metal surfaces is reinvestigated and found to be similar except for the Ir and Pt substrates, for which the interaction is weak as in the case of Al and the noble metal substrates. A phenomenological model is also developed on the basis of the rigid-band picture appropriate to physisorption. This model provides a relation between the Fermi-level shift and work-function difference and can conveniently be used in interpreting the DFT results for the transfer doping of both a SWNT and graphene on metal surfaces. We also identify the effect of hybridization between the graphene \ensuremath{\pi} orbitals and metallic valence states on the Fermi-level shift and find that the hybridization induces an extra downward shift of the linear-dispersion bands near the Dirac point relative to the other bands.

Polypyrrole/Poly(Methylene Blue) Composite Electrode Films on Stainless Steel

Polymerized methylene blue films have been shown to be efficient electron mediators for biological redox compounds. Previously these films have been deposited on noble metal and carbon substrates. In this work, methylene blue has been polymerized on stainless steel by first applying a layer of an electronically conductive polymer to inhibit passivation or corrosion of the metal and to increase the active surface area. The redox activity of the resulting electrodes has been examined by electrochemical impedance spectroscopy and fit to an equivalent circuit model for conductive polymers. The film with methylene blue shows a large decrease in charge transfer resistance, from 130 Ω to 15 Ω, when compared to the bare polypyrrole film. The stability of the films was studied by measuring the impedance changes over time when stored in aqueous solutions. Degradation of the films was found to depend mostly on the doping ion used in the polypyrrole synthesis. NADH oxidation was also measured at different concentrations by CV.

Effects of fcc Noble Metal Underlayer and Substrate Temperature on the Formation of Ni(111) Epitaxial Thin Films

Ni(111)fcc epitaxial thin films were prepared on fee noble metal, X [X = Cu, Au, Ag], underlayers hetero-epitaxially grown on MgO(111) substrates by ultra-high vacuum molecular beam epitaxy. The microstructure and the lattice strain of Ni epitaxial films are influenced by the underlayer material and the substrate temperature. Ni films formed on Cu and Au underlayers are strained, which is interpreted to be caused by atomic mixing around the interface. The atomic mixing is enhanced with increasing the substrate temperature. On the contrary, Ni films with small strain are formed on Ag underlayers. The small film strain is possibly due to formation of sharp Ni/Ag interface resulting from immiscibility of the two elements and introduction of misfit dislocations. It is also shown that parts of Ag atoms segregate from the underlayer to the surface during Ni deposition and Ag(111)fcc crystal is coexisting with Ni(111)fcc crystal in the surface layer.