salmeron group

Research and Labs

 

Ongoing Projects:

Surface Science at Ambient Pressures Part I: Atomic Structure with High-Pressure STM

Project leading scientist: Heath Kersell. Other members involved: Baran Eren.

We use high-pressure scanning tunneling microscopy to investigate the model single crystal catalyst surface reconstructions at gas pressures as high as 1 bar. Flat and stepped single metal surfaces are used as model catalysts. Ambient-pressure X-ray photoelectron spectroscopy (see below) and infrared reflection-adsorption spectroscopy are employed to identify the chemical states and adsorbate coverages relevant to the restructuring processes.

Related publications:

Eren, B.; Zherebetskyy, D.; Patera, L. L.; Wu, C. H.; Bluhm, H.; Africh, C.; Wang, L.-W.; Somorjai, G. A.; Salmeron, M.
Activation of Cu(111) surface by Decomposition into Nanoclusters Driven by CO Adsorption
Science, 2016 351 475-478. http://www.sciencemag.org/cgi/content/full/351/6272/475?ijkey=u8TEuHJL7OWUY&keytype;=ref&siteid;=sci

Eren, B.; Zherebetskyy, D.; Hao, Y.; Wang, L.-W.; Somorjai, G. A.; Salmeron, M.
One-dimensional Nanoclustering of the Cu(100) Surface under CO Gas in the mbar Pressure Range
Surf. Sci. 2016 xx xxx-xxx. http://dx.doi.org/10.1016/j.susc.2016.04.016

Eren, B.; Liu, Z.; Stacchiola, D.; Somorjai, G. A.; Salmeron, M.
Structural Changes of Cu(110) and C (110)-(2x1)-O Surfaces Under Carbon Monoxide in the Torr Pressure Range Studied With Scanning Tunneling Microscopy and Infrared Reflection Absorption Spectroscopy
J. Phys. Chem. C, 2016 120 8227-8231. http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b02143

 

Surface Science at Ambient Pressures Part II: Chemical States with Ambient Pressure XPS

Members involved: Baran Eren, Christian Heine, Heath Kersell, Robert S. Weatherup.

Ambient-pressure X-ray photoelectron spectroscopy is now a widely used technique in many labs around the world. Using a multi-stage differential pumping system with electrostatic lenses is an approach first taken in our group that drastically increased its capabilities and use. In this project, we employ this technique together with NEXAFS to identify the chemical states relevant to the restructuring processes (see HPSTM section above). Furthermore, we use this technique to measure reaction activation energies on different crystal faces in order to relate them to different macroscopic phenomena like adsorption energies, activation energies, etc. Currently, we are working on carbon monoxide adsorption on copper surfaces as well as its reaction with oxygen to produce carbon dioxide, and its reaction with water to produce carbon dioxide and hydrogen.

Related publications:

Eren, B.; Heine, Ch.; Bluhm, H.; Somorjai, G. A.; Salmeron, M.
Catalyst Chemical State during CO Oxidation Reaction on Cu(111) Studied with Ambient Pressure XPS and NEXAFS
J. Am. Chem. Soc. 2015 12 1491-1497. http://dx.doi.org/10.1021/jacs.5b07451

Eren, B.; Lichtenstein, L.; Wu, C. H.; Bluhm, H.; Somorjai, G. A.; Salmeron, M.
Reaction of CO with Preadsorbed Oxygen on Low-Index Copper Surfaces: An Ambient Pressure X-ray Photoelectron Spectroscopy and Scanning Tunneling Microscopy Study
J. Phys. Chem. C, 2015 119 14669-14674. http://dx.doi.org/10.1021/jp512831f

 

Surface Science at Ambient Pressures Part III: Alcohol Oxidation on Gold, Silver and Gold/Silver Alloys

Project leading scientist: Christian Heine.

The project is involved in the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC) project (http://efrc.harvard.edu/). Applied Nanoporous catalyst are investigated with Ambient Pressure (AP) X-ray Photoelectron Spectroscopy (XPS)/ Absorption Spectroscopy (XPS). The project aims the fundament understanding of the surfaces dynamics during catalytic reactions. XPS and XAS in the electron mode are highly surface sensitive methods and therefore provide great insides in the chemical state of catalyst surfaces. First investigation were done with Nano porous Au/Ag alloy catalysts during oxidative coupling of methanol. These studies are completed with model Ag/Au single crystal studies to understand the complex surface dynamics of the applied catalysts. We further move on to study nickel based catalysts in CO₂ recycling reactions.

Related publications:

Heine, Ch.; Eren, B.; Lechner, B.A.J.; Salmeron, M.
A study of the O/Ag (111) System with Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy at Ambient Pressures
Surf. Sci., 2016 652 51-57. http://www.sciencedirect.com/science/article/pii/S003960281600087X

Heine, Ch.; Lechner, B.A.J.; Eren, B.; Salmeron, M.
Recycling of CO2: Probing the Chemical State of the Ni(111) Surface during the Methanation Reaction with Ambient-Pressure X-Ray Photoelectron Spectroscopy
J. Am. Chem. Soc., 2016 xxx xxx-xxx. http://dx.doi.org/10.1021/jacs.6b06939

 

In situ Studies of Electrode Interfaces Part I: X-ray Adsorption Studies with In Situ Cells

Project leading scientist: Cheng Hao Wu.

This project aims to investigate the molecules / ions at the electrolyte / electrode interfaces by means of in-situ x-ray spectroscopy techniques (XAS, XES, RIXS etc.) at the Advance Light Source, LBNL. Such liquid / solid interfaces are extremely important in most of the electrochemical reactions, but the chemical nature of the interfacial region as well as how the interfacial molecules / ions respond to the electrical fields is not well understood. We have been developing new characterization techniques based on regular XAS instrument with modulated x-ray source and static / flow liquid cell systems, with which we will be able to study such electrolyte / electrode interfaces under real electrochemical reaction conditions. Such in-situ characterization techniques can be utilized to investigate many useful electrochemical reactions, e.g., electrocatalysis, photoelectrochemistry (including water splitting and CO₂ reduction), intercalation process in lithium ion batteries, etc.

Related publications:

Velasco-Velez, J.-J.; Wu, C. H.; Pascal, T. A.; Wan, L. F.; Guo, J.; Prendergast, D.; Salmeron, M.
The structure of Interfacial Water on Gold Electrodes Studied by X-ray Absorption Spectroscopy
Science 2014, 346, 831-834. http://dx.doi.org/10.1126/science.1259437

 

In situ Studies of Electrode Interfaces Part II: 2D Membranes for Operando Studies

Project leading scientist: Robert Weatherup. Other members involved: Baran Eren.

This project aims to develop a fundamental understanding of the atomic-scale processes occurring at battery electrodes under realistic conditions. We use 2D materials as model electrodes of well-defined structure that, thanks to their extreme thinness, allow new in situ metrology to be applied. This includes complementary techniques to probe their chemical (XPS, Auger), electronic (LEEM), and structural (liquid STM and AFM) evolution during electrochemical cycling. We thereby examine the key mechanisms involved in the formation of the solid-electrolyte interphase and ion insertion into electrode materials. Furthermore, we employ the same system for probing the solid-gas interface at pressures of up to 1.5 bar.

Related publications:

Weatherup, R. S.; Eren, B.; Hao, Y.; Bluhm, H.; Salmeron, M.
Graphene Membranes for Atmospheric Pressure Photoelectron Spectroscopy
J. Phys. Chem. Lett., 2016 7 1622-1627. http://pubs.acs.org/doi/abs/10.1021/acs.jpclett.6b00640

Velasco-Velez, J.-J.; Pfeifer, V.; Hävecker, M.; Weatherup, R. S.; Arrigo, R.; Chuang, C. H.; Stotz, E.; Weinberg, G.; Salmeron, M.; Schlögl, R.; Knop-Gericke, A.
Photoelectron Spectroscopy at the Graphene-liquid Interface Reveals Electrodeposition of Reduced Cobalt in Aqueous Solutions
Angew. Chem. Int. Ed., 2015 54 14554-14558. http://pubs.acs.org/doi/abs/10.1002/anie.201506044

 

Single Molecule and Co-adsorption Studies at the Atomic scale

Project leading scientist: Barbara A. J. Lechner.

We study the adsorption behavior and interactions of molecules at the atomic scale using low temperature scanning tunneling microscopy (LT-STM). Recent work includes single molecule and co-adsorption studies of molecules on metal surfaces, such as the atomic-scale wetting mechanism of single crystal surfaces and the interaction of ammonia and water on a Pt(111) surface. We further investigate the co-adsorption of reactant molecules on model catalyst surfaces to gain a detailed atomic-scale understanding of the interplay of metal-adsorbate and inter-adsorbate interactions

Related publications:

Maier, S.; Lechner, B. A. J. ; Somorjai, G. A.; Salmeron, M.
Growth and Structure of the First Layers of Ice on Ru (0001) and Pt (111)
J. Am. Chem. Soc., 2016 138 3145-3151. http://dx.doi.org/10.1021/jacs.5b13133

Lechner, B. A. J.; Kim, Y.; Feibelman, P. J.; Henkelman, G.; Kang, H.; Salmeron, M.
Solvation and Reaction of Ammonia in Molecularly Thin Water Films
J. Phys. Chem. C, 2015 119 23052-23058. http://dx.doi.org/10.1021/acs.jpcc.5b07525

Feng, X.; Cerdá, I. ; Salmeron, M.
Orientation-Dependent Interaction between CO2 Molecules Adsorbed on Ru(0001)
J. Phys. Chem. Lett., 2015 6 1780-1784. http://dx.doi.org/10.1021/acs.jpclett.5b00643

 

Mechanical and Electronic Properties with KPFM Part I: Molecules in Self-assembled Films

Project leading scientist: Alexander Buyanin.

Organic semiconducting materials are investigated using atomic force microscopy to understand the relationship between molecular structure and fundamental electronic properties. Self-assembled organic nanostructures are investigated by techniques such as Kelvin probe force microscopy and conductive AFM. In addition these semiconductors are chosen so that chemically sensitive films can be prepared and studied in a unique environmental AFM system where gaseous and liquid molecules are introduced and the films are monitored for structural and electronic changes occurring due to specific binding events.

Related publications:

Hendriksen, B. L. M.; Martin, F.; Qi, Y.; Mauldin, C.; Vukmirovic, N.; Ren, J.; Wormeeste, H.; Katan, A. J.; Altoe, V.; Aloni, S.; Fréchet, J. M. J.; Wang, L.-W.; Salmeron, M.
Electrical transport properties of oligothiophene-based molecular films studied by current sensing atomic force microscopy
Nano Lett., 2011 11 4107-4112. http://www.ncbi.nlm.nih.gov/pubmed/21848283

Zhang, Y.; Ziegler, D.; Salmeron, M.
Charge Trapping States at the SiO2–Oligothiophene Monolayer Interface in Field Effect Transistors Studied by Kelvin Probe Force Microscopy
ACS Nano, 2013 7 8258-8265. http://dx.doi.org/10.1021/nn403750h

Yin, N.; Buyanin, A.; Riechers, S.; Lee, O.; Fréchet, J. M. J.; Salmeron, M.; Liu, G.
In Situ and Real-Time Atomic Force Microscopy Studies of the Stability of Oligothiophene Langmuir-Blodgett Monolayers in Liquid
J. Phys. Chem. C, 2014 118 5789-5795. http://dx.doi.org/10.1021/jp410767h

 

Mechanical and Electronic Properties with KPFM Part II: Imaging Charge Transport of Organic-Inorganic Nanocomposite Materials

Project leading scientist: Yingjie Zhang.

We are performing systematic experimental and theoretical studies of the atomic scale surface structure and electronic defects of nanoscale semiconductors, with a focus on colloidal quantum dots. We found that random distribution of defects generally induce heterogeneity in the energy landscape of disordered semiconductor systems, by studying a model system of artificial quantum dot solid. Counterintuitively, certain defects themselves can assist charge transport, paving the way for high-mobility percolative transport in heterogeneous artificial solids. We expect the discovered defect physics, percolation transport phenomena and the invented ultrasensitive photodetectors to have significant impacts on both the fundamental understanding of nanoscale semiconductors and their large-area device applications

Related publications:

Zhang, Y.; Pluchery, O.; Caillard, L.; Lamic-Humblot, A.; Casale, S.; Chabal, Y. J.; Salmeron, M.
Sensing the Charge State of Single Gold Nanoparticles via Work Function Measurements
Nano Lett., 2015 15 51-55. http://dx.doi.org/10.1021/nl503782s

Zhang, Y.; Zherebetskyy, D.; Bronstein, N. D.; Barja, S.; Lichtenstein, L.; Schuppisser, D.; Wang, L.-W.; Alivisatos, A. P.; Salmeron, M.
Charge Percolation Pathways Guided by Defects in Quantum Dot Solids
Nano Lett., 2015 15 3249-3253 http://dx.doi.org/10.1021/acs.nanolett.5b00454

Zhang, Y.; Zherebetskyy, D.; Barja, S.; Lichtenstein, L.; Bronstein, N. D.; Alivisatos, A. P.; Wang, L.-W.; Salmeron, M.
Molecular Oxygen Induced In-Gap States in PbS Quantum Dots
ACS Nano, 2015 9 10445-10452 http://dx.doi.org/10.1021/acsnano.5b04677

 

Investigation of Heterogeneous Catalysis on Nanoparticles

Project leading scientist: Nikos Liakakos.

We study the reactivity of metal nanoparticle catalysts of varying size, shape, and composition (synthesized by Nikos in Prof. Peidong Yang's labs) under relevant conditions of pressure and temperature. We follow changes in the electronic, chemical, and physical structure of the particles as they are exposed to reactive gases using ambient pressure x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) at the Advanced Light Source (ALS), the Berkeley Lab synchrotron. Typically these x-ray techniques require ultra high vacuum environments, but our group has developed unique tools for performing experiments near atmospheric pressures. Therefore, we can study the catalyst reactivity in situ, under realistic conditions. We are also in collaboration with Prof. Paul Alivisatos's group and Prof. Alexis Bell's group for the XPS analysis of their samples

Related publications:

Tuxen, A.; Carenco, S.; Chintapalli, M.; Chuang, C.-H.; Escudero, C.; Pach, E.; Jiang, P.; Borondics, F.; Beberwyck, B.; Alivisatos, A. P.; Thornton, G.; Pong, W.-F.; Guo, J.; Perez, R.; Besenbacher, F.; M. Salmeron, M.
Size-dependent Dissociation of Carbon Monoxide on Cobalt Nanoparticles
J. Am. Chem. Soc., 2013 135 2273-2278. http://dx.doi.org/10.1021/ja3105889

Carenco, S.; Tuxen, A.; Chintapalli, M.; Pach, E.; Escudero, C.; Ewers, T. D.; Jiang, P.; Borondics, F.; Thornton, G.; Alivisatos, A. P.; Bluhm, H.; Guo, J.; Salmeron, M.
De-alloying of Cobalt from CuCo Nanoparticles under Syngas Exposure
J. Phys. Chem. C, 2013 117 6259-6266 http://dx.doi.org/10.1021/jp4000297

Escudero, C.; Jiang, P.; Pach, E.; Borondics, F.; West, M. W.; Tuxen, A.; Chintapalli, M.; Carenco, S.; Guo, J.; Salmeron, M.
A reaction cell with sample laser heating for in situ soft X-ray absorption spectroscopy studies under environmental conditions.
J. Synchrotron. Rad., 2013 20 504-508. http://dx.doi.org/10.1107/S0909049513002434

 

 

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Labs

Variable Temperature STM

Low Temperature STM

Low Temperature STM/AFM

Air/liquid AFM

Air/liquid STM

APPES ALS

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