Cody Friesen

Arizona State University, Phoenix, Arizona, United States

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Publications (15)73.84 Total impact

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    ABSTRACT: The corrosion behavior of nanometer-scale solids is important in applications ranging from sensing to catalysis. Here we present a general thermodynamic analysis of this for the case of elemental metals and use the analysis to demonstrate the construction of a particle-size-dependent potential-pH diagram for the case of platinum. We discuss the data set required for the construction of such diagrams in general and describe how some parameters are accessible via experiment while others can only be reliably determined from first-principles-based electronic structure calculations. In the case of Pt, our analysis predicts that particles of diameter less than approximately 4 nm dissolve via the direct electrochemical dissolution pathway, Pt --> Pt(2+) + 2e(-), while larger particles form an oxide. As an extension of previously published work by our group, electrochemical scanning tunneling microscopy is used to examine the stability of individual Pt-black particles with diameters ranging from 1 to 10 nm. Our experimental results confirm the thermodynamic predictions, suggesting that our analysis provides a general framework for the assessment of the electrochemical stability of nanoscale elemental metals.
    Journal of the American Chemical Society 08/2010; 132(33):11722-6. · 10.68 Impact Factor
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    ABSTRACT: The compressive plastic strength of nanosized single-crystal metallic pillars is known to depend on their diameter D. Herein, the role of pillar height h is analyzed instead, and the suppression of the generalized crystal plasticity below a critical value h(CR) is observed. Novel in situ compression tests on regular pillars as well as nanobuttons, that is, pillars with h < h(CR), show that the latter are much harder, withstanding stresses >2 GPa. A statistical model that holds for both pillars and buttons is formulated. Owing to their superhard nature, the nanobuttons examined here underline with unprecedented resolution the extrinsic effects-often overlooked-that naturally arise during testing when the Saint-Venant assumption ceases to be accurate. The bias related to such effects is identified in the test data and removed when possible. Finally, continuous hardening is observed to occur under increasing stress level, in analogy to reports on nanoparticles. From a metrological standpoint the results expose some difficulties in nanoscale testing related to current methodology and technology. The implications of the analysis of extrinsic effects go beyond nanobuttons and extend to nano-/microelectromechanical system design and nanomechanics in general.
    Small 02/2010; 6(4):528-36. · 7.82 Impact Factor
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    ABSTRACT: Understanding and controlling the electrochemical stability or corrosion behavior of nanometer-scale solids is vitally important in a variety of applications such as nanoscale electronics, sensing, and catalysis. For many applications, the increased surface to volume ratio achieved by particle size reduction leads to lower materials cost and higher efficiency, but there are questions as to whether the intrinsic stability of materials also decreases with particle size. An important example of this relates to the stability of Pt catalysts in, for example, proton exchange fuel cells. In this Article, we use electrochemical scanning tunneling microscopy to, for the first time, directly examine the stability of individual Pt nanoparticles as a function of applied potential. We combine this experimental study with ab initio computations to determine the stability, passivation, and dissolution behavior of Pt as a function of particle size and potential. Both approaches clearly show that smaller Pt particles dissolve well below the bulk dissolution potential and through a different mechanism. Pt dissolution from a nanoparticle occurs by direct electro-oxidation of Pt to soluble Pt(2+) cations, unlike bulk Pt, which dissolves from the oxide. These results have important implications for understanding the stability of Pt and Pt alloy catalysts in fuel cell architectures, and for the stability of nanoparticles in general.
    Journal of the American Chemical Society 12/2009; 132(2):596-600. · 10.68 Impact Factor
  • Larry L Mickelson, Cody Friesen
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    ABSTRACT: The surface stress response during the electrooxidation of CO at Pt{111}, Ru{0001}, and Ru(theta=0.37)/Pt{111} textured electrodes was studied in 0.1 M HClO(4) electrolytes. The surface stress signal resolves for the first time the adsorption of OH(-) at the CO-covered Ru{0001} surface prior to significant CO oxidation, a phenomenon that is not discernible in the voltammetry. The surface stress signal shows that significant tensile surface stress occurs upon oxidation of the adsorbed CO and occurs at nearly the same potential on Ru{0001} and Ru/Pt{111} surfaces. These observations demonstrate that the mechanism of bifunctionality is the OH(ads) provided to the Pt surface sites via Ru sites.
    Journal of the American Chemical Society 09/2009; 131(41):14879-84. · 10.68 Impact Factor
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    ABSTRACT: This article presents an experimental procedure to perform highly localized compression tests on nanoscale structures/features, such as nanospheres and nanopillars, via standard nanoindentation equipment. Current manufacturing capabilities, such as focused ion beam (FIB), lend themselves well to the creation of micron-spaced nanostructures, but it is fundamental to target an individual instance with little or no damage to the surrounding ones. The procedure successfully addresses the problem of locating and testing purposely designed nanostructures of order of 50 nm or less. The technique is illustrated for the case of closely spaced arrays of nanopillars, which were successfully manufactured, characterized, and tested through several pieces of equipment. For the purposes of compression, along with a traditional Berkovich tip, a new multifunctional (MF) tip was devised. This last tip is endowed with a complex contact geometry enabling both atomic force microscope (AFM) scanning and flat punch compression of the nanostructure. The levels of accuracy in tip positioning as well as robustness to alignment errors are unprecedented in comparison with previous in situ compression tests. As a consequence, the MF tip becomes a versatile tool that can be used beyond uniform compression. As an example, ancillary shear tests in controlled conditions are reported. Such results may lay the bases for metal-forming processes at the nanoscale, such as nanoforging or cutting operations, which are relevant to MEMS design and manufacturing.
    Journal of Materials Research. 02/2009; 24(03):768 - 775.
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    ABSTRACT: The compressive plastic strength of nanosized single crystal metallic pillars is known to depend on the diameter D, but little attention has been given to the pillar height h. The important role of h is analyzed here, observing the suppression of generalized crystal plasticity below a critical value hCR that can be estimated a priori. Novel in-situ compression tests on regular pillars (D = 300-900 nm) as well as nanobuttons (i.e. very short pillars with h less than hCR, such as D = 200 nm and h < 120 nm in this case) show that the latter ones are exceedingly harder than ordinary Ni pillars, withstanding stresses greater than 2 GPa. This h-controlled transition in the plastic behaviour is accompanied by extrinsic plastic effects in the harder nanobuttons. Such effects normally arise as Saint-Venant’s assumption ceases to be accurate. Some bias related to those effects is identified and removed from test data. Our results underline that nanoscale testing is challenging when current methodology and technology are pushed to the limit.
    MRS Proceedings. 12/2008; 1224.
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    ABSTRACT: The compressive plastic strength of nanometer-scale single-crystal metallic pillars is larger than that found in conventionally sized samples. This behavior is generally associated with a change in the length scale that determines plastic behavior and the consequent inability of nanoscale samples to store dislocations. Here, we show in the case of nanocrystalline nickel pillars, for which there is a fixed microstructural length scale set by the grain size, that smaller is still stronger and find that this behavior derives from statistical expec-tations that have long been used to understand the size-dependent strength of brittle solids such as glass.
    Acta Materialia - ACTA MATER. 01/2008; 56(3).
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    ABSTRACT: Significant effects of sample dimension on the yield strength of metallic crystals have been known for more than 50 years when researchers identified this phenomenon in metallic whiskers. These sample-size effects are once again attracting great interest with the discovery of the indentation size effect and the enhanced yield strength found for sub-micrometer diameter focused ion beam (FIB)-machined metallic pillars. Here, we discuss these issues and suggest mechanisms that may be responsible for the observed behaviors. In the case of FIB-machined pillars we draw an analogy between the yield strength of these structures and the fracture strength of glass rods and suggest that the experimentally observed yield behavior in these pillars is consistent with that expected from extreme value statistics. Additionally, we revisit the topic of surface effects in crystal plasticity and suggest a new mechanism via which a free surface could act as a measurable source of hardening for a crystal that has a bulk interior free of defects such as dislocations or grain boundaries. Finally we suggest experimental approaches that can be used to test the ideas discussed herein.
    Acta Materialia. 01/2006;
  • Cody Friesen, Carl V Thompson
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    ABSTRACT: A Comment on the Letter by R. Koch, Dongzhi Hu, and A. K. Das, Phys. Rev. Lett. 94, 146101 (2005)PRLTAO0031-900710.1103/PhysRevLett.94.146101. The authors of the Letter offer a Reply.
    Physical Review Letters 12/2005; 95(22):229601; author reply 229602. · 7.94 Impact Factor
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    ABSTRACT: Experimental results are presented for stress evolution, in vacuum and electrolyte, for the first monolayer of Cu on Au(111). In electrolyte the monolayer is pseudomorphic and the stress-thickness change is -0.60 N/m, while conventional epitaxy theory predicts a value of +7.76 N/m. In vacuum, the monolayer is incoherent with the underlying gold. Using a combination of first-principles based calculations and molecular dynamic simulations we analyzed these results and demonstrate that in electrolyte, overlayer coherency is maintained owing to anion adsorption.
    Physical Review Letters 11/2005; 95(16):166106. · 7.94 Impact Factor
  • C Friesen, C V Thompson
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    ABSTRACT: Stress evolution during intermittent homoepitaxial growth of (111)-oriented Cu and Ag thin films has been studied. A tensile stress change is observed when growth is stopped, but the change is reversed when growth is resumed. Reflection high energy electron diffraction analysis of the atomic scale surface roughness during intermittent growth demonstrates a strong correlation between the surface structure and reversible stress evolution. The results are discussed in terms of an evolving surface defect population.
    Physical Review Letters 08/2004; 93(5):056104. · 7.94 Impact Factor
  • Cody Friesen, Carl V. Thompson
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    ABSTRACT: Stress evolution during the intermittent growth of Volmer-Weber Cu thin films and homoepitaxial growth of (111)-oriented Cu and Ag thin films has been studied. In all systems a tensile stress change is observed when growth is stopped, but the change is reversed when growth is resumed. In addition to direct experimental evidence, thermodynamic and kinetic arguments are employed to show that the reversible stress phenomenology is due to the entire ensemble of surface defects evolving during the growth process. In the earliest stages of growth a direct correlation is made between the stress evolution and an increase in the adatom population. At longer timescales, when a more complex set of defects are expected, reflection high energy electron diffraction analysis of the atomic scale surface roughness is used to explain the stress evolution phenomenology. These observations are correlated to stress evolution in nanometer scale thin film islands to demonstrate the importance of surface defect densities on stress in nanostructures.
    02/2004; -1:32008.
  • C. Friesen, S. C. Seel, C. V. Thompson
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    ABSTRACT: Stresses caused by Volmer–Weber growth of polycrystalline Cu films have been measured in situ during: Island nucleation and growth, island coalescence, and post-coalescence film thickening. Growth interruptions followed by resumption of growth resulted in the observation of reversible stress changes in all regimes. Reversible stress changes in the pre-coalescence and post-coalescence regimes are similar in that: The stress evolves in the tensile direction during growth interruptions, the initial rate of stress evolution is significantly faster when growth is resumed than when growth is first interrupted, and the magnitude of the reversible stress change increases with increasing pre-interruption deposition rate. It is argued that reversible stress changes are associated with changes in adatom and other surface defect concentrations, corresponding with changes in the growth flux. It is shown that the change in stress-thickness product with changing film thickness (the instantaneous stress) can be related to the adatom–surface interaction energy. High sensitivity stress measurements were made at a rate of 1000 measurements per second, and the instantaneous stress at the initiation of growth was measured at all stages of growth. The initial instantaneous stress and the adatom–surface interaction energy increased in the pre-coalescence regime and reached a fixed, maximum value once coalescence had occurred. The measured interaction energy in the post-coalescence regime is 0.67±0.1 eV, which corresponds well with values calculated using molecular dynamics. © 2004 American Institute of Physics.
    Journal of Applied Physics 01/2004; 95(3):1011-1020. · 2.21 Impact Factor
  • C Friesen, C V Thompson
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    ABSTRACT: From in situ stress measurements, we have observed that a large component of the precoalescence compressive stress that develops during Volmer-Weber growth of polycrystalline Cu films relaxes reversibly. This phenomenon is similar to the reversible stress relaxation previously observed in the postcoalescence regime. We have also observed that less than a tenth of a monolayer of deposition leads to an instantaneous stress of order 1 GPa. The stress changes in both the precoalescence and postcoalescence regimes of growth are explained by changes in the adatom population during and after deposition.
    Physical Review Letters 10/2002; 89(12):126103. · 7.94 Impact Factor
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    ABSTRACT: There are two fundamental excess thermodynamic parameters that characterize a surface, the surface free energy and the surface stress. The surface free energy is the reversible work per unit area to form new surface while maintaining a constant equilibrium density of surface atoms. The surface stress is the reversible work per unit area required to form new surface by elastic deformation of a preexisting surface, and thus the atom density is altered. For a fluid surface the surface free energy is equal to the surface stress, but for a solid this is in general not true. We develop thermodynamic arguments that describe proper interpretations of wafer curvature experiments that are typically used in electrocapillarity experiments of solid electrodes. Additionally, we consider stress evolution during underpotential deposition. The sources of stress relate to electrocapillarity differences between overlayer and substrate, interface stress, and coherency stress. Experimental results are presented for the systems Pb2+/Au(111), Pb2+/ Ag(111), and Ag+/Au(111). We show how it is possible to use the experimental data to extract results for the interface stresses in each of these systems. The following values of interface stress were determined:  for the incommensurate Pb/Au(111) interface, 1.76 ± 0.04 N/m; for the incommensurate Pb/Ag(111) interface, 0.9 ± 0.04 N/m; and for the coherent Ag/Au(111) interface, −0.08 ± 0.04 N/m. Finally, we employ the thermodynamic arguments developed to consider two important problems in the electrocapillarity of solids. The first is a comparison of the magnitude of the change in surface free energy and surface stress that result from pure double − layer effects. The second is the potential-induced 23 × √3 (111) reconstruction that occurs on Au surfaces. Here, we calculate the difference in surface stress between the reconstructed and unreconstructed surface, obtaining −0.43 N/m, which compares favorably with recently published experimental results.
    01/2001;

Publication Stats

112 Citations
73.84 Total Impact Points

Institutions

  • 2005–2010
    • Arizona State University
      • Department of Mechanical Engineering
      Phoenix, Arizona, United States
  • 2009
    • Università degli Studi di Roma "Tor Vergata"
      • Dipartimento di Scinze e Tecnologie Chimiche
      Roma, Latium, Italy
  • 2002–2004
    • Massachusetts Institute of Technology
      • Department of Materials Science and Engineering
      Cambridge, MA, United States