Article

‘Illusional’ Nano-Size Effect Due to Artifacts of in-Plane Conductivity Measurements of Ultra-Thin Films

High-Temperature Energy Materials Center, Korea Institute of Science and Technology, Seoul, Republic of Korea.
Physical Chemistry Chemical Physics (Impact Factor: 4.49). 02/2011; 13(13):6133-7. DOI: 10.1039/c0cp02673e
Source: PubMed

ABSTRACT

The nano-size effect, which indicates a drastic increase in conductivity in solid electrolyte materials of nano-scale microstructures, has drawn substantial attention in various research fields including in the field of solid oxide fuel cells (SOFCs). However, especially in the cases of the conductivity of ultra-thin films measured in an in-plane configuration, it is highly possible that the 'apparent' conductivity increase originates from electrical current flowing through other conduction paths than the thin film. As a systematic study to interrogate those measurement artifacts, we report various sources of electrical current leaks regarding in-plane conductivity measurements, specifically insulators in the measurement set-up. We have observed a 'great conductivity increase' up to an order of magnitude at a very thin thickness of a single layer yttria-stabilized zirconia (YSZ) film in a set-up with an intentional artifact current flow source. Here we propose that the nano-size effect, reported to appear in ultra-thin single layer YSZ, can be a result of misinterpretation.

0 Followers
 · 
28 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ionic conducting metal oxide thin films for Si-wafer based electroceramic devices are of high relevance to allow for new applications, quicker response times, and higher efficiencies. Metal oxide thin films are deposited via various processes on substrates. Depending on the synthesis method their microstructures differ on an atomistic length scale in their anionic and cationic lattice displacement fields and packing densities. Local changes in ionic bond strength can affect the oxygen migration barriers and ionic diffusion is no longer to be assumed as equal to zero-strained bulk material. This article proposes lattice strain measurements to characterize the defect states of metal oxide thin films that depend on their processing history and to correlate this measure for atomistic disorder. It is suggested to discuss differences in ionic conductivity observed relative to lattice strain and atomistic disorder in addition to other microstructure characteristics such as the grain size. The interplay of grain size, degree of crystallinity, phase changes and ionic conductivity are discussed with respect to lattice-strain for state-of-the-art ionic conducting thin films, i.e. ceria or zirconia solid solutions. Previous findings on the fields of compressive or tensile strain in epitaxial heterolayers or free-standing membrane films are discussed and compared with processing-dependent lattice strain of fully crystalline ceramic thin films of more than 200nm in thickness. Finally, guidelines for processing of highly strained films with high ionic conduction are given for functional oxide thin films in Si-based electroceramic devices.
    No preview · Article · Jan 2011 · Solid State Ionics
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ultra-thin (less than 200 nm) yttria-stabilized zirconia (YSZ) blocking layers are employed at the anode side of a 1-μm-thick gadolinia-doped ceria (GDC) thin-film electrolyte by pulsed laser deposition. Their effects on a GDC thin-film electrolyte solid-oxide fuel cell (TF-SOFC) are presented. Without blocking layers, the open cell voltage (OCV) of the GDC TF-SOFC is about 0.6 V. By inserting the blocking layer, the OCV increases to over 1 V. As a result, the maximum power density of the TF-SOFC increases from 377 mW cm−2 to over 1 W cm−2 at 600 °C. The present study demonstrates the possibility of obtaining the critical performance at a low temperature regime using thin-film GDC electrolytes.
    No preview · Article · May 2012 · Journal of Power Sources
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The electrical cross-plane conductivity of 8 mol% yttria stabilized zirconia (YSZ) thin films prepared by different deposition techniques, namely aerosol assisted chemical vapor deposition, wet spray pyrolysis (SP), and pulsed laser deposition (PLD), is correlated with their microstructure. Depending on deposition technique and process conditions, microstructures ranging from amorphous to randomly oriented nanocrystalline or columnar with preferred (111) orientation are obtained. Cross-plane AC impedance measurements of these thin films show that the oxygen ion conductivity of randomly oriented nanocrystalline samples is determined by the grain boundaries, which show significantly lower transport properties than the grain interior. In columnar microstructures, the conductivity is determined by ionic transport through the grains only. The same conduction behavior is found for amorphous and randomly oriented microstructures with grain sizes between 3 nm and 9 nm, indicating that no true size effects occur in 8 mol% YSZ. Grain and grain boundary conductivity determined for nanocrystalline 8 mol% yttria stabilized zirconia thin films of different microstructures.
    Full-text · Article · Aug 2012 · Physica Status Solidi (A) Applications and Materials
Show more