Research Highlights

About Me

Hello, my name is Steven Spurgeon!

 

As a materials scientist I use analytical scanning transmission electron microscopy to understand structure-property relationships in complex materials. I am also a passionate writer and scientific communicator. Please look around to learn more about my work.

Recent News

Upcoming Talks

Registration Open for NexTEM 2019 @ Microscopy & Microanalysis

March 19, 2019

 

We're pleased to host the second annual NexTEM meeting as a Pre-Meeting Congress @ Microscopy and Microanalysis 2019. Please visit here to register!

 

 

MRS Spring 2019

Phoenix, AZ

04.24.19 – 2:15 pm

 

ACS Norm 2019

Portland, OR

06.16.19 – 06.19.19

 

Microscopy & Microanalysis 2019

Portland, OR

08.04.19 – 08.08.19

 

Review of Fiscal Year 2018

October 12, 2018

 

This year was extremely productive, resulting in a book chapter and 11 peer-reviewed journal articles, as well as several invited talks and presentations. Here is an overview of our work, spanning interface science and radiation damage, neutron scattering and vibrational EELS.

 

The whole collection is available on ResearchGate.

 

 

Article on In-Gap STO States Published in Physical Review B

June 12, 2018

 

Our newest article, titled, "Interconversion of intrinsic defects in SrTiO3 (001) monitored using deep in-gap photoemission," has just been published in Physical Review B. In this paper we study the origin of ubiquitous in-gap states in STO using a combination of XPS, VEELS, and DFT

 

From the abstract: "Photoemission features associated with states deep in the band gap of n-SrTiO3(001) are found to be ubiquitous in bulk crystals and epitaxial films. These features are present even when there is little signal near the Fermi level. Analysis reveals that these states are deep-level traps associated with defects. The commonly investigated defects—O vacancies, Sr vacancies, and aliovalent impurity cations on the Ti sites—cannot account for these features. Rather, ab initio modeling points to these states resulting from interstitial oxygen and its interaction with donor electrons."

 

You can download the article directly here.

 

The original article can be viewed on the APS website here.

Save-the-date for NexTEM Workshop October 8-10 @ PNNL

April 27, 2018

Article on Defects in WO3-δ Published in ACS Applied Materials and Interfaces

April 25, 2018

 

Our newest article, titled, "Creation and ordering of oxygen vacancies at WO3-δ and perovskite interfaces," has just been published in ACS Applied Materials and Interfaces. In this paper we explore defects induced at the interface between oxygen-deficient WO3 and perovskites using a combination of local and electronic structure probes.

 

From the abstract: "Changes in structure and composition resulting from oxygen deficiency can strongly impact the physical and chemical properties of transition metal oxides, which may lead to new functionalities for novel electronic devices. Oxygen vacancies (Vo) can be readily formed to accomodate the lattice mismatch during epitixial thin film growth. In this paper, the effects of substrate strain and oxidizing power on the creation and distribution of Vo in WO3-δ thin films are investigated in detail. An 18O2 isotope labeled time-of-flight secondary ion mass spectrometry study reveals that WO3-δ films grown on SrTiO3 substrates display a significantly larger oxygen vacancy gradient along the growth direction compared to those grown on LaAlO3 substrates...."

 

You can download the article directly here.

 

The original article can be viewed on the ACS website here.

Article on Delayed Oxide Phase Separation Published in Physical Review B

March 13, 2018

 

Our newest article, titled, "Onset of phase separation in the double perovskite oxide La2MnNiO6," has just been published in Physical Review B. In this paper we examine the curious delayed phase separation in double perovskites, influenced by oxygen vacancy accumulation due a polar mismatch at the film-substrate interface.

 

From the abstract: "Identification of kinetic and thermodynamic factors that control crystal nucleation and growth represents a central challenge in materials synthesis. Here we report that apparently defect-free growth of La2MnNiO6 (LMNO) thin films supported on SrTiO3 (STO) proceeds up to 1–5 nm, after which it is disrupted by precipitation of NiO phases. Local geometric phase analysis and ensemble-averaged x-ray reciprocal space mapping show no change in the film strain away from the interface, indicating that mechanisms other than strain relaxation induce the formation of the NiO phases. Ab initio simulations suggest that the electrostatic potential build-up associated with the polarity mismatch at the film-substrate interface promotes the formation of oxygen vacancies with increasing thickness..."

 

You can download the article directly here.

 

The PNNL news release is available here.

 

The original article can be viewed on the APS website here.

Article on Oxide-Based Photocatalyst Published in MRS Communications

March 2, 2018

 

Our newest article, titled, "Chemical and electronic structure analysis of a SrTiO3 (001) / p-Ge (001) hydrogen evolution photocathode," has just been published in Scientific Reports. In this paper we explore a novel perovskite / semiconductor based heterojunction for more efficient electron-hole pair separation using a combination of electrochemical measurements, electron microscopy, and X-ray photoemission.

 

From the abstract: "Germanium is a small-gap semiconductor that efficiently absorbs visible light, resulting in photoexcited electrons predicted to be sufficiently energetic to reduce H2O for H2 gas evolution. In order to protect the surface from corrosion and prevent surface charge recombination in contact with aqueous pH 7 electrolyte, we grew epitaxial SrTiO3 layers of different thicknesses on p-Ge (001) surfaces. Four-nanometer SrTiO3 allows photogenerated electrons to reach the surface and evolve H2 gas, while 13 nm SrTiO3 blocks these electrons. Ambient pressure x-ray photoelectron spectroscopy indicates that the surface readily dissociates H2O to form OH species, which may impact surface band bending."

 

You can download the article directly here.

 

The original article can be viewed on the MRS website here.

Article on Piezoelectric Properties of Perovskite-Like Thin Films Published in Scientific Reports

February 14, 2018

 

Our newest article, titled, "Tuning piezoelectric properties through epitaxy of La2Ti2O7 and related thin films," has just been published in Scientific Reports. We examine the crystallography, phase distribution, and piezoelectric response of these materials.

 

From the abstract: "Current piezoelectric sensors and actuators are limited to operating temperatures less than ~200 °C due to the low Curie temperature of the piezoelectric material. Strengthening the piezoelectric coupling of high-temperature piezoelectric materials, such as La2Ti2O7 (LTO), would allow sensors to operate across a broad temperature range. The crystalline orientation and piezoelectric coupling direction of LTO thin films can be controlled by epitaxial matching to SrTiO3(001), SrTiO3(110), and rutile TiO2(110) substrates via pulsed laser deposition. . . ."

 

You can download the article directly here.

 

The original article can be viewed on the Nature website here.

Article on Oxide Interface Rearrangement Published in Physical Review Materials

November 6, 2017

 

Our newest article, titled, "Dynamic interface rearrangement in LaFeO3/n-SrTiO3 heterojunctions," has just been published online in Physical Review Materials. We examine these interfaces using high-resolution electron energy loss spectroscopy (EELS), observing that dynamic changes can occur in interface layers during the growth of oxide heterojunctions.

 

From the abstract: "Thin-film synthesis methods that have developed over the past decades have unlocked emergent interface properties ranging from conductivity to ferroelectricity. However, our attempts to exercise precise control over interfaces are constrained by a limited understanding of growth pathways and kinetics. Here we demonstrate that shuttered molecular beam epitaxy induces rearrangements of atomic planes at a polar/nonpolar junction of LaFeO3 (LFO)/n-SrTiO3 (STO) depending on the substrate termination. . . ."

 

You can download the article directly here.

 

The original article can be viewed on the APS website here.

Article on Ion-Irradiation of SiC Published in Journal of Nuclear Materials

October 15, 2017

 

Our newest article, titled, "Precipitates and voids in cubic silicon carbide implanted with 25Mg+ ions," has just been published online in Journal of Nuclear Materials. We use ion irradiation to simulate damage in SiC, which has possible applications in fusion reactors, and we examine the resulting defects using STEM, APT, and EDS.

 

From the abstract: "Single crystal cubic phase silicon carbide (3C-SiC) films on Si were implanted to 9.6×1016 25Mg+ / cm2 at 673 K and annealed at 1073 and 1573 K for 2, 6, and 12 h in an Ar environment. The data from scanning transmission election microscopy (STEM) and electron energy loss spectroscopy (EELS) mapping suggest a possible formation of unidirectionally aligned tetrahedral precipitates of core (MgC2)-shell (Mg 2 Si) in the implanted sample annealed at 1573 K for 12 h. There are also small spherical voids near the surface and larger faceted voids around the region of maximum vacancy concentration. . . ."

 

You can download the article directly here.

 

The original article can be viewed on the Elsevier website here.

New Staff Position in Energy and Environment Directorate

October 1, 2017

 

I'm excited to announce that I have started a staff position in our Irradiated Materials group, which is part of PNNL's Energy and Environment Directorate. I've had a great two and a half years working with Scott Chambers and I look forward to exciting new projects investigating nanoscale materials systems. In addition, I will be leading high-resolution spectroscopy work on our latest GrandARM microscope, which is currently being installed.

 

 

Pathway to Excellence Award

October 1, 2017

 

I'm thrilled to receive a Pathway to Excellence Award from PNNL for my postdoctoral research, which resulted in an award from the Microscopy and Microanalysis Society. These awards are given to staff members each year who demonstrate exceptional technical, leadership, and business talent.

 

 

Article on Perovskite-Based Photovoltaic Published in Applied Physics Letters

August 1, 2017

 

Our newest article, titled, "An all-perovskite p-n junction based on transparent conducting p-La1−xSrxCrO3 epitaxial layers," has just been published online in Applied Physics Letters. We use a combination of X-ray photoelectron spectroscopy and aberration-corrected STEM to evaluate the properties of promising new photovoltaic materials.

 

From the abstract: "Transparent, conducting p-La1−xSrxCrO3 epitaxial layers were deposited on Nb-doped SrTiO3(001) by oxygen-assisted molecular beam epitaxy to form structurally coherent p-n junctions. X-ray photoelectron spectroscopy reveals a type II or “staggered” band alignment, with valence and conduction band offsets of 2.0 eV and 0.9 eV, respectively. Diodes fabricated from these heterojunctions exhibit rectifying behavior, and the I-V characteristics are different from those for traditional semiconductor p-n junctions. A rather large ideality factor is ascribed to the complex nature of the interface."

 

You can download the article directly here.

 

The original article can be viewed on the APL website here.

© 2015–2018 STEVEN R. SPURGEON

The contents of this website represent the sole opinions of the author and are not associated with PNNL or Battelle.

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