Next Article in Journal
Grey Relational Analysis and Grey Prediction Model (1, 6) Approach for Analyzing the Electrode Distance and Mechanical Properties of Tandem MIG Welding Distortion
Previous Article in Journal
The Effect of In-Office Bleaching with Different Concentrations of Hydrogen Peroxide on Enamel Color, Roughness, and Color Stability
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Materials
Volume 16
Issue 4
10.3390/ma16041387
materials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

The Piezoresponse in WO3 Thin Films Due to N2-Filled Nanovoids Enrichment by Atom Probe Tomography

by
Pamela M. Pineda-Domínguez
1,
Torben Boll
2,3,4,*,
John Nogan
5,
Martin Heilmaier
2,
Abel Hurtado-Macías
6 and
Manuel Ramos
1,*
1
Departamento de Física y Matemáticas, Instituto de Ingeniería y Tecnología, Universidad Autónoma de Ciudad Juárez, Avenida del Charro 450 N, Cd. Juárez, Chihuahua 32310, Mexico
2
Institut für Angewandte Materialien-Werkstoffkunde (IAM-WK), Karlsruhe Institute of Technology, Engelbert-Arnold-Strasse 4, 76131 Karlsruhe, Germany
3
Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
4
Institute for Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
5
Center for Integrated Nanotechnologies, 1101 Eubank Bldg. SE, Albuquerque, NM 87110, USA
6
Laboratorio Nacional de Nanotecnología, Centro de Investigación en Materiales Avanzados S.C., Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chihuahua 31109, Mexico
*
Authors to whom correspondence should be addressed.
Materials 2023, 16(4), 1387; https://doi.org/10.3390/ma16041387
Submission received: 13 January 2023 / Revised: 2 February 2023 / Accepted: 4 February 2023 / Published: 7 February 2023
(This article belongs to the Topic Materials and Surface Treatment Processes Used for Engineering Applications)
Browse Figures
Versions Notes

Abstract

:
Tungsten trioxide (WO3) is a versatile n-type semiconductor with outstanding chromogenic properties highly used to fabricate sensors and electrochromic devices. We present a comprehensive experimental study related to piezoresponse with piezoelectric coefficient d33 = 35 pmV−1 on WO3 thin films ~200 nm deposited using RF-sputtering onto alumina (Al2O3) substrate with post-deposit annealing treatment of 400 °C in a 3% H2/N2-forming gas environment. X-ray diffraction (XRD) confirms a mixture of orthorhombic and tetragonal phases of WO3 with domains with different polarization orientations and hysteresis behavior as observed by piezoresponse force microscopy (PFM). Furthermore, using atom probe tomography (APT), the microstructure reveals the formation of N2-filled nanovoids that acts as strain centers producing a local deformation of the WO3 lattice into a non-centrosymmetric structure, which is related to piezoresponse observations.
Keywords:
WO3; films; PFM; APT; nanovoids

1. Introduction

Tungsten trioxide (WO3) is an n-type semiconductor with chromogenic and catalytic properties that has been used as an electrochromic layer for smart windows [1,2], gas sensors [3,4], and water-splitting devices [5,6,7]. A piezoelectric behavior of WO3 would open an opportunity for diverse applications in the field of the Internet of Things (IoT) [8,9] and micro-electromechanical systems (MEMS) [10,11]. The piezoelectric effect has been explained to occur only in crystal structures with non-centrosymmetric space group [12,13], which lack an inversion point, and hence, a decompensation of charges provides the formation of polarized domains. The piezoelectric property is usually found in ceramic materials [13] and semiconductors [14], with lead zirconate titanate (PZT) as the most common material with remarkable piezoresponse derived from an interaction at the morphotropic phase boundary (MPB) [15,16]. The piezoelectric effect is usually measured by piezoresponse force microscopy (PFM), through the estimation of the piezoelectric coefficient d33, the obtention of hysteresis loops and switching imaging of the topography showing piezo-active domains [17,18]. However, non-piezoelectric effects [10,18,19,20,21,22,23,24] can induce electromechanical (EM) responses in PFM measurements that resemble the piezoresponse. These can be electrostatic effects [25,26,27], electrochemical strain [28,29,30,31], induced polarization (electrostriction) [32], flexoelectricity [33,34,35,36], or thermal expansion due to Joule heating [37]. Such so-called “non-piezoelectric effects” in the literature are strongly related to ionic migration and diffusion along oxygen vacancies [38], which are considered the most common functional defects [1,38,39,40,41] in transition metal oxides, and can induce electronic structure-related properties in oxides. Li et al. described how oxygen vacancies can promote dislocations, and thus induce ion diffusion on lattice sites of WO3 [42]. In a non-stoichiometric WO3-x, those are also active sites for chemical adsorption of light molecules for gas sensing of H2 [3,43,44], N2 [45], NO2 [46], and NH3 [47,48] among other species, and are mobile defects with a high diffusion coefficient [38], which can be tuned by electric fields, temperature, pressure, or light. Park et al. observed that the rearrangement of oxygen vacancies while applying a direct electric field can break the crystallographic symmetry [49,50], inducing a large piezoelectric effect in Gd-doped CeO2-x, an intrinsically centrosymmetric fluorite, by electric field-induced redistribution of mobile oxygen vacancies. The formation of oxygen vacancy can produce a micro volume expansion of the films, leading to bending and to a strain–electrical field relationship. Seol et al. proved the electrochemical strain contribution to piezoresponse in non-piezoelectric TiO2 thin films, attributing the effect to oxygen vacancies redistribution by an applied electric field during PFM measurement [23].
Although WO3 is not a natural piezoelectric, there is strong evidence of piezoresponse in this material. Yun et al. found a lateral (in-plane) PFM piezoresponse for WO3 of d33 = 6 pmV−1 attributed to induced flexoelectric polarizations due to strain-gradients at ferroelastic domain walls of a monoclinic (P21/n) structure [33]. Kim et al. found a piezoresponse measured by PFM in vertical (out-of-plane) mode in an oxygen-deficient WO2.96 film with a d33 coefficient of 7.9 pmV−1, attributed to the conductivity in twin walls in a non-centrosymmetric tetragonal phase [51]. This conductivity is explained by the accumulation of oxygen vacancies at the domain walls, donating free charges and increasing local charge flow near twin walls [51,52]. As well as non-centrosymmetric structures, or functional defects such as oxygen vacancies, there is also a relation between piezoelectric effect and other functional defects, such as porosity or nanovoids. Liu and Wang reported a model indicating a notable role of porosity distribution on the eigenfrequency of functionally graded piezoelectric materials (FGPM) [53]. Li et al. modeled the influence of voids in piezoelectric coefficients considering permeability and volume fraction of the voids [54].
Here, we report a piezoresponse measured by PFM in a WO3 film deposited on sapphire (Al2O3) by radio-frequency sputtering technique with post-deposit annealing at 400 °C under forming gas conditions. Structural and chemical characterization carried out by X-ray diffraction (XRD) and atom probe tomography (APT) reveals that our piezoresponse is related to local polar structure produced by nanovoids filled with N2.

2. Materials and Methods

The tungsten trioxide (WO3) thin films were deposited by radio frequency (RF) magnetron sputtering technique in a Kurt J. Lesker PVD75 equipment using a commercial target of WO3 (99.95%) and Al2O3 (99.9%) as substrate. The base pressure was set up to 1.3 × 10−4 Pa and the deposition process was run with a working pressure of 0.4 Pa and 225 W of RF power, achieving a deposition rate of 1 Å/s. As-deposited samples were annealed in a Qualiflow-Jiplec Jetfirst 100 furnace at a reduced pressure processing in a 3% H2/N2 forming gas environment (0 to 200 scm in 15 s). The temperature was increased with a ramp of 1°/s until reaching 400 °C or 500 °C, respectively, and after a dwell time of 45 min, it was cooled down with a ramp of 1°/s for 15 min. A film thickness of 220 nm was measured for the as-deposited film using an Ambios XP-2 profilometer (Supplemental Material).
The domain imaging and hysteresis loops were obtained using a Dual AC Resonance Tracking (DART) mode with Switching Spectroscopy Piezoresponse Force Microscopy (SS-PFM) using an Atomic Force Microscope (AFM) model Infinity 3D Asylum Research® equipped with two internal lock-ins amplifiers. Identification of the surface domain structure was performed in vertical mode with an AC voltage amplitude of 5 Vpk-pk at a drive frequency of 398 kHz, far below the cantilever’s resonance, and applied between the bottom electrode and the Pt/Ir conductive tip during PFM imaging. SS-PFM obtained local polarization and hysteresis loop evaluation with an applied voltage from −10 V to 10 V. In order to diminish electrostatic effects, an electrically charged Ag landing electrode was placed near the measured area.
The crystallographic structure was studied using a Panalytical Empyrean system with a Cu Kα radiation source (λ = 1.54 Å) at an operating voltage of 40 kV and emission current of 30 mA with a scanning angle of 20° to 80° and step size of 0.05°. Structure analysis was completed using a high-resolution transmission electron microscopy (HRTEM) model JEOL® JEM-2200FS+Cs equipped with a spherical aberration corrector in the condenser lens and operated at an accelerating voltage of 200 kV. Samples were prepared using a JEOL® JEM-9320 focused ion beam (FIB) system operated at 30 kV (Supplemental Material).
The chemical elemental distribution was studied using a Cameca® Local Electrode Atom Probe (LEAP 4000X HR) system equipped with a UV laser (λ~355 nm). For the measurements, the temperature was set to 50 K with a detection rate of 0.3%, a pulse frequency of 100 kHz, and a laser beam energy of 30 pJ. The specimens were prepared using the standard lift-out process and annular milling with focused ion-beam (FIB) [55] in a scanning electron microscope (Zeiss® Auriga 60©). All data were reconstructed with Cameca AP Suite 6.1. Compositional profiles were obtained along the z-axis of the images corresponding to film growth direction, with a bin width of 0.1 nm and background corrected.

3. Results and Discussion

3.1. Piezoresonse by PFM

By local switching and hysteresis behavior during PFM measurements, a piezoresponse was confirmed for WO3 films processed at 400 °C. Figure 1a shows the surface topography and grain domains. The phase signals before and after measurements, revealing the existence of domains with different polarization orientations, as described by Kholkin et al. [56,57], are presented in Figure 1b,c, respectively. Insets show the region directly affected by the SS-PFM measurement, where the reorientation of polarization with the applied electric field is observed, due to an indirect piezoelectric effect. White regions correspond to positive polarization domains (Pz), dark violet regions correspond to polarization in-plane (Px) towards the bottom electrode, while yellow regions correspond to a remanent polarization; thus, an evident reorientation of polarization is achieved as found by many authors with this technique [17,18,19,58,59]. The hysteresis loop from switching polarization domains at a phase difference of 180° using AC voltage is presented in Figure 1e. The amplitude (nm) versus bias voltage (V) plot in Figure 1d exhibits a butterfly loop related to local deformation under the applied bias, which demonstrates polarization in granular domains, as described by Roelofs et al. [60]. Even with DART mode it was possible to see that loops can be shifted towards a negative applied bias, suggesting electrostatic contributions to the electromechanical response. These are commonly explained by oxygen vacancies, which produce a high surface electrostatic potential [23,25,27,61]. The local d33 coefficient in Figure 1f was estimated using the relation (V − V1)d33 = D − D1 [62,63], where D is the piezoelectric deformation or amplitude and V the applied voltage, respectively. D1 and V1 designate the values at the intersection in the butterfly loop in Figure 1d. A coercive voltage of 2.7 V was obtained by using the relation (Vc+ − Vc−)/2, where Vc+ and Vc− are forward and reverse coercive bias voltages, respectively. A piezoelectric coefficient d33 of 35 pmV−1 was obtained for a maximum voltage of 10 V, which is four times higher than that reported by Kim et al. for WO2.96 [51]. The piezoresponse was only observed for the film annealed at 400 °C, but neither for the as-deposited nor for the 500 °C specimen (Supplemental Material).

3.2. Crystal Structure Analysis

The crystallographic structures were studied using the X-ray diffraction technique; the results indicate an amorphous structure for the as-deposited film and crystalline structures for films annealed at 400 °C and 500 °C, as presented in Figure 2. It is known that WO3 crystal structures may form during the annealing process as follows: monoclinic (γ-WO3) above 300 °C, orthorhombic (β-WO3) between 400 °C and 600 °C, and tetragonal (α-WO3) above 700 °C [64,65]. The diffraction pattern of the sample showing the piezoresponse correspond to a mixture of phases; the plane diffraction at ~23° is a contribution of (001) plane of orthorhombic (PDF 00-020-1324) and (110) of tetragonal (PDF 00-018-1417) WO3 phases. Diffraction planes at 28.7°, 33.5°, 41.2°, 48.8°, 54.5°, and 59.7° may correspond to any of those phases.
By using HRTEM, we were able to confirm the presence of a non-centrosymmetric α-WO3, as presented in Figure 3, which shows a clear interface between film and single crystal sapphire (α-Al2O3) substrate. The selected area electron diffraction (region in yellow frame) corresponds to a polycrystalline structure, which allows for distinguishing the diffraction planes (200) and (220) with an interplanar distance d110 = 3.74 Å of a non-centrosymmetric α-WO3 (P4/nmm) (PDF 01-018-1417). Diffraction planes (012) and (104) with an interplanar distance d012 = 3.47 Å corresponding to the sapphire (α-Al2O3) substrate with space group R-3c (167) (PDF 01-077-2135) were also identified, in agreement with previous results with the diffraction plane (110) at ~38°. The film annealed at 500 °C has a predominant contribution of an orthorhombic structure (PDF 00-020-1324), but also traces of α-WO3; however, no piezoresponse was found in this film, suggesting different features related to its final crystal structure.

3.3. Composition Distribution Analysis by APT

Mass spectra corresponding to time-of-flight events were analyzed to achieve volume rendering of the as-deposited samples and those annealed at 400 °C and 500 °C. The mass spectra show a significant difference in the range of mass-to-charge ratios corresponding to N-species and Ar between the analyzed samples (Supplemental Material). The overlapping peaks at 28 Da in the mass spectra can lead to wrong interpretations since it can be attributed to AlH or N2. In this case, the presence of AlH was excluded because the Al3+ is missing in the spectrum. The as-deposited sample mass spectrum presents a low intensity of peaks attributed to N2, which increase significantly at 400 °C of annealing treatment under forming gas and decrease at 500 °C. A significant amount of Ar is present in the as-deposited sample, with a peak at 41 Da, which we attribute to ArH−. The Ar concentration decreases significantly in the sample annealed at 400 °C, and increases at 500 °C.
The peak identification in each mass spectra allows us to obtain the chemical volume distributions and composition profile of the specimens. Tomographies of the whole FIB-needled tip reveal defined interfaces, meaning strong adherence between WO3 and the α-Al2O3 ([0001] sapphire) substrate. The analysis ahead was performed for reconstructions of 160 nm of the tips, at 20 nm far from the sapphire, as presented in Figure 4, with WO3 ions and isosurfaces for Ar and N2 ions. Composition profiles elucidate the atomic composition shown in Table 1, supporting the observations in the mass spectra for Ar and N2.
To characterize the spatial environment of ions the radial distribution function (RDF) and nearest neighbor distribution (NND) (Supplemental Material) were applied. RDF describe how many neighboring ions of a particular ion type have a specific direction and radial distance, while NND gives the distribution of distances between ions of the same type and their individual nearest neighbor [66]. In order to identify chemical compounds that might be clustering, RDF was obtained for several atom centers, such as Ar, W-species (W, WO, WO2, W2O5, W2O), and N-species (N2, NO, N2O, NO2). Except for Ar and N2, RDF do not show good qualities for any other center ion to proceed further in the clustering analysis, either because the compounds are found in a very low atomic percentage or because the distribution is homogeneous. RFD for the as-deposited sample (Figure 5a) reveal some clustering distribution of Ar with a small gradient towards the interface with the sapphire, suggesting the formation of defects, i.e., oxygen vacancies, during the deposition process. At this stage, N-species are homogeneously distributed in the film matrix.
For the samples annealed at 400 °C and 500 °C, clustered platelet-shaped regions with high N2 or Ar content were observed in the reconstructions, suggesting the formation of nanovoids filled with these atomic species and “spilled out” during evaporation in the APT measurement. The nanovoids in the 400 °C sample showing the piezoresponse consist mainly of N2. It is expected that the annealing process induces crystallization, and also the formation of oxygen vacancies [40,64,67], which can act as active sites for the chemical adsorption of N molecules [45,68,69]. At 400 °C the Ar is released from the film leaving behind nanovoid distribution inside the polycrystalline WO3 matrix, allowing N2 trapping during the annealing treatment in a forming gas environment. Fewer nanovoids were observed in the sample processed at 500 °C (Figure 5c), filled predominantly with Ar. In this specimen it was determined that the N-concentration is homogeneously distributed as N-species (NO, N2O, NO2), proving the temperature-dependence of the action of the forming gas, as it has been observed in tin oxide layers [70]. RDF shows some Ar clustering, which suggests that it must be a competition of reactions in which the formation of N-species is preventing the Ar from becoming trapped in the nanovoids. The non-centrosymmetric structure (α-WO3) was also found in the films without piezoresponse; hence, the presence of a non-centrosymmetric structure is not sufficient in this material to achieve piezo-active domains detected by PFM. However, nanovoids observed by APT may be indirectly related to the piezoresponse. Such nanovoids could act as strain centers promoting a local break symmetry, and thus, the defect-induced polarity related with the piezoresponse measured by PFM.

4. Conclusions

Fabrication of tungsten trioxide WO3 thin films using RF-sputtering over sapphire substrates with post-deposit annealing processing at 400 °C and 500 °C in a forming gas environment were studied by piezo-force microscopy (PFM), obtaining a piezoresponse with d33 = 35 pmV−1 by domain piezoresponse imaging and piezoelectric hysteresis loops in thin films processed at 400 °C. The piezoresponse is mainly attributed to a local break in the symmetry related to N2-filled nanovoid distribution as revealed by atom probe tomography. Complementary characterization by electron microscopy in scanning and transmission mode and X-ray diffraction, indicates a mixture of orthorhombic and tetragonal phases for samples processed at 400 °C.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/ma16041387/s1, Figure S1: Mass spectra. Figure S2: Radial distribution function. Figure S3: Nearest neighbor distribution. Figure S4: Annealing profile. Figure S5: Profilometry. Figure S6: PFM off field for WO3 at 500 °C. Figure S7: EDS and SEM for WO3 thin film. Figure S8: Cross-sectional SEM image of WO3. Figure S9: Lamella preparation for TEM. Figure S10: Mass spectra of WO3 thin films measured by APT.

Author Contributions

Sample preparation, P.M.P.-D., J.N., and M.R.; PFM measurements were completed by A.H.-M.; structural characterization was completed by P.M.P.-D.; APT measurements were completed by T.B.; APT analysis was completed by P.M.P.-D. and T.B.; writing—original draft preparation, P.M.P.-D.; writing—review and editing, M.H., M.R., and T.B.; supervision, M.R., T.B., and M.H.; funding acquisition, M.R. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded partially by the Consejo Nacional de Ciencia y Tecnología-México (CONACyT) under the Sistema Nacional de Investigadores Fellowship Program # 222146 for period 2020-2024 (M.R.). Part of this work was performed at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a fully owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. Additional funding was provided by the Karlsruhe Micro and Nano Facility (KNMF) of the Karlsruhe Institute of Technology for the usage of atom probe tomography and FIB instruments under proposal 2019-022-026969. The KNMF grants measurement time to external users for proposals pertinent to KNMF goals. Article Publication Charges was supported by Institutional Open Access Program (IOAP) of Karlsruhe Institute of Technology-Helmholtz.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No data are shared.

Acknowledgments

P.M.P.-D. thanks Delphine Chassaing and Roberto Talamantes for FIB preparation under HRTEM and APT measurements, and Consejo Nacional de Ciencia y Tecnología for graduate scholarship #956889 under the Materials Science Doctoral Program at the Universidad Autónoma de Ciudad Juárez and Dirección General de Vinculación e Intercambio of UACJ for the summer 2022 international traveling stipend. All authors thank the Instituto de Ingeniería y Tecnología of UACJ, the Centro de Investigación en Materiales Avanzados-Chihuahua, Center for Integrated Nanotechnologies of Sandia National Laboratories at Albuquerque, NM, and to Karlsruhe Micro and Nano Facilities of the Karlsruhe Institute of Technology in Germany for usage of all laboratory facilities and equipment.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Yu, H.; Guo, J.; Wang, C.; Zhang, J.; Liu, J.; Dong, G.; Zhong, X.; Diao, X. Essential Role of Oxygen Vacancy in Electrochromic Performance and Stability for WO3-y Films Induced by Atmosphere Annealing. Electrochimica Acta 2020, 332, 135504. [Google Scholar] [CrossRef]
  2. Arslan, M.; Firat, Y.E.; Tokgöz, S.R.; Peksoz, A. Fast Electrochromic Response and High Coloration Efficiency of Al-Doped WO3 Thin Films for Smart Window Applications. Ceram. Int. 2021, 47, 32570–32578. [Google Scholar] [CrossRef]
  3. Chang, C.-H.; Chou, T.-C.; Chen, W.-C.; Niu, J.-S.; Lin, K.-W.; Cheng, S.-Y.; Tsai, J.-H.; Liu, W.-C. Study of a WO3 Thin Film Based Hydrogen Gas Sensor Decorated with Platinum Nanoparticles. Sens. Actuators B Chem. 2020, 317, 128145. [Google Scholar] [CrossRef]
  4. Castillo, C.; Cabello, G.; Chornik, B.; Huentupil, Y.; Buono-Core, G.E. Characterization of Photochemically Grown Pd Loaded WO3 Thin Films and Its Evaluation as Ammonia Gas Sensor. J. Alloys Compd. 2020, 825, 154166. [Google Scholar] [CrossRef]
  5. Limwichean, S.; Kasayapanand, N.; Ponchio, C.; Nakajima, H.; Patthanasettakul, V.; Eiamchai, P.; Meng, G.; Horprathum, M. Morphology-Controlled Fabrication of Nanostructured WO3 Thin Films by Magnetron Sputtering with Glancing Angle Deposition for Enhanced Efficiency Photo-Electrochemical Water Splitting. Ceram. Int. 2021, 47, 34455–34462. [Google Scholar] [CrossRef]
  6. Mohamedkhair, A.K.; Drmosh, Q.A.; Qamar, M.; Yamani, Z.H. Tuning Structural Properties of WO3 Thin Films for Photoelectrocatalytic Water Oxidation. Catalysts 2021, 11, 381. [Google Scholar] [CrossRef]
  7. Shabdan, Y.; Markhabayeva, A.; Bakranov, N.; Nuraje, N. Photoactive Tungsten-Oxide Nanomaterials for Water-Splitting. Nanomaterials 2020, 10, 1871. [Google Scholar] [CrossRef]
  8. Kumar, A. Methods and Materials for Smart Manufacturing: Additive Manufacturing, Internet of Things, Flexible Sensors and Soft Robotics. Manuf. Lett. 2018, 15, 122–125. [Google Scholar] [CrossRef]
  9. Zaia, E.W.; Gordon, M.P.; Yuan, P.; Urban, J.J. Soft Electronics: Progress and Perspective: Soft Thermoelectric Materials for Wearable and Internet-of-Things Applications (Adv. Electron. Mater. 11/2019). Adv. Electron. Mater. 2019, 5, 1970056. [Google Scholar] [CrossRef]
  10. Peng, Y.; Han, G.; Liu, F.; Xiao, W.; Liu, Y.; Zhong, N.; Duan, C.; Feng, Z.; Dong, H.; Hao, Y. Ferroelectric-like Behavior Originating from Oxygen Vacancy Dipoles in Amorphous Film for Non-Volatile Memory. Nanoscale. Res. Lett. 2020, 15, 134. [Google Scholar] [CrossRef]
  11. Yuan, K.; Wang, C.-Y.; Zhu, L.-Y.; Cao, Q.; Yang, J.-H.; Li, X.-X.; Huang, W.; Wang, Y.-Y.; Lu, H.-L.; Zhang, D.W. Fabrication of a Micro-Electromechanical System-Based Acetone Gas Sensor Using CeO 2 Nanodot-Decorated WO3 Nanowires. ACS Appl. Mater. Interfaces 2020, 12, 14095–14104. [Google Scholar] [CrossRef]
  12. Ok, K.M.; Chi, E.O.; Halasyamani, P.S. Bulk Characterization Methods for Non-Centrosymmetric Materials: Second-Harmonic Generation, Piezoelectricity, Pyroelectricity, and Ferroelectricity. Chem. Soc. Rev. 2006, 35, 710. [Google Scholar] [CrossRef]
  13. Jaffe, B. Piezoelectric Ceramics; Elsevier Science: Saint Louis, MO, USA, 2014. [Google Scholar]
  14. Oh, H.; Dayeh, S.A. Physics-Based Device Models and Progress Review for Active Piezoelectric Semiconductor Devices. Sensors 2020, 20, 3872. [Google Scholar] [CrossRef]
  15. Ahart, M.; Somayazulu, M.; Cohen, R.E.; Ganesh, P.; Dera, P.; Mao, H.; Hemley, R.J.; Ren, Y.; Liermann, P.; Wu, Z. Origin of Morphotropic Phase Boundaries in Ferroelectrics. Nature 2008, 451, 545–548. [Google Scholar] [CrossRef]
  16. Ibrahim, A.B.; Murgan, R.; Rahman, M.K.; Osman, J. Morphotropic Phase Boundary in Ferroelectric Materials; INTECH Open Access Publisher: London, UK, 2011. [Google Scholar]
  17. Soergel, E. Piezoresponse Force Microscopy (PFM). J. Phys. Appl. Phys. 2011, 44, 464003. [Google Scholar] [CrossRef]
  18. Gruverman, A.; Alexe, M.; Meier, D. Piezoresponse Force Microscopy and Nanoferroic Phenomena. Nat. Commun. 2019, 10, 1661. [Google Scholar] [CrossRef]
  19. Guan, Z.; Jiang, Z.-Z.; Tian, B.-B.; Zhu, Y.-P.; Xiang, P.-H.; Zhong, N.; Duan, C.-G.; Chu, J.-H. Identifying Intrinsic Ferroelectricity of Thin Film with Piezoresponse Force Microscopy. AIP Adv. 2017, 7, 095116. [Google Scholar] [CrossRef]
  20. Schulz, A.D.; Röhm, H.; Leonhard, T.; Wagner, S.; Hoffmann, M.J.; Colsmann, A. On the Ferroelectricity of CH3NH3PbI3 Perovskites. Nat. Mater. 2019, 18, 1050. [Google Scholar] [CrossRef]
  21. Liu, Y.; Collins, L.; Proksch, R.; Kim, S.; Watson, B.R.; Doughty, B.; Calhoun, T.R.; Ahmadi, M.; Ievlev, A.V.; Jesse, S.; et al. Reply to: On the Ferroelectricity of CH3NH3PbI3 Perovskites. Nat. Mater. 2019, 18, 1051–1053. [Google Scholar] [CrossRef]
  22. Liu, Y.; Sun, Y.; Lu, W.; Wang, H.; Wang, Z.; Yu, B.; Li, T.; Zeng, K. Variation of Contact Resonance Frequency during Domain Switching in PFM Measurements for Ferroelectric Materials. J. Materiomics 2020, 6, 109–118. [Google Scholar] [CrossRef]
  23. Seol, D.; Kim, B.; Kim, Y. Non-Piezoelectric Effects in Piezoresponse Force Microscopy. Curr. Appl. Phys. 2017, 17, 661–674. [Google Scholar] [CrossRef]
  24. Kim, S.; Seol, D.; Lu, X.; Alexe, M.; Kim, Y. Electrostatic-Free Piezoresponse Force Microscopy. Sci. Rep. 2017, 7, 41657. [Google Scholar] [CrossRef] [PubMed]
  25. Seol, D.; Kang, S.; Sun, C.; Kim, Y. Significance of Electrostatic Interactions Due to Surface Potential in Piezoresponse Force Microscopy. Ultramicroscopy 2019, 207, 112839. [Google Scholar] [CrossRef]
  26. Qiao, H.; Seol, D.; Sun, C.; Kim, Y. Electrostatic Contribution to Hysteresis Loop in Piezoresponse Force Microscopy. Appl. Phys. Lett. 2019, 114, 152901. [Google Scholar] [CrossRef]
  27. Qiao, H.; Kwon, O.; Kim, Y. Electrostatic Effect on Off-Field Ferroelectric Hysteresis Loop in Piezoresponse Force Microscopy. Appl. Phys. Lett. 2020, 116, 172901. [Google Scholar] [CrossRef]
  28. Proksch, R. Electrochemical Strain Microscopy of Silica Glasses. J. Appl. Phys. 2014, 116, 066804. [Google Scholar] [CrossRef]
  29. Zhang, G.; Liu, W.; Chen, J.; Shen, S. Nonlinear Electrochemomechanical Modelling of Electrochemical Strain Microscopy Imaging. Nanotechnology 2020, 31, 315704. [Google Scholar] [CrossRef]
  30. Qiu, H.; Mativetsky, J.M. Nanoscale Light- and Voltage-Induced Lattice Strain in Perovskite Thin Films. Nanoscale 2021, 13, 746–752. [Google Scholar] [CrossRef]
  31. Yu, J.; Esfahani, E.N.; Zhu, Q.; Shan, D.; Jia, T.; Xie, S.; Li, J. Quadratic Electromechanical Strain in Silicon Investigated by Scanning Probe Microscopy. J. Appl. Phys. 2018, 123, 155104. [Google Scholar] [CrossRef]
  32. Korobko, R.; Patlolla, A.; Kossoy, A.; Wachtel, E.; Tuller, H.L.; Frenkel, A.I.; Lubomirsky, I. Giant Electrostriction in Gd-Doped Ceria. Adv. Mater. 2012, 24, 5857–5861. [Google Scholar] [CrossRef]
  33. Yun, S.; Song, K.; Chu, K.; Hwang, S.-Y.; Kim, G.-Y.; Seo, J.; Woo, C.-S.; Choi, S.-Y.; Yang, C.-H. Flexopiezoelectricity at Ferroelastic Domain Walls in WO3 Films. Nat. Commun. 2020, 11, 4898. [Google Scholar] [CrossRef] [PubMed]
  34. Abdollahi, A.; Domingo, N.; Arias, I.; Catalan, G. Converse Flexoelectricity Yields Large Piezoresponse Force Microscopy Signals in Non-Piezoelectric Materials. Nat. Commun. 2019, 10, 1266. [Google Scholar] [CrossRef] [PubMed]
  35. Liu, W.; Deng, F.; Xie, S.; Shen, S.; Li, J. Electromechanical Analysis of Direct and Converse Flexoelectric Effects under a Scanning Probe Tip. J. Mech. Phys. Solids 2020, 142, 104020. [Google Scholar] [CrossRef]
  36. Očenášek, J.; Lu, H.; Bark, C.W.; Eom, C.B.; Alcalá, J.; Catalan, G.; Gruverman, A. Nanomechanics of Flexoelectric Switching. Phys. Rev. B 2015, 92, 035417. [Google Scholar] [CrossRef]
  37. Kim, Y.; Kumar, A.; Tselev, A.; Kravchenko, I.I.; Han, H.; Vrejoiu, I.; Lee, W.; Hesse, D.; Alexe, M.; Kalinin, S.V.; et al. Nonlinear Phenomena in Multiferroic Nanocapacitors: Joule Heating and Electromechanical Effects. ACS Nano. 2011, 5, 9104–9112. [Google Scholar] [CrossRef]
  38. Gunkel, F.; Christensen, D.V.; Chen, Y.Z.; Pryds, N. Oxygen Vacancies: The (in)Visible Friend of Oxide Electronics. Appl. Phys. Lett. 2020, 116, 120505. [Google Scholar] [CrossRef]
  39. Bielański, A.; Haber, J. Oxygen in Catalysis on Transition Metal Oxides. Catal. Rev. 1979, 19, 1–41. [Google Scholar] [CrossRef]
  40. Corby, S.; Francàs, L.; Kafizas, A.; Durrant, J.R. Determining the Role of Oxygen Vacancies in the Photoelectrocatalytic Performance of WO 3 for Water Oxidation. Chem. Sci. 2020, 11, 2907–2914. [Google Scholar] [CrossRef]
  41. Liu, D.; Zhang, C.; Yu, Y.; Shi, Y.; Yu, Y.; Niu, Z.; Zhang, B. Hydrogen Evolution Activity Enhancement by Tuning the Oxygen Vacancies in Self-Supported Mesoporous Spinel Oxide Nanowire Arrays. Nano. Res. 2018, 11, 603–613. [Google Scholar] [CrossRef]
  42. Li, J.-J.; Zhang, M.; Weng, B.; Chen, X.; Chen, J.; Jia, H.-P. Oxygen Vacancies Mediated Charge Separation and Collection in Pt/WO3 Nanosheets for Enhanced Photocatalytic Performance. Appl. Surf. Sci. 2020, 507, 145133. [Google Scholar] [CrossRef]
  43. Jolly Bose, R.; Illyaskutty, N.; Tan, K.S.; Rawat, R.S.; Matham, M.V.; Kohler, H.; Mahadevan Pillai, V.P. Hydrogen Sensors Based on Pt-Loaded WO3 Sensing Layers. EPL Europhys. Lett. 2016, 114, 66002. [Google Scholar] [CrossRef]
  44. Li, H.; Wu, C.-H.; Liu, Y.-C.; Yuan, S.-H.; Chiang, Z.-X.; Zhang, S.; Wu, R.-J. Mesoporous WO3-TiO2 Heterojunction for a Hydrogen Gas Sensor. Sens. Actuators B Chem. 2021, 341, 130035. [Google Scholar] [CrossRef]
  45. Ren, X.; Xia, M.; Chong, B.; Yan, X.; Wells, N.; Yang, G. Uniform NiPx Nanospheres Loaded onto Defective HxWO3-y with Three-Dimensionally Ordered Macroporous Structure for Photocatalytic Nitrogen Reduction. Appl. Catal. B Environ. 2021, 297, 120468. [Google Scholar] [CrossRef]
  46. Urasinska-Wojcik, B.; Vincent, T.A.; Chowdhury, M.F.; Gardner, J.W. Ultrasensitive WO3 Gas Sensors for NO2 Detection in Air and Low Oxygen Environment. Sens. Actuators B Chem. 2017, 239, 1051–1059. [Google Scholar] [CrossRef]
  47. Wang, Y.; Liu, J.; Cui, X.; Gao, Y.; Ma, J.; Sun, Y.; Sun, P.; Liu, F.; Liang, X.; Zhang, T.; et al. NH3 Gas Sensing Performance Enhanced by Pt-Loaded on Mesoporous WO3. Sens. Actuators B Chem. 2017, 238, 473–481. [Google Scholar] [CrossRef]
  48. Wang, G.; Ji, Y.; Huang, X.; Yang, X.; Gouma, P.-I.; Dudley, M. Fabrication and Characterization of Polycrystalline WO3 Nanofibers and Their Application for Ammonia Sensing. J. Phys. Chem. B 2006, 110, 23777–23782. [Google Scholar] [CrossRef]
  49. Park, D.-S.; Hadad, M.; Riemer, L.M.; Ignatans, R.; Spirito, D.; Esposito, V.; Tileli, V.; Gauquelin, N.; Chezganov, D.; Jannis, D.; et al. Induced Giant Piezoelectricity in Centrosymmetric Oxides. Science 2022, 375, 653–657. [Google Scholar] [CrossRef]
  50. Aktas, O.; Kangama, M.; Linyu, G.; Catalan, G.; Ding, X.; Zunger, A.; Salje, E.K.H. Piezoelectricity in Nominally Centrosymmetric Phases. Phys. Rev. Res. 2021, 3, 043221. [Google Scholar] [CrossRef]
  51. Kim, Y.; Alexe, M.; Salje, E.K.H. Nanoscale Properties of Thin Twin Walls and Surface Layers in Piezoelectric WO3−x. Appl. Phys. Lett. 2010, 96, 032904. [Google Scholar] [CrossRef]
  52. Yadav, P.; Sharma, A.; Srivastava, H.; Bhaumik, I.; Singh, G.; Tiwari, V.S. A Correlation of Piezoelectricity and Photoluminescence of Europium Doped (Na0.41K0.09Bi0.5)TiO3 with Ferroelectric and Structural Ordering. Ceram. Int. 2022, 48, 3243–3253. [Google Scholar] [CrossRef]
  53. Liu, Y.F.; Wang, Y.Q. Thermo-Electro-Mechanical Vibrations of Porous Functionally Graded Piezoelectric Nanoshells. Nanomaterials 2019, 9, 301. [Google Scholar] [CrossRef]
  54. Li, Z.; Wang, C.; Chen, C. Effective Electromechanical Properties of Transversely Isotropic Piezoelectric Ceramics with Microvoids. Comput. Mater. Sci. 2003, 27, 381–392. [Google Scholar] [CrossRef]
  55. Larson, D.J. Local Electrode Atom Probe Tomography: A User’s Guide; Springer: New York, NY, USA, 2013. [Google Scholar]
  56. Kholkin, A.L.; Bdikin, I.K.; Kiselev, D.A.; Shvartsman, V.V.; Kim, S.-H. Nanoscale Characterization of Polycrystalline Ferroelectric Materials for Piezoelectric Applications. J. Electroceramics 2007, 19, 83–96. [Google Scholar] [CrossRef]
  57. Kholkin, A.L.; Kalinin, S.V.; Roelofs, A.; Gruverman, A. Review of Ferroelectric Domain Imaging by Piezoresponse Force Microscopy. In Scanning Probe Microscopy; Kalinin, S., Gruverman, A., Eds.; Springer: New York, NY, USA, 2007; pp. 173–214. [Google Scholar] [CrossRef]
  58. Jesse, S.; Baddorf, A.P.; Kalinin, S.V. Switching Spectroscopy Piezoresponse Force Microscopy of Ferroelectric Materials. Appl. Phys. Lett. 2006, 88, 062908. [Google Scholar] [CrossRef]
  59. Ramos-Cano, C.J.; Miki-Yoshida, M.; Herrera-Basurto, R.; Mercader-Trejo, F.; Fuentes-Cobas, L.; Auciello, O.; Hurtado-Macías, A. Effect of the Orientation Polarization and Texturing on Nano-Mechanical and Piezoelectric Properties of PZT (52/48) Films. Appl. Phys. A 2023, 129, 113. [Google Scholar] [CrossRef]
  60. Roelofs, A.; Schneller, T.; Szot, K.; Waser, R. Towards the Limit of Ferroelectric Nanosized Grains. Nanotechnology 2003, 14, 250–253. [Google Scholar] [CrossRef]
  61. Balke, N.; Jesse, S.; Li, Q.; Maksymovych, P.; Baris Okatan, M.; Strelcov, E.; Tselev, A.; Kalinin, S.V. Current and Surface Charge Modified Hysteresis Loops in Ferroelectric Thin Films. J. Appl. Phys. 2015, 118, 072013. [Google Scholar] [CrossRef]
  62. Chen, Z.; Huang, J.; Yang, Y.; Wang, Y.; Wu, Y.; He, H.; Wei, X.; Ye, Z.; Zeng, H.; Cong, H.; et al. Piezoelectric Properties of Rhombic LiNbO3 Nanowires. RSC Adv. 2012, 2, 7380. [Google Scholar] [CrossRef]
  63. Yang, Y.C.; Song, C.; Wang, X.H.; Zeng, F.; Pan, F. Giant Piezoelectric d33 Coefficient in Ferroelectric Vanadium Doped ZnO Films. Appl. Phys. Lett. 2008, 92, 012907. [Google Scholar] [CrossRef]
  64. Manciu, F.S.; Enriquez, J.L.; Durrer, W.G.; Yun, Y.; Ramana, C.V.; Gullapalli, S.K. Spectroscopic Analysis of Tungsten Oxide Thin Films. J. Mater. Res. 2010, 25, 2401–2406. [Google Scholar] [CrossRef]
  65. Enriquez-Carrejo, J.L.; Ramos, M.A.; Mireles-Jr-Garcia, J.; Hurtado-Macias, A. Nano-Mechanical and Structural Study of WO3 Thin Films. Thin Solid Films 2016, 606, 148–154. [Google Scholar] [CrossRef]
  66. Kühbach, M.; Bajaj, P.; Celik, M.H.; Jägle, E.A.; Gault, B. On Strong Scaling and Open Source Tools for Analyzing Atom Probe Tomography Data. arXiv 2020, arXiv:2004.05188. Available online: http://arxiv.org/abs/2004.05188 (accessed on 26 October 2022). [CrossRef]
  67. Sequeira, C.A.C.; Rodrigues, L.F.F.T.T.G.; Santos, D.M.F. Cation Diffusivity in Nonstoichiometric Tungsten Trioxide Films. ECS J. Solid State Sci. Technol. 2012, 1, R136–R139. [Google Scholar] [CrossRef]
  68. Sun, Z.; Huo, R.; Choi, C.; Hong, S.; Wu, T.-S.; Qiu, J.; Yan, C.; Han, Z.; Liu, Y.; Soo, Y.-L.; et al. Oxygen Vacancy Enables Electrochemical N2 Fixation over WO3 with Tailored Structure. Nano Energy 2019, 62, 869–875. [Google Scholar] [CrossRef]
  69. Zhang, N.; Jalil, A.; Wu, D.; Chen, S.; Liu, Y.; Gao, C.; Ye, W.; Qi, Z.; Ju, H.; Wang, C.; et al. Refining Defect States in W18O49 by Mo Doping: A Strategy for Tuning N 2 Activation towards Solar-Driven Nitrogen Fixation. J. Am. Chem. Soc. 2018, 140, 9434–9443. [Google Scholar] [CrossRef]
  70. Dong, C.C.; Yu, F.; Bao, T.; Zhang, W.; Dai, F.; Yang, D. Fluxless Bump Reflow in Activated Hydrogen Atmosphere. In 2018 19th International Conference on Electronic Packaging Technology (ICEPT); IEEE: Shanghai, China, 2018; pp. 652–655. [Google Scholar] [CrossRef]
Materials 16 01387 g001 550
Figure 1. (a) Topography in contact mode of WO3 thin film annealed at 400 °C. PFM phase signal images (b) before and (c) after measurement of the local hysteresis loops revealing variation of the structure of domains with different orientation of polarization; (d) amplitude, (e) phase, and (f) piezoelectric coefficient (d33) versus applied bias.
Figure 1. (a) Topography in contact mode of WO3 thin film annealed at 400 °C. PFM phase signal images (b) before and (c) after measurement of the local hysteresis loops revealing variation of the structure of domains with different orientation of polarization; (d) amplitude, (e) phase, and (f) piezoelectric coefficient (d33) versus applied bias.
Materials 16 01387 g001
Materials 16 01387 g002 550
Figure 2. X-ray diffraction pattern for WO3 thin films deposited onto sapphire (Al2O3) as deposited and annealed at 400 °C and 500 °C in a 3% H2/N2 forming gas environment.
Figure 2. X-ray diffraction pattern for WO3 thin films deposited onto sapphire (Al2O3) as deposited and annealed at 400 °C and 500 °C in a 3% H2/N2 forming gas environment.
Materials 16 01387 g002
Materials 16 01387 g003 550
Figure 3. (a) High-resolution Cs-corrected TEM images. A selected area electron diffraction pattern of (b) WO3 thin film corresponding to a polycrystalline structure, including a tetragonal (P4/nmm) structure, and of (c) the sapphire substrate with monocrystal of an Rc3 structure. Atomic arrays of (d) film and (e) substrate structures, with lattice plane distances of d(110) = 3.74 Å and d(012) = 3.47 Å, respectively.
Figure 3. (a) High-resolution Cs-corrected TEM images. A selected area electron diffraction pattern of (b) WO3 thin film corresponding to a polycrystalline structure, including a tetragonal (P4/nmm) structure, and of (c) the sapphire substrate with monocrystal of an Rc3 structure. Atomic arrays of (d) film and (e) substrate structures, with lattice plane distances of d(110) = 3.74 Å and d(012) = 3.47 Å, respectively.
Materials 16 01387 g003
Materials 16 01387 g004 550
Figure 4. Atom probe tomographs (up) with corresponding concentration profiles (down) for (a) as deposited and annealed at (b) 400 °C and (c) 500 °C WO3 thin films deposited onto Al2O3.
Figure 4. Atom probe tomographs (up) with corresponding concentration profiles (down) for (a) as deposited and annealed at (b) 400 °C and (c) 500 °C WO3 thin films deposited onto Al2O3.
Materials 16 01387 g004
Materials 16 01387 g005 550
Figure 5. Radial distribution function (RDF) and heatmaps for cluster analysis of Ar and N2 in WO3 thin films as deposited and annealed at 400 °C and 500 °C in a forming gas (3% H2/N2).
Figure 5. Radial distribution function (RDF) and heatmaps for cluster analysis of Ar and N2 in WO3 thin films as deposited and annealed at 400 °C and 500 °C in a forming gas (3% H2/N2).
Materials 16 01387 g005
Table
Table 1. Atomic composition of O, W, Ar, and N2 in WO3 thin films as deposited and annealed at 400 °C and 500 °C.
Table 1. Atomic composition of O, W, Ar, and N2 in WO3 thin films as deposited and annealed at 400 °C and 500 °C.
As Deposited400 °C500 °C
O66.269.471.3
W27.125.227.4
Ar1.90.040.4
N1.23.10.8
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Pineda-Domínguez, P.M.; Boll, T.; Nogan, J.; Heilmaier, M.; Hurtado-Macías, A.; Ramos, M. The Piezoresponse in WO3 Thin Films Due to N2-Filled Nanovoids Enrichment by Atom Probe Tomography. Materials 2023, 16, 1387. https://doi.org/10.3390/ma16041387

AMA Style

Pineda-Domínguez PM, Boll T, Nogan J, Heilmaier M, Hurtado-Macías A, Ramos M. The Piezoresponse in WO3 Thin Films Due to N2-Filled Nanovoids Enrichment by Atom Probe Tomography. Materials. 2023; 16(4):1387. https://doi.org/10.3390/ma16041387

Chicago/Turabian Style

Pineda-Domínguez, Pamela M., Torben Boll, John Nogan, Martin Heilmaier, Abel Hurtado-Macías, and Manuel Ramos. 2023. "The Piezoresponse in WO3 Thin Films Due to N2-Filled Nanovoids Enrichment by Atom Probe Tomography" Materials 16, no. 4: 1387. https://doi.org/10.3390/ma16041387

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop