HRTEM Microstructural Characterization of β-WO3 Thin Films Deposited by Reactive RF  Magnetron Sputtering

Faudoa-Arzate, Alejandro; Arteaga-Duran, Alvaro; Sáenz-Hernández, Renee Joselin; Botello-Zubiate, M. E.; Realyvazquez-Guevara, Paula Rebeca; Matutes-Aquino, J.A.

doi:10.3390/ma10020200

Cited by 20 publications

(6 citation statements)

References 18 publications

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“…Figure 12 illustrates the theoretically modeled Pnma structure of the system (16 atoms in the unit-cell). Several phases of this system were experimentally characterized and analysed by exploring the sequence of temperature-induced phase transitions in WO 3 219 . They were rationalized in terms of changes in the octahedral tilt of the system and/or displacements of W from the center of the WO 6 octahedron.…”

Section: Resultsmentioning

confidence: 99%

Significance of hydrogen bonding and other noncovalent interactions in determining octahedral tilting in the CH3NH3PbI3 hybrid organic-inorganic halide perovskite solar cell semiconductor

Varadwaj

Marques

Yamashita

2019

Sci Rep

116

100

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The CH3NH3PbI3 (methylammonium lead triiodide) perovskite semiconductor system has been viewed as a blockbuster research material during the last five years. Because of its complicated architecture, several of its technological, physical and geometrical issues have been examined many times. Yet this has not assisted in overcoming a number of problems in the field nor in enabling the material to be marketed. For instance, these studies have not clarified the nature and type of hydrogen bonding and other noncovalent interactions involved; the origin of hysteresis; the actual role of the methylammonium cation; the nature of polarity associated with the tetragonal geometry; the unusual origin of various frontier orbital contributions to the conduction band minimum; the underlying phenomena of spin-orbit coupling that causes significant bandgap reduction; and the nature of direct-to-indirect bandgap transition features. Arising from many recent reports, it is now a common belief that the I···H–N interaction formed between the inorganic framework and the ammonium group of CH3NH3+ is the only hydrogen bonded interaction responsible for all temperature-dependent geometrical polymorphs of the system, including the most stable one that persists at low-temperatures, and the significance of all other noncovalent interactions has been overlooked. This study focussed only on the low temperature orthorhombic polymorph of CH3NH3PbI3 and CD3ND3PbI3, where D refers deuterium. Together with QTAIM, DORI and RDG based charge density analyses, the results of density functional theory calculations with PBE with and without van der Waals corrections demonstrate that the prevailing view of hydrogen bonding in CH3NH3PbI3 is misleading as it does not alone determine the a−b+a− tilting pattern of the PbI64− octahedra. This study suggests that it is not only the I···H/D–N, but also the I···H/D–C hydrogen/deuterium bonding and other noncovalent interactions (viz. tetrel-, pnictogen- and lump-hole bonding interactions) that are ubiquitous in the orthorhombic CH3NH3PbI3/CD3ND3PbI3 perovskite geometry. Their interplay determines the overall geometry of the polymorph, and are therefore responsible in part for the emergence of the functional optical properties of this material. This study also suggests that these interactions should not be regarded as the sole determinants of octahedral tilting since lattice dynamics is known to play a critical role as well, a common feature in many inorganic perovskites both in the presence and the absence of the encaged cation, as in CsPbI3/WO3 perovskites, for example.

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Section: Resultsmentioning

confidence: 99%

Significance of hydrogen bonding and other noncovalent interactions in determining octahedral tilting in the CH3NH3PbI3 hybrid organic-inorganic halide perovskite solar cell semiconductor

Varadwaj

Marques

Yamashita

2019

Sci Rep

116

100

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“…Among various applications, the photocatalyst application for degrading organic pollutants receives much attention as WO 3 has the advantages of low cost, high chemical stability, and excellent process-dependent reproducibility. In general, pure WO 3 crystal shows five phase transitions at temperatures ranging from −180 to 900 • C [3]. Among the five crystal forms, a monoclinic I WO 3 phase is the stable phase at room temperature.…”

Section: Introductionmentioning

confidence: 99%

Preparation of Orthorhombic WO3 Thin Films and Their Crystal Quality-Dependent Dye Photodegradation Ability

Liang

Chang

2019

Coatings

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Direct current (DC) magnetron sputtering deposited WO3 films with different crystalline qualities were synthesized by postannealing at various temperatures. The in-situ DC sputtering deposited WO3 thin film at 375 °C exhibited an amorphous structure. The as-grown WO3 films were crystallized after annealing at temperatures of 400–600 °C in ambient air. Structural analyses revealed that the crystalline WO3 films have an orthorhombic structure. Moreover, the crystallite size of the WO3 film exhibited an explosive coarsening behavior at an annealing temperature above 600 °C. The density of oxygen vacancy of the WO3 films was substantially lowered through a high temperature annealing procedure. The optical bandgap values of the WO3 films are highly associated with the degree of crystalline quality. The annealing-induced variation of microstructures, crystallinity, and bandgap of the amorphous WO3 thin films explained the various photoactivated properties of the films in this study.

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“…This can be attributed to a higher kinetic energy leading to diffusion of the impinging species on the substrate surface with increasing T s . As such, the grain boundary migration and restructuring become prevalent, leading to a dense microstructure. − As noted in the literature, the sputter-deposited film interface microstructure is highly dependent on the adatom/particle energy of the growing film. − In general, the volume of voids/pores in the films tends to increase with decreasing adatom or particle energy. These voids can also form as a consequence of surface roughness and shadowing effects, leading to the development of the loose columnar structure.…”

Section: Results and Discussionmentioning

confidence: 99%

Phase-Control-Enabled Enhancement in Hydrophilicity and Mechanical Toughness in Nanocrystalline Tungsten Oxide Films for Energy-Related Applications

Ramana

Battu

Dubey

et al. 2020

ACS Appl. Nano Mater.

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We report on the phase-control-enabled enhancement in the hydrophilicity and mechanical properties of nanostructured WO3 films for energy-related applications. Nanostructured WO3 films were fabricated by utilizing reactive magnetron sputter deposition onto silicon (100) substrates with varying deposition temperature (T s = 25–500 °C) at a fixed oxygen partial pressure of ∼4 mTorr. Extensive characterization performed indicates that the fundamental surface/interface structure–phase–hydrophilicity–mechanical property correlation enables tailoring nanocrystalline WO3 films to meet the requirements of various technological applications. Crystal structure, surface/interface morphology, and microstructure characterization indicate the deposition processing conditions induce phase transformations and surface/interface quality variation, which in turn controls the hydrophilicity and mechanical behavior, in WO3 films. Carefully tuned processing conditions induce an amorphous to crystalline structural transformation, which progresses through amorphous to monoclinic to tetragonal phases, coupled with variation in surface roughness and crystallite size. Mechanical characterization using nanoindentation reveals that the mechanical response, in terms of hardness (H), elastic modulus (E), and scratch parameters, of WO3 films is highly sensitive to their phase and microstructure evolution. Nanostructured WO3 films crystallized in monoclinic phase exhibit superior mechanical response compared to either amorphous or tetragonal phase WO3 films. The maximum hardness (∼38 GPa) and elastic modulus (∼320 GPa) values were obtained for WO3 films deposited at T s = 400 °C. The phase transformation sequence coupled with surface/interface structure affects the contact angle values significantly. The contact angle decreases significantly from 70° to nearly 5° with variation in phase, microstructure, and surface/interface quality of WO3 films. A direct structure–phase–microstructure–hydrophilicity–mechanical property relationship found suggest that tuning properties of WO3 films for photoelectrochemical, photocatalytic, and energy-related applications can be achieved by tuning the deposition conditions and controlling the phase at the nanoscale dimensions.

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HRTEM Microstructural Characterization of β-WO3 Thin Films Deposited by Reactive RF Magnetron Sputtering

Cited by 20 publications

References 18 publications

Significance of hydrogen bonding and other noncovalent interactions in determining octahedral tilting in the CH3NH3PbI3 hybrid organic-inorganic halide perovskite solar cell semiconductor

Significance of hydrogen bonding and other noncovalent interactions in determining octahedral tilting in the CH3NH3PbI3 hybrid organic-inorganic halide perovskite solar cell semiconductor

Preparation of Orthorhombic WO3 Thin Films and Their Crystal Quality-Dependent Dye Photodegradation Ability

Phase-Control-Enabled Enhancement in Hydrophilicity and Mechanical Toughness in Nanocrystalline Tungsten Oxide Films for Energy-Related Applications

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