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

Abstract

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.

Development of WO3–Nafion Based Membranes for Enabling Higher Water Retention at Low Humidity and Enhancing PEMFC Performance at Intermediate Temperature Operation

“…The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/polym14122492/s1, Figure S1: Representative advancing (θa) and receding (θr) water contact angles of the membranes; Table S1: Reported (static) water contact angles of different WO 3 layers. References [75][76][77][78][79][80][81][82][83][84][85][86][87] are cited in the supplementary materials. Funding: This research was funded by Project no.…”

Aluminum Doping and Nanostructuring Enabled Designing of Magnetically Recoverable Hexaferrite Catalysts

“… 24 , 28 , 35 , 40 − 44 However, the catalytic studies on the hard magnetic materials such as barium- and strontium-hexaferrites and their derivatives are yet to be explored. On the other hand, based on our previous work on magnetic and electronic materials, 45 , 46 we recognize that tailoring the materials’ structure and controlled phase in nanostructured materials can provide opportunities to design inexpensive nanomaterials for the desired applications. Furthermore, most recently, we demonstrated that the surface/interface magnetic properties can be tailored 46 and have made successful attempts to derive catalytic properties in Cu-substituted strontium hexaferrites synthesized using a tartrate-gel method.…”

“…Therefore, conversion of nitrophenol into other chemicals such as para -aminophenol is highly beneficial as these chemicals can be used as starting materials for industrial dyes, photography development agents, rubber chemicals, and so forth. ,− While there are recent attempts to design and develop catalysts for the purpose based on environmental friendly, cost-effective, and high-performance materials, catalysts based on noble metals, such as Au, Pd, Pt, Ag, and so forth, have been studied for a long time to convert para -nitrophenol to para -aminophenol. − ,,− Realizing that the noble metals are expensive, which exhibit sintering and related problems at the nanoscale dimensions, many researchers directed their recent efforts to design and develop various other catalysts, which are based on inexpensive, green, and highly stable metal oxides and/or composites, for the para -nitrophenol reduction reaction. ,,,− However, the catalytic studies on the hard magnetic materials such as barium- and strontium-hexaferrites and their derivatives are yet to be explored. On the other hand, based on our previous work on magnetic and electronic materials, , we recognize that tailoring the materials’ structure and controlled phase in nanostructured materials can provide opportunities to design inexpensive nanomaterials for the desired applications. Furthermore, most recently, we demonstrated that the surface/interface magnetic properties can be tailored and have made successful attempts to derive catalytic properties in Cu-substituted strontium hexaferrites synthesized using a tartrate-gel method. , Therefore, in the present study, Al is chosen for the substitution in place of Fe in SrFe 12 O 19 and evaluated its activity toward the nitrophenol reduction reaction.…”

Correlation between Crystal Structure, Surface/Interface Microstructure, and Electrical Properties of Nanocrystalline Niobium Thin Films

“…Today’s world is increasingly shaped by information technology and the need for advanced materials with enhanced properties and performance is ubiquitous in the current scenario [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. The technical advancements in the recent years have paved way for miniaturization of electronic, magnetic, and optoelectronic devices with high performance, which is fundamentally dependent on the physical, chemical, and electromagnetic properties of their respective electronic, optical, magnetic, and electromagnetic components [ 1 , 2 , 3 , 4 ].…”

“…This is important since it gives a clear understanding of the underlying mechanisms that governs the properties that are of direct relevance for the desired technological application. In most applications, electrically conducting or mechanically protective materials used are in the form of thin films, where improved efficiency and cost effectiveness is important [ 6 ].…”