hafnium dioxide
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Crystals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 90
Author(s):  
Emiliano Laudadio ◽  
Pierluigi Stipa ◽  
Luca Pierantoni ◽  
Davide Mencarelli

Background: Hafnium Dioxide (HfO2) represents a hopeful material for gate dielectric thin films in the field of semiconductor integrated circuits. For HfO2, several crystal structures are possible, with different properties which can be difficult to describe in detail from an experimental point of view. In this study, a detailed computational approach has been shown to present a complete analysis of four HfO2 polymorphs, outlining the intrinsic properties of each phase on the basis of atomistic displacements. Methods: Density functional theory (DFT) based methods have been used to accurately describe the chemical physical properties of the polymorphs. Corrective Hubbard (U) semi-empirical terms have been added to exchange correlation energy in order to better reproduce the excited-state properties of HfO2 polymorphs. Results: the monoclinic phase resulted in the lowest cohesive energy, while the orthorhombic showed peculiar properties due to its intrinsic ferroelectric behavior. DFT + U methods showed the different responses of the four polymorphs to an applied field, and the orthorhombic phase was the least likely to undergo point defects as oxygen vacancies. Conclusions: The obtained results give a deeper insight into the differences in excited states phenomena in relation to each specific HfO2 polymorph.


2022 ◽  
Author(s):  
Ran An ◽  
Adrienne Minerick

The ability to generate stable, spatiotemporally controllable concentration gradients is critical for both electrokinetic and biological applications such as directional wetting and chemotaxis. Electrochemical techniques for generating solution and surface gradients display benefits such as simplicity, controllability, and compatibility with automation. Here, we present an exploratory study for generating micro-scale spatiotemporally controllable gradients using a reaction-free electrokinetic technique in a microfluidic environment. Methanol solutions with ionic Fluorescein isothiocyanate (FITC) molecules were used as an illustrative electrolyte. Spatially non-uniform alternating current (AC) electric fields were applied using hafnium dioxide (HfO2) coated Ti/Au electrode pairs. Results from spatial and temporal analysis, along with control experiments suggest that the FITC ion concentration gradient in bulk fluid (over 50 µm from the electrode) was established due to spatial variation of electric field density, and was independent of electrochemical reactions at the electrode surface. The established ion concentration gradients depended on both amplitudes and the frequencies of the oscillating AC electric field. Overall, this work reports a novel approach for generating stable and spatiotemporally tunable gradients in a microfluidic chamber using a reaction-free electrochemical methodology.


2022 ◽  
Author(s):  
Ran An ◽  
Adrienne Minerick

The ability to generate stable, spatiotemporally controllable concentration gradients is critical for both electrokinetic and biological applications such as directional wetting and chemotaxis. Electrochemical techniques for generating solution and surface gradients display benefits such as simplicity, controllability, and compatibility with automation. Here, we present an exploratory study for generating micro-scale spatiotemporally controllable gradients using a reaction-free electrokinetic technique in a microfluidic environment. Methanol solutions with ionic Fluorescein isothiocyanate (FITC) molecules were used as an illustrative electrolyte. Spatially non-uniform alternating current (AC) electric fields were applied using hafnium dioxide (HfO2) coated Ti/Au electrode pairs. Results from spatial and temporal analysis, along with control experiments suggest that the FITC ion concentration gradient in bulk fluid (over 50 µm from the electrode) was established due to spatial variation of electric field density, and was independent of electrochemical reactions at the electrode surface. The established ion concentration gradients depended on both amplitudes and the frequencies of the oscillating AC electric field. Overall, this work reports a novel approach for generating stable and spatiotemporally tunable gradients in a microfluidic chamber using a reaction-free electrochemical methodology.


2021 ◽  
Vol 2064 (1) ◽  
pp. 012071
Author(s):  
Thant Sin Win ◽  
A P Kuzmenko ◽  
V V Rodionov ◽  
Min Myo Than

Abstract In this work investigated the effect of the annealing temperature on hafnium nanofilms obtained by DC magnetron sputtering on Si substrates. The nanofilms annealed through 100°C to 700°C by a High-Temperature Strip Heater Chambers (HTK-16N) on an X-ray Diffractometer (XRD). The microstructure and morphology of the films at different temperatures were investigated by XRD, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Raman Microspectrometer (RS). It was found that annealing affects changes in the lattice strains, texture, grain size, and roughness of Hf nanofilms. According to XRD data, the structure of the thin films showed amorphous from room temperature to 100°C and starting from a temperature of 200°C were changed crystallization. At 500°C a monoclinic structure corresponding to hafnium dioxide HfO2was formed in hafnium nanofilms.


2021 ◽  
Vol 8 (10) ◽  
pp. 105901
Author(s):  
Thipok Bovornratanaraks ◽  
Rajeev Ahuja ◽  
Prutthipong Tsuppayakorn-aek

2021 ◽  
Author(s):  
Thipok Bovornratanaraks ◽  
Rajeev Ahuja ◽  
Prutthipong Tsuppayakorn-aek

Abstract Allotrope of HfO2 is explored by using first-principles evolutionary algorithm technique, based on density functional theory. The tetragonal structure with a space group of P4/nmm is found to be thermodynamically stable within the harmonic level. Arising particularly from the relative enthalpy, hafnium dioxide allotrope is taken into account in appraising the dynamic stability. Following this, the phonon calculations display that hafnium dioxide allotrope is dynamically stable under compressed conditions. Along with, the density of states suggests that hafnium dioxide allotrope is demonstrated that it is a semiconductor. Besides, the more significant change in the shape of density of states is observed when the pressure increased, by adopting an effect of this electronic topological transition, resulting in the energy gap is falling down monotonically. By inspecting their elastic constants and Vicker's hardness, the P4/nmm structure displayed the Vicker's hardness of 26.1GPa at a pressure of 200GPa. These findings suggest HfO2 is more likely to be attained experimentally and theoretically in the metal oxides family.


2021 ◽  
Author(s):  
Thipok Bovornratanaraks ◽  
Rajeev Ahuja ◽  
Prutthipong Tsuppayakorn-aek

Abstract The phase stability of the hafnium dioxide compounds HfO2, a novelmaterial with a wide range of application due to its versatility and biocompatibility,is predicted to be achievable by using evolutionary technique, based on first-principlescalculations. Herein, the candidate structure of HfO2 is revealed to adopt a tetragonalstructure under high-pressure phase with P4/nmm space group. This evidentlyconfirms the stability of the HfO2 structures, since the decomposition into thecomponent elements under pressure does not occur until the pressure is at least200GPa. Moreover, phonon calculations can confirm that the P4/nmm structure isdynamically stable. The P4/nmm structure is mainly attributed to the semiconductingproperty within using the Perdew{Burke{Ernzerhof, the modified Becke-Johnsonexchange potential in combination with the generalized gradient approximations, andthe quasi-particle GW approximation, respectively. Our calculation manifests that theP4/nmm structure likely to be metal above 200GPa, arising particularly from GWapproximation. The remarkable results of this work provide more understanding ofthe high-pressure structure for designing metal-oxide-based semiconducting materials.


Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 5190
Author(s):  
Cristina Medina-Bailon ◽  
Naveen Kumar ◽  
Rakshita Pritam Singh Dhar ◽  
Ilina Todorova ◽  
Damien Lenoble ◽  
...  

In this work, we present a comprehensive analytical model and results for an absolute pH sensor. Our work aims to address critical scientific issues such as: (1) the impact of the oxide degradation (sensing interface deterioration) on the sensor’s performance and (2) how to achieve a measurement of the absolute ion activity. The methods described here are based on analytical equations which we have derived and implemented in MATLAB code to execute the numerical experiments. The main results of our work show that the depletion width of the sensors is strongly influenced by the pH and the variations of the same depletion width as a function of the pH is significantly smaller for hafnium dioxide in comparison to silicon dioxide. We propose a method to determine the absolute pH using a dual capacitance system, which can be mapped to unequivocally determine the acidity. We compare the impact of degradation in two materials: SiO2 and HfO2, and we illustrate the acidity determination with the functioning of a dual device with SiO2.


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