Real-time atomistic observation of structural phase transformations in individual hafnia nanorods

Hudak, Bethany M.; Depner, Sean W.; Waetzig, Gregory R.; Talapatra, Anjana; Arróyave, Raymundo; Banerjee, Sarbajit; Guiton, Beth S.

doi:10.1038/ncomms15316

Cited by 61 publications

(71 citation statements)

References 52 publications

(94 reference statements)

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“…Assuming that the nucleation and growth behavior in HZO thin film follows the JMA model, the natural logarithm of the transformed m-phase ratio versus annealing time is plotted in Figure 3. However, the obtained dimensionality factors are quite low compared to the normal n value (between 1 and 3) reported, [28][29][30] although it is comparable to the value of ≈0.3, obtained by Toriumi et al [15] They, however, did not conduct further analysis on such low dimensionality, even though the dimensionality of the nucleation and growth to be less than 1 is difficult to comprehend. Rest of the constant values are summarized in Table 1.…”

Section: Resultssupporting

confidence: 38%

“…The slope of the best-fitted line indicates the dimensionality of the nucleation and growth behavior, which came out to be 0.17-0.37 and 0.20-0.44 for PMA and PDA samples for all temperature ranges. [28,29] When the value is equivalent to 1, it refers to a constant nucleation and growth time. The slope value increment as annealing temperature increases indicates a faster transformation rate into the m-phase as the RTA temperature increases, which is a reasonable outcome considering that the t-to-m phase transformation is a thermally activated process.…”

Section: Resultsmentioning

confidence: 99%

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Nucleation‐Limited Ferroelectric Orthorhombic Phase Formation in Hf_0.5Zr_0.5O₂ Thin Films

Lee

Hyun

Kim

et al. 2018

Adv Elect Materials

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Various possibilities have been proposed as the cause of the doped‐ or undoped‐HfO2 thin film materials showing unusual ferroelectricity. These assumptions are based on empirical results, yet finding the origin of the unprecedented ferroelectricity within HfO2 has suffered from a serious gap between its theoretical calculation, mostly based on thermodynamic approach and the actual experimental results. To fill the gap, this study proposes to consider the kinetic energy, providing the evidence of the kinetic energy barrier upon a phase transformation from the tetragonal phase to the monoclinic phase affected by the TiN top electrode (capping layer). 10 nm thick Hf0.5Zr0.5O2 thin films are deposited and annealed with or without the TiN capping layer with subsequent annealing at different time and temperature. Arrhenius plot is constructed to obtain the activation energy for the tetragonal‐to‐monoclinic phase transformation by calculating the amount of the transformed phase using X‐ray diffraction pattern. Johnson–Mehl–Avrami and nucleation‐limited transformation models are utilized to describe the characteristic nucleation and growth time and calculate the activation energy for the monoclinic phase transformation of the Hf0.5Zr0.5O2 thin film. Both models demonstrate that the TiN capping layer provides a kinetic energy barrier for tetragonal‐to‐monoclinic phase transformation and enhances the ferroelectric property.

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Section: Resultssupporting

confidence: 38%

Section: Resultsmentioning

confidence: 99%

Nucleation‐Limited Ferroelectric Orthorhombic Phase Formation in Hf_0.5Zr_0.5O₂ Thin Films

Lee

Hyun

Kim

et al. 2018

Adv Elect Materials

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“…There might be a thermal contraction with decreasing temperature, but the magnitude of change is small when the TEC of HfO 2 and Si substrate are considered. [52,53] Park et al recently estimated the activation energy for the t-phase to m-phase transition in ferroelectric Hf 0.5 Zr 0.5 O 2 thin film, and received a value of about 315 meV f.u. When the temperature is higher than about 500 °C, the o111 diffraction peak strongly shifts to lower 2θ values, implying an increase of the unit cell volume.…”

Section: Wwwadvelectronicmatdementioning

confidence: 99%

Effect of Annealing Ferroelectric HfO₂ Thin Films: In Situ, High Temperature X‐Ray Diffraction

Park

Chung

Schenk

et al. 2018

Adv Elect Materials

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crystalline phase in doped HfO 2 thin film. [17,18] However, this phase cannot be observed in the phase diagram of bulk HfO 2 and ZrO 2 , [19,20] even when doped with elements that are used in the thin film counterparts. [21] Therefore, multiple factors were suggested as origin of the stabilization of the ferroelectric phase. Materlik et al. suggested that the o-phase can be stabilized due to surface energy effects, [22] and Park et al. comprehensively examined the surface energy model and their experimental observations. [23] In the latter study, it was confirmed that the o-phase can be stabilized within the nuclei formed during the atomic layer deposition (ALD) process, but the interface/grain boundary effect is not sufficient to stabilize the o-phase within the final grain size after annealing. [23] Therefore, it was suggested that the crystalline phase of the initial nuclei can remain even after crystallization, implying that the phase transformation to the monoclinic phase (m-phase, space group: P2 1 /c) can be kinetically suppressed. [23,24] Stress in thin films was also suggested as a possible origin, [1,25,26] and Shiraishi et al. experimentally proved that the polymorphism of Hf 0.5 Zr 0.5 O 2 thin films is strongly affected by the thermal expansion coefficient (TEC) of the used substrate. [27] However, the detailed mechanism of the formation of the unexpected o-phase is not yet resolved.It is generally known that the structure and electrical properties of perovskite ferroelectrics are strongly coupled. [28][29][30] The ferroelectric properties of doped HfO 2 thin films are also believed to be determined by their crystalline structure. ParkThe ferroelectricity in fluorite oxides has gained increasing interest due to its promising properties for multiple applications in semiconductor as well as energy devices. The structural origin of the unexpected ferroelectricity is now believed to be the formation of a non-centrosymmetric orthorhombic phase with the space group of Pca2 1 . However, the factors driving the formation of the ferroelectric phase are still under debate. In this study, to understand the effect of annealing temperature, the crystallization process of doped HfO 2 thin films is analyzed using in situ, high-temperature X-ray diffraction. The change in phase fractions in a multiphase system accompanied with the unit cell volume increase during annealing could be directly observed from X-ray diffraction analyses, and the observations give an information toward understanding the effect of annealing temperature on the structure and electrical properties. A strong coupling between the structure and the electrical properties is reconfirmed from this result.

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“…In a 2D system, however, the GBs are exposed, and their movement in response to thermal annealing can be observed in real time using STEM . Taking advantage of this to monitor and analyze such GB motion, we grew few‐layer MoSe 2 films by molecular beam epitaxy (MBE) and transferred them onto microelectromechanical systems (MEMS)‐based heating chips for the in situ annealing experiments (see Experimental Section) …”

Section: Methodsmentioning

confidence: 99%

Healing of Planar Defects in 2D Materials via Grain Boundary Sliding

Zhao

Chen

et al. 2019

Advanced Materials

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carrier traps, and reduce coherence in light emission. The growth of single phase TMDC films is complicated by the intralayer sliding in each monolayer (resulting in polymorphs, as in 1T and 1H) [9,10] and interlayer sliding in multilayer films (creating different stacking polytypes, for example, 2H and 3R). [7,11] The inherent threefold symmetry as well as fluctuations in chemical potential during growth, coupled with the small energy barriers for rotation and translation of the atomic layers, provides many possibilities for freezing-in dislocations and stacking faults.Among the different CVD approaches, van der Waals (vdW) epitaxy has emerged as the most promising approach to grow large-scale highly crystalline TMDC films, although the films are not free of stacking faults. [12] The key to the success of vdW epitaxy lies in the fact that the surface of 2D TMDC has no dangling bonds, thereby relaxing the lattice matching conditions between the two crystals. Nevertheless, our previous studies have shown that the interlayer vdW interaction between two atomic layers is sufficiently strong to align the grains so that stacking configurations with the lowest energy can be attained, [4,7] which has implications for the healing of planar defects.In polycrystalline TMDCs, GBs are intrinsic 1D topological defects which divide the film into a cellular network of Understanding the mechanisms and kinetics of defect annihilations, particularly at the atomic scale, is important for the preparation of highquality crystals for realizing the full potential of 2D transition metal dichalcogenides (TMDCs) in electronics and quantum photonics. Herein, by performing in situ annealing experiments in an atomic resolution scanning transmission electron microscope, it is found that stacking faults and rotational disorders in multilayered 2D crystals can be healed by grain boundary (GB) sliding, which works like a "wiper blade" to correct all metastable phases into thermodynamically stable phases along its trace. The driving force for GB sliding is the gain in interlayer binding energy as the more stable phase grows at the expanse of the metastable ones. Density functional theory calculations show that the correction of 2D stacking faults is triggered by the ejection of Mo atoms in mirror twin boundaries, followed by the collective migrations of 1D GB. The study highlights the role of the often-neglected interlayer interactions for defect repair in 2D materials and shows that exploiting these interactions has significant potential for obtaining large-scale defect-free 2D films. 2D MaterialsLarge-scale growth of single-crystalline transition metal dichalcogenide (TMDC) films with a low density of defects is yet to be realized, posing a bottleneck for implementing 2D electronics in industrial applications. To date, most chemical vapor deposition (CVD) grown films are polycrystalline and contain multiple imperfections, such as point defects, [1,2] line defects, [3] grain boundaries (GBs), [4,5] stacking faults, [6,7] and rotational disorder, ...

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Real-time atomistic observation of structural phase transformations in individual hafnia nanorods

Cited by 61 publications

References 52 publications

Nucleation‐Limited Ferroelectric Orthorhombic Phase Formation in Hf_0.5Zr_0.5O₂ Thin Films

Nucleation‐Limited Ferroelectric Orthorhombic Phase Formation in Hf_0.5Zr_0.5O₂ Thin Films

Effect of Annealing Ferroelectric HfO₂ Thin Films: In Situ, High Temperature X‐Ray Diffraction

Healing of Planar Defects in 2D Materials via Grain Boundary Sliding

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Real-time atomistic observation of structural phase transformations in individual hafnia nanorods

Cited by 61 publications

References 52 publications

Nucleation‐Limited Ferroelectric Orthorhombic Phase Formation in Hf0.5Zr0.5O2 Thin Films

Nucleation‐Limited Ferroelectric Orthorhombic Phase Formation in Hf0.5Zr0.5O2 Thin Films

Effect of Annealing Ferroelectric HfO2 Thin Films: In Situ, High Temperature X‐Ray Diffraction

Healing of Planar Defects in 2D Materials via Grain Boundary Sliding

Contact Info

Product

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About

Nucleation‐Limited Ferroelectric Orthorhombic Phase Formation in Hf_0.5Zr_0.5O₂ Thin Films

Nucleation‐Limited Ferroelectric Orthorhombic Phase Formation in Hf_0.5Zr_0.5O₂ Thin Films

Effect of Annealing Ferroelectric HfO₂ Thin Films: In Situ, High Temperature X‐Ray Diffraction