Prediction of stable hafnium carbides: Stoichiometries, mechanical properties, and electronic structure

Zeng, Qingfeng; Peng, Junhui; Oganov, Artem R.; Zhu, Qiang; Xie, Congwei; Zhang, Xiaodong; Dong, Dong; Zhang, Litong; Cheng, Laifei

doi:10.1103/physrevb.88.214107

Cited by 61 publications

(55 citation statements)

References 39 publications

(31 reference statements)

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“…[34][35][36][37][38] The stability of the three low-index Miller surfaces has been studied in detail for HfC, 39 which is consistent with previous theoretical studies for the HfC surfaces 40,41 that the (001) surface is the most stable one. These calculations have provided a large number of insights and helped to answer the long standing questions about the interpretation of experimental measurements.…”

Section: The Models and Calculation Detailssupporting

confidence: 71%

Efficient noble metal nanocatalysts supported on HfC(001) for O2 dissociation

Wang

Zhang

et al. 2017

AIP Advances

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The adsorption and dissociation of O2 on the M4 (M=Au, Pd, Pt) clusters supported on HfC(001) (Hafnium Carbide) are investigated using ab initio density functional theory calculations. The geometric and electronic structures are analyzed in detail. It is found that the dissociation barriers of O2 on Au4/HfC(001) (0.26 eV), Pd4/HfC(001) (0.49 eV) and Pt4/HfC(001) (0.09 eV) are much smaller than those on the clean surfaces of HfC(001) (1.60 eV), Au(111) (1.37 eV), Pd(111) (1.0 and 0.91 eV) and Pt(111) (0.27–0.7 eV), respectively. The low dissociation barriers imply that the Pt4/HfC(001) exhibits the highest catalytic activity for O2 dissociation, and the Au4/HfC(001) and Pd4/HfC(001) may also be possible substitutes with lower cost for the current Pt/C catalyst for O2 dissociation. The present study is conductive to designing new efficient noble metal catalyst using HfC support for efficiently promoting O2 dissociation.

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Section: The Models and Calculation Detailssupporting

confidence: 71%

Efficient noble metal nanocatalysts supported on HfC(001) for O2 dissociation

Wang

Zhang

et al. 2017

AIP Advances

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“…Since conducting filaments in RRAM devices are modeled as aggregation of oxygen vacancies, this process might occur in such devices due to Joule heating which easily can produce temperature of several 100 degrees given the nano diameter of the filaments. In our experiments, we have two possible sources of carbon, the incorporated carbon during thin film growth with a concentration of 2·10 19 /cm³, or adsorbed carbon-based molecules due to the ex situ processing of our samples. In order to distinguish between these two sources, we have performed the following experiments: Two films of highly deficient hafnium oxide were synthesized in the same deposition.…”

Section: Fig 2 (B)(i) and (Ii) Shows The Variation Of The Componentsmentioning

confidence: 99%

“…The valence band spectra can then be interpreted as hybridized C-p and Hf-d states. 19 There is no change in the O1s core line as compared to lower temperatures. It can always be refined by one peak originating from Hf-O bonds (see Fig.…”

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confidence: 93%

“…1 shows the depth profile of a 100 nm thick oxygen deficient HfO2-x thin film deposited on c-cut sapphire. Based on the nearly constant intensity for the carbon C -signal between 20 and 80 nm film depth, a carbon concentration of 2·10 19 /cm³ was determined. This concentration is comparably low to known carbon concentrations for ALD-grown films, which are in the range of 7·10 19 /cm³.…”

mentioning

confidence: 99%

“…Based on the nearly constant intensity for the carbon C -signal between 20 and 80 nm film depth, a carbon concentration of 2·10 19 /cm³ was determined. This concentration is comparably low to known carbon concentrations for ALD-grown films, which are in the range of 7·10 19 /cm³. 17 The source of carbon impurities in the here described experiments is residual graphite from the UHV chamber due to the use of carbon spray.…”

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confidence: 99%

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Hafnium carbide formation in oxygen deficient hafnium oxide thin films

Rodenbücher

Hildebrandt

Szot

et al. 2016

Applied Physics Letters

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On highly oxygen deficient thin films of hafnium oxide (hafnia, HfO2-x) contaminated with adsorbates of carbon oxides the formation of hafnium carbide (HfCx) at the surface during vacuum annealing at temperatures as low as 600 °C is reported. Using X-ray photoelectron spectroscopy the evolution of the HfCx surface layer related to a transformation from insulating into metallic state is monitored in situ. In contrast, for fully stoichiometric HfO2 thin films prepared and measured under identical conditions, the formation of HfCx was not detectable suggesting that the enhanced adsorption of carbon oxides on oxygen deficient films provides a carbon source for the carbide formation. This shows that a high concentration of oxygen vacancies in carbon contaminated hafnia lowers considerably the formation energy of hafnium carbide. Thus the presence of a sufficient amount of residual carbon in resistive random access memory devices might lead to a similar carbide formation within the conducting filaments due to Joule heating. HfO2 (hafnia) has been studied extensively in the last decades as a high- dielectric being used as replacement of the standard gate dielectric SiO2 in order to produce high-density logic and memory devices.1 Furthermore, it was found that HfO2 can undergo a local insulator-metal (IM) transition under the influence of an electric field opening up the possibility to use it as resistive switching material in redox-based random access memories (RRAM). 2,3During resistive switching in HfO2, a local redox reaction associated with a formation or modification of conducting filaments takes place, in which the movement of oxygen vacancies plays the key role for the modulation of the electric properties. [4][5][6] Hence, the investigation of the behavior of oxygen vacancies is important for RRAM device performance.In contrast to the local insulator-metal transition as observed in conducting filaments in HfO2 on the nanoscale, also a global insulator-metal transition on a macroscopic scale has been found in oxygen deficient hafnium oxide thin films grown by molecular beam epitaxy (MBE). 7,8 The oxygen deficiency in these films is created during growth under oxygen deficient conditions leading to a homogeneous distribution of oxygen vacancies. With increasing amount of oxygen vacancies, the band gap is consistently reduced and defect states inside the gap eventually form a defect band at the Fermi level.7,8 RRAM devices based on these films show forming free resistive switching and the forming voltage is independent on the thickness of the highly oxygen deficient HfO2-x layer. 9,10 In this paper we discuss the reaction of carbon impurities to hafnium carbide and its influence on hafnium oxide-based resistive switching. The role of carbon impurities is of extremely high importance, as they are inherent to most of today's deposition techniques commonly used for fabricating complementary metal oxide semiconductor (CMOS) devices, such as atomic layer deposition (ALD) based on organic precursors. Based on an in-ope...

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Indirect phase transition of TiC, ZrC, and HfC crystal structures

Abavare

Dodoo

Uchida

et al. 2016

Physica Status Solidi (b)

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We have performed first‐principles calculations to analyze the electronic structures, static, and dynamical structural stabilities of the pressure‐induced phase transformation of refractory compounds (transition‐metal carbides) from NaCl‐type (B1) to CsCl‐type (B2) via zinc‐blende phase using the plane‐wave pseudopotential approach in the framework of the generalized gradient approximation (GGA) for the exchange and correlation functional. The ground‐state properties, equilibrium lattice constant, bulk moduli, and band structures are determined for the stoichiometry of the compounds and compared with known experimental and theoretical values. We find that the phase‐transition pressure for the indirect phase transition from B1→B2 via zinc‐blende structure is about 17‐fold for TiC, 12‐fold for both ZrC and HfC, respectively, when compared with the direct phase transition. Calculated phonon instability exists for the CsCl‐B2 phase, which can prevent the structures from forming and contrary to the zinc‐blende and the NaCl‐B1 phases. The band dispersion and electronic density of states for B1 and B2 crystal phases were explored and found to indicate metallic character in contrast with the zinc‐blende phase, which has a pseudogap opening in the bandgap region suggesting a semiconducting property and also a frequency gap in the phonon spectrum.

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Prediction of stable hafnium carbides: Stoichiometries, mechanical properties, and electronic structure

Cited by 61 publications

References 39 publications

Efficient noble metal nanocatalysts supported on HfC(001) for O2 dissociation

Efficient noble metal nanocatalysts supported on HfC(001) for O2 dissociation

Hafnium carbide formation in oxygen deficient hafnium oxide thin films

Indirect phase transition of TiC, ZrC, and HfC crystal structures

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