Elevated transition temperature in Ge doped VO2 thin films

Krammer, Anna; Magrez, Arnaud; Vitale, Wolfgang A.; Mocny, Piotr; Jeanneret, Patrick; Guibert, Edouard; Whitlow, Harry J.; Ionescu, Adrian M.; Schüler, Andreas

doi:10.1063/1.4995965

Cited by 65 publications

(60 citation statements)

References 45 publications

(60 reference statements)

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“…We then predict that by controlling the amount of Ge doping, we can control the phase‐change temperature. A calculation of the total energy with the non‐magnetic and AFM spin ordering finds that the energy difference between the metallic and non‐metallic phases increases slightly, equivalent to a rise in transition temperature, as observed experimentally …”

Section: Resultssupporting

confidence: 58%

“…The spin‐pairing is weakened as a result of the overall spatial separation of V, thus reducing the gap to 0.78 eV. Krammer shows that the transition temperature can be raised by Ge doping, indicating the magnetic ground state energy is lower.…”

Section: Resultsmentioning

confidence: 99%

“…For example, if T C is near to the room temperature, and the direct bandgap lies within the visible spectrum range, then VO 2 is useful for window coatings for indoor temperature control . Various experimental reports show that alloying MgO can widen the bandgap and alloying with GeO 2 can increase the phase‐change temperature . However, there is no full explanation of these effects in simulation and some simulations show no increase in the bandgap .…”

Section: Introductionmentioning

confidence: 99%

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Density Functional Theory Studies of the Metal–Insulator Transition in Vanadium Dioxide Alloys

Robertson

2019

Physica Status Solidi (b)

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Vanadium dioxide (VO2) is of great interest because it has a metal–insulator transition involving a change in structure and electronic structure. For certain applications, it is useful to vary the bandgap and the transition temperature. Although strain can be used, another method is to alloy VO2 with oxides such as GeO2 or MgO. Herein, density functional supercell calculations are carried out on these alloys. The bandgap of the alloys does not change because the band edges of the M1 phase consist of V 3d bands, where V is sixfold bonded. However, there is also a fivefold VO2/MgO structure with a much larger bandgap of up to 2.1 eV. For Ge alloying, the structure reverts to the rutile phase but with a bandgap, because GeO2 has a rutile phase. It is also found that hydrogen doping varies the oxide gap between 0 to 1 eV. The result is consistent with experimental observations and it gives an important view to explain the mechanism of alloying.

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Section: Resultssupporting

confidence: 58%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Density Functional Theory Studies of the Metal–Insulator Transition in Vanadium Dioxide Alloys

Robertson

2019

Physica Status Solidi (b)

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“…Apart from understanding the physics of pure VO 2 , for applications it is of interest to vary the band gap of the insulating phase and vary the phase-transition temperature, while keeping the ability to switch between phases [22][23][24]. For instance, it is useful to shift the transition temperature T C towards room temperature to enhance its suitability as a smart-window coating, or to raise the T C to favor its use as a robust electrical or optical switch.…”

Section: Introductionmentioning

confidence: 99%

“…Experimentally, it is found that alloying VO 2 with MgO will widen its p-d band gap to 2.3 eV for alloying fraction n = 19% [22,23], whereas alloying VO 2 with GeO 2 will raise * jr214@cam.ac.uk its T C [24]. However, so far there is little explanation of these effects in terms of electronic structure.…”

Section: Introductionmentioning

confidence: 99%

Electronic structure of metallic and insulating phases of vanadium dioxide and its oxide alloys

Guo

Robertson

2019

Phys. Rev. Materials

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VO 2 attracts much attention due to its metal-insulator transition. Alloying VO 2 with MgO and GeO 2 allows the band gap and the transition temperature to be varied. We find that the spin order plays a key role in creating the band gap in the low-temperature M 1 phase. For MgO alloying, the alloying fraction n (Mg n V 1−n O 2−n) is varied from 12.5 to 33.3%. The minimum band gap does not change without a structural rearrangement because both band edges of insulating VO 2 consist of only V 3d states on sixfold-coordinated V sites. A crystal search finds that if the Mg fraction in the alloy is large enough (>20%), fivefold-coordinated V sites can have lower energy than the sixfold sites, and the band gaps are doubled. For GeO 2 alloying, the insulating M 1 structure reverts to rutile because GeO 2 has a rutile phase. The result matches the experimental observation and is very important in guiding VO 2 's applications such as smart coating and nonlinear resistor.

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Harnessing the Metal–Insulator Transition of VO₂ in Neuromorphic Computing

et al. 2022

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Future‐generation neuromorphic computing seeks to overcome the limitations of von Neumann architectures by colocating logic and memory functions, thereby emulating the function of neurons and synapses in the human brain. Despite remarkable demonstrations of high‐fidelity neuronal emulation, the predictive design of neuromorphic circuits starting from knowledge of material transformations remains challenging. VO2 is an attractive candidate since it manifests a near‐room‐temperature, discontinuous, and hysteretic metal–insulator transition. The transition provides a nonlinear dynamical response to input signals, as needed to construct neuronal circuit elements. Strategies for tuning the transformation characteristics of VO2 based on modification of material properties, interfacial structure, and field couplings, are discussed. Dynamical modulation of transformation characteristics through in situ processing is discussed as a means of imbuing synaptic function. Mechanistic understanding of site‐selective modification; external, epitaxial, and chemical strain; defect dynamics; and interfacial field coupling in modifying local atomistic structure, the implications therein for electronic structure, and ultimately, the tuning of transformation characteristics, is emphasized. Opportunities are highlighted for inverse design and for using design principles related to thermodynamics and kinetics of electronic transitions learned from VO2 to inform the design of new Mott materials, as well as to go beyond energy‐efficient computation to manifest intelligence.

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Elevated transition temperature in Ge doped VO2 thin films

Abstract: A metal-insulator transition study of VO 2 thin films grown on sapphire substrates

Cited by 65 publications

References 45 publications

Density Functional Theory Studies of the Metal–Insulator Transition in Vanadium Dioxide Alloys

Density Functional Theory Studies of the Metal–Insulator Transition in Vanadium Dioxide Alloys

Electronic structure of metallic and insulating phases of vanadium dioxide and its oxide alloys

Harnessing the Metal–Insulator Transition of VO₂ in Neuromorphic Computing

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Elevated transition temperature in Ge doped VO2 thin films

Abstract: A metal-insulator transition study of VO 2 thin films grown on sapphire substrates

Cited by 65 publications

References 45 publications

Density Functional Theory Studies of the Metal–Insulator Transition in Vanadium Dioxide Alloys

Density Functional Theory Studies of the Metal–Insulator Transition in Vanadium Dioxide Alloys

Electronic structure of metallic and insulating phases of vanadium dioxide and its oxide alloys

Harnessing the Metal–Insulator Transition of VO2 in Neuromorphic Computing

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Product

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Harnessing the Metal–Insulator Transition of VO₂ in Neuromorphic Computing