Growth mechanism for nanotips in high electric fields

Jansson, Ville; Baibuz, Ekaterina; Kyritsakis, Andreas; Vigonski, Simon; Zadin, Vahur; Parviainen, S.; Aabloo, Alvo; Djurabekova, Flyura

doi:10.1088/1361-6528/ab9327

Cited by 24 publications

(16 citation statements)

References 51 publications

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“…Most of these breakdown events are related to the presence on the cathode of micro/nano-protrusions, whose shape and density depend on the surface roughness 4 . Besides, such protrusions may also emerge and evolve via electromigration 5 and field-induced surface atom diffusion 6 . Locally enhancing at their apex the high applied electric field, these protrusions act as field electron emitters.…”

Section: Introductionmentioning

confidence: 99%

Unveiling the Nottingham Inversion Instability during the thermo-field emission from refractory metal micro-protrusions

Mofakhami

Seznec

Minea

et al. 2021

Sci Rep

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The electron emission by micro-protrusions has been studied for over a century, but the complete explanation of the unstable behaviors and their origin remains an open issue. These systems often evolve towards vacuum breakdown, which makes experimental studies of instabilities very difficult. Modeling studies are therefore necessary. In our model, refractory metals have shown the most striking results for discontinuities or jumps recorded on the electron emitted current under high applied voltages. Herein, we provide evidence on the mechanisms responsible for the initiation of a thermal instability during the field emission from refractory metal micro-protrusions. A jump in the emission current at steady state is found beyond a threshold electric field, and it is correlated to a similar jump in temperature. These jumps are related to a transient runaway of the resistive heating that occurs after the Nottingham flux inversion. That causes the hottest region to move beneath the apex, and generates an emerging heat reflux towards the emitting surface. Two additional conditions are required to initiate the runaway. The emitter geometry must ensure a large emission area and the thermal conductivity must be high enough at high temperatures so that the heat reflux can significantly compete with the heat diffusion towards the thermostat. The whole phenomenon, that we propose to call the Nottingham Inversion Instability, can explain unexpected thermal failures and breakdowns observed with field emitters.

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Section: Introductionmentioning

confidence: 99%

Unveiling the Nottingham Inversion Instability during the thermo-field emission from refractory metal micro-protrusions

Mofakhami

Seznec

Minea

et al. 2021

Sci Rep

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show abstract

“…Thus, even at moderate electric field val-ues the formation of such surface protrusion becomes expectable. Moreover, once the protrusion growth is initiated, positive feedback loops, as reported in [39,40], can become active, finally leading to the breakdown events.…”

Section: Discussionmentioning

confidence: 99%

“…Recent kinetic Monte Karlo simulations [17] have shown that starting from surface protrusions of a few nm size, larger scale field-enhancing tips can grow due to the biased diffusion effect [18,19]. However, the dynamics and the possible mechanisms behind the formation of the initial nano-protrusions has not been explored yet.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Spontaneous Surface Modifications on Polycrystalline Cu Due to Electric Fields

et al. 2021

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We present a credible mechanism of spontaneous field emitter formation in high electric field applications, such as Compact Linear Collider in CERN (The European Organization for Nuclear Research). Discovery of such phenomena opens new pathway to tame the highly destructive and performance limiting vacuum breakdown phenomena. Vacuum breakdowns in particle accelerators and other devices operating at high electric fields is a common problem in the operation of these devices. It has been proposed that the onset of vacuum breakdowns is associated with appearance of surface protrusions while the device is in operation under high electric field. Moreover, the breakdown tolerance of an electrode material was correlated with the type of lattice structure of the material. Although biased diffusion under field has been shown to cause growth of significantly field-enhancing tips starting from initial nm-size protrusions, the mechanisms and the dynamics of the growth of the latter have not been studied yet. In the current paper we conduct molecular dynamics simulations of nanocrystalline copper surfaces and show the possibility of protrusion growth under the stress exerted on the surface by an applied electrostatic field. We show the importance of grain boundaries on the protrusion formation and establish a linear relationship between the necessary electrostatic stress for protrusion formation and the temperature of the system. Finally, we show that the time for protrusion formation decreases with the applied electrostatic stress, we give the Arrhenius extrapolation to the case of lower fields, and we present a general discussion of the protrusion formation mechanisms in the case of polycrystalline copper surfaces.

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“…[35,37,[45][46][47][48]). We use the same ν also for second-nearest jumps and exchange processes, as discussed in [49]. The migration energy E m will depend on the local environment of the transitions; i.e.…”

Section: Theorymentioning

confidence: 99%

Growth mechanism for nanotips in high electric fields

Jansson,

Baibuz,

Kyritsakis

et al. 2019

Preprint

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In this work we show using atomistic simulations that the biased diffusion in high electric field gradients may cause growth of nanotips from small surface asperities. It has long been known that atoms on a metallic surface have biased diffusion if electric fields are applied and that microscopic tips may be sharpened using fields, but the exact mechanisms have not been well understood. Our Kinetic Monte Carlo simulation model uses a recently developed theory for how the migration barriers are affected by the presence of an electric field. All parameters of the model are physically motivated and no fitting parameters are used. The model has been validated by reproducing characteristic faceting patterns of tungsten surfaces that have in previous experiments been observed to only appear in the presence of strong electric fields. The growth effect is found to be enhanced by increasing fields and temperatures.

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Growth mechanism for nanotips in high electric fields

Cited by 24 publications

References 51 publications

Unveiling the Nottingham Inversion Instability during the thermo-field emission from refractory metal micro-protrusions

Unveiling the Nottingham Inversion Instability during the thermo-field emission from refractory metal micro-protrusions

Mechanism of Spontaneous Surface Modifications on Polycrystalline Cu Due to Electric Fields

Growth mechanism for nanotips in high electric fields

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