Trapping and Characterization of a Single Hydrogen Molecule in a Continuously Tunable Nanocavity

Wang, Hui; Li, Shaowei; He, Hong; Yu, Arthur; Toledo, Freddy; Han, Zhumin; Ho, W.; Wu, Ruqian

doi:10.1021/acs.jpclett.5b01501

Cited by 23 publications

(28 citation statements)

References 37 publications

(63 reference statements)

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“…When the distance between the second-topmost surface layers of the Au-H 2 -Au junction is set to 22.0Å (the distance between the electrodes is arbitrary, since in real experiments, it is set by the break junction setup) [38][39][40][41][42], the equilibrium distance between the electrodes' topmost layers is optimized to 17.82Å, and the conductance is 0.74G 0 , in agreement with Ref. [43].…”

Section: Resultssupporting

confidence: 70%

Current-induced phonon renormalization in molecular junctions

et al. 2016

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We explain how the electrical current flow in a molecular junction can modify the vibrational spectrum of the molecule by renormalizing its normal modes of oscillations. This is demonstrated with first-principles self-consistent transport theory, where the current-induced forces are evaluated from the expectation value of the ionic momentum operator. We explore here the case of H 2 sandwiched between two Au electrodes and show that the current produces stiffening of the transverse translational and rotational modes and softening of the stretching modes along the current direction. Such behavior is understood in terms of charge redistribution, potential drop, and elasticity changes as a function of the current.

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Section: Resultssupporting

confidence: 70%

Current-induced phonon renormalization in molecular junctions

et al. 2016

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“…The depth appears to increase rather linearly with tip charge such that energies in the range of a few hundred meV are attainable. We thus observe already in this simple system a trapping of the molecule that has been stated by Wang et al [7] for nanocavities built by an atomic environment at a surface. Additionally, the trapped H 2 in this potential well, where the tip distance can be mapped onto the tip bias, experiences a bias-dependent varying force.…”

Section: Ground Statesupporting

confidence: 79%

“…This implies that we must dispense here with charge neutrality, which would characterize normal environments of a H 2 molecule, such as in a crystal or a liquid. Oppositely charged tips are also of interest because of the voltage drop and the electric current characteristic in the H 2 bridge experiments [7][8][9][10][11][12][13]. This will be pursued in later work.…”

Section: A Hydrogen Molecule Between Two Tipsmentioning

confidence: 99%

“…There is a vast literature on these topics. Here we cite only a few examples that come closer to our investigations: Nanocavities built by atomic assembly at a metal surface with a scanning tunneling microscope (STM) [7][8][9] as well as nanogaps formed with the mechanically controllable break junction technique [10][11][12][13] are both able to hold in place, bind, and subsequently excite a hydrogen molecule (H 2 ) to perform the desired motion, e.g., vibration or rotation. At low temperatures, the interaction between the externally applied electronic current and a trapped molecule can be revealed as inelastic variations in the second derivative of the current-voltage characteristics when the bias voltage coincides with an excitation energy of the junction.…”

Section: Introductionmentioning

confidence: 98%

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Nanomechanics of a hydrogen molecule suspended between two equally charged tips

et al. 2020

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The geometric configuration and energy of a hydrogen molecule centered between two point-shaped tips of equal charge are calculated with the variational quantum Monte Carlo (QMC) method without the restriction of the Born-Oppenheimer (BO) approximation. The ground-state nuclear distribution, stability, and low-vibrational excitations are found to deviate significantly from the BO treatment based on a potential energy surface obtained with the same QMC accuracy. The quantum-mechanical distribution of the molecular axis direction and the bond length at a subnanometer level is fundamental for understanding nanomechanical dynamics with embedded hydrogen. The cylindrical symmetry of the tip arrangement yields a uniform azimuthal distribution of the molecular axis vector relative to the tip-tip axis. For fixed tip separation, the QMC sampling shows that the polar angle distribution of the molecular axis is centered around the equatorial plane for positive tip charge (transverse alignment) and around the tip-tip direction for negative tip charge (bridge alignment). These deviations from spherical symmetry are magnified as the tip-tip distance decreases. Our results thus show that the molecular orientation in the junction can be controlled by the tip charge and separation, suggesting an application in the field of molecular machines.

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“…However, it was reported that the enhanced resolution also occurs at a relatively large tip to surface distance where the Pauli repulsion is negligible [11]. A theoretical study has proposed that the enhanced resolution results from the change of the adsorption state of the trapped H 2 in the junction [12]. Hydrogen molecular junctions (HMJs) have also been studied as a simple model of molecular junctions, and conductivity and mechanical properties of the HMJs have been measured using mechanical break junction [13][14][15][16][17], STM [18][19][20], and AFM experiments [21].…”

mentioning

confidence: 99%

Enhanced resolution imaging of ultrathin ZnO layers on Ag(111) by multiple hydrogen molecules in a scanning tunneling microscope junction

et al. 2018

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Molecular hydrogen in a scanning tunneling microscope (STM) junction has been found to enhance the lateral spatial resolution of the STM imaging, referred to as scanning tunneling hydrogen microscopy (STHM). Here we report atomic resolution imaging of 2-and 3-monolayer (ML) thick ZnO layers epitaxially grown on Ag(111) using STHM. The enhanced resolution can be obtained at a relatively large tip to surface distance and resolves a more defective structure exhibiting dislocation defects for 3-ML-thick ZnO than for 2 ML. In order to elucidate the enhanced imaging mechanism, the electric and mechanical properties of the hydrogen molecular junction (HMJ) are investigated by a combination of STM and atomic force microscopy. It is found that the HMJ shows multiple kinklike features in the tip to surface distance dependence of the conductance and frequency shift curves, which are absent in a hydrogen-free junction. Based on a simple modeling, we propose that the junction contains several hydrogen molecules and sequential squeezing of the molecules out of the junction results in the kinklike features in the conductance and frequency shift curves. The model also qualitatively reproduces the enhanced resolution image of the ZnO films.

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Trapping and Characterization of a Single Hydrogen Molecule in a Continuously Tunable Nanocavity

Abstract: KEYWORDS: Nanocavity, nano-reactors, vibrational and rotational modes, scanning tunneling microscope, electronic density of states, van der Waals interaction. + These two authors contributed equally to this work.

Cited by 23 publications

References 37 publications

Current-induced phonon renormalization in molecular junctions

Current-induced phonon renormalization in molecular junctions

Nanomechanics of a hydrogen molecule suspended between two equally charged tips

Enhanced resolution imaging of ultrathin ZnO layers on Ag(111) by multiple hydrogen molecules in a scanning tunneling microscope junction

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