Direct mapping of electrical noise sources in molecular wire-based devices

Cho, Duckhyung; Lee, Hyungwoo; Shekhar, Shashank; Yang, Moon Sik; Park, Jae Yeol; Hong, Sung Ju

doi:10.1038/srep43411

Cited by 13 publications

(51 citation statements)

References 39 publications

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“…The S I / I 2 exhibited a 1/ f noise behavior, as reported in previous noise studies on MoS 2 devices 11 – 14 . In our previous work, we showed that noise PSDs exhibited 1/ f 2 (or Lorentzian) noise behavior when a current noise was generated by a few trap states that had rather uniform trapping times 15 , 17 . However, noise spectra exhibited 1/ f behavior 15 – 17 when there were many trap states with various trapping times.…”

Section: Resultsmentioning

confidence: 99%

“…In our previous work, we showed that noise PSDs exhibited 1/ f 2 (or Lorentzian) noise behavior when a current noise was generated by a few trap states that had rather uniform trapping times 15 , 17 . However, noise spectra exhibited 1/ f behavior 15 – 17 when there were many trap states with various trapping times. The 1/ f noise behavior in our plot implies that the noise was generated by many different noise sources such as charge traps in the MoS 2 sample.…”

Section: Resultsmentioning

confidence: 99%

“…For example, the characteristics and origins of electrical noise in MoS 2 devices were revealed by measuring the gating effect on electrical noise in MoS 2 -based electrical channels 11 – 14 . Meanwhile, a method using a conducting atomic force microscopy (AFM) enabled the direct imaging of localized noise sources such as charge traps in materials 15 – 17 . A previous study utilized this noise microscopy method to obtain a map of the charge traps on a graphene sample 15 .…”

Section: Introductionmentioning

confidence: 99%

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Nanoscale enhancement of photoconductivity by localized charge traps in the grain structures of monolayer MoS2

Yang

Kim

Lee

et al. 2018

Sci Rep

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We report a method for mapping the nanoscale anomalous enhancement of photoconductivity by localized charge traps in the grain structures of a molybdenum disulfide (MoS2) monolayer. In this work, a monolayer MoS2 film was laterally scanned by a nanoscale conducting probe that was used to make direct contact with the MoS2 surface. Electrical currents and noise maps were measured through the probe. By analyzing the data, we obtained maps for the sheet resistance and charge trap density for the MoS2 grain structures. The maps clearly show grains for which sheet resistance and charge trap density were lower than those of the grain boundaries. Interestingly, we found an unusual inverse proportionality between the sheet resistance and charge trap density in the grains, which originated from the unique role of sulfur vacancies acting as both charge hopping sites and traps in monolayer MoS2. In addition, under light illumination, the larger the trap density of a region was, the larger the photocurrent of the region was, indicating anomalous enhancement of the photocurrent by traps. Since our method provides valuable insights to understand the nanoscale effects of traps on photoconductive charge transport, it can be a powerful tool for noise studies and the practical application of two-dimensional materials.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nanoscale enhancement of photoconductivity by localized charge traps in the grain structures of monolayer MoS2

Yang

Kim

Lee

et al. 2018

Sci Rep

Self Cite

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“…We now consider the equation of motion for the lesser Green's function which is given by (17). The expansions (18) and (19) are substituted into (17) and, as before, split based on order to give…”

Section: B Non-adiabatic Expansion Of Kadanoff-baym Equations In Wigmentioning

confidence: 99%

“…Another experimental manifestation of the currentinduced forces in molecular junctions is the telegraph noise, which is the stochastic switching over time between two different values of the electric current. Numerous studies of molecular junctions have observed a discrete switching between two or more states in the system, which can be observed via analysis of the measured time-evolution of the current through the system [15][16][17][18]20 . While the exact source of telegraph noise in molecular junctions depends on the particular experimental configuration, it is usually due to either dynamic switching between two different conformations of the molecular bridge or, more often, due to bond fluctuations of the metal-molecule contact.…”

Section: Introductionmentioning

confidence: 99%

Current-induced atomic motion, structural instabilities, and negative temperatures on molecule-electrode interfaces in electronic junctions

2020

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Molecule-electrode interfaces in molecular electronic junctions are prone to chemical reactions, structural changes, and localized heating effects caused by electric current. These can be exploited for device functionality or may be degrading processes that limit performance and device lifetime. We develop a nonequilibrium Green's function based transport theory in which the central region atoms and, more importantly, atoms on molecule-electrode interfaces are allowed to move. The separation of time-scales of slow nuclear motion and fast electronic dynamics enables the algebraic solution of the Kadanoff-Baym equations in the Wigner space. As a result, analytical expressions for dynamical corrections to the adiabatically computed Green's functions are produced. These dynamical corrections depend not only on the instantaneous molecular geometry but also on the nuclear velocities. To make the theoretical approach fully self-consistent, the same time-separation approach is used to develop expressions for the adiabatic, dissipative, and stochastic components of current-induced forces in terms of adiabatic Green's functions. Using these current induced forces, the equation of motion for the nuclear degrees of freedom is cast in the form of a Langevin equation. The theory is applied to model molecular electronic junctions. We observe that the interplay between the value of the spring constant for the molecule-electrode chemical bond and electronic coupling strength to the corresponding electrode is critical for the appearance of structural instabilities and, consequently, telegraphic switching in the electric current. The range of model parameters is identified to observe structurally stable molecular junctions as well as various different kinds of current-induced telegraphic switching. The interfacial structural instabilities are also quantified based on current noise calculations.

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Molecular Electronics

Vuillaume

2023

Beyond‐CMOS

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The term molecular junction (MJ) refers to a simple device where molecules (from a monolayer to a single molecule) are connected between two electrodes (metal or semiconductor), Fig. 1. The number of molecules in the MJ depends on the size of these electrodes and the MJs are usually classified as "large area MJ" and "single (or a few) MJ". Albeit the Langmuir-Blodgett method was used in the early times of ME to deposit molecules on the electrode surfaces (only large area MJs), chemisorption is nowadays widely used because it is also suitable at the nanoscale to attach few molecules between electrodes of a nanometer dimension. In that case, the molecules are equipped with anchor groups at both (or only one) ends. The chemical nature of the anchor group is chosen depending on the nature of the electrodes to permit a chemical reaction with the electrode by forming a chemical bond between the molecule and the electrode. Archetypes of anchor groups are thiols (-SH) on metals (Au, Ag,…), alkenes (-C=C-) on hydrogenated-silicon surfaces, a detailed review is given in Refs [14][15][16] . This approach is widely versatile to adapt the molecules on the electrodes of interest. However, this chemical link also has a pronounced effect on the global electronic properties of the MJs, mainly governing the electronic coupling between molecules and electrodes (see below in this chapter) and this point has been extensively studied (see a At the nanoscale, scanning tunneling microscope (STM) and conductive probe atomic force microscope (C-AFM), are the tools of choice to study a single or a few (typically ≲ 100) molecules (right part of Fig. 1). For single molecule experiments, STM break-junctions (STM-BJ) 25 and mechanically controlled break junctions (MCBJ) 26 have been developed (see a review 27,28 ). In these BJ approaches, the two electrodes are repeatedly (up to thousands or more) moved close and apart and a molecule bridges the electrode gap when its size matches the electrode gap. The signature of the molecule conductance appears as plateaus in the current vs. gap electrode distance traces. C-AFM is used to gently contact (weak loading force) the monolayer [29][30][31] on large surfaces and to measure the current voltage at few hundreds places on the monolayer. Another approach is the use of tiny nanodot electrodes (nanodot-molecule junction, NMJ). 32,33 In this latter case, hundreds to thousands of nanodots (typically 5-40 nm in diameter) are fabricated by e-beam lithography and can be measured in a "one shot" single C-AFM image. Note that all these techniques require a large number of measurements and a solid statistic analysis to get reliable conductance values of the MJs. Finally, another approach is to use a 2D network of metal

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Direct mapping of electrical noise sources in molecular wire-based devices

Cited by 13 publications

References 39 publications

Nanoscale enhancement of photoconductivity by localized charge traps in the grain structures of monolayer MoS2

Nanoscale enhancement of photoconductivity by localized charge traps in the grain structures of monolayer MoS2

Current-induced atomic motion, structural instabilities, and negative temperatures on molecule-electrode interfaces in electronic junctions

Molecular Electronics

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