Surface Conductance near the Order-Disorder Phase Transition on Si(100)

Yoo, Kyung Seun; Weitering, Hanno H.

doi:10.1103/physrevlett.87.026802

Cited by 22 publications

(25 citation statements)

References 24 publications

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“…One can obtain a rough estimate of a charging time from the 2D conductivity σ S ¼ ρe 2 ℓ∕m Ã e υ F , which gives ca. 4 × 10 −3 Ω −1 ∕□ when the Fermi velocity υ F ≈ 1 × 10 4 m∕s, the effective mass m Ã e ≈ 0.1m e , the carrier density ρ ≈ 2 × 10 12 ∕cm 2 , and the mean free path ℓ ≈ 10 nm of the surface state are used (20,21); it takes approximately 10 −15 s for a quantum dot of 10-nm radius to be filled by 10 electrons at band bending of 0.1 V, which is too short by 8 orders of magnitude. The large discrepancy between the estimated charging time and our data raises the intriguing possibility that two different timescales exist in charging dynamics, one for charging of the quantum capacitor and another for deexcitation of a quantum dot.…”

Section: Resultsmentioning

confidence: 99%

Time-resolved energy transduction in a quantum capacitor

Jung

Cho

Kim

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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The capability to deposit charge and energy quantum-by-quantum into a specific atomic site could lead to many previously unidentified applications. Here we report on the quantum capacitor formed by a strongly localized field possessing such capability. We investigated the charging dynamics of such a capacitor by using the unique scanning tunneling microscopy that combines nanosecond temporal and subangstrom spatial resolutions, and by using Si(001) as the electrode as well as the detector for excitations produced by the charging transitions. We show that sudden switching of a localized field induces a transiently empty quantum dot at the surface and that the dot acts as a tunable excitation source with subangstrom site selectivity. The timescale in the deexcitation of the dot suggests the formation of long-lived, excited states. Our study illustrates that a quantum capacitor has serious implications not only for the bottom-up nanotechnology but also for future switching devices.field switching | silicon | soliton C harge and energy transfers play a key role in the chemical and physical processes in materials. Manipulating the flow of energy and charge quantum-by-quantum into a specific site with the subangstrom precision would not only shed light on excitation dynamics, but also provide the capability to control the interactions at the atomic and molecular level. Manipulating their flows typically takes a form of atomically localized, dynamically switchable external field. Understanding the interaction between charge and such field may help us to handle the challenges of bottom-up nanotechnology. Scanning tunneling microscopy (STM) is capable of providing the necessary spatial resolution and highly localized field (1, 2). It had been demonstrated that the atomistic control of direct deposition of charge and energy is possible in many applications such as desorption (3), single molecular synthesis (4), dissociation (5, 6), and configuration switching (7) just to name a few, by using STM.Unexplored thus far, another route one may exploit to deposit charge and energy site selectively is the quantum dot. In a capacitor whose lateral dimension is in the subnanoscale, the strongly confined electric field between the electrodes would not only induce extra charge on their surfaces, but also place the charge in a quantum dot. Dynamic discharging and charging of such a quantum dot may serve as a unique excitation source. Conversely, energy dissipation through a quantum capacitor has serious implications for future switching devices by raising the unavoidable minimum energy cost for the logic operation (8). Such a subnanosize capacitor can be realized between the STM tip and the conducting counterelectrode. On semiconductor surfaces without conducting surface states such as InAs (110), a zero-dimensional quantum dot is formed in the bulk by tip-induced localized band bending (9). Typical STM geometry produces capacitance on the order of 10 −18 F (10), and thus the dot may be charged with only a few electrons per volt.Ordin...

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Section: Resultsmentioning

confidence: 99%

Time-resolved energy transduction in a quantum capacitor

Jung

Cho

Kim

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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“…It has been assigned to low temperature freezing of specific surface electronic channels whose energies are located within the electronic bulk band gap [5]. Recent measurements of the total surface conductivity of the Si(100) surface [7] have shown that, on the contrary, the surface conductivity increases at low temperature. One cannot completely exclude that the conductivity of the specific surface electronic channels whose energies are located within the bulk band gap would decrease at low temperature whereas the total surface conductivity would increase.…”

Section: Highly Doped N-type Si(100)mentioning

confidence: 99%

Low-temperature electron transport on semiconductor surfaces

Lastapis

Riedel

Mayne

et al. 2003

Low Temperature Physics

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The low-temperature electron transport on semiconductor surfaces has been studied using an ultrahigh-vacuum, variable temperature scanning tunneling microscope (STM). The STM I(V) spectroscopy performed at various temperatures has made it possible to investigate the temperature dependence (300 K to 35 K) of the surface conductivity of three different semiconductor surfaces: highly doped n-type Si(100), p-type Si(100), and hydrogenated C(100). Low temperature freezing of specific surface electronic channels on the highly doped n-type Si(100) and moderately doped p-type Si(100) surfaces could be achieved, whereas the total surface conductivity on the hydrogenated C(100) surface can be frozen below only 180 K.

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“…Apart from the substrate bulk conductance, however, electrical transport within the surface states of clean Si͑001͒ may contribute to curve a. In fact, the surface state conductance of a clean SOI͑001͒ surface has been determined by Yoo and Weitering 25,26 as Ϸ2.5ϫ 10 −6 ⍀ −1 at a temperature of 200 K, showing a clear signature of the c͑4 ϫ 2͒ → 2 ϫ 1 orderdisorder phase transition at about 200 K and an increase by a factor of 3 as the temperature is decreased to 140 K. While the absolute value of the sheet conductance of our clean Si͑001͒ substrate is on the order of the result of Refs. 25 and 26 for the surface state contribution, our data show no sign of the structural phase transition, and the sheet conductance varies by only Ϸ20% in the temperature range 140-220 K. Furthermore, we do not observe significant changes of the conductance upon the deposition of the first 0.5 ML Cs, which would be expected if the Si͑001͒ surface states contributed significantly.…”

Section: Dependence On Temperaturementioning

confidence: 99%

“…In this way we obtain an upper limit for the space charge layer conductance because the mobilities at the surface are always reduced with respect to the bulk values due to scattering at surface roughness. 25,26 At the clean dimerized Si͑001͒ surface the Fermi level is pinned by surface defects 28 at 0.4 eV above VBM. 27 The band bending upon Cs adsorption was estimated from photo emission spectroscopy data by Chao et al 18 As Si core level spectra show, the Fermi level shifts by 0.15 eV towards VBM after initial Cs deposition and then by 0.45 eV towards the conduction band minimum till the saturation coverage at room temperature is reached.…”

Section: Surface Contribution To the Sheet Conductancementioning

confidence: 99%

Electrical transport in ultrathin Cs layers on Si(001)

et al. 2005

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Electrical transport in ultrathin Cs layers on Si͑001͒ has been studied combining macroscopic conductivity measurements with low-energy electron diffraction, energy loss spectroscopy, and measurements of the work function. At temperatures around 150 K, growth of the first three atomic layers proceeds layer-by-layer. The completion of each layer correlates with stepwise increases of the surface sheet conductance with coverage. Calibrating the Cs coverage by combined conductivity and work function measurements, the areal density of a single atomic layer is determined as 0.5 monolayers ͑3.39ϫ 10 14 cm −2 ͒. Electron spectroscopy reveals a semiconductor-metal transition of the surface upon completion of the first atomic layer, which correlates with the onset of a macroscopically measured sheet conductance in the 10 −5 ⍀ −1 range. While the conductance can be ascribed to electrical transport within surface states, its dependence on temperature indicates an activation barrier, which, most likely, is due to domain boundaries. At coverages of one monolayer and beyond, the Cs/ Si͑001͒ surface exhibits a high metal-like conductance in the 10 −3 ⍀ −1 range.

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Surface Conductance near the Order-Disorder Phase Transition on Si(100)

Cited by 22 publications

References 24 publications

Time-resolved energy transduction in a quantum capacitor

Time-resolved energy transduction in a quantum capacitor

Low-temperature electron transport on semiconductor surfaces

Electrical transport in ultrathin Cs layers on Si(001)

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