Band gap of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Ge</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mn>111</mml:mn><mml:mo>)</mml:mo></mml:mrow><mml:mi>c</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mn>2</mml:mn><mml:mo>×</mml:mo><mml:mn>8</mml:mn><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math>surface by scanning tunneling spectroscopy

Feenstra, R. M.; Lee, J. Y.; Kang, Myung Ho; Meyer, Gerhard; Rieder, Karl–Heinz

doi:10.1103/physrevb.73.035310

Cited by 81 publications

(22 citation statements)

References 28 publications

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“…To extract the position of onset bias from measured (dI/dV)/(I/V), STS modeling was employed as shown by the dashed lines; the detailed method is described in previous STM/STS studies. 46,47 Note the standard error is obtained by the fitting process in STS. The given uncertainties provided by the present fitting employing leastsquares fitting are statistical, are less than thermal broadening, and do not account for band edge states.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Growth Mode Transition from Monolayer by Monolayer to Bilayer by Bilayer in Molecularly Flat Titanyl Phthalocyanine Film

et al. 2017

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To avoid defects associated with inhomogeneous crystallites and uneven morphology that degrade organic device performance, the deposition of ultraflat and homogeneous crystalline organic active layers is required. The growth mode transition of organic semiconducting titanyl phthalocyanine (TiOPc) molecule from monolayer-by-monolayer to bilayerby-bilayer can be observed on highly ordered pyrolytic graphic (HOPG), while maintaining large and molecularly flat domains. The first monolayer of TiOPc lies flat on HOPG with a ∼98% face-up orientation. However, as the thickness of the TiOPc increases to over 15 monolayers (ML), the growth mode transitions to bilayer-by-bilayer with the repeated stacking of bilayers (BL), each of which has face-to-face pairs. Density functional theory calculations reveal that the increasing of thickness induces weakening of the substrate effect on the deposited TiOPc layers, resulting in the growth mode transition to BL-by-BL. The asymmetric stacking provides the driving force to maintain nearly constant surface order during growth, allowing precise, subnanometer thickness control and large domain growth. ■ INTRODUCTIONAlthough inorganic Si and III-V materials have led the modern semiconductor industry for half a century, the integration of organic thin films has been expanded to microelectronics for displays, solar cells, and platforms for electronic skins. 1−8 These organic thin film transistors (OTFT) and organic photovoltaics (OPV) provide low cost, mechanical flexibility, and direct bandgap modulation for electroluminescence. In flexible organic electronics, molecular orientation, degree of crystallinity, and morphology govern carrier transport and injection between organic layers and electrodes; 9−14 therefore, the development of homogeneous crystalline organic channels on flexible electrodes is crucial. Taking advantage of its high strength and enhanced photovoltaic efficiency during deformation, graphene has recently been employed as a flexible electrode for OTFTs and OPV. 15−17 Therefore, to fabricate flexible organic devices integrated onto graphene electrodes, it is essential to deposit organic layers on graphene, while maintaining the growth of ultraflat large domains. Moreover, the growth of organic layers with nearly atomic flat surfaces and large domain sizes is not only required to template uniform deposition of organic heterostructures but may also enable bandgap engineering of the contacts.The growth of aromatic organic films relies on van der Waals interactions between organic molecules. 18−20 During the deposition of organic layers, the growth of the films can involve directional molecular packing, resulting from the shape anisotropy of molecules. In many cases, the molecule−substrate interaction is stronger than molecule−molecule interaction; therefore, the molecules form a flat monolayer on substrates in the initial growth stage. 20−22 However, upon additional organic molecular deposition, the molecule−substrate interaction can be overwhelmed by molecule−molecule inte...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Growth Mode Transition from Monolayer by Monolayer to Bilayer by Bilayer in Molecularly Flat Titanyl Phthalocyanine Film

et al. 2017

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“…For instance, the apparent gap measured with tunneling spectroscopy can significantly differ from the intrinsic bandgap in the density of states of the sample, as it has been observed, e.g., on the surfaces of Ge(111) [9], FeS 2 (100) [10], and ZnO [11]. Moreover, TIBB can also cause the ionization of donors/acceptors in the semiconductor [12][13][14], and the effect has even been used in tip-induced quantum dot experiments [15].…”

Section: Introductionmentioning

confidence: 99%

“…Being able to quantitatively calculate TIBB is necessary for the interpretation of data: Only if the values of TIBB are known, can the intrinsic bandgap be retrieved from the data, and the binding energies of the donors/acceptors can be extracted. Using the known dielectric constants and carrier concentration, this is often done for semiconductors with a Poisson's equation solver developed by Feenstra [16], yielding apparent bandgaps around 15-20% larger than the intrinsic ones [9,10].…”

Section: Introductionmentioning

confidence: 99%

Poor electronic screening in lightly doped Mott insulators observed with scanning tunneling microscopy

et al. 2017

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The effective Mott gap measured by scanning tunneling microscopy (STM) in the lightly doped Mott insulator (Sr 1−x La x ) 2 IrO 4 differs greatly from values reported by photoemission and optical experiments. Here we show that this is a consequence of the poor electronic screening of the tip-induced electric field in this material. Such effects are well known from STM experiments on semiconductors and go under the name of tip-induced band bending (TIBB). We show that this phenomenon also exists in the lightly doped Mott insulator (Sr 1−x La x ) 2 IrO 4 and that, at doping concentrations of x 4%, it causes the measured energy gap in the sample density of states to be bigger than the one measured with other techniques. We develop a model able to retrieve the intrinsic energy gap leading to a value which is in rough agreement with other experiments, bridging the apparent contradiction.At doping x ≈ 5% we further observe circular features in the conductance layers that point to the emergence of a significant density of free carriers in this doping range and to the presence of a small concentration of donor atoms. We illustrate the importance of considering the presence of TIBB when doing STM experiments on correlated-electron systems and discuss the similarities and differences between STM measurements on semiconductors and lightly doped Mott insulators.

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“…As commonly observed in tunneling experiments on semiconductors, a tip-induced band bending [23] alters the absolute energy scale and complicates the interpretation of the spectra, especially at low temperatures. In particular, the experimental gaps are usually overestimated [24,25]. Figures 3(f) and 3(g) show the tip-sample energy diagram of the junction at equilibrium (V tip = 0).…”

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confidence: 99%

“…3(k)], because an accumulation of holes occurs at the top of the valence band at low voltages. These holes strongly screen the tip's negative charge at higher voltages [24].…”

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confidence: 99%

Atomic and electronic structure of a Rashbap–njunction at the BiTeI surface

et al. 2014

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The non-centro-symmetric semiconductor BiTeI exhibits two distinct surface terminations that support spinsplit Rashba surface states. Their ambipolarity can be exploited for creating spin-polarized p-n junctions at the boundaries between domains with different surface terminations. We use scanning tunneling microscopy (STM) and spectroscopy (STS) to locate such junctions and investigate their atomic and electronic properties. The Te-and I-terminated surfaces are identified owing to their distinct chemical reactivity and an apparent height mismatch of electronic origin. The Rashba surface states are revealed in the STS spectra by the onset of a van Hove singularity at the band edge. Eventually, an electronic depletion is found on interfacial Te atoms, consistent with the formation of a space-charge area in typical p-n junctions. In inversion-asymmetric systems, the spin-orbit interaction lifts the spin degeneracy. This effect can occur either at surfaces (the Rashba-Bychkov effect [1]) or in the bulk of non-centro-symmetric crystals (the Rashba-Dresselhaus effect [2,3]). Such Rashba systems are promising candidates for manipulating electron spin by means of electric field in the context of emerging spintronic devices [4]. Significant research efforts are currently directed toward the search of materials exhibiting a "giant" Rashba effect that would enable nanometer-scale spintronic devices operating at room temperature. To date, the largest spin splitting, measured by angle-resolved photoemission spectroscopy (ARPES), has been reported in the BiAg 2 /Ag(111) surface alloy [5] and both the surface and bulk states of non-centro-symmetric semiconductor BiTeI [6][7][8][9].In BiTeI, photoemission data show two distinct types of surface domains with different surface terminations (Te and I) and opposite surface band bendings that support p-or n-type surface states [8]. We anticipate that Rashba p-n junctions can be observed at the boundaries between such domains. This can be used for fulfilling another requirement for fabricating logic devices-ambipolarity, which is the possibility to control carriers' nature (electrons or holes). Moreover, a number of novel transport phenomena have been predicted for p-n junctions in systems with strong spin-orbit coupling [10][11][12][13] that can be further exploited in practical applications. In view of applications, the questions of current dissipation to the bulk or controlled growth of the junction by epitaxy are important, but well beyond the scope of this paper. Here, cleaved BiTeI is rather considered as a toy-system providing a quite unique opportunity to study a p-n junction in two dimensions.In this work, we employ scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) to locate and investigate p-n junctions naturally occurring at a cleaved BiTeI surface. The surface domains with Te and I terminations are identified owing to their distinct chemical reactivity, apparent height, and electronic structure. The onset of a van * cedric.tournier@epfl.ch Hov...

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Band gap of theGe(111)c(2×8)surface by scanning tunneling spectroscopy

Cited by 81 publications

References 28 publications

Growth Mode Transition from Monolayer by Monolayer to Bilayer by Bilayer in Molecularly Flat Titanyl Phthalocyanine Film

Growth Mode Transition from Monolayer by Monolayer to Bilayer by Bilayer in Molecularly Flat Titanyl Phthalocyanine Film

Poor electronic screening in lightly doped Mott insulators observed with scanning tunneling microscopy

Atomic and electronic structure of a Rashbap–njunction at the BiTeI surface

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