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Christian Joachim - One of the best experts on this subject based on the ideXlab platform.
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electronic properties of a single Dangling Bond and of Dangling Bond wires on a si 001 h surface
On-surface atomic wires and logic gates, 2017Co-Authors: Hiroyo Kawai, Christian Joachim, Olga Neucheva, T L Yap, Mark SaeysAbstract:Single Dangling Bonds created on a Si(001):H surface are considered as potential fundamental building blocks for the fabrication of atom-scale electronic circuits. Therefore, it is critical to characterize the structural and electronic properties of single Dangling Bonds to begin to design and construct such devices. Using low-temperature scanning tunneling spectroscopy, imaging, density functional theory, and quantum transport calculations, we demonstrate the influence of doping, charging, and buckling on the electronic properties of a single Dangling Bond and a line of Dangling Bonds created along a dimer row.
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band engineering of Dangling Bond wires on the si 100 h surface
2017Co-Authors: Roberto Robles, Christian Joachim, Michael Kepenekian, Ricardo Rurali, Nicolas LorenteAbstract:Nanoscale devices need to be connected among them and to the macroscopic world. Ideally, interconnects embedded in the environment holding the device will have an undeniable practical and technological advantage. Since silicon surfaces dominate nano- and micro-technologies, the crafting of nanowires on these surfaces has been suggested to be the way to create effective interconnecting wires. Here, we review the work done on Dangling-Bond wires formed by removing passivated agents from the Si(100)-H surface. These wires are formed by adjacent Dangling Bonds that rehybridize and create a surface-confined band structure capable of driving charge and spin along the surface. Unfortunately, the 1-D character of these wires leads to instabilities that create band gaps. The way to go is then to engineer the band gaps so as to create low-gap systems or directly metallic wires. Two strategies are reviewed in this chapter. One is the atom manipulation of wires to find the geometries that favored low-gap Dangling-Bond wires. The second one is the use of doping to change the electronic properties of the wires.
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electronic characterization of a single Dangling Bond on n and p type si 001 2 1 h
Surface Science, 2016Co-Authors: Hiroyo Kawai, Christian Joachim, Olga Neucheva, T L Yap, Mark SaeysAbstract:Single Dangling Bonds created on a Si(001):H surface have emerged as the fundamental building block for the construction of atom-scale electronic circuits. A detailed characterization of the electronic properties of a single Dangling Bond is therefore critical. Combining low-temperature scanning tunneling spectroscopy, imaging, density functional theory and quantum transport calculations, we demonstrate the strong influence of substrate doping, charging and buckling on the electronic properties of a depassivated Si atom.
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interaction of a conjugated polyaromatic molecule with a single Dangling Bond quantum dot on a hydrogenated semiconductor
Physical Chemistry Chemical Physics, 2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Mark Saeys, Marek Kolmer, Antonio M. Echavarren, Mads Engelund, Rafal Zuzak, Aran Garcialekue, Christian JoachimAbstract:Controlling the strength of the coupling between organic molecules and single atoms provides a powerful tool for tuning electronic properties of single-molecule devices. Here, using scanning tunneling microscopy and spectroscopy (STM/STS) supported by theoretical modeling, we study the interaction of a planar organic molecule (trinaphthylene) with a hydrogen-passivated Ge(001):H substrate and a single Dangling Bond quantum dot on that surface. The electronic structure of the molecule adsorbed on the hydrogen-passivated surface is similar to the gas phase structure and the measurements show that HOMO and LUMO states contribute to the STM filled and empty state images, respectively. Furthermore, we show that the electronic properties are not significantly affected when the molecule is attached to the single Dangling Bond, which is in contrast with the strong interaction of the molecule with a Dangling Bond dimer. Our results show that the Dangling Bond quantum dots could stabilize organic molecules on a hydrogenated semiconductor without affecting their originally designed gas phase electronic properties. Together with the ability to laterally manipulate the molecules on the surface, this will be advantageous in the construction of single-molecule devices, where the coupling and positioning of the molecules on the substrate could be tuned by a proper design of the surface quantum dot arrays, comprising both single and dimerized Dangling Bonds.
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Single-Molecule Rotational Switch on a Dangling Bond Dimer Bearing
2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Christian Joachim, Marek Kolmer, Rafał Zuzak, Antonio M. Echavarren, Marek Szymonski, Mark SaeysAbstract:One of the key challenges in the construction of atomic-scale circuits and molecular machines is to design molecular rotors and switches by controlling the linear or rotational movement of a molecule while preserving its intrinsic electronic properties. Here, we demonstrate both the continuous rotational switching and the controlled step-by-step single switching of a trinaphthylene molecule adsorbed on a Dangling Bond dimer created on a hydrogen-passivated Ge(001):H surface. The molecular switch is on-surface assembled when the covalent Bonds between the molecule and the Dangling Bond dimer are controllably broken, and the molecule is attached to the dimer by long-range van der Waals interactions. In this configuration, the molecule retains its intrinsic electronic properties, as confirmed by combined scanning tunneling microscopy/spectroscopy (STM/STS) measurements, density functional theory calculations, and advanced STM image calculations. Continuous switching of the molecule is initiated by vibronic excitations when the electrons are tunneling through the lowest unoccupied molecular orbital state of the molecule. The switching path is a combination of a sliding and rotation motion over the Dangling Bond dimer pivot. By carefully selecting the STM conditions, control over discrete single switching events is also achieved. Combined with the ability to create Dangling Bond dimers with atomic precision, the controlled rotational molecular switch is expected to be a crucial building block for more complex surface atomic-scale devices
Valeri Afanasev - One of the best experts on this subject based on the ideXlab platform.
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generation of si Dangling Bond defects at si insulator interfaces induced by oxygen scavenging
Physica Status Solidi B-basic Solid State Physics, 2014Co-Authors: Florin Cerbu, Valeri Afanasev, A P D Nguyen, Jacek Kepa, Andre StesmansAbstract:In this work we analyse the influence of the O-scavenging process on interface traps in (100)Si/SiOx/HfO2(1.8 nm)/TiNx/Si stacks by using electrical measurements and electron spin resonance spectroscopy. The reduction of interfacial SiOx by high-temperature annealing in O-free ambient is found to lead to severe interface degradation exposed as generation of additional Si Dangling Bond defects (paramagnetic Pb0 centres). The density of these centres, well known to be electron traps impairing device operation, increases from ∼1 × 1012 cm−2 – the value typical for thermally oxidized Si – to >3 × 1012 cm−2 upon annealing at 1100 °C. This interface degradation is accompanied by the development of a hysteresis in the MOS capacitance–voltage curves indicating generation of additional oxide traps with areal density in the range of 1012 cm−2. However, the trap generation can be alleviated if the O-scavenging annealing step is performed in helium ambient, suggesting formation of silicon monoxide molecules at the Si/SiOx interface as the origin of the observed trap generation.
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impact of strain on the passivation efficiency of ge Dangling Bond interface defects in condensation grown sio2 gexsi1 x sio2 100 si structures with nm thin gexsi1 x layers
Applied Surface Science, 2014Co-Authors: Oreste Madia, Valeri Afanasev, Andre Stesmans, Laurent Souriau, A P D Nguyen, N H Thoan, J Slotte, Filip TuomistoAbstract:Abstract Hydrogen passivation of germanium Dangling Bond defects observed as paramagnetic GePb1 centers at the GexSi1−x/SiO2 interfaces is studied as a function of Ge concentration and thickness of the GexSi1−x layer. By correlating the results obtained by three independent defect-sensitive methods – electron spin resonance spectroscopy, ac conductance of the GexSi1−x layer, and the positron annihilation spectroscopy – with the results of strain measurements by high-resolution X-ray diffractometry, we found that the density of the Ge Dangling Bonds reflects residual strain in the GexSi1−x layer. Furthermore, in the layers with high strain the hydrogen passivation efficiency of Dangling Bonds is found to decrease, suggesting a considerable spread in the activation energies of the passivation/depassivation reactions.
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inherent si Dangling Bond defects at the thermal 110 si sio 2 interface
Physical Review B, 2011Co-Authors: Koen Keunen, Andre Stesmans, Valeri AfanasevAbstract:Stimulated by the growing manifestation in advanced semiconductor device development, an extensive multifrequency electron spin resonance (ESR) study has been carried out on the thermal (110)Si/SiO${}_{2}$ interface in terms of occurring paramagnetic point defects as a function of oxidation temperature ${T}_{\mathit{ox}}$ (200--1125 \ifmmode^\circ\else\textdegree\fi{}C), with seclusion of the H-passivation factor. The main type of defect observed is a P${}_{\mathrm{b}}$-type interface center closely related to the P${}_{\mathrm{b}}$${}^{(111)}$ and P${}_{\mathrm{b}0}$${}^{(100)}$ variants (Si${}_{3}$ \ensuremath{\equiv} Si${}^{\ifmmode\bullet\else\textbullet\fi{}}$) characteristic for the (111) and (100)Si faces, respectively. The inferred principal g matrix values (${g}_{//}$ = 2.0018 and ${g}_{\ensuremath{\perp}}$ = 2.0082 for ${T}_{\mathit{ox}}$ = 800 \ifmmode^\circ\else\textdegree\fi{}C), splitting parameters of the resolved ${}^{29}$Si hyperfine doublet, and line width behavior closely resemble those of P${}_{\mathrm{b}0}$${}^{(100)}$, from which the defect is typified as P${}_{\mathrm{b}0}$${}^{(110)}$. For low ${T}_{\mathit{ox}}$, an unexpectedly high density of P${}_{\mathrm{b}0}$${}^{(110)}$ defects (\ensuremath{\sim}7 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}2}$) is observed, which gradually dwindles for ${T}_{\mathit{ox}}$ increasing above \ensuremath{\sim}700 \ifmmode^\circ\else\textdegree\fi{}C to approach \ensuremath{\sim}4 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}2}$ for ${T}_{\mathit{ox}}$ \ensuremath{\rightarrow} 1125 \ifmmode^\circ\else\textdegree\fi{}C. The behavior is related to interfacial stress release as a result of global structural relaxation of the top SiO${}_{2}$ layer, an effect also signaled by attendant alterations in ESR parameters, including a drop in ESR line width and a change in line shape symmetry and ${g}_{\ensuremath{\perp}}$. Comparison with previous ESR data on (111)Si/SiO${}_{2}$ and (100)Si/SiO${}_{2}$ interfaces indicates that, in terms of P${}_{\mathrm{b}}$ type, the (110) face is the worst of all three low-index Si interfaces, i.e., [P${}_{\mathrm{b}0}$${}^{(100)}$] [P${}_{\mathrm{b}}$${}^{(111)}$] [P${}_{\mathrm{b}0}$${}^{(110)}$], in contrast with the common electrically inferred interface trap density order; only for ${T}_{\mathit{ox}}$ \ensuremath{\geqslant} 900 \ifmmode^\circ\else\textdegree\fi{}C does the (110) face slightly improve on the (111)Si one, raising caution with the application of (110)Si/SiO${}_{2}$ in terms of vulnerability during device operation. The comparison further shows that, unlike a textbook quote, the density of occurring P${}_{\mathrm{b}(0)}$ centers is not found to be proportional to Si surface areal atom density or available Si Bond density. Instead, an empirically inferred matching criterion appears to be the surface areal Si atom density scaled by the number of Bonds per atom directed into the oxide. Besides P${}_{\mathrm{b}0}$${}^{(110)}$, an apparently isotropic second type of interface center is revealed, baptized ${I}_{\mathrm{x}}$, at $g$ = 2.0048 with a density of \ensuremath{\sim}1 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}2}$ that is rather independent of ${T}_{\mathit{ox}}$. Showing a similar passivation behavior in H${}_{2}$ as the P${}_{\mathrm{b}0}$${}^{(110)}$ center, it is also interpreted as a Si Dangling-Bond-type defect, now residing in an interfacial randomized Si environment---a variant of the D center.
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electronic properties of ge Dangling Bond centers at si1 xgex sio2 interfaces
Applied Physics Letters, 2009Co-Authors: Valeri Afanasev, Andre Stesmans, Michel Houssa, Laurent Souriau, Roger Loo, Marc MeurisAbstract:Comparison between densities of paramagnetic Ge Dangling Bond defects and shallow acceptor traps at interfaces of the condensation-grown Si1−xGex layers (0.28≤x≤0.93) with thermal SiO2 as a function of Ge fraction, x, reveals quantitative agreement. Moreover, defect densities detected in both magnetic resonance and electrical experiments exhibit reversible passivation-depassivation behavior with respect to hydrogen indicating observation of the same defect (Ge Pb1 center). The corresponding energy level is estimated to lie at 0.35±0.10 eV above the valence band in bulk Si, which makes these defects behave as shallow acceptors in Ge-rich Si1−xGex.
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nontrigonal ge Dangling Bond interface defect in condensation grown 100 si1 xgex sio2
Physical Review B, 2009Co-Authors: Andre Stesmans, P Somers, Valeri AfanasevAbstract:Multifrequency electron-spin-resonance (ESR) study has revealed a nontrigonal Ge Dangling Bond (DB)-type interface defect in ${\text{SiO}}_{2}/(100){\text{Ge}}_{x}{\text{Si}}_{1\ensuremath{-}x}/{\text{SiO}}_{2}/\text{Si}$ heterostructures grown by the condensation method. The center, exhibiting monoclinic-I $({C}_{2v})$ symmetry, with principal $g$ values ${g}_{1}=2.0338\ifmmode\pm\else\textpm\fi{}0.0003$, ${g}_{2}=2.038\text{ }6\ifmmode\pm\else\textpm\fi{}0.000\text{ }6$, and ${g}_{3}=2.005\text{ }4$ and lowest $g$ value (DB) direction $24\ifmmode\pm\else\textpm\fi{}2\ifmmode^\circ\else\textdegree\fi{}$ off a $⟨111⟩$ direction toward the [100] interface normal, is observed in maximum densities for $x\ensuremath{\sim}0.7$, the signal disappearing for $x\ensuremath{\le}0.45$ and $x\ensuremath{\ge}0.93$. Neither $\text{Si}\text{ }{P}_{b}$ type nor trigonal Ge Dangling Bond defects is observed, enabling unobscured spectral analysis. Based on its ESR parameters, including $g$ matrix and symmetry, it is suggested to concern a $\text{Ge}\text{ }{P}_{b1}$-type center, that is, not a trigonal basic $\text{Ge}\text{ }{P}_{b(0)}$-type center $({\text{Ge}}_{3}\ensuremath{\equiv}{\text{Ge}}^{\ifmmode\bullet\else\textbullet\fi{}})$, thus exposing a unique interface mismatch healing as function of substrate Ge fraction. Its properties are discussed within the context of the thus far elusive role of interfacial Ge DB defects in Ge insulator structures, encompassing theoretical inferences.
Szymon Godlewski - One of the best experts on this subject based on the ideXlab platform.
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interaction of a conjugated polyaromatic molecule with a single Dangling Bond quantum dot on a hydrogenated semiconductor
Physical Chemistry Chemical Physics, 2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Mark Saeys, Marek Kolmer, Antonio M. Echavarren, Mads Engelund, Rafal Zuzak, Aran Garcialekue, Christian JoachimAbstract:Controlling the strength of the coupling between organic molecules and single atoms provides a powerful tool for tuning electronic properties of single-molecule devices. Here, using scanning tunneling microscopy and spectroscopy (STM/STS) supported by theoretical modeling, we study the interaction of a planar organic molecule (trinaphthylene) with a hydrogen-passivated Ge(001):H substrate and a single Dangling Bond quantum dot on that surface. The electronic structure of the molecule adsorbed on the hydrogen-passivated surface is similar to the gas phase structure and the measurements show that HOMO and LUMO states contribute to the STM filled and empty state images, respectively. Furthermore, we show that the electronic properties are not significantly affected when the molecule is attached to the single Dangling Bond, which is in contrast with the strong interaction of the molecule with a Dangling Bond dimer. Our results show that the Dangling Bond quantum dots could stabilize organic molecules on a hydrogenated semiconductor without affecting their originally designed gas phase electronic properties. Together with the ability to laterally manipulate the molecules on the surface, this will be advantageous in the construction of single-molecule devices, where the coupling and positioning of the molecules on the substrate could be tuned by a proper design of the surface quantum dot arrays, comprising both single and dimerized Dangling Bonds.
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Single-Molecule Rotational Switch on a Dangling Bond Dimer Bearing
2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Christian Joachim, Marek Kolmer, Rafał Zuzak, Antonio M. Echavarren, Marek Szymonski, Mark SaeysAbstract:One of the key challenges in the construction of atomic-scale circuits and molecular machines is to design molecular rotors and switches by controlling the linear or rotational movement of a molecule while preserving its intrinsic electronic properties. Here, we demonstrate both the continuous rotational switching and the controlled step-by-step single switching of a trinaphthylene molecule adsorbed on a Dangling Bond dimer created on a hydrogen-passivated Ge(001):H surface. The molecular switch is on-surface assembled when the covalent Bonds between the molecule and the Dangling Bond dimer are controllably broken, and the molecule is attached to the dimer by long-range van der Waals interactions. In this configuration, the molecule retains its intrinsic electronic properties, as confirmed by combined scanning tunneling microscopy/spectroscopy (STM/STS) measurements, density functional theory calculations, and advanced STM image calculations. Continuous switching of the molecule is initiated by vibronic excitations when the electrons are tunneling through the lowest unoccupied molecular orbital state of the molecule. The switching path is a combination of a sliding and rotation motion over the Dangling Bond dimer pivot. By carefully selecting the STM conditions, control over discrete single switching events is also achieved. Combined with the ability to create Dangling Bond dimers with atomic precision, the controlled rotational molecular switch is expected to be a crucial building block for more complex surface atomic-scale devices
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Single-Molecule Rotational Switch on a Dangling Bond Dimer Bearing
ACS Nano, 2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Christian Joachim, Marek Kolmer, Rafał Zuzak, Antonio M. Echavarren, Marek Szymonski, Mark SaeysAbstract:One of the key challenges in the construction of atomic-scale circuits and molecular machines is to design molecular rotors and switches by controlling the linear or rotational movement of a molecule while preserving its intrinsic electronic properties. Here, we demonstrate both the continuous rotational switching and the controlled step-by-step single switching of a trinaphthylene molecule adsorbed on a Dangling Bond dimer created on a hydrogen-passivated Ge(001):H surface. The molecular switch is on-surface assembled when the covalent Bonds between the molecule and the Dangling Bond dimer are controllably broken, and the molecule is attached to the dimer by long-range van der Waals interactions. In this configuration, the molecule retains its intrinsic electronic properties, as confirmed by combined scanning tunneling microscopy/spectroscopy (STM/STS) measurements, density functional theory calculations, and advanced STM image calculations. Continuous switching of the molecule is initiated by vibronic excitations when the electrons are tunneling through the lowest unoccupied molecular orbital state of the molecule. The switching path is a combination of a sliding and rotation motion over the Dangling Bond dimer pivot. By carefully selecting the STM conditions, control over discrete single switching events is also achieved. Combined with the ability to create Dangling Bond dimers with atomic precision, the controlled rotational molecular switch is expected to be a crucial building block for more complex surface atomic-scale devices.
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Diels-Alder attachment of a planar organic molecule to a Dangling Bond dimer on a hydrogenated semiconductor surface
Physical Chemistry Chemical Physics, 2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Marek Kolmer, Antonio M. Echavarren, Mads Engelund, Rafal Zuzak, Aran Garcia-lekue, Gerard Novell-leruth, Daniel Sanchez-portal, Christian JoachimAbstract:Construction of single-molecule electronic devices requires the controlled manipulation of organic molecules and their properties. This could be achieved by tuning the interaction between the molecule and individual atoms by local “on-surface” chemistry, i.e., the controlled formation of chemical Bonds between the species. We demonstrate here the reversible attachment of a planar conjugated polyaromatic molecule to a pair of unpassivated Dangling Bonds on a hydrogenated Ge(001):H surface via a Diels–Alder [4+2] addition using the tip of a scanning tunneling microscope (STM). Due to the small stability difference between the covalently Bonded and a nearly undistorted structure attached to the Dangling Bond dimer by long-range dispersive forces, we show that at cryogenic temperatures the molecule can be switched between both configurations. The reversibility of this covalent Bond forming reaction may be applied in the construction of complex circuits containing organic molecules with tunable properties.
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tunneling spectroscopy of close spaced Dangling Bond pairs in si 001 h
Scientific Reports, 2015Co-Authors: Mads Engelund, Szymon Godlewski, Marek Kolmer, Rafal Zuzak, Aran Garcialekue, Thomas Frederiksen, Daniel Sanchezportal, Marek SzymonskiAbstract:We present a combined experimental and theoretical study of the electronic properties of close-spaced Dangling-Bond (DB) pairs in a hydrogen-passivated Si(001):H p-doped surface. Two types of DB pairs are considered, called “cross” and “line” structures. Our scanning tunneling spectroscopy (STS) data show that, although the spectra taken over different DBs in each pair exhibit a remarkable resemblance, they appear shifted by a constant energy that depends on the DB-pair type. This spontaneous asymmetry persists after repeated STS measurements. By comparison with density functional theory (DFT) calculations, we demonstrate that the magnitude of this shift and the relative position of the STS peaks can be explained by distinct charge states for each DB in the pair. We also explain how the charge state is modified by the presence of the scanning tunneling microscopy (STM) tip and the applied bias. Our results indicate that, using the STM tip, it is possible to control the charge state of individual DBs in complex structures, even if they are in close proximity. This observation might have important consequences for the design of electronic circuits and logic gates based on DBs in passivated silicon surfaces.
Andre Stesmans - One of the best experts on this subject based on the ideXlab platform.
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Dangling Bond defects in silicon passivated strained si 1 x ge x channel layers
Journal of Materials Science: Materials in Electronics, 2020Co-Authors: Oreste Madia, Jacek Kepa, V V Afanasev, J Franco, B Kaczer, Andriy Hikavyy, Andre StesmansAbstract:Dangling Bond defects (DBs) in silicon-passivated (1- or 3-nm thick Si cap) strained-(100)Si1−xGex (x = 0.25–0.55) layers at interfaces with 1.8-nm thick HfO2 gate dielectric are studied by means of Electron Spin Resonance (ESR) spectroscopy. The results suggest a dominant contribution of Si DBs (Pb0 centers), a considerable fraction of which is located at the interface between the Si substrate crystal and the pseudomorphic Si1−xGex film. The density of Si DBs in the Ge containing samples is significantly lower than at the reference (100)Si/ HfO2 interface and decreases below the ESR detection limit (≈ 0.8 × 1011cm−2) with increasing thickness and Ge concentration in the Si1−xGex layer. However, the beneficial effect of Ge becomes less pronounced when the thickness of the Si cap is reduced to 1 nm or in the case of direct deposition of HfO2 on top of uncapped Si1−xGex. From these observations we conclude that DBs are eliminated due to in-diffusion of Ge from the Si1−xGex channel into interfacial Si layers, bringing the concentration of Ge to the range in which generation of Si DBs becomes energetically unfavourable, in agreement with previous observations on condensation-grown Si1−xGex layers.
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generation of si Dangling Bond defects at si insulator interfaces induced by oxygen scavenging
Physica Status Solidi B-basic Solid State Physics, 2014Co-Authors: Florin Cerbu, Valeri Afanasev, A P D Nguyen, Jacek Kepa, Andre StesmansAbstract:In this work we analyse the influence of the O-scavenging process on interface traps in (100)Si/SiOx/HfO2(1.8 nm)/TiNx/Si stacks by using electrical measurements and electron spin resonance spectroscopy. The reduction of interfacial SiOx by high-temperature annealing in O-free ambient is found to lead to severe interface degradation exposed as generation of additional Si Dangling Bond defects (paramagnetic Pb0 centres). The density of these centres, well known to be electron traps impairing device operation, increases from ∼1 × 1012 cm−2 – the value typical for thermally oxidized Si – to >3 × 1012 cm−2 upon annealing at 1100 °C. This interface degradation is accompanied by the development of a hysteresis in the MOS capacitance–voltage curves indicating generation of additional oxide traps with areal density in the range of 1012 cm−2. However, the trap generation can be alleviated if the O-scavenging annealing step is performed in helium ambient, suggesting formation of silicon monoxide molecules at the Si/SiOx interface as the origin of the observed trap generation.
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impact of strain on the passivation efficiency of ge Dangling Bond interface defects in condensation grown sio2 gexsi1 x sio2 100 si structures with nm thin gexsi1 x layers
Applied Surface Science, 2014Co-Authors: Oreste Madia, Valeri Afanasev, Andre Stesmans, Laurent Souriau, A P D Nguyen, N H Thoan, J Slotte, Filip TuomistoAbstract:Abstract Hydrogen passivation of germanium Dangling Bond defects observed as paramagnetic GePb1 centers at the GexSi1−x/SiO2 interfaces is studied as a function of Ge concentration and thickness of the GexSi1−x layer. By correlating the results obtained by three independent defect-sensitive methods – electron spin resonance spectroscopy, ac conductance of the GexSi1−x layer, and the positron annihilation spectroscopy – with the results of strain measurements by high-resolution X-ray diffractometry, we found that the density of the Ge Dangling Bonds reflects residual strain in the GexSi1−x layer. Furthermore, in the layers with high strain the hydrogen passivation efficiency of Dangling Bonds is found to decrease, suggesting a considerable spread in the activation energies of the passivation/depassivation reactions.
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inherent si Dangling Bond defects at the thermal 110 si sio 2 interface
Physical Review B, 2011Co-Authors: Koen Keunen, Andre Stesmans, Valeri AfanasevAbstract:Stimulated by the growing manifestation in advanced semiconductor device development, an extensive multifrequency electron spin resonance (ESR) study has been carried out on the thermal (110)Si/SiO${}_{2}$ interface in terms of occurring paramagnetic point defects as a function of oxidation temperature ${T}_{\mathit{ox}}$ (200--1125 \ifmmode^\circ\else\textdegree\fi{}C), with seclusion of the H-passivation factor. The main type of defect observed is a P${}_{\mathrm{b}}$-type interface center closely related to the P${}_{\mathrm{b}}$${}^{(111)}$ and P${}_{\mathrm{b}0}$${}^{(100)}$ variants (Si${}_{3}$ \ensuremath{\equiv} Si${}^{\ifmmode\bullet\else\textbullet\fi{}}$) characteristic for the (111) and (100)Si faces, respectively. The inferred principal g matrix values (${g}_{//}$ = 2.0018 and ${g}_{\ensuremath{\perp}}$ = 2.0082 for ${T}_{\mathit{ox}}$ = 800 \ifmmode^\circ\else\textdegree\fi{}C), splitting parameters of the resolved ${}^{29}$Si hyperfine doublet, and line width behavior closely resemble those of P${}_{\mathrm{b}0}$${}^{(100)}$, from which the defect is typified as P${}_{\mathrm{b}0}$${}^{(110)}$. For low ${T}_{\mathit{ox}}$, an unexpectedly high density of P${}_{\mathrm{b}0}$${}^{(110)}$ defects (\ensuremath{\sim}7 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}2}$) is observed, which gradually dwindles for ${T}_{\mathit{ox}}$ increasing above \ensuremath{\sim}700 \ifmmode^\circ\else\textdegree\fi{}C to approach \ensuremath{\sim}4 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}2}$ for ${T}_{\mathit{ox}}$ \ensuremath{\rightarrow} 1125 \ifmmode^\circ\else\textdegree\fi{}C. The behavior is related to interfacial stress release as a result of global structural relaxation of the top SiO${}_{2}$ layer, an effect also signaled by attendant alterations in ESR parameters, including a drop in ESR line width and a change in line shape symmetry and ${g}_{\ensuremath{\perp}}$. Comparison with previous ESR data on (111)Si/SiO${}_{2}$ and (100)Si/SiO${}_{2}$ interfaces indicates that, in terms of P${}_{\mathrm{b}}$ type, the (110) face is the worst of all three low-index Si interfaces, i.e., [P${}_{\mathrm{b}0}$${}^{(100)}$] [P${}_{\mathrm{b}}$${}^{(111)}$] [P${}_{\mathrm{b}0}$${}^{(110)}$], in contrast with the common electrically inferred interface trap density order; only for ${T}_{\mathit{ox}}$ \ensuremath{\geqslant} 900 \ifmmode^\circ\else\textdegree\fi{}C does the (110) face slightly improve on the (111)Si one, raising caution with the application of (110)Si/SiO${}_{2}$ in terms of vulnerability during device operation. The comparison further shows that, unlike a textbook quote, the density of occurring P${}_{\mathrm{b}(0)}$ centers is not found to be proportional to Si surface areal atom density or available Si Bond density. Instead, an empirically inferred matching criterion appears to be the surface areal Si atom density scaled by the number of Bonds per atom directed into the oxide. Besides P${}_{\mathrm{b}0}$${}^{(110)}$, an apparently isotropic second type of interface center is revealed, baptized ${I}_{\mathrm{x}}$, at $g$ = 2.0048 with a density of \ensuremath{\sim}1 \ifmmode\times\else\texttimes\fi{} 10${}^{12}$ cm${}^{\ensuremath{-}2}$ that is rather independent of ${T}_{\mathit{ox}}$. Showing a similar passivation behavior in H${}_{2}$ as the P${}_{\mathrm{b}0}$${}^{(110)}$ center, it is also interpreted as a Si Dangling-Bond-type defect, now residing in an interfacial randomized Si environment---a variant of the D center.
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electronic properties of ge Dangling Bond centers at si1 xgex sio2 interfaces
Applied Physics Letters, 2009Co-Authors: Valeri Afanasev, Andre Stesmans, Michel Houssa, Laurent Souriau, Roger Loo, Marc MeurisAbstract:Comparison between densities of paramagnetic Ge Dangling Bond defects and shallow acceptor traps at interfaces of the condensation-grown Si1−xGex layers (0.28≤x≤0.93) with thermal SiO2 as a function of Ge fraction, x, reveals quantitative agreement. Moreover, defect densities detected in both magnetic resonance and electrical experiments exhibit reversible passivation-depassivation behavior with respect to hydrogen indicating observation of the same defect (Ge Pb1 center). The corresponding energy level is estimated to lie at 0.35±0.10 eV above the valence band in bulk Si, which makes these defects behave as shallow acceptors in Ge-rich Si1−xGex.
Marek Kolmer - One of the best experts on this subject based on the ideXlab platform.
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interaction of a conjugated polyaromatic molecule with a single Dangling Bond quantum dot on a hydrogenated semiconductor
Physical Chemistry Chemical Physics, 2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Mark Saeys, Marek Kolmer, Antonio M. Echavarren, Mads Engelund, Rafal Zuzak, Aran Garcialekue, Christian JoachimAbstract:Controlling the strength of the coupling between organic molecules and single atoms provides a powerful tool for tuning electronic properties of single-molecule devices. Here, using scanning tunneling microscopy and spectroscopy (STM/STS) supported by theoretical modeling, we study the interaction of a planar organic molecule (trinaphthylene) with a hydrogen-passivated Ge(001):H substrate and a single Dangling Bond quantum dot on that surface. The electronic structure of the molecule adsorbed on the hydrogen-passivated surface is similar to the gas phase structure and the measurements show that HOMO and LUMO states contribute to the STM filled and empty state images, respectively. Furthermore, we show that the electronic properties are not significantly affected when the molecule is attached to the single Dangling Bond, which is in contrast with the strong interaction of the molecule with a Dangling Bond dimer. Our results show that the Dangling Bond quantum dots could stabilize organic molecules on a hydrogenated semiconductor without affecting their originally designed gas phase electronic properties. Together with the ability to laterally manipulate the molecules on the surface, this will be advantageous in the construction of single-molecule devices, where the coupling and positioning of the molecules on the substrate could be tuned by a proper design of the surface quantum dot arrays, comprising both single and dimerized Dangling Bonds.
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Single-Molecule Rotational Switch on a Dangling Bond Dimer Bearing
2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Christian Joachim, Marek Kolmer, Rafał Zuzak, Antonio M. Echavarren, Marek Szymonski, Mark SaeysAbstract:One of the key challenges in the construction of atomic-scale circuits and molecular machines is to design molecular rotors and switches by controlling the linear or rotational movement of a molecule while preserving its intrinsic electronic properties. Here, we demonstrate both the continuous rotational switching and the controlled step-by-step single switching of a trinaphthylene molecule adsorbed on a Dangling Bond dimer created on a hydrogen-passivated Ge(001):H surface. The molecular switch is on-surface assembled when the covalent Bonds between the molecule and the Dangling Bond dimer are controllably broken, and the molecule is attached to the dimer by long-range van der Waals interactions. In this configuration, the molecule retains its intrinsic electronic properties, as confirmed by combined scanning tunneling microscopy/spectroscopy (STM/STS) measurements, density functional theory calculations, and advanced STM image calculations. Continuous switching of the molecule is initiated by vibronic excitations when the electrons are tunneling through the lowest unoccupied molecular orbital state of the molecule. The switching path is a combination of a sliding and rotation motion over the Dangling Bond dimer pivot. By carefully selecting the STM conditions, control over discrete single switching events is also achieved. Combined with the ability to create Dangling Bond dimers with atomic precision, the controlled rotational molecular switch is expected to be a crucial building block for more complex surface atomic-scale devices
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Single-Molecule Rotational Switch on a Dangling Bond Dimer Bearing
ACS Nano, 2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Christian Joachim, Marek Kolmer, Rafał Zuzak, Antonio M. Echavarren, Marek Szymonski, Mark SaeysAbstract:One of the key challenges in the construction of atomic-scale circuits and molecular machines is to design molecular rotors and switches by controlling the linear or rotational movement of a molecule while preserving its intrinsic electronic properties. Here, we demonstrate both the continuous rotational switching and the controlled step-by-step single switching of a trinaphthylene molecule adsorbed on a Dangling Bond dimer created on a hydrogen-passivated Ge(001):H surface. The molecular switch is on-surface assembled when the covalent Bonds between the molecule and the Dangling Bond dimer are controllably broken, and the molecule is attached to the dimer by long-range van der Waals interactions. In this configuration, the molecule retains its intrinsic electronic properties, as confirmed by combined scanning tunneling microscopy/spectroscopy (STM/STS) measurements, density functional theory calculations, and advanced STM image calculations. Continuous switching of the molecule is initiated by vibronic excitations when the electrons are tunneling through the lowest unoccupied molecular orbital state of the molecule. The switching path is a combination of a sliding and rotation motion over the Dangling Bond dimer pivot. By carefully selecting the STM conditions, control over discrete single switching events is also achieved. Combined with the ability to create Dangling Bond dimers with atomic precision, the controlled rotational molecular switch is expected to be a crucial building block for more complex surface atomic-scale devices.
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Diels-Alder attachment of a planar organic molecule to a Dangling Bond dimer on a hydrogenated semiconductor surface
Physical Chemistry Chemical Physics, 2016Co-Authors: Szymon Godlewski, Hiroyo Kawai, Marek Kolmer, Antonio M. Echavarren, Mads Engelund, Rafal Zuzak, Aran Garcia-lekue, Gerard Novell-leruth, Daniel Sanchez-portal, Christian JoachimAbstract:Construction of single-molecule electronic devices requires the controlled manipulation of organic molecules and their properties. This could be achieved by tuning the interaction between the molecule and individual atoms by local “on-surface” chemistry, i.e., the controlled formation of chemical Bonds between the species. We demonstrate here the reversible attachment of a planar conjugated polyaromatic molecule to a pair of unpassivated Dangling Bonds on a hydrogenated Ge(001):H surface via a Diels–Alder [4+2] addition using the tip of a scanning tunneling microscope (STM). Due to the small stability difference between the covalently Bonded and a nearly undistorted structure attached to the Dangling Bond dimer by long-range dispersive forces, we show that at cryogenic temperatures the molecule can be switched between both configurations. The reversibility of this covalent Bond forming reaction may be applied in the construction of complex circuits containing organic molecules with tunable properties.
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tunneling spectroscopy of close spaced Dangling Bond pairs in si 001 h
Scientific Reports, 2015Co-Authors: Mads Engelund, Szymon Godlewski, Marek Kolmer, Rafal Zuzak, Aran Garcialekue, Thomas Frederiksen, Daniel Sanchezportal, Marek SzymonskiAbstract:We present a combined experimental and theoretical study of the electronic properties of close-spaced Dangling-Bond (DB) pairs in a hydrogen-passivated Si(001):H p-doped surface. Two types of DB pairs are considered, called “cross” and “line” structures. Our scanning tunneling spectroscopy (STS) data show that, although the spectra taken over different DBs in each pair exhibit a remarkable resemblance, they appear shifted by a constant energy that depends on the DB-pair type. This spontaneous asymmetry persists after repeated STS measurements. By comparison with density functional theory (DFT) calculations, we demonstrate that the magnitude of this shift and the relative position of the STS peaks can be explained by distinct charge states for each DB in the pair. We also explain how the charge state is modified by the presence of the scanning tunneling microscopy (STM) tip and the applied bias. Our results indicate that, using the STM tip, it is possible to control the charge state of individual DBs in complex structures, even if they are in close proximity. This observation might have important consequences for the design of electronic circuits and logic gates based on DBs in passivated silicon surfaces.
