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Quantum engineering at the silicon surface using dangling bonds.

Schofield SR, Studer P, Hirjibehedin CF, Curson NJ, Aeppli G, Bowler DR - Nat Commun (2013)

Bottom Line: Here we use a scanning tunnelling microscope to fabricate interacting chains of dangling bond defects on the hydrogen-passivated silicon (001) surface.We image both the ground-state and the excited-state probability distributions of the resulting artificial molecular orbitals, using the scanning tunnelling microscope tip bias and tip-sample separation as gates to control which states contribute to the image.Our results demonstrate that atomically precise quantum states can be fabricated on silicon, and suggest a general model of quantum-state fabrication using other chemically passivated semiconductor surfaces where single-atom depassivation can be achieved using scanning tunnelling microscopy.

View Article: PubMed Central - PubMed

Affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, UK. s.schofield@ucl.ac.uk

ABSTRACT
Individual atoms and ions are now routinely manipulated using scanning tunnelling microscopes or electromagnetic traps for the creation and control of artificial quantum states. For applications such as quantum information processing, the ability to introduce multiple atomic-scale defects deterministically in a semiconductor is highly desirable. Here we use a scanning tunnelling microscope to fabricate interacting chains of dangling bond defects on the hydrogen-passivated silicon (001) surface. We image both the ground-state and the excited-state probability distributions of the resulting artificial molecular orbitals, using the scanning tunnelling microscope tip bias and tip-sample separation as gates to control which states contribute to the image. Our results demonstrate that atomically precise quantum states can be fabricated on silicon, and suggest a general model of quantum-state fabrication using other chemically passivated semiconductor surfaces where single-atom depassivation can be achieved using scanning tunnelling microscopy.

No MeSH data available.


Related in: MedlinePlus

Linear chains of five and six DBs.(a) STM topographs of the five-DB chain at +1.8, +1.4 and −1.4 V, respectively (15 pA; 4.5 × 2 nm2). (b) Line profiles taken along the DB structures as indicated for each of the images in a. (c) Simulated line profiles generated from linear combinations, Σci/ψi/2, of the individual bound-state solutions to the five-DB system. (d) Five-DB potential well and the probability distributions of its bound-state wavefunctions, ψ1 to ψ7 with binding energies given in eV. (e–h) Repeat of panels a–d for a six-DB chain (images are 5.3 × 2 nm2). The coefficients ci were calculated using ci=e−Ei/α where α=0.15 and 0.3 for filled and empty states, respectively, and Ei is the binding energy of the i-th state. For the low empty-state bias (+1.4 V) simulation of the five-DB, only contributions from ψ4 and ψ5 were included, whereas for the six-DB states ψ5, ψ6 and ψ7 were included with c7=1.5c6 (see text).
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f6: Linear chains of five and six DBs.(a) STM topographs of the five-DB chain at +1.8, +1.4 and −1.4 V, respectively (15 pA; 4.5 × 2 nm2). (b) Line profiles taken along the DB structures as indicated for each of the images in a. (c) Simulated line profiles generated from linear combinations, Σci/ψi/2, of the individual bound-state solutions to the five-DB system. (d) Five-DB potential well and the probability distributions of its bound-state wavefunctions, ψ1 to ψ7 with binding energies given in eV. (e–h) Repeat of panels a–d for a six-DB chain (images are 5.3 × 2 nm2). The coefficients ci were calculated using ci=e−Ei/α where α=0.15 and 0.3 for filled and empty states, respectively, and Ei is the binding energy of the i-th state. For the low empty-state bias (+1.4 V) simulation of the five-DB, only contributions from ψ4 and ψ5 were included, whereas for the six-DB states ψ5, ψ6 and ψ7 were included with c7=1.5c6 (see text).

Mentions: Our ability to write arbitrary combinations of DBs supported by the periodicity of the underlying crystal lattice, together with control of the bias voltage and tip-sample separation permit the creation and observation of engineered quantum states. We have observed similar LBE states for various combinations of DB pairs, including pairs separated by an additional Si dimer (1.15 nm separation, Fig. 4a-d), pairs perpendicular to the dimer rows separated by a single H-terminated Si atom (Fig. 4e-h) and pairs separated only by the dimer trough (Fig. 4i-l). The behaviour of these structures with changing imaging parameters is in agreement with the band alignment model presented above, and the data presented for the DB pair in Fig. 3. We have also created and imaged DBs aligned diagonally across dimer rows; Fig. 5 shows a series of STM images of a three-DB chain in one linear (Fig. 5a–c) and two separate ‘kinked’ configurations (Fig. 5d–f, respectively). The filled-state images resolve three protrusions at the locations of the missing H atoms, whereas the high-bias empty-state images reveal protrusions located between the missing H atoms, consistent with the DB pair data presented above and the extended DB chain data to be presented below (Fig. 6). In the linear configuration, all of the DBs are lined up along one side of a dimer row. However, imaging this structure at elevated bias and current (±2.1 V and 25 pA) caused the leftmost DB to move to the opposite side of the dimer row (that is, the H atom of the Si–Si–H hemihydride dimer shifted from one side of the dimer to the other). This then produced a ‘kinked’ three-DB structure, which is shown in Fig. 5d–f. Subsequently, imaging this structure again with elevated bias and current caused the middle DB to also switch to the opposite side of the dimer row (Fig. 5g–i). Observing the empty-state images in Fig. 5a, we notice a slightly reduced size in the protrusion that occurs between the DB separated diagonally across the dimer row, and a distinct angular appearance consistent with the formation of a molecular orbital between diagonally separated DBs.


Quantum engineering at the silicon surface using dangling bonds.

Schofield SR, Studer P, Hirjibehedin CF, Curson NJ, Aeppli G, Bowler DR - Nat Commun (2013)

Linear chains of five and six DBs.(a) STM topographs of the five-DB chain at +1.8, +1.4 and −1.4 V, respectively (15 pA; 4.5 × 2 nm2). (b) Line profiles taken along the DB structures as indicated for each of the images in a. (c) Simulated line profiles generated from linear combinations, Σci/ψi/2, of the individual bound-state solutions to the five-DB system. (d) Five-DB potential well and the probability distributions of its bound-state wavefunctions, ψ1 to ψ7 with binding energies given in eV. (e–h) Repeat of panels a–d for a six-DB chain (images are 5.3 × 2 nm2). The coefficients ci were calculated using ci=e−Ei/α where α=0.15 and 0.3 for filled and empty states, respectively, and Ei is the binding energy of the i-th state. For the low empty-state bias (+1.4 V) simulation of the five-DB, only contributions from ψ4 and ψ5 were included, whereas for the six-DB states ψ5, ψ6 and ψ7 were included with c7=1.5c6 (see text).
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Related In: Results  -  Collection

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f6: Linear chains of five and six DBs.(a) STM topographs of the five-DB chain at +1.8, +1.4 and −1.4 V, respectively (15 pA; 4.5 × 2 nm2). (b) Line profiles taken along the DB structures as indicated for each of the images in a. (c) Simulated line profiles generated from linear combinations, Σci/ψi/2, of the individual bound-state solutions to the five-DB system. (d) Five-DB potential well and the probability distributions of its bound-state wavefunctions, ψ1 to ψ7 with binding energies given in eV. (e–h) Repeat of panels a–d for a six-DB chain (images are 5.3 × 2 nm2). The coefficients ci were calculated using ci=e−Ei/α where α=0.15 and 0.3 for filled and empty states, respectively, and Ei is the binding energy of the i-th state. For the low empty-state bias (+1.4 V) simulation of the five-DB, only contributions from ψ4 and ψ5 were included, whereas for the six-DB states ψ5, ψ6 and ψ7 were included with c7=1.5c6 (see text).
Mentions: Our ability to write arbitrary combinations of DBs supported by the periodicity of the underlying crystal lattice, together with control of the bias voltage and tip-sample separation permit the creation and observation of engineered quantum states. We have observed similar LBE states for various combinations of DB pairs, including pairs separated by an additional Si dimer (1.15 nm separation, Fig. 4a-d), pairs perpendicular to the dimer rows separated by a single H-terminated Si atom (Fig. 4e-h) and pairs separated only by the dimer trough (Fig. 4i-l). The behaviour of these structures with changing imaging parameters is in agreement with the band alignment model presented above, and the data presented for the DB pair in Fig. 3. We have also created and imaged DBs aligned diagonally across dimer rows; Fig. 5 shows a series of STM images of a three-DB chain in one linear (Fig. 5a–c) and two separate ‘kinked’ configurations (Fig. 5d–f, respectively). The filled-state images resolve three protrusions at the locations of the missing H atoms, whereas the high-bias empty-state images reveal protrusions located between the missing H atoms, consistent with the DB pair data presented above and the extended DB chain data to be presented below (Fig. 6). In the linear configuration, all of the DBs are lined up along one side of a dimer row. However, imaging this structure at elevated bias and current (±2.1 V and 25 pA) caused the leftmost DB to move to the opposite side of the dimer row (that is, the H atom of the Si–Si–H hemihydride dimer shifted from one side of the dimer to the other). This then produced a ‘kinked’ three-DB structure, which is shown in Fig. 5d–f. Subsequently, imaging this structure again with elevated bias and current caused the middle DB to also switch to the opposite side of the dimer row (Fig. 5g–i). Observing the empty-state images in Fig. 5a, we notice a slightly reduced size in the protrusion that occurs between the DB separated diagonally across the dimer row, and a distinct angular appearance consistent with the formation of a molecular orbital between diagonally separated DBs.

Bottom Line: Here we use a scanning tunnelling microscope to fabricate interacting chains of dangling bond defects on the hydrogen-passivated silicon (001) surface.We image both the ground-state and the excited-state probability distributions of the resulting artificial molecular orbitals, using the scanning tunnelling microscope tip bias and tip-sample separation as gates to control which states contribute to the image.Our results demonstrate that atomically precise quantum states can be fabricated on silicon, and suggest a general model of quantum-state fabrication using other chemically passivated semiconductor surfaces where single-atom depassivation can be achieved using scanning tunnelling microscopy.

View Article: PubMed Central - PubMed

Affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, UK. s.schofield@ucl.ac.uk

ABSTRACT
Individual atoms and ions are now routinely manipulated using scanning tunnelling microscopes or electromagnetic traps for the creation and control of artificial quantum states. For applications such as quantum information processing, the ability to introduce multiple atomic-scale defects deterministically in a semiconductor is highly desirable. Here we use a scanning tunnelling microscope to fabricate interacting chains of dangling bond defects on the hydrogen-passivated silicon (001) surface. We image both the ground-state and the excited-state probability distributions of the resulting artificial molecular orbitals, using the scanning tunnelling microscope tip bias and tip-sample separation as gates to control which states contribute to the image. Our results demonstrate that atomically precise quantum states can be fabricated on silicon, and suggest a general model of quantum-state fabrication using other chemically passivated semiconductor surfaces where single-atom depassivation can be achieved using scanning tunnelling microscopy.

No MeSH data available.


Related in: MedlinePlus