Surface Structures of SrTiO<sub>3</sub> (001):  A TiO<sub>2</sub>-rich Reconstruction with a c(4 × 2) Unit Cell

Erdman, Natasha; Warschkow, Oliver; Asta, Mark; Poeppelmeier, Kenneth R.; Ellis, Donald E; Marks, Laurence D.

doi:10.1021/ja034933h

Cited by 136 publications

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“…The template patterns and molecular ordering are investigated through UHV scanning tunneling microscopy (STM) at room temperature. Etched W tips are used for imaging the sample surfaces at room temperature with a bias voltage applied to the sample.Close-packed surface ordering of fullerenes is achieved on a c(4 × 2) surface reconstruction, 22,23 as shown in the STM images of Figure 1b,c. The c(4 × 2) surface was formed by annealing at 1090°C for 30 min after sputtering.…”

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confidence: 83%

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Template Ordered Open-Grid Arrays of Paired Endohedral Fullerenes

et al. 2006

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Developing useful molecular systems, such as planar networks of molecules for novel molecular-electronic architectures, 1-4 requires the ability to control the way molecules assemble at surfaces. Many techniques exploit non-covalent directional bonding interactions between molecules, such as hydrogen bonding, to facilitate the molecular assembly process. [5][6][7][8][9] However, if the molecules lack such directional bonding attributes then it becomes difficult to develop novel molecular architectures using this approach. Fullerenes 10 are molecules that do lack these directional bonds but are otherwise very attractive candidates for molecular based nanotechnologies. Endohedral fullerenes 11 are of particular interest in this area, because the atomic species bounded within the fullerenes could be manipulated for storing and processing bits of information. For example, the magneto-optical activity 12 of the Er 3 N@C 80 molecule 13 ( Figure 1a) may prove useful in solid-state quantum information processing systems. [2][3][4]14 Overcoming the challenge of coercing endohedral fullerenes to order into useful spatial configurations can be achieved through template-assisted assembly. A successful template requires the surface to be made up of patterned arrays of bonding sites for the fullerenes to adsorb onto. Impressive demonstrations of this have been achieved using pre-assembled molecular templates on metal or metal-terminated substrates. [15][16][17][18] Here we report how oxide crystal surfaces can be used as a template to controllably order endohedral fullerenes into two-dimensional (2D) open-grid arrays. This is compared to the ordinary close-packed ordering of endohedral fullerenes. The template is a nanostructured surface phase of (001) strontium titanate, 19 and the endohedral fullerenes are Er 3 N@C 80 molecules 13 (Figure 1a).The surfaces are prepared through an Ar + sputtering and annealing procedure, described in earlier work, 19 on 0.5%-weight Nb-doped SrTiO 3 (001) single crystals in ultrahigh vacuum (UHV) conditions. Er 3 N@C 80 molecules, or fullerenes, were deposited onto the surfaces from the vapor phase. Createc Knudsen cells, heated at 480°C, were used to evaporate Er 3 N@C 80 molecules for 20-30 min, allowing 0.15-0.20 monolayer coverage for each deposition. Er 3 N@C 80 has advantages over other endohedral fullerenes 3,4 (e.g. N@C 60 ) in that M 3 N@C 80 species (M ) metal forming a planar M 3 N species) are thermally stable 20,21 and can be readily evaporated onto heated substrates in UHV. The template patterns and molecular ordering are investigated through UHV scanning tunneling microscopy (STM) at room temperature. Etched W tips are used for imaging the sample surfaces at room temperature with a bias voltage applied to the sample.Close-packed surface ordering of fullerenes is achieved on a c(4 × 2) surface reconstruction, 22,23 as shown in the STM images of Figure 1b,c. The c(4 × 2) surface was formed by annealing at 1090°C for 30 min after sputtering. Er 3 N@C 80 is deposited on the c(4 × 2)...

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“…Close-packed surface ordering of fullerenes is achieved on a c(4 × 2) surface reconstruction, 22,23 The open-grid ordering of fullerenes is achieved on a template made of 2D arrays of trenches with highly ordered crosslike structures along them (Figure 2a). These trench arrays, termed waffles, 19 have an associated (6 × 8) surface periodicity.…”

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Template Ordered Open-Grid Arrays of Paired Endohedral Fullerenes

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“…A large number of studies have been performed in recent years to understand and to determine a variety of SrTiO 3 surface structures realized under different experimental conditions. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Some of the reported experimental observations are summarized in Table I.…”

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Electronic structure and thermodynamic stability of double-layeredSrTiO3(001)surfaces:Ab initiosimulations

et al. 2007

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Using the B3PW hybrid exchange-correlation functional within density-functional theory and employing Gaussian-type basis sets, we calculated the atomic and electronic structures and thermodynamic stability of three double-layered ͑DL͒ SrTiO 3 ͑001͒ surfaces: ͑i͒ SrO-terminated, ͑ii͒ TiO 2 -terminated, and ͑iii͒ ͑2 ϫ 1͒ reconstruction of TiO 2 -terminated SrTiO 3 ͑001͒ recently suggested by Erdman et al. ͓Nature ͑London͒ 419, 55 ͑2002͔͒. A thermodynamic stability diagram obtained from first-principles calculations shows that regular TiO 2 -and SrO-terminated surfaces are the most stable. The stability regions of ͑2 ϫ 1͒ DL TiO 2 -and DL SrO-terminated surfaces lie beyond the precipitation lines of SrO and TiO 2 compounds and thus are less stable with respect to regular SrTiO 3 ͑001͒ surfaces. Analysis of the stability diagram suggests that Sr precipitation on SrTiO 3 surface never occurs. Our simulations show a substantial increase of Ti-O covalency on the DL surfaces as compared to the regular surfaces, which are themselves more covalent than the crystalline bulk. The implications of our calculated results for recent experimental observations are discussed.

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“…Now, it is understood that the common (2 × 1) and c(4 × 2) surfaces feature a single TiO 2 overlayer on top of a TiO 2 bulk termination. [14][15][16][17] It is also likely that the c(4 × 4) and c(6 × 2) reconstructions have a similar Ti-rich composition. 11, 18 Other near-stoichiometric reconstructions, including the ( 5 × 5)-R26.6 surface and similar "square" configurations, e.g.…”

Section: Introductionmentioning

confidence: 99%

“…STM reveals that these phases are composed of two-dimensional (2D) domains of highly ordered nanostructures. According to AES, these nanostructures are more Ti-rich than the (2 × 1) and c(4 × 2) surfaces [14][15][16] and are composed of Ti 4+ -based species. This study reveals a wealth of unique structures, expanding on the scope of nanostructures reported on previously.…”

Section: Introductionmentioning

confidence: 99%

Ordering of TiO₂-Based Nanostructures on SrTiO₃(001) Surfaces

et al. 2006

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A class of nanostructured surface phases on SrTiO 3 (001) is reported and characterized through atomic-resolution scanning tunneling microscopy and Auger electron spectroscopy. These surface phases are created via argon ion sputtering and UHV annealing and form close-packed domains of highly ordered nanostructures. Depending on the type of nanostructures present, the domain ordering exhibit either (6 × 2), (9 × 2), (12 × 2), (6 × 8), or (7 × 4) surface patterning. The nanostructures are composed of TiO 2 -derived complexes surrounded by a TiO 2 surface termination. Such surface ordering phenomena introduce another level of complexity in the chemistry of perovskite oxide surfaces and provide a basis from which potential photocatalytic and molecularordering applications may be developed.

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Surface Structures of SrTiO₃ (001): A TiO₂-rich Reconstruction with a c(4 × 2) Unit Cell

Cited by 136 publications

References 44 publications

Template Ordered Open-Grid Arrays of Paired Endohedral Fullerenes

Template Ordered Open-Grid Arrays of Paired Endohedral Fullerenes

Electronic structure and thermodynamic stability of double-layeredSrTiO3(001)surfaces:Ab initiosimulations

Ordering of TiO₂-Based Nanostructures on SrTiO₃(001) Surfaces

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Surface Structures of SrTiO3 (001): A TiO2-rich Reconstruction with a c(4 × 2) Unit Cell

Cited by 136 publications

References 44 publications

Template Ordered Open-Grid Arrays of Paired Endohedral Fullerenes

Template Ordered Open-Grid Arrays of Paired Endohedral Fullerenes

Electronic structure and thermodynamic stability of double-layeredSrTiO3(001)surfaces:Ab initiosimulations

Ordering of TiO2-Based Nanostructures on SrTiO3(001) Surfaces

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Surface Structures of SrTiO₃ (001): A TiO₂-rich Reconstruction with a c(4 × 2) Unit Cell

Ordering of TiO₂-Based Nanostructures on SrTiO₃(001) Surfaces