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Phase transition on the Si(001) clean surface prepared in UHV MBE chamber: a study by high-resolution STM and in situ RHEED.

Arapkina LV, Yuryev VA, Chizh KV, Shevlyuga VM, Storojevyh MS, Krylova LA - Nanoscale Res Lett (2011)

Bottom Line: A fraction of the surface area covered by the c(8 × 8) structure decreased, as the sample cooling rate was reduced.A model of the c(8 × 8) structure formation has been built on the basis of the STM data.Origin of the high-order structure on the Si(001) surface and its connection with the epinucleation phenomenon are discussed.PACS 68.35.B-·68.37.Ef·68.49.Jk·68.47.Fg.

View Article: PubMed Central - HTML - PubMed

Affiliation: A, M, Prokhorov General Physics Institute of RAS, 38 Vavilov Street, Moscow, 119991, Russia. arapkina@kapella.gpi.ru.

ABSTRACT
The Si(001) surface deoxidized by short annealing at T ~ 925°C in the ultrahigh vacuum molecuar beam epitaxy chamber has been in situ investigated using high-resolution scanning tunneling microscopy (STM)and redegreesected high-energy electron diffraction (RHEED. RHEED patterns corresponding to (2 × 1) and (4 × 4) structures were observed during sample treatment. The (4 × 4) reconstruction arose at T ≲ 600°C after annealing. The reconstruction was observed to be reversible: the (4 × 4) structure turned into the (2 × 1) one at T ≳ 600°C, the (4 × 4) structure appeared again at recurring cooling. The c(8 × 8) reconstruction was revealed by STM at room temperature on the same samples. A fraction of the surface area covered by the c(8 × 8) structure decreased, as the sample cooling rate was reduced. The (2 × 1) structure was observed on the surface free of the c(8 × 8) one. The c(8 × 8) structure has been evidenced to manifest itself as the (4 × 4) one in the RHEED patterns. A model of the c(8 × 8) structure formation has been built on the basis of the STM data. Origin of the high-order structure on the Si(001) surface and its connection with the epinucleation phenomenon are discussed.PACS 68.35.B-·68.37.Ef·68.49.Jk·68.47.Fg.

No MeSH data available.


Schematic representation of the surface stress fields interactions during formation of the c(8 × 8) structure: (a) ordering of the "rectangles" within the rows; (b) ordering of the rows relative to each other; (c) the ordered c(8 × 8) structure.
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Figure 12: Schematic representation of the surface stress fields interactions during formation of the c(8 × 8) structure: (a) ordering of the "rectangles" within the rows; (b) ordering of the rows relative to each other; (c) the ordered c(8 × 8) structure.

Mentions: The following scenario may be proposed to describe the c(8 × 8) structure formation. A large number of ad-dimers remains on the surface during the sample annealing after the oxide film removal. They form the uppermost layer of the structure. The underlying layer is (2 × 1) reconstructed. Ad-dimers are mobile and can form different complexes (islands). Calculations show that the most energetically favorable island configurations are single dimer on a row in non-epitaxial orientation [43,45,48,49] (Figure 5b), complexes of two dimers (pairs of dimers) in epiorientation (metastable [43]) and two dimers on a row in non-epitaxial orientation separated by a divacancy, and tripple-dimer epi-islands considered as critical epinuclei [43]. These mobile dimers and complexes migrate in the stress field of the (2 × 1) structure. The sinks for ad-dimers are (A) steps, (B) vacancy defects of the underlying (2 × 1) reconstructed layer, and (C) "fastening" them to the (2 × 1) surface as a c(8 × 8) structure. The main sinks at high temperatures are A and B. As the sample is cooled, the C sink becomes dominating. Ad-dimers on the Si(001)-(2 × 1) surface are known to tend to form dimer rows [50]. In this case, such rows are formed by metastable dimer pairs gathered in the "rectangles". The "rectangles" are ordered with a period of eight translations in the rows. The ordering is likely controlled by the (2 × 1) structure of the underlying layer and interaction of the stress fields arising around each "rectangle". Effect of the underlying (2 × 1) layer is that the "rectangle" position on the surface relative to its dimer rows is strictly defined: dimers of the "rectangle" edges must be placed on tops of the rows. Interaction of the stress fields initially arranges the "rectangles" within the rows (Figure 12a); then it arranges adjacent rows with respect to one an-other (Figure 12b). The resultant ordered structure is shown in Figure 12c. The described behavior of "rectangles" can be derived from the STM images presented in the previous sections. In addition, investigation of appearance of the RHEED patterns allowed us to conclude that the process of dimer ordering in the c(8 × 8) structure is gradual: the pattern reflexes appearing on transition from (2 × 1) to (4 × 4) reach maximum brightness gradually; it means that the c(8 × 8) structure does not arise instantly throughout the sample surface, but originally form some nuclei ("standalone rectangles" like those in Figure 5a) on which mobile ad-dimers crystallize in the ordered surface configuration.


Phase transition on the Si(001) clean surface prepared in UHV MBE chamber: a study by high-resolution STM and in situ RHEED.

Arapkina LV, Yuryev VA, Chizh KV, Shevlyuga VM, Storojevyh MS, Krylova LA - Nanoscale Res Lett (2011)

Schematic representation of the surface stress fields interactions during formation of the c(8 × 8) structure: (a) ordering of the "rectangles" within the rows; (b) ordering of the rows relative to each other; (c) the ordered c(8 × 8) structure.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211275&req=5

Figure 12: Schematic representation of the surface stress fields interactions during formation of the c(8 × 8) structure: (a) ordering of the "rectangles" within the rows; (b) ordering of the rows relative to each other; (c) the ordered c(8 × 8) structure.
Mentions: The following scenario may be proposed to describe the c(8 × 8) structure formation. A large number of ad-dimers remains on the surface during the sample annealing after the oxide film removal. They form the uppermost layer of the structure. The underlying layer is (2 × 1) reconstructed. Ad-dimers are mobile and can form different complexes (islands). Calculations show that the most energetically favorable island configurations are single dimer on a row in non-epitaxial orientation [43,45,48,49] (Figure 5b), complexes of two dimers (pairs of dimers) in epiorientation (metastable [43]) and two dimers on a row in non-epitaxial orientation separated by a divacancy, and tripple-dimer epi-islands considered as critical epinuclei [43]. These mobile dimers and complexes migrate in the stress field of the (2 × 1) structure. The sinks for ad-dimers are (A) steps, (B) vacancy defects of the underlying (2 × 1) reconstructed layer, and (C) "fastening" them to the (2 × 1) surface as a c(8 × 8) structure. The main sinks at high temperatures are A and B. As the sample is cooled, the C sink becomes dominating. Ad-dimers on the Si(001)-(2 × 1) surface are known to tend to form dimer rows [50]. In this case, such rows are formed by metastable dimer pairs gathered in the "rectangles". The "rectangles" are ordered with a period of eight translations in the rows. The ordering is likely controlled by the (2 × 1) structure of the underlying layer and interaction of the stress fields arising around each "rectangle". Effect of the underlying (2 × 1) layer is that the "rectangle" position on the surface relative to its dimer rows is strictly defined: dimers of the "rectangle" edges must be placed on tops of the rows. Interaction of the stress fields initially arranges the "rectangles" within the rows (Figure 12a); then it arranges adjacent rows with respect to one an-other (Figure 12b). The resultant ordered structure is shown in Figure 12c. The described behavior of "rectangles" can be derived from the STM images presented in the previous sections. In addition, investigation of appearance of the RHEED patterns allowed us to conclude that the process of dimer ordering in the c(8 × 8) structure is gradual: the pattern reflexes appearing on transition from (2 × 1) to (4 × 4) reach maximum brightness gradually; it means that the c(8 × 8) structure does not arise instantly throughout the sample surface, but originally form some nuclei ("standalone rectangles" like those in Figure 5a) on which mobile ad-dimers crystallize in the ordered surface configuration.

Bottom Line: A fraction of the surface area covered by the c(8 × 8) structure decreased, as the sample cooling rate was reduced.A model of the c(8 × 8) structure formation has been built on the basis of the STM data.Origin of the high-order structure on the Si(001) surface and its connection with the epinucleation phenomenon are discussed.PACS 68.35.B-·68.37.Ef·68.49.Jk·68.47.Fg.

View Article: PubMed Central - HTML - PubMed

Affiliation: A, M, Prokhorov General Physics Institute of RAS, 38 Vavilov Street, Moscow, 119991, Russia. arapkina@kapella.gpi.ru.

ABSTRACT
The Si(001) surface deoxidized by short annealing at T ~ 925°C in the ultrahigh vacuum molecuar beam epitaxy chamber has been in situ investigated using high-resolution scanning tunneling microscopy (STM)and redegreesected high-energy electron diffraction (RHEED. RHEED patterns corresponding to (2 × 1) and (4 × 4) structures were observed during sample treatment. The (4 × 4) reconstruction arose at T ≲ 600°C after annealing. The reconstruction was observed to be reversible: the (4 × 4) structure turned into the (2 × 1) one at T ≳ 600°C, the (4 × 4) structure appeared again at recurring cooling. The c(8 × 8) reconstruction was revealed by STM at room temperature on the same samples. A fraction of the surface area covered by the c(8 × 8) structure decreased, as the sample cooling rate was reduced. The (2 × 1) structure was observed on the surface free of the c(8 × 8) one. The c(8 × 8) structure has been evidenced to manifest itself as the (4 × 4) one in the RHEED patterns. A model of the c(8 × 8) structure formation has been built on the basis of the STM data. Origin of the high-order structure on the Si(001) surface and its connection with the epinucleation phenomenon are discussed.PACS 68.35.B-·68.37.Ef·68.49.Jk·68.47.Fg.

No MeSH data available.