Surface phase transformations in the Ni/Si(111) system observed in real time using low-energy electron microscopy

Bennett, Peter; Lee, M. Y.; Parikh, S.; Wurm, K.; Phaneuf, R. J.

doi:10.1116/1.579759

Cited by 29 publications

(7 citation statements)

References 15 publications

(21 reference statements)

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“…The growth mode of the ͑1 3 1͒-RC structure indicates limited solubility of RC's in regions of the ordered ͑7 3 7͒ phase. We have earlier observed a qualitatively similar separation for Ni͞Si(111) [4]. p 7 ͒ as gray at these conditions.…”

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Two Dimensional Phase Separation for Co Adsorbed on Si(111)

et al. 1997

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We have used low energy electron microscopy to monitor the high-temperature behavior of surface phases in the Co͞Si(111) system at submonolayer coverages. We observe a reversible phase separation from a disordered "͑1 3 1͒" phase to well-defined coexisting regions of ordered ͑7 3 7͒-reconstructed and disordered phases. The transition temperature is depressed by nearly 200 ± C by the addition of 0.1 monolayer of cobalt. The shape of the coverage-temperature phase boundary allows us to estimate the latent heat of the ͑7 3 7͒ order-disorder transition. [S0031-9007(97)03320-6] PACS numbers: 68.35.Rh, 81.30.Hd, 82.65.Dp Surface effects in bulk alloying systems is a topic of long-standing interest, with important fundamental and practical aspects such as surface segregation, grain boundary embrittlement, impurity gettering, and faceting behavior. More recently, studies of heteroepitaxial growth have highlighted the importance of understanding the thermodynamics of coupling between overlayers and substrate. In view of the above, and the ubiquity of compositional phase separations in bulk systems, it is perhaps surprising to find no report in the literature of two-dimensional (2D) phase separation of a surface segregant. One reason for this is that surface segregants in most systems are essentially equilibrated with the bulk at temperatures of interest. This results in a single-phase surface structure at all temperatures, even though the surface may exhibit a phase transition in which coverage increases suddenly below a critical temperature, following a miscibility gap phase diagram [1]. A second reason may be that it is experimentally difficult to observe phase separation with diffraction techniques, which are almost exclusively used for such studies. On the other hand, phase separation is directly observable using surface imaging techniques such as low energy electron microscopy (LEEM), which is capable of distinguishing phases with differing atomic structure, with approximately 100 Å lateral resolution, high contrast, and at high temperature [2]. In this paper, we report direct LEEM observations of a reversible phase separation between ordered and disordered 2D phases for a prototype metal-semiconductor system, Co͞Si(111).Previously, Bennett et al., using scanning tunneling microscopy (STM) and medium energy ion scattering (MEIS) found that a remarkably stable "ring-cluster" (RC) structure exists for all group VIII metals adsorbed on Si(111), with each RC consisting of a single metal atom in a substitutional silicon site plus an overlying ring of six silicon adatoms [3]. In the case of cobalt an ordered arrangement of RC's with a ͑ p 7 3 p 7 ͒R19.1 ± unit cell forms at the close-packed density of 1 7 ML. At lower coverages a disordered, or "͑1 3 1͒," variable density lattice gas arrangement of RC's exists at domain boundaries of the ͑7 3 7͒ reconstruction. It was not clear from STM "quench and look" observations whether these structures exist at high temperature or what their interactions might be.As we describe be...

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“…The principle of operation of the LEEM is described in detail elsewhere [2], as is the microscope used in this work [4]. The base pressure in the instrument was 2 3 10 210 torr.…”

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Two Dimensional Phase Separation for Co Adsorbed on Si(111)

et al. 1997

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“…19 -R23.4°, and (1 × 1)-ring cluster (RC) phases. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] These surface silicides are thought to be intermediate states before the formation of thick epitaxial silicides. It has been reported that ´n 2 and 2 2-R45°phases form on a Si(100) substrate depending on the Ni coverages and substrate temperatures.…”

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Formation of two-dimensional silicide on Ni(100) surface

Fukuda¹,

Kishida²,

Umezawa³

2020

Jpn. J. Appl. Phys.

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The initial formation of two-dimensional silicide on a Ni(100) surface was studied by scanning tunneling microscopy in an ultrahigh vacuum. Less than 0.5 ML of Si deposition at 473 K created a two-dimensional Si-Ni mixed layer by displacing the substrate Ni with impinged Si. On a 0.5 ML Si deposited surface, the Si and Ni atoms were alternately aligned in the close-packed á ñ 011 directions and formed a 2 2-R45°[or c(2 × 2)] structure. For Si deposition beyond 0.5 ML, excess Si did not react with surface Ni up to 573 K; instead, Si islands were formed on the twodimensional silicide layer. A first-principles total-energy calculation showed preferential alignments of alternating Si and Ni in the á ñ 011 directions, and higher formation energies when the embedded Si atoms were more than 0.5 ML. Since the 2 2-R45°structure was robust, impinged excess Si atoms did not penetrate the two-dimensional silicide layer and react with the subsurface Ni layer.

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“…Several 2D phases are reported to appear during the reaction of an ultrathin Ni film with a Si (111) substrate, ( phases [13][14][15][16][17]. The last two phases are the most likely intermediate steps to epitaxial growth of 3D NiSi 2 onto Si (111) [18,19,20]. On Si (001), depending on the Ni coverage and thermal annealing conditions, several nickel-silicide compounds can be formed [22].…”

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confidence: 99%

Formation and stability of a two-dimensional nickel silicide on Ni(111): An Auger, LEED, STM, and high-resolution photoemission study

et al. 2012

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Using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), scanning tunnelling microscopy (STM) and high resolution photo-electron spectroscopy (HR-PES) techniques we have studied the annealing effect of one silicon monolayer deposited at room temperature onto a Ni (111) substrate.The variations of the Si surface concentration, recorded by AES at 300°C and 400°C, show at the beginning a rapid Si decreasing followed by a slowing down up to a plateau equivalent to about 1/3 silicon monolayer.STM images and LEED patterns, both recorded at room temperature just after annealing, reveal the formation of an ordered hexagonal superstructure ( 3 3) 30 R ×°-type. From these observations and from a quantitative analysis of HR-PES data, recorded before and after annealing, we propose that the ( 3 3) 30 R ×°superstructure corresponds to a two dimensional (2D) Ni 2 Si surface silicide.

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Surface phase transformations in the Ni/Si(111) system observed in real time using low-energy electron microscopy

Cited by 29 publications

References 15 publications

Two Dimensional Phase Separation for Co Adsorbed on Si(111)

Two Dimensional Phase Separation for Co Adsorbed on Si(111)

Formation of two-dimensional silicide on Ni(100) surface

Formation and stability of a two-dimensional nickel silicide on Ni(111): An Auger, LEED, STM, and high-resolution photoemission study

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