Atomic structure of cobalt silicide islands formed by reactive epitaxy

Bennett, Peter; Parikh, S.; Lee, M. Y.; Cahill, David G.

doi:10.1016/0039-6028(94)90729-3

Cited by 25 publications

(20 citation statements)

References 39 publications

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“…In this experiment, the surface Fermi level was adjusted by depositing Co onto Si͑111͒-7 ϫ 7 at 650°C, producing a "1 ϫ 1 ring-cluster structure." 17,18 We assume that the surface Fermi level changes linearly with coverage from 0.65 eV at 0 ML to 0.42 eV at the saturation coverage of 1/7 ML. 14,19 A quantitative fit can be obtained, as shown in Fig.…”

Section: A Influence Of the Surface Fermi Level On Zero-bias Conductmentioning

confidence: 99%

Analytic model for minority carrier effects in nanoscale Schottky contacts

Hao

Bennett

2010

Journal of Applied Physics

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We present an analytic model for the current-voltage ͑I-V͒ behavior for a nanoscale Schottky contact, emphasizing the role of minority carriers. The minority carriers give rise to a surface recombination current that can strongly dominate the majority current flow throughout the bias range. The I-V curve for the surface recombination current shows a weak rectifying behavior, which could be misinterpreted as large variations of ideality factor and effective barrier height. The model calculations show a good match with experimental I-V curves for nanoscale CoSi 2 epitaxial islands on Si͑111͒ and for direct scanning tunnel microscope tip point contacts, for a range of island size, doping type, and surface Fermi level.

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Section: A Influence Of the Surface Fermi Level On Zero-bias Conductmentioning

confidence: 99%

Analytic model for minority carrier effects in nanoscale Schottky contacts

Hao

Bennett

2010

Journal of Applied Physics

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“…It also grows inward from step edges. By ML, we begin to observe the formation of small particles which we believe to be CoSi 2 islands [6]. Interestingly, the observed sequence of surface phases formed during Co deposition follows that of a bulk binary eutectic system above the eutectic temperature [7].…”

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confidence: 99%

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 nominal coverage for the ffiffiffi 7 p reconstruction, we believe that there are probably more than one Co atom per ffiffiffiffiffiffi 13 p cluster, as already pointed out by Löffler et al [4]. Moreover, we assume that the protrusions that appear on the dark clusters at positive and negative polarization correspond to Si atoms, as can be observed for the initial growth of Co-Si silicides [12], or the ffiffiffi 7 p reconstruction [3]. Therefore, on the basis of the experimental STM results and previous statements, we propose the structural model shown in Fig.…”

Section: Atomic Structurementioning

confidence: 76%

“…At least, three additional Si adatoms (orange full circles) are located above the six Si atoms to form the bright clusters. In this configuration the Co is 7-fold coordinated as in CoSi 2 islands grown on Si(1 1 1) [12]. According to this model we believe that the ffiffiffiffiffiffi 13 p structure, as well as the ffiffiffi 7 p , are formed by consumption and incorporation of the Si atoms supplied by the step edges.…”

Section: Atomic Structurementioning

confidence: 88%