Electronic Structure of 1 to 2 nm Diameter Silicon Core/Shell Nanocrystals:  Surface Chemistry, Optical Spectra, Charge Transfer, and Doping

Zhou, Zhiyong; Friesner, Richard A.; Brus, L. E.

doi:10.1021/ja036443v

Cited by 90 publications

(75 citation statements)

References 53 publications

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“…The band gap energy derived from our UV/visible spectra suggests a size of less than 1.5 nm diameter of the Si core. 32,41 The distinct PLE energy at 307.5 nm is close to the band gap. This and the high luminescence efficiency exhibit typical characteristics of excitons.…”

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confidence: 79%

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In situ passivation and blue luminescence of silicon clusters using a cluster beam/H2O codeposition production method

Brewer¹,

Haeften²

2009

Applied Physics Letters

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Si clusters are produced in a gas aggregation source and fly through ultrahigh vacuum onto a cold target where they are codeposited with water vapor. Melting of the ice yields immediately a suspension of nanoparticles that emits intense, nondegrading luminescence in the blue wavelength range. Spectroscopic analysis reveals a Si/SiO core-shell structure where the luminescence stems from oxygen deficient defects. The main advantage of our production method is that it yields the luminescent Si nanoparticles in one step. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3167355͔The process of light emission from materials with an indirect band gap in the bulk has attracted much interest both from a fundamental point of view and from the prospect of applications.1,2 Since the discovery of luminescence from porous silicon at room temperature 3,4 twenty years ago, fabrication of devices such as silicon-based light emitting diodes ͑Ref. 5͒ and lasers 6 has been achieved, and a large variety of types of photoluminescent silicon have been reported in the literature. These include nanowires and nanorods, 7-13 Si/SiO, Si/SiOH sandwich, and core-shell systems, [14][15][16] as well as Si clusters produced by laser photolysis 17,18 or by Si ion implantation in silica glass. 19,20 Furthermore, luminescent Si quantum dots in solutions have been investigated. [21][22][23] Nanoparticles in solution receive great attention because of applications in biological imaging and diagnostic labeling. 24In all the above-mentioned examples the production method plays a crucial role in the way the luminescence wavelength and luminescence efficiency is controlled. Some industrial production methods require specific conditions. For instance, in complementary metal-oxide-semiconductor ͑CMOS͒ processing, a maximum process temperature of only 450°C is allowed. The compatibility with the CMOS production process will become important because integration of light emitters is one of the major goals on the road map in semiconductor industries. This is because the performance of electronic integrated circuits is expected to be greatly increased by using optical signal transmission. 25 While the origins of the luminescence of porous silicon are still debated, the imperative of quantum confinement is generally accepted.26 Free Si clusters down to the size of a few atoms can be produced in molecular beam machines.17,27-31 A further and major requirement to achieve luminescence from Si is a suitable passivation of the surface.32 Pure free Si clusters exhibit dangling bonds that efficiently quench luminescence. 33 In this paper we report on a combination of the cluster beam approach and a passivation technique that overcomes this limitation. Central to this method is the in situ chemical interaction between the surface of pure silicon clusters and a passivation agent. The method yields luminescent clusters in aqueous suspensions immediately and the luminescence intensity remains stable over a period of more than three months. High temperature treatments ...

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confidence: 79%

“…32 Pure free Si clusters exhibit dangling bonds that efficiently quench luminescence. 33 In this paper we report on a combination of the cluster beam approach and a passivation technique that overcomes this limitation.…”

mentioning

confidence: 99%

In situ passivation and blue luminescence of silicon clusters using a cluster beam/H2O codeposition production method

Brewer¹,

Haeften²

2009

Applied Physics Letters

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“…Among the systems that have been investigated are carbon nanostructures (buckyballs and nanotubes) (25,(74)(75)(76) and semiconductor quantum dots (26,77,78). The effects of quantum confinement and structural modification imposed by various nanostructures on chemical and electrical properties can be investigated in a rigorous fashion, which will be essential as attempts are made to use these materials in various types of devices.…”

Section: Applicationsmentioning

confidence: 99%

Ab initioquantum chemistry: Methodology and applications

Friesner

2005

Proc. Natl. Acad. Sci. U.S.A.

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294

224

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This Perspective provides an overview of state-of-the-art ab initio quantum chemical methodology and applications. The methods that are discussed include coupled cluster theory, localized second-order Moller-Plesset perturbation theory, multireference perturbation approaches, and density functional theory. The accuracy of each approach for key chemical properties is summarized, and the computational performance is analyzed, emphasizing significant advances in algorithms and implementation over the past decade. Incorporation of a condensed-phase environment by means of mixed quantum mechanical͞molecular mechanics or self-consistent reaction field techniques, is presented. A wide range of illustrative applications, focusing on materials science and biology, are discussed briefly.coupled cluster ͉ density functional theory ͉ second-order Modler-Plesser perturbation theory ͉ mixed quantum͞molecular mechanics O ver the past three decades, ab initio quantum chemistry has become an essential tool in the study of atoms and molecules and, increasingly, in modeling complex systems such as those arising in biology and materials science. The underlying core technology is computational solution of the electronic Schrodinger equation; given the positions of a collection of atomic nuclei, and the total number of electrons in the system, calculate the electronic energy, electron density, and other properties by means of a well defined, automated approximation (a ''model chemistry''). The ability to obtain ''goodenough'' solutions to the electronic Schrodinger equation for systems containing tens, or even hundreds, of atoms has revolutionized the ability of theoretical chemistry to address important problems in a wide range of disciplines; the Nobel Prize awarded to John Pople and Walter Kohn in 1998 is a reflection of this observation.In its exact form, the electronic Schrodinger equation is a many-body problem, whose computational complexity grows exponentially with the number of electrons, and hence, a brute force solution is intractable. Hartree-Fock theory, a mean field approach, produces reasonable results for many properties but is incapable of providing a robust description of reactive chemical events in which electron correlation has a major role. Thus, a key problem has been the development of treatments of electron correlation that exhibit a tractable scaling in computational effort with the size of the system. The considerable progress that has been made along these lines is outlined below.Given a well defined theoretical framework of approximation, the next requirement is efficient computational implementation. Considerable sophistication is required to achieve acceptable accuracy and efficiency; the leading quantum chemistry programs are millions of lines of computer code, and mathematical algorithms to reduce formal scaling of computational effort with system size have an increasingly crucial role in meeting the challenge of handling complex system relevant to practical applications. Below, the most important comp...

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“…14 Silicon (Si) is one of the most important semiconductors for microelectronic and energy applications, and Si quantum dots (QDs) have also attracted many attentions. [15][16][17][18][19][20][21][22][23] Experimentally, free-standing Si QDs have been synthesized in either liquid phase or gas phase. [24][25][26][27][28] Gas-phase doping of P and B in these free-standing Si QDs with at least partial hydrogen coverage of their surface has also been achieved by introducing dopant precursors (diborane and phosphine) into the plasma.…”

Section: Introductionmentioning

confidence: 99%

Chemical trend of the formation energies of the group-III and group-V dopants in Si quantum dots

Wei

2013

Phys. Rev. B

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Doping behavior in quantum dots (QDs) differs from that in the bulk. Despite many efforts, the doping properties are still not fully understood. Using first-principles methods, we have calculated the formation energies of various group-III acceptors and group-V donors doping at all non-equivalent sites in a Si QD (Si147H100). To analyze the trend of the formation energy, we decompose it into two terms: the unrelaxed formation energy (chemical energy) and the relaxation energy. We find that the unrelaxed formation energy generally increases as the dopant moves from the center of the QD to the surface. The variation of the unrelaxed formation energy in the surface region is explained by the variation of the local potential of the QD and the size effect. The relaxation energy gain increases as the size mismatch between the dopant and Si atom increases. Generally, the relaxation effect becomes more significant as the dopant moves toward the surface of the QD. The trend of the formation energy is determined by the two terms discussed above. If the size mismatch between the dopant and Si atom is small, the trend of the formation energy generally follows that of the unrelaxed formation energy, increasing as the dopant moves from the center to the surface; thus, these dopants have a better chance of staying in the core region. On the other hand, if the size mismatch is large, the relaxation effect dominates and the formation energy decreases, which indicates these dopants cannot enter the core region under equilibrium growth conditions.

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Electronic Structure of 1 to 2 nm Diameter Silicon Core/Shell Nanocrystals: Surface Chemistry, Optical Spectra, Charge Transfer, and Doping

Cited by 90 publications

References 53 publications

In situ passivation and blue luminescence of silicon clusters using a cluster beam/H2O codeposition production method

In situ passivation and blue luminescence of silicon clusters using a cluster beam/H2O codeposition production method

Ab initioquantum chemistry: Methodology and applications

Chemical trend of the formation energies of the group-III and group-V dopants in Si quantum dots

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