Isolated SiC nanocrystals in SiO2

Makkai, Zs.; Pécz, B.; Bársony, I.; Vida, Gy.; Pongrácz, Anita; Josepovits, Katalin; Deák, Péter

doi:10.1063/1.1952577

Cited by 23 publications

(9 citation statements)

References 8 publications

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“…In addition, the surface states may modify not just the absorption treshold of the ideal nanocrystals, but the other part of the spectrum as well.In this Letter we investigate ideal and recon-structed hydrogenated cubic silicon carbide nanocrystals (SiCNC). The choice of this material was made for several reasons: i) as a binary compound material one can study the effect of two types of termination ii) SiCNC is one of the most promising candidates for bioinert biomarkers [8,9,10] and environmental friendly nanooptics [11,12,13] iii) the experimental absorption spectrum is available for small-medium sized colloidal SiCNCs [9]. We determined the structure by standard DFT calculations (PBE) while the absorption spectrum was calculated by hybrid functional based time-dependent DFT (TDPBE0) calculations.…”

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The absorption spectrum of hydrogenated silicon carbide nanocrystals from ab initio calculations

Vörös

Deák

Frauenheim

et al. 2010

Applied Physics Letters

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The electronic structure and absorption spectrum of hydrogenated silicon carbide nanocrystals (SiCNC) have been determined by first principles calculations. We show that the reconstructed surface can significantly change not just the onset of absorption, but the shape of the spectrum at higher energies. We found that the absorption treshold of the reconstructed SiCNs cannot be accurately predicted from traditional density functional theory calculations. PACS numbers: 78.67.Bf, 71.15.Qe Semiconductor nanocrystals (NC) are objects of intense interest in fields ranging from biology [1] to third generation solar cells [2,3]. NCs are small pieces of crystal with a surface to volume ratio that is much larger than is typical for bulk crystals. Therefore, understanding the surface states of NCs could be critical in the interpretation of the measurements, or in applications [4]. Pure covalent semiconductor NCs have dangling bonds at the surface that can easily react with the molecules present in the environment. The simplest example is when the dangling bonds are saturated by hydrogen atoms. It is well-known from surface studies of bulk covalent semiconductors that saturation can happen either by conserving the bulk-like structure at the surface or by reconstruction at the surface with formation of long bonds. In what follows, we will refer to a non-reconstructed surface as an "ideal" surface. While the structure of surface reconstruction and its effect on the electrical/optical properties can be monitored by experiments and first principles simulations for the bulk crystals, our understanding of semiconductor NCs remains undeveloped. Traditional ab initio density functional theory (DFT) calculations have been successfully applied to explore the geometry and electronic structure of small covalent semiconductor NCs, and rarely, up to experimental sizes [5]. However, accurate calculation of the absorption spectrum of NCs requires methods beyond DFT that are usually computationally prohibitive. While DFT is a ground state theory, it is usually assumed that one can use the DFT electronic gap [6] with some "rigid shift" to calculate the absorption treshold of the NCs. For example, a difference of ≈1.5 eV was deduced by comparing the DFT and Quantum Monte Carlo results on ideal very small hydrogenated silicon nanocrystals [7]. However, it is not clear whether this type of correction may hold for the reconstructed surface. In addition, the surface states may modify not just the absorption treshold of the ideal nanocrystals, but the other part of the spectrum as well.In this Letter we investigate ideal and recon-structed hydrogenated cubic silicon carbide nanocrystals (SiCNC). The choice of this material was made for several reasons: i) as a binary compound material one can study the effect of two types of termination ii) SiCNC is one of the most promising candidates for bioinert biomarkers [8,9,10] and environmental friendly nanooptics [11,12,13] iii) the experimental absorption spectrum is available for small-medium sized co...

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The absorption spectrum of hydrogenated silicon carbide nanocrystals from ab initio calculations

Vörös

Deák

Frauenheim

et al. 2010

Applied Physics Letters

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“…A new experimental procedure allows to grow 3C-SiC nanocrystals of well-controlled size distribution embedded in in a SiO 2 matrix on Si substrates [1,2]. The symmetrical band offsets of 3 eV at the conduction and valence band edges provide equally good electronic confinement for electrons as well as holes and thus make SiC/SiO 2 a very interesting system to build quantum dots (QD).…”

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Annealing simulations to determine the matrix interface structure of SiC quantum dots embedded in SiO₂

Knaup

Vörös

Deák

et al. 2010

Phys. Status Solidi (c)

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We use the Density Functional based Tight‐Binding (SCC‐DFTB) method in a Quantum Mechanics/Molecular Mechanics embedding scheme to simulate single SiC quantum dots of different shapes and with diameters of up to 1 nm, embedded in a block of α ‐Quartz with cell vectors of a = 15 nm and c = 13 nm. First results show that during the annealing process three recurring motives appear at the SiC/SiO2 interface of the embedded nanocrystals: Si‐Si bonds often in Si interstitial‐like configurations, C‐C bonds involving all possible combinations of sp3 and sp2 hybridized carbon and threefold coordinated oxygen atoms. All of these defects, alone or in complexes, may play a crucial role in quenching the luminescence of these embedded nanocrystals. Detailed studies of the spectroscopic properties if the point defects identified in this work is indicated (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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“…Full SiC coverage of the silicon surface cannot be achieved due to the limits of that method. However, nanocrystals were prepared which were also separated later from the Si substrate [2].…”

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Ion implantation enhanced formation of 3C-SiC grains at the SiO₂/Si interface after annealing in CO gas

Pécz¹,

Stoëmenos²,

Voelskow³

et al. 2010

J. Phys.: Conf. Ser.

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Isolated SiC nanocrystals in SiO2

Cited by 23 publications

References 8 publications

The absorption spectrum of hydrogenated silicon carbide nanocrystals from ab initio calculations

The absorption spectrum of hydrogenated silicon carbide nanocrystals from ab initio calculations

Annealing simulations to determine the matrix interface structure of SiC quantum dots embedded in SiO₂

Ion implantation enhanced formation of 3C-SiC grains at the SiO₂/Si interface after annealing in CO gas

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Isolated SiC nanocrystals in SiO2

Cited by 23 publications

References 8 publications

The absorption spectrum of hydrogenated silicon carbide nanocrystals from ab initio calculations

The absorption spectrum of hydrogenated silicon carbide nanocrystals from ab initio calculations

Annealing simulations to determine the matrix interface structure of SiC quantum dots embedded in SiO2

Ion implantation enhanced formation of 3C-SiC grains at the SiO2/Si interface after annealing in CO gas

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Product

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Annealing simulations to determine the matrix interface structure of SiC quantum dots embedded in SiO₂

Ion implantation enhanced formation of 3C-SiC grains at the SiO₂/Si interface after annealing in CO gas