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- Perraud, Simon, et al.
(författare)
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Silicon nanocrystals : Novel synthesis routes for photovoltaic applications
- 2013
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Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 210:4, s. 649-657
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Tidskriftsartikel (refereegranskat)abstract
- Novel processes were developed for fabricating silicon nanocrystals and nanocomposite materials which could be used as absorbers in third generation photovoltaic devices. A conventional high-temperature annealing technique was studied as a reference process, with some new insights in crystallisation mechanisms. Innovative methods for silicon nanocrystal synthesis at much lower temperature were demonstrated, namely chemical vapour deposition (CVD), physical vapour deposition (PVD) and aerosol-assisted CVD. Besides the advantage of low substrate temperature, these new techniques allow to fabricate silicon nanocrystals embedded in wide bandgap semiconductor host matrices, with a high density and a narrow size dispersion.
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| 2. |
- van Sebille, Martijn, et al.
(författare)
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Nanocrystal size distribution analysis from transmission electron microscopy images
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 7:48, s. 20593-20606
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Tidskriftsartikel (refereegranskat)abstract
- We propose a method, with minimal bias caused by user input, to quickly detect and measure the nanocrystal size distribution from transmission electron microscopy (TEM) images using a combination of Laplacian of Gaussian filters and non-maximum suppression. We demonstrate the proposed method on bright-field TEM images of an a-SiC:H sample containing embedded silicon nanocrystals with varying magnifications and we compare the accuracy and speed with size distributions obtained by manual measurements, a thresholding method and PEBBLES. Finally, we analytically consider the error induced by slicing nanocrystals during TEM sample preparation on the measured nanocrystal size distribution and formulate an equation to correct this effect.
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| 3. |
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| 4. |
- Xie, Ling, et al.
(författare)
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3D electron tomography analysis of silicon nanoparticles in SiC matrices by quantitative determination of EELS plasmon intensities
- 2014
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Konferensbidrag (refereegranskat)abstract
- Silicon nanoparticles (NPs) embedded in insulating or semiconducting matrices has attracted much interest for the third generation of photovoltaics, “all-Si” tandem solar cells. This study is to show how silicon NPs are distributed in 3D on a silicon carbide thin film using the electron tomography technique in the transmission electron microscopy (TEM). [2]We first have assessed Si NPs distributions in such SiCx sample with a low degree of crystalline using bright field (BF) TEM tomography (figure 1) and found an average nearest neighbor spacing of two NPs of about 12nm. For more crystalline NPs, the projection requirement is no more fulfilled and only those Si NPs that are both crystalline and oriented to a Bragg reflection are detectable. [3] Therefore, in this case, conventional BF TEM signal is unsuitable for electron tomography and we applied spectrum imaging (SI) techniques: EELS SI imaging and EFTEM SI imaging. Since Si and SiCx have different plasmon energies, [4] we can extract Si plasmon and SiCx plasmon images from the spectrum images. We observed that only a proper fit of the plasmon spectrum with subsequent extraction of Si and SiCx plasmon images results in the correct Si ad SiCx distribution (figures 2 and 3), whereas just EFTEM images taken from windows around the Si and the SiC plasmon energy resulted in overlaps in the image. For both, STEM and EFTEM SI signals, in figure 2 and 3, we are able to detect the entire population of NPs. In figure 3, the stripes like contrast inside of crystalline NPs shown in the BF TEM image persist in plasmon images. This is due to parallel beam illumination in EFTEM SI mode thus making the STEM SI imaging more suitable for tomography of these NPs. In Figure 2, for STEM SI, the contrast evolution during the tilting is thickness dependent, thicker part of the sample gives stronger contrast in the extracted plasmon images, and this nonlinear thickness effect can be corrected by introducing attenuation coefficient. [5]In summary, to study the 3D distribution of Si NPs in SiCx matrix, we compared three signals from BF TEM, STEM and EFTEM SI signals. In order to overcome the non-linearity of contrast change during the tilting process, STEM-SI signal in combination with quantitative treatment of the plasmon spectra shows clear Si NP contrasts and overcomes limits set by the projection requirement.[1] S. Perraud et al., Phys. Status Solidi A, 1–9 (2012).[2] J. Frank, Electron Tomography: Three Dimensional Imaging with the Transmission ElectronMicroscope, Plenum, New York, London, 1992.[3] P. A. Midgley et al., Ultramicroscopy 96 (2003) 413.[4] R.F. Egerton, Electron Energy-Loss Spectroscopy in the Electron Microscope, 420, 2011.[5] W. Van den Broek et al. Ultramicroscopy 116 (2012) 8–12
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| 5. |
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| 6. |
- Xie, Ling, 1982-, et al.
(författare)
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Electron tomography analysis of 3D interfacial nanostructures appearing in annealed Si rich SiC films
- 2017
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Ingår i: Nanoscale. - : ROYAL SOC CHEMISTRY. - 2040-3364 .- 2040-3372. ; 9:20, s. 6703-6710
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Tidskriftsartikel (refereegranskat)abstract
- The optical and electrical properties of Si rich SiC (SRSC) solar cell absorber layers will strongly depend on interfacial layers between the Si and the SiC matrix and in this work, we analyze hitherto undiscovered interfacial layers. The SRSC thin films were deposited using a plasma-enhanced chemical vapor deposition (PECVD) technique and annealed in a nitrogen environment at 1100 degrees C. The thermal treatment leads to metastable SRSC films spinodally decomposed into a Si-SiC nanocomposite. After the thermal treatment, the coexistence of crystalline Si and SiC nanostructures was analysed by high resolution transmission electron microscopy (HRTEM) and electron diffraction. From the quantitative extraction of the different plasmon signals from electron energy-loss spectra, an additional structure, amorphous SiC (a-SiC) was found. Quantitative spectroscopic electron tomography was developed to obtain three dimensional (3D) plasmonic maps. In these 3D spectroscopic maps, the Si regions appear as network structures inside the SiC matrix where the a-SiC appears as an interfacial layer separating the matrix and Si network. The presence of the a-SiC interface can be explained in the framework of the nucleation and growth model.
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