Room-temperature atmospheric oxidation of Si nanocrystals after HF etching

Pi, Xiaodong; Mangolini, Lorenzo; Campbell, Stephen A.; Kortshagen, Uwe R.

doi:10.1103/physrevb.75.085423

Cited by 117 publications

(137 citation statements)

References 32 publications

Supporting

Mentioning

127

Contrasting

Unclassified

Order By: Relevance

“…51 However, some other researchers hold a different viewpoint that such a change of steady-state PL in Si QDs is caused by a blue emission surface center induced during the oxidation process. 52 In our sample, a new red-shifted PL occurred during oxidation. A possible explanation for this phenomenon is that new surface states constitute during oxidation.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

Wang

et al. 2015

Light Sci Appl

View full text Add to dashboard Cite

In this work, the fundamental mechanism of ultrabright fluorescence from surface-modified colloidal silicon quantum dots is investigated in depth using ultrafast spectroscopy. The underlying energy band structure corresponding to such highly efficient direct bandgap-like emissions in our surface-modified silicon quantum dots is unraveled by analyzing the transient optical spectrum, which demonstrates the significant effect of surface molecular engineering. It is observed that special surface modification, which creates novel surface states, is responsible for the different emission wavelengths and the significant improvement in the photoluminescence quantum yields. Following this essential understanding, surface-modified silicon quantum dots with deep blue to orange emission are successfully prepared without changing their sizes. Keywords: quantum confinement; silicon quantum dots; surface molecular engineering; ultrafast spectroscopy; wave function modification INTRODUCTIONCrystalline silicon has been the most important semiconductor material in the modern electronics industry due to its excellent electronic properties. However, as a well-known indirect bandgap semiconductor, the optical properties of crystalline silicon are relatively poor, which limits its applications in silicon photonics. To pursue the desired optical performance in silicon materials, nanostructured silicon objects with enhanced photoluminescence (PL) have attracted increasing interest. 1213 Most notably, due to the three-dimensional quantum confinement effect in silicon nanocrystals (Si NCs), the momentum conservation rule is relaxed, and the spatial distributions of photogenerated exciton wave functions tend to extend to the surface of nanoparticles, which provides an efficient approach to manipulate the energy structure of silicon. 14218 Thus, the excitonic emission from Si NCs are usually thought to follow three models: (i) 'direct' transition from a quantization-related bandgap; (ii) indirect approaches, i.e., with the help of other emission centers; and (iii) surface and/or strain engineering. 19 For the 'direct' approach, the observed size-dependent PL behavior in Si NCs can be well explained by the quantum confinement effect. However, such Si NCs can hold strong PL only in the deep red region with limited stability, and their PL lifetimes from these 'direct'

show abstract

Section: Resultsmentioning

confidence: 99%

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

Wang

et al. 2015

Light Sci Appl

View full text Add to dashboard Cite

show abstract

“…The light emission from Si and Ge NCs is usually inherently dependent on the NC-size-induced quantum confinement effect. [12][13][14][15] However, other structural factors such as surface chemistry, [16][17][18][19][20] alloying, 21,22 doping 23,24 and defects [25][26][27] have also been found to affect the light emission from Si and Ge NCs. Regarding defects, dangling bonds at the NC surface have been the most extensively investigated.…”

Section: Introductionmentioning

confidence: 99%

“…Regarding defects, dangling bonds at the NC surface have been the most extensively investigated. Both experiments 26,28 and calculations 29,30 showed that the light emission from Si and Ge NCs might be significantly affected by dangling bonds at the NC surface. As a type of planar defects, twins have been frequently observed in transmission electron microscopy (TEM) analysis.…”

Section: Introductionmentioning

confidence: 99%

Twinned silicon and germanium nanocrystals: Formation, stability and quantum confinement

et al. 2015

AIP Advances

View full text Add to dashboard Cite

Although twins are often observed in Si/Ge nanocrystals (NCs), little theoretical investigation has been carried out to understand this type of important planar defects in Si/Ge NCs. We now study the twinning of Si/Ge NCs in the frame work of density functional theory by representatively considering single-twinned and fivefold-twinned Si/Ge NCs. It is found that the formation of twinned Si/Ge NCs is thermodynamically possible. The effect of twinning on the formation of Si NCs is different from that of Ge NCs. For both Si and Ge NCs twinning enhances their stability. The quantum confinement effect is weakened by twinning for Si NCs. Twinning actually enhances the quantum confinement of Ge NCs when they are small (<136 atoms), while weakening the quantum confinement of Ge NCs as their size is large (>136 atoms). The current results help to better understand the experimental work on twinned Si/Ge NCs and guide the tuning of Si/Ge-NC structures for desired properties.

show abstract

“…The majority of the oxygen gets incorporated in a Si-Si bond as shown by the Si-O-Si stretching modes (1050, 1107, and 1160 cm À1 ). [36][37][38] This is also shown in the Si-H stretching modes with at least one oxygen atom back-bonded to the Si atom (OSi 2 -Si-H @ 2140 cm À1 , O 2 Si-Si-H @ 2190 cm À1 , and O 3 -Si-H @ 2250 cm À1 ). This demonstrates that most of the oxygen is incorporated in the back bonds of the Si atoms at the surface of Si NCs.…”

mentioning

confidence: 99%

“…4(a). Besides the typical stretching modes for hydrogenated Si surfaces (Si 4Ày -Si-H y @$ 2106 cm À1 ), 36 various stretching modes can be observed that represent bonding configurations that include oxygen as well. The majority of the oxygen gets incorporated in a Si-Si bond as shown by the Si-O-Si stretching modes (1050, 1107, and 1160 cm À1 ).…”

mentioning

confidence: 99%

Size control, quantum confinement, and oxidation kinetics of silicon nanocrystals synthesized at a high rate by expanding thermal plasma

Han

Zeman

Smets

2015

Applied Physics Letters

View full text Add to dashboard Cite

The growth mechanism of silicon nanocrystals (Si NCs) synthesized at a high rate by means of expanding thermal plasma chemical vapor deposition technique are studied in this letter. A bimodal Gaussian size distribution is revealed from the high-resolution transmission electron microscopy images, and routes to reduce the unwanted large Si NCs are discussed. Photoluminescence and Raman spectroscopies are employed to study the size-dependent quantum confinement effect, from which the average diameters of the small Si NCs are determined. The surface oxidation kinetics of Si NCs are studied using Fourier transform infrared spectroscopy and the importance of postdeposition passivation treatments of hydrogenated crystalline silicon surfaces are demonstrated. Ensembles of nanocrystals (NCs) have attracted intensive attention in research due to their various special properties. NCs can be considered as zero-dimensional nano-structures whose excitons are confined in all three spatial dimensions. They have the ability to tune the band gap by varying their sizes and have unique interactions with photons like the multiple exciton generation (MEG) 1 or up-/down-spectral conversion by space separated quantum cutting (SSQC). 2 These unique mechanisms make NCs promising novel applications in thin-film transistors (TFTs), 3 water-splitting devices, 4 batteries, 5 and solar cells. 6,7 For instance, the utilization of MEG or SSQC properties of NCs might open new routes to conquer the Shockley-Queisser limit of single-junction solar cells, 8 if the Shockley-Read-Hall charge carrier recombination at the surfaces can be tackled. In 2011, above 100% external quantum-efficiency (EQE) value in the blue spectral range has been achieved in a cell using PbSe NCs. 9

show abstract

Room-temperature atmospheric oxidation of Si nanocrystals after HF etching

Cited by 117 publications

References 32 publications

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

Twinned silicon and germanium nanocrystals: Formation, stability and quantum confinement

Size control, quantum confinement, and oxidation kinetics of silicon nanocrystals synthesized at a high rate by expanding thermal plasma

Contact Info

Product

Resources

About