A Novel Sold-Solid-Vapor Growth Mode

This article describes a novel solid−solid−vapor growth mode which can be used instead of the vapor−solid−solid or vapor−liquid−solid mechanisms employed for nanowires growth.

Driven by Cd evaporation and utilizing the TEM technique in situ heating, temperature-induced epitaxial growth of PbSe nanocrystal at the CdSe phase was observed.

Purpose

  • Produce new techniques for the design and synthesis of heteronanocrystals
  • New interface design through the heat treatment of heteronanocrystals
  • Driving force: Possible application of semiconductor nanowires in optoelectronics and nanoscale electronics

Challenges

  • High-temperature chemical mapping
  • Sample stability at greater temperatures decreases TEM resolution
  • Interpretation of the images
  • Beam damage of the specimen during EDX mapping

EDX mapping of the nanodumbbells and HAADF-STEM images. (a) HAADF-STEM image of CdSe-PbSe nanodumbbells. PbSe tips at both ends of CdSe nanorods can be seen. (b) Dumbbell HNCs at 160 °C. PbSe was extended gradually inside the nanorod (solid arrows). (c) Dumbbell HNCs at 200 °C. PbSe, was seen over the whole nanorods (solid arrows). HAADF-STEM images and corresponding EDX elemental maps of dumbbell HNCs annealed for 5 minutes at (d - g) 100 °C, nanorods of CdSe with PbSe tips. (h - k) 170 °C, Pb tips extant to the middle part of the nanorod, while Cd disappeared. (l - o) 200 °C, bright contrast, which correspond to Pb, can be seen within complete nanorods. At 200 °C, the nanorod transforms to PbSe.

Figure 1. EDX mapping of the nanodumbbells and HAADF-STEM images. (a) HAADF-STEM image of CdSe-PbSe nanodumbbells. PbSe tips at both ends of CdSe nanorods can be seen. (b) Dumbbell HNCs at 160 °C. PbSe was extended gradually inside the nanorod (solid arrows). (c) Dumbbell HNCs at 200 °C. PbSe, was seen over the whole nanorods (solid arrows). HAADF-STEM images and corresponding EDX elemental maps of dumbbell HNCs annealed for 5 minutes at (d - g) 100 °C, nanorods of CdSe with PbSe tips. (h - k) 170 °C, Pb tips extant to the middle part of the nanorod, while Cd disappeared. (l - o) 200 °C, bright contrast, which correspond to Pb, can be seen within complete nanorods. At 200 °C, the nanorod transforms to PbSe.

HAADF-STEM images of CdSe-PbSe HNCs at (a) 160 °C and (b) 180 °C. Hexagonal wurtzite CdSe nanorods began to change to cubic rock-salt PbSe. The insets are FTs taken from the white squares in each image.

Figure 2. HAADF-STEM images of CdSe-PbSe HNCs at (a) 160 °C and (b) 180 °C. Hexagonal wurtzite CdSe nanorods began to change to cubic rock-salt PbSe. The insets are FTs taken from the white squares in each image.

Results

In this example, utilizing in situ heating, TEM authors noticed a novel process, which can be referred to as solid−solid− vapor (SSV) growth mechanism compared to the commonly used vapor–solid–solid (VSS) and vapor−liquid−solid (VLS).

PdSe nanocrystals can be grown under particular conditions in the SSV reaction at CdSe by the evaporation of Cd and simultaneous supply of Pd.

The Wildfire S3 holder from DENSsolutions, which is optimized for EDX, allowed the recording of HAADF-STEM images and the corresponding EDX elemental maps of CdSe-PbSe heteronanocrystals at high temperatures (Figure 1).

Temperature increase results in the extension of PbSe domains at a detriment to CdSe (Figure 1). Temperature induced transformation from CdSe to PbSe was therefore recorded.

High-resolution images and the related Fourier transforms (FTs) patterns are detailed in Figure 2 (a, b) and verify the presence of structural changes that were temperature induced (Figure 2).

It is a possibility to observe structural changes during heating in situ while upholding the highest TEM performance because of the high stability of the holder (Movie 1).

It was demonstrated that the SSV growth mechanism, where one solid-phase epitaxially develops at the expense of another solid phase, can offer a different method for growing semiconductor nanowires.

References and Further Reading

  • Anil O Yalcin, Zhaochuan Fan, Bart Goris, Wun-Fan Li, Rik S Koster, Chang-Ming Fang, Alfons Van Blaaderen, Marianna Casavola, Frans D Tichelaar, and Sara Bals, Nano letters 14 (6), 3661 (2014).

This information has been sourced, reviewed and adapted from materials provided by DENSsolutions.

For more information on this source, please visit DENSsolutions.

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