![Best Results
Figures 3&4: Domain sectioning [Same as
Figure 2]
Figure 1: Graphite addition.
Figure 2: The first instance
There is clear forest-like axial
of uniform, nonradial
growth, with some branched
nanowire growth seen in
growth as well [Powder
the project [Powder
Temperature 900°C; Substrate
Temperature 900°C;
Temperature 528.7-165.9°C;
Substrate Temperature
Pressure 0.85 Torr; Flow Rate
650-400°C; Pressure 1.50
60 SCCM; Time 4 Hours]
Torr; Flow Rate 50 SCCM;
Time 0.5 Hours]](https://image.slidesharecdn.com/sigmaxinws-130308142401-phpapp02/85/Sigma-xin-ws-8-320.jpg)
![Best Results
Figure 6: Same substrate as Figure 5, but
a different temperature zone. The
growth direction is more random and
the domains seen in Figures 3&4 are
absent [Same as Figure 2]
Figure 5: This is the best result, with
crystalline growth and uniform
dimensionality [Powder Temperature
900°C; Substrate Temperature 650-400°C;
Pressure 1.50 Torr; Flow Rate 50 SCCM;
Time 0.5 Hours]](https://image.slidesharecdn.com/sigmaxinws-130308142401-phpapp02/85/Sigma-xin-ws-9-320.jpg)
Sigma xin ws
- 1. In2Se3 Nanowire Growth and Physical Characterization for Photovoltaic Use Anna Dubovitskaya North Carolina School of Science and Mathematics
- 2. Introduction: Why Nanowires? The interest in the use of nanowires for photovoltaic cells stems from their unique properties: • Higher efficiencies due to increased absorption • Higher tolerance for defects • Shorter diffusion lengths, which reduce trapping or recombination of photoexcited charge carriers • Nanowires of the same high crystalline quality and excellent charge transport as bulk/thin films can be made at a lower cost • Better resistance to photodegradation compared to existing photovoltaics.
- 3. Goals and Hypothesis The objective for this project was to grow In2Se3 nanowires and document the parameter ranges for optimal growth. Hypothesis: there exist nanowire growth parameters that produce ideal or near-ideal nanowires suitable for further characterization.
- 4. Method: Growing Nanowires We used the vapor-liquid-solid (VLS) method: 1. supersaturate a substrate with vaporized In2Se3 powder 2. Gold catalyzes the growth 3. Solid deposition results in nanowire growth The following diagram shows this process with silicon nanowires: Garnett et al. Nanowire Solar Cells
- 5. Method: Growing Nanowires The ideal temperature and atomic percentage parameter for nanowire growth can be approximated using a binary phase diagram, where the shaded area represents ideal silicon nanowire growth: Garnett et al. Nanowire Solar Cells
- 6. Procedure The nanowires were grown using In2Se3 powder (mixed with graphite in some experiments) 1. Silicon substrates cleaned using RCA-1 2. Poly-l-lysine solution, left for 10 minutes (positive surface) 3. Rinsed with deionized water and dried. 4. Nanoparticles (10-50nm) placed on wafer 5. Horizontal tube furnace • Temperature • Pressure • Ratio 6. Analyzed with SEM and EDX
- 7. Procedure: Horizontal Tube Furnace The growth of the nanowires occurred in a horizontal tube furnace: • A controlled atmosphere: • Evacuate the tube furnace to 1x10-3 torr • Backfill with Argon to the growth pressure • gas flow is controlled with a mass flow controller, • constant pressure is maintained by a throttle valve connected to a capacitance manometer.
- 8. Best Results Figures 3&4: Domain sectioning [Same as Figure 2] Figure 1: Graphite addition. Figure 2: The first instance There is clear forest-like axial of uniform, nonradial growth, with some branched nanowire growth seen in growth as well [Powder the project [Powder Temperature 900°C; Substrate Temperature 900°C; Temperature 528.7-165.9°C; Substrate Temperature Pressure 0.85 Torr; Flow Rate 650-400°C; Pressure 1.50 60 SCCM; Time 4 Hours] Torr; Flow Rate 50 SCCM; Time 0.5 Hours]
- 9. Best Results Figure 6: Same substrate as Figure 5, but a different temperature zone. The growth direction is more random and the domains seen in Figures 3&4 are absent [Same as Figure 2] Figure 5: This is the best result, with crystalline growth and uniform dimensionality [Powder Temperature 900°C; Substrate Temperature 650-400°C; Pressure 1.50 Torr; Flow Rate 50 SCCM; Time 0.5 Hours]
- 10. Best Results: EDX The previous results showed SEM images of the best results. For figure 5, the EDX analysis graph is below: This shows In:Se ratios of around 1:1 or 3:4
- 11. Conclusions It was found that the ideal parameters include: • Pressure: 1.0~1.5 torr • Flow rate: 27~40 SCCM • higher flow rates can impede the pressure, placing a limit on it due to the pump’s inability to deal with the flow rate of the incoming gas • Substrate Temperature: 640°C • manipulation of the Furnace Distance vs Temperature graph. • Powder Temperature: 825°C • Gold Particle Diameter : 50nm • double coating.
- 12. Conclusions: Observations The following additional observations were made: • Graphite addition does not have as much impact as first thought with regard to NW growth • Figure 5, the most ideal out of the 6 figures, had nanowire diameter ranges from 45-55nm using 50nm gold nanoparticle catalysts • Ordered nanowires (the opposite of the sectioning effect in Figure 4) may be better for light trapping • EDX results for Figures 2-6 showed no leftover presence of gold nanoparticles, which may indicate non-VLS growth • High powder temperatures result in increased uncontrollable deposition (2D growth) as well as deposition before the start of the attempt • Using gold particles that are spatially far apart or small in size results in greater 2D excess deposition
- 13. Future Work Having physically characterized the In2Se3 nanowires, the next step will be to optically characterize them. Since these nanowires were made with the intention of use in photovoltaic solar cells, their optical properties are crucial in determining their usefulness and maximum efficiency. In particular, we want to test the time it takes for recombination of electron-hole pairs, and the absorption efficiency of In2Se3 nanowires.
- 14. Acknowledgements Dr. Jonathan Bennett Department of Physics North Carolina School of Science and Mathematics Dr. Todd Roberts Chancellor North Carolina School of Science and Math Dr. Marvin Wu, Department of Physics North Carolina Central University Funding provided by: NCSSM Foundation Summer Physical Science Research Program, National Science Foundation, National Aeronautics and Space Administration