1. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Characterization of layered gallium telluride (GaTe) Omotayo O Olukoya (Chabot College) PI : Oscar Dubon Mentor : Jose Fonseca Vega Lawrence Berkeley National lab 1

2. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Layered semiconductors Complex structure Manipulate band-gap. 2 GaTe (1.045 nm) Recent discovery 0.8 1.6 2.4 3.2 nm adapted from D. V. Rybkovskiy et al., PRB (2011) Mak, K.F., et al., Phys Rev Lett. 105, 136805 (2010). GaSe MoS 2 Chalcogenide

3. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) GaTe a.Monoclinic crystalline structure in bulk. parameter constant: a = 17.44 Å, b = 10.456 Å, c = 4.077 Å, ϒ = 104.4 o 3 b. Goes from monoclinic to hexagonal in thin films d. P - type What to look for? c. Direct band gap of 1.69 eV at room temperature. What do we know?

4. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Method 4 300 nm of thermally oxidized SiO 2 on Si was used. Ultra sonication  Isopropyl alcohol  Acetone Oxygen plasma Standard RCA cleansing method  Substrate treatment

5. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Method cont.  Scotch tape method was develop by Andre Geim 5  Optical microscopy  Mechanical exfoliation  Transfer

6. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Method cont. 6  Atomic Force microscopy (AFM) Tapping mode AFM images 8 nm

7. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Method cont. 7  Raman spectroscopy o A 15mW Ar ion laser (514.5 nm) was used.  Photoluminescence spectroscopy (PL) o A 488 nm blue laser

8. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Raman result Raman spectra cont. a. New peaks between 140 & 280 of Raman shift 8

9. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Raman’s result cont. Raman spectra b. Horizontal shift

10. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) PL result 10 Correlation between laser intensity and counts

11. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) PL result cont. Correlation between thickness and count 11

12. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Conclusion  GaTe exhibits some anisotropic features.  It will take further research to know what properties are actually isolated from bulk.  Great chances of being able to cleave down to a monolayer on SiO 2 substrate. 12

13. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Next step Cleave down to a monolayer Take more Raman Take low temperature PL Devices and application? 13

14. 2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) Acknowledgment Prof Oscar Dubon (PI) Jose Fonseca Vega (mentor) Dubon’s Group –Alex Luce (PL) –Erick Ulin-Avila Dr. Sharnia Artis Shuk H Chan Center for Energy Efficient Electronics (E3S) National Science Foundation (NSF) Q & A ? 14