1. Catalytic Segregation of Graphene Using Silver Nanoparticles
Brandon R. Reed
CHEM318

2. Introduction A fast developing field Desirable to cut correct shapes
Few techniques currently available
This research illustrates reproducible results.

3. Catalytic Environment
Catalysis occurs at the “step edges” of graphene.
At high temperatures, silver nanoparticles located at these edges are able to channel trenches through the graphene.
nanoparticle

4. Catalytic Environment
Mechanism of channeling
Particles cling to surface defects
Energetically favorable
Reaction involves oxygen  chemisorbed by particle (Silver oxide).
Oxidize atoms of graphene into CO2.
Follows the receding edge
Chemiabsorbed> reaction silveroxide?

5. 3nm graphene fold resonate 00: 22:38 - resonate
00: 50:54 - film uplifts
3nm graphene fold
resonate

6. Ag Nanoparticles-Multiple Methods
NaBH4 and AgNO3  on ice
Laser reflection  colloidal solution.
No aggregation, citrate buffer: double layer of charge, stabilizes particles and prevents aggregation

7. Ag Nanoparticles - Buffers
Magnetite Nanoparticle – Buffers & aggregation

8. Materials & Methods “highly oriented pyrolytic graphene (HOPG)”
Aqueous AgNO2 vs AgNO3
High temp (650 °C ).
In heated quartz tube (D = 3cm).
Imaging Ag particles : Scanning Force Microscopy (SFM) & Scanning Tunneling Microscope (STM).
HOPG= high purity of crystal lattice.
Note D = diameter

9. HOPG structure Lattice  multi-layered
highest degree of three dimensional ordering
Essentially low imperfections vs regular graphene samples
Mosaic Spread roughness
Less cleavability

10. Data & Results SFM surface morphology
SFM images  graphene 1 min anneal = no etching.
Cutting speed/trench length correlated to size of the nanoparticles.
Properties
Findings
Trench Length
9.0 uM
Trench Width
6-100 nm
Max Speed
250 nm s-1

11. (a) SFM height image of a sample annealed for 45 s
(a) SFM height image of a sample annealed for 45 s. The area is chosen to demonstrate that trenches channeled through graphene
layers of different thickness.
(b) Dependence of trench length on trench width for trenches formed in graphene bilayer on a sample annealed
for 1 min (see Supporting Information for dependencies for other graphene thickness). The dashed line is the linear fit.
(c) STM image of
a monolayer trench on a sample annealed for 1 min reveals smooth edges with peak-to-peak roughness (i.e., d) below 2 nm. The width of
the imaged trench is about 9 nm.
(d) SFM height image of a sample annealed for 1 min, a few examples of spiral (S) and zigzag (Z)
trenches are outlined. Notice that particles can switch back and forth between spiral or zigzag and straight channeling.

12. Trenching Types
Silver nanoparticles stay along the defects or step edges of the graphene.
3 types of trenches:
Straight segmented trenches
Spiral tranches
Zig zag trenches
Alternate trench formation causes
Pollution of sample  Sulfur Dioxide
HOPG vs regular graphene. The roughness of the regular would skew data.

13. Spiral Trenching
Talk about how spiral trenching occurs.

14. Pollution Insight
HOPG covered with silver nitrite in the presence of a small amount of sulfur. 1-min run.
Annealing of a new sample  brief ventilation
Spiral trenching.
Insight  poisoning of the catalyst responsible for formation of spiral trenches
Further studies needed.
Just silver dioxide?

15. Conclusions Fast channeling of large nanoparticles vs small
Rate-limiting step is the adsorption of molecular oxygen
Larger particles assemble at higher step edges
Max channeling speed  250 nm/s is of importance
Implications: any size particle capable given enough oxygen

16. Future Possibilities? YES!
New applications
High precision lithography on graphenes.
Catalysis applications  probe tip.

17. Current Research Developments - kirigami

18. Current Research Developments - kirigami

19. Current Research Developments - Shape
Slater, J.A. Thomas; Macedo, Alexandra; Schroeder, L. M. Sven; et al; Correlating Catalytic Activity of Ag-Au Nanoparticles with 3D compositional Variations. ACS, 2014, 14,
Ag and AuCl4-

20. Current Research Developments - Shape
Slater, J.A. Thomas; Macedo, Alexandra; Schroeder, L. M. Sven; et al; Correlating Catalytic Activity of Ag-Au Nanoparticles with 3D compositional Variations. ACS, 2014, 14,

21. References
Severin, N.; Kirstein, I. M. Sokolov; Rabe, J. P.; Rapid Trench Channeling of Graphenes with Catalytic Silver Nanoparticles. 2009, 9,
Slater, J.A.; Macedo, A.; Schroeder, L. M. Sven; et al; Correlating Catalytic Activity of Ag-Au Nanoparticles with 3D compositional Variations. ACS, 2014, 14,
Barberio, M.; Barone, P.; Imbrogno, A.; Xu, Fang.; CO2 adsorption on silver nanoparticle/carbon nanotube nanocomposites: A study of adsorption characteristics, J. physica status solidi, 2015, Vol. 252, 9, 1955–1959.
Bahadory, M. S.; Synthesis of Silver Nanoparticles, Journal of Chemical Education, 2007, 84,
Oldenburg, J. S.; Silver Nanoparticles: Uses and Applications, Sigma Aldrich, NanoComposix Inc
HOPG Detailed Description, , accessed: 8 October 2015.
Blees, M.; Nature-Video Research-Graphene Kirigami. edge/, 2015, accessed: 14 September 2015.

22. Questions
Additional Notes/ Questions

23. Quad image-notes
(a) SFM height image of a sample annealed for 45 s. The area is chosen to demonstrate that trenches channeled through graphene layers of different thickness.
(b) Dependence of trench length on trench width for trenches formed in graphene bilayer on a sample annealed for 1 min. The dashed line is the linear fit.
(c) STM image of a monolayer trench on a sample annealed for 1 min reveals smooth edges with peak-to-peak roughness below 2 nm. The width of the imaged trench is about 9 nm.
(d) SFM height image of a sample annealed for 1 min, a few examples of spiral (S) and zigzag (Z) trenches are outlined. Notice that particles can switch back and forth between spiral or zigzag and straight channeling.

24. Sulfur Dioxide Pollution-Notes
To propve pollution of catalyst, team annealed HOPG covered with silver nitrite in the presence of a small amount of sulfur. SFM imaging of results showed inhibition of channeling: the trenches were no longer than 50 nm (not shown). Annealing of a new sample after a brief ventilation produced mostly spiral type of trenches, which proves the poisoning of the catalyst to be responsible for the formation of spiral trenches. Thus these experiments give a nanoscopic insight into the poisoning mechanism of catalysts. Quantitative characterization of catalyst poisoning will require further investigations. NOT DETERMINITIVE