Structure and Chemical Analysis of Carbon Nanotubes Grown on Diamond Substrate Using Three Different Techniques MRS: November 30, 2010 Betty T. Quinton Wright State University, PhD. Student Material Science Engineering Air Force Research Laboratory Propulsion Directorate
Outline Contributors Introduction Experimental Set up SEM Raman TEM and EDS Summary 2
Contributors Betty Quinton and Jack Burke (UDRI) Dr. Paul N. Barnes (AFRL), Dr. Sharmila M. Mukhopadhyay (WSU), Dr. Chakrapani V. Varanasi (ARO), Dr.Yongli Xu (UES) Lt. Breanna Ruter-Schoppman (AFRL), Kevin Yost (AFRL), Dr. James Scofield (AFRL), Dr. Bang Tsao (UDRI), Jacob Lawson (UDRI), Dr. Robert Wheeler (UES), Hema Vijwani (WSU) Funding support by Air Force Office of Scientific Research (AFOSR) and AFRL/RZPG 3
Introduction CNTs are being studied for their thermal properties CNTs on diamond are grown to increase rate of cooling Common methods to grow CNTs on various substrates is chemical vapor deposition (CVD) Thermal CVD (T - CVD) Microwave Plasma Enhanced CVD (MPE - CVD) Floating catalyst Thermal CVD (FCT- CVD) Microscopy analysis: Understanding the growth mechanism SEM: General structure, size, density TEM: Cross sectional analysis at the interface, track the catalyst particles. EDS: Chemical analysis 4
Experimental Setup Growth at AFRL T CVD Sputtered 10nm Ni thin film onto the diamond substrate Heat treatment and growth at 800 o C C 2 H 2 as carbon feed-stock, Ar/H 2 as diluting gas MPE CVD Sputtered 10nm Fe thin film onto the diamond substrate Hydrogen plasma Heat treatment at 400 o C and growth at 650 o C CH 4 as carbon feed-stock, H 2 as diluting gas Growth at WSU FCT-CVD Sputter 100nm Si/O 2 thin film on to the diamond substrate Xylenene/ Ferrocene as carbon source and catalyst source Growth at 750 o C 5
Experimental Setup Commercial CVD Diamond 1)AFM : Surface roughness measurement 2)SEM Growth of CNTs 1)T-CVD 2)FCT-CVD 3)MPE-CVD Microscopy 1) SEM 2) TEM 3) EDS Raman Spectroscopy Thermal measurements 6
CVD Diamond Substrate Surface Roughness AFM Cross sectional image Smooth Side Rough side Commercial Diamond RMS Roughness for the smooth side is 5.043nm 7
Catalyst Island particles are formed after heat treatment The particles sizes are uniform and distributed evenly on the surface of the diamond Average particle sizes are 55nm Minimum 33nm and maximum sizes are 75nm 8
SEM: Top view Thermal CVD Microwave Plasma Enhanced CVD Floating catalyst thermal CVD Scale bar is 4um Scale bar is 200 nm ~50nm ~15nm
Normalized Intensity Average Raman Spectroscopy Diamond Peak 1332 cm -1, measured 1338 cm -1 D peak = 1355cm -1, measured 1366cm -1(TCVD), 1360cm -1(PECVD), 1360cm -1(FCTCVD) G peak = 1575 cm -1, measured 1588cm -1(TCVD), 1607cm -1(PECVD), 1604cm -1(FCTCVD) 20 18 D/G =.84 16 14 12 10 8 6 D/G = 1.94 D/G = 0.3 Diamond TCVD PECVD FlowCVD 1355 Reference 4 2 0 0 500 1000 1500 2000 2500 3000 3500 4000 Wave Numbers
TEM preparation 1) Protective cap layer from Pt or C were deposited onto the surface to protect CNTs. 2) Trench out a foil ~ 5um wide by 30um long 3) Undercut the foil until it break loose 4) Lift and attach the foil onto a TEM grid 5) Thin the sample until it is electron transparent ~100nm thick
TEM: Cross-sectional Image (T-CVD: C 2 H 2 ) 2um [Cap, CNT, Interface, Diamond] 1 µm 12
EDS Mapping (T-CVD: C 2 H 2 ) Carbon Diamond and CNT Scanned Area Ni - Catalysts Pt Protective Coating Some particles are imbedded into the diamond substrate Particles that are not imbedded into the substrate provided growth for CNT Ga Ion Beam 13
TEM: Acetate Tape Pull-Off (T-CVD: C 2 H 2 ) C Nickel Ni Cu 4um 1um Ni particle is attached at one of ends of the CNT Ni particles can be found along the CNTs 500nm 50nm
TEM: Floating Catalysts (Xylene/ Ferrocene) Catalyst particles are visible along the interface Catalyst particles looks like they are imbedded into the silica layer Catalyst particles are visible along the CNT, and away from the interface 1um 200 nm 100 nm 50nm
Fe particles are detected throughout the foil. They are found along the interface all the way towards the cap EDS: Floating Catalyst (Xylene/ Ferrocene) ) C Si Diamond SiO 2 O C Tube_1(Interface) Pt 200 nm Cap Pt Tube_3 Tube_2 Mo Fe Ga Pt Fe Fe
EDS: MPE-CVD (CH 4 with hydrogen plasma) C Diamond 1 um Fe particles was not detected at the interface but rather towards the mid portion of the CNT 500 nm Interface Pt Cap Tube_2 Ga Tube_1 Pt Fe Pt Ga
Summary High resolution microscopy was performed on 3 different CNTs growth techniques. SEM/ Raman T-CVD samples has the largest diameter with smoothest appearance. T-CVD also have the strongest G peak, with lowest D/G ratio of 0.3 Thermal CVD EDS mapping suggests some Ni particle are absorbed into the diamond substrate Only the Ni particles that are lifted away from the interface provides CNT growth (but not tip growth) Particles are found imbedded along CNTs: Much like FCT-CVD Floating catalyst thermal CVD Fe particles are imbedded into the silica layer along the interface Fe particles are found along the CNT Microwave plasma CVD EDS did not detect Fe along the interface Fe was detected towards the middle of CNT section Thermal Measurements will be the next step for this study. 18
Thank You
Methods (1 of 3) TCVD at WPAFB Growing CNT using a furnace at 800 o C 10nm (Ni or Fe) catalysts thin film pre-sputter onto the substrate Growth time = 2hrs. Pressure = 90 torr 300sccm Ar/5%H 2 400 sccm Ar/ 10%C 2 H 2 Heating Source Sample Load Gas line
Methods (2 of 3) PECVD at WPAFB Microwave Plasma Chemical Vapor Deposition (1.5kW) Base pressure 1 x 10-3 Torr 20 Torr growth chamber pressure 130 sccm H 2, 15 sccm CH 4 CH 4 used as precursor gas Growth temperature at 650 0 C, 1000W 5 minute pretreatment in Hydrogen plasma 400 0 C, 400W Microwave unit Control panel Loading chamber Heating unit
Methods (3 of 3) Flowing Catalyst TCVD (FCTCVD) at WSU Microwave plasma to deposit a layer of silica total silica thickness ~80nm Growth parameter 600 sccm Ar (40-45) sccm H 2 Xylene = 10ml Ferrocene =.12g Flow rate = 3ml/hr Growth time = 20min Growth temperature = 750⁰C Overnight cool down