YIA: Interaction of Radiation with Graphene-based Nanomaterials for Sensing Fissile Materials (Grant # HDTRA0-09-1-0047) Yong P. Chen (yongchen@purdue.edu), Purdue University DTRA Technical Review 10/21/2009
Introduction & Background Radiation detection has been very closely coupled with advances in semiconductors.. How Can graphene do it (well)? The gravest danger we face---nuclear terrorism --- 07/16/08 at Purdue University (Summit on Confronting New Threats) And the biggest threat that we face right now is not a nuclear missile coming over the skies. It's in a suitcase. --- 09/28/2008 during 1 st Presidential debate 2
Radiation Detection SNM/FM Radiation Sensing --- some state of art: High Resolution is Desirable HPGE (High Purity Ge) [charge collection] Superconductor TES (Transition Edge Sensor) [NOT charge collection; use a sharp feature] Can we have a sharp feature @ ~ room T that couples to radiation(effect) 3
What is Graphene Usual solid graphene 1000+ papers in 2008 (electrically isolated) discovered in 2004 Building block of many carbon (nano)materials New wonder semiconductor/semimetal Amazing Electrical Properties ( post Si electronics/ Moore ) Amazing Mechanical Properties --- highest strength (~CNT) Amazing Thermal properties highest thermal conductivity Easy to make and work with (2D planar fabrication) Electrons in graphene E v F pv F ~ 1 10 kv 6 m/s Dirac equation Chiral massless fermions [QED/QCD in graphene] High conductivity/mobility (>10X Si @ room T) Low (electronic) noise Tunable (electr.) properties Exposed to environment --- excellent sensor mat. F 4
Sharp Electric Field Effect in Graphene GFET insulator graphene V gate semiconductor (doped) Dirac pt (<n>=0) p n Finite R (quantum R) Low noise High mobility (can ballistic) High speed [THz] High sensitivity [de/e<10-3 ] Bandgap eng possible all these even at 300K the sharp feature F. Schedin et al 2007 5
GFET for radiation sensing 2.0 1.5 Graphene resistance 2.0 1.5 R (kohm) 1.0 0.5 R (kohm) 1.0 0.5 How well can GFET detect radiation [rare events] -3x10 7-2 -1 0 1 2 3 Electric Field (V/m) -3x10 7-2 -1 0 1 2 3 Electric Field (V/m) Sensitivity/energy resolution? V gate insulator semiconductor graphene Small E field (undoped/~insulating) V gate insulator semiconductor (conductive) graphene Large E field Graphene a highly sensitive to detect local Efield-chage [single molecule sensitivity] Vgate tunable - sensitivity and resolution NOT relying on collecting/drifting ionizded charges; appearance of ionized charges changes electric field sensing Efield intrinsically faster than sensing drfited/collected charges can work with variety of absorber substrates for gamma/neutron interaction; thin insulator layer 6
Possible alternative schemes: Physico/Chemical Change due to radiation Stolyarova et al 2009 Also: electron-beam irradiation creates defects (see later) [Baladin 09] J-H.Chen et al 2009 (Ne+/He+ irradiation) 7
Graphene Composite+ for Radiation Sensing Stankovich et al 06 Graphene composite: Graphene sheets dispersed in polymer matrix bottom up approach (graphene composite+) : semiconductor/absorber nanoparticles How would radiation interacts with such material How would composite respond to radiation in a detectable way? 8
Research Summary Objective: 1) Understand the basic science about how ionizing radiation (gamma rays, neutrons) and associated charged particles interact with nano-materials/structures based on graphene, which has shown extreme sensitivity to local environmental perturbations; 2) Develop scientific foundation that may lead to graphene based radiation sensors with sensitivity & energy resolution in par or exceeding HPGe sensors and operating at close to room T for long distance fissile material detection. Approach: Two material systems: Graphene on radiation absorbing (semiconductor) substrates [Yr1 focus] and Graphene composite with radiation absorbing fillings [Yr2 focus]. Electrical, Raman and microscopy measurements will be used to study both transient and accumulative radiation effects [gamma/neutrons]. Collaboration: Purdue (Nucl. Eng.; Applied Physics Lab); NWU (Materials Sci. [graphene composite]); U. Houston (ECE [large scale CVD graphene]); leverage from NSF/DHS-ARI Program (GFET) 9
Research Facilities @ Purdue Birck Nanotechnology Center (BNC) Applied Physics Laboratory Nuclear/Civil Engineering Physics 10
Preliminary Work and Related Technical Accomplishments V gate insulator semiconductor absorber graphene GFET based radiation sensor (eg. sharp change of resistivity due to change of electrical field caused by ionizing radiation) Graphene composite Modeling of radiation-material interaction; Modeling of possible radiation detection schemes using graphene-based sensors Fabricating/Developing/Characterizing suitable graphene-based materials and devices Proof of concept experiments with graphene field effect transistors: radiation responses; local electric field sensitivity Physico-chemical changes: studies of effects of charged-particles irradiation on graphene and GFET 11
Modeling: radiation-substrate (absorber) interaction MCNP and MCNP-Polimi modeling of interaction of ionizing radiation (gamma, neutrons) with absorber materials: various semiconductors (Si, Ge, InSb), polystyrene etc. Compton electron transport through substrate (CASINO) recently also started using Geant4 (collab. I. Jovanovic [Purdue Nucl E]) 12
Modeling: radiation-substrate (absorber) interaction Geant4 CASINO 13
COMSOL Modeling: GFET response to radiation ionized charges Gabe Lopez et al., 2.0 1.5 R (kohm) 1.0 0.5-3x10 7-2 -1 0 1 2 3 Electric Field (V/m) V gate insulator semiconductor absorber graphene Simplified model with straight tracks --- good for neutrons? Ionized/conducting region 14
Detection schemes; Sensitivity and Energy Resolution radiation GFET absorber Also want large, high quality graphene to cover all generated charges Various possible detections schemes under investigation: remote detection FET (better for straight tracks/neutrons?) drift charges, but do not collect them use graphene (as effective low noise amplifier to read out the charges (for gammas?). 15
Material/Device Fabrication of Graphene and GFET exfoliation (scotch tape) Graphene on doped Si with 300 nm oxide E-beam lithography e - e - Lithography Nanodevices Develop PMMA Cr/Au evaporation Photo by Sambandamurthy Doped Si Lift off SiO 2 PMMA Cr/Au 16
How to identify graphene light Ni et al 2007 300nm Optical microscopy -- seeing is believing Raman Spectroscopy (also sensitive to defects in graphene) Many layers Gupta et al 2007 Resistance (ohms) 30x10 3 20 10 0-10 Rxx Rxy (h/e 2 )/14 Quantum Hall Effect (magnetoresistance) (h/e 2 )/6 (h/e 2 )/10 (h/e 2 )/2 I.Childres et al (see poster 3) -10 0 10 Gate Voltage (V) 20 17
GFET Characterization S D (grounded) Semiconductor=Si Insulator=300nm SiO2 V gate insulator semiconductor (doped) graphene Want: high-mobilty graphene [sharp FET] 2.0 G 500x10-9 400 4 mv R (kohm) 1.5 1.0 I DS 300 200 Dirac 3 mv 2 mv 0.5 100 1 mv -3x10 7-2 -1 0 1 2 3 Electric Field (V/m) -5 0 5 10 V GS 15 20 25 18
Large-scale Graphene Available by CVD 4-in graphene! Q. Yu (UH) Quantum Hall Effect h/2e 2 H. Cao et al 2009 19
Other Graphene-based Materials [Work done by undergrads] Fabricating Graphene on Ge & other substrates Stephen (ECE-Y3) Caleb (NE-Y4) (w/t 30nm germanium oxide) Synthesizing Graphene Oxide & Graphene Composite Stankovich et al 06 Sarah (CheE-Y2) 20
Proof of Concept: Photo-actuated GFET Radiation [this case, laser] chopper (doped) Also tried photo-resistor similar to photodiode Also tried MOSFET G.Lopez et al. Experiments currently underway with undoped Si-substrate hospital X-ray source 82mC gamma source Voltage (volt) 0.10 0.08 0.06 0.04 0.02 Photodiode Vds of GFET at 20HZ Vds of GFET at 100HZ Vds of GFET at 500HZ @Vg=6V Ids=10uA -40x10-3 -30-20 -10 0 10 20 time (sec) 21
Local Field Effect: by Side Gate Graphene is sensitive to local electric field side gate J. Tian et al., 22
Local Electric Field Effect by AFM tip R(kohm) R (Kohm) 7.2 7.0 6.8 3.60 3.55 3.50 3.45 5 m Vbg = 0V Location1 Location2 Location3 100 nm Vbg = 11V location1 location2 location3-20 -10 0 10 20 V top gate (V) -20 0 20 V top gate (V) R(Kohm) R (Kohm) 8 7 6 5 4 8.0 7.9 7.8 7.7 7.6 0 10 20 30 back gate voltage (V) Vbg = 13 V Location1 Location2 Location3-20 -10 0 10 20 V top gate (V) R (Kohm) R (Kohm) 6.8 6.4 6.0 5.0 4.9 4.8 4.7 Electric feild (V/m) 300x10 6 200 100 0-2x10-6 -1 0 1 2 Distance (m) Vbg = 16 V location1 location2 location3-20 0 20 V top gate (V) Vbg=20V location1 location2 location3-20 0 20 V top gate (V) Graphene SiO 2 p-type Si Apply I ds Read V ds Jalilian et al 09 unexpected scientific discovery: charge inhomogeneity (puddles) near Dirac point V bg V tg
Charged-particles irradiation: e-beam effect of energetic charged particles (eg. electrons) also relevant for (long term) reliability of GFET radiation sensors 30keV electron beam I= 0.15nA; Time=5mins; Expose area: 50um x 50um Estimated dose: 112.5 e-/nm 2 e- beam adds to graphene negative (n-) charges Raman spectra [cf also Baladin APL 09] (I.Childres et al) 24
Charged-particles irradiation: O + ions Resistance (ohms) 4500 4000 3500 3000 2500 2000 1500 Before Exposure (4-terminal) 1100 1000 900 800 1s exposure 1600 1400 1200 (3-terminal) 1000 3s exposure (3-terminal) 0 5 10 15 Gate Voltage (V) 20 0 10 20 30 40 Gate Voltage (V) 0 20 40 60 80 100 Intensity (offset) 3.0 2.5 2.0 1.5 1.0 0.5 D Raman spectra Increasing exposure O+ ions add to graphene positive (p+) charges Defect creation studied also by: Raman spectroscopy AFM (atomic force microscopy) time-dependent behavior I. Childres et al., in preparation These studies also relevant for rad-hard graphene electronics! O+ ions generated in a microwave plasma chamber 1500 2000 2500 Wavenumber (cm-1) 3000 25
Presentations/Publications 10th International Conference on Applications of Nuclear Techniques (Crete, Greece June 2009) (I. Childres et al. on e- beam irradiated GFET) In preparation: IEEE NSS/MIC (Orlando 2009) on graphene radiation detector & modeling [accepted] Manuscript(s) on charged-particle irradiation effect Manuscript(s) on local gate/charge FET 26
YIA: Interaction of Radiation with Graphene-based Nanomaterials for Sensing Fissile Materials Compton electron transport Sharp field effect Physicochemical change Objectives/Metrics: We aim to elucidate how ionizing radiation (gamma rays, neutrons) and associated charged particles interact with nano-materials/structures based on graphene, which has shown extreme sensitivity to local environmental perturbations. Performer: Prof. Yong P. Chen, Purdue University Status: Program started in Fall 09 Accomplishments (Preliminary Results): Raman, AFM and electronic measurements of GFET and effect of charged particles (O+ ions and electron beams) on graphene Geant4/MCNP-CASINO & COMSOL modeling of gamma rays interaction with absorber and electrical field effect on graphene Description: This Young Investigator Award (YIA) program is funded under Topic Y-4: Sensing Fissile Materials at Long Range using Nano-Structured Detector Materials (Thrust 1). It will study the interaction of radiation with various nanomaterials based on graphene, whose exceptional properties may enable remote detection of fissile materials with great sensitivity. Electrical, Raman and microscopy measurements will be used to study transient and accumulative radiation effects. Key deliverables: Data on from experiments and simulations Regular reports Peer-reviewed journal publications Conference presentations and proceeding papers Graduate and undergraduate students trained in related areas Funding Profile: Current: FY10: $0.1M FY11: $0.1M Key Milestones: FY10: Understand the mechanisms of radiation interaction with graphene on semiconductor substrates and how the interaction changes graphene properties FY11:Understand the mechanisms of radiation interaction with graphene composites and how the interaction changes the composite material properties 27
YIA: Interaction of Radiation with Graphene-based Nanomaterials for Sensing Fissile Materials, Dr. Yong P. Chen, Purdue University, Grant # HDTRA0-09-1-0047 Description of Effort: This project studies the interaction of ionizing radiations with various nanomaterials based on graphene, whose exceptional properties may enable remote detection of fissile materials with great sensitivity. Electrical, Raman and microscopy measurements will be used to study transient and accumulative radiation effects. Challenges: Sensing fissile materials at very long range (>>100m): likely to require new mechanisms unexplored previously Nanostructured materials have great, largely untapped potential for radiation detection: need to fundamentally understand how radiation interacts with such materials. Status of effort: Funding arrived and program starts in Fall 09; Preliminary results: Raman, AFM and electronic measurements of effect of charged particles (O+ ions and electron beams) on graphene; CASINO-COMSOL modeling of gamma rays interaction with absorber and electrical field effect on graphene. Personnel Supported: 1 faculty (Chen), 1 post-doc, several graduate/undergrad students supported by or associated with the research effort. Publications & Meetings: previous 12 months: 1 invited presentations; 2 contributed presentations. (graphene on radiationabsorbing semiconductor substrate) graphene (highly sensitive to local perturbations) (graphene composite) : semiconductor nanoparticles How do ionizing radiations interact with such graphene based nanostructured materials and change the local physical or chemical environment in a detectable way? Major Goals/Milestones: Yr 1: study graphene on various semiconducting substrates (radiation absorber); observe effects of gamma rays and ionized charged particles Yr 2: study graphene composites with semiconductor nanoparticle fillings; observe effects of neutrons Funding Profile ($100K/yr): Year 1 (07/01/09-06/30/10); Year 2 (07/01/10-06/30/11) PI Contact: Prof. Yong P. Chen, Purdue University, West Lafayette, IN 47907 (yongchen@purdue.edu) Phone: (765) 494-0947 Fax: (765) 494-0706 28