Post on 12-Jan-2016
transcript
Spin Dependent Transport Spin Dependent Transport Properties of Magnetic Properties of Magnetic
NanostructuresNanostructures
Amédée d’Aboville,Amédée d’Aboville,
with Dr. J. Philip, Dr. S. Kang, with Dr. J. Philip, Dr. S. Kang,
J. BattogtokhJ. Battogtokh
OutlineOutline
Introduction to NanostructuresIntroduction to Nanostructures Magnetic NanostructuresMagnetic Nanostructures
GrowthGrowth PropertiesProperties Device fabricationDevice fabrication Device characterizationDevice characterization
What is Nano?What is Nano? SI unit of length = 1mSI unit of length = 1m Other units are the millimeter: 1x 10Other units are the millimeter: 1x 10 -3-3 m m
micrometer : 1 x 10micrometer : 1 x 10-6-6 m m
nanometer : 1 x 10nanometer : 1 x 10-9-9 m m
1 meter = 1 billion nanometers1 meter = 1 billion nanometers The width of a hair is about 50 000 nmThe width of a hair is about 50 000 nm Nanostructures have at least one dimension Nanostructures have at least one dimension
less than 100nmless than 100nm
What is Nanotechnology?What is Nanotechnology?
Nanotechnology is the manipulation, Nanotechnology is the manipulation, fabrication, and characterization of fabrication, and characterization of nanostructuresnanostructures
What are the What are the Applications of Applications of
Nanotechnology?Nanotechnology? Better food packagingBetter food packaging Stronger, lighter materialsStronger, lighter materials Optical ComputingOptical Computing Better DisplaysBetter Displays SunscreenSunscreen Quantum ComputingQuantum Computing Spin-dependent electronicsSpin-dependent electronics
GalfenolGalfenol
Galfenol is a Gallium Iron compound with a Galfenol is a Gallium Iron compound with a specific stoichiometric composition (Gaspecific stoichiometric composition (Ga0.20.2FeFe0.80.8))
Galfenol is ferromagnetic, and has a Curie Galfenol is ferromagnetic, and has a Curie Temperature of 1000 KTemperature of 1000 K
There are also a range of interesting properties (ie. There are also a range of interesting properties (ie. Magnetostriction).Magnetostriction).
Nanowire Growth: Nanowire Growth: Electro-SpinningElectro-Spinning
A syringe is filled with a A syringe is filled with a solution of correct solution of correct stochiometric compositionsstochiometric compositions
A high potential is applied A high potential is applied between the tip of the needle between the tip of the needle and the collectorand the collector
Nanowires spin out of the Nanowires spin out of the syringesyringe
Optical Microscope picture of Electro-spun GaFe NW
mm
Sample Preparation: Sample Preparation: SonicationSonication
•Nanowires are separated from the substrate by placing in an ultrasonic bath
•The Nanowires are left in an IPA solution
PreparationPreparation
Coordinates of the NW are obtained Coordinates of the NW are obtained using an SEMusing an SEM
Electrodes designed are designed using Electrodes designed are designed using a Computer Aided Design programa Computer Aided Design program
The CAD file is fed into a computerThe CAD file is fed into a computer The computer controls a finely focused The computer controls a finely focused
electron beamelectron beam
LithographyLithography
A sample is coated with electron sensitive resist A sample is coated with electron sensitive resist material, similar to photographic filmmaterial, similar to photographic film
A computer controlled Electron Beam exposes certain A computer controlled Electron Beam exposes certain parts of the resistparts of the resist
The exposed sections change molecular weight and The exposed sections change molecular weight and can be dissolved in a particular solventcan be dissolved in a particular solvent
Si Wafer
Resist
Nanowire
Ultra-High Vacuum Ultra-High Vacuum DepositionDeposition
State of the art technique to deposit high State of the art technique to deposit high quality materialquality material
High vacuum can be achieved ( up to 10High vacuum can be achieved ( up to 10-10-10 torr) torr) Ti and Cu electrodes are deposited in thin Ti and Cu electrodes are deposited in thin
sheets ( 5nm and 100nm, respectively)sheets ( 5nm and 100nm, respectively)
Metallization and liftoffMetallization and liftoff
Electrodes are deposited with the Ultra High Vacuum Electrodes are deposited with the Ultra High Vacuum Deposition systemDeposition system
The sheet of resist is removed with acetone, leaving The sheet of resist is removed with acetone, leaving only the metal in the exposed partsonly the metal in the exposed parts
Si Wafer
Resist
Nanowire
Galfenol Nanowire with Ti and Cu electrodes(500x)
Spin Dependent Spin Dependent Transport PropertiesTransport Properties
Placing Galfenol NW in an external field can Placing Galfenol NW in an external field can orient its electron spin in the desired directionorient its electron spin in the desired direction
The NW resistance changes with the The NW resistance changes with the orientation of its electrons relative to the orientation of its electrons relative to the currentcurrent
Property MeasurementsProperty Measurements
We apply a voltage and measure the resultant drain to We apply a voltage and measure the resultant drain to source currentsource current
Wafer acts as gate
Source
Nanowire acts as a channel
Drain
Expected ResultsExpected Results
There is a thin sheet of oxide on top of the There is a thin sheet of oxide on top of the nanowire which acts as an insulatornanowire which acts as an insulator
The electrons get through the sheet by The electrons get through the sheet by quantum tunnelingquantum tunneling
The oxide is a Quantum Tunneling BarrierThe oxide is a Quantum Tunneling Barrier
Source DrainNanowire
Wafer
GaFe Oxide
Measured propertiesMeasured properties
ConclusionConclusion
We have grown Galfenol NWWe have grown Galfenol NW Analyzed their structureAnalyzed their structure Built devices out of single NWsBuilt devices out of single NWs Measured these device propertiesMeasured these device properties Analyzed these device measurementsAnalyzed these device measurements