Electrical & Computer Engineering - Materials & NanoTechnology

Investigators: Mitra Dutta, ECE; Michael Stroscio, ECE, BioE, Physics Primary Grant Support: AFSGO

Problem Statement and Motivation •

Mercury ions and other heavy metals are found in environmental waters, which can lead to toxicity in humans

•

A rapid detection method for environmental monitoring and exposure levels in humans is needed

•

Engineering a nanoconstruct to detect these heavy metals in fluids can be done using quantum dots and single stranded DNA

Hg 2+ 10000

: eFluor® 650NC

: DNA aptamer

Intensity (a. u.)

: Nanogold : Hg 2+

0 Hg

5000

500 nM Hg 824 mM Hg

0 600

650

700

Wavelength (nm)

Key Achievements and Future Goals

Technical Approach •

DNA aptamers used as molecular recognition elements in sensing strategies for ions and biomolecules

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Mercury ions were detected using a spectrometer to measure the fluorescence intensity of the QD

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Aptamers can perform like antibodies with affinity to a wide range of targets which can result in a conformational change as in the figure

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Detection is achieved in the nanomolar range, while higher levels of mercury were shown to interfere with QD fluorescence

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Quantum dots (QD) are robust and stable fluorophores and gold nanoparticles are stable quenchers

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Future targets include lead, zinc, and cadmium, which have been shown to interact with specific DNA aptamers

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Conjugating QDs and gold nanoparticles to aptamers provides the detection signal

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Optical detection platform to be applied to biomarkers

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Translate detection assay to portable handheld device

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Surface energy transfer between QD and gold nanoparticle is the mechanism for optical detection

Investigators: M. Dutta, ECE, M. Stroscio, ECE and BioE Primary Grant Support: AFOSR, ARO, NSF, SRC, DARPA, DHS Quantum Dots in MEH-PPV Polymer

Problem Statement and Motivation

Gold contacts •

Design, fabrication, characterization of QD-based photon-absorbing media embedded in conductive polymers for optoelectronic devices

•

For underlying concepts see group’s paper on “Applications of Colloidal Quantum Dots,” Microelectronics Journal, 40, 644-649 (2009).

ITO Glass

Top view MEH-PPV Polymer / CdSe Quantum Dot Composite

Key Achievements and Future Goals

Technical Approach •

Design of quantum-dot (QD) ensembles in conductive polymers

•

Fabricating quantum-dot (QD) ensembles in conductive polymers

•

Modeling electrical and optical properties including robustness and sensitivity to QD-QD separation

•

Experimental characterization of integrated structures

•

Multi-wavelength optoelectronics

•

Numerous simulations of electrical and optical properties including robustness and sensitivity to QD-QD separation

•

Numerous simulations for a variety of QD—conductive-polymer systems

•

Current sensing AFM measurements of I-V curves for a variety of QDs embedded in conducting polymers

•

Ultimate goal is realization of multi-wavelength photodetectors

P.I. Igor Paprotny Funding: new faculty startup, California Energy Commission

Problem Statement and Motivation • • •

•

•

Integrating discrete components on flexible substrates Using ultra low-power wireless radios and microcontrollers to implement low-power wireless networks Algorithms reconstruct system parameters from sparse (distributed) sensory data

Energy harvesting enables potentially perpetual operation of the sensor nodes

Key Achievements and Future Goals

Technical Approach • •

Low-power radios and ancillary electronics introduce the possibility of ubiquitous low-cost wireless sensor networks.

Distributed sensors are predicted to be an integral part of our every day life Enable many important applications: • Energy systems sensing • Body sensor networks • Environment systems

• • •

Created a 4 mm x 4 mm sized low-power sensor node using discrete components Developed a self-calibrating current sensor system Future goals: • Develop a co-location system for 1 mm3 wireless sensor node • Integrate a wireless sensor network in underground coal mines • Create a smart bandaid body sensor node

Wenjing Rao, ECE department

Problem Statement and Motivation

Post-manufacturing defect-tolerant logic implementation on nano-crossbars • Models, algorithms, yield analysis

•

Exploiting time / hardware / information redundancy at multiple design hierarchical levels and granularities • Logic gate level: nano-PLAs • Arithmetic level: fault tolerant adders • Processor architecture level: speculative computation based fault tolerance paradigm

•

Redundancy sharing on a locally connected network • Flexible, dynamic assignment schemes • Network analysis

Future electronic systems on nanoscale devices

•

Promises • Boosts of computational power • Wide application domains

•

Challenges • Severe unreliability (manufacturing defects + run time faults) • Localized interconnect

•

Need: • New system design and computational paradigms for constructing future reliable nanoelectronic systems.

Key Achievements and Future Goals

Technical Approach •

•

•

Low-cost defect / fault tolerance approaches exploiting • Reconfigurability • Multiple hierarchical levels and granularities • Regularity

•

Decentralized resource allocation protocol on locally connected network • Low communication overhead • Scalable • Generalizable framework for self-adaptive systems

P.I. Igor Paprotny Funding: new faculty startup, Intel, DOE

Problem Statement and Motivation • • •

Airborne particulate matter (PM) is harmful to our health In particular fine PM smaller than 2.5 µm in diameter (PM2.5) Includes: • Diesel exhaust • Tobacco smoke • Bio-aerosols

• •

Current instruments are too big and expensive to be portable Personal PM2.5 sensor does not exist

Key Achievements and Future Goals

Technical Approach • • •

•

Use MEMS techniques to create air-microfluidic lab-on-a-chip that measures airborne PM by direct mass deposition Inertial separation (virtual impaction) is used to separate PM2.5 from the rest of the airstream.

Thermophoretic precipitation is used to deposit the separated PM2.5 on top of a mass-sensitive film-bulk acoustic resonator (FBAR) The rate of the frequency shift in the FBAR corresponds to the PM2.5 concentration.

• • • •

Demonstrated a microfabricated PM2.5 direct-mass sensor • 5 cm x 2.5 cm x 1 cm in size Sensitivity comparable to large instruments • 1-2 µg/m3 PM2.5 concentration Form factor enables integration into a regular cellphone Future goals: • Improve sensitivity • Measure particle-size distribution • Chemical speciation

P.I. Igor Paprotny Funding: Department of Health and Human Services

Problem Statement and Motivation • • • •

Key Achievements and Future Goals

Technical Approach • • • •

A flat surface placed in a mine environment collects deposited dust Incident light at several wave-lengths is reflected from the deposited layer, and is collected by a photo-detector Microfabricated mass sensors and humidity sensors helps to determine the true explosibility of the deposited layers Connects to a communication backbone to automate the operation of the rock dusting equipment

Excessive build-up of coal dust in underground mines leads to explosion risk Rock-dusting (dispensing of inert lime-stone dust) is used to mitigate the explosion risk • Increasing total incombustible content (TIC) Currently manual sampling of dust in mines to determine TIC and control rock dusting A low-cost reliable automated method is needed

• • •

Verified the viability of using multi-wavelength optical method to detected the layers of deposited dust Created preliminary sensor prototype Future goals: • Determine the dependence of the optical method on humidity content and particle size, as well as the layer thickness • Create a MEMS mass and humidity sensor • Integrate with a communication backbone in the underground mine

Investigators: M. Dutta, ECE, and M. Stroscio, ECE and BioE

Problem Statement and Motivation

Bare QDs

FRET

• Organic-inorganic hybrid structures enable integration of useful organic and inorganic characteristics for novel optoelectronic applications.

• The time required for resonant energy transfer in the composite of inorganic quantum dots (QDs) and photosystem I (PS-I) has not been determined previously.

Transfer time ~ 6 ps).

Colloidal Quantum Dots and Photosystem-I Composite

Technical Approach • Synthesis of the composite of inorganic CdSe QDs and organic PS-I, hexahistadine-tagged PS-I from Chalamydomonas reinhardtii - green unicellular algea • Experimental measurement of the energy transfer between QDs and PS-I • Investigation of structural, optical and transport properties by means of photoluminescence, time-resolved photoluminescence, absorption, capacitance-voltage and I-V measurements

Key Achievements and Future Goals • Observed energy transfer from CdSe QDs to PS-I by optical and electrical measurements.

• Photoluminescence data and absorption data show that the energy of excited carriers of CdSe QDs to PS-I by processes that include fluorescent resonant energy transfer (FRET) between the inorganic and organic components of the system.

• I-V measurement data are sensitive to incident light in the composite CdSe QDs/PS-I material.

Investigators: ; M. Dutta, ECE, and M. Stroscio, ECE and BioE

Problem Statement and Motivation • Design, fabrication, characterization of QD-based nanosensors on a variety of platforms • For underlying concepts see group’s paper on “Applications of Colloidal Quantum Dots,” Microelectronics Journal, 40, 644-649 (2009).

Technical Approach • Design of quantum-dot (QD) based nanosensors

Key Achievements and Future Goals • Numerous demonstration of nanosensors based on beacon like structures

• Fabricating quantum-dot (QD) ensembles • Modeling electrical and optical properties including robustness and sensitivity to QD-QD separation

• Numerous nanosensors demonstarted for a variety of QD systems

• QD blinking modeled and observed • Experimental characterization of integrated structures • Multi-analyte detection

• Ultimate goal is realization of multi-analyte detectors on a single platform

P.I. Igor Paprotny Funding: new faculty startup

Problem Statement and Motivation • • • •

200 mm •

Key Achievements and Future Goals

Technical Approach • • •

• •

Use MEMS techniques to create robotic chassis several micrometers in size A stress-engineering post processing solution adds precisely controlled curvature to planar silicon structures Power is provided externally through a set of underlying interdigitated electrodes to the propulsion component, which is a scratch drive actuator (electrostatic inchworm) Patterned stress-engineering layer defines the out-of-plane deflection of the steering arms Difference in deflection results in different control voltage, which can be used to independently control several microrobots

New, largely unexplored area of robotics Difficult to achieve due to component scaling Microelectromechanical systems (MEMS) Components difficult to implement at the microscale: • On-board power • Sensing • On-board control Many application opportunities, such as in: • Medicine, • Manufacturing • Information security

• • • •

Demonstrated independent control of several (four) MEMS microrobots Controlled self-assembly of microscale structures Developed a new stress-engineering process to design the robots that does not require a photo lithography stage Future goals: • Develop designs and algorithms that allow for simultaneous control of large numbers of microrobots • Create new microrobotic systems that operate in liquids • Use 2-photon stereolithography to create new types of microrobotic systems

Mitra Dutta, ECE and Michael Stroscio, ECE & BioE Primary Grant Support: ARO, AFOSR (a) 0 1 2

-4

Fluorescence

-3 LUMO

3 4 5 6 7

HOMO

•

Organic-inorganic hybrid structures enable integration of useful organic and inorganic characteristics for novel applications such as solar cell, chemical sensors, and fluorescent biotags.

•

Energy transfer in the composite of inorganic quantum dots (QDs) and photosystem I (PS-I) is not understood although it is very important and well studied for photosynthesis.

0 +1

+- +-

+2 CdSe QDs

QDs

-2 -1

En1 Ec hv Ev Eh1

8

Problem Statement and Motivation

NEH(V)

Evac(eV)

+3

PS-I

QDs+PS1

Glass

Glass

Key Achievements and Future Goals

Technical Approach •

Synthesis of the composite of inorganic CdSe QDs and organic PS-I

•

Observed energy transfer from CdSe QDs to PS-I by optical and electrical measurements.

•

Experimental measurement of the energy transfer between QDs and PS-I

•

Photoluminescence data and absorption data show that the energy of excited carriers of CdSe QDs to PS-I by means of radiative emission, FRET, and electron/hole transfer between the inorganic-organic system.

•

I-V measurement data are sensitive to incident light in the composite CdSe QDs/PS-I material.

•

Further studies continue to identify each energy transfer method.

•

Investigation of structural, optical and transport properties by means of photoluminescence, time-resolved photoluminescence, absorption, capacitance-voltage and current-voltage measurements

Investigators: ; M. Dutta, ECE M. Stroscio, ECE and BioE

Problem Statement and Motivation Example of ZnO Nanowires

• Design, fabrication, and characterization of quantum-wire based optoelectronic devices and structures including those incorporating conductive polymers • Design, fabrication, and characterization of quantum-wire based piezoelectric devices and structures for energy harvesting

Technical Approach • Growth of quantum wires

Key Achievements and Future Goals • Numerous simulations of electrical, optical and piezoelectric properties of quantum-wire structures

• Fabrication of quantum-wire based devices • Modeling electrical and optical properties including robustness of quantum-wire-based devices

• Numerous simulations and predictions for a variety of quantum-wire—conductive-polymer structures and piezoelectric structures

• Experimental characterization of integrated structures quantum-wire-based structures

• Demonstrated polarization-dependent light inteactions with arrays of quantum wires • Strong Enhancement of Near-BandEdge PLof ZnO Nanowires

M. Dutta, ECE; M. Stroscio,ECE and BioE Primary Grant Support: ARO, NSF, AFOSR, SRC, DARPA

Problem Statement and Motivation Au wire

CdS

CdSe-ZnS

•

Future electronic and optoelectronic systems must be integrated on the terascale and beyond

•

This research effort explores the use of biomolecules as molecular interconnects for such terascale systems

CdSe-ZnS-GGGC

Key Achievements and Future Goals

Technical Approach •

Synthesis of semiconductor nanostructures

•

Chemical self-assembly of semiconductor nanostructures

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Modeling electrical, optical and mechanical properties of ensembles of nanostructures

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Experimental characterization of massively integrated networks of semiconductor nanostructures

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Numerous manmade semiconducting nanostructures have been synthesized

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Integrated semiconductor quantum dots have been assembled chemically in the Nanoengineering Research Laboratory at UIC

•

Interactions between semiconductor nanostructures and molecular wires have been modeled for a wide variety of systems

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Ultimate goal is massive integration of semiconductor nanostructures in functional electronic and optoelectronic networks

Mitra Dutta, ECE. Primary Grant Support: NASA Ames Research Center

Problem Statement and Motivation •

Annealing at specific conditions and environment would refresh the Tin Oxide nanowire used in gas sensing applications.

•

Minimization of defects in nanowires which determine the electrical and optical properties for high performance applications.

Key Achievements and Future Goals

Technical Approach •

Synthesis of Tin Oxide nanowires using a special carbothermal reduction process.

•

Identifying various inherent structural defects in nanowires and understanding their role in modifying the electronic and optical properties using various experimental characterization techniques.

•

Obtain a specific Annealing condition which would serve to minimize the defects as well pre-charge/refresh the nanowires for future gas sensing applications.

•

Nanowires of various diameters have been synthesized in large scale.

•

Intrinsic defect levels/states/traps have been identified and minimized by annealing in oxygen and nitrogen under specific conditions.

Luminescence and structural properties of the wires have improved/changed by a significant extent post annealing.

•

Specific annealing condition used for refreshing nanowires has been obtained.

•

Ultimate goal is massive integration of tin oxide nanowires for gas sensing and nuclear radiation detection.

Mitra Dutta, ECE Primary Grant Support: Intelligent Expitaxy Technology and MDA

[011] [011] aAs 1mm G

GaAs 150nm

•

Robust low cost Infrared photodetectors as well as those with room or near room temperature operation

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Quantum well infrared photodetectors (QWIPs) due to the well developed mature GaAs technology

•

High-pass filter for the photocurrent which blocks the tunneling dark current

[100]

s 0.79A l0.21Ga 5nm A 0.9As In0.1Ga 3.5nm a0.79As Al0.21G 50nm

Quantum Well Infrared Photodectetor (QWIP) with a energy filter between base and collector

Problem Statement and Motivation

d grade filter 40nm a0.79As Al0.21G

Key Achievements and Future Goals

Technical Approach •

InxGa1-xAs/AlyGa1-yAs multi quantum wells, three terminal structure grown by molecular beam epitaxy

•

The atomic resolution images and x-ray diffraction patterns verified a lattice matched and band-gap engineered device structure of IHET.

•

Modeling of electrical properties based on its composition and doping

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Photoluminescence data indicated the composition and a deep energy level in hot electron filter

•

Investigation of structural, optical and transport properties by means of transmission electron microscopy, x-ray diffraction, Photoluminescence, Raman spectroscopy, current-voltage measurement

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Current-voltage data showed high-pass filter blocks the tunneling dark current, with resulting satisfactory detectivity

•

Optimization of the composition, thickness, and doping of high-pass filter

Mitra Dutta, ECE and Michael A. Stroscio, ECE and BioE Primary Grant Support: ARO AFOSR

Problem Statement and Motivation •

Semiconductor nanocrystals functionalized with conductive polymers promote efficient charge transfer

•

Low cost, light weight and tunable conductivities

•

Explore the application of nanocomposite heterostructures in novel electronic and optoelectronic devices

Key Achievements and Future Goals

Technical Approach •

Fabrication of nanocomposite heterostructures incorporating semiconductor quantum dots and inorganic polymers

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Different types of nanocomposite heterostructures have been synthesized

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Numerical modeling of the electrical properties

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Electrical and optical properties have been studied with modeling and experimental methods

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Experimental characterization with optical and electrical measurements

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Developing high efficiency photodetectors and solar cells

Investigators: Banani Sen, ECE, Mitra Dutta, ECE, Physics, Michael Stroscio, ECE, BioE, Physics Alex Yarin, MIE, Suman Sinha-Ray, MIE

Problem Statement and Motivation

V

•

Piezoelectric energy harvesting is necessary to meet today’s energy requirement.

•

ZnO nanofibers have drawn much attention because of its promising material characteristics.

•

Bulk production of substrate free nanofibers are needed for various application, viz. power shirts.

L L ± L (a) TEM image of ZnO nanofiber deposited by electrospinning. (b) Schematic representation of energy harvesting measurement setup.

Key Achievements and Future Goals

Technical Approach •

Synthesis of ZnO nanofibers by electrospinning followed by annealing in oxygen ambient.

•

TEM image shows single crystalline stoichiometric ZnO nanofibers deposited by electrospinning.

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Investigation of morphological, optical and material properties by means of Transmission electron microscopy, Photoluminescence and Raman spectroscopy.

•

Photoluminescence spectrum shows UV peak (near band), Vis peak ( antisite defects and interstitial oxygen).

•

•

Synthesis of ZnO nanofiber and PVDF polymer composite by electrospinning for energy harvesting.

Raman scattering- E2 (high), quasi LO and TO modes of mixed A1 and E1 symmetry.

• •

Piezoelectric voltage measurement on application of mechanical strain.

Preliminary electrical measurement results indicate the composite to be promising for energy harvesting. Further systematic study will be continued to evaluate the power density from this piezoelectric composite.

Investigators: Mohsen Purahmed, Mitra Dutta, ECE Department of Electrical Engineering, University of Illinois at Chicago

Problem Statement and Motivation •

ZnO NWs are one of the promising candidates for future nanostructure devices such as short-wavelength semiconductor lasers, light-emitting diodes and energy harvesting devices.

•

ZnO NWs have a weak near-band-emission (NBE), numerous studies have been done to enhance the NBE and photoluminescence efficiency of ZnO Nanowires (NWs).

ZnO nanowires (NWs) grown by PVD method

Key Achievements and Future Goals

Technical Approach •

Growth of ZnO NWs by PVD method

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Optical characterization of ZnO NWs

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Enhancement of near-band-emission (NBE )of ZnO

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Photoluminescence (PL) of ZnO nanowires coated with the metallic nano particles deposited by rf-magnetron sputtering .

•

Very strong enhancement of ultraviolet emission is observed after coating with metallic nanoparticles and Ar plasma treatment.

•

Future goals include studying the waveguiding and lasing effects in these ZnO NWs and making a nano laser with a low threshold lasing power.

Hyeson Jung and Mitra Dutta Department of Electrical and Computer Engineering

Current Density (mA/cm2)

0

Problem Statement and Motivation

68SE1-68AE10

-5 -10 -15

Voc : 0.79V Jsc : 22.96 mA Vmp : 0.62 V Jmp : 19.62 mA FF : 67.06% eff :12.16 %

•

Current commercial solar cells - single/poly crystalline silicon

•

Recent crystalline silicon wafer prices increases make second generation cells more attractive

•

The Second-generation cells – thin film of amorphous Si, CdTe, and CIGS can be competitive

•

Energy band gap of CdTe is 1.5 eV, considered optimal band gap for solar cells

•

CdTe solar cell higher efficiency than a-Si

-20 -25 -30 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Voltage (V)

Key Achievements and Future Goals

Technical Approach •

Fabrication of CdTe thin film solar cell: CdTe, CdS thin film deposition by means of e-beam followed by cell fabrication

•

Development of alternative post-treatment, and optimization of the treatment condition

•

Investigation of structural, optical and transport properties by means of Photoluminescence, X-ray spectroscopy, absorption measurement, Scanning Electron Microscopy, Atomic Force Microscope, and current-voltage measurement

•

CdTe solar cells were fabricated and tested; the CdTe was grown by e-beam evaporation or magnetron sputtering, followed by post treatment.

•

Alternative post treatment system was developed.

•

12 % efficiency achieved with first efforts.

•

Incorporating nanostructures we hope to achieve higher efficiency

Hyeson Jung, Michael Stroscio, Mitra Dutta Department of Electrical and Computer Engineering

(111) 110

En1 ,h1 

 2 212  2 212   Eg * * 2me a 2 2mh a 2

Problem Statement and Motivation •

To explore materials for tandem solar cells, PbSe nanowires were investigated. By adjusting diameter of the wires, bandgap can be engineered. This is one of advantages of nanotechnology.

•

Nanowires of PbSe are of enhanced interest due to their special properties where the relatively large Bohr excitonic radius and small effective masses lead to strong electron and hole confinement in PbSe nanowires.

PbSe

EC En1 EF EV Eh1

Depletion region, W

Oxidized PbSe surface

Key Achievements and Future Goals

Technical Approach •

•

•

Growth of quality PbSe nanowires which are contamination free, compatible with device processing, less expensive and simple by using RF sputter deposition.

The optical properties of the wires were characterized by absorption and photoluminescence.

Investigate possibility of achieving nanowire behavior in PbSe larger wires that are grown by sputter deposition due to the effect of surface field and a strong depletion layer.

•

PbSe nanowires grown by magnetron sputtering

•

Though of large size wires showed a large blue shift demonstrating quantum confining

•

Attributed to Fermi level and strong band pinning, large band bending and a wide depletion layer

•

We have demonstrated that effective diameter of the nanowires are adjustable for different band gap materials.

•

Development of solar cells using these PbSe nanowires in the near future

Ayan Kar and Mitra Dutta, ECE Primary Grant Support: DoE

Problem Statement and Motivation •

Long term need for an inexpensive sensor for the detection of special nuclear materials.

•

Ideally sensors which are small, with minimal circuit complexity, and non-cryogenic cooling and requiring small manufacturing costs would provide ideal solutions to this problem.

•

Tin oxide (SnO2) nanowires have demonstrated to have excellent sensing performance which is comparable to or even surpasses the best thin film counterparts.

Key Achievements and Future Goals

Technical Approach •

Nanowire surface modification using annealing.

•

Fabrication of SnO2 nanowire Schottky diode sensors.

•

Expose the nanowire sensors to ionizing 20 Curies of Cesium-137 (137Cs) γ –radiation having an energy of 667 KeV.

•

Investigation of change in diode electrical properties on being exposed to radiation using current-voltage measurements. Change in nanowire structural properties using photoluminescence.

•

Large changes (~14.8 MΩ) in resistance in the forward bias region were observed after exposure to the 137Cs) γ –radiation.

•

A maximum sensitivity of 254% was obtained at a radiation dosage of 42,371 mR/hr.

•

A short sensor response time of 8 seconds with the permanent change in the nanowire resistance after the radiation is turned off.

•

Future possibility of stand-off remote detection of radioactive sources using a mm-wave (MMW) technique.

Investigators: ; M. Dutta, ECE and M. Stroscio, ECE and BioE

Problem Statement and Motivation Quantum Dots in MEH-PPV Polymer

Gold contacts

ITO

Glass

• Design, fabrication, characterization of QD-based photonabsorbing media embedded in conductive polymers for optoelectronic devices • For underlying concepts see group’s paper on “Applications of Colloidal Quantum Dots,” Microelectronics Journal, 40, 644-649 (2009).

Top view

MEH-PPV Polymer / CdSe Quantum Dot Composite

Technical Approach

Key Achievements and Future Goals

• Design of quantum-dot (QD) ensembles in conductive polymers

• Numerous simulations of electrical and optical properties including robustness and sensitivity to QD-QD separation

• Fabricating quantum-dot (QD) ensembles in conductive polymers

• Numerous simulations for a variety of QD—conductivepolymer systems

• Modeling electrical and optical properties including robustness and sensitivity to QD-QD separation

• Current sensing AFM measurements of I-V curves for a variety of QDs embedded in conducting polymers

• Experimental characterization of integrated structures

• Ultimate goal is realization of multi-wavelength photodetectors

• Multi-wavelength optoelectronics

Vitali Metlushko, Department of Electrical & Computer Engineering and Nanotechnology Core Facility (NCF) Primary Grant Support: NSF ECS grant # ECS-0202780, Antidot and Ring Arrays for Magnetic Storage Applications and NSF NIRT grant # DMR-0210519 : Formation and Properties of Spin-Polarized Quantum Dots in Magnetic Semiconductors by Controlled Variation of Magnetic Fields on the Nanoscale, B. Janko (P.I.), J. K. Furdyna (co-P.I.), M. Dobrowolska (co-P.I.), University of Notre Dame is leading organization, A. M. Chang (Purdue) and V. Metlushko, (UIC)

Problem Statement and Motivation Lorentz image of magnetic nanostructure.

The field of nanoelectronics is overwhelmingly dedicated to the exploitation of the behavior of electrons in electric fields. Materials employed are nearly always semiconductor-based, such as Si or GaAs, and other related dielectric and conducting materials. An emerging basis for nanoelectronic systems is that of magnetic materials. In the form of magnetic random access memories (MRAM), nanoscale magnetic structures offer fascinating opportunities for the development of low-power and nonvolatile memory elements.

SEM image of 700nm MRAM cells.

UIC’s Nanoscale Core Facility

Key Achievements and Future Goals

Technical Approach In past few years, the interest in nano-magnetism has encreased rapidly because they offer potential application in MRAM. Modern fabrication techniques allow us to place the magnetic elements so close together that element-element interactions compete with singleelement energies and can lead to totally different switching dynamics.

To visualize the magnetization reversal process in individual nanomagnets as well as in high-density arrays, Metlushko and his coauthors employed several different imaging techniques- magnetic force microscopy (MFM), scanning Hall microscopy, magneto-optical (MO) microscopy, SEMPA and Lorentz microscopy (LM).

•

This project has led to collaboration with MSD, CNM and APS ANL, Katholieke Univesiteit Leuven, Belgium, University of Notre Dame, NIST, Universita` di Ferrara, Italy, Inter-University Micro-Electronics Center (IMEC), Belgium, Cornell University, McGill University and University of Alberta, Canada

•

During the past 3 years this NSFsupported work resulted in 21 articles in refereed journals already published and 10 invited talks in the US, Europe and Japan.

Investigators: M. Stroscio, ECE and BioE; and M. Dutta, ECE 0 1

Evac

Al0.25Ga0.75N

CdSe Quantum Dot PDCTh Polymer

2 3 4 5 6 7 8 Al0.125Ga0.875N

PDCTh Polymer

Technical Approach • Design of single-photon detectors • Fabricating quantum-dot (QD) ensembles in conductive polymers • Modeling electrical and optical properties including robustness and sensitivity to QD-QD separation

Problem Statement and Motivation • Design, fabrication, characterization of QD-based optoelectronic devices as components of single-photon detectors • For underlying concepts see Mitra Dutta, et al., Colloidal Quantum Dots (QDs) in Optoelectronic Devices --- Solar Cells, Photodetectors, Light-emitting Diodes, in Handbook for SelfAssembled Semiconductor Nanostructures for Novel Devices in Photonics and Electronics, edited by M. Henini, Elsever Publ.

(2008) and Ke Sun, Milana Vasudev, Hye-Son Jung, Jianyong Yang, Ayan Kar, Yang Li, Kitt Reinhardt, Preston Snee, Michael A. Stroscio, and Mitra Dutta, Applications of Colloidal Quantum Dots, Microelectronics Journal, 40, 644-649 (2009).

Key Achievements and Future Goals • Numerous simulations of electrical and optical properties including robustness and sensitivity to QD-QD separation • Numerous simulations for a variety of QD—conductivepolymer systems

• Current sensing AFM measurements of I-V curves for a variety of QDs embedded in conducting polymers

• Experimental characterization of integrated structures • Ultimate goal is realization of photodetectors capable of single-photon detection

Zheng Yang, Department of Electrical and Computer Engineering

Problem Statement and Motivation Diluted magnetic semiconductor is a kind of electronic materials with properties of both a semiconductor and a ferromagnetic material. In modern technology, semiconductor materials are used for logic devices such as the CPU in the computers due to its tunable electric conductivity under external electric field (arisen from the bandgap); while the ferromagnetic materials are used for memory devices such as the hard drive in the computers, in which the information storage is carried by the orientation of the majority spin polarization. Diluted magnetic semiconductor material is a combination of both.

In a layman language, if a diluted magnetic semiconductor is successfully demonstrated, we may have the CPU and hard drive integrated in one device chip in our computers in the future. The major two obstacles hindering the practical application of diluted magnetic semiconductor are the Curie temperature and whether the ferromagnetism therein is intrinsic. Curie temperature is a critical temperature above which the material loses ferromagnetism.

Technical Approach Whether the ferromagnetism in the diluted magnetic semiconductor is intrinsic or not is determined by whether the spin polarization is carried by the free carriers or localized ions. If it is localized, sometime we call “extrinsic�, it is not applicable for device applications generally. Several diluted magnetic semiconductors have been confirmed as intrinsic ferromagnetism such as Mn-doped GaAs, however, all of them show Curie temperature below room temperature. On the other hand, it has been observed above-room-temperature Curie temperatures in ZnO diluted magnetic semiconductor materials, but whether the ferromagnetism therein is intrinsic is still controversial and needs further clarification from experiments. The most straightforward experiment to investigate whether the ferromagnetism in diluted magnetic semiconductor is intrinsic or not is to study whether the ferromagnetism shows free carrier concentration dependent property.

Key Achievements and Future Goals It has been originally demonstrated that the free carrier concentration dependent ferromagnetism in ZnO diluted magnetic semiconductors. First, It has been experimentally achieved precise control of free carrier concentration in ZnO thin films with Ga doping. Then these ZnO thin films with different free carrier concentration were doped with magnetic dopants. It has been first time observed that the larger free carrier concentration leads to larger magnetization.

Comprehensive electron microscopy and x-ray diffraction studies have been performed to exclude the possibility of the existence of localized magnetic clusters inside the ZnO diluted magnetic semiconductors. In the next steps, two major research projects will be carried out. The first is to study electrostatic doping (via a gate voltage instead of chemical doping) effect on the magnetic properties of ZnO diluted magnetic semiconductors. The second is to investigate the magnetic properties of ZnO diluted magnetic semiconductor in lowdimensional systems, such as nanowries.