Weinstock - Quantum Electronic Solids - Spring Review 2013

1 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution 19 February 2013

Integrity Service Excellence

Dr. Harold Weinstock Program Officer

AFOSR/RTD Air Force Research Laboratory

Quantum Electronic Solids

07 March 2013

2

2013 AFOSR SPRING REVIEW 3001H PORTFOLIO OVERVIEW

NAME: Quantum Electronic Solids BRIEF DESCRIPTION OF PORTFOLIO: Physics and electronics at the nanoscale: superconductivity, metamaterials and nanoelectronics - exploiting quantum phenomena to create faster, smarter, smaller and more energy-efficient devices SUB-AREAS IN PORTFOLIO: Superconductivity: find more-useful materials for high magnetic fields, microwave electronics, power reduction and distribution Metamaterials: microwave, IR & optical sensing and signal processing with smaller sizes and unique properties Nanoelectronics: NTs, graphene, diamond, SiC for sensing, logic & memory storage

Distribution A: Approved for public release; distribution is unlimited

3 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution

SC Power Transmission for DE

A. Dietz, Creare Inc., L. Bromberg, MIT

• Two-stage current leads with integrated heat exchangers cooled by cycle gas from a two-stage turbo-Brayton cryocooler

• Current lead design minimizes cold heat load and ensures even current distribution

• Cryocooler design offers high efficiency with low weight

• Advantages over copper cables – 90% less weight – 40% less power consumed

Current Lead Design System Configuration

Cryocooler Performance

Presenter

Presentation Notes

Phase II STTR Project. Objective of this project is to design and test a new compact and lightweight superconducting power transmission (SPT) system for directed energy applications. The design goals are to maximize the transmitted power-to-weight ratio of the system and to minimize the power required by the cryocooler. System configuration is shown in the lower right. The turbo-Brayton cycle is on the right and the current lead and power transmission cable is on the left. This system configuration minimizes power consumption through the use of cooling two stages, routes the cooling flow to preferentially cool the superconducting cable, and cools the current lead via integrated heat exchangers. The current lead design model is shown on the lower left. The design ensures uniform current distribution between the superconducting tapes in the cable by connecting individual current leads to each tape. The cryocooler design offers high efficiency with low weight as shown in the graph in the upper right. Result is 90% less weight and 40% less power consumed than with a copper cable. This is an enabling technology for airborne directed energy weapons and for electric aircraft.

4

Ivan K. Schuller, UCSD

MURI Supersearch Fast, Selective, Sensitive Scanning Method

Nb

MgB2

GdBa2CuOx

10 20 30 40 50 60 70 80 90 1001

10

100

MFM

MS

sign

al (a

rb. u

nits

)

Temperature (K)Study of intimately mixed

superconductors DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution

Presenter

Presentation Notes

The search for new superconducting (SC) materials by combinatorial techniques requires an effective and fast screening method. Magnetic Field Modulated Microwave Spectroscopy (MFMMS) relies on the temperature-dependent microwave absorption with an ac magnetic field applied to the sample. Using this technique, we are able to distinguish SC phase transitions of intimately mixed superconductors. Figure 1 (left): Schematic of the microwave cavity illustrating the location of the sample in the RF magnetic and electric fields HRF and ERF, respectively. Figure 2 (right): MFMMS temperature scan of Nb, MgB2 and GdBa2Cu3Ox combined in one sample. All superconducting transitions are clearly distinguishable.

5

Ω

Ivan K. Schuller, UCSD

MURI Supersearch New Superconductors Discovered

Service to Others

Phase Spread Alloys Bulk Synthesis • High-Pressure

• High-Temperature

Meteorites

Discoveries (#): Borides (10), Carbides (6),

Calchogenides (4), Silicides (2), Bismuthates(1),

Antimonides (1), Other Intermetallics (2)

Presenter

Presentation Notes

The project is oriented towards the search and discovery of new superconductors via combinatorial methods and bulk synthesis techniques. In order to stabilize new materials phases, high-pressure and high-temperature instrumentation is used. Such conditions appear deep in the earth crust, or during birth and impact of meteorites, which now complement our sample cabinet for the search for new materials. The group offers mail-in service to measure potential superconducting candidates with fast screening magnetic field modulated microwave spectroscopy (http://ischuller.ucsd.edu/research/new_SC.php).

Empirical Search for New Superconductors U Maryland-Iowa State-UC San Diego MURI (PI-R.L. Greene)

Development of viable solutions for the synthesis of sulfur-bearing single crystals Xiao Lin, Sergey L. Bud’ko and Paul C. Canfield*

Have grown single crystals of mineral types: Parkerite (above, SC below 1K), Shandite, Paracostibite, and sulfide variants of olivine (not shown and not SC).

DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution

Presenter

Presentation Notes

The growth of mineral based compounds has lead to several outcomes so far. First, development of growth techniques for S- and Se-based mineral compounds. Our advances with this technique were part of a Symposium issue of Phil. Mag. 92, 2436 (2012) (created and edited by Paul Canfield) that focused on the design, discovery and growth of novel materials, many of which were indeed superconductors.

Superconducting Flexible Wire: MgB2@CNT; FeSe@CNT

A. Zakhidov, University of Texas at Dallas MgB2 nanowires

Resistance drops to exact zero after RF oxygen plasma treatment,

Resistance drops at Tc but not to zero : needs optimization of barrier coating.

FeSe0.5Te0.5 on CNT

0 50 100 150 2005.5

6.0

6.5

7.0

Current direction perpendicular to the CNT

Resi

stan

ce(Ω

)

Temperature (K)

Resistance(Ω)


Presenter

Presentation Notes

UTD team has significantly improved a process of making superconducting wires based on templating CNT sheets by superconducting materials (MgB2 and recently FeSeTe): Now MgB2 coating is done semi-continuously by roll-to-roll type process, when CNT sheet is dry-spinned from forest inside the processing chamber and rolled onto a drum, while being coated by Boron. Then it is unrolled and exposed to Mg vapors. The resulting MgB2@CNT microwires showed high Tc and reasonably good Jc, but R droped to exact zero only at very low T and always the horisontal “R-plato” has been observed due to Josephson junctions network. To eliminate this JJ (appearing due to micro cracks within the wires and their interconnwects) the oxygen plasma treatment has been developed, that significantly impoved SC-ing properties, shown at the left part of Fig.2. Now R abruptly drops to exact zero and R-plato is mostly eliminated by burning the CNT core and leaving the nearly 100 % MgB2 nanowires. (SEM will be provided later though). Upper and middle right: SEM image of MgB2 coated MWCNT yarn with high enough critical current density of 3x108 A/m2, extracted from I-V curves which has been now dramatically improved by recent optimization. R(T): temperature dependence of resistance of MgB2@CNT after RF oxygen plasma treatment at the step of B coated CNT. Resistance directly and abruptly drops to exact zero, without previously seen R-plato, which proves that Josephson juntcion network is eliminated by plasma treatemnet, that burns away most of CNT template. Upper and middle right: SEM of CNT sheet (with TiN buffer on it) coated by FeSeTe thin film by PLD. Resistance R(T) curves, showing abrupt (but modest yet) drop of R. R(T) does not drop to zero due to un-optimized yet buffer barrier coating and non-optimal FeSeTe layer thickness

8 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution

Integrated MBE – ARPES Kyle Shen, Cornell U.


9

Investigating the “Mother” of all High-Tc Superconductors Kyle M. Shen, Cornell University

J.W. Harter et al., Phys. Rev. Lett. (in press)

Cu O Sr / La

Sr1-xLaxCuO2 epitaxial thin films ARPES measurements

Regions of suppressed intensity on the Fermi surface (yellow circles) indicate presence of

strong antiferromagnetic fluctuations

0

+π

−π

ky

kx

0 +π +2π

• Simple, archetypal structure of cuprates (square, flat CuO2 sheets)

• Can be doped either with holes or electrons (only ambipolar SC cuprate)

• Bulk single crystals do not exist (epitaxial stabilization)


Presenter

Presentation Notes

SrCuO2 is the archetypal “parent” or “mother” structure of all high-Tc cuprate. Because its structure is extremely simple (CuO2 sheets, separated only by a single Sr/La layer), it is devoid of all the structural complications (bilayer interactions, orthorhombic distortions, structural instabilities) which plague all other cuprate materials, this is an ideal material to investigate 1) the underlying mechanism of high temperature superconductivity, 2) how to enhance Tc, and 3) how to create atomically thin super lattices or superstructures of high temperature superconductors. However, this material does not exist in bulk single crystalline form, so in order to investigate this material, we have used epitaxial stabilization by molecular beam epitaxy growth. Using our combined, in situ MBE + Photoemission system, we have, for the first time, been able to investigate the intrinsic electronic structure of this elusive material. In particular, by substituting La for Sr, we can dope electrons into the CuO2 sheets, and our photoemission measurements reveal that strong antiferromagnetic fluctuations (symbolized by the dashed green lines) cause gaps in the Fermi surface to open where the Fermi surface (red, orange) intersect the green lines, resulting in regions of suppressed intensity (yellow circles). The observation of these strong antiferromagnetic fluctuations answers a major, long-standing question in the field of high-temperature superconductivity : is the phase diagram naturally electron-hole asymmetric, in terms of the robustness of stabilizing antiferromagnetism. These experiments clearly indicate that this is the case – that the cuprates are intrinsically electron-hole asymmetric. This not only has strong implications for microscopic theories which try to explain superconductivity, but also point to new ways of creating superconducting heterostructures with optimized properties.

10

Semiconducting Graphene (S-Gr) Walt de Heer, Georgia Tech

On-off ratio > 105

Factor 104 greater than for pure graphene FETs.

• SGr (bandgap~1eV) is graphene that is bonded to the SiC surface. •It seamlessly connects to graphene to make atomically thin, gateable SGr-Gr junctions. • Digital electronics is feasible; • SGr is stable at extreme temperatures;

I SD

(µA

)

VSD (V)

2 4 6 -2 -4 -6 0 10-5

10-4

10-3

10-2

10-1

100

101

102

graphene Semiconducting

graphene

AFM

Epitaxial graphene on SiC (C-face)

Gate

Drain

S D G graphene Gr

S-Gr Gr

EFM

Gate

Source Drain S-Gr

SiC


Presenter

Presentation Notes

Semiconducting graphene-graphene junctions are made in a two step ultrahigh temperature annealing process. The first (at 1500 C) produces uniform (multilayer) graphene layer on the semi-insulating SiC wafer. In a patterned etching process, graphene is removed from selected areas. The SiC wafer is reannealed (at 1300 C) to produce semiconducting graphene on the exposed areas. The transistors are supplied with gates and contacts in the usual way. S-Gr/Gr based transistors are suitable for digital electronics (which is not the case for current Gr transistors). The nature of semiconducting graphene (that can be formed on both the Si and the C terminated face) is still debated but it may be a Peierls distorted graphene sheet. The mobility is not yet known. (EFM =Electrostatic Force Microscopy, provides good contrast between S-gr and Gr) S-Gr and Gr are extremely stable, and when protected can withstand temperatures up to 1000 C, which is useful for operation in extreme conditions. .

11

Graphene on crystallized sidewall

Res

ista

nce

(h/e

2 )

Number of passive probes 0 1 2

0

1

2

3

V I

V I

V I

• 40 nm wide graphene ribbons grown on crystallized sidewalls of trenches etched in SiC are ballistic conductors. • Resistances (≈h/e2=25.8 kΩ) are essentially independent of length and temperature. • Touching a ribbon with a probe, scatters electrons and (reversibly) doubles the resistance. Touching it with 2 probes, triples it.

Room Temp Ballistic Transport in Graphene Nano-ribbons Walt de Heer, Georgia Tech

0 1 2 3 4 5

R (h

/e2 )

1

2

Probe spacing L(µm)

d L

SEM image of four nano probes contacting graphene ribbon

R2p

p (h/

e2)

0.8

1.0

1.4

1.6

1.2

0 10 20 L (µm)


Presenter

Presentation Notes

Graphene nanoribbons are made by annealing 20 nm deep trenches (T=1500C) that are etched in single crystal SiC, causing the sidewalls to facet (q~ 30° ) and nanoribbons to selectively grow on the sidewalls (as shown in the schematic diagram, upper left, that also shows an AFM image of an array of trenches). Using an Omicron 4 probe STM, equipped with an SEM (upper middle), the probes are placed on a selected ribbon and the resistance is measured (either in 2 or in 4 probe configuration). The resistance is measured as a function of probe distance (lower left, main graph). The resistance is close to h/e2≈26 kW. It is only weakly dependent on length and essentially independent of temperature (from T=4K to 300K). The slopes correspond to the ballistic mean free path which exceeds 50 µm for several ribbons. This is a factor of 1000 greater than observed in lithographically patterned ribbons and 50 greater that observed in carbon nanotubes. The inset shows 2 point room temperature measurements over a longer length scale (the limit of the apparatus) on two different ribbons. A non-linear component is observed that is reminiscent of strong localization. However the length scale is extraordinary. (Upper right). The 2 point resistance (reversibly) doubles when a probe simply touches the ribbon at a random location. It triples with two probes (that are not connected to a voltage source) touch the ribbon. This increase is caused by scattering of electrons by the probe. This is a spectacular and definitive demonstration of ballistic transport. The fact that we observe e^2/h rather than 2 e^2/h indicates that the spin degeneracy is lifted. In fact this is consistent with our recent observation that the edge state is spin polarized. The observations are consistent with a topologically protected edge state that is closely related to topological insulators. There is no question that this is one of the most important discoveries in graphene.

12

Our work (CVD GNR) Exfoliated GNR Thick CVD GMR GNR from CNTs

101 102 103 104 105

107

108

109

J BD (A

/cm

2 )

ρ (µΩ-cm)

Nanoscale Interconnects from CVD Graphene Eric Pop, UIUC

• First study of large-scale graphene nanoribbon (GNR) interconnects from graphene grown by chemical vapor deposition (CVD)

• Examined temperature range 2-900 K

tox

tsi

W (GNR)W (wide graphene)

• Achieved record current densities >109 A/cm2 in small GNRs due to improved heat dissipation through the substrate and contacts (see bottom left).

• Thermal engineering of the substrate and its interface with graphene can further improve the performance of GNRs

See: A. Behnam, A. S. Lyons, M-H. Bae, E. K. Chow, S. Islam, C. H. Neumann, E. Pop, Nano. Lett. 12, 4424 (2012).

300 µm

S D 50 nm

1 µm

5.0−ραBDJ


Presenter

Presentation Notes

We have examined the fabrication, electrical, and thermal behavior of graphene nanoribbon (GNR) interconnects from graphene grown by chemical-vapor-deposition (CVD), a fundamental step toward their integration into large-scale applications. After the initial CVD growth on copper, graphene is transferred to Si/SiO2 substrate. Then electrical contacts are defined by lithography and metal evaporation. Finally, GNRs are patterned on graphene by electron-beam lithography and O2 plasma etching. (top left image). The GNRs defined here have mobility and Raman signatures comparable to GNRs obtained by other methods (e.g. exfoliated graphene, unzipped carbon nanotubes (CNTs), etc). Transport in relatively short GNRs (L < 100 nm) appears to be dominated by contacts rather than by edge roughness, defects, or grain boundaries. Thermal engineering of GNRs allows us to reach the highest current densities reported for any graphene interconnects (>109 A/cm2). These current density levels are significantly higher than the expectations of International Technology Roadmap for Semiconductors (ITRS), but further improvement in contact resistance is still needed.

13

Questions: Stress, Performance, Fabrication

• Back gate (gold-palladium alloy), PEN substrate

• Hafnium-oxide gate dielectric • CVD graphene transferred over gates

20 μm Source

Gate

Drain Drain

x y

Graphene Yields High Performance Flexible FETs Ken Shepard and Jim Hone, Columbia University

Performance • fT, fmax of 10.7 GHz, 3.7 GHz w/o de-embedding • fT/fmax=0.35, entire strain range. • Mobility, output resistance unchanged by strain;

gm ~1/2 its 0% strain value at ~2% strain

Inherent flexibility of monolayer graphene, and its environmental inertness, make it a natural candidate for flexible electronics. GHz frequency response can be obtained with little sensitivity to strain, a major advance in flex-FET speed.


Presenter

Presentation Notes

Our MURI team has been a leader in developing high-speed graphene electronics, i.e. FETs. Recently we have come to realize that monolayer graphene has the potential to be an ideal active semiconductor for high-performance flexible FETs, which are used in displays, handheld electronics, etc. As a result our team has worked this year to demonstrate that gigahertz FETs can be made if care is taken to develop the correct fabrication protocols. Our device have shown fmax of ~3.4GHz, many orders of magnitude faster than those obtainable with other flexible device materials and the devices have not been sensitive to the strains typically encountered in these devices.

14

Nanoscale NMR with a Single Electron Spin Sensor D. D. Awschalom, University of California – Santa Barbara

Science, in press (2012)

• Room temperature detection of external protons • No magnetic field gradients needed • 13 nm3 detection volume PMMA ~8nT sensitivity • Collaboration with IBM Research Division

T2 ~ 600 µs 20 nm from surface

isotopically pure

1H NMR


Presenter

Presentation Notes

The one major deficiency of NMR is the low sensitivity of the conventional coil-based induction method of detection, which prevents its application to samples at the nanometer scale. Much improved detection sensitivity has been achieved with magnetic resonance force microscopy, which is based on detecting weak magnetic forces in the presence of a strong field gradient and has demonstrated nanometer-scale NMR imaging at cryogenic temperatures. Here we present an alternative nanoscale detection method that works in the absence of a magnetic field gradient, thus preserving spectroscopic information, and is operable over a wide range of temperatures, including room temperature. A single near-surface nitrogen-vacancy (NV) center in diamond is used as an atomic-size sensor to detect weak magnetic fields originating from nuclear spins external to the diamond. In an initial demonstration, we detected randomly polarized hydrogen nuclei (protons) in an organic polymer. Both time domain and spectroscopic information were obtained by appropriately manipulating the protons so as to affect the precession phase of the highly coherent NV electron spin. The results suggest that NV-based NMR detection may provide a path toward three-dimensional nanoscale magnetic resonance imaging (nanoMRI) under ambient conditions. This was successful solely due to the AFOSR growth of spin-engineered single crystal diamond films, enabling us to develop a delta-doping technique to place spins with long coherence times near the surface.

15

Spontaneous Hyper-Emission Eli Yablonovitch & Ming Wu, UC Berkeley

hν

λ 2

molecule

M substrate

Au antenna

Au antenna InGaAs quantum well

Antenna slot defined by quantum well thickness!

Using an optical antenna, Spontaneous Emission Rate can be ~0.1×ωo !!! Faster than stimulated emission, but antenna slot must be very narrow.


Presenter

Presentation Notes

Figure on the left schematically explains the idea of enhanced spontaneous emission Every fluctuating internal oscillating dipole moment will emit radiation. The fundamental problem is that the molecule, quantum dot, or oscillating dipole moment, is far too small to act as an efficient antenna for electromagnetic radiation. The most efficient optical antenna is a half wavelength dipole. According to Wheeler’s limit1, any smaller antenna will have a radiation rate proportional to (a/λ)3, where a is the atomic dipole length, slowing down the spontaneous emission rate by many orders of magnitude. Since atoms, molecules, and quantum dots emit wavelengths that are much larger than the atoms themselves, they are simply too small to act as their own efficient antennas. The key issue in speeding up spontaneous emission is to couple the radiating molecule to a proper antenna at the nano-scale. Figure on the right is one device structure we are currently focusing on: Current fabrication focuses on lithographically defined dipole antennas with an active medium in between the antenna arms (currently GaAs − AlGaAs) .The final structure of the device is shown above, and consists of a quantum-well layer in between two antenna arms. The gap between the antenna arms is defined by the thickness of the quantum-well layer and can be made very small. Antenna dimensions range from 40 to 200 nm, but the gap in between the antenna arms is <10nm. One advantage of this fabrication scheme is the small gap dimension is controlled by film thickness rather than lithography. H. A. Wheeler, “Fundamental Limitations of Small Antennas”, Proc. of the I.R.E. 35, 1479 (1947).

16

0200400600800

100012001400160018002000

1200 1300 1400 1500 1600

Cou

nts

Wavelength (nm)

Emission Parallel to Antenna

400nm Antenna

Au Au

150nm

InG

aAsP

Pump Polarization

no antenna

~35X

no antenna

~35X Spontaneous Emission Enhancement

Single Arm Antenna Eli Yablonovitch & Ming Wu, UC Berkeley


Presenter

Presentation Notes

Single continuous arm antenna with an inductively loaded center section. Also showing about 35X enhancement. We need to improve our understanding of the electromagnetic anomalous skin effect to get the additional 6X we need, in order to beat stimulated emission.

Protecting Superconducting Antennas with Metamaterial Cloaks

Frank Trang, Horst Rogalla, Zoya Popovic, University of Colorado, Boulder

Transmitter Cloak

HTS Receiver

1cm

4.58cm

≈5200

≈42000

88K

One of 5 layers of the proposed cloak constructed of SRRs.

Proposed cloak geometry HTS Split Ring Resonator (SRR) and its temperature dependent quality factor Q

Simulated EM-field: the far field is restored behind the cloak

Parameter extraction of µ and ε

Transmitter

Receiver


Presenter

Presentation Notes

(1) Starting point: small superconducting antennas suffer from non-linearity in the presence of high electromagnetic fields. A superconducting antenna (e.g. on a conducting wall) with dimension small compared to λ can be broadband, low-loss and linear if shielded from a nearby narrow-band transmitter by a superconducting 2-dim meta-material cloak (figure on the top left). (2) High-Tc split ring resonators have excellent properties for a cloak in a small band around their resonant frequency (middle top and right) and are easy to cool. (3) The extraction of parameters (µ and ε) (bottom right) allows for: - the simulation of the shielding by the cloak (left bottom) - and the design of a real structure (one ring of 5 rings shown in the bottom middle). (4) The next step will be the measurement of an experimental model cloak similar to the one depicted in the simulation (bottom left) using 5 cylindrical layers of split-ring resonators.

18

Metamaterials for Computational Imaging D. R. Smith, Duke University

Comparison of (A) conventional, (B) single pixel, and (C) metamaterial imagers. In the metamaterial imager, a set of randomized modes sequentially samples a scene. Scene data can subsequently be reconstructed using sparse algorithms. The imager shown makes use of frequency-diversity to sample an image: no active tuning or mechanical scanning is necessary—just a frequency sweep.

J. Hunt et al., Science, in press DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution

Presenter

Presentation Notes

We introduce a new approach for imaging, in which a guided wave metamaterial is used to produce diverse mode patterns that sample a scene. The device consists of a planar waveguide, with an array of complementary metamaterial elements patterned into the top plate. Radiation that enters into the guided planar wave structure leaks out through the complementary metamaterial elements, producing the radiation pattern. If the resonance frequencies of the resonant complementary metamaterial elements are randomized over a bandwidth, then at a given frequency the mode pattern will be a set of lobes that span the field-of-view. As the frequency is varied, the mode pattern changes, and we obtain a set of modes that can be used with computational imaging schemes simply by scanning over a set of frequencies. This coherent, single-pixel approach provides new opportunities for imaging, which is in the process of undergoing revolutionary changes due to the increased understanding of computational imaging approaches. In particular, since natural scenes contain far less information than the diffraction limit would imply, virtually all scenes can be undersampled without loss of image fidelity. Single-pixel imagers are well suited to implement compression on the physical layer, leading to potential improved performance for RF and IR sensors and better integration into sensor fusion schemes.

19

Approaches to Large Area Absorber Materials David R. Smith, Duke University

Film-coupled nanocubes can produce strong absorption resonances that can create surfaces with controlled reflectance. The advantage is that perfect absorbing materials with large surface area can be fabricated cheaply and easily.

A. Moreau et al., Nature (2012)


Presenter

Presentation Notes

When plasmon resonance nanocubes are coupled to a metallic film, the combination produces strong absorption resonances. For a pure population of nanocubes (all the same size), the absorption resonance can be quite narrow, absorbing nearly 100% at the design wavelength with only a few percent coverage of nanoparticles. Narrowband absorber is desirable to construct surface with controlled emissivity for thermo-photovoltaic and incandescent lighting applications. With a larger spread in nanoparticle sizes, the absorption resonance broadens. The position of the absorption resonance is tunable across the visible and IR spectrums. In our experimental realization, we use silver nanocubes spaced by polyelectrolyte layers a controlled distance from a gold film (3-17 nm). Under white light, darkfield illumination, striking colors are evident, that result from the scattered light at all BUT the absorption wavelength (see panel above). The experimentally obtained data confirms the presence of the absorption resonance, as predicted. Absorption resonances can also be used as components in imaging systems. For example, thermal cameras often lack spectral sensitivity across the IR bands (e.g., 8-12 microns). The use of narrowband, tuned absorber structures can be incorporated to form hyperspectral imagers and sensors.

0 100 200 300T (K)

0

0.2

0.4

0.6

0.8

zT

Bi89.5Sb10.5

Bi94Sb6

Bi93Sb7 + 0.1% K

~ 50%

Cryogenic Peltier Cooling: record zT J. P. Heremans Ohio State; D. T. Morelli, Michigan State

κσ2STzT ≡

0

0.1

0.2

0.3

50 150 250 350

zT

T(K)

x=0x=0.5x=1 (1)x=1 (2)CePd2.655Pt.3

(1)

Record Thermoelectric Figure of Merit below 150 K

n-type material: Bi93Sb7:K p-type material: CePd2Pt

CePd3-xPtx

E

DO

SE

DO

S

Principle: K is a resonant level in BiSb

Principle: Tune EF in the Ce - 4f level BiSb

band

K-level Ce 4f level


Presenter

Presentation Notes

1. Potassium is a resonant impurity; increases S2 in Bi93Sb7 alloys (OSU): sets record zT=0.7 for n-type material has useful zT>0.5 from 50 K to room temperature 2. Metallic CePd2Pt has Fermi energy close to Ce-4f level (MSU): sets record zT=0.3 for p-type material

21

Dirac cones in BiSb and Electron Cloaking M. S. Dresselhaus and Gang Chen, MIT

Dirac dispersion relations in BiSb alloy thin

films Modulation doping with impurities in

core-shell nanoparticles Nanoparticles invisible to free electrons


Presenter

Presentation Notes

3. Dirac dispersion relations in Bi1-xSbx depend on crystal orientation and size quantization (MIT) => theory offers new avenue to optimize zT based on the use of surface states 4. “Cloaked” modulation doping (MIT): Modulation doping of bulk semicondictors: add impurities in nanoparticles The nanoparticle can be tailored as core-shell with different gaps so that the free electrons in the bulk do not see them (electron cloaking): => core-shell nanoparticles with engineered band structure to enhance mobility

Weinstock - Quantum Electronic Solids - Spring Review 2013

Technology

distribution metamaterials

public release distribution

unlimited distribution19

graphene ribbon r2pphe2

pure graphene fets

graphene nanoribbons

cnt resistance temperature

nm wide graphene ribbons