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materialsscienceandengineering · 7 days

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Researchers develop a novel strategy for growing two-dimensional transition metal dichalcogenides

National University of Singapore (NUS) researchers have developed a novel phase-selective in-plane heteroepitaxial strategy for growing two-dimensional transition metal dichalcogenides (2D TMDs). This approach provides a promising method for phase engineering of 2D TMDs and fabricating 2D heterostructure devices. 2D TMDs exhibit various polymorphic structures, including 2H (trigonal prismatic), 1T (octahedral), 1T′ and Td phases. These phases confer a range of properties such as superconductivity, ferroelectricity and ferromagnetism. By manipulating these structural phases, the rich physical properties of TMDs can be tuned, enabling precise control over their characteristics through what is known as phase engineering. In this work, a research team led by Professor Andrew Wee from the Department of Physics under the NUS Faculty of Science, in collaboration with international partners, utilized molecular beam epitaxy (MBE) to grow molybdenum diselenide (MoSe2) nanoribbons as an in-plane heteroepitaxial template to seed the growth of H-phase chromium diselenide (CrSe2).

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sunaleisocial · 2 months

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Propelling atomically layered magnets toward green computers

New Post has been published on https://sunalei.org/news/propelling-atomically-layered-magnets-toward-green-computers/

Propelling atomically layered magnets toward green computers

Globally, computation is booming at an unprecedented rate, fueled by the boons of artificial intelligence. With this, the staggering energy demand of the world’s computing infrastructure has become a major concern, and the development of computing devices that are far more energy-efficient is a leading challenge for the scientific community.

Use of magnetic materials to build computing devices like memories and processors has emerged as a promising avenue for creating “beyond-CMOS” computers, which would use far less energy compared to traditional computers. Magnetization switching in magnets can be used in computation the same way that a transistor switches from open or closed to represent the 0s and 1s of binary code.

While much of the research along this direction has focused on using bulk magnetic materials, a new class of magnetic materials — called two-dimensional van der Waals magnets — provides superior properties that can improve the scalability and energy efficiency of magnetic devices to make them commercially viable.

Although the benefits of shifting to 2D magnetic materials are evident, their practical induction into computers has been hindered by some fundamental challenges. Until recently, 2D magnetic materials could operate only at very low temperatures, much like superconductors. So bringing their operating temperatures above room temperature has remained a primary goal. Additionally, for use in computers, it is important that they can be controlled electrically, without the need for magnetic fields. Bridging this fundamental gap, where 2D magnetic materials can be electrically switched above room temperature without any magnetic fields, could potentially catapult the translation of 2D magnets into the next generation of “green” computers.

A team of MIT researchers has now achieved this critical milestone by designing a “van der Waals atomically layered heterostructure” device where a 2D van der Waals magnet, iron gallium telluride, is interfaced with another 2D material, tungsten ditelluride. In an open-access paper published March 15 in Science Advances, the team shows that the magnet can be toggled between the 0 and 1 states simply by applying pulses of electrical current across their two-layer device.

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The Future of Spintronics: Manipulating Spins in Atomic Layers without External Magnetic Fields Video: Deblina Sarkar

“Our device enables robust magnetization switching without the need for an external magnetic field, opening up unprecedented opportunities for ultra-low power and environmentally sustainable computing technology for big data and AI,” says lead author Deblina Sarkar, the AT&T Career Development Assistant Professor at the MIT Media Lab and Center for Neurobiological Engineering, and head of the Nano-Cybernetic Biotrek research group. “Moreover, the atomically layered structure of our device provides unique capabilities including improved interface and possibilities of gate voltage tunability, as well as flexible and transparent spintronic technologies.”

Sarkar is joined on the paper by first author Shivam Kajale, a graduate student in Sarkar’s research group at the Media Lab; Thanh Nguyen, a graduate student in the Department of Nuclear Science and Engineering (NSE); Nguyen Tuan Hung, an MIT visiting scholar in NSE and an assistant professor at Tohoku University in Japan; and Mingda Li, associate professor of NSE.

Breaking the mirror symmetries

When electric current flows through heavy metals like platinum or tantalum, the electrons get segregated in the materials based on their spin component, a phenomenon called the spin Hall effect, says Kajale. The way this segregation happens depends on the material, and particularly its symmetries.

“The conversion of electric current to spin currents in heavy metals lies at the heart of controlling magnets electrically,” Kajale notes. “The microscopic structure of conventionally used materials, like platinum, have a kind of mirror symmetry, which restricts the spin currents only to in-plane spin polarization.”

Kajale explains that two mirror symmetries must be broken to produce an “out-of-plane” spin component that can be transferred to a magnetic layer to induce field-free switching. “Electrical current can ‘break’ the mirror symmetry along one plane in platinum, but its crystal structure prevents the mirror symmetry from being broken in a second plane.”

In their earlier experiments, the researchers used a small magnetic field to break the second mirror plane. To get rid of the need for a magnetic nudge, Kajale and Sarkar and colleagues looked instead for a material with a structure that could break the second mirror plane without outside help. This led them to another 2D material, tungsten ditelluride. The tungsten ditelluride that the researchers used has an orthorhombic crystal structure. The material itself has one broken mirror plane. Thus, by applying current along its low-symmetry axis (parallel to the broken mirror plane), the resulting spin current has an out-of-plane spin component that can directly induce switching in the ultra-thin magnet interfaced with the tungsten ditelluride.

“Because it’s also a 2D van der Waals material, it can also ensure that when we stack the two materials together, we get pristine interfaces and a good flow of electron spins between the materials,” says Kajale.

Becoming more energy-efficient

Computer memory and processors built from magnetic materials use less energy than traditional silicon-based devices. And the van der Waals magnets can offer higher energy efficiency and better scalability compared to bulk magnetic material, the researchers note.

The electrical current density used for switching the magnet translates to how much energy is dissipated during switching. A lower density means a much more energy-efficient material. “The new design has one of the lowest current densities in van der Waals magnetic materials,” Kajale says. “This new design has an order of magnitude lower in terms of the switching current required in bulk materials. This translates to something like two orders of magnitude improvement in energy efficiency.”

The research team is now looking at similar low-symmetry van der Waals materials to see if they can reduce current density even further. They are also hoping to collaborate with other researchers to find ways to manufacture the 2D magnetic switch devices at commercial scale.

This work was carried out, in part, using the facilities at MIT.nano. It was funded by the Media Lab, the U.S. National Science Foundation, and the U.S. Department of Energy.

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jcmarchi · 2 months

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Propelling atomically layered magnets toward green computers

New Post has been published on https://thedigitalinsider.com/propelling-atomically-layered-magnets-toward-green-computers/

Propelling atomically layered magnets toward green computers

Globally, computation is booming at an unprecedented rate, fueled by the boons of artificial intelligence. With this, the staggering energy demand of the world’s computing infrastructure has become a major concern, and the development of computing devices that are far more energy-efficient is a leading challenge for the scientific community.

Use of magnetic materials to build computing devices like memories and processors has emerged as a promising avenue for creating “beyond-CMOS” computers, which would use far less energy compared to traditional computers. Magnetization switching in magnets can be used in computation the same way that a transistor switches from open or closed to represent the 0s and 1s of binary code.

While much of the research along this direction has focused on using bulk magnetic materials, a new class of magnetic materials — called two-dimensional van der Waals magnets — provides superior properties that can improve the scalability and energy efficiency of magnetic devices to make them commercially viable.

Although the benefits of shifting to 2D magnetic materials are evident, their practical induction into computers has been hindered by some fundamental challenges. Until recently, 2D magnetic materials could operate only at very low temperatures, much like superconductors. So bringing their operating temperatures above room temperature has remained a primary goal. Additionally, for use in computers, it is important that they can be controlled electrically, without the need for magnetic fields. Bridging this fundamental gap, where 2D magnetic materials can be electrically switched above room temperature without any magnetic fields, could potentially catapult the translation of 2D magnets into the next generation of “green” computers.

A team of MIT researchers has now achieved this critical milestone by designing a “van der Waals atomically layered heterostructure” device where a 2D van der Waals magnet, iron gallium telluride, is interfaced with another 2D material, tungsten ditelluride. In an open-access paper published March 15 in Science Advances, the team shows that the magnet can be toggled between the 0 and 1 states simply by applying pulses of electrical current across their two-layer device.

Play video

The Future of Spintronics: Manipulating Spins in Atomic Layers without External Magnetic Fields Video: Deblina Sarkar

“Our device enables robust magnetization switching without the need for an external magnetic field, opening up unprecedented opportunities for ultra-low power and environmentally sustainable computing technology for big data and AI,” says lead author Deblina Sarkar, the AT&T Career Development Assistant Professor at the MIT Media Lab and Center for Neurobiological Engineering, and head of the Nano-Cybernetic Biotrek research group. “Moreover, the atomically layered structure of our device provides unique capabilities including improved interface and possibilities of gate voltage tunability, as well as flexible and transparent spintronic technologies.”

Sarkar is joined on the paper by first author Shivam Kajale, a graduate student in Sarkar’s research group at the Media Lab; Thanh Nguyen, a graduate student in the Department of Nuclear Science and Engineering (NSE); Nguyen Tuan Hung, an MIT visiting scholar in NSE and an assistant professor at Tohoku University in Japan; and Mingda Li, associate professor of NSE.

Breaking the mirror symmetries

When electric current flows through heavy metals like platinum or tantalum, the electrons get segregated in the materials based on their spin component, a phenomenon called the spin Hall effect, says Kajale. The way this segregation happens depends on the material, and particularly its symmetries.

“The conversion of electric current to spin currents in heavy metals lies at the heart of controlling magnets electrically,” Kajale notes. “The microscopic structure of conventionally used materials, like platinum, have a kind of mirror symmetry, which restricts the spin currents only to in-plane spin polarization.”

Kajale explains that two mirror symmetries must be broken to produce an “out-of-plane” spin component that can be transferred to a magnetic layer to induce field-free switching. “Electrical current can ‘break’ the mirror symmetry along one plane in platinum, but its crystal structure prevents the mirror symmetry from being broken in a second plane.”

In their earlier experiments, the researchers used a small magnetic field to break the second mirror plane. To get rid of the need for a magnetic nudge, Kajale and Sarkar and colleagues looked instead for a material with a structure that could break the second mirror plane without outside help. This led them to another 2D material, tungsten ditelluride. The tungsten ditelluride that the researchers used has an orthorhombic crystal structure. The material itself has one broken mirror plane. Thus, by applying current along its low-symmetry axis (parallel to the broken mirror plane), the resulting spin current has an out-of-plane spin component that can directly induce switching in the ultra-thin magnet interfaced with the tungsten ditelluride.

“Because it’s also a 2D van der Waals material, it can also ensure that when we stack the two materials together, we get pristine interfaces and a good flow of electron spins between the materials,” says Kajale.

Becoming more energy-efficient

Computer memory and processors built from magnetic materials use less energy than traditional silicon-based devices. And the van der Waals magnets can offer higher energy efficiency and better scalability compared to bulk magnetic material, the researchers note.

The electrical current density used for switching the magnet translates to how much energy is dissipated during switching. A lower density means a much more energy-efficient material. “The new design has one of the lowest current densities in van der Waals magnetic materials,” Kajale says. “This new design has an order of magnitude lower in terms of the switching current required in bulk materials. This translates to something like two orders of magnitude improvement in energy efficiency.”

The research team is now looking at similar low-symmetry van der Waals materials to see if they can reduce current density even further. They are also hoping to collaborate with other researchers to find ways to manufacture the 2D magnetic switch devices at commercial scale.

This work was carried out, in part, using the facilities at MIT.nano. It was funded by the Media Lab, the U.S. National Science Foundation, and the U.S. Department of Energy.

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testbank-zone · 3 months

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Solution Manuals For Diode Lasers and Photonic Integrated Circuits 2nd Edition By Larry A. Coldren

TABLE OF CONTENTS Preface xvii Acknowledgments xxi List of Fundamental Constants xxiii 1 Ingredients 1 1.1 Introduction 1 1.2 Energy Levels and Bands in Solids 5 1.3 Spontaneous and Stimulated Transitions: The Creation of Light 7 1.4 Transverse Confinement of Carriers and Photons in Diode Lasers: The Double Heterostructure 10 1.5 Semiconductor Materials for Diode Lasers 13 1.6 Epitaxial Growth Technology 20 1.7 Lateral Confinement of Current, Carriers, and Photons for Practical Lasers 24 1.8 Practical Laser Examples 31 References 39 Reading List 40 Problems 40 2 A Phenomenological Approach to Diode Lasers 45 2.1 Introduction 45 2.2 Carrier Generation and Recombination in Active Regions 46 2.3 Spontaneous Photon Generation and LEDs 49 2.4 Photon Generation and Loss in Laser Cavities 52 2.5 Threshold or Steady-State Gain in Lasers 55 2.6 Threshold Current and Power Out Versus Current 60 2.6.1 Basic P–I Characteristics 60 2.6.2 Gain Models and Their Use in Designing Lasers 64 2.7 Relaxation Resonance and Frequency Response 70 2.8 Characterizing Real Diode Lasers 74 2.8.1 Internal Parameters for In-Plane Lasers: ‹αi›, ηi , and g versus J 75 2.8.2 Internal Parameters for VCSELs: ηi and g versus J, ‹αi›, and αm 78 2.8.3 Efficiency and Heat Flow 79 2.8.4 Temperature Dependence of Drive Current 80 2.8.5 Derivative Analysis 84 References 86 Reading List 87 Problems 87 3 Mirrors and Resonators for Diode Lasers 91 3.1 Introduction 91 3.2 Scattering Theory 92 3.3 S and T Matrices for Some Common Elements 95 3.3.1 The Dielectric Interface 96 3.3.2 Transmission Line with No Discontinuities 98 3.3.3 Dielectric Segment and the Fabry–Perot Etalon 100 3.3.4 S-Parameter Computation Using Mason’s Rule 104 3.3.5 Fabry–Perot Laser 105 3.4 Three- and Four-Mirror Laser Cavities 107 3.4.1 Three-Mirror Lasers 107 3.4.2 Four-Mirror Lasers 111 3.5 Gratings 113 3.5.1 Introduction 113 3.5.2 Transmission Matrix Theory of Gratings 115 3.5.3 Effective Mirror Model for Gratings 121 3.6 Lasers Based on DBR Mirrors 123 3.6.1 Introduction 123 3.6.2 Threshold Gain and Power Out 124 3.6.3 Mode Selection in DBR-Based Lasers 127 3.6.4 VCSEL Design 128 3.6.5 In-Plane DBR Lasers and Tunability 135 3.6.6 Mode Suppression Ratio in DBR Laser 139 3.7 DFB Lasers 141 3.7.1 Introduction 141 3.7.2 Calculation of the Threshold Gains and Wavelengths 143 3.7.3 On Mode Suppression in DFB Lasers 149 References 151 Reading List 151 Problems 151 4 Gain and Current Relations 157 4.1 Introduction 157 4.2 Radiative Transitions 158 4.2.1 Basic Definitions and Fundamental Relationships 158 4.2.2 Fundamental Description of the Radiative Transition Rate 162 4.2.3 Transition Matrix Element 165 4.2.4 Reduced Density of States 170 4.2.5 Correspondence with Einstein’s Stimulated Rate Constant 174 4.3 Optical Gain 174 4.3.1 General Expression for Gain 174 4.3.2 Lineshape Broadening 181 4.3.3 General Features of the Gain Spectrum 185 4.3.4 Many-Body Effects 187 4.3.5 Polarization and Piezoelectricity 190 4.4 Spontaneous Emission 192 4.4.1 Single-Mode Spontaneous Emission Rate 192 4.4.2 Total Spontaneous Emission Rate 193 4.4.3 Spontaneous Emission Factor 198 4.4.4 Purcell Effect 198 4.5 Nonradiative Transitions 199 4.5.1 Defect and Impurity Recombination 199 4.5.2 Surface and Interface Recombination 202 4.5.3 Auger Recombination 211 4.6 Active Materials and Their Characteristics 218 4.6.1 Strained Materials and Doped Materials 218 4.6.2 Gain Spectra of Common Active Materials 220 4.6.3 Gain versus Carrier Density 223 4.6.4 Spontaneous Emission Spectra and Current versus Carrier Density 227 4.6.5 Gain versus Current Density 229 4.6.6 Experimental Gain Curves 233 4.6.7 Dependence on Well Width, Doping, and Temperature 234 References 238 Reading List 240 Problems 240 5 Dynamic Effects 247 5.1 Introduction 247 5.2 Review of Chapter 2 248 5.2.1 The Rate Equations 249 5.2.2 Steady-State Solutions 250 Case (i): Well Below Threshold 251 Case (ii): Above Threshold 252 Case (iii): Below and Above Threshold 253 5.2.3 Steady-State Multimode Solutions 255 5.3 Differential Analysis of the Rate Equations 257 5.3.1 Small-Signal Frequency Response 261 5.3.2 Small-Signal Transient Response 266 5.3.3 Small-Signal FM Response or Frequency Chirping 270 5.4 Large-Signal Analysis 276 5.4.1 Large-Signal Modulation: Numerical Analysis of the Multimode Rate Equations 277 5.4.2 Mode Locking 279 5.4.3 Turn-On Delay 283 5.4.4 Large-Signal Frequency Chirping 286 5.5 Relative Intensity Noise and Linewidth 288 5.5.1 General Definition of RIN and the Spectral Density Function 288 5.5.2 The Schawlow–Townes Linewidth 292 5.5.3 The Langevin Approach 294 5.5.4 Langevin Noise Spectral Densities and RIN 295 5.5.5 Frequency Noise 301 5.5.6 Linewidth 303 5.6 Carrier Transport Effects 308 5.7 Feedback Effects and Injection Locking 311 5.7.1 Optical Feedback Effects—Static Characteristics 311 5.7.2 Injection Locking—Static Characteristics 317 5.7.3 Injection and Feedback Dynamic Characteristics and Stability 320 5.7.4 Feedback Effects on Laser Linewidth 321 References 328 Reading List 329 Problems 329 6 Perturbation, Coupled-Mode Theory, Modal Excitations, and Applications 335 6.1 Introduction 335 6.2 Guided-Mode Power and Effective Width 336 6.3 Perturbation Theory 339 6.4 Coupled-Mode Theory: Two-Mode Coupling 342 6.4.1 Contradirectional Coupling: Gratings 342 6.4.2 DFB Lasers 353 6.4.3 Codirectional Coupling: Directional Couplers 356 6.4.4 Codirectional Coupler Filters and Electro-optic Switches 370 6.5 Modal Excitation 376 6.6 Two Mode Interference and Multimode Interference 378 6.7 Star Couplers 381 6.8 Photonic Multiplexers, Demultiplexers and Routers 382 6.8.1 Arrayed Waveguide Grating De/Multiplexers and Routers 383 6.8.2 Echelle Grating based De/Multiplexers and Routers 389 6.9 Conclusions 390 References 390 Reading List 391 Problems 391 7 Dielectric Waveguides 395 7.1 Introduction 395 7.2 Plane Waves Incident on a Planar Dielectric Boundary 396 7.3 Dielectric Waveguide Analysis Techniques 400 7.3.1 Standing Wave Technique 400 7.3.2 Transverse Resonance 403 7.3.3 WKB Method for Arbitrary Waveguide Profiles 410 7.3.4 2-D Effective Index Technique for Buried Rib Waveguides 418 7.3.5 Analysis of Curved Optical Waveguides using Conformal Mapping 421 7.3.6 Numerical Mode Solving Methods for Arbitrary Waveguide Profiles 424 7.4 Numerical Techniques for Analyzing PICs 427 7.4.1 Introduction 427 7.4.2 Implicit Finite-Difference Beam-Propagation Method 429 7.4.3 Calculation of Propagation Constants in a z–invariant Waveguide from a Beam Propagation Solution 432 7.4.4 Calculation of Eigenmode Profile from a Beam Propagation Solution 434 7.5 Goos–Hanchen Effect and Total Internal Reflection Components 434 7.5.1 Total Internal Reflection Mirrors 435 7.6 Losses in Dielectric Waveguides 437 7.6.1 Absorption Losses in Dielectric Waveguides 437 7.6.2 Scattering Losses in Dielectric Waveguides 438 7.6.3 Radiation Losses for Nominally Guided Modes 438 References 445 Reading List 446 Problems 446 8 Photonic Integrated Circuits 451 8.1 Introduction 451 8.2 Tunable, Widely Tunable, and Externally Modulated Lasers 452 8.2.1 Two- and Three-Section In-plane DBR Lasers 452 8.2.2 Widely Tunable Diode Lasers 458 8.2.3 Other Extended Tuning Range Diode Laser Implementations 463 8.2.4 Externally Modulated Lasers 474 8.2.5 Semiconductor Optical Amplifiers 481 8.2.6 Transmitter Arrays 484 8.3 Advanced PICs 484 8.3.1 Waveguide Photodetectors 485 8.3.2 Transceivers/Wavelength Converters and Triplexers 488 8.4 PICs for Coherent Optical Communications 491 8.4.1 Coherent Optical Communications Primer 492 8.4.2 Coherent Detection 495 8.4.3 Coherent Receiver Implementations 495 8.4.4 Vector Transmitters 498 References 499 Reading List 503 Problems 503 Appendices 1 Review of Elementary Solid-State Physics 509 A1.1 A Quantum Mechanics Primer 509 A1.1.1 Introduction 509 A1.1.2 Potential Wells and Bound Electrons 511 A1.2 Elements of Solid-State Physics 516 A1.2.1 Electrons in Crystals and Energy Bands 516 A1.2.2 Effective Mass 520 A1.2.3 Density of States Using a Free-Electron (Effective Mass) Theory 522 References 527 Reading List 527 2 Relationships between Fermi Energy and Carrier Density and Leakage 529 A2.1 General Relationships 529 A2.2 Approximations for Bulk Materials 532 A2.3 Carrier Leakage Over Heterobarriers 537 A2.4 Internal Quantum Efficiency 542 References 544 Reading List 544 3 Introduction to Optical Waveguiding in Simple Double-Heterostructures 545 A3.1 Introduction 545 A3.2 Three-Layer Slab Dielectric Waveguide 546 A3.2.1 Symmetric Slab Case 547 A3.2.2 General Asymmetric Slab Case 548 A3.2.3 Transverse Confinement Factor, Γx 550 A3.3 Effective Index Technique for Two-Dimensional Waveguides 551 A3.4 Far Fields 555 References 557 Reading List 557 4 Density of Optical Modes, Blackbody Radiation, and Spontaneous Emission Factor 559 A4.1 Optical Cavity Modes 559 A4.2 Blackbody Radiation 561 A4.3 Spontaneous Emission Factor, βsp 562 Reading List 563 5 Modal Gain, Modal Loss, and Confinement Factors 565 A5.1 Introduction 565 A5.2 Classical Definition of Modal Gain 566 A5.3 Modal Gain and Confinement Factors 568 A5.4 Internal Modal Loss 570 A5.5 More Exact Analysis of the Active/Passive Section Cavity 571 A5.5.1 Axial Confinement Factor 572 A5.5.2 Threshold Condition and Differential Efficiency 573 A5.6 Effects of Dispersion on Modal Gain 576 6 Einstein’s Approach to Gain and Spontaneous Emission 579 A6.1 Introduction 579 A6.2 Einstein A and B Coefficients 582 A6.3 Thermal Equilibrium 584 A6.4 Calculation of Gain 585 A6.5 Calculation of Spontaneous Emission Rate 589 Reading List 592 7 Periodic Structures and the Transmission Matrix 593 A7.1 Introduction 593 A7.2 Eigenvalues and Eigenvectors 593 A7.3 Application to Dielectric Stacks at the Bragg Condition 595 A7.4 Application to Dielectric Stacks Away from the Bragg Condition 597 A7.5 Correspondence with Approximate Techniques 600 A7.5.1 Fourier Limit 601 A7.5.2 Coupled-Mode Limit 602 A7.6 Generalized Reflectivity at the Bragg Condition 603 Reading List 605 Problems 605 8 Electronic States in Semiconductors 609 A8.1 Introduction 609 A8.2 General Description of Electronic States 609 A8.3 Bloch Functions and the Momentum Matrix Element 611 A8.4 Band Structure in Quantum Wells 615 A8.4.1 Conduction Band 615 A8.4.2 Valence Band 616 A8.4.3 Strained Quantum Wells 623 References 627 Reading List 628 9 Fermi’s Golden Rule 629 A9.1 Introduction 629 A9.2 Semiclassical Derivation of the Transition Rate 630 A9.2.1 Case I: The Matrix Element-Density of Final States Product is a Constant 632 A9.2.2 Case II: The Matrix Element-Density of Final States Product is a Delta Function 635 A9.2.3 Case III: The Matrix Element-Density of Final States Product is a Lorentzian 636 Reading List 637 Problems 638 10 Transition Matrix Element 639 A10.1 General Derivation 639 A10.2 Polarization-Dependent Effects 641 A10.3 Inclusion of Envelope Functions in Quantum Wells 645 Reading List 646 11 Strained Bandgaps 647 A11.1 General Definitions of Stress and Strain 647 A11.2 Relationship Between Strain and Bandgap 650 A11.3 Relationship Between Strain and Band Structure 655 References 656 12 Threshold Energy for Auger Processes 657 A12.1 CCCH Process 657 A12.2 CHHS and CHHL Processes 659 13 Langevin Noise 661 A13.1 Properties of Langevin Noise Sources 661 A13.1.1 Correlation Functions and Spectral Densities 661 A13.1.2 Evaluation of Langevin Noise Correlation Strengths 664 A13.2 Specific Langevin Noise Correlations 665 A13.2.1 Photon Density and Carrier Density Langevin Noise Correlations 665 A13.2.2 Photon Density and Output Power Langevin Noise Correlations 666 A13.2.3 Photon Density and Phase Langevin Noise Correlations 667 A13.3 Evaluation of Noise Spectral Densities 669 A13.3.1 Photon Noise Spectral Density 669 A13.3.2 Output Power Noise Spectral Density 670 A13.3.3 Carrier Noise Spectral Density 671 References 672 Problems 672 14 Derivation Details for Perturbation Formulas 675 Reading List 676 15 Multimode Interference 677 A15.1 Multimode Interference-Based Couplers 677 A15.2 Guided-Mode Propagation Analysis 678 A15.2.1 General Interference 679 A15.2.2 Restricted Multimode Interference 681 A15.3 MMI Physical Properties 682 A15.3.1 Fabrication 682 A15.3.2 Imaging Quality 682 A15.3.3 Inherent Loss and Optical Bandwidth 682 A15.3.4 Polarization Dependence 683 A15.3.5 Reflection Properties 683 Reference 683 16 The Electro-Optic Effect 685 References 692 Reading List 692 17 Solution of Finite Difference Problems 693 A17.1 Matrix Formalism 693 A17.2 One-Dimensional Dielectric Slab Example 695 Reading List 696 Index 697 Read the full article

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enetarch-electronic-engr · 4 months

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jhavelikes · 5 months

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the experimental realization and room-temperature operation of a low-power (20 pW) moiré synaptic transistor based on an asymmetric bilayer graphene/hexagonal boron nitride moiré heterostructure. The asymmetric moiré potential gives rise to robust electronic ratchet states, which enable hysteretic, non-volatile injection of charge carriers that control the conductance of the device. The asymmetric gating in dual-gated moiré heterostructures realizes diverse biorealistic neuromorphic functionalities, such as reconfigurable synaptic responses, spatiotemporal-based tempotrons and Bienenstock–Cooper–Munro input-specific adaptation. In this manner, the moiré synaptic transistor enables efficient compute-in-memory designs and edge hardware accelerators for artificial intelligence and machine learning.

Moiré synaptic transistor with room-temperature neuromorphic functionality | Nature

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dipsiven · 8 months

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Chiral AuCu heterostructures with site-specific geometric control and tailored plasmonic chirality – The Lifestyle Insider

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y2fear · 4 months

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A new 'metal swap' method for creating lateral heterostructures of 2D materials

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materialsscienceandengineering · 6 months

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Examining advances in additive manufacturing of promising heterostructures and their biomedical applications

To the authors' knowledge, there have been no review papers that summarize the biomedical applications of heterostructures prepared by additive manufacturing. This paper aims to highlight the research progress in additive manufacturing of promising heterostructure for bioimplants. The unique interfaces, robust architectures, and synergistic effects inherent in heterostructures position them as a highly promising option for advanced biomaterials in meeting the stringent requirements for highly variable anatomy and complex functionalities from individual patients. However, the advancement of heterostructures has encountered obstacles in the precise control of crystal/phase evolution and distribution/fraction of components and structures. Luckily, additive manufacturing, known for its high efficiency, design flexibility, and high dimensional accuracy, provides a strategic solution to regulate structure and composition across multiple scales, holding the potential for developing heterostructure with unprecedented properties. But an evident void exists in the scientific literature, as comprehensive review articles that summarize the biomedical applications of heterostructures via additive manufacturing are notably absent.

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mxenemedicalservicesci · 10 months

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"Nature" sub-journal: two-dimensional materials to create intelligent mid-infrared optoelectronic "imitation eyes" The perception and recognition of objects by infrared machine vision systems is becoming more and more important in the Internet of Things era. However, current systems are bulky and inefficient compared to the human retina, which has an intelligent and compact neural structure. Here, we propose a retina-inspired mid-infrared (MIR) optoelectronic device based on two-dimensional (2D) heterostructures for simultaneous data sensing and encoding. Aided by the stochastic near-infrared (NIR) sampling-terminal all-optical excitation mechanism, a single device can sense the illumination intensity of the MIR stimulus signal while encoding the intensity into a pulse train based on a rate-encoding algorithm for subsequent neuromorphic computing. The device has a wide dynamic working range, high coding accuracy, and flexible adaptability to MIR intensity. Furthermore, the inference accuracy on the MIR-MNIST dataset encoded with the device using a trained spiking neural network (SNN) achieved over 96% inference accuracy.

A bionic retinal mid-infrared optoelectronic device is proposed and realized, which can sense and encode mid-infrared light stimulation signals simultaneously. Using a bilayer black phosphorus arsenic/MoTe2 van der Waals material, the device is capable of sensing mid-infrared signals at 4.6 microns at zero bias, while encoding using random near-infrared light pulses.

The device realizes the adaptive adjustment function similar to the retina of the human eye. By adjusting the parameters of the near-infrared light, the dynamic range and precision of the encoding can be flexibly adjusted to adapt to targets with different mid-infrared light intensities.

Input the mid-infrared MNIST data set encoded by the device into the trained spiking neural network, achieving a digit recognition accuracy rate of over 96%. It shows that the device can support the intelligent information processing of mid-infrared images by pulse-based neural network. Overall, this dual-function mid-infrared optoelectronic retinal device has the ability to sense, encode and support neural network processing, and can be developed towards a highly compact and efficient mid-infrared machine vision system, which can be used in night vision, military, medical, etc. The field has application prospects. This article proposes a biomimetic mid-infrared optoelectronic retinal device using a black phosphorus arsenic/MoTe2 two-dimensional material heterojunction. The device can simultaneously realize mid-infrared light sensing and pulse encoding under zero bias. The device uses random near-infrared light pulses for sampling, and realizes the pulse rate encoding of mid-infrared light intensity according to the threshold current. By adjusting the near-infrared light parameters, the adaptive adjustment of the dynamic encoding range and encoding accuracy of targets with different mid-infrared light intensity can be realized, and the visual adaptation ability of the eyes can be simulated. The mid-infrared MNIST data set encoded by the device was input into the trained spiking neural network, and the digit recognition accuracy rate of more than 96% was achieved. This dual-function mid-infrared retinal device supports pulse-based intelligent processing of mid-infrared images, and provides a way to realize an efficient and compact mid-infrared machine vision system.

Literature reference source: https://doi.org/10.1038/s41467-023-37623-5

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sisiad · 11 months

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Shaping free-electron radiation via van der Waals heterostructures

http://dlvr.it/SssD7b

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desaletushki · 11 months

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Dental Equipment Market Size, Share & Revenue Forecast 2030

Dental Equipment Market Growth & Trends

The global dental equipment market size is expected to reach USD 17.06 billion by 2030, according to a new report by Grand View Research, Inc., registering a CAGR of 6.2% over the forecast period. These tools help with an oral health diagnosis, care, and maintenance and allow practitioners to plan a precise course of action. The introduction of supportive government efforts for oral health, an increase in medical tourism for dental operations, and the incidence of dental problems all contribute to the industry's growth. In addition, manufacturers like Planmeca are always introducing fresh computer-aided technology to the market.

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For instance, the industry demand is being driven by the company's March 2019 launch of the Planmeca Creo C5, an innovative 3D printer created to deliver chairside CAD/CAM dentistry and restorative dental treatments in a single visit.According to the estimates published by the United Nations in 2019, there were 703 million people aged over 65 years globally, and the number of older individuals is projected to double to 1.5 billion by 2050. The rising prevalence of various oral conditions in the geriatric population is likely to increase the demand for preventive, restorative, and surgical services in the future. According to the American Dental Association, 85% of individuals in the United States, value dental health and consider it an essential aspect of overall care.

The realization of the importance and maintenance of oral health combined with better access to advanced dental services will help in the growth of the industry. However, the “emergency-only” mode of dental care delivery due to the COVID-19 pandemic had a rippling effect and the industry witnessed an imminent increase in availing cost of dental care. According to the Journal of Contemporary Dental Practice, dental services were among the last to relaunch in post-pandemic relaxations since dental procedures are at high risk of transmission. This resulted in serious financial problems and revenue loss for the overall dental market.

Dental Equipment Market Report Highlights

Dental systems and parts emerged as the largest product segment in 2022 as these equipment are used for digital imaging and diagnosis of dental ailments

The dental lasers segment is expected to witness the highest CAGR during the forecast period. This is owing to its increasing application in surgical and teeth-whitening procedures.

North America dominated the global industry in 2022 owing to the high demand for new technologies & the prevalence of dental disorders and the presence of a large pool of key players & advanced healthcare infrastructure

Asia Pacific, on the other hand, is expected to register the highest CAGR over the forecast period

Dental Equipment Market Segmentation

Grand View Research has segmented the global dental equipment market on the basis of product type and region:

Dental Equipment Product Type (Revenue, USD Million, 2018 - 2030)

Dental Radiology Equipment

Intra-Oral

Digital X-ray Units

Digital Sensors

Extra-Oral

Digital Units

Analog Units

Dental Lasers

Diode Lasers

Quantum well lasers

Distributed feedback lasers

Vertical cavity surface emitting lasers

Heterostructure lasers

Quantum cascade lasers

Separate confinement heterostructure lasers

Vertical external cavity surface emitting lasers

Carbon Dioxide Lasers

Yttrium Aluminium Garnet Lasers

Systems & Parts

Instrument Delivery systems

Vacuums & Compressors

Cone Beam CT Systems

Cast Machine

Furnace and Ovens

Electrosurgical Equipment

Other System and Parts

CAD/CAM

Laboratory Machines

Ceramic Furnaces

Hydraulic Press

Electronic Waxer

Suction Unit

Micro Motor

Hygiene Maintenance Devices

Sterilizers

Air Purification & Filters

Hypodermic Needle Incinerator

Other Equipment

Chairs

Hand Piece

Light Cure

Scaling Unit

Regional Insights

North America dominated the global industry in 2022 with a market share of more than 38.35% and is expected to showcase a significant CAGR over the forecast period. This is attributed to the rising geriatric population, strong medical infrastructure, well-established reimbursement policies, the existence of key players, and advancement in preventive and restorative dental treatments. Moreover, according to the American Dental Association, 85% of individuals in the United States truly value dental health and consider oral health an essential aspect of overall care. The combination of all these factors will make North America the most promising regional market over the forecast period.

The APAC region is expected to witness the highest CAGR over the forecast period. China, Japan, and India are emerging economies with well-developed healthcare infrastructure & facilities and are now more focused on leading on the basis of R&D activities. They have suitable infrastructure and fundings for the same. A total of 43.6% of the spending is expected to emanate from Asia with countries like China, Japan, and India being the topmost to spend on R&D activities.

Attributes like favorable government policies, the rising geriatric population, the presence of key players, and the rise in the demand for dental procedures are paving way for the market in the Asia Pacific region. Moreover, medical tourism in the region is rapidly increasing due to shorter patient waiting times, low-cost treatment, availability of a large pool of skilled dental practitioners & high-end technology, and the presence of tourist destinations & quality accommodations. These aforementioned factors will assist in the market growth in the region.

List of Key Players of Dental Equipment Market

A-Dec Inc.

Planmeca Oy

Dentsply Sirona

Patterson Companies Inc.

Straumann

GC Corp.

Carestream Health Inc.

Biolase Inc.

Danaher Corp.

3M EPSE

Authoritative Research: https://www.grandviewresearch.com/industry-analysis/dental-equipment-market

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