Novel Degree Of Freedom Research Articles

Top–Down Fabrication of Gate-All-Around Vertically Stacked Silicon Nanowire FETs With Controllable Polarity

As the current MOSFET scaling trend is facing strong limitations, technologies exploiting novel degrees of freedom at physical and architecture level are promising candidates to enable the continuation of Moore's predictions. In this paper, we report on the fabrication of novel ambipolar Silicon nanowire (SiNW) Schottky-barrier (SB) FET transistors featuring two independent gate-all-around electrodes and vertically stacked SiNW channels. A top-down approach was employed for the nanowire fabrication, using an e-beam lithography defined design pattern. In these transistors, one gate electrode enables the dynamic configuration of the device polarity (n - or p-type) by electrostatic doping of the channel in proximity of the source and drain SBs. The other gate electrode, acting on the center region of the channel switches ON or OFF the device. Measurement results on silicon show I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</sub> >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> and subthreshold slopes approaching the thermal limit, ≈ 64 mV/dec (70 mV/dec) for p(n)-type operation in the same physical device. Finally, we show that the XOR logic operation is embedded in the device characteristic, and we demonstrate for the first time a fully functional two-transistor XOR gate.

New degrees of freedom in metaheuristic optimization of component-based systems architecture: Architecture topology and load balancing

Today's complex systems require software architects to address a large number of quality attributes. These quality attributes can be in contradiction with each other. In practice, software architects manually try to come up with a set of different architectural designs and then try to identify the most suitable one. This is a time-consuming and error-prone process. Also, this process may lead the architect to suboptimal designs. To tackle this problem, metaheuristic approaches for automating architecture design have been proposed by researchers.Metaheuristic approaches, such as genetic algorithms (GA), use degrees of freedom to automatically generate new alternative solutions. In this paper, we present two novel degrees of freedom for the optimization of system architectures. These two degrees of freedom: (i) the topology of the hardware platform, and (ii) load balancing of software components, can improve the results of the optimization algorithm. Our approach is implemented as part of the AQOSA (Automated Quality-driven Optimization of Software Architectures) framework. The AQOSA framework aids architects by automatically synthesizing optimal solutions by using multi-objective evolutionary algorithms and it reports the trade-offs between multiple quality properties as output.We analyze the effectiveness of our proposed degrees of freedom, by running a computationally-intensive optimization experiment using an industrial case study from automotive domain. The results show that two new degrees of freedom, (i) architecture topology and (ii) load balancing, help the evolutionary algorithm to find better solutions by enlarging the search space.

Rapid acquisition of novel interface control by small ensembles of arbitrarily selected primary motor cortex neurons.

Pioneering studies demonstrated that novel degrees of freedom could be controlled individually by directly encoding the firing rate of single motor cortex neurons, without regard to each neuron's role in controlling movement of the native limb. In contrast, recent brain-computer interface work has emphasized decoding outputs from large ensembles that include substantially more neurons than the number of degrees of freedom being controlled. To bridge the gap between direct encoding by single neurons and decoding output from large ensembles, we studied monkeys controlling one degree of freedom by comodulating up to four arbitrarily selected motor cortex neurons. Performance typically exceeded random quite early in single sessions and then continued to improve to different degrees in different sessions. We therefore examined factors that might affect performance. Performance improved with larger ensembles. In contrast, other factors that might have reflected preexisting synaptic architecture-such as the similarity of preferred directions-had little if any effect on performance. Patterns of comodulation among ensemble neurons became more consistent across trials as performance improved over single sessions. Compared with the ensemble neurons, other simultaneously recorded neurons showed less modulation. Patterns of voluntarily comodulated firing among small numbers of arbitrarily selected primary motor cortex (M1) neurons thus can be found and improved rapidly, with little constraint based on the normal relationships of the individual neurons to native limb movement. This rapid flexibility in relationships among M1 neurons may in part underlie our ability to learn new movements and improve motor skill.

Nonlinear response via intrinsic rotation in metamaterials

We propose and experimentally verify a way to achieve strong nonlinear coupling between the electromagnetic and elastic properties in metamaterials. This coupling is provided through a novel degree of freedom in metamaterial design: the internal rotation within structural elements. Our meta-atoms have high sensitivity to electromagnetic wave power, and the elastic and electromagnetic properties can be independently designed to optimize the response. We demonstrate a rich range of nonlinear phenomena including self-tuning and bistability, and provide a comprehensive experimental demonstration of the predicted effects.

Graphene quantum dots for valley-based quantum computing: A feasibility study

At the center of quantum computing1 realization is the physical implementation of qubits - two-state quantum information units. The rise of graphene2 has opened a new door to the implementation. Because graphene electrons simulate two-dimensional relativistic particles with two degenerate and independent energy valleys,3 a novel degree of freedom (d.o.f.), namely, the valley state of an electron, emerges as a new information carrier.4 Here, we expand the Loss-DiVincenzo quantum dot (QD) approach in electron spin qubits,5,6 and investigate the feasibility of double QD (DQD) structures in gapful graphene as "valley qubits", with the logic 0 / 1 states represented by the "valley" singlet / triplet pair. This generalization is characterized by 1) valley relaxation time ~ O(ms), and 2) electric qubit manipulation on the time scale ~ ns, based on the 1st-order "relativistic effect" unique in graphene. A potential for valley-based quantum computing is present.

Double-walled carbon nanotube-based polymer composites for electromagnetic protection

In this paper, we present a microwave absorber based on carbon nanotubes (CNT) dispersed inside a BenzoCycloButen® (BCB) polymer. The high aspect ratio and remarkable conductive characteristics of CNT give rise to good absorbing properties for electromagnetic protecting in microelectronic devices with very low concentration. In this article, nanocomposites are prepared using a solution-mixing method and are then evaluated and modeled by means of coplanar test structures. First, CNT concentrations are quantified by image processing. The nanocomposites implemented with coplanar test waveguides are then characterized using a vector network analyzer from 40 MHz to 20 GHz. An algorithm is developed to calculate the propagation constant “γ”, attenuation constant “α”, and relative effective complex permittivity (ɛreff = ɛreff′ − jɛreff″) for each CNT concentration. The extracted effective parameters are verified using the electromagnetic FEM-based Ansoft's® high frequency structure simulator (HFSS). Power absorption (PA) of 7 dB at 15 GHz is obtained with only 0.37 weight percent of CNT concentration in the polymer matrix. The resulting engineerable and controllable composite provides consequently a novel degree of freedom to design and optimize innovative microwave components.

Crystal Phase Quantum Dots

In semiconducting nanowires, both zinc blende and wurtzite crystal structures can coexist. The band structure difference between the two structures can lead to charge confinement. Here we fabricate and study single quantum dot devices defined solely by crystal phase in a chemically homogeneous nanowire and observe single photon generation. More generally, our results show that this type of carrier confinement represents a novel degree of freedom in device design at the nanoscale.

Chiral quantum excitations in the anisotropic antiferromagnet CsCoBr 3

Chirality is shown to emerge as a novel degree of freedom of a quantum soliton in the anisotropic spin- 1 2 compound CsCoBr 3. The soliton chirality, detected via polarized neutron scattering, is in agreement with theoretical predictions and is a manifestation of Berry's phase. Our observations provide an explicit example of the emergence of spin currents and hidden chiral order that accompany the disappearance of antiferromagnetic order.

Evidence for Interfacial-Storage Anomaly in Nanocomposites for Lithium Batteries from First-Principles Simulations

We present theoretical support for a mass storage anomaly proposed for nanocomposites in the context of lithium batteries which forms the transition between an electrostatic capacitive mechanism and an electrode mechanism. Ab initio atomic and electronic structure calculations, performed on the Ti(0001)/Li2O(111) model interface, indicate the validity of the phenomenological model of interfacial Li storage and provide a deeper insight into the local situation. Beyond the specific applicability to storage devices, the possibility of a two-phase effect on mass storage generally highlights the availability of novel degrees of freedom in materials research when dealing with nanocomposites.

Interaction between non-Bragg band gaps in 1D metamaterial photonic crystals

We consider periodic multilayers combining ordinary positive index materials and dispersive metamaterials with negative index in some frequency range. These structures can exhibit photonic band gaps which, in contrast with the usual Bragg gaps, are not based on interference mechanisms. We focus on effects produced by the interaction between non-Bragg gaps of different nature: a) the zero averaged refractive index, b) the zero permeability and c) the zero permittivity gaps. Our analysis highlights the role played by the unavoidable dispersive character of metamaterials. We show that the degree of overlap between these bands can be varied by a proper selection of the constructive parameters, a feature that introduces novel degrees of freedom for the design of photonic band gap structures. The numerical examples illustrate the evolution of the dispersion diagrams of a periodic multilayer with the filling fraction of the ordinary material constituent and show a range of filling fractions where propagation in the multilayer is forbidden for any propagation angle and polarization.

Electronics and sensors based on pyroelectric AlGaN/GaN heterostructures

Electronic transport in semiconductors that possess high internal spontaneous and piezoelectric polarization opens up a new field of pyroelectronics and pyrosensors. The pyroelectric character of group-III-nitrides with wurtzite crystal structure yields a novel degree of freedom in designing and tailoring devices for modern micro- and nanoelectronic applications. Furthermore, spontaneous and piezoelectric polarization induced surface and interface charges can be used to develop very sensitive but robust sensors for the detection of ions, gases and polar liquids. We present a review of both theoretical and experimental studies of spontaneous and piezoelectric polarization present in AlGaN/GaN heterostructures as well as the electronic transport properties of polarization induced two-dimensional electron gases which are formed at the AlGaN/GaN interface due to the difference in the total polarization of two adjacent III-nitride layers. We demonstrate that the two-dimensional electron gases (2DEGs) achieved without modulation doping are very suitable as channel of high electron mobility transistors optimally suited for high power and high frequency applications (PART A) as well as for various kinds of sensors which can be operated in harsh environments (PART B). (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Topology change and quantum physics

The role of topology in elementary quantum physics is discussed in detail. It is argued that attributes of classical spatial topology emerge from properties of state vectors with suitably smooth time evolution. Equivalently, they emerge from considerations on the domain of the quantum Hamiltonian, this domain being often specified by boundary conditions in elementary quantum physics. Examples are presented where classical topology is changed by smoothly altering the boundary conditions. When the parameters labelling the latter are treated as quantum variables, quantum states need not give a well-defined classical topology, instead they can give a quantum superposition of such topologies. An existing argument of Sorkin based on the spin-statistics connection and indicating the necessity of topology change in quantum gravity is recalled. It is suggested therefrom and our results here that Einstein gravity and its minor variants are effective theories of a deeper description with additional novel degrees of freedom. Other reasons for suspecting such a microstructure are also summarized.