Although carbon nanotube (CNT) transistors have been promoted for years as a replacement for silicon technology, there is limited theoretical work and no experimental reports on how nanotubes will perform at sub-10 nm channel lengths. In this manuscript, we demonstrate the first sub-10 nm CNT transistor, which is shown to outperform the best competing silicon devices with more than four times the diameter-normalized current density (2.41 mA/μm) at a low operating voltage of 0.5 V. The nanotube transistor exhibits an impressively small inverse subthreshold slope of 94 mV/decade-nearly half of the value expected from a previous theoretical study. Numerical simulations show the critical role of the metal-CNT contacts in determining the performance of sub-10 nm channel length transistors, signifying the need for more accurate theoretical modeling of transport between the metal and nanotube. The superior low-voltage performance of the sub-10 nm CNT transistor proves the viability of nanotubes for consideration in future aggressively scaled transistor technologies.

As the active dimensions of metal-oxide field-effect transistors are approaching the atomic scale, the electronic properties of these "nanowire" devices must be treated on a quantum mechanical level. In this paper, the transmission coefficients and the density of states of biased and unbiased Si and GaAs nanowires are simulated using the sp 3 d 5 s * empirical tight-binding method. Each atom, as well as the connections to its nearest neighbors, is represented explicitly. The material parameters are optimized to reproduce bulk band-structure characteristics in various crystal directions and various strain conditions. A scattering boundary method to calculate the open boundary conditions in nanowire transistors is developed to reduce the computational burden. Existing methods such as iterative or generalized eigenvalue problem approaches are significantly more expensive than the transport simulation through the device. The algorithm can be coupled to nonequilibrium Green's function and wave function transport calculations. The speed improvement is even larger if the wire transport direction is different from ͓100͔. Finally, it is demonstrated that strain effects can be easily included in the present nanowire simulations.

Phonons and their interactions with other phonons, electrons or photons drive energy gain, loss and transport in materials. Although the phonon density of states has been measured and calculated in bulk crystalline semiconductors, phonons remain poorly understood in nanomaterials, despite the increasing prevalence of bottom-up fabrication of semiconductors from nanomaterials and the integration of nanometre-sized components into devices. Here we quantify the phononic properties of bottom-up fabricated semiconductors as a function of crystallite size using inelastic neutron scattering measurements and ab initio molecular dynamics simulations. We show that, unlike in microcrystalline semiconductors, the phonon modes of semiconductors with nanocrystalline domains exhibit both reduced symmetry and low energy owing to mechanical softness at the surface of those domains. These properties become important when phonons couple to electrons in semiconductor devices. Although it was initially believed that the coupling between electrons and phonons is suppressed in nanocrystalline materials owing to the scarcity of electronic states and their large energy separation, it has since been shown that the electron-phonon coupling is large and allows high energy-dissipation rates exceeding one electronvolt per picosecond (refs 10-13). Despite detailed investigations into the role of phonons in exciton dynamics, leading to a variety of suggestions as to the origins of these fast transition rates and including attempts to numerically calculate them, fundamental questions surrounding electron-phonon interactions in nanomaterials remain unresolved. By combining the microscopic and thermodynamic theories of phonons and our findings on the phononic properties of nanomaterials, we are able to explain and then experimentally confirm the strong electron-phonon coupling and fast multi-phonon transition rates of charge carriers to trap states. This improved understanding of phonon processes permits the rational selection of nanomaterials, their surface treatments, and the design of devices incorporating them.

The Landauer approach to diffusive transport is mathematically related to the solution of the Boltzmann transport equation, and expressions for the thermoelectric parameters in both formalisms are presented. Quantum mechanical and semiclassical techniques to obtain from a full description of the bandstructure, E(k), the number of conducting channels in the Landauer approach or the transport distribution in the Boltzmann solution are developed and compared. Thermoelectric transport coefficients are evaluated from an atomistic level, full band description of a crystal. Several example calculations for representative bulk materials are presented, and the full band results are related to the more common effective mass formalism. Finally, given a full E(k) for a crystal, a procedure to extract an accurate, effective mass level description is presented. 1) IntroductionMuch experimental and theoretical effort has been directed at improving the thermoelectric (TE) figure of merit, ZT = S 2 GT K , where T is the temperature, S is the 2 Seebeck coefficient, G is the electrical conductance, and K is the thermal conductance, which is the sum of the electronic contribution, K e , and the lattice thermal conductance, K l . Careful tradeoffs are needed to obtain high ZT. Recent experimental reports of high ZT 1-8 are attributed to suppressing the lattice thermal conductivity, and now the question of whether the electronic performance can be enhanced is being asked 9-11 . New materials 1,12-15 , new structures (e.g. nanowires [16][17][18][19][20][21][22][23][24][25][26] , quantum wells 2,27,28 , superlattices 10,11,17,[29][30][31][32][33][34][35][36] , and nanocomposites 3,4,37-39 ), and strain engineering 29,40-42 , which has been so successful for enhancing the electronic performance of nanotransistors, are all being explored. To address these opportunities, thermoelectric coefficients must be related to an accurate description of the electronic structure of the material.Thermoelectric parameters are usually evaluated by solving the Boltzmann Transport Equation (BTE) 43 . For low temperature thermoelectrics in mesoscopic structures, the Landauer approach is commonly used 44,45 . The Landauer approach applies to high temperature diffusive samples as well, and it provides an alternative formulation that can be insightful 46 . One objective for this paper is to discuss the mathematical relation between the Landauer and Boltzmann approaches.In both the Landauer and Boltzmann approaches the thermoelectric parameters are related to the electronic structure of the material. The effective mass approach is widelyused to analyze experiments and to design devices. For more complex materials, full band treatments (ab initio or empirical tight binding) have been used 12,47-56 . It is still not clear, however, exactly how full band treatments relate to effective mass level treatments

An atomistic full-band quantum transport simulator has been developed to study three-dimensional Si nanowire field-effect transistors in the presence of electron-phonon scattering. The nonequilibrium Green's function ͑NEGF͒ formalism is solved in a nearest-neighbor sp 3 d 5 s ‫ء‬ tight-binding basis. The scattering selfenergies are derived in the self-consistent Born approximation to inelastically couple the full electron and phonon energy spectra. The band dispersion and the eigenmodes of the confined phonons are calculated using a dynamical matrix that includes the bond and the angle deformations of the nanowires. The optimization of the numerical algorithms and the parallelization of the NEGF scheme enable the investigation of nanowire structures with diameters up to 3 nm and lengths over 40 nm. It is found that the reduction in the device drain current, caused by electron-phonon scattering, is more important in the ON state than in the OFF state of the transistor. Ballistic transport simulations considerably overestimate the device ON currents by artificially increasing the charge injection mechanism at the source contact.

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We perform ab initio molecular dynamics on experimentally relevant-sized lead sulfide (PbS) nanocrystals (NCs) constructed with thiol or Cl, Br, and I anion surfaces to determine their vibrational and dynamic electronic structure. We show that electron-phonon interactions can explain the large thermal broadening and fast carrier cooling rates experimentally observed in Pb-chalcogenide NCs. Furthermore, our simulations reveal that electron-phonon interactions are suppressed in halide-terminated NCs due to reduction of both the thermal displacement of surface atoms and the spatial overlap of the charge carriers with these large atomic vibrations. This work shows how surface engineering, guided by simulations, can be used to systematically control carrier dynamics.

The atom sets an ultimate scaling limit to Moore's law in the electronics industry. While electronics research already explores atomic scales devices, photonics research still deals with devices at the micrometer scale. Here we demonstrate that photonic scaling, similar to electronics, is only limited by the atom. More precisely, we introduce an electrically controlled plasmonic switch operating at the atomic scale. The switch allows for fast and reproducible switching by means of the relocation of an individual or, at most, a few atoms in a plasmonic cavity. Depending on the location of the atom either of two distinct plasmonic cavity resonance states are supported. Experimental results show reversible digital optical switching with an extinction ratio of 9.2 dB and operation at room temperature up to MHz with femtojoule (fJ) power consumption for a single switch operation. This demonstration of an integrated quantum device allowing to control photons at the atomic level opens intriguing perspectives for a fully integrated and highly scalable chip platform, a platform where optics, electronics, and memory may be controlled at the single-atom level.