Paulo V. C. Medeiros

Unfolding spinor wave functions and expectation values of general operators: Introducing the unfolding-density operator

We show that the spectral weights W mK (k ) used for the unfolding of two-component spinor eigenstates ∣ ∣ ψ SC mK ⟩=|α⟩|ψ SC mK ,α⟩+|β⟩|ψ SC mK ,β⟩ can be decomposed as the sum of the pa ...

Single-atom scale structural selectivity in Te nanowires encapsulated inside ultranarrow, single-walled carbon nanotubes.

Extreme nanowires (ENs) represent the ultimate class of crystals: They are the smallest possible periodic materials. With atom-wide motifs repeated in one dimension (1D), they offer a privileged perspective into the physics and chemistry of low-dimensional systems. Single-walled carbon nanotubes (SWCNTs) provide ideal environments for the creation of such materials. Here we present a comprehensive study of Te ENs encapsulated inside ultranarrow SWCNTs with diameters between 0.7 nm and 1.1 nm. We combine state-of-the-art imaging techniques and 1D-adapted ab initio structure prediction to treat both confinement and periodicity effects. The studied Te ENs adopt a variety of structures, exhibiting a true 1D realization of a Peierls structural distortion and transition from metallic to insulating behavior as a function of encapsulating diameter. We analyze the mechanical stability of the encapsulated ENs and show that nanoconfinement is not only a useful means to produce ENs but also may actually be necessary, in some cases, to prevent them from disintegrating. The ability to control functional properties of these ENs with confinement has numerous applications in future device technologies, and we anticipate that our study will set the basic paradigm to be adopted in the characterization and understanding of such systems.

Hybrid platforms of graphane–graphene 2D structures: prototypes for atomically precise nanoelectronics

First-principles calculations demonstrate that line/ribbon defects, resulting from a controlled dehydrogenation in graphane, lead to the formation of low-dimensional electron-rich tracks in a monolayer. The present simulations point out that hybrid graphane-graphene nanostructures exhibit important elements, greatly required for the fabrication of efficient electronic circuits at the atomic level.

Encapsulated nanowires : boosting electronic transport in carbon nanotubes

The electrical conductivity of metallic carbon nanotubes (CNTs) quickly saturates with respect to bias voltage due to scattering from a large population of optical phonons. The decay of these dominant scatterers in pristine CNTs is too slow to offset an increased generation rate at high voltage bias. We demonstrate from first principles that encapsulation of one-dimensional atomic chains within a single-walled CNT can enhance the decay of “hot” phonons by providing additional channels for thermalization. Pacification of the phonon population growth reduces the electrical resistivity of metallic CNTs by 51% for an example system with encapsulated beryllium.

Electronic Structure Control of Sub-Nanometer 1D SnTe via Nanostructuring within Single-Walled Carbon Nanotubes

Nanostructuring, e. g., reduction of dimensionality in materials, offers a viable route toward regulation of materials electronic and hence functional properties. Here, we present the extreme case of nanostructuring, exploiting the capillarity of single-walled carbon nanotubes (SWCNTs) for the synthesis of the smallest possible SnTe nanowires with cross sections as thin as a single atom column. We demonstrate that by choosing the appropriate diameter of a template SWCNT, we can manipulate the structure of the quasi-one-dimensional (1D) SnTe to design electronic behavior. From first principles, we predict the structural re-formations that SnTe undergoes in varying encapsulations and confront the prediction with TEM imagery. To further illustrate the control of physical properties by nanostructuring, we study the evolution of transport properties in a homologous series of models of synthesized and isolated SnTe nanowires varying only in morphology and atomic layer thickness. This extreme scaling is predicted to significantly enhance thermoelectric performance of SnTe, offering a prospect for further experimental studies and future applications.