No abstract

Thermodynamic measurements reveal that the Pauli spin susceptibility of strongly correlated twodimensional electrons in silicon grows critically at low electron densities-behavior that is characteristic of the existence of a phase transition.

The inhomogeneity of as-grown single-walled carbon nanotubes (SWCNTs), in terms of chiral structure, is a major obstacle to integration of these novel materials in advanced electronics. While separation methods have circumvented this problem, current synthesis approaches must be refined for large-scale production of SWCNTs with uniform properties. In addition, it is highly desirable to alter the initial chirality distribution which constrains fundamental study and applications. Here, we demonstrate that semiconducting SWCNTs are selectively produced in the gas phase by engineering catalysts at the nanoscale with precise size and composition. The semiconducting content in as-grown mixtures of SWCNTs is assessed by UV-visible-NIR absorbance and micro-Raman spectroscopy and reaches a maximum purity of 90% for samples catalyzed by Ni(0.27)Fe(0.73) nanoparticles (2.0 nm mean diameter). Electrical studies are performed on thin film transistors (TFTs) fabricated from as-grown SWCNTs and reveal high on/off current ratios of 10(3).

We report on low temperature (2-30K) electron transport and magneto-transport measurements of a chemically synthesized InAs nanowire. Both the temperature, T, and transverse magnetic field dependences of the nanowire conductance are consistent with the functional forms predicted in onedimensional (1D) weak localization theory. By fitting the magneto-conductance data to theory, the phase coherence length of electrons is determined to be tens of nanometers with a T -1/3 dependence.Moreover, as the electron density is increased by a gate voltage, the magneto-conductance shows a possible signature of suppression of weak localization in multiple 1D subbands.

A new fabrication technique is used to produce quantum dots with read-out channels in silicon/silicon-germanium two-dimensional electron gases. The technique utilizes Schottky gates, placed on the sides of a shallow etched quantum dot, to control the electronic transport process. An adjacent quantum point contact gate is integrated to the side gates to define a read-out channel and thus allow for noninvasive detection of the electronic occupation of the quantum dot. Reproducible and stable Coulomb oscillations and the corresponding jumps in the read-out channel resistance are observed at low temperatures. The fabricated dot combined with the read-out channel represent a step towards the spin-based quantum bit in Si/SiGe heterostructures.

We measure the thermodynamic magnetization of a low-disordered, strongly correlated twodimensional electron system in silicon in perpendicular magnetic fields. A new, parameter-free method is used to directly determine the spectrum characteristics (Landé g factor and the cyclotron mass) when the Fermi level lies outside the spectral gaps and the interlevel interactions between quasiparticles are avoided. Intralevel interactions are found to strongly modify the magnetization, without affecting the determined g and m . DOI: 10.1103/PhysRevLett.96.046409 PACS numbers: 71.30.+h, 73.40.Qv Magnetization is one of the least studied properties of two-dimensional (2D) electron systems: signals associated with the magnetization of 2D electrons are weak, and measuring them is a challenging experiment. Few experimental observations of the de Haas-van Alphen effect in 2D electron systems were made using SQUID magnetometers [1], pick up coils lithographed above the gate [2], or torque magnetometers [3]. A novel method has recently been used by Prus et al. [4] and Shashkin et al. [5] to measure the spin magnetization of 2D electrons in silicon metaloxide-semiconductor field-effect transistors (MOSFETs). This method entails modulating the magnetic field with an auxiliary coil and measuring the imaginary (out-of-phase) component of the ac current induced between the gate and the 2D electron system, which is proportional to @ =@B (where is the chemical potential). Using the Maxwell relation, @ =@B ÿ@M=@n s , one can then obtain the magnetization M by integrating the induced current over the electron density, n s . Pauli spin susceptibility has been observed to behave critically near the 2D metal-insulator transition, in agreement with previous transport measurements [6,7].Here we apply a similar method to study the thermodynamic magnetization of a low-disordered, strongly correlated 2D electron system in silicon MOSFETs in perpendicular and tilted magnetic fields. By measuring @ =@B at noninteger filling factors, we directly determine the spectrum characteristics without any fitting procedures or parameters. As compared to previously used measuring techniques, the remarkable advantage of the novel method is that it probes the spectrum of the 2D electron system with the Fermi level lying outside the spectral gaps so that the effects of interactions between quasiparticles belonging to different energy levels (interlevel interactions) are avoided. Although intralevel interactions are found to strongly affect the magnetization, the extracted Landé g factor and the cyclotron mass are insensitive to them. Therefore, measured spectrum characteristics are likely to be identical with those of a continuous spectrum. The so-obtained g factor has been found to be weakly enhanced and practically independent of the electron density down to the lowest densities reached ( 1:5 10 11 cm ÿ2 ), while the cyclotron mass becomes strongly enhanced at low n s .Measurements were made in an Oxford dilution refrigerator on clean (100)-silicon samples...

Low-frequency noise in strained SiGe core-shell nanowire p-channel field effect transistors Appl. Phys. Lett. 97, 073505 (2010); 10.1063/1.3480424High-performance, fully transparent, and flexible zinc-doped indium oxide nanowire transistors

We have studied corrections to conductivity due to the coherent backscattering in low-disordered two-dimensional electron systems in silicon for a range of electron densities including the vicinity of the metal-insulator transition, where the dramatic increase of the spin susceptibility has been observed earlier. We show that the corrections, which exist deeper in the metallic phase, weaken upon approaching the transition and practically vanish at the critical density, thus suggesting that the localization is suppressed near and at the transition even in zero field.