Structural and functional analysis of nanopillar spin electronic devices fabricated by 3D focused ion beam lithography

Topical review: recent progress of charge density waves in 2D transition metal dichalcogenide-based heterojunctions and their applications

Charge density wave (CDW) is an intriguing physical phenomenon especially found in two-dimensional (2D) layered systems such as transition-metal dichalcogenides (TMDs). The study of CDW is vital for understanding lattice modification, strongly correlated electronic behaviors, and other related physical properties. This paper gives a review of the recent studies on CDW emerging in 2D TMDs. First, a brief introduction and the main mechanisms of CDW are given. Second, the interplay between CDW patterns and the related unique electronic phenomena (superconductivity, spin, and Mottness) is elucidated. Then various manipulation methods such as doping, applying strain, local voltage pulse to induce the CDW change are discussed. Finally, examples of the potential application of devices based on CDW materials are given. We also discuss the current challenge and opportunities at the frontier in this research field.

Plasmonic Structures, Materials and Lenses for Optical Lithography beyond the Diffraction Limit: A Review

The rapid development of nanotechnologies and sciences has led to the great demand for novel lithography methods allowing large area, low cost and high resolution nano fabrications. Characterized by unique sub-diffraction optical features like propagation with an ultra-short wavelength and great field enhancement in subwavelength regions, surface plasmon polaritons (SPPs), including surface plasmon waves, bulk plasmon polaritons (BPPs) and localized surface plasmons (LSPs), have become potentially promising candidates for nano lithography. In this paper, investigations into plasmonic lithography in the manner of point-to-point writing, interference and imaging were reviewed in detail. Theoretical simulations and experiments have demonstrated plasmonic lithography resolution far beyond the conventional diffraction limit, even with ultraviolet light sources and single exposure performances. Half-pitch resolution as high as 22 nm (~1/17 light wavelength) was observed in plasmonic lens imaging lithography. Moreover, not only the overview of state-of-the-art results, but also the physics behind them and future research suggestions are discussed as well.

Strongly bias-dependent tunnel magnetoresistance in manganite spin filter tunnel junctions

A highly unconventional bias-dependent tunnel magnetoresistance (TMR) response is observed in Sm0.75 Sr0.25 MnO3 -based nanopillar spin filter tunnel junctions (SFTJs) with two different behaviors in two different thickness regimes of the barrier layer. Thinner barrier devices exhibit conventional SFTJ behaviors; however, for larger barrier thicknesses, the TMR-bias dependence is more complex and reverses sign at higher bias.

Nanopillar spin filter tunnel junctions with manganite barriers

The potential of a manganite ferromagnetic insulator in the field of spin-filtering has been demonstrated. For this, an ultrathin film of Sm0.75Sr0.25MnO3 is integrated as a barrier in an epitaxial oxide nanopillar tunnel junction and a high spin polarization of up to 75% at 5 K has been achieved. A large zero-bias anomaly observed in the dynamic conductance at low temperatures is explained in terms of the Kondo scattering model. In addition, a decrease in spin polarization at low bias and hysteretic magneto-resistance at low temperatures are reported. The results open up new possibilities for spin-electronics and suggest exploration of other manganites-based materials for the room temperature spin-filter applications.

High aspect subdiffraction-limit photolithography via a silver superlens

Photolithography is the technology of choice for mass patterning in semiconductor and data storage industries. Superlenses have demonstrated the capability of subdiffraction-limit imaging and been envisioned as a promising technology for potential nanophotolithography. Unfortunately, subdiffraction-limit patterns generated by current superlenses exhibited poor profile depth far below the requirement for photolithography. Here, we report an experimental demonstration of sub-50 nm resolution nanophotolithography via a smooth silver superlens with a high aspect profile of ~45 nm, as well as grayscale subdiffraction-limit three-dimensional nanopatterning. Theoretical analysis and simulation show that smooth interfaces play a critical role. Superlens-based lithography can be integrated with conventional UV photolithography systems to endow them with the capability of nanophotolithography, which could provide a cost-effective approach for large scale and rapid nanopatterning.

Nanopillar junctions

The fabrication of nanopillar devices has been essential to the understanding and development of metallic spin electronics. This paper discusses the processes that can be used for the fabrication of such structures and the challenges in which they present, with particular emphasis on extreme sub-micrometre pillar structures suitable for the study of spin-transfer torque effects.

Nonlinear giant magnetoresistance in dual spin valves

Giant magnetoresistance (GMR) arises from differential scattering of the majority and minority spin electrons by a ferromagnet (FM) so that the resistance of a heterostructure depends on the relative magnetic orientation of the FM layers within it separated by nonmagnetic spacers. Here, we show that highly nonequilibrium spin accumulation in metallic heterostructures results in a current-dependent nonlinear GMR which is not predicted within the present understanding of GMR. The behavior can be explained by allowing the scattering asymmetries in an ultrathin FM layer to be current dependent.