Semiconducting field-effect transistors are the workhorses of the modern electronics era. Recently, application of the field-effect approach to compounds other than semiconductors has created opportunities to electrostatically modulate types of correlated electron behaviour—including high-temperature superconductivity and colossal magnetoresistance—and potentially tune the phase transitions in such systems. Here we provide an overview of the achievements in this field and discuss the opportunities brought by the field-effect approach.

Electric field effect in correlated oxide systems

ALIS Corporation has developed a new helium ion microscope which has many advantages over both traditional scanning electron microscopes (SEMs) and focused ion beams (FIBs). This new technology is expected to produce an ultimate focused spot size of 0.25nm. This high resolution is attributed to the high source brightness (B>4×109A∕cm2sr), low energy spread (ΔE∕E∼2×10−5), and small diffraction effects (λ∼80fm). The interaction of helium ions with matter offers several valuable contrast mechanisms and a surface interaction volume which is much smaller than a SEM or conventional FIB.

https://www.iap.uni-jena.de/iapmedia/de/Lecture/Nanomaterials1367272800/NanoMat13_Paper_optional_03a.pdf

Helium ion microscope: A new tool for nanoscale microscopy and metrology

Langmuir-Blodgett (LB) films are prepared by transferring floating organic monolayers onto solid substrates. A combination of innovative chemistry and a carefully engineered instrument (a Langmuir trough) can result in high quality monomolecular assemblies displaying a high degree of structural order. The technique was first reported about fifty years ago and since then, LB films have been widely used as model systems in fundamental research. However, it is only during the past decade that the extensive applied potential has been recognised. Their precise thickness, coupled with the degree of control over the molecular architecture, has now firmly established a role for these layers in thin film technology. Following a historical introduction, this review describes the preparation and characterization of LB films and summarizes their importance in basic science. Particular emphasis is then placed on their potential applications, especially in fields related to electronics. The article concludes w...

An applied science perspective of Langmuir-Blodgett films

We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kOhm to 225 kOhm at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10^{12} cm^{-2} per graphene sheet. The most highly-ordered sample exhibits Shubnikov - de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.

Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics

Helium Ion Microcopy (HIM) based on Gas Field Ion Sources (GFIS) represents a new ultra high resolution microscopy and nano-fabrication technique. It is an enabling technology that not only provides imagery of conducting as well as uncoated insulating nano-structures but also allows to create these features. The latter can be achieved using resists or material removal due to sputtering. The close to free-form sculpting of structures over several length scales has been made possible by the extension of the method to other gases such as Neon. A brief introduction of the underlying physics as well as a broad review of the applicability of the method is presented in this review.

/pdf/helium-ion-microscopy-20lveyia0z.pdf

Helium ion microscopy

We have designed, simulated and optimized a capacitively shunted RF MicroElectroMechanical (MEM) superconducting switch. The switch consists of a High Temperature Superconducting (HTS) YBa/sub 2/Cu/sub 3/O/sub 7/ coplanar waveguide (CPW) structure with a gold membrane bridge suspended above the center conductor and anchored at the ground planes (air gap 3 /spl mu/m). A thin layer of BaTiO/sub 3/, in the shape of a patch, lies on top of the center conductor and underneath the suspended gold membrane. Under an applied voltage, the gold bridge membrane actuates downwards and collapses on top of the dielectric layer of BaTiO/sub 3/ thereby capacitively shunting the RF signal to ground. Using Sonnet, simulations were conducted to optimize the switch design. An analysis of these results revealed interesting relationships between the switch mechanical and electrical parameters; this paper discusses and analyzes these results, along with measured data.

Design of a superconducting MEM shunt switch for RF applications

We have observed evidence of superconductivity at temperatures in the vicinity of 260 K in phosphorus-doped graphite and graphene. This evidence includes transport current, magnetic susceptibility, Hall effect and (pancake) vortex state measurements. All of these measurements indicate a transition which is that of a type II superconductor with no type I phase until below the limits of our measurement capabilities. Vortex states are inferred from periodically repeated steps in the resistance versus temperature characteristics of highly oriented pyrolytic graphite and exfoliated doped multilayer graphene. Magnetic susceptibility measurements have shown results qualitatively similar to those expected (and experimentally observed by others) for ultra-thin (thickness λ L) films. The magnetization is negative for field-cooled and zero-field-cooled measurements. The magnetization for field cooled and zero-field-cooled measurements begin to diverge at approximately 260 K. Hall effect measurements show a sign reversal in the Hall voltage as the temperature is reduced from 300 K to 78 K.

https://iopscience.iop.org/article/10.1088/0953-2048/29/1/015015/pdf

Evidence of superconductivity in doped graphite and graphene

We have developed a fabrication process for a superconducting MicroElectroMechanical (MEM) shunt switch. The design of the switch has been optimized using Sonnet simulations. The switch consists of a YBa/sub 2/Cu/sub 3/O/sub 7/ Coplanar Waveguide (CPW) transmission line with a gold membrane bridge anchored at the ground planes and suspended above an area of the center conductor covered with BaTiO/sub 3/. Under an applied electric field this membrane bridge actuates downwards and shunts the RF signal to ground. The membrane returns to its original shape when the electric field is removed. In the up position the device exhibits an s/sub 21/ insertion loss of less than 0.25 dB from dc through 900 MHz (most of which is due to radiated loss). In the down position the s/sub 21/ loss in the same frequency range is greater than 30 dB.

Grover L. Larkins

Papers

Design of a superconducting MEM shunt switch for RF applications

Evidence of superconductivity in doped graphite and graphene

Fabrication of a superconducting MEM shunt switch for RF applications

On the full-width-at-half-maximum of field ion energy distributions

Langmuir-Blodgett films as barrier layers in Josephson tunnel junctions