Vanadium dioxide as a natural disordered metamaterial: perfect thermal emission and large broadband negative differential thermal emittance

We experimentally demonstrate that a thin (~150 nm) film of vanadium dioxide (VO2) deposited on sapphire has an anomalous thermal emittance profile when heated, which arises due to the optical interaction between the film and the substrate when the VO2 is at an intermediate state of its insulator-metal transition (IMT). Within the IMT region, the VO2 film comprises nanoscale islands of metal- and dielectric-phase, and can thus be viewed as a natural, disordered metamaterial. This structure displays "perfect" blackbody-like thermal emissivity over a narrow wavelength range (~40 cm-1), surpassing the emissivity of our black soot reference. We observed large broadband negative differential thermal emittance over a >10 {\deg}C range: upon heating, the VO2/sapphire structure emitted less thermal radiation and appeared colder on an infrared camera. We anticipate that emissivity engineering with thin film geometries comprising VO2 will find applications in infrared camouflage, thermal regulation, infrared tagging and labeling.Comment: 3 figure

Three-terminal field effect devices utilizing thin film vanadium oxide as the channel layer

Electrostatic control of the metal-insulator transition (MIT) in an oxide semiconductor could potentially impact the emerging field of oxide electronics. Vanadium dioxide (VO2) is of particular interest due to the fact that the MIT happens in the vicinity of room temperature and it is considered to exhibit the Mott transition. We present a detailed account of our experimental investigation into three-terminal field effect transistor-like devices using thin film VO2 as the channel layer. The gate is separated from the channel through an insulating gate oxide layer, enabling true probing of the field effect with minimal or no interference from large leakage currents flowing directly from the electrode. The influence of the fabrication of multiple components of the device, including the gate oxide deposition, on the VO2 film characteristics is discussed. Further, we discuss the effect of the gate voltage on the device response, point out some of the unusual characteristics including temporal dependence. A reversible unipolar modulation of the channel resistance upon the gate voltage is demonstrated for the first time in optimally engineered devices. The results presented in this work are of relevance toward interpreting gate voltage response in such oxides as well as addressing challenges in advancing gate stack processing for oxide semiconductors

Nanoscale Imaging and Control of Resistance Switching in VO[sub]2 at Room Temperature

We demonstrate controlled local phase switching of a VO[sub]2 film using a biased conducting atomic force microscope tip. After application of an initial, higher ‘training’ voltage, the resistance transition is hysteretic with IV loops converging upon repeated voltage sweep. The threshold Vset to initiate the insulator-to-metal transition is on order ∼ 5 V at room temperature, and increases at low temperature. We image large variations in Vset from grain to grain. Our imaging technique opens up the possibility for an understanding of the microscopic mechanism of phase transition in VO[sub]2 as well as its potential relevance to solid state devices.Engineering and Applied SciencesPhysic

Pressurizing Field-Effect Transistors of Few-Layer MoS2 in a Diamond Anvil Cell

Hydrostatic pressure applied using diamond anvil cells (DAC) has been widely explored to modulate physical properties of materials by tuning their lattice degree of freedom. Independently, electrical field is able to tune the electronic degree of freedom of functional materials via, for example, the field-effect transistor (FET) configuration. Combining these two orthogonal approaches would allow discovery of new physical properties and phases going beyond the known phase space. Such experiments are, however, technically challenging and have not been demonstrated. Herein, we report a feasible strategy to prepare and measure FETs in a DAC by lithographically patterning the nanodevices onto the diamond culet. Multiple-terminal FETs were fabricated in the DAC using few-layer MoS2 and BN as the channel semiconductor and dielectric layer, respectively. It is found that the mobility, conductance, carrier concentration, and contact conductance of MoS2 can all be significantly enhanced with pressure. We expect that the approach could enable unprecedented ways to explore new phases and properties of materials under coupled mechano-electrostatic modulation.Comment: 15 pages, 5 figure

Pressure-Temperature Phase Diagram of Vanadium Dioxide

The complexity of strongly correlated electron physics in vanadium dioxide is exemplified as its rich phase diagrams of all kinds, which in turn shed light on the mechanisms behind its various phase transitions. In this work, we map out the hydrostatic pressure - temperature phase diagram of vanadium dioxide nanobeams by independently varying pressure and temperature with a diamond anvil cell. In addition to the well-known insulating M1 (monoclinic) and metallic R (tetragonal) phases, the diagram identifies the existence at high pressures of the insulating M1' (monoclinic, more conductive than M1) phase, and two metallic phases of X (monoclinic) and O (orthorhombic, at high temperature only). Systematic optical and electrical measurements combined with density functional calculations allow us to delineate their phase boundaries as well as reveal some basic features of the transitions.Comment: 9 pages, 4 figure

Comparison of pork belly characteristics and weights of primal cuts between gilt and barrow of Landrace × Yorkshire × Duroc pigs measured by AutoFomIII

Currently, pigs breed in Korea are LYD (Landrace × Yorkshire × Duroc) crossbred pigs. Pigs used as fresh meat are gilts and barrows. However, the current supply of pork is not satisfying Korean consumers. In addition, the comparison of carcasses between gilts and barrows only studies carcass weight, backfat thickness, or meat quality, and there are very few studies comparing carcass characteristics. The purpose of this study was to compare characteristics of 7 primal cuts of gilts and barrows as measured by AutoFom III. A total of 350,179 pigs were used, including 176,461 gilts and 173,718 barrows. Characteristics of seven primal cuts were measured using AutoFom III. In the case of carcass weight, there was no significant difference in grade 1+. For all other survey items except for grade 2, gilts showed significantly (p < 0.05) higher values. For all grades except for pork belly, amounts of the remaining six primal cuts were higher in gilts (all p < 0.05,). In addition, the ratio of intermuscular fat in the pork belly of barrows showed a higher value than that in the pork belly of gilts (p < 0.05). The amount of pork belly, which is the most popular among consumers in Korea, not only produced more production than gilts in barrows, but also showed a higher value than gilts in barrows for the ratio of intermuscular fat affecting taste. In summary, gilts produced higher yields than barrows in all parts except pork belly. For the production of only pork belly, barrows showed higher production than gilts