Structural Integrity Preserving and Residue-Free Transfer of Large-Area Wrinkled Graphene onto Polymeric Substrates.

Wrinkled graphene offers many advantageous features resulting from modifying the structural and physical properties as well as the chemical reactivity of graphene. However, its inadequate transferability to other substrates has limited its usability. This paper reports a roll-based clean transfer approach that enables the damage-free and contamination-free transfer of large-area wrinkled graphene onto polymeric substrates without compromising the integrity of wrinkle structures. The method implements the simultaneous imidazole-assisted etching and doping of chemical vapor-deposited graphene to fabricate multilayer graphene on a thermoplastic polystyrene (PS) substrate coated with a water-soluble poly(4-styrenesulfonic acid) (PSS) sacrificial layer via a roll-based transfer process. The compliant PSS layer affords the conformal contact between the PS substrate and graphene during the wrinkle formation process, enabling the controllable fabrication of graphene wrinkle structures on a large area. The water-soluble properties of PSS simplify the typically difficult separation of wrinkled graphene from the PS substrate after its transfer onto a target substrate. This improves the transferability of wrinkled graphene, rendering the transfer process solvent-free and residue-free. This work demonstrates the feasibility of the formulated method by transferring centimeter-scale wrinkled graphene onto currently used transparent flexible substrates (i.e., polyethylene terephthalate and polydimethylsiloxane). The results indicate that the transferred wrinkled graphene possesses the desirable combination of superior stretchability, optical transmittance, sheet resistance, and electromechanical stability, rendering its suitable application to transparent flexible and stretchable electronics.

Single-layer metamaterial bolometer for sensitive detection of low-power terahertz waves at room temperature.

This study demonstrates a metamaterial bolometer that can detect terahertz (THz) waves by measuring variations in electrical resistance. A metamaterial pattern for enhanced THz waves absorption and a composite material with a high temperature coefficient of resistance (TCR) are incorporated into a single layer of the bolometer chip to realize a compact and highly sensitive device. To detect the temperature change caused by the absorption of the THz waves, a polydimethylsiloxane mixed with carbon black microparticles is used. The thermosensitive composite has TCR ranging from 1.88%/K to 3.11%/K at room temperature (22.2-23.8°C). In addition, a microscale metamaterial without a backside reflector is designed to enable the measurement of the resistance and to enhance the sensitivity of the bolometer. The proposed configuration effectively improves thermal response of the chip as well as the absorption of the THz waves. It was confirmed that the irradiated THz waves can be detected via the increment in the electrical resistance. The resistance change caused by the absorption of the THz waves is detectable in spite of the changes in resistance originating from the background thermal noise. The proposed metamaterial bolometer could be applied to detect chemical or biological molecules that have fingerprints in the THz band by measuring the variation of the resistance without using the complex and bulky THz time-domain spectroscopy system.

Graphene-based stretchable and transparent moisture barrier.

We propose an alumina-deposited double-layer graphene (2LG) as a transparent, scalable, and stretchable barrier against moisture; this barrier is indispensable for foldable or stretchable organic displays and electronics. Both the barrier property and stretchability were significantly enhanced through the introduction of 2LG between alumina and a polymeric substrate. 2LG with negligible polymeric residues was coated on the polymeric substrate via a scalable dry transfer method in a roll-to-roll manner; an alumina layer was deposited on the graphene via atomic layer deposition. The effect of the graphene layer on crack generation in the alumina layer was systematically studied under external strain using an in situ micro-tensile tester, and correlations between the deformation-induced defects and water vapor transmission rate were quantitatively analyzed. The enhanced stretchability of alumina-deposited 2LG originated from the interlayer sliding between the graphene layers, which resulted in the crack density of the alumina layer being reduced under external strain.

Realization of large-area wrinkle-free monolayer graphene films transferred to functional substrates.

Structural inhomogeneities, such as the wrinkles and ripples within a graphene film after transferring the free-standing graphene layer to a functional substrate, degrade the physical and electrical properties of the corresponding electronic devices. Here, we introduced titanium as a superior adhesion layer for fabricating wrinkle-free graphene films that is highly applicable to flexible and transparent electronic devices. The Ti layer does not influence the electronic performance of the functional substrates. Experimental and theoretical investigations confirm that the strong chemical interactions between Ti and any oxygen atoms unintentionally introduced on/within the graphene are responsible for forming the clean, defect-free graphene layer. Our results accelerate the practical application of graphene-related electronic devices with enhanced functionality. The large-area monolayer graphenes were prepared by a simple attachment of the Ti layer with the multi-layer wrinkle-free graphene films. For the first time, the graphene films were addressed for applications of superior bottom electrode for flexible capacitors instead of the novel metals.

Transparent nanoscale floating gate memory using self-assembled bismuth nanocrystals in Bi(2) Mg(2/3) Nb(4/3) O(7) (BMN) pyrochlore thin films grown at room temperature.

Bismuth nanocrystals for a nanoscale floating gate memory device are self-assembled in Bi(2) Mg(2/3) Nb(4/3) O(7) (BMN) dielectric films grown at room temperature by radio-frequency sputtering. The TEM cross-sectional image shows the "real" structure grown on a Si (001) substrate. The image magnified from the dotted box (red color) in the the cross-sectional image clearly shows bismuth nanoparticles at the interface between the Al(2) O(3) and HfO(2) layer (right image). Nanoparticles approximately 3 nm in size are regularly distributed at the interface.

Phase-change InSbTe nanowires grown in situ at low temperature by metal-organic chemical vapor deposition.

Phase-change InSbTe (IST) single crystalline nanowires were successfully synthesized at a low temperature of 250 degrees C by metalorganic chemical vapor deposition (MOCVD). The growth of IST nanowires by MOCVD, at very high working pressure, was governed by supersaturation. The growth mechanism of the IST nanowires by MOCVD is addressed in this paper. Under high working pressure, the InTe phase was preferentially formed on the TiAlN electrode, and the InTe protrusions were nucleated on the InTe films under high supersaturation. The Sb was continuously incorporated into the InTe protrusions, which was grown as an IST nanowire. Phase-change-induced memory switching was realized in IST nanowires with a threshold voltage of about 1.6 V. The ability to grow IST nanowires at low temperature by MOCVD should open opportunities for investigation of the nanoscale phase-transition phenomena.