Abnormal phase transition in BiNbO4 powders prepared by a citrate method

<font face="times new roman,times" size="3">Triclinic beta-BiNbO4 prepared below 750 degrees C and above 1040 degrees C (denoted as Low-beta and High-beta, respectively) and pure orthorhombic alpha-BiNbO4 at 900 degrees C were successfully derived from a citrate method and the phase transition from beta-BiNbO4 to alpha-BiNbO4 was first observed in BiNbO4 powders. This phenomenon proves that the abnormal phase transition from beta-BiNbO4 to alpha-BiNbO4 exists in BiNbO4 powder system. The synthesis of Low-beta powders can be attributed to the formation of the intermediate phase of Bi5Nb3O15 by the citrate method. With increasing temperature, the Low-beta phase gradually turns into alpha-BiNbO4 due to the thermodynamically metastable state of Low-beta. We also identified that the stress in pellet format can accelerate the phase transition from Low-beta to alpha phase of BiNbO4 in comparison with powder samples. It brings us new understanding of the BiNbO4 system and also provides a simple way to obtain BiNbO4 for microwave and photocatalytic applications.</font

Can graphene make better HgCdTe infrared detectors?

We develop a simple and low-cost technique based on chemical vapor deposition from which large-size graphene films with 5-10 graphene layers can be produced reliably and the graphene films can be transferred easily onto HgCdTe (MCT) thin wafers at room temperature. The proposed technique does not cause any thermal and mechanical damages to the MCT wafers. It is found that the averaged light transmittance of the graphene film on MCT thin wafer is about 80% in the mid-infrared bandwidth at room temperature and 77 K. Moreover, we find that the electrical conductance of the graphene film on the MCT substrate is about 25 times larger than that of the MCT substrate at room temperature and 77 K. These experimental findings suggest that, from a physics point of view, graphene can be utilized as transparent electrodes as a replacement for metal electrodes while producing better and cheaper MCT infrared detectors

Many body effect induced energy gap in an optically pumped graphene system

<span lang="EN-US" style="font-family: &quot;Calibri&quot;,&quot;sans-serif&quot;; font-size: 10.5pt; mso-bidi-font-size: 11.0pt; mso-ascii-theme-font: minor-latin; mso-fareast-font-family: 宋体; mso-fareast-theme-font: minor-fareast; mso-hansi-theme-font: minor-latin; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-bidi-theme-font: minor-bidi; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><font color="#000000">We develop a simple way to investigate the energy gap induced by many body effect in optically pumped graphene at different carrier densities. The exchange self-energy and energy dispersions are obtained analytically at the long wave limit. An energy gap depending on the carrier density is observed at the Dirac point. The energy gap induced by many body effect lies in the microwave range which is in accordance with the experimental measurements. Our theoretical results indicate that the exchange interaction via Coulomb interaction can be a mechanism to create an energy gap in optically pumped graphene. (C) 2014 AIP Publishing LLC.</font></span

Electronic transport properties of graphene nanoribbon arrays fabricated by unzipping aligned nanotubes

We report on the electronic transport of graphene nanoribbon (GNR) arrays fabricated by a chemical unzipping of well-aligned single-walled carbon nanotubes. The high quality of narrow GNRs is implied by the existence of high-field current saturation and the relatively low intensity of disorder peak in parallel polarized Raman spectra. We find the zero-bias anomaly and the power-law behavior in differential conductance as a function of bias voltage and temperature in the one-dimensional GNRs, which can be well described as Luttinger liquid. Furthermore, this Luttinger-liquid behavior can be tuned by changing the gate voltage

Electron-electron interaction, weak localization and spin valve effect in vertical-transport graphene devices

We fabricated a vertical structure device, in which graphene is sandwiched between two asymmetric ferromagnetic electrodes. The measurements of electron and spin transport were performed across the combined channels containing the vertical and horizontal components. The presence of electron-electron interaction (EEI) was found not only at low temperatures but also at moderate temperatures up to similar to 120 K, and EEI dominates over weak localization (WL) with and without applying magnetic fields perpendicular to the sample plane. Moreover, spin valve effect was observed when magnetic filed is swept at the direction parallel to the sample surface. We attribute the EEI and WL surviving at a relatively high temperature to the effective suppress of phonon scattering in the vertical device structure. The findings open a way for studying quantum correlation at relatively high temperature.&nbsp

Reduced Graphene Oxide Electrically Contacted Graphene Sensor for Highly Sensitive Nitric Oxide Detection

<p>We develop graphene-based devices fabricated by alternating current dielectrophoresis (ac-DEP) for highly sensitive nitric oxide (NO) gas detection. The novel device comprises the sensitive channels of palladium-decorated reduced graphene oxide (Pd-RGO) and the electrodes covered with chemical vapor deposition (CVD)-grown graphene. The highly sensitive, recoverable, and reliable detection of NO gas ranging from 2 to 420 ppb with response time of several hundred.. seconds has been achieved at room temperature. The facile and scalable route for high performance suggests a promising application of graphene devices toward the human exhaled NO and environmental pollutant detections. </p

Interlayer catalytic exfoliation realizing scalable production of large-size pristine few-layer graphene

Mass production of reduced graphene oxide and graphene nanoplatelets has recently been achieved. However, a great challenge still remains in realizing large-quantity and high-quality production of large-size thin few-layer graphene (FLG). Here, we create a novel route to solve the issue by employing one-time-only interlayer catalytic exfoliation (ICE) of salt-intercalated graphite. The typical FLG with a large lateral size of tens of microns and a thickness less than 2 nm have been obtained by a mild and durative ICE. The high-quality graphene layers preserve intact basal crystal planes owing to avoidance of the degradation reaction during both intercalation and ICE. Furthermore, we reveal that the high-quality FLG ensures a remarkable lithium-storage stability (&gt;1,000 cycles) and a large reversible specific capacity (&gt;600 mAh g(-1)). This simple and scalable technique acquiring high-quality FLG offers considerable potential for future realistic applications