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We report on a direct comparison of the out-of-plane thermoelectric properties, such as Seebeck coefficient and electrical conductivity, of atomically thin MoS2 films. The films were prepared by a chemical vapor deposition method and were simultaneously investigated using a Cu-sandwiched structure. Specifically, this is the first study that measures the out-of-plane Seebeck coefficients of atomically thin mono- and bilayer MoS2 at 300 K. At room temperature, out-of-plane Seebeck coefficients for MoS2 films with one, two, and seven layers were measured to be approximately 129.4, 143.3, and 152.2 μV/K, respectively. Such behavior is seen because the increasing number of MoS2 layers increases the density of states of a system. In contrast to conventional thermoelectric materials, the electrical conductivities of these MoS2 films have the same tendency as the Seebeck coefficients. Our results show that thermoelectric devices can utilize the out-of-plane properties of MoS2 thin films with high power factors. [ABSTRACT FROM AUTHOR]

A new electrogenerated chemiluminescence detection method is investigated for use in detection in reversed-phase and reversed-phase ion-pair HPLC with Ru[(bpy).sub.[3.sub.2+]] in the mobile phase. In this method, different concentrations of Ru[(bpy).sub.[3.sup.2+]] are dissolved in the mobile phase and the HPLC column flushed with the mobile phase for 1 h until the column is saturated with Ru[(bpy).sub.[3.sup.2+]]. The separated analytes along with Ru[(bpy).sub.[3.sup.2+]] pass through an optical-electrochemical flow cell which has a dual platinum electrode held at a potential of 1250 mV vs a Ag/AgCI reference electrode. On the surface of the electrode, Ru[(bpy).sub.[3.sup.2+]] is oxidized to Ru[(bpy).sub.[3.sup.3+]] which reacts with the analytes to emit light. The retention times, retention orders, detection limits, and linearity in working curves are compared to those obtained with the conventional postcolumn Ru[(bpy).sub.[3.sup.2+]] addition method. The retention times for dansyl amino acids with Ru[(bpy).sub.[3.sup.2+]] in the mobile phase are longer than those obtained with the postcolumn addition approach. This may be caused by [Pi]-to-[Pi] interactions between the aromatic groups of the dansyl derivatives and the bipyridyl groups of Ru[(bpy).sub.[3.sup.2+]] in the Ru[(bpy).sub.[3.sup.2+]]-saturated reversed-phase column. Similarly, oxalate is separated from urine and blood plasma samples by reversed-phase ion-pair HPLC. Plasma samples are obtained using ultrafiltration to remove proteins from whole blood. Retention times for oxalate with the two detection techniques are identical, and detection limits for these techniques are compared.

Three approaches are comparatively evaluated for the use of tris(2,2'-bipyridyl)ruthenium(II), [[Ru(bpy).sub.3].sup.3+], as a chemiluminescent reagent in flowing streams: (1) external generation of the reactive [[Ru(bpy).sub.3].sup.3+] oxidation state followed by contact with the analyte, (2) in situ generation of the [[Ru(bpy).sub.3].sup.3+] species from a solution mixture of the analyte and the [[Ru(bpy).sub.3].sup.2+] species as it passes through the reaction/observation cell, and (3) in situ generation of the [[Ru(bpy).sub.3].sup.3+] species from the [[Ru(bpy).sub.3].sup.2+] species immobilized within the observation cell. Oxalate and proline were used as representative analytes for comparison of these three modes with respect to the influence of experimental variables (reagent concentration, flow rate, pH) and resulting analytical performance (detection limit, working range, measurement precision). Additionally, a comparison was made of the relative ECL intensities obtained for a variety of analytes including oxalate, amino acids, aliphatic amines, peptides, and NADH. We find that each approach has its unique set of strengths and weaknesses. The external generation mode yields the most intense emission, especially for simple aliphatic amines, but working curves have poor linearity, and emission intensifies have a large dependence on solution flow rate. The in situ immobilized approach results in lower intensities but yields the widest linear dynamic ranges, is most conservative of reagent, and has a particular sensitivity advantage for proline and NADH determinations. The in situ solution mode is superior for the detection of amino acids such as tryptophan, 5-hydroxytryptophan, and histidine and has time, convenience, and reliability advantages.