3 research outputs found

    Investigation of the Interfaces in Schottky Diodes Using Equivalent Circuit Models

    No full text
    The metal–semiconductor contact is one of the most critical factors that determine the performance of semiconductor devices such as Schottky barrier diodes (SBDs). SBDs between conductive carbon thin films and silicon have attracted attention due to their high performance and potential low cost of fabrication. Here, we introduce impedance spectroscopy (IS) as a powerful technique to characterize such SBDs. The electrical and structural characteristics of carbon–silicon SBDs between silicon and two different types of conductive carbon thin films have been investigated. Modeling the data with an extended equivalent circuit model reveals the effects of the metal electrode contacts of SBDs for the first time. From dc current–voltage measurements, diode parameters including the ideality factor, the Schottky barrier height, and the series resistance are extracted. Through use of analysis with IS, additional information on the Schottky contact is obtained, such as the built-in potential and more reliable barrier height values. Thus, IS can be utilized to analyze interfaces between metals and semiconductors in great detail by electrical means

    Chemically Modulated Graphene Diodes

    No full text
    We report the manufacture of novel graphene diode sensors (GDS), which are composed of monolayer graphene on silicon substrates, allowing exposure to liquids and gases. Parameter changes in the diode can be correlated with charge transfer from various adsorbates. The GDS allows for investigation and tuning of extrinsic doping of graphene with great reliability. The demonstrated recovery and long-term stability qualifies the GDS as a new platform for gas, environmental, and biocompatible sensors

    Stereospecific Formation of the (<i>R</i>)-γ-Hydroxytrimethylene Interstrand <i>N</i><sup>2</sup>-dG:<i>N</i><sup>2</sup>-dG Cross-Link Arising from the γ-OH-1,<i>N</i><sup>2</sup>-Propano-2′-deoxyguanosine Adduct in the 5′-CpG-3′ DNA Sequence

    No full text
    Acrolein reacts with dG to form hydroxylated 1,<i>N</i><sup>2</sup>-propanodeoxyguanosine (OH-PdG) adducts. Most abundant are the epimeric 3-(2-deoxy-β-d-<i>erythro</i>-pentofuranosyl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2<i>a</i>] purin-10(3<i>H</i>)-ones, commonly referred to as the γ-OH-PdG adducts. When placed complementary to deoxycytosine in duplex DNA, these undergo rearrangement to the <i>N</i><sup>2</sup>-(3-oxopropyl)-dG aldehyde. The latter forms diastereomeric interstrand <i>N</i><sup>2</sup>-dG:<i>N</i><sup>2</sup>-dG cross-links in the 5′-CpG-3′ sequence. Here we report the structure of the stereochemically favored (<i>R</i>)-γ-hydroxytrimethylene <i>N</i><sup>2</sup>-dG:<i>N</i><sup>2</sup>-dG interstrand DNA cross-link in 5′-d(G<sup>1</sup>C<sup>2</sup>T<sup>3</sup>A<sup>4</sup>G<sup>5</sup>C<sup>6</sup>X<sup>7</sup>A<sup>8</sup>G<sup>9</sup>T<sup>10</sup>C<sup>11</sup>C<sup>12</sup>)-3′·5′-d(G<sup>13</sup>G<sup>14</sup>A<sup>15</sup>C<sup>16</sup>T<sup>17</sup>C<sup>18</sup>Y<sup>19</sup>C<sup>20</sup>T<sup>21</sup>A<sup>22</sup>G<sup>23</sup>C<sup>24</sup>)-3′ (X<sup>7</sup> is the dG linked to the α-carbon of the carbinolamine linkage, and Y<sup>19</sup> is the dG linked to the γ-carbon of the carbinolamine linkage; the cross-link is in the 5′-CpG-3′ sequence). The structure was characterized using isotope-edited <sup>15</sup>N nuclear Overhauser enhancement spectroscopy heteronuclear single quantum correlation (NOESY-HSQC) NMR, in which the exocyclic amines at X<sup>7</sup> or Y<sup>19</sup> were <sup>15</sup>N-labeled. Analyses of NOE intensities involving Y<sup>19</sup> <i>N</i><sup>2</sup>H indicated that the (<i>R</i>)-γ-hydroxytrimethylene linkage was the major cross-link species, constituting 80−90% of the cross-link. The X<sup>7</sup> and Y<sup>19</sup> imino resonances were observed at 65 °C. Additionally, for the 5′-neighbor base pair G<sup>5</sup>·C<sup>20</sup>, the G<sup>5</sup> imino resonance remained sharp at 55 °C but broadened at 65 °C. In contrast, for the 3′-neighbor A<sup>8</sup>·T<sup>17</sup> base pair, the T<sup>17</sup> imino resonance was severely broadened at 55 °C. Structural refinement using NOE distance restraints obtained from isotope-edited <sup>15</sup>N NOESY-HSQC data indicated that the (<i>R</i>)-γ-hydroxytrimethylene linkage maintained the C<sup>6</sup>·Y<sup>19</sup> and X<sup>7</sup>·C<sup>18</sup> base pairs with minimal structural perturbations. The (<i>R</i>)-γ-hydroxytrimethylene linkage was located in the minor groove. The X<sup>7</sup> <i>N</i><sup>2</sup> and Y<sup>19</sup> <i>N</i><sup>2</sup> atoms were in the gauche conformation with respect to the linkage, which maintained Watson−Crick hydrogen bonding of the cross-linked base pairs. The anti conformation of the hydroxyl group with respect to C<sup>α</sup> of the tether minimized steric interaction and, more importantly, allowed the formation of a hydrogen bond between the hydroxyl group and C<sup>20</sup> <i>O</i><sup>2</sup> located in the 5′-neighboring base pair G<sup>5</sup>·C<sup>20</sup>. The formation of this hydrogen bond may, in part, explain the thermal stability of this carbinolamine interstrand cross-link and the stereochemical preference for the (<i>R</i>) configuration of the cross-link
    corecore