3 research outputs found
Investigation of the Interfaces in Schottky Diodes Using Equivalent Circuit Models
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
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
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