4 research outputs found
Molecule/Electrode Interface Energetics in Molecular Junction: A “Transition Voltage Spectroscopy” Study
We assess the performances of the transition voltage
spectroscopy
(TVS) method to determine the energies of the molecular orbitals involved
in the electronic transport through molecular junctions. A large number
of various molecular junctions made with alkyl chains but with different
chemical structure of the electrode/molecule interfaces are studied.
In the case of molecular junctions with “clean, unoxidized”
electrode/molecule interfaces, that is, alkylthiols and alkenes directly
grafted on Au and hydrogenated Si, respectively, we measure transition
voltages in the range 0.9–1.4 V. We conclude that the TVS method
allows estimating the onset of the tail of the LUMO density of states,
at energy located 1.0–1.2 eV above the electrode Fermi energy.
For “oxidized” interfaces (e.g., the same monolayer
measured with Hg or eGaIn drops, or monolayers formed on a slightly
oxidized silicon substrate), lower transition voltages (0.1–0.6
V) are systematically measured. These values are explained by the
presence of oxide-related density of states at energies lower than
the HOMO/LUMO of the molecules. As such, the TVS method is a useful
technique to assess the quality of the molecule/electrode interfaces
in molecular junctions
Charge Blinking Statistics of Semiconductor Nanocrystals Revealed by Carbon Nanotube Single Charge Sensors
We demonstrate the
relation between the optical blinking of colloidal semiconductor nanocrystals
(NCs) and their electrical charge blinking for which we provide the
first experimental observation of power-law statistics. To show this,
we harness the performance of CdSe/ZnS NCs coupled with carbon nanotube
field-effect transistors (CNTFETs), which act as single charge-sensitive
electrometers with submillisecond time resolution, at room temperature.
A random telegraph signal (RTS) associated with the NC single-trap
charging is observed and exhibits power-law temporal statistics (τ<sup>–α</sup>, with α in the range of ∼1–3),
and a Lorentzian current noise power spectrum with a well-defined
1/<i>f</i><sup>2</sup> corner. The spectroscopic analysis
of the NC–CNTFET devices is consistent with the charging of
NC defect states with a charging energy of <i>E</i><sub>c</sub> ≥ 200 meV. These results pave the way for a deeper
understanding of the physics and technology of nanocrystal-based optoelectronic
devices
Langmuir–Blodgett Films of Amphiphilic Thieno[3,4‑<i>c</i>]pyrrole-4,6-dione-Based Alternating Copolymers
The synthesis of four amphiphilic
thieno[3,4-<i>c</i>]pyrrole-4,6-dione (TPD)-based alternating
copolymers and their behavior at the air–water interface are
reported. Homogeneous and stable monolayers of TPD-based copolymers
were prepared. Brewster angle microscopy (BAM) was utilized to characterize
the morphology and topography of these Langmuir films. UV–vis
absorption spectroscopy as well as atomic force microscopy has revealed
a regular transfer of some copolymers on glass substrates. It was
possible to obtain homogeneous Langmuir–Blodgett films of up
to 30 layers. Infrared dichroic measurements revealed an edge-on orientation.
These Langmuir–Blodgett films made of conjugated polymers are
therefore good candidates for organic field-effect transistors (OFETs)
Probing Frontier Orbital Energies of {Co<sub>9</sub>(P<sub>2</sub>W<sub>15</sub>)<sub>3</sub>} Polyoxometalate Clusters at Molecule–Metal and Molecule–Water Interfaces
Functionalization
of polyoxotungstates with organoarsonate coligands
enabling surface decoration was explored for the triangular cluster
architectures of the composition [Co<sup>II</sup><sub>9</sub>(H<sub>2</sub>O)<sub>6</sub>(OH)<sub>3</sub>(<i>p</i>-RC<sub>6</sub>H<sub>4</sub>As<sup>V</sup>O<sub>3</sub>)<sub>2</sub>(α-P<sup>V</sup><sub>2</sub>W<sup>VI</sup><sub>15</sub>O<sub>56</sub>)<sub>3</sub>]<sup>25–</sup> ({Co<sub>9</sub>(P<sub>2</sub>W<sub>15</sub>)<sub>3</sub>}, R = H or NH<sub>2</sub>), isolated as Na<sub>25</sub>[Co<sub>9</sub>(OH)<sub>3</sub>(H<sub>2</sub>O)<sub>6</sub>(C<sub>6</sub>H<sub>5</sub>AsO<sub>3</sub>)<sub>2</sub>(P<sub>2</sub>W<sub>15</sub>O<sub>56</sub>)<sub>3</sub>]·86H<sub>2</sub>O (<b>Na-1</b>; triclinic, <i>P</i>1̅, <i>a</i> = 25.8088(3) Å, <i>b</i> = 25.8336(3) Å, <i>c</i> = 27.1598(3) Å, α = 78.1282(11)°, β
= 61.7276(14)°, γ = 60.6220(14)°, <i>V</i> = 13888.9(3) Å<sup>3</sup>, <i>Z</i> = 2) and Na<sub>25</sub>[Co<sub>9</sub>(OH)<sub>3</sub>(H<sub>2</sub>O)<sub>6</sub>(H<sub>2</sub>NC<sub>6</sub>H<sub>4</sub>AsO<sub>3</sub>)<sub>2</sub>(P<sub>2</sub>W<sub>15</sub>O<sub>56</sub>)<sub>3</sub>]·86H<sub>2</sub>O (<b>Na-2</b>; triclinic, <i>P</i>1̅, <i>a</i> = 14.2262(2) Å, <i>b</i> = 24.8597(4) Å, <i>c</i> = 37.9388(4) Å,
α = 81.9672(10)°, β = 87.8161(10)°, γ
= 76.5409(12)°, <i>V</i> = 12920.6(3) Å<sup>3</sup>, <i>Z</i> = 2). The axially oriented <i>para</i>-aminophenyl groups in <b>2</b> facilitate the formation of
self-assembled monolayers on gold surfaces and thus provide a viable
molecular platform for charge transport studies of magnetically functionalized
polyoxometalates. The title systems were isolated and characterized
in the solid state, in aqueous solutions, and on metal surfaces. Using
conducting tip atomic force microscopy, the energies of {Co<sub>9</sub>(P<sub>2</sub>W<sub>15</sub>)<sub>3</sub>} frontier molecular orbitals
in the surface-bound state were found to directly correlate with cyclic
voltammetry data in aqueous solution