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^–α, with α in the range of ∼1–3), and a Lorentzian current noise power spectrum with a well-defined 1/<i>f</i>² 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>_c ≥ 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 {Co₉(P₂W₁₅)₃} 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^II₉(H₂O)₆(OH)₃(<i>p</i>-RC₆H₄As^VO₃)₂­(α-P^V₂W^VI₁₅O₅₆)₃]^25– ({Co₉(P₂W₁₅)₃}, R = H or NH₂), isolated as Na₂₅[Co₉(OH)₃(H₂O)₆­(C₆H₅AsO₃)₂­(P₂W₁₅O₅₆)₃]·86H₂O (<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) ų, <i>Z</i> = 2) and Na₂₅[Co₉(OH)₃­(H₂O)₆­(H₂NC₆H₄AsO₃)₂­(P₂W₁₅O₅₆)₃]·86H₂O (<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) ų, <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 {Co₉(P₂W₁₅)₃} frontier molecular orbitals in the surface-bound state were found to directly correlate with cyclic voltammetry data in aqueous solution