TCNQ Grown on Cu (001): Its Atomic and Electronic Structure Determination

Abstract

In this paper we have resolved by means of “in situ” X-ray diffraction studies the atomic structure of the TCNQ films from 0.4 to 17 ML thickness grown on Cu(001) substrate. The film grown at low temperature, is a well crystallized and well oriented single phase. The TCNQ film has a (020) orientation. The electronic properties of the film have been studied by means of XPS and UPS spectroscopies. The measured electronic density has been compared to the theoretical ab-inito calculations. In this paper we have studied the structural and electronic properties of relatively thick films of TCNQ on Cu(100). Our results demonstrate that the strong charge transfer between the metallic substrate and the first layer of TCNQ molecules have important consequences for the film electronic and structural properties of films even as thick as 17 ML. From the structural point of view, the films grow with a well-defined (020) orientation that matches the modified molecular structure of the first layer. This first monolayer structure was previously explained in literature in terms of adsorbate-induced reconstruction of the Cu surface. From the electronic point of view, charge transfer leads to band bending and determines that barrier for electron injection across the metal/organic interface.

High Hole-Mobility Molecular Layer Made from Strong Electron Acceptor Molecules with Metal Adatoms

“…At the TCNQ/Au(111) interface at 20 K, the HOMO-derived peak is observable behind the Au 5d band at the constant E b position with θ ( E b = 2.6 eV), and a quite weak signal from the deeper lying TCNQ-derived electronic state (HOMO–1) can be seen at E b = 4.0 eV at θ = 20–30°. The energy separation between HOMO and HOMO–1 by 1.4 eV corresponds well with the electronic structure of the TCNQ thick film . The nondispersive HOMO and HOMO–1 peaks indicate the localized molecular electronic states at the TCNQ/Au(111) interface, while the CT-induced peaks (CT 1 and CT 2 ) at the F 4 TCNQ/Au­(111) interface at 20 K show a large dispersion with θ, which is direct evidence for the delocalization of molecular electronic states.…”

“…The energy separation between HOMO and HOMO−1 by 1.4 eV corresponds well with the electronic structure of the TCNQ thick film. 30 The nondispersive HOMO and HOMO−1 peaks indicate the localized molecular electronic states at the TCNQ/Au(111) interface, while the CT-induced peaks (CT 1 and CT 2 ) at the F 4 TCNQ/Au(111) interface at 20 K show a large dispersion with θ, which is direct evidence for the delocalization of molecular electronic states. As shown in Figure 3c, the CTinduced peaks are getting visibly clearer at the higher θ (k ∥ ) region, which is the reflection of the orbital-specific spatial electron distribution in ARPES.…”

Interface-Enhanced Catalytic Selectivity on the C2 Products of CO2 Electroreduction

“…The Cu−TCNQ precursor exhibits XPS peaks at 932.7 and 934.4 eV, which are also assigned to Cu 0 and Cu(I), respectively. 42,43 For the Cu@ N x C catalyst, however, only metallic Cu was detected, indicating that the N x C layer on the surface of Cu NPs protects well the Cu core from oxidation. This information is consistent with the EELS analysis (vide ante) and the XRD profiles (Figures 3b and S23), where only the metallic Cu phase is observed for Cu@N x C, while the Cu 2 O phase and Cu(I) signals can be seen in Cu NPs and the Cu−TCNQ precursor, respectively.…”

Organometallic MTCNQ films: a comparative study of CuTCNQ versus AgTCNQ

“…The cool TCNQ film had a monoclinic lattice 29,30 with the TCNQ c-axis lying normal to the substrate surface direction. 17 When the TCNQ film was set at room temperature, the metal-substrate atoms diffuse along the whole film thickness, resulting in the formation of an organometallic MTCNQ film, with M = Cu or Ag depending on the used substrate (Cu(001) or Ag(001), respectively). The result was a very well-ordered and highly oriented film, comprised the stacked MTCNQ c-axis perpendicular to the substrate (001) surface in both cases (Cu and Ag).…”

“…16 In the case of growing CuTCNQ by a solid-phase reaction, it is crucial to control the growth mode, structure, and morphology of the former TCNQ film acting as a precursor for the cooper reaction and diffusion. We have shown in previous work 16,17 that the growth of TCNQ films on bare substrates can form very crystalline and oriented films by evaporating TCNQ molecules under UHV conditions at a low evaporation rate and low substrate temperature. The crystallinity of the TCNQ layers grown on Cu substrates is of great importance in order to grow well-ordered CuTCNQ films by a solid-phase reaction.…”