Unsubstituted and Fluorinated Cu-Phthalocyanine Overlayers on Si(111)

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C: Surfaces, Interfaces, Porous Materials, and Catalysis

Unsubstituted and Fluorinated Cu-Phthalocyanine Overlayers on Si(111)-(#7×#3)-in Surface: Adsorption Geometry, Charge Polarization, and Effects on Superconductivity Naoya Sumi, Yoichi Yamada, Masahiro Sasaki, Ryuichi Arafune, Noriaki Takagi, Shunsuke Yoshizawa, and Takashi Uchihashi J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b12424 • Publication Date (Web): 18 Mar 2019 Downloaded from http://pubs.acs.org on March 21, 2019

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The Journal of Physical Chemistry

Unsubstituted and Fluorinated Cu-phthalocyanine Overlayers on Si(111)(√7×√3)-In Surface: Adsorption Geometry, Charge Polarization, and Effects on Superconductivity Naoya Sumi,1 Yoichi Yamada,1,* Masahiro Sasaki,1, 2 Ryuichi Arafune,3 Noriaki Takagi,4 Shunsuke Yoshizawa5 and Takashi Uchihashi3,* 1University

of Tsukuba, Faculty of Pure and Applied Sciences, 1-1-1, Tennodai, Tsukuba,

Ibaraki, 305-8573, Japan 2Tsukuba

Research Center for Interdisciplinary Materials Science (TREMS), 1-1-1,

Tennodai, Tsukuba, Ibaraki, 305-8571, Japan 3International

Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for

Materials Science (NIMS) 1-1, Namiki, Tsukuba, Ibaraki 305-0044, Japan 4Graduate

School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501,

Japan 5Surface

Characterization Group, Research Center for Advanced Measurement and

Characterization, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan * [email protected], [email protected]

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ABSTRACT: Surface superconductors such as Si(111)-( 7 × 3)-In (referred to as ( 7 × 3)-In, hereafter) can be sensitively doped by surface dopants to tune their transition temperature (Tc) even via a weak interaction induced by molecular overlayers. Here, we examined the effect of Cu-phthalocyanine (CuPc) and Cu-hexadecafluorophthalocyanine (F16CuPc) overlayers on the electronic structure on ( 7 × 3)-In. While both molecules formed well-ordered monolayers, molecular adsorption geometries were found to be different; CuPc formed an ordered monolayer of face-on molecules, while F16CuPc tended to adsorb in a slightly tilted geometry. The normal-state electronic structures of ( 7 × 3)-In covered with these molecules were found to be similar. Photoelectron spectroscopy have suggested that the charge transfer to the molecules was negligible and that the interaction between the molecules and ( 7 × 3)-In were weak. Nevertheless, CuPc enhanced the superconducting transition temperature (Tc) of ( 7 × 3)-In by approximately 0.2 K, while F16CuPc suppressed it by approximately 1.0 K. The density functional theory (DFT) calculations combined with work function measurements showed that the surface electrons were accumulated in the region between the surface In atoms and the molecules, while molecules remain nearly uncharged. The increase in Tc in the case of CuPc overlayer is explained by a hole doping into ( 7 × 3)In due to the extraction of surface electrons. In contrast, the decrease in Tc for F16CuPc


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overlayer is attributable to the tilting adsorption geometry, possibly inducing an enhanced exchange interaction between spin magnetic moments of the molecular orbitals of inclined F16CuPc and the conduction electrons of ( 7 × 3)-In. The high sensitivity of Tc to the small difference in the adsorption geometry of weakly interacting molecules suggests the possibilities of modifying the superconducting properties of various surface materials.



INTRODUCTION

The surface superconductors have attracted significant attentions and their intrinsic possibilities to tune their electronic structure through the interaction with adsorbates on substrates, i.e., the surface doping, is one of the major topics in the field of surface science and superconductivity

1,2.

One of the remarkable examples of surface doping of the surface

superconductors is the realization of extremely high transition temperatures (Tc) up to 100 K for FeSe monolayer on a strontium titanate (STO) substrate3–7. Intercalation of dopant underneath a surface superconductor has also been shown to be effective8,9. It is therefore important to understand the detailed doping mechanisms of surface superconductors using a well-defined model system. Here, we utilized the double layers of In on a Si(111) substrate, i.e., Si(111)-( 7 × 3)-In (referred to as ( 7 × 3)-In, hereafter). The ( 7 × 3)-In layer hosts nearly free, twodimensional surface electronic states which undergo a superconducting transition at approximately 3.0 K10–13. Its surface atomic structure has been well defined and homogeneous14–17. Recently, Yoshizawa et al. have shown that the transition temperature of ( 7 × 3)-In can be modified by adsorbing two kinds of metal-phthalocyanine (Pc) monolayers18. The Tc was found to be enhanced by 0.2 K when CuPc was deposited as a dopant, 4 ACS Paragon Plus Environment

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while the Tc was suppressed when MnPc were used. The mechanism of the transition temperature tuning was discussed from the viewpoint of the two effects: a positive effect of an electron transfer from the substrate to the molecules and a negative effect of the exchange interaction between the spin magnetic moments originating from the centered transition metals. In the present work, in order to gain a better understanding of the doping effects of the Pc molecules, we studied in detail the structures and electronic states of the CuPc- and F16CuPccovered ( 7 × 3)-In. F16CuPc was chosen here because it is more electronegative than CuPc and is expected to work as a stronger hole dopant. F16CuPc has a larger electron affinity than CuPc, which is shifted by approximately 1 eV in the gas phase, while their spin states remain same19. Our DFT calculations combined with work function measurements revealed that both molecules attracted surface electrons into the interface region between the molecules and the surface In atoms, causing a polarization of surface conduction electrons. In contrast, the molecules themselves remained effectively uncharged. This resulted in a significant change in Tc of these molecule-covered systems; F16CuPc suppressed the Tc of ( 7 × 3)-In by approximately 1.0 K, while CuPc enhanced it by 0.2 K. Since the amounts of the hole doping and the electronic structures of CuPc- and F16CuPc-covered ( 7 × 3)-In were similar, the difference in Tc is attributed to slightly different adsorption geometries of the two molecules;



indeed, F16CuPc was found to be in a slightly inclined adsorption geometry while CuPc in the face-on geometry. The difference in the adsorption geometry modifies the strength of the exchange interaction between the spin magnetic moments of the molecular orbitals and the conduction electrons in the ( 7 × 3)-In surface, which tend to decrease Tc. These results revealed that the Tc of a surface superconductor is sensitive to even a weak interaction with nearly physisorbed molecules.

EXPERIMENTAL All of the experiments were performed under ultra-high vacuum (UHV) conditions. Nondoped Si(111) was flashed to 1200 ℃ several times by the direct current heating in order to obtain the clean 7×7 reconstructions. Indium was deposited using a home-made K-cell, where the amount of evaporation was monitored using a quartz crystal microbalance (QCM). Following the deposition of a small amount of In onto the clean Si(111)-7×7 substrate, the substrate was annealed around 400 ℃ for 10 s to prepare the ( 7 × 3)-In surface. The surface structure was checked using a scanning tunneling microscope (STM) system configured for stable molecular imaging at room temperature. After preparing the ( 7 × 3)-In surface, CuPc and F16CuPc were deposited in the same chamber. The molecule coverage θ was estimated by STM


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observation. Electronic states of CuPc and F16CuPc on ( 7 × 3)-In were examined using angle resolved photoelectron spectroscopy (ARUPS) performed at beamline BL13B of KEKPF facility using an excitation photon energy of 89.5 eV. The work function was determined from the high-binding energy cut-off of the secondary electrons. In situ surface electric transport experiments were conducted in a home-built UHV apparatus which was described elsewhere10,20. In the transport-measurement, four gold-coated spring probes were tightly pressed onto the surface and the sheet resistance was measured by means of the four probes method. The temperature of the specimen can be varied from room temperature to 1.5 K. The ab initio calculations were performed based on the density functional theory (DFT) using the plane wave-based Vienna ab initio simulation package (VASP)

21,22

with the

projected augmented wave (PAW) method23. We used the local-density approximation exchange-correlation functional 24. For the modeling of the ( 7 × 3)-In surface, a slab of the double In layer and eight Si(111) layers terminated with H at the backside was used. The adsorption site for CuPc and F16CuPc molecules was chosen to be the on-top site of In, which were found to be of the lowest energy for molecules. The in-plane mirror axis of the CuPc molecule was set at an angle of 15° with respect to the [112] direction based on the previous report. The positions of all atoms were optimized until the forces on individual atoms were less



than 0.02 eV/Å. Because of the large dimensions of the supercell, the Brillouin zone was sampled only at the Γ point. The Bader charge analysis was used to evaluate the amount of the electron transfer between the molecule and substrate 25–28.

RESULTS AND DISCUSSION

We prepared samples with a well-ordered ( 7 × 3)-In layer with wide terraces and a distinct atomic arrangement, as shown in Fig. 1a and the inset. We also confirmed a well-defined superconducting transition at 3.0 K through surface resistivity measurements as shown in Fig. 1b, fully consistent with the previous study10. Then, we supplied F16CuPc and CuPc on the ( 7 × 3)-In. First, we will argue the molecular arrangements of the F16CuPc in comparison with that of CuPc, where we found noticeable differences. Fig. 1c-f shows molecular-resolved STM image of the F16CuPc monolayer. From the overall images shown in Fig. 1c, it is seen that most part of the monolayer of F16CuPc is well ordered with a rectangle unit cell, as in the case of CuPc (Fig. 1g,h). The size of the rectangle unit cell of F16CuPc monolayer of 1.49 ± 0.02 nm ×1.52 ± 0.02 nm, which is slightly larger from that of CuPc, 1.33 ± 0.02 nm×1.38 ± 0.02 nm. Except for the well-ordered region with a characteristic rectangle unit cell, F16CuPc monolayer exhibited enhanced numbers of the domain boundaries, as shown in Fig. 1e. It is known that 8 ACS Paragon Plus Environment

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the CuPc lattice matches to the ( 7 × 3)-In substrate18. Therefore, in the case of the slightly enlarged lattice of F16CuPc monolayer, lattice matching against the substrate become imperfect. This fact results in the enhanced domain boundaries in the F16CuPc monolayer on ( 7 × 3)In. Furthermore, it is important to note that F16CuPc molecules tended to adsorb in slightly inclined geometry as seen in the close images (Fig. 1d and 1f), while CuPc took the face-on adsorption geometry (Fig. 1h). In the STM image of F16CuPc molecules both in the rectangle domain and in the domain boundaries, it is clearly seen that most of the molecules, especially those around the domain boundaries, do not take the flat adsorption geometry. We found that the difference in the apparent height within the molecule due to the molecular tilt was approximately 0.7 Å at maximum. Due to this tilted adsorption geometry, STM image of the F16CuPc layer became slightly fuzzy, compared to those of CuPc. In order to resolve the electronic structure of the F16CuPc- and the CuPc-covered ( 7 × 3)-In system, we compare their photoelectron spectra. Fig. 2 displays angle-integrated UPS spectra of the monolayer of F16CuPc and CuPc-covered ( 7 × 3)-In acquired at room temperature. The valence band of the ( 7 × 3)-In layer is shown in Fig. 2a as a black line. When the monolayers of F16CuPc and CuPc were formed (red and blue curves, respectively), the intensity of the valence bands of ( 7 × 3)-In was decreased and the molecular levels



(indicated by arrows) were superimposed. UPS spectra of F16CuPc and CuPc monolayer on ( 7 × 3)-In are found to be similar to the reported results of the UPS of the multilayer 29,30 and gas phase molecules

31

respectively, indicating the weak interaction between molecule and

substrate. The dashed and dotted lines under the UPS spectra indicate the simulated UPS spectrum for the isolated and adsorbed molecules, respectively, deduced from the DFT calculations (details of the calculated models for the adsorbed system are described later). Note that the calculated orbital energies were shifted so that the HOMO coincides the experimental spectra, and the amount of energy shift was set to the same value of 0.4 eV for both molecules. Firstly, it is found that the calculated spectra of the free and adsorbed molecules found to be quite similar, suggesting that the interaction between molecule and substrate is indeed weak. Then, it is also seen that the calculated spectra are in fair agreement with the experimental UPS spectra. Altogether, these facts suggest that the the interaction between these molecules and ( 7 × 3)-In substrate is substantially weak. The left and right panels of Fig. 2b show the detailed changes of the UPS spectra near the HOMO levels of F16CuPc and CuPc, respectively. It is seen that the HOMO state of both molecules situated at the relatively similar binding energy of approximately 1.7 eV, i.e., the energy level alignment of HOMO of these molecules with respect to the Fermi level of ( 7 ×


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3)-In is similar. This is also consistent with the DFT results. This result implies that the LUMO of these molecules were also aligned at nearly the same position above the Fermi level of ( 7 × 3)-In, because the sizes of HOMO-LUMO gap of these molecules are close 19,32,33. It is also notable that, there is no additional features between HOMOs of F16CuPc/CuPc and the Fermi levels of the systems, and the intensity just at the Fermi edge decreases with increasing the molecular coverage. Therefore, there was no clear indication of the formation of the in-gap states due to electron transfer to these molecules from the substrate. The UPS results of F16CuPc/CuPc monolayer on ( 7 × 3)-In, i.e., no significant modification of the molecular orbital energies and the absent of the in-gap state, indicate that these molecules were essentially physisorbed on ( 7 × 3)-In and that the electron transfer to the molecule was negligibly small. It is also noted that the effect of the lattice mismatch in the case of F16CuPc monolayer, such as broadening of the molecular orbitals, were not evident in the UPS spectra, because of the weak interaction between molecule and substrate. Although the molecule-substrate interaction is the region of the physisorption, the work function measurements showed that the occurrence of the polarization of the conduction electrons in the In layer. Fig. 2c shows the work functions of the two systems, determined from the cut-off energy of the secondary electrons in the UPS spectrum. It is seen that the work



function was increased with F16CuPc doping, while it stayed nearly unchanged with CuPc doping. This change in the work function is not common for the organic semiconductor-metal interfaces. Adsorption of relatively large molecules such as CuPc on the surface usually reduces the work function of the surface due to so-called "push-back effect", in which the spilled electrons at the surface are forced back toward the bulk, reducing the surface electric dipole strength and hence the work function. Therefore, unchanged work function in the case of CuPc monolayer suggests that there must be a polarization of electrons at the interface towards vacuum region, which compensates the push-back effect. The same scenario should also be applied to F16CuPc, and in this case, the charge polarization should have overcome the push-back effect, judging from the observed increase in work function. Our DFT calculations support the above scenario of the polarization of the substrate electrons. Here, for the simplicity, we consider the isolated and flat CuPc and F16CuPc molecules on the In double layer, calculated using much larger unit cell of 30.3×19.8 Å2 for the x-y plane. The relaxed adsorption structures of CuPc and F16CuPc on the substrate are shown in Fig. 3a,b respectively, where the Cu atoms of both F16CuPc and CuPc reside on the ontop site of the In atoms. The molecules are essentially adsorbed in the face-on geometry. The distance of the molecular planes of CuPc and F16CuPc measured from the first layer of In atoms


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were 3.08 Å and 3.15 Å, respectively, showing that the adsorption height of F16CuPc was slightly larger than that of CuPc. The differential charge density due to the adsorbed molecules, defined as the difference in the charge density of the molecule-adsorbed surface and that of the pristine surface and the molecule, are shown in Fig.3d,e. It is seen that, in both cases, significant accumulations of charges are visible in the region between the surface In atoms and the molecule. It is seen that the induced charges are localized below the central Cu atom for CuPc molecule, while they are more spread out below F16CuPc. Meanwhile, rearrangement of the valence charges in the molecules was found to be subtle for both molecules. The amounts of electron-transfer from the substrate into the interface region evaluated from the Bader analysis are 1.4 e for CuPc and 1.8 e for F16CuPc, respectively. The amount of the electron transfer is indeed larger for F16CuPc, despite of large adsorption height, possibly due to a larger electronegativity. The observed extraction of electrons into the interface region forms the downward surface electric dipole. This electric dipole increases the work function and compensate the push back effect, explaining the results of the work function change. On the other hand, the subtle modification of the electrons in the molecule suggests that electron transfer into the molecules is indeed negligible, consistent with the absence of the gap state in the UPS spectra of the molecule-covered surface. Therefore, these molecules act as an



"electron extractor" for the substrate; i.e., hole doping into substrate occurs without charging the molecules itself. Here, we also analyzed the electronic properties of the inclined F16CuPc molecule. For this purpose, a detailed information on the adsorption geometry of F16CuPc is necessary. However, at the present stage of investigation, the molecular adsorption geometry of F16CuPc can hardly be obtained only from STM images. Therefore, in the present study, we made a tentative model of the tilted F16CuPc as follows. We started with the geometry of the CuPc monolayer on ( 7 × 3)-In, which has been well established, and we replaced CuPc by F16CuPc without changing the adsorption sites. By relaxing the molecular structure of F16CuPc while fixing the unit cell size, we obtained a significant tilting of the F16CuPc molecules, as shown in Fig. 3c. The height difference within the molecule in this geometry is approximately 0.51 Å and this value roughly agrees with the experimentally obtained apparent height difference within the molecule in Fig. 1c,d. Although the geometry should not be perfectly identical to the experimental situation, this would be useful approximation of the tilted adsorption geometry. We found that the electronic structure of F16CuPc is not very sensitive to the tilting. The calculated DOS for the tilted F16CuPc shown in Fig. 2a was indeed fairly similar to those of the free molecule, as discussed earlier, reflecting the weak interaction with substrate. The


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differential charges for this adsorption geometry are plotted in Fig. 3f, which also exhibited charge accumulation below the central Cu atom. It is noted that the electron accumulation can also be seen below the benzene ring which situate closer to the In atom as a result of tilting, different from the case of CuPc. The overall charge extraction from the In layer obtained from the Bader analysis amounted to 1.3 e. which is somewhat smaller than that for the flat F16CuPc discussed above, but is comparable to the case of CuPc. In order to discuss the changes in the electronic structure of the substrate due to the electron extraction, we checked the s-p band of the In layer with and without molecular doping. Fig. 4a shows the band structure of a clean ( 7 × 3)-In. The position of the Fermi surface of the clean ( 7 × 3)-In was located at approximately 1.41 A-1 from the  point, in agreement with the previous reports18,34. Fig. 4b,c show the detailed dispersion of the substrate s-p band along [110] direction near the Fermi level, for F16CuPc and CuPc covered ( 7 × 3)-In, respectively. For both molecules-covered surfaces, the dispersion of the s-p band did not change significantly. However, in both cases, the Fermi wavevector shrank by 0.1~0.2 Å-1, which is consistent with a previous report 18. We note that these changes are not clear because they are comparable to the resolution of our experimental apparatus. The electron transfers to the interface region described above, 1.3 e for F16CuPc and 1.4 e for CuPc, correspond to



approximately 0.038 and 0.039 electrons per one In atom, respectively. These are rather small compared to the number of electrons in the valence band of In layer. We conclude that the effect of the molecular adsorption on the normal-state electronic system is rather small, although there exists a hole doping (charge extraction from the In layer) for both F16CuPc and CuPc. Finally, we measured the superconducting transition temperature of ( 7 × 3)-In as a function of the coverage of the molecules. As shown in Fig. 5a, in the case of F16CuPc, the Tc was found to decrease with increasing coverage of the molecules. At the monolayer coverage, Tc was suppressed down to 2.0 K. This result is in contrast to the effect of the CuPc doping, as shown in Fig 5b; we observed that Tc was enhanced up to 3.2 K at 0.8 ML. This result seems to contradict to the enhanced hole doping into the ( 7 × 3)-In layer due to F16CuPc. Note that resistivity of the normal state were seen to increase with the molecular coverage, in consistent with previous reports18. The precise origin of this behavior, however, have yet to be clarified. In order to consider the origin of the opposite effects of F16CuPc and CuPc on superconductivity, we recall that the face-on geometry of CuPc plays an important role in retaining a potential increase in Tc. DFT calculations clarified that CuPc hosts spin magnetic


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moments in the molecular orbitals originating from the centered Cu atom, which spreads within the molecular plane 18,21. This means that the interaction between the spin magnetic moments and the conduction electrons in the substrate is negligibly small. Consequently, superconductivity is not suppressed despite the presence of the spin magnetic moments. Thus, the modification of Tc due to the adsorption of CuPc can be solely discussed from the viewpoint of the charge polarization effects. However, the above arguments can no longer be hold for the inclined F16CuPc, although nearly same amount of hole doping was deduced by DFT calculations. Fig. 3g-i shows the plot of the spin density for the flat molecules and tilted F16CuPc. It is found for all the case, that the spin density is indeed confined in the molecular plane. For the tilted adsorption, where one benzene ring comes closer to the substrate (distance between F and In atoms is reduced to approximately 3.09Å at minimum, from that of the flat molecule of 3.39 Å), the spins on this benzene ring situate slightly closer to the In layer. This may induce the exchange interaction between the spin magnetic moments in the molecular orbitals and the substrate, which competes with the hole doping effect and eventually suppresses Tc. Nevertheless, from the plot of spin density, spins are mostly concentrated at the center of molecule and therefore, the induced exchange interaction may not be drastic. These observations suggest that surface superconductors are generally very sensitive to physisorbed



molecules even when they do not induce a significant modification of the electronic structure of the system.

CONCLUSION

In summary, the molecular arrangement and the electronic structure of the CuPc and F16CuPccovered ( 7 × 3)-In were examined. The electronic structures of these systems were found to be similar; for both cases, the charge transfer to the molecule was not observed, while the charge polarization at the molecular interface were found. Nevertheless, a noticeable difference between the two molecules was also observed; CuPc was adsorbed in the flat-lying geometry while F16CuPc in the tilted adsorption configuration. The surface doping of CuPc and F16CuPc on ( 7 × 3)-In layer resulted in the enhancement and suppression of the superconducting transition temperature by 0.2 and 1.0 K, respectively. The non-flat adsorption of F16CuPc was proposed as an origin for the suppression of the Tc despite of the presence of a similar hole doping effect degree. In this scenario, the enhanced exchange interaction between the spin magnetic moments in the molecular orbitals and the conduction electrons of ( 7 × 3)-In compensates the hole-doping effect and suppresses the Tc. The observed high sensitivity of Tc to the adsorption geometry of the nearly physisorbed molecules indicates the possibilities of 18 ACS Paragon Plus Environment

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tuning the superconducting properties of various organic-inorganic hybrid systems even via a weak interaction.

Acknowledgements This study was supported by JSPS KAKENHI Grant Numbers JP26286011, JP16K13678, JP16H03875, 25247053, 18H01875, and World Premier International Research Center (WPI) Initiative on Materials Nanoarchitechtonics. This work was performed under the approval of the Photon Factory Program Advisory Committee (Proposal No. 2016G539, 2017G030 and 2018S2-005).



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Fig. 1(a) 500 nm×500 nm- STM image of ( 7 × 3)-In with wide terraces. Scale bar = 100 nm. Inset is the 5.8 nm × 5.8 nm detailed scan showing atomic structure of ( 7 × 3)-In. Scale bar = 1 nm. (b) Superconducting transition of Si(111)-( 7 × 3)-In revealed by electron transport measurements with dc bias currents of 1μA. (c, d) 28 nm × 28 nm (Scale bar = 10 nm) and 7.0 nm × 7.0 nm (scale bar = 2 nm) molecular-resolved STM image of F16CuPc monolayer on ( 7 × 3)-In with rectangle lattice and detailed image, respectively. (e, f) 30 nm × 30 nm- (scale bar = 10 nm) and 10 nm ×10 nm (scale bar = 2 nm)-STM image of the 27 ACS Paragon Plus Environment


domain boundaries of F16CuPc monolayer, respectively. (g, h) STM images of CuPc monolayer on ( 7 × 3)-In, respectively. Scale bars are 10 and 2 nm.


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Fig. 2(a) Valence-band photoemission spectra measured for the clean ( 7 × 3)-In surface (black), F16CuPc/( 7 × 3)-In (red) and CuPc/( 7 × 3)-In-(blue). The dotted and broken lines show the simulated DOS of the adsorbed and isolated molecule, respectively. (b) Coverage-dependent photoelectron spectra near the HOMO level of F16CuPc/( 7 × 3)-In (left) and CuPc/( 7 × 3)-In (right). (c) Work function change upon F16CuPc (red) and CuPc (blue) deposition on ( 7 × 3)-In.



Fig. 3 (a, b, c) Relaxed structure of the flat CuPc, the flat F16CuPc and the tilted F16CuPc on ( 7 × 3)-In, respectively. (d, e, f) 3D view of the differential charges distribution of the flat CuPc, the flat F16CuPc

and the tilted F16CuPc on ( 7 × 3)-In, respectively. The yellow and

light-blue colors correspond to positive and negative charges, respectively. Isosurface value is 6.5 × 10-4 e/Bohr3 for all the cases. (g, h, i) 3D view of the spin density distribution of the flat CuPc, the flat F16CuPc and the tilted F16CuPc on ( 7 × 3)-In, respectively. The isosurface value was set to 5.3 × 10-5 e/ Bohr3. The red and blue colors correspond to majority and


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minority spins, respectively.

Fig. 4(a) ARUPS spectrum of clean ( 7 × 3)-In substrate measured in the [110] direction. (b) Upper panel：Magnified ARUPS scans of 0.2 ML F16CuPc-covered ( 7 × 3)-In along the [110] direction. Lower panel：Horizontal line scans of the ARPES spectrum of 0.2 ML F16CuPc-covered ( 7 × 3)-In around the Fermi level (blue line), in comparison with that of



the clean ( 7 × 3)-In

(red line). (c) Upper panel ：Magnified ARUPS scans of 0.2 ML

CuPc-covered ( 7 × 3)-In along the [110] direction. Lower panel：Horizontal line scans of the ARPES spectrum of 0.2 ML CuPc-covered ( 7 × 3)-In around the Fermi level (blue line), in comparison with that of the clean ( 7 × 3)-In

(red line).

Fig. 5 Temperature dependences of the 2D resistivity of the (√7 × √3)-In surface with overlayers of F16CuPc (a) and CuPc (b) for different molecule coverages (0 ≤ θ ≤ 1.0 ML).


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TOC


The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

ACS Paragon Plus Environment

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(a)

(b)

(c)

F16CuPc

k (Å-1)

CuPc

k (Å-1)

×3


Figure 4 Sumi et al.

×3

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41


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Unsubstituted and Fluorinated Cu-Phthalocyanine Overlayers on Si(111)

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