FePc在铜币表面吸附构象的理论研究

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本文主要探讨了通过密度泛函理论(Density Functional Theory, DFT)计算方法对铁酞菁(FePc)分子在硬币金属表面，即铜(100)和铜(110)晶面的吸附性质进行了深入研究。FePc是一种具有环状结构的有机金属配合物，其分子中的苯并吡唑环对电子结构和吸附行为有显著影响。首先，研究集中在电子和结构特性上，以理解FePc与铜基底的相互作用强度。作者发现，当FePc分子吸附在铜(100)表面时，其苯并吡唑环呈现出非垂直于晶面的吸附几何构型，具体角度约为9°或3°，这表明存在一定程度的取向选择性。这种角度倾斜可能影响分子在表面的排列方式和稳定性。其次，研究还揭示了FePc分子平面的特殊弯曲现象，即分子平面相对于理想平面有一个约7°至10°的向上弯曲。这种弯曲导致了分子在表面上形成近似"扭曲"的形态，这可能会影响其能级分布、电荷转移以及与铜表面的化学反应性。对于铜(110)表面，尽管没有给出具体的数值结果，但可以推测，由于铜晶面的不同，FePc的吸附模式和结构特征可能会有所变化。DFT模拟可以帮助分析这种差异，包括可能的吸附能量、键合类型以及电子态的改变。此外，该研究还可能涉及到表面科学领域的其他关键参数，如吸附热、吸附能垒以及可能的自组装行为。通过比较铜(100)和铜(110)表面的吸附结果，研究人员能够深入理解FePc在不同晶体方向上的吸附行为的异同，这对于设计和优化纳米材料的表面功能，比如用于电子器件或者光催化应用具有重要意义。这篇研究论文提供了关于FePc在硬币金属表面的精细结构和物理性质的详细见解，对于理解和控制这类有机金属分子在表面的吸附行为具有重要的理论基础和技术指导价值。

Chin. Phys. B Vol. 22, No. 6 (2013) 063101

Differences in the adsorption of FePc on coinage metal surfaces

∗

R.A. Rehman

a)b)†

, Cai Yi-Liang(蔡亦良)

, Zhang Han-Jie(张寒洁)

, Wu Ke(吴珂)

Dou Wei-Dong(窦卫东)

, Li Hai-Yang(李海洋)

, He Pi-Mo(何丕模)

, Bao Shi-Ning(鲍世宁)

Physics Department, Zhejiang University, Hangzhou 310027, China

Physics Department, Forman Christian College University, Lahore-Pakistan

(Received 18 November 2012; revised manuscript received 18 December 2012)

A study of the electronic and structural properties of iron phthalocyanine (FePc) molecules adsorbed on coinage metal

surfaces Cu (100) and Cu (110) has been conducted by means of density functional theory calculations. The strength of

the molecule–substrate interactions is interpreted in terms of the lateral adsorption geometry and the site speciﬁc electronic

structure of the molecule. In the case of FePc on a (100)-oriented copper surface, the benzopyrrole leg is found to be oriented

at an angle of 9

◦

or 3

◦

from the [01-1] substrate direction. Further, an upward bend in the molecular plane ranging from 7

◦

to 10

◦

is also observed; giving an almost buckled shape to the molecule. However, in the case of FePc on Cu (110), neither

a bend nor a sizable rotation is observed. From the knowledge of the principle structural and electronic properties, it is

concluded that FePc–Cu (100) interaction is relatively stronger than FePc–Cu (110) interaction, which is further evidenced

by the charge transfer, work function changes, changes in the shape of the adsorbed molecular orbitals, and the orbital

shifts. Furthermore, density of states analysis shows that the valence band level shift is surface- and site-dependent.

Keywords: iron phthalocyanine, copper, electronic and structural properties, density functional theory

PACS: 31.15.A, 31.15.ae, 71.15.Mb, 71.15.Ap DOI: 10.1088/1674-1056/22/6/063101

1. Introduction

Planar and nonplanar phthalocyanine molecules have re-

cently gained tremendous attention due to their widespread ap-

plications (e.g., molecular electronics,

[1]

photodynamic can-

cer therapy (PDT),

[2]

gas-sensing devices, and fuel cells

[3]

Further development of applications requires results from fun-

damental scientiﬁc research, raising an ever-increasing interest

among scientists. Owing to their outstanding electronic and

optical properties,

[4]

they have been recognized as promising

building blocks for nanotechnology.

[5]

Furthermore, individ-

ual molecular layers have been proposed as active components

in information storage systems.

[6]

However, one of the limita-

tions of current organic technologies is the difﬁculty of grow-

ing a ﬁrst monolayer of very high quality. Thus, precise con-

trol of the ﬁrst monolayer is a prerequisite for fabricating high-

quality organic thin ﬁlms that would ultimately play a crucial

role in the performance of metal phthalocyanine (MPc)-based

organic electronic devices. On the other hand, the ordering of

molecules at the organic–metal interface as well the adsorption

conﬁguration is important for charge transfer over the inter-

face. By and large, the adsorption and ordering of molecules

on solid surfaces is governed mainly by a complex balance

between the substrate–molecule interaction and weak interac-

tions among the adsorbed molecules.

[7]

A strong intermolec-

ular interaction leads to the formation of three-dimensional

clusters.

[8]

Whereas the dominant molecule–substrate interac-

tion favors speciﬁc adsorption sites and gives rise to a highly

ordered structures such as long chains.

[9]

Dou et al.

[10]

studied

zinc phthalocyanine-Ag (100) interface with X-ray diffraction

and photoemission spectroscopy techniques. They observed a

strong π–d interaction between the adsorbate and the substrate

in addition to the two molecular patterns which are oriented at

an angle of 78

◦

from each other.

The electronic structure of individual copper phthalocya-

nine (CuPc) molecules deposited on Cu (100) has been inves-

tigated by using scanning tunneling microscopy (STM).

[11]

In this work, the authors found that CuPc molecules ad-

sorb in the ﬂat-lying geometry with two different rotational

orientations. However, the degree of rotation has not been

measured/estimated.

[11]

It is well known that the adsorption

conﬁguration plays a signiﬁcant role in the performance of or-

ganic molecular devices.

[12,13]

Therefore, to gain a better un-

derstanding of the ordering and phase transformation, a va-

riety of other experiments have been carried out. For exam-

ple, P. Palmgren et al. studied iron phthalocyanine (FePc) on

Ag (110) surface in order to investigate self-assembly, the or-

dering of molecules at the interface, and the electronic and

structural properties of thin ﬁlms. Their study shows that the

ﬁrst monolayer relatively strongly binds to the substrate. Ad-

ditionally, they observed two molecular patterns which are ro-

tated ± 27

◦

relative to the substrate.

[14]

More recently, in the case of FePc–Ag (110) two simi-

∗

Project supported by the National Natural Science Foundation of China (Grant Nos. 10974172, 10774129, and 61106131) and the Fundamental Research Funds

for the Central Universities.

†

Corresponding author. E-mail: ateeq215@gmail.com

063101-1

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