مهندسی ویژگی‌های الکترونی نانوساختار فولرن باکی‌بال از راه آلایش شیمیایی: روش نظریه‌ تابعی چگالی

محاسبات نظریه ی تابعی چگالی نشان می دهد که شکاف هومو- لوموی فولرین باکی‌بال چون شکاف انرژی یک نیمه‌رسانا است. با توجه به اینکه باکی‌بال گزینه‌ای برای اداوات مولترونیکی به شمار می آید، در این پژوهش، تلاش شده تا اثربخشی عامل آلایش شیمیایی در ساختار باکی‌بال، روی کنترل رفتار الکترونی آن بررسی شود. بدین منظور یکی از اتم های کربن باکی بال برداشته و به جای آن یک تک اتم از گروه سه یا پنج اصلی جدول تناوبی مثل بور یا نیتروژن جایگزین می شود. با توجه به اینکه ظرفیت کربن چهار است، انتظار می رود که با ورود اتم هایی از گروه پنج، الکترونی در ساختار، اضافه باقی بماند که نقش الکترون آزاد در آن را داشته باشد. همچنین امکان تشکیل حفره در ساختار باکی‌بال را با ورود اتم از گروه سه بررسی شد. در ادامه نمودار بسامد این ساختارها، برای تشخیص پایداری آن ها رسم شد. در پایان مشخصات ساختار های موردنظر با کمک نظریه تابعی چگالی و به کارگیری تابعی هیبریدی b3lyp بدست آمد.

engineering the electronic properties of buckyball fullerene nanostructures through chemical doping: density functional theory approach

1. introductionfullerenes are nanocages composed of pentagonal and hexagonal structures. a fullerene contains twelve pentagons in its structure, but the number of hexagons can vary depending on the size of the structure's cage. the fullerene family's most famous structure is the buckminster fullerene, also known as the buckyball for short. buckminsterfullerene was first identified by robert floyd curl and his colleagues in 1985, by astronomical spectroscopy in space, and then prepared in the laboratory. this molecule is a carbon structure consisting of sixty carbon atoms, including twelve pentagons and twenty hexagons. it can also be considered a semiconducting molecule because an energy gap of 2 to 3 ev has been reported for it. but just as in electronics, the properties of intrinsic semiconductors are engineered after chemical doping under the titles of n- and p-type semiconductors, in this effort, the electronic properties of buckyballs will be engineered using chemical methods. 2. methodologythe calculations are based on density functional theory (dft). the geometries of the energetically optimal structures in the ground state were obtained using the b3lyp hybrid functional. we describe the orbitals of the atoms by the basis set 6-31 + g (d,p). the doped structures examined in this research are stable because calculations show that the frequencies of the vibrational modes do not show any negative frequencies. the gaussian software performs the calculations for the simulations. 3. results and discussionsilicon doping is arguably the most effective form of doping for buckyballs, as it leads to considerable alterations in electronic properties when compared to other doping methods. however, it does not diminish chemical hardness to the same extent as nitrogen does and possesses the highest ionization potential among the various doping options. consequently, this structure retains its electrons more effectively than other doped structures and exhibits the highest electron affinity among all the structures examined in this study. by drawing the density of state diagrams, it can be concluded that, except for silicon doping, the other dopings, in addition to changing the position of the electron levels, have pushed the state of the structure towards spintronic systems. because with the introduction of boron, aluminum, nitrogen, and phosphorus atoms, the number of electrons in the structure has become odd, and in this case, the high and low spin electrons form separate levels, and these structures can be considered candidates for the design of spintronic circuits. these structures can also be the components for the construction of fullerene-based multitronic devices because fullerene transistors are placed in a phase transition state for switching by electric and magnetic fields. nevertheless, the presence of each doped atom significantly reduces the switching energy because the chemical potential of the doped atoms acts as a site energy in the hamiltonian of the structure. 4. conclusionsince fullerene is an intrinsic semiconductor, its electronic properties can be controlled by chemical doping. in this article, the control of the electronic properties of fullerene was investigated using the same method. by placing a nitrogen atom or one of its family atoms, such as phosphorus with a valence of 5, instead of one of the buckyball carbon atoms with a valence of 4, an electron remains in the structure that plays the role of a free electron. also, if bromine or aluminum with a valence of 3 is used instead of nitrogen and phosphorus atoms, the carbon capacity is not completed, and a hole is created, which plays an important role in conduction.