Sains Malaysiana 45(2)(2016): 297-303

Kesan Pempasifan Permukaan Bahan Bukan Organik dan Organik terhadap Sifat Struktur dan Ciri Elektronik bagi Noktah Kuantum Silikon: Kajian ab-initio

(Inorganic and Organic Surface Passivation Effects on the Structural and Electronic

Properties of Silicon Quantum Dots: ab-initio Study)

M.M. Anas* & G. Gopir

Pusat Pengajian Fizik Gunaan, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia,

43600 Bangi, Selangor Darul Ehsan, Malaysia

Received: 2 April 2015/Accepted: 2 July 2015

ABSTRAK

Beberapa siri pengiraan ab-initio telah dijalankan bagi meneliti perubahan bentuk struktur dan ciri elektronik noktah kuantum silikon berdasarkan kesan pempasifan bahan bukan organik, hidroksil (OH) dan bahan organik, metil (CH3). Hasil pengoptimuman geometri menunjukkan bahawa noktah kuantum yang dipasifkan secara tepu dengan bahan organik dan bukan organik perlu menjalani proses penstrukturan semula keadaan permukaan bagi membolehkan pempasifan permukaan tepu dijalankan tanpa meninggalkan sebarang ikatan terjuntai. Kajian juga mendapati bahawa panjang ikatan meningkat pada ikatan silikon-hidroksil pada permukaan noktah kuantum. Manakala, herotan diperhatikan semasa proses pengenduran dinamik di bahagian teras noktah kuantum. Bagi pempasif metil pula, peningkatan ikatan silikon-metil pada permukaan meningkat lebih ketara, sementara pembentukan geometri tetrahedral pada bahagian teras dikekalkan. Hal ini menyumbang kepada kesan pengurungan elektron yang lebih jelas. Ringkasnya, kedua-dua jenis pempasif memberikan kesan perubahan penting pada ciri elektronik dalam tiga perspektif. Pertama, terdapat pengurangan nilai jurang tenaga apabila bahan pempasif yang digunakan mempunyai darjah kebebasan pergerakan yang sangat dinamik menyebabkan pengherotan pada bahagian teras. Kedua, walaupun kehadiran kedua-dua pempasif mempengaruhi nilai jurang tenaga, namun ia tetap menunjukkan sifat elektronik tenaga jurang-langsung. Ketiga, kewujudan jurang tenaga kecil juga diperhatikan agak ketara dalam jalur tenaga bagi noktah kuantum bersaiz kecil, dengan kesan kehadirannya boleh menyebabkan pengurangan hasil kuantum semasa proses eksiton berlaku.

Kata kunci: Kesan pempasifan; ketumpatan keadaan; noktah kuantum silikon; teori fungsian ketumpatan

ABSTRACT

A series of an ab-initio calculation has been done to study the change of structural and electronic properties of silicon quantum dot caused by inorganic compound, hydroxyl (OH) and organic compound, methyl (CH3) passiviants. Geometrical optimization shows that the fully saturated passivated structures were possible, after undergone surface reconstruction without any dangling bond left. We also found that there were a bond increment for the silicon-hydroxyl bond at structural surface. Meanwhile, distortion were also noticed during dynamical relaxation process at the quantum dots core region. For methyl passivation compound, there were significant increments of bond length for the silicon-methyl bond, while the symmetrical of tetrahedral geometry were preserved at core region. This will contribute to the clear confinement effect on methyl passivated quantum dots. Shortly, both passiviants effect on electronic properties of the silicon quantum dots can be simplified in three perspectives. First, there were significant reduction of the energy-gap when the passiviants used were highly dynamical movement that caused a distortion on the core structure. Second, both passiviants does influenced the energy-gap of quantum dots, however the direct gap behaviour of this nanocrystal still preserved. Third, the presence of mini-gaps energy gap were quite noticeable for small clusters, unfortunately it can reduce the quantum yield of exitonic process.

Keywords: Density functional theory; density of states; passivation effect; silicon quantum dots

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*Corresponding author; email: mus_physics@yahoo.com