نوع مقاله : مقاله کامل پژوهشی

نویسندگان

1 کارشناسی ارشد، پژوهشکده نیمه‌هادی‌ها، پژوهشگاه مواد و انرژی، مشکین دشت، البرز، ایران

2 دانشیار، پژوهشکده نیمه‌هادی‌ها، پژوهشگاه مواد و انرژی، مشکین دشت، البرز، ایران

چکیده

ویژگی‌های منحصربه‌فرد چارچوب‌های زئولیتی ایمیدازولی (ZIF) مانند قابلیّت تنظیم اندازه حفرات، تنوع ساختاری، پایداری شیمیایی، مکانیکی و حرارتی، این ساختار‌ها را به کاندید مناسبی برای کابردهای عملی تبدیل کرده است. از این رو در این کار ZIF-8 به‌عنوان یک ماده مزو-متخلخل بر پایه روی به وسیله طیف سنجی افت انرژی الکترون بازتابی (REELS) و با الگوریتم یوبرو- توگارد که بر پایه تئوری پاسخ دی الکتریک بنا شده است، مورد مطالعه قرار گرفته است. برون‌یابی اعمال شده بر روی یک طیف REELS، شکاف انرژی (Eg) مربوط به ZIF-8 مقدار eV2/4 را نشان داده است. همچنین تابع افت انرژی سطحی و توده‌ای تعیین گردیده و مقادیر مسافت آزاد میانگین ناکشسان (IMFP) الکترون‌هایی که‌ با انرژی‌های متفاوت به ZIF-8 منتقل شده‌اند مشخص گردیده و همچنین اختلاف آن‌ها با مقادیر به دست آمده از رابطه تانوما-پاول-پِن (TPP) مورد بررسی قرار گرفته است. افزون بر این، از ELF به دست آمده، با استفاده از تبدیلات کرامرز-کرونیگ قسمت حقیقی (1ε) و قسمت موهومی (2ε) تابع دی‌الکتریک (ε)، ضریب شکست (n)، ضریب میرایی (k)، ضریب بازتاب (R) و ضریب جذب (µ) به‌عنوان پارامترهای مهم اپتیکی این ماده تعیین شده اند.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Determination of Dielectric and Optical Properties of Zeolitic Imidazolate Framework-8 (ZIF-8) by Reflection Electron Energy Loss Spectroscopy (REELS)

نویسندگان [English]

  • Mehdi Pooriraj 1
  • Shaaker Hajati 2
  • Morteza Moradi 2

1 M. Sc., Department of Semiconductors, Materials and Energy Research Center (MERC), MeshkinDasht, Alborz, Iran

2 Associate Professor, Department of Semiconductors, Materials and Energy Research Center (MERC), MeshkinDasht, Alborz, Iran

چکیده [English]

Specific properties such as pore tunability, structural variety as well as chemical, mechanical, and thermal stability, make zeolitic imidazolate frameworks (ZIFs) suitable and of high importance for practical applications. Optical and chemical sensors and supercapacitors are among these applications which necessitate the detailed study of optical and dielectric properties of ZIFs. Therefore, ZIF-8 as a zinc-based mesoporous material was studied by reflection electron energy loss spectroscopy (REELS) applying the Yubero-Tougaard algorithm which is based on dielectric response theory. The band gap energy (Eg) of ZIF-8 was determined to be 4.2 eV using an extrapolation procedure applied to an experimental REELS spectrum. Its bulk and surface energy loss functions were also determined. Inelastic mean free path (IMFP) values of electrons of different energies transported in ZIF-8 were determined and their large differences with values calculated from the Tanuma-Powell-Penn (TPP) formula were discussed. In addition, the obtained ELF was used to apply the Kramers-Kronig transformation to obtain the real part (ε1) and imaginary part (ε2) of the dielectric function (ε), refractive index (n), extinction coefficient (k), reflection coefficient (R) and absorption coefficient (µ) of ZIF-8 as important optical properties of this widely applicable material.

کلیدواژه‌ها [English]

  • Optical properties
  • Dielectric properties
  • REELS
  • ZIF-8
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