AN INVESTIGATION OF THE POROUS SILICON OPTICAL-ABSORPTION POWER-LAW NEAR THE BAND-EDGE

A theoretical investigation of the absorption coefficient of p-type doped porous silicon near the band edge is presented. We assume that the absorption coefficient is constructed by taking an average over a distribution (in terms of band gap) of absorption coefficients of individual crystallites. Exploiting physics fundamental to the crystallite optical absorption process, we derive the relation between the absorption coefficient and the averaged conduction density of states near the band edge for porous silicon. By postulating a specific form for the effective conduction density of states we find excellent agreement with recent optical absorption data for p-type doped porous silicon. We attempt to explain the basis for this postulate phenomenologically by suggesting a certain large-scale behaviour of the particle size distribution. The implication of further experimental verification will be discussed

Crystallite size distribution and dislocation structure determined by diffraction profile analysis: principles and practical application to cubic and hexagonal crystals

Two different methods of diffraction profile analysis are presented. In the first, the breadths and the first few Fourier coefficients of diffraction profiles are analysed by modified Williamson-Hall and Warren-Averbach procedures. A simple and pragmatic method is suggested to determine the crystallite size distribution in the presence of strain. In the second, the Fourier coefficients of the measured physical profiles are fitted by Fourier coefficients of well established ab initio functions of size and strain profiles. In both procedures, strain anisotropy is rationalized by the dislocation model of the mean square strain. The procedures are applied and tested on a nanocrystalline powder of silicon nitride and a severely plastically deformed bulk copper specimen. The X-ray crystallite size distributions are compared with size distributions obtained from transmission electron microscopy (TEM) micrographs. There is good agreement between X-ray and TEM data for nanocrystalline loose powders. In bulk materials, a deeper insight into the microstructure is needed to correlate the X-ray and TEM results

Free-energy barrier to melting of single-chain polymer crystallite

We report Monte Carlo simulations of the melting of a single-polymer crystallite. We find that, unlike most atomic and molecular crystals, such crystallites can be heated appreciably above their melting temperature before they transform to the disordered "coil" state. The surface of the superheated crystallite is found to be disordered. The thickness of the disordered layer increases with superheating. However, the order-disorder transition is not gradual but sudden. Free-energy calculations reveal the presence of a large free-energy barrier to melting.Comment: AMS-Latex, 4 pages with 5 figures, submitted to Phys. Rev. Let

Pengaruh elemen gamifikasi terhadap motivasi pelajar menggunakan aplikasi quizizz

Pelajar generasi abad ke 21 sekarang lebih berminat belajar menggunakan gadjet atau alat-alat komunikasi canggih tanpa wayar yang berasaskan teknologi. Sejajar dengan hasrat kerajaan dalam mempraktikkan Pendidikan Abad ke-21 (PAK 21) dalam melahirkan pelajar yang berkolaboratif dan berfikiran kritis, satu kajian telah dilaksanakan untuk mengkaji tahap motivasi intrinsik dan ekstrinsik pelajar terhadap kaedah pembelajaran gamifikasi menggunakan aplikasi Quizizz. Reka bentuk kajian yang digunakan dalam kajian ini adalah berbentuk tinjauan deskriptif dan infrensi dengan menggunakan pendekatan kuantitatif melalui instrumen soal selidik. Lokasi sampel kajian dilakukan di Kolej Kemahiran Tinggi Mara (KKTM) Sri Gading, Batu Pahat, Johor terhadap pelajar Diploma Kejuruteraan Bangunan yang mengambil kursus Kejuruteraan Matematik 3. Kajian rintis telah dijalankan kepada pelajar Diploma Kejuruteraan Awam UTHM seramai 30 orang. Manakala responden bagi kajian ini adalah sebanyak 63 orang pelajar KKTM. Data dianalisis menggunakan SPSS versi 22.0 bagi menentukan purata skor min dan analisis regresi berganda. Secara keseluruhannya, hasil analisis data menunjukkan bahawa tahap motivasi intrinsik adalah (min=3.52) dan tahap motivasi ekstrinsik adalah (min=3.53) selepas menggunakan kaedah gamifikasi. Kedua-dua nilai purata skor min tahap motivasi intrinsik dan ekstrinsik pelajar berada pada tahap sederhana. Manakala hasil daripada ujian infrensi menggunakan analisis regresi berganda menunjukkan 48.6% variasi tahap motivasi intrinsik dipengaruhi oleh elemen tahap dan kutipan mata. Seterusnya bagi tahap motivasi ekstrinsik, sejumlah 62.5% variasi tahap motivasi ekstrinsik dipengaruhi oleh elemen kutipan mata, tahap, ganjaran dan avatar. Oleh itu, kajian ini dapat membantu tenaga pengajar agar mudah mencipta dan menggunakan kaedah gamifikasi yang boleh meningkatkan motivasi intrinsik dan ekstrinsik pelajar dalam sesi pengajaran dan pembelajaran mereka selaras dengan visi PAK 21

Nanoscale Equilibrium Crystal Shapes

The finite size and interface effects on equilibrium crystal shape (ECS) have been investigated for the case of a surface free energy density including step stiffness and inverse-square step-step interactions. Explicitly including the curvature of a crystallite leads to an extra boundary condition in the solution of the crystal shape, yielding a family of crystal shapes, governed by a shape parameter c. The total crystallite free energy, including interface energy, is minimized for c=0, yielding in all cases the traditional PT shape (z x3/2). Solutions of the crystal shape for c≠0 are presented and discussed in the context of meta-stable states due to the energy barrier for nucleation. Explicit scaled relationships for the ECS and meta-stable states in terms of the measurable step parameters and the interfacial energy are presented.Comment: 35 page