Synthesis and Characterization of Low Dimensional Materials

Abstract

In chapter 1, the controlled thermal evaporation growth allows the achievement of uniform composition with structural perfection of wide band-gap rutile metal oxide (SnO₂) semiconductor nanowires. The morphology of the tin dioxide (SnO₂) was examined by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). The structure of the SnO₂ nanowires was determined by HR-TEM, Raman spectroscopy and PXRD analysis. These result verified that the SnO₂ nanowires have a tetragonal rutile crystal structure (a = 4.74 A and c = 3.19 A ). The optical band gap of SnO₂ nanowires was 3.78eV determined by UV-visible diffuse reflectance spectra. Gold, palladium, and platinum nanoparticles are decorated on surface of tin oxide nanowires via reduction process of metal ion precursors. The morphology of these metal nanoparticles decorated on SnO₂ nanowire was examined by HR-TEM and SEM. The nanoparticles were uniform and evenly distributed on the surface of SnO₂ nanowires. The diameters of nanoparticles are 3-5nm (Au) and 7-10nm (Pd and Pt). EDS spectra reveal that the synthesized nanowires are composed of Sn, O and metal (Au, Pd and Pt). X-ray photoelectron spectroscopic (XPS) studies were performed to investigate the oxidation state of the metal (Au, Pd, Pt) nanoparticles. XPS results indicate that all nanoparticles have the zero oxidation state and it suggest that reduction process of metal ion is successfully completed. Band gaps acquired from UV-visible diffuse reflectance spectra were reduced relative to pure SnO₂ nanowires. Band gap energies were 2.87eV, 2.88eV, 2.88eV for gold, palladium, platinum nanoparticle decorated SnO2 nanowire. In chapter 2, we developed new synthetic routes to obtain 1-D quaternary thiophosphate compounds and 0-D molecular complex containing Nb2S4 core from a 2-D ternary thiophosphate Nb4P2S21. When Nb4P2S21 was reacted with alkali metal halides (ACl; A= Na, K, Rb, Cs) or TlCl at 500~700℃, the -S-S-S- bridges in 2-D Nb2PS10-S-S10PNb2 are excised to form 1-D chain and cations are inserted between the chains to form ANb2PS10 (A= Na, K, Rb, Cs, Tl). We also found that the thallium chloride (TlCl) is an excellent reagent for further excision and substitution of sulfur ligands of 2-dimensional Nb₄P₂S_(21) to form a molecular complex Tl_(5)[Nb₂S₄Cl_(8)]Cl.;본 연구의 제 1장은 1차원의 SnO₂ 나노와이어와 그 표면 개질에 관한 연구이다. Thermal evaporation 방법을 이용하여 일정한 구조와 형태를 가지는 wide band gap 반도체인 SnO₂ 나노와이어를 합성하였다. 이렇게 합성한 와이어는 SEM, HR-TEM을 이용하여 그 구조와 형태를 분석하였으여, PXRD와 Raman을 이용하여 구조 증명을 하였다. UV-vis defuse reflectance spectroscopy를 통하여 Band gap을 추정할 수 있었다. 또한 합성한 나노와이어를 이용하여 그 표면을 개질시키는 실험을 수행하였다. 용액상에서 금속 이온 전구체를 환원시키는 방법을 이용하여 Palladium, Gold, Platinum 나노 파티클을 합성한 SnO₂ 나노와이어의 표면에 붙이는 데에 성공하였다. 이렇게 붙여진 파티클은 일정한 크기와 형태를 가지고 있었으며, SEM과 HR-TEM을 이용하여 확인할 수 있었다. XPS를 이용하여 붙여진 나노 파티클의 산화수를 확인하였고 UV-vis defuse reflectance spectroscopy로 Band gap을 추정하였다. 제 2장은 2차원의 Nb₄P₂S_(21) 화합물로부터 metal ion이 들어간 0, 1차원의 화합물을 얻어내는 연구이다. 고체 반응을 통하여 Alakli metal halide를 dimensional reducing reagent로 이용하여 1차원의 quaternary thiophosphate 물질 ANb₂PS_(10)(A= Na, K, Rb, Cs)를 만들었다. 그리고 Thalium chloride(TlCl)를 더 낮은 온도에서 반응시켜 1차원의 quaternary thiophosphate TlNb2PS10 를 얻었다. TlCl는 또한 Nb₄P₂S_(21)의 sulfur bridge를 끊어주는 강력한 reagent로 작용하여 Nb₄P₂S_(21)를 0차원의 molecular complex Tl_(5)[Nb₂S₄Cl_(8)]Cl로 만들었다. 새롭게 만들어진 화합물은 단결정을 얻어 그 구조를 풀었다.