My own mini thermoelectric generator?

ok guys. Im an A2 physics pupil. i wanna build a little thermoelectric generator. For fun. I have did research and i think americium is best isotope to use. I need yur advice on this. I worked out from about a hundred grams i can harvest w of power. I will use thermocouples or make one to harvest energy. The idea is to increase my understnading. Not just to build it. I ant an output of about a w of power after losses. I will use an enclosure for the isotope that will absorb all radiation, generating heat. The idea is to generate enough power to power a tiny device, if i adjust voltage from config of thermocouples ect. Please give me tips on building it. Best materials for thermocouple? or should i buy one. Is k type best because of temperature range? the thermocouple will be insulted. The end exposed to cold air. Convection will carry away heat. If i get a voltage reading , it means im successful with it basically. I just wanna see it wrk. Where can i buy pure silicon. Isnt this costly? Does the width of n junction and p junction matter? does this effect current? what should i make hot and cold junction out of? i would type more but i have ocd and it ***** me up.