一、電子顯微鏡的組成
電子顯微(wei)鏡(jing)(jing)由鏡(jing)(jing)筒、真空裝置和電源柜三部分組成。
1、鏡筒
主要(yao)有電(dian)子(zi)源、電(dian)子(zi)透鏡(jing)、樣品架、熒光屏和探測器等(deng)部件,這些部件通常是自上而下地(di)裝配成(cheng)一個柱體。
電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)透鏡(jing)(jing)用(yong)(yong)(yong)來聚(ju)(ju)焦(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)子(zi),是(shi)電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)顯(xian)微(wei)鏡(jing)(jing)鏡(jing)(jing)筒(tong)中最重要的(de)(de)(de)部件(jian)。一(yi)(yi)(yi)(yi)般使(shi)用(yong)(yong)(yong)的(de)(de)(de)是(shi)磁(ci)透鏡(jing)(jing),有(you)時也(ye)有(you)使(shi)用(yong)(yong)(yong)靜電(dian)(dian)(dian)(dian)(dian)(dian)透鏡(jing)(jing)的(de)(de)(de)。它用(yong)(yong)(yong)一(yi)(yi)(yi)(yi)個(ge)對稱于鏡(jing)(jing)筒(tong)軸線的(de)(de)(de)空間電(dian)(dian)(dian)(dian)(dian)(dian)場或磁(ci)場使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)軌(gui)跡向軸線彎曲形成聚(ju)(ju)焦(jiao)(jiao),其作(zuo)用(yong)(yong)(yong)與光學(xue)(xue)顯(xian)微(wei)鏡(jing)(jing)中的(de)(de)(de)光學(xue)(xue)透鏡(jing)(jing)(凸透鏡(jing)(jing))使(shi)光束聚(ju)(ju)焦(jiao)(jiao)的(de)(de)(de)作(zuo)用(yong)(yong)(yong)是(shi)一(yi)(yi)(yi)(yi)樣(yang)的(de)(de)(de),所(suo)以(yi)稱為電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)透鏡(jing)(jing)。光學(xue)(xue)透鏡(jing)(jing)的(de)(de)(de)焦(jiao)(jiao)點(dian)是(shi)固定的(de)(de)(de),而電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)透鏡(jing)(jing)的(de)(de)(de)焦(jiao)(jiao)點(dian)可(ke)以(yi)被調節,因此電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)顯(xian)微(wei)鏡(jing)(jing)不像光學(xue)(xue)顯(xian)微(wei)鏡(jing)(jing)那樣(yang)有(you)可(ke)以(yi)移動的(de)(de)(de)透鏡(jing)(jing)系(xi)統。現(xian)代電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)顯(xian)微(wei)鏡(jing)(jing)大多采用(yong)(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)磁(ci)透鏡(jing)(jing),由很穩定的(de)(de)(de)直流勵磁(ci)電(dian)(dian)(dian)(dian)(dian)(dian)流通過帶(dai)極(ji)靴的(de)(de)(de)線圈(quan)產(chan)生(sheng)的(de)(de)(de)強磁(ci)場使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)聚(ju)(ju)焦(jiao)(jiao)。電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)源是(shi)一(yi)(yi)(yi)(yi)個(ge)釋放自由電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)的(de)(de)(de)陰(yin)極(ji),柵極(ji),一(yi)(yi)(yi)(yi)個(ge)環狀(zhuang)加速(su)(su)電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)的(de)(de)(de)陽(yang)極(ji)構成的(de)(de)(de)。陰(yin)極(ji)和(he)陽(yang)極(ji)之(zhi)間的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓差(cha)必須非常高,一(yi)(yi)(yi)(yi)般在(zai)數千伏到(dao)3百(bai)萬伏特之(zhi)間。它能發射(she)并形成速(su)(su)度均勻的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)束,所(suo)以(yi)加速(su)(su)電(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)(de)穩定度要求不低(di)于萬分之(zhi)一(yi)(yi)(yi)(yi)。
樣(yang)品(pin)可(ke)以穩定地(di)放在樣(yang)品(pin)架(jia)上,此外往往還有可(ke)以用來改(gai)變樣(yang)品(pin)(如移動、轉動、加(jia)熱、降溫、拉長等)的裝置。
探(tan)測器用來(lai)收(shou)集電(dian)子的信(xin)號或次級信(xin)號。
2、真空裝置
用以保障顯微鏡內的(de)真空狀(zhuang)態(tai),這樣(yang)電子在其路徑上(shang)不會被吸(xi)收或(huo)偏(pian)向,由機械真空泵(beng)、擴(kuo)散(san)泵(beng)和真空閥門等構(gou)成(cheng),并通過抽氣管道與(yu)鏡筒相(xiang)聯接。
3、電源柜
由高壓發生器、勵磁電流穩流器和各種調節控制單元組成。
二、電子顯微鏡如何進行樣本處理
1、固(gu)定:為了盡量保(bao)存樣本(ben)的原樣使(shi)用戊(wu)二醛來硬化樣本(ben)和使(shi)用鋨(e)酸(suan)來染色脂肪。
2、冷(leng)固定(ding):將樣本(ben)放(fang)在液態的乙烷(wan)中速凍,這(zhe)樣水不會(hui)結晶,而形成非晶體(ti)的冰。這(zhe)樣保存的樣品(pin)損壞比較小(xiao),但圖像(xiang)的對(dui)比度非常低。
3、脫干:使用乙醇和(he)丙(bing)酮來取代水。
4、墊(dian)(dian)入:樣本(ben)被墊(dian)(dian)入后可以分割。
5、分割:將樣本使用(yong)金(jin)剛(gang)石刃切成(cheng)薄片(pian)。
6、染色:重(zhong)的(de)原(yuan)子如鉛或(huo)鈾比輕(qing)的(de)原(yuan)子散射(she)電(dian)子的(de)能(neng)力高,因此可(ke)被用來提高對(dui)比度。