一、電子顯微鏡的組成
電子(zi)顯(xian)微鏡由鏡筒、真(zhen)空(kong)裝置和電源柜三部分組成。
1、鏡筒
主(zhu)要有電子(zi)源(yuan)、電子(zi)透鏡、樣(yang)品(pin)架、熒光屏和探測器等部件,這些部件通常是(shi)自上而下地裝配(pei)成一個柱體。
電(dian)(dian)(dian)(dian)(dian)子(zi)透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing)用來聚(ju)焦(jiao)電(dian)(dian)(dian)(dian)(dian)子(zi),是電(dian)(dian)(dian)(dian)(dian)子(zi)顯(xian)(xian)微(wei)鏡(jing)(jing)(jing)(jing)(jing)(jing)鏡(jing)(jing)(jing)(jing)(jing)(jing)筒(tong)中最重要的(de)(de)部件。一(yi)(yi)般(ban)使用的(de)(de)是磁(ci)透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing),有時(shi)也有使用靜電(dian)(dian)(dian)(dian)(dian)透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing)的(de)(de)。它用一(yi)(yi)個(ge)(ge)對稱于(yu)(yu)鏡(jing)(jing)(jing)(jing)(jing)(jing)筒(tong)軸(zhou)線(xian)(xian)的(de)(de)空(kong)間電(dian)(dian)(dian)(dian)(dian)場或磁(ci)場使電(dian)(dian)(dian)(dian)(dian)子(zi)軌跡向軸(zhou)線(xian)(xian)彎曲形成聚(ju)焦(jiao),其(qi)作用與光學(xue)顯(xian)(xian)微(wei)鏡(jing)(jing)(jing)(jing)(jing)(jing)中的(de)(de)光學(xue)透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing)(凸透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing))使光束聚(ju)焦(jiao)的(de)(de)作用是一(yi)(yi)樣的(de)(de),所(suo)以稱為(wei)電(dian)(dian)(dian)(dian)(dian)子(zi)透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing)。光學(xue)透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing)的(de)(de)焦(jiao)點(dian)是固定(ding)的(de)(de),而電(dian)(dian)(dian)(dian)(dian)子(zi)透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing)的(de)(de)焦(jiao)點(dian)可以被調(diao)節,因(yin)此電(dian)(dian)(dian)(dian)(dian)子(zi)顯(xian)(xian)微(wei)鏡(jing)(jing)(jing)(jing)(jing)(jing)不像(xiang)光學(xue)顯(xian)(xian)微(wei)鏡(jing)(jing)(jing)(jing)(jing)(jing)那樣有可以移動的(de)(de)透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing)系統。現代電(dian)(dian)(dian)(dian)(dian)子(zi)顯(xian)(xian)微(wei)鏡(jing)(jing)(jing)(jing)(jing)(jing)大(da)多采用電(dian)(dian)(dian)(dian)(dian)磁(ci)透(tou)(tou)(tou)鏡(jing)(jing)(jing)(jing)(jing)(jing),由(you)很穩(wen)定(ding)的(de)(de)直流勵磁(ci)電(dian)(dian)(dian)(dian)(dian)流通(tong)過帶極(ji)(ji)靴的(de)(de)線(xian)(xian)圈產(chan)生的(de)(de)強磁(ci)場使電(dian)(dian)(dian)(dian)(dian)子(zi)聚(ju)焦(jiao)。電(dian)(dian)(dian)(dian)(dian)子(zi)源是一(yi)(yi)個(ge)(ge)釋放(fang)自由(you)電(dian)(dian)(dian)(dian)(dian)子(zi)的(de)(de)陰極(ji)(ji),柵極(ji)(ji),一(yi)(yi)個(ge)(ge)環狀(zhuang)加(jia)速電(dian)(dian)(dian)(dian)(dian)子(zi)的(de)(de)陽極(ji)(ji)構成的(de)(de)。陰極(ji)(ji)和陽極(ji)(ji)之間的(de)(de)電(dian)(dian)(dian)(dian)(dian)壓差必(bi)須(xu)非常高(gao),一(yi)(yi)般(ban)在(zai)數千伏到3百萬伏特之間。它能發射并形成速度(du)均勻(yun)的(de)(de)電(dian)(dian)(dian)(dian)(dian)子(zi)束,所(suo)以加(jia)速電(dian)(dian)(dian)(dian)(dian)壓的(de)(de)穩(wen)定(ding)度(du)要求不低于(yu)(yu)萬分之一(yi)(yi)。
樣(yang)(yang)品可以穩定地放在樣(yang)(yang)品架(jia)上,此外往(wang)(wang)往(wang)(wang)還有可以用來(lai)改變(bian)樣(yang)(yang)品(如移(yi)動(dong)、轉動(dong)、加熱、降(jiang)溫(wen)、拉長等)的裝(zhuang)置。
探(tan)測(ce)器用來(lai)收集電子(zi)的信號(hao)或次級信號(hao)。
2、真空裝置
用(yong)以保障(zhang)顯微鏡(jing)內的真(zhen)空狀態(tai),這樣電子在其路徑上(shang)不(bu)會被吸收(shou)或偏向,由機械真(zhen)空泵、擴散(san)泵和真(zhen)空閥門等構成,并通過抽氣管道與鏡(jing)筒相聯接。
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、固定:為了盡量保存樣本的(de)原(yuan)樣使(shi)用(yong)戊二醛來硬化樣本和使(shi)用(yong)鋨酸(suan)來染色脂(zhi)肪。
2、冷固定:將樣(yang)(yang)(yang)本放(fang)在(zai)液態(tai)的(de)(de)乙(yi)烷(wan)中速凍,這樣(yang)(yang)(yang)水不會(hui)結晶,而形(xing)成(cheng)非(fei)晶體的(de)(de)冰。這樣(yang)(yang)(yang)保存的(de)(de)樣(yang)(yang)(yang)品損壞(huai)比較小,但圖像的(de)(de)對比度非(fei)常低。
3、脫干:使用乙(yi)醇和丙(bing)酮來取代水。
4、墊(dian)入:樣本被墊(dian)入后可以分割。
5、分(fen)割:將樣本使(shi)用金剛石刃切成薄(bo)片(pian)。
6、染色(se):重(zhong)的(de)原(yuan)子如鉛或鈾比輕(qing)的(de)原(yuan)子散射電(dian)子的(de)能力(li)高,因此(ci)可被用來提高對比度。