RESUMO
Radiation damage is one of the most severe problems in the electron microscopy of organic materials. Observations which were made in an electron microscope with a superconducting lens system have shown that the damage caused by the electron beam is considerably reduced by one to two orders of magnitude if the specimen is cooled to liquid helium temperature (4.2 K). This cryoprotection is even higher in favorable cases, particularly when embedded specimens are used. The cryoprotection decreases for specimens mounted on plastic carrier films due to the low thermal and electrical conductivity of these materials at low temperatures.
Assuntos
Temperatura Baixa , Microscopia Eletrônica , Aminoácidos/efeitos da radiação , Elétrons , Hélio , Hidrocarbonetos , Lentes , Microscopia Eletrônica de Varredura , Nucleotídeos/efeitos da radiação , Peptidoglicano , Manejo de Espécimes/métodosAssuntos
Temperatura Baixa , Microscopia Eletrônica/métodos , Aminoácidos/efeitos da radiação , Colódio/efeitos da radiação , Cristalização , Elétrons , Escherichia coli/efeitos da radiação , Ligação de Hidrogênio , Microscopia Eletrônica/instrumentação , Manejo de Espécimes , Vírus do Mosaico do Tabaco/efeitos da radiaçãoRESUMO
Radiation damage on a holey carbon foil was investigated in an electron microscope with a superconducting lens system, where the temperature of the specimen and its environment initially was 4 K. Due to an electron dose of 2 X 10(4) As/cm2 the diameter of a hole increased 5 nm. Rough calculations show that this increase can be ascribed to knock-on processes. Estimates of the rise in specimen temperature during the irradiation are given.
Assuntos
Carbono/efeitos da radiação , Temperatura Baixa , Microscopia Eletrônica , Elétrons , Lentes , MatemáticaRESUMO
Resolution tests on amorphous carbon foils were carried out in an electron microscope with a superconducting system containing 4 lenses including a shielding lens at 200 kV beam voltage. Due to the mechanical and electrical stability of the system and the absence of contamination of the specimen the highest space frequencies transferred at vertically incident beam were 6 nm-1 corresponding to a resolution of 0.17 nm, a value which approaches the theoretical resolving power of the electron optical system. It should also be feasible to apply such a lens system for microprobe analysis without strongly reducing the theoretical resolution limit, if the construction of the shielding lens is slightly changed.
