Abstract:
The electron beam apparatus sample holding means has a diaphragm which is placed on upper and lower sides of a sample to form a cell for separating a gas atmosphere and a vacuum atmosphere of a sample chamber and sealing an ambient atmosphere of the sample; a gas supply means for supplying gas to an inside of the cell; and exhaust means for exhausting gas. The exhaust means includes a gas exhaust pipe provided in the inside of the cell and an openable/closable exhaust hole provided in a sidewall of the sample holding means so as to pass through the cell. The diaphragm is an amorphous film made of light elements which can transmit an electron beam, such as carbon films, oxide films, and nitride films.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electron microscope and a sample holder used therefor. 
       BACKGROUND ART 
       [0002]    There are growing needs for analyzing the structure and characteristics of substances not in vacuum but in a gas atmosphere and for performing in-situ observation of the synthetic process of the substances in the gas atmosphere with use of transmission electron microscopes (TEMs), scanning transmission electron microscopes (STEMs) and the like. 
         [0003]    For observation in the gas atmosphere, there is a method as disclosed in Patent Literature 1 and Patent Literature 2, in which a sample holder includes a mechanism for holding a sample between two grids and introducing and exhausting gas into and from a space between the grids. There is another method as disclosed in Patent Literature 3 in which, in order to protect a diaphragm from pressure variations in the inside of a cell and to prevent gas diffusion, a sample is enclosed with a cell membrane and the membrane is provided with two holes which are covered with diaphragms so that an electron beam passes through the membrane. There is still another method as disclosed in Patent Literature 4 in which a sample holder has a dual-stage cell structure for preventing gas diffusion in the case where a diaphragms is damaged, the dual-stage cell structure having another diaphragms placed outside the cell formed from the diaphragms. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: JP Patent Publication (Kokai) No. 2009-117196 A 
         Patent Literature 2: JP Patent Publication (Kokai) No. 9-129168 A (1997) 
         Patent Literature 3: U.S. Pat. No. 5,326,971 
         Patent Literature 4: JP patent No. 3610245 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    In all of the above-stated conventional techniques, a gas exhaust pipe was provided in the inside of a cell which divides a gas atmosphere and a vacuum atmosphere. The exhaust pipe was connected to a vacuum pump to the outside of a column of the electron microscope, by which gas in the inside of the cell was exhausted. However, the exhaust pipe had a diameter as small as about several millimeters due to restriction by the size of the cell. Accordingly, the exhaust pipe had a large conductance and took time to discharge gas, which made it difficult to conduct gas displacement and made it also difficult to evacuate the cell to a degree of vacuum (10 −5  Pa) that is equivalent to that in an electron microscope sample chamber. It also took time to conduct the gas displacement. 
         [0009]    In the case of using a sleeve having a removable cell membrane and a dual cell structure involving placement of a cell membrane in some of the above-stated conventional techniques, large dispersion of an electron beam caused a blurred image, resulting in deteriorated image quality. 
         [0010]    Moreover, in all of the conventional techniques, consideration is not given to high temperature heating. 
         [0011]    An object of the present invention is to provide a sample holding unit for an electron beam apparatus which can exhaust gas and replace with gas in the inside of a cell in a short time, easily cover a wide range of gas pressures in the inside of the cell from a degree of vacuum (10 5  Pa) equivalent to that in an electron microscope sample chamber to the atmospheric pressure (10 5  Pa), and which allows observation of a reaction between a sample and gas under a wide range of gas pressures without damaging a diaphragm for use in the cell. Another object of the present invention is to provide a sample holding unit for an electron beam apparatus which allows high-temperature observation of a sample under any gas environment. 
       Solution to Problem 
       [0012]    In order to solve one of the above-stated problems, in the present invention, an electron beam apparatus having a function of separately exhausting gas from an electron beam irradiation section, a sample chamber, and an observation chamber in a column includes: sample holding means in which a diaphragm is placed on an upper and lower sides of a sample to form a cell for separating a gas atmosphere and a vacuum atmosphere of the sample chamber and sealing an, atmosphere around the sample; gas supply means for supplying gas to an inside of the cell; and exhaust means for exhausting gas. The exhaust means includes a gas exhaust pipe provided in the inside of the cell and an openable/closable exhaust hole provided in a sidewall of the sample holding means so as to pass through the cell. 
         [0013]    The diaphragm is an amorphous film made of light elements which can transmit an electron beam, such as carbon films, oxide films, and nitride films. 
       Advantageous Effects of Invention 
       [0014]    According to the present invention, a minute gas space (environmental cell) of atmospheric gas for enclosing a sample with the diaphragm is formed in the inside of the sample chamber, so that gas can be exhausted and replaced with gas in the inside of the cell in a short time and a reaction between the sample and gas can be observed under a wide range of gas pressures with use of the electron beam apparatus. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a basic structure view of an electron beam apparatus  1  and a sample holding unit for the electron beam apparatus  6  in one embodiment of the present invention. 
           [0016]      FIG. 2  is a structure view of a top end of the sample holding unit for the electron beam apparatus  6  in one embodiment. 
           [0017]      FIG. 3  is a structure view of an electron beam apparatus sample chamber  14  and the sample holding unit for the electron beam apparatus  6  in one embodiment. 
           [0018]      FIG. 4  is a cross sectional view of an area in the vicinity of an exhaust hole  38  of the sample holding unit for the electron beam apparatus  6  in one embodiment. 
           [0019]      FIG. 5  is a cross sectional view of an area in the vicinity of the exhaust hole  38  of the sample holding unit for the electron beam apparatus  6  in one embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]      FIG. 1  shows a basic structure view of an electron beam apparatus  1  and a sample holding unit for the electron beam apparatus  6  in one embodiment of the present invention. A column of the electron beam apparatus  1  includes an electron gun  2 , a condenser lens  3 , an objective lens  4 , and a projector lens  5 . The sample holding unit for the electron beam apparatus  6  is inserted in between the condenser lens  3  and the objective lens  4 . A fluorescent screen  7  is mounted below the projector lens  5 , and a TV camera  8  is mounted below the fluorescent screen  7 . The TV camera  8  is connected to an image recording section  9   b  via an image display section  9   a . An EELS detector  10  is mounted on the lower side of the TV camera  8  and is connected to an EELS control section  11 . An EDX detector  12  is set above the sample holding unit for the electron beam apparatus  6 , and is connected to an EDX control section  13 . 
         [0021]    Vacuum pumps  17  are connected to the vicinity of the electron gun  2 , the vicinity of the condenser lens  3 , the electron beam apparatus sample chamber  14 , and an observation chamber  15  via valves  16 , respectively. The sample holding unit for the electron beam apparatus  6  has a cell  19  sealed with a diaphragm  18  which is formed from an amorphous material such as carbon, oxide and nitride. The cell  19  has a sample  20  loaded therein and also has a top end portion of a gas introducing pipe  21  and a top end portion of a gas exhaust pipe  22  inserted therein. The electron beam apparatus sample chamber  14  is connected to a preliminary sample evacuation chamber  27 , and the preliminary sample evacuation chamber  27  is connected to a vacuum pump  17  via a valve  16 . 
         [0022]    The gas introducing pipe  21  is connected to a gas storage section  24  via a gas pressure control valve  23 . The gas exhaust pipe  22  is connected to a vacuum pump  17  via a valve  16 . 
         [0023]    An electron beam  25  emitted from the electron gun  2  is focused by the condenser lens  3  and is applied to the sample  20 . The electron beam  25  which transmitted the sample  20  is imaged by the objective lens  4 , and the image is magnified by the projector lens  5  and projected onto the fluorescent screen  7 . Alternatively, the fluorescent screen  7  is lifted to project the transmitted image on the TV camera  8 , so that the image is displayed on the image display section  9   a  and is recorded on the image recording section  9   b.    
         [0024]    When the sample holding unit for the electron beam apparatus  6  is inserted into the electron beam apparatus sample chamber  14 , a top end portion of the sample holding unit for the electron beam apparatus  6  is put in the preliminary sample evacuation chamber  27  in advance for gas exhaust and is then inserted into the electron beam apparatus sample chamber  14 . 
         [0025]      FIG. 2  shows a structure view of the top end of the sample holding unit for the electron beam apparatus  6  in one embodiment. The sample holding unit for the electron beam apparatus  6  has an electron beam transmission hole  28  for passing the electron beam  25  therethrough. A lower diaphragm support plate  29   a  having a lower diaphragm  18   a  bonded thereto is mounted on the sample holding unit  6  so that the electron beam transmission hole  28  is covered with the lower diaphragm support plate  29   a . The lower diaphragm support plate  29   a  is fixed without any gap with use of adhesives and the like so that gas does not pass through the gap. Above the lower diaphragm support plate  29   a , a heater  30  is fixed in a floating state with both ends thereof being screwed with heater fixing screws  31   a  so that the heater  30  does not come into contact with the lower diaphragm  18   a . One side of the heater  30  screwed with the heater fixing screw  31   a  is connected to a lead wire  32 , and the lead wire  32  is connected to a heating source  33  which is in the outside of the column of the electron beam apparatus  1 . The sample  20  is directly applied to the heater  30 . An upper diaphragm support plate  29   b  is fixed to a pressing plate  34  without any gap with use of adhesives and the like. The pressing plate  34  is screwed to the sample holding unit for the electron beam apparatus  6  with screws  31   b  via a gasket  35 . Thus, the cell  19  is formed which can seal the sample  20  and a surrounding area of the sample  20 . The cell  19  has the top end portions of the gas introducing pipe  21  and the gas exhaust pipe  22  inserted therein, so that any gas can be introduced to or exhausted from the inside of the cell  19 . Accordingly, it becomes possible to heat the sample  20  in any gas atmosphere and to directly observe a changing process thereof. 
         [0026]    In this embodiment, the lower diaphragm support plate  29   a  and the upper diaphragm support plate  29   b  are fixed with use of adhesives. However, they may be structured to be directly screwed to the sample holding unit for the electron beam apparatus  6  via gaskets. 
         [0027]    Also in this embodiment, the heater  30  is placed in the inside of the cell  19  and the sample  20  is directly applied to the heater  30  so that the sample  20  can be heated in the inside of the cell  19 . However, it may be possible to set a general electron microscope sample stand such as a 3 mm-mesh instead of using the heater  30 . 
         [0028]      FIG. 3  shows a structure view of the electron beam apparatus sample chamber  14  and the sample holding unit for the electron beam apparatus  6  in one embodiment. The electron beam apparatus sample chamber  14  adjoins to the preliminary sample exhaust chamber  27 , which is connected to a vacuum exhaust pump  17  so that preliminary exhaust can be performed when the sample holding unit for the electron beam apparatus  6  is inserted into or taken out of the electron beam apparatus sample chamber  14 . Since the environmental cell  19  is formed with the lower diaphragm  18   a  and the upper diaphragm  18   b  at the top end of the sample holding unit for the electron beam apparatus  6 , an environment different from that of the electron beam apparatus sample chamber  14  can be formed at the top end portion of the sample holding unit for the electron beam apparatus  6 . The sample  20  is mounted on the heater  30  in the inside of the cell  19 , and the heater  30  is connected to the heating source  33  via the lead wire  32 . Accordingly, it becomes possible to heat the sample  20  while controlling the environment in the inside of the cell  19 . 
         [0029]    A shaft portion of the sample holding unit for the electron beam apparatus  6  includes an outer shaft  36  and a center shaft  37  which can move in a horizontal direction. Exhaust holes  38  are provided in a lateral surface of the outer shaft  36 . O rings  39  are set in the center shaft  37  so that the exhaust holes  38  of the outer shaft  36  can be closed. The center shaft  37  is connected to a center shaft drive tab  40  which is in the outside of the column of the electron beam apparatus  1 . As the center shaft drive tab  40  is rotated, the center shaft  37  can be operated in the horizontal direction. As the center shaft  37  moves, the positions of the O rings  39  shift from the exhaust holes  38  of the outer shaft  36 . As a result, the inside of the environmental cell  19  communicates with the exhaust hole  38 . Since gas in the electron beam apparatus sample chamber  14  is exhausted with the vacuum pump  17 , simultaneous exhaust through the gas exhaust pipe  22  and the exhaust hole  38  becomes possible. This makes it possible to exhaust gas in the inside of the cell  19  in a short time. In this embodiment, two exhaust holes  38  are provided. However, two or more exhaust holes  38  may be provided, or when the capacity of the cell  19  is small, one exhaust hole  38  may be provided. 
         [0030]    After the gas in the cell  19  is exhausted through the exhaust holes  38  and the gas exhaust pipe  22 , the center shaft  37  is horizontally operated so that the positions of the O rings  39  move to the positions of the exhaust holes  38  of the outer shaft  36 . As a result, the inside of the environmental cell  19  is sealed. Then, gas is introduced through the gas introducing pipe  21 , and the gas pressure is controlled to obtain a target pressure. The temperature of the sample  20  is controlled and set by adjusting the heating temperature of the heater  30 . The change thereof is observed with use of an electron beam  25  which has transmitted the diaphragm  18 . 
         [0031]    The gas in the cell  19  may be exhausted not by using the electron beam apparatus sample chamber  14  but by setting the positions of the exhaust holes  38  to be at the preliminary sample evacuation chamber  27 , opening the exhaust holes  38 , and exhausting the gas in the preliminary sample evacuation chamber  27  so that the gas in the inside of the cell  19  is exhausted through the exhaust holes  38 . 
         [0032]    For example, at the time of inserting the sample holding unit for the electron beam apparatus  6  into the column of the electron beam apparatus  1 , if the top end portion of the sample holding unit for the electron beam apparatus  6  is inserted into the preliminary sample evacuation chamber  27  and gas in the preliminary sample evacuation chamber  27  is exhausted while the inside of the cell  19  is at the atmospheric pressure, then rapid pressure change affects the diaphragm  18 , and thereby the diaphragm  18  is damaged. Accordingly, prior to start preliminary exhaust, it is necessary to exhaust gas from the cell  19  of the sample holding unit for the electron beam apparatus  6  through the gas exhaust pipe  22  in the inside of the cell  19 . However, the gas exhaust pipe  22  has a diameter of 1 mm or less so as to be fitted into the sample holding unit for the electron beam apparatus  6 , and so the gas exhaust pipe  22  has a large conductance, takes time to discharge gas, and is not efficient. Accordingly, the gas in the preliminary sample evacuation chamber  27  is exhausted while the exhaust holes  38  are opened, so that the gas inside the cell  19  is directly exhausted, the pressure applied to the diaphragm  18  is reduced, and the diaphragm  18  is protected. 
         [0033]      FIG. 4  shows a cross sectional view of an area in the vicinity of the exhaust hole  38  of the sample holding unit for the electron beam apparatus  6  in one embodiment. In the sample holding unit for the electron beam apparatus  6 , the exhaust holes  38  are provided in the outer shaft  36 . The O rings  39  are mounted on the portions which come into contact with the mirror body of the electron beam apparatus  1 , so that the electron beam apparatus sample chamber  14  is maintained in vacuum. The center shaft  37  portion is connected to the center shaft drive tab  40  which is hollow and movable in the horizontal direction and which is in the outside of the mirror body of the electron beam apparatus  1 . As the center shaft drive tab  40  is rotated, the center shaft  37  can be operated in the horizontal direction. The O rings  39  are set in the center shaft  37  so that the outer shaft  36  and the exhaust holes  38  can be closed. The center shaft  37  is hollow, so that the lead wire  32 , the gas introducing pipe  21 , and the gas exhaust pipe  22  pass through the center shaft  37 . One end of the lead wire  32  is connected to the heater  30  in the inside of the cell  19 , while the other end is connected to the heating source  33  which is in the outside of the column of the electron beam apparatus  1 . The gas introducing pipe  21  is connected to the gas storage section  24  via the gas pressure control valve  23  which is in the outside of the mirror body of the electron beam apparatus  1 . The gas exhaust pipe  22  is connected to the vacuum pump  17 , which is in the outside of the column of the electron beam apparatus  1 , via the valve  16 . As the center shaft drive tab  40  is rotated, the center shaft  37  is further driven in the horizontal direction, so that the positions of the O rings  39  shift from the exhaust holes  38  of the outer shaft  36 . As a result, the inside of the environmental cell  19  communicates with the exhaust hole  38 . Since gas in the electron beam apparatus sample chamber  14  is exhausted with the vacuum pump  17 , simultaneous exhaust through the gas exhaust pipe  22  and the exhaust hole  38  becomes possible. This makes it possible to exhaust gas in the inside of the cell  19  in a short time. In this embodiment, two exhaust holes  38  are provided. However, two or more exhaust holes  38  may be provided, or when the capacity of the cell  19  is small, one exhaust hole  38  may be provided. 
         [0034]      FIG. 5  shows a cross sectional view of an area in the vicinity of the exhaust hole  38  of the sample holding unit for the electron beam apparatus  6  in another embodiment. A top end portion of the center shaft  37  in  FIG. 5 , which is different from that in  FIG. 4 , may be formed into a tapered shape so as to have a function as a needle valve which allows fine adjustment of the amount of exhaust in the inside of the cell  19 . 
         [0035]    By combining the foregoing structures, precise control can be performed on a wide range of pressures inside the environmental cell  19 , and the pressure applied to the diaphragm  18  can be adjusted when the sample holding unit  6  is inserted into and taken out of the electron beam apparatus  1 . This makes it possible to prevent the diaphragm  18  from being damaged by the rapid pressure change, and thereby a thinner diaphragm  18  becomes applicable. Therefore, a reaction process in a gas atmosphere, such as a crystal growth process by a high-temperature gas reaction and an oxidation-reduction reaction process, can be observed at high resolution. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Electron beam apparatus 
           2  Electron gun 
           3  Condenser lens 
           4  Objective lens 
           5  Projector lens 
           6  Sample holding unit for electron beam apparatus 
           7  Fluorescent screen 
           8  TV camera 
           9   a  Image display section 
           9   b  Image recording section 
           10  EELS detector 
           11  EELS control section 
           12  EDX detector 
           13  EDX control section 
           14  Electron beam apparatus sample chamber 
           15  Observation chamber 
           16  Valve 
           17  Vacuum pump 
           18   a  Lower diaphragm 
           18   b  Upper diaphragm 
           19  Cell 
           20  Sample 
           21  Gas introducing pipe 
           22  Gas exhaust pipe 
           23  Gas pressure control valve 
           24  Gas storage section 
           25  Electron beam 
           26  Intermediate chamber 
           27  Preliminary sample evacuation chamber 
           28  Electron beam transmission hole 
           29   a  Lower diaphragm support plate 
           29   b  Upper diaphragm support plate 
           30  Heater 
           31   a  Heater fixing screw 
           31   b  Screw 
           32  Lead wire 
           33  Heating source 
           34  Pressing plate 
           35  Gasket 
           36  Outer shaft 
           37  Center shaft 
           38  Exhaust hole 
           39  O ring 
           40  Center shaft drive tab