Patent Publication Number: US-2012037815-A1

Title: Tem phase plate loading system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Non-provisional application claims the benefit of the filing date of provisional application No. 61/374,077 filed Aug. 16, 2010, under 35 USC &amp; 119 (e) (1). 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a phase plate loading system of a transmission electron microscope (TEM). 
     2. Related Art 
     The success of a phase TEM adopting a phase plate device is considered to have a high potential to make some impact in various fields, including biology and materials sciences. With a proper phase TEM and the appropriate wave reconstruction method, it is possible to reveal bio-structure information, which can never be obtained by the conventional TEM. In order to develop a phase TEM that is applicable for imaging, tremendous technical difficulties have to be overcome: (1) loading the phase plate into a TEM must not degrade the functions of the TEM; (2) the phase plate needs to be positioned at the back focal plane with a high scale of precision; (3) fabrication of a reliable phase plate is technically challenging; (4) low dose imaging is needed while taking images of vulnerable specimens. 
     Various phase plate designs have been proposed, including Zernike-type and Hilbert-type phase plates. The Zernike-type phase plate is suitable for thin-film type, electrostatic type and magnetic (vector potential) type phase plates. The Hilbert-type phase plate is suitable for thin-film style and magnetic style phase plates. In any case, it is essential to load a phase plate in any form into the limited space within the TEM chamber for increasing the phase contrast, without affecting the normal operation of the TEM. 
     In the conventional art, the optical design of the TEM must be modified in order to load the phase plate into the TEM. For example, the optical design may be modified by adding a transfer lens doublet in the TEM. The modification of the TEM optical design is complicated and expensive, thus is not preferred by TEM users. The users may choose another method to place the phase plate into the TEM, which includes the following steps: shutting down the TEM, opening the TEM chamber, placing the phase plate into the TEM chamber, sealing the chamber, vacuuming the TEM, and finally restarting the TEM. However, this method is very inconvenient and risky, because of the time consuming for changing the phase plate (usually several days) and the possibility of damaging expensive internal components while opening the TEM chamber. 
     Therefore, it is an important subject of the present invention to provide a phase plate loading system, which can load the phase plate into the TEM without modifying its optical design, and perform the phase plate loading procedure safely without shutting down the TEM, thereby decreasing the time consumption for the phase plate loading procedure, and avoiding damaging internal components of the TEM. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of the present invention is to provide a phase plate loading system, which can load the phase plate into the TEM without modifying its optical design, and perform the phase plate loading procedure without shutting down the TEM, thereby decreasing the time consumption for the phase plate loading procedure and avoiding damaging internal components of the TEM. 
     To achieve the above object, the present invention discloses a phase plate loading system applied to a TEM. The phase plate loading system includes an airlock chamber and a transport unit. The airlock chamber is disposed adjacent to a specimen section of the TEM. The transport unit transfers a phase plate into the TEM through the airlock chamber and an opening port of the specimen section. 
     In one embodiment of the invention, the airlock chamber is connected with a pump unit. Herein, the pump unit can be an independent pump unit or a pumping unit of the TEM. 
     In one embodiment of the invention, the opening port of the specimen section includes an EDS (energy dispersive x-ray spectroscope) port or an objective aperture port. 
     In one embodiment of the invention, the specimen section includes a specimen chamber; and the airlock chamber and the specimen chamber are linked to each other and separated by a gate valve. 
     In one embodiment of the invention, the transport unit further includes a guiding rail disposed on the airlock chamber. 
     In one embodiment of the invention, the phase plate is an electrostatic type phase plate, or a magnetic type phase plate, or a thin-film type phase plate. 
     In one embodiment of the invention, the transport unit includes a motor for transferring the phase plate. Preferably, the transport unit further includes a loading rod connected with the motor. Preferably, the transport unit further includes a phase plate holder connected with the motor. Herein, the phase plate holder carries the phase plate. 
     In one embodiment of the invention, the system further includes a loading monitor unit for monitoring the specimen section, more particularly, a position of the phase plate in the specimen section. Preferably, the loading monitor unit includes a camera or a sensor. 
     In one embodiment of the invention, the specimen section includes an ACD fin (anti-contamination device fin), and the phase plate is installed inside the ACD fin. Preferably, the specimen section includes a specimen holder, and the phase plate is installed between the specimen holder and the ACD fin. 
     As mentioned above, the TEM phase plate loading system of the invention can transfer the phase plate into the TEM through the airlock chamber, which is disposed adjacent to the specimen section of the TEM, so that modifying the optical design of the TEM is not necessary. In other words, the phase plate loading system of the invention can be installed on any commercial TEM. Compared with the prior art, the present invention discloses an airlock chamber for pre-vacuuming the phase plate before transferring it into the TEM. Thus, the conventional procedure for loading the phase plate including the steps of shutting down the TEM, opening the TEM chamber, sealing the chamber, and vacuuming the TEM is unnecessary, thereby reducing the time consuming for the loading procedure. For instance, the loading time may be reduced from several days to less than one hour. Moreover, the phase plate can be loaded without opening the chamber of the TEM. The present invention allows user to rapidly operate the phase TEM without damaging the internal components of the TEM. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become more fully understood from the detailed description and accompanying drawings, which are given for illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a schematic diagram showing a TEM equipped with a phase plate loading system of the present invention; 
         FIG. 2  is a schematic diagram showing the airlock chamber and the transport unit of the phase plate loading system of  FIG. 1 ; 
         FIG. 3  is a schematic diagram showing the detailed structure of the transport unit of the invention; 
         FIG. 4A  is a side view of the transport unit equipped in the TEM of the invention; 
         FIG. 4B  is a top view of the transport unit equipped in the TEM of the invention; and 
         FIG. 4C  and  FIG. 4D  are schematic diagrams showing the phase plate, which is positioned and aligned. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
       FIG. 1  is a schematic diagram showing a TEM equipped with a phase plate loading system  1  of the present invention. With reference to  FIG. 1 , the phase plate loading system  1  applied to a TEM  2  includes an airlock chamber  11  and a transport unit  12 . 
     As shown in  FIG. 1 , the TEM  2  is a transmission electron microscope, which is composed of a column portion  21 , a vacuum system (not shown) and a control system (not shown). The column portion  21  includes an electron gun section, several lenses sections, a specimen loading section, a fluorescent screen section, a camera, etc. These components are usually installed from top to bottom so as to form a cylindrical configuration. The vacuum system is composed of various pumps and several vacuum gate valves, and is connected to the column portion  21 . 
     In the present invention, an airlock chamber  11  is additionally configured outside the TEM  2 . The airlock chamber  11  is installed adjacent to the specimen section  211  of the TEM  2 . The specimen section  211  is the section where the specimen loading port is configured, and it includes a specimen chamber  217 . The opening ports of the specimen section  211  may include an objective aperture port  212  and an EDS (energy dispersive x-ray spectroscope) port  213 . The airlock chamber  11  can be positioned in any idle opening port of the specimen section  211  and linked with the specimen chamber  217  inside the TEM  2  through a gate valve  111 . The material analysis function of EDS is usually not needed in the TEM  2  cooperated with the phase plate  13  when the TEM  2  is dedicated for bio-imaging, thus the EDS port  213  is an open port. Therefore, the EDS port  213  can be used to install the phase plate loading system  1  of the invention. 
     The airlock chamber  11  has to be small enough to fit into the limited space around the opening ports of the specimen section  211  without blocking other components. 
       FIG. 2  is a schematic diagram showing the airlock chamber  11  and the transport unit  12  of the phase plate loading system  1 , and  FIG. 3  is a schematic diagram showing the detailed structure of the transport unit  12  of the invention. Referring to  FIG. 2  and  FIG. 3 , the airlock chamber  11  is connected with a pump unit  14 . In this embodiment, the pump unit  14  is a pump independent from the vacuum system of the TEM  2 . In practice, the pump unit  14  may be a pumping unit of the TEM  2  depending on the needs of the users. Moreover, the pumping unit may be integrated in the vacuum system. 
     The transport unit  12  transfers a phase plate  13  into the TEM  2 . In this embodiment, the transport unit  12  includes a motor  121  for driving to transfer the phase plate  13 . Any driving mechanism other than a motor driving can also be adopted on the transport unit  12 . The detailed structure of the transport unit  12  will be described hereinafter. 
     After loading the phase plate  13 , one end of the transport unit  12  enters the airlock chamber  11 . Then, the phase plate pre-pumping valve  141  is opened, so that the pump unit  14  can pump out the air inside the airlock chamber  11 . After the airlock chamber  11  reaches the desired vacuum state, the gate valve  111  between the airlock chamber  11  and the column is opened, and then the phase plate  13  is transferred into the column inside the TEM  2 . In this embodiment, the complex procedure of the prior art, which includes the following steps of shutting down the TEM  2 , opening the specimen chamber, placing the phase plate  13  into the specimen chamber, sealing the chamber, vacuuming the TEM  2 , and finally restarting the TEM  2 , is not needed. The phase plate loading system  1  of the invention does not need the exhaust time for vacuum after loading the phase plate  13 . Moreover, the present invention does not need to open the TEM  2  so as to prevent it from being damaged. For example, if the phase plate loading system  1  of the invention is installed on a commercial TEM equipped with a turbo molecular pumping system, the time needed for replacing a phase plate  13  and reloading it into the airlock chamber  11  and for the system to reach the vacuum condition for operating can be accomplished within 30 minutes. This is quite efficient and useful for practical applications, considering the phase plates  13  often need to be replaced and reloaded. It should be noted that pumping times for the TEM  2  vary with the equipped pumping systems. 
     Referring to  FIG. 2  and  FIG. 3 , the transport unit  12  further includes a loading rod  122 , a guiding rail  123 , and a phase plate holder  124 . The loading rod  122  and the phase plate holder  124  are connected to two ends of the motor  121 , respectively. The guiding rail  123  can be attached on the top of the airlock chamber  11  to guide the loading rod  122  into the column of the TEM  2 . This is a safety design so that the risk of damaging the phase plate holder  124  during loading and unloading is greatly reduced. In addition, the phase plate holder  124  is used to carry the phase plate  13 . 
       FIG. 4A  is a side view of the transport unit  12 , and  FIG. 4B  is a top view of the transport unit  12  when the phase plate  13  is placed inside the TEM  2  of the invention. The phase plate holder  124  is used to carry the phase plate  13 , such as an electrostatic type phase plate, a magnetic type phase plate, or a thin-film type phase plate. In addition, the specimen section  211  may further include an ACD (anti-contamination device) fin  215  and a specimen holder  216 , which are disposed between two pole pieces  214  of the TEM  2 . The phase plate  13  is carried by the phase plate holder  124 , which is connected to the motor  121 , and is transferred into the specimen chamber. More particularly, the phase plate  13  is transferred to the location between the specimen holder  216  and the ACD fin  215 . In this embodiment, the ACD fin  215  near the EDS port  213  is slightly trimmed to clear out a path for loading the phase plate  13 , and kept in place to serve its function. 
     With reference to  FIG. 4B , a phase plate loading system  1  of the invention further includes a loading monitor unit  15  for monitoring the phase plate  13  transferred from the airlock chamber  11  to the column  21 . More particularly, the loading monitor unit  15  can monitor whether the phase plate  13  reaches a specific position. In this embodiment, the loading monitor unit  15  includes a camera or a sensor for monitor the position of the phase plate  13  inside the specimen section  211 . The loading monitor unit  15  can be disposed outside the specimen section  211 . 
       FIG. 4C  and  FIG. 4D  are schematic diagrams showing the phase plate  13 , which is positioned and aligned by utilizing the loading monitor unit  15 . Practically, the loading monitor unit  15  allows users to observe the movement of the phase plate holder  124  carrying the phase plate  13  on a computer screen, and thus greatly decreases the chances of breaking the vulnerable phase plate  13  and the phase plate holder  124 , and also significantly speeds up the positioning of the phase plate  131 . For example, as shown in  FIG. 4D , the phase plate  13  can be positioned and aligned with the electron beam passing through the specimen holder  216 . As shown in  FIGS. 4C and 4D , a line  1241  can be marked on the side surface of the phase plate holder  124  in advance with respect to different phase plates  13 , thereby identifying the exact position of the phase plate  131 . When the phase plate holder  124  is inserted to a position under the specimen holder  216 , the user can observe the phase plate holder  124  from one side so as to position the phase plate  13  by aligning the line  1241  to the center of the specimen holder  216 , thereby positioning the phase plate  131  on the beam path of the electron beam. Besides, when different phase plates  13  are used, the line  1241  can be easily erased and re-marked for positioning different phase plates  13 . The phase plate  13  can be aligned by manual control or by automatic control. In either control method, the time consumption for loading the phase plate  13  can be sufficiently reduced. 
     As mentioned above, the TEM phase plate loading system of the invention can transfer the phase plate into the TEM through the airlock chamber, which is disposed adjacent to the specimen section of the TEM, so that it is unnecessary to either modify the optical design of the TEM or shut down and re-start the TEM. In other words, the phase plate loading system of the invention can be installed on any commercial TEM. Compared with the prior art, the present invention discloses an airlock chamber for pre-vacuuming the phase plate before transferring it into the TEM. Thus, the conventional procedure for loading the phase plate including the steps of shutting down the TEM, opening the TEM, placing the phase plate into the TEM, and re-starting the TEM, is unnecessary, thereby reducing the time consuming for the TEM phase plate loading procedure. For instance, the loading time may be reduced from several days to less than one hour. Moreover, the phase plate can be loaded without opening the chamber of the TEM, so that TEM can be protected from being damaged. The present invention allows the user to rapidly operate the TEM equipped with TEM phase plates. 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.