Abstract:
An arrangement for holding a particle beam apparatus such as a transmission electron microscope. The arrangement is sufficient for receiving a good resolution in the area of 1 Å or less, said arrangement still being under more or less no influence of the environment, in particular, building vibrations. In one embodiment, the arrangement comprises a base structure comprising a plurality of hollow bodies, at least one of said hollow bodies having a first length extension in a first direction, a second length extension in a second direction and a third length extension in a third direction, said first length extension being larger than said second and third length extensions, and wherein a cross section of said at least one of said hollow bodies perpendicular to said first direction is substantially triangular. Due to the hollow body shape, a very stiff structure is provided with a very good eigenfrequency.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   This application relates to the field of holding arrangements and more particularly to the field of arrangements for holding a particle beam apparatus, in particular a transmission electron microscope. 
   2. Description of Related Art 
   A particle beam apparatus, in particular a transmission electron microscope, is well known in the art. A particle beam apparatus comprises several components, such as a particle source for providing particles for a particle beam, several lenses for forming the particle beam, a specimen holder for holding a specimen to be examined and detection means for detecting particles which arise from the interaction of the particle beam&#39;s particles and the specimen, e.g. a camera for recording an image. These components are generally arranged in a column of the particle beam apparatus. 
   Transmission electron microscopes are also well known in the art. A transmission electron microscope (hereinafter referred to as TEM) substantially comprises the components mentioned-above, whereby the particle source is an electron source and an electron optical setup is provided in the column (electron optical column). For many applications it is required that the TEM has a high resolution. A resolution of 1 Å or less is required for many important applications. However, ultimate stable operating conditions of the electron optical setup are required, otherwise it is difficult to reach a good resolution. Accordingly, the TEM environment must be stable, thereby preventing alterations in the optical conditions of the TEM. In particular, any AC-stray fields, mechanical instabilities caused by building vibrations, acoustic noises and temperature changes have to be avoided or at least to be kept to a minimum. In particular, the electron optical column has to be of high robustness regarding environmental influences. 
   From “ELECTRONIC, MECHANICAL AND ELECTRON-OPTICAL ENGINEERING DESIGN FEATURES OF THE CAMBRIDGE UNIVERSITY 600 kV RESOLUTION MICROSCOPE” by Nixon et. al, Ninth International Congress on Electron Microscopy, Toronto 1978, VOL I, and “A SUSPENSION SYSTEM FOR A VERY HIGH RESOLUTION ELECTRON MICROSCOPE” by Timbs et. al., Ninth International Congress on Electron Microscopy, Toronto 1978, VOL I, a suspension system is known which supports a complete electron optical column somewhat above its centre of gravity by three wall mounted units, which contain compressed air cylinders with rolling rubber diaphragms. However, this wall mounted suspension system has several practical disadvantages: It requires a serious structural engineering measure and can not be displaced. Furthermore, it leads to a much more extensive mounting of the TEM at the costumers place and offer only poor possibilities for purposes of system integration such as mounting of cables, tubes and peripheral devices. 
   SUMMARY OF THE INVENTION 
   According to the present invention, an arrangement for holding a particle beam apparatus, in particular a transmission electron microscope, comprises a base structure comprising a plurality of hollow bodies. At least one of said hollow bodies has a first length extension in a first direction, a second length extension in a second direction and a third length extension in a third direction, said length extension in said first direction being larger than said length extensions in said second and third directions. Moreover, a cross section of said at least one of said hollow bodies perpendicular to said first direction is substantially triangular. 
   Due to the hollow body shape of one embodiment of the invention, a very stiff structure is provided with a very good (i.e. high) natural frequency (eigenfrequency). Thus, an embodiment of the invention is very insensitive with respect to mechanical excitations, especially building vibrations, when holding a particle beam apparatus. Furthermore, the embodiment allows a hanging column approach by providing a suspension center close to or above the center of gravity of the column of a particle beam apparatus. 
   The cross section of said at least one of said hollow bodies may vary in said first direction. Furthermore, said at least one of said hollow bodies may have a first and a second outer surface being in contact to each other and forming an edge, and wherein a cross section through said edge having the form of the letter “L”. 
   According to the present invention, said cross section of said at least one of said hollow bodies may have curved boundaries. Moreover, the base structure may have a hollow base element and at least two arms extending from said base element. 
   The arms of the base structure may each comprise an end arranged opposite to the base element. The distance between the arms diminishes from the ends of the arms in the direction of the base element. For reasons of access, the arms and the base element may form substantially a U-shape or a V-shape. 
   The base element may comprise a front wall, a back wall and a side wall which together form the hollow body of the base element. The arms may extend from the front wall of the base element. 
   At least one of the arms of the base structure according to the invention may be formed as a hollow body. One embodiment of the invention comprises the at least one arm having surfaces which form the hollow body which may comprise a front wall, a back wall and at least one side wall. The front wall, the back wall and the side wall of the arm provide the hollow body of the corresponding arm. The side wall of said at least one arm may be arranged (e.g. mounted) at the base element, especially at the back wall of the base element. 
   According to the present invention, an embodiment of the base structure may comprise a support element arranged on the base element. The support element may comprise a back wall and at least two side walls. The back wall of the support element may be arranged at the back wall of the base element. Additionally, the back wall of the support element may be integrated with the back wall of said base element. 
   According to the present invention, one embodiment may comprise one or several side elements arranged at the base element. Each side element may comprise a triangular profile. Moreover, each side element may be formed at least partially of a side wall of the support element. 
   In one embodiment, the side walls of the support element or of the side elements may be preferably connected with each other in a connecting area. The connecting area may comprise a link element. The side walls may be connected with each other via the link element in said connecting area. A bracket may be arranged at the connecting area and extends in a curve along the side walls from the connecting area to said arms. 
   Another embodiment of the invention may comprise at least three bedding devices for bedding a supporting structure. The bedding devices may be damping elements which are preferably pneumatic. 
   The arrangement, in particular the base structure may also comprise at least three footings. Preferably, there may be four footings provided. One of these footings may be mounted force loaded, preferably spring mounted. 
   According to the present invention, an embodiment of the base structure may have a lowest eigenfrequency of greater than or equal to 40 Hz. One embodiment of the invention may comprise a base structure having a lowest eigenfrequency of greater than or equal to 70 Hz, and may be preferably greater than or equal to 80 Hz. 
   The base element may comprise a box-like structure with a top wall and a bottom wall, wherein said top wall is inclined with respect to said bottom wall. The support element and/or a side element may also be formed at least partially as a closed profile. 
   According to the invention, an embodiment may include at least one of said hollow bodies comprises surfaces with at least one opening. For example, the closed profile of the support element may comprise a surface, whereby at least 30% of the surface comprises at least one opening which is used to access the particle beam apparatus for operating, service or mounting purposes. 
   The arrangement according to the invention may be at least partially casted or a welded steel construction. 
   According to the present invention, an embodiment of the base structure may also comprise a supporting structure for holding a particle beam apparatus. The supporting structure may be formed at least partially as a space truss and may comprise a mounting device, e.g. a mounting ring, for mounting a particle beam apparatus, in particular a TEM. An embodiment of the supporting structure may be preferably arranged in the bedding devices mentioned above. It may have a much higher eigenfrequency than the base structure. Preferably, the supporting structure may have an eigenfrequency of greater than or equal to 80 Hz, preferably 120 Hz or preferably 140 Hz. 
   In accordance with another aspect of the present invention, a particle beam apparatus comprising a particle optical column including a particle source and particle optical components, a base structure comprising a plurality of hollow bodies, said particle optical column being suspended on said base structure. At least one of said hollow bodies has a first length extension in a first direction, a second length extension in a second direction and a third length extension in a third direction, said length extension in said first direction being larger than said length extensions in said second and third directions, and wherein a cross section of said at least one of said hollow bodies perpendicular to said first direction is substantially triangular. 
   In accordance with another aspect of the present invention is a particle beam apparatus comprising a particle optical column including a particle source and particle optical components and a base structure comprising a plurality of hollow bodies. The particle optical column has a centre of gravity and is suspended on said base structure with a suspension center near or above said center of gravity of the particle optical column. 
   In accordance with yet another aspect of the present invention is an arrangement for holding a particle beam apparatus, in particular a transmission electron microscope, comprising a base structure. The base structure has four footings, wherein one of said footings being moveable with respect to said base structure, and wherein a movement of said one of said footings is force loaded. 
   The movable footing may comprise a brake by which a movement of the footing with respect to the base structure can be blocked. 
   The footings may be arranged at the base structure at attachment regions. The base structure has values of stiffness in the attachment regions. The at least one of the footings which is moveable with respect to said base structure may be attached to said base structure at one of said attachment regions in which said base structure has the lowest value of stiffness. 
   In accordance with another aspect of the invention is a particle beam apparatus holding arrangement for holding a particle beam apparatus, in particular a TEM, comprising an arrangement, in particular a base structure, having at least one of the features mentioned above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Features and advantages of the present invention will become more apparent from the following detailed description of exemplary embodiments thereof taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a schematic view of a first embodiment of an arrangement for holding a transmission electron microscope according to the present invention with a TEM mounted in the arrangement; 
       FIG. 2  is a schematic view of the arrangement of  FIG. 1 , seen inclined from the front side; 
       FIG. 3  is a schematic view of the base structure of the arrangement of  FIG. 1 , seen inclined from the back side; and 
       FIG. 4  is a schematic top view of the base structure of the arrangement of FIG.  1  and 
       FIG. 5  is a schematic view of the cross section of a hollowed body of a base structure. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The invention as now described refers to an arrangement for holding a TEM by way of example only. It should be noted that the invention also refers to any other arrangement for holding devices, particularly particle beam apparatus. 
   Referring to  FIG. 1 , shown is a first embodiment of an arrangement  1  for holding a TEM  5  comprises a base structure  7  with a base element  2  and a support element  3 . The arrangement further comprises a supporting structure  4 . 
   The TEM  5  is mounted in the supporting structure  4  and comprises a column  6  which is suspended freely on the supporting structure  4  into an interior space which is surrounded at least partially by the support element  3 . This construction of the base structure  7  will now be explained in more detail by reference to  FIGS. 2  to  4 . The grey lines shown in  FIG. 4  are hidden lines. 
     FIGS. 2 and 3  are schematic views from the front and back of the arrangement  1 , respectively. The TEM  5  is not shown in  FIGS. 2 and 3  for reasons of clarity. 
   As mentioned above, the base structure  7  comprises the support element  3  and the base element  2 . The base element  2  has a hollow body formed by a front wall  21 , a back wall  24 , a top wall  22 , side walls and a bottom wall, which is not shown in the Figures. In  FIG. 2  only side walls  22  and  23  are provided with reference numbers for reasons of clarity. The side wall  23  of the base element  2  is formed by a side wall of a side element  50  which is arranged at the side of the base element  2 . The side wall of the base element  2  opposite to the side wall  23  is constructed accordingly. 
   In front of the base element  2 , arms  8  and  9  are arranged extending from the base element  2 . The arms  8  and  9  also have a hollow body formed by side walls, a front wall, a bottom wall, a top wall and a back wall. For the arm  8 , this is now explained in more detail and is shown in  FIG. 2  to  4 . The arm  8  comprises a front wall  80  as well as side walls  81  to  83 . It also comprises a side wall which is a bottom wall (not shown) and a side wall which is a top wall. The front wall  80  forms an end arranged opposite to the base element  2 . The sidewall  82  projects into the base element  2  and is mounted at the back wall  24  of the base element  2 . The side wall  81  of the arm  8  is formed by the side wall  30  of the support element  3 . The construction of arm  9  is substantially identical with the construction of arm  8 . Only differences relating to symmetry are given. 
   There is a space  10  between the arms  8  and  9  which extends from the ends  80  and  90  of the arms  8  and  9  to the front wall  21  of the base element  2 . The distance between the arms  8  and  9  decreases from the ends  80  and  90  in the direction of the front wall  21  of the base element  2 . The arms  8  and  9  substantially form, together with the base element  2 , a U-like structure. 
   The base element  2  as well as the arms  8  and  9  have footings  11  to  14 . The footings  1   1  and  14  are arranged in the area of the ends  80  and  90  of the arms  8  and  9 . The footings provide contact with a building&#39;s floor on which the arrangement  1  is placed. 
   As mentioned above, the base structure  7  comprises four footings  11  to  14 . Due to the four footings  11  to  14 , the base structure  7  is statically over defined. However, this provides a large footprint for the base structure  7  and the space  10 , which enables the access of the operator to the TEM. For providing load compensation, the footing  14  is spring mounted, resulting in a statically well defined situation for the remaining three footings  11  to  13 . The additional force transferred by the footing  14  is determined by the spring characteristics and the compression of the spring. After the mounting of the arrangement  1  and the TEM  5 , the position of the spring mounted footing  14  is blocked by a brake. The load distribution between the four footings is represented by the deformation of the base structure  7  under the load of itself and of the TEM  5 . This deformation does not change during the blockage of the spring mounted footing  14 . Thus the load distribution remains constant. The blockage is realised in a very stiff way, e.g. by clamping. Taking the stiffness of the ground into account, the lowest eigenfrequency of the base structure is strongly improved due to the stiff connection to the ground by all four footings. In the embodiment of  FIG. 1  to  4  wedge shoes are used for the footings  11  to  13  as adjustable footings with very high stiffness. Every footing uses a calotte (not shown) in order to enable a stiff connection to the ground. The operation of the spring might be adjustable. Alternatively, the spring characteristics may be calculated and chosen regarding the specific requirements given by the load distribution and the desired tolerance range for the mounting. By the same technique it is also possible to reach a large footprint and a statically well defined situation with a stiff connection to the ground with five or more footings. 
   Referring again to  FIG. 2  to  4 , the support element  3  will now be described in more detail. The support element  3  is arranged substantially above the base element  2  and the arms  8  and  9 . The support element  3  comprises side walls  30  and  31  turning to side walls  32  and  33  of the support element  3 , respectively. The side walls  30 ,  32  as well as the side walls  31 ,  33  are integrated. Alternatively, they are formed by separate wall pieces connected to each other, for example by a bolt connection. The side walls  30  to  33  comprise side surfaces extending in a curve substantially from the ends  80  and  90  of the arms  8  and  9  to a connecting area  34 , where side walls  32  and  33  are adjacent to each other and are integrated with each other. 
   The support element  3  also comprises an upper side  35  having an opening  36 . The column  6  of the TEM  5  (not shown in  FIG. 2  to  4 ) projects into the interior space through that opening  36 . The upper side  35  has substantially a triangular shape comprising corner areas on which bedding devices  37  to  39  are arranged for bedding the supporting structure  4 . The bedding devices  37  to  39  comprise pneumatic damping elements and are used for the hanging suspension of the TEM  5  in the base structure  7 . 
   In the connecting area  34 , a link element  52  is arranged between the side walls  32  and  33 . The link element  52  has the form of a shoulder. A bedding device  39  is arranged on the link element  52 . The link element  52  is used for stiffening the connecting area  34 . Moreover, the link element  52  comprises openings  53  and  54  for purposes of reducing weight and for easy access for mounting and service purposes. 
   Furthermore, a bracket  57  is provided. The bracket  57  extends in a curve from the connecting area  34  in the direction of the arms  8  and  9 . The bracket enhances the stiffness of the base structure  7 , especially to avoid pitching of the base structure  7  in the connecting area  34 . 
   The support element  3  also comprises a back wall  19  integrated with the back wall  24  of the base element  2 . The back wall  19  has openings  15  and which are used substantially for an easy access to the TEM  5 , for example for access to the column  6  of the TEM  5  or to a vacuum system associated with the TEM  5 . 
   As mentioned above, side elements  50  and  51  are arranged at the side of the base element  2  in the back area of the base structure  7 . The side elements  50  and  51  have substantially triangular shapes (as seen in FIG.  4 ). The side walls of the side elements are formed partially from the side walls and  32  as well as the side walls  23  which are at least partially side walls of the base element  2  as mentioned above. The bedding devices  37  and  38  are arranged in the upper area of the side elements  50  and  51 . Moreover, the side walls of the side elements  50  and  51  comprise openings  17  and  18 , which, on the one hand, have the effect of reducing the weight of the base structure  7 . On the other hand, the openings  17  and  18  are used for easy access to the base structure  7  and the TEM  5  for mounting and service purposes. 
   As mentioned above, the sidewalls  30  to  33  and the bracket  57  comprise a surface extending in a curve from the ends  80  and  90  of the arms and  9  to the connecting area  34 . These sidewalls  30  to  33 , together with the space  10 , form an access opening  58  (shown in  FIG. 1 ) which gives easy access to the column  6  of the TEM  5 , in particular to the viewing glass arranged at the lower part of the column  6  (see also FIG.  1 ). 
   Referring again to  FIGS. 2 and 3 , the supporting structure  4  is described in more detail. The supporting structure  4  is formed as a stiff profile framework. It also comprises a substantially triangular shape formed substantially by the arrangement of three connecting elements  40  to  42 . Bedding devices  44  to  46  are arranged in the corner areas of the supporting structure  4 , which operate together with the support element  3 &#39;s bedding devices  37  to  39 . Furthermore, the supporting structure  4  comprises a mounting ring  43  connected to the connecting elements  40  to  42  by a rigid frame system  47 . The column  6  of the TEM  5  is fixed on the mounting ring  43  by connecting means (not shown in FIG.  2 ). 
   Each of the above mentioned walls may have a thickness of about 5 to 20 mm. (0. 197 inch to 0.787 inch). Due to the hollow body shape and the substantially triangular shape of most components of the base structure  7 , a very stiff structure is provided with a very good eigenfrequency. It has been found that the complete base structure  7 —including, as far as present, the base element  2 , the support element  3 , the arms  8  and  9 , the side elements  50  and  51  and the link element—has a eigenfrequency preferably above 80 Hz. The eigenfrequency of the supporting structure  4  is preferably above 140 Hz. The eigenfrequencies of above-mentioned damping elements is below 3 Hz, preferably in the area of 1.8 Hz or lower in the lateral as well as in the vertical direction. The eigenfrequency of the column  6  of the TEM  5  is in the area of over 100 Hz. 
   With this arrangement, one can expect minimized excitation of the eigenmodes of the column  6  which is obtained by optimized isolation of the column  6  from floor vibrations. The base structure  7  provides bearing points (bedding devices) which are at least 1.2 m (47.25 inches) above floor level and preferably 1.8 m (70.87 inches) or more above floor level. Therefore, an arrangement is provided which is sufficient for receiving a good resolution in the area of 1 Å or less, since an optimized isolation of the vibrations is provided. 
   The above described embodiment of the invention has hollow bodies with outer surfaces, having holes therein. The ratio between the surfaces of the holes and the surfaces of material can be strongly enlarged as long as the edges of the hollow bodies remain from material with fringes of the adjacent surfaces also from material. In the marginal case the complete arrangement can be in the form of a space truss. Also in this marginal case the trusses of the space truss form edges of hollow bodies which substantially define the stiffness of the arrangement, therefore this marginal case has to be regarded as to comprise hollow bodies in the meaning of the invention. 
     FIG. 5  shows alternative embodiments of the cross section of the components of the base structure  7 , the components having the above mentioned hollow body structure. These embodiments show that the components (hollow bodies) have at least one curved boundary.  FIG. 5  shows cross sections of components with all boundaries curved. In particular,  FIG. 5  A shows boundaries curved to the outside of the component and FIG  5   b  shows boundaries curved to the inside of the component. 
   While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is to be limited only by the following claims.