the figures show only an extraction region of an ion column assembly . in addition , where shown , the source is placed at the top of the drawing , and the beam points downward toward the work piece . it should be understood in practice the beam can point in any direction . fig2 – 9 illustrate a first group of embodiments of the invention wherein sputtered material is inhibited from reaching the source by directing the sputter flux away from the source . fig1 – 16 illustrate a second group of embodiments wherein sputtered material is captured thereby inhibiting sputtered material from reaching the source . fig1 – 20 illustrate a third group of embodiments wherein a microscopically textured or forested surface is used to inhibit sputter from reaching the ion source . it will be understood that other geometric shapes or combinations of shapes can be used , and elements from any one group of embodiments can be mixed with elements from the same or other groups of embodiments , and any combination of each of the embodiments illustrated can be combined for great advantage while keeping within the spirit of the invention . fig2 is a cross - sectional view showing the extraction region of an ion column assembly according to a first embodiment of the invention generally identified by reference numeral 50 wherein the shield and the bottom wall of the extraction electrode are made integrally as one piece identified in this example as the extraction electrode 52 . the extraction electrode 52 accelerates the ions in a direction toward the work piece . as the ion flux leaves the source 53 the ions spread out into an emission cone 56 . only the centermost portion of the emission cone 56 reaches a beam defining aperture 54 . in this example of the invention the beam defining aperture 54 is made as a separate piece fit into the bottom of the extraction electrode 52 , and held in place by a suitable means such as detent 51 . a small portion of the beam passes through bore 55 and an even smaller portion passes through a hole 57 defined in the center of the beam defining aperture 54 . a majority portion of the emission cone 56 strikes the angled surface 58 . material knocked free by the beam is harmlessly sputtered in a direction away from the source 53 . an illustrative path of an incident ion is shown by arrow 60 . sputtered material is shown leaving the angled surface 58 in direction 62 where direction 62 is normal to the angled surface 58 . fig3 is a cross - sectional view showing a second embodiment according the invention wherein the extraction electrode 52 has an angled surface 58 forming a cone . a beam defining aperture 54 is mounted near the apex of the cone in line with a bore 59 defined along the axis of the cone . an illustrative path of an incident ion 60 causes material to sputter in direction 62 , away from the source 53 . fig4 is a cross - sectional view showing a third embodiment according to the invention wherein the shield 63 is separate from the extraction electrode 64 . the shield has an angled surface 65 which when impacted by ions within the emission cone 56 deflects sputtered material in direction 66 . fig5 is a cross - sectional view illustrating the invention , as a forth embodiment similar to the first and second embodiment shown in fig2 and 3 , wherein the shield and the extraction electrode are made integrally . the integral extraction electrode 67 has angled surfaces 68 pointing inwardly . again an illustrative path of an incident ion is shown by arrow 69 . sputtered material is shown to be ejected from the angled surface 68 in direction 70 inhibiting it from reaching the source 53 . fig6 is a cross - sectional view showing a fifth embodiment similar to fig2 , 3 and 5 in that the shield is made integral with the extraction electrode , identified in this example as extraction electrode 72 . the extraction electrode in this example includes a plurality of angled surfaces 74 . here again an illustrative path of an incident ion is shown by arrow 76 , and sputtered material is shown to be ejected from one of the angled surfaces 74 in direction 78 . fig7 is a cross - sectional view showing a sixth embodiment according to the invention wherein a shield 80 has a plurality of angular surfaces 82 . here again an illustrative path of an incident ion is shown by arrow 81 , and sputtered material is shown to be ejected from one of the angled surfaces 82 in direction 83 . fig8 is a cross - sectional view showing a seventh embodiment according to the invention wherein the shield 80 and the extraction electrode 82 both include a plurality of angled surfaces 84 . here two illustrative ion beams 86 are shown impacting the angled surfaces 84 . sputtered material is shown ejected normal to the angles surfaces 84 in direction 88 . fig9 is a cross - sectional view with a portion blown up within a circle to illustrate detail . the figure shows an eighth embodiment according to the invention wherein a beam defining aperture 90 has a plurality of angled surfaces 92 . an illustrative ion beam 94 is shown striking one angled surface 92 . sputtered material is shown ejected normal to the angled surface 92 in direction 96 . fig1 begins illustrating a second group of embodiments according to a second aspect of the invention illustrating another method of inhibiting back sputtered material from impacting the ion source . a ninth embodiment is illustrated wherein a beam defining aperture is made integral with the extraction electrode 98 . the extraction electrode includes a plurality of holes or cups 100 which trap sputtered material ejected when ions impact the inside surface of the cups 100 . while the cups shown are cylindrical , the term “ cups ” is used to include any holes or depressions in the surface , regardless of shape . fig1 is a cross - sectional view showing a tenth embodiment according to the invention wherein a shield 102 defines a plurality of cups 104 arranged to trap back sputtered material released when impacted by ions from the source 53 . this embodiment also includes cups 100 defined by the extraction electrode 98 similar to those shown in fig1 . fig1 is a cross - sectional view with a portion blown up within a circle to illustrate detail . the figure shows an eleventh embodiment according to the invention wherein the beam defining aperture 106 defines a plurality of cups 108 to trap sputtered material released upon impact from ions as represented by path of an incident ion 110 . fig1 is a cross - sectional blown up view of a twelfth embodiment according to the invention . a beam defining aperture 112 defines a plurality of cups 114 which trap sputtered material as discussed . included in this embodiment is a plurality of angle surfaces 116 between each of the plurality of cups 114 . when ions strike the portion of the beam defining aperture 112 between the cups 114 the sputtered material is deflected away from the ion source . the detail also shows the bottom of the cups 114 having angled surfaces 118 which deflects sputtered material released upon being struck by an ion at the bottom of the cup . the cups in fig1 – 12 are shaped similarly to provide the same advantage . the cups can also be arranged such that their central axes are non - normal to the surface . it should be understood any angled surface such as those discussed can also define cups therein to provide both a trapping means and deflecting means according to the invention . the cups can also have a plurality of different diameters in order that performance and cost can be optimized . the walls of the cups can also be angled from the axis of the cups . fig1 , 15 and 16 are top views which illustrate a number of different ways the cups shown in fig1 – 13 can be configured . fig1 shows circular cups configured in a grid pattern . fig1 shows circular cups configured in a close packed configuration . fig1 illustrates how the cups can be configured in a honeycomb pattern . the invention can be configured with one cup being a through hole , and the beam defining aperture can be positioned within the through hole . the cups are advantageously configured to have diameter to depth aspect ratio of at least 5 : 1 and ideally a diameter to depth aspect ratio of 10 : 1 . it should be understood any suitable aspect ratio which inhibits sputtered material from reaching the source can be used without departing from the invention . fig1 is a cut - away detailed view showing an added surface contour on a beam defining aperture 120 having a plurality of surfaces 122 with normals at random angles . the figure also illustrates use of surface texturing prior to use with the ion column by pre - exposure to an ion source . the surfaces 122 can also be added by any suitable means such as by machining . fig1 shows how an ion stream has been used to form a forested surface 124 of dendrite cones 126 on a flat surface . the cones can also be created using any suitable means including pre - exposure to an ion source prior to use within the ion column . fig1 illustrates how dendrite cones 128 can be used to advantage on surfaces 130 having normals angled away from the incident beam . in this example the cones 128 are oriented normal to the surfaces 130 . the angles shown are relatively shallow but can be made to vary greatly without departing from the invention . fig2 illustrates added surface contours 132 comprising steep angles and dendrite cones 134 which are oriented toward the ion source . fig2 is a flow chart showing generically a method according to the invention wherein material caused to sputter from impact with ions accelerated from a source is inhibited from sputtering toward the source . fig2 is a flow chart showing a method according to the invention similar to fig2 wherein separate detailed steps of capturing material and deflecting material are shown as separate steps of inhibiting material from being sputtered toward the source . fig2 is a flow chart showing a method according to the invention showing steps to optimize ion column design by selectively adding and / or adjusting added surface contours and other ion column parameters according to the invention . illustrative steps include : observing the stability of the ion source ; adjusting at least one of : a the normal direction of said added surface feature , amount of pre - texturing of said added surface feature ; cup diameter of cups defined in said added surface feature ; cup location of cups defined in said added surface feature ; a cup density of cups defined in said added surface feature ; a distance from the source to an extraction cup ; a distance from the source to a bda ; a distance from the source to a source shield ; determining whether or not the stability of the ion source has improved ; repeating said adjusting step and said determining step until an optimal level of stability of the ion source has been achieved . fig2 is a flow chart showing steps involved in a method of designing an ion column optimized for a specific application . an ion column is constructed by selecting a first material having good dimensional stability and forming the material into a shape which inhibits sputtered material , released when impacted by ions from the ion source , from traveling in a direction toward the ion source ; and selecting a second material being made from a source friendly material and constructing other portions of the ion beam arrangement . a material having good dimensional stability is one which is neither too soft nor too brittle , and one which is not too porous . an example of a material with good dimensional stability is molybdenum . some embodiments of the invention provides an ion beam arrangement which inhibits back sputtered material from traveling in a direction toward the ion source . some embodiments of the invention capture back sputtered material by providing a surface defining cups proportioned to let ions enter but which prevents material freed from impact by ions from leaving the holes . some embodiments of the invention enable the distance between the source and the bda to be reduced thereby increasing column performance . in some embodiments , the invention does not require an additional shield element to be added to the particle beam column ; the surface contours can be added directly onto components such as an extractor element or a beam - defining aperture , or other optical element . if a separate shield is used , it can be spaced between other optical elements or can rest directly on another element . the invention can be applied to elements at any position in the optical column from which material can be back - sputtered . although the invention is useful in a liquid metal ion source column , it is also useful in other particle or energy beam columns , such as ion columns using other types of ion sources and electron beam columns . the invention has broad applicability and can provide many benefits as described and shown in the examples above . the embodiments will vary greatly depending upon the specific application , and not every embodiment will provide all of the benefits and meet all of the objectives that are achievable by the invention . although the present invention and its advantages have been described in detail , it should be understood that various changes , substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims . moreover , the scope of the present application is not intended to be limited to the particular embodiments of the process , machine , manufacture , composition of matter , means , methods and steps described in the specification . as one of ordinary skill in the art will readily appreciate from the disclosure of the present invention , processes , machines , manufacture , compositions of matter , means , methods , or steps , presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention . accordingly , the appended claims are intended to include within their scope such processes , machines , manufacture , compositions of matter , means , methods , or steps .