turn now to the drawings and initially to figure 1 which generally depicts in block and diagrammatic form apparatus 20 which is appropriate to investigate surface structures 22 in accordance with the invention . unlike the scanning tunneling microscope as disclosed in u . s . pat . no . 4 , 343 , 993 mentioned above , the apparatus 20 does not require an isolated , ultra - high vacuum , ultra - low temperature environment for its operation . indeed , the apparatus 20 is operable at normal room temperatures and pressures , although some degree of isolation may be desirable . the sample surface structure 22 may be composed of any material , without restriction , whether the material is electrically conductive , insulative , or is semi - conductive . even surfaces of liquids can be investigated so long as they are different from the environment of the probe . furthermore , the roughness of the sample surface structure 22 can be extreme since the apparatus 20 is capable of investigating even the most irregular of surfaces . as illustrated in fig1 a probe 24 including a fine scanning tip 26 is poised only a short distance away from the sample surface structure 22 . it will be appreciated that both the structure 22 and the scanning tip 26 are drawn schematically in exaggerated size . in any suitable manner , the structure 22 and the scanning tip 26 can be moved relative to each other in three dimensions . symbolically , this is shown by three axes crossing rectangularly and designated by x , y , and z . for ease of illustration , the probe 24 , in fig1 is illustrated as being provided with a suitable drive mechanism 27 , such as one having three piezo drives , 28 , 30 , and 32 . piezo drives 28 and 30 operate in the lateral dimensions x and y . for example , they may act on the probe 24 to move the tip 26 in those directions generally parallel to the surface structure 22 . alternatively , the probe 24 may be fixed and the surface structure 22 moved relative to the scanning tip 26 . the vertical piezo drive 32 adjusts the relative positions of the surface structure 22 and scanning tip 26 in the z dimension . means for control of the probe 24 and for analyzing and indicating the investigation results are also represented schematically in fig1 . specifically , measuring equipment 34 is part of the electronic control means and is connected to the probe 24 in an appropriate fashion as well as to the piezo drives 28 , 30 , and 32 . a control system 36 is connected to the measuring equipment 34 and acts upon the vertical piezo drive 32 . the measuring equipment 34 is connected to analyzing system 38 which , in turn , is connected to suitable display means , for example , to a plotter 40 and to a display screen 42 . typically , the mechanical dimensions of the structure 22 and probe 24 , as well as their possible ranges of adjustment are extraordinarily tiny . also , the electronic control equipment must be able to operate in a precise manner and the measuring equipment must be extremely sensitive . the scanning tip 26 is typically moved above the sample surface structure 22 at a distance in the order of magnitude of about 10 angstroms to 1000 angstroms . a scanning tip 26 should not be permitted to strike against the surface structure 22 so as to avoid the possibility of damage to either element . at the same time the scanning tip 26 must not be so far removed from the surface structure 22 that the latter does not have any heat sinking capability with respect to the scanning tip 26 . turn now to fig2 which diagrammatically illustrates the construction of the scanning tip 26 . the scanning tip 26 is generally cylindrical in shape tapered down to an extreme end 44 . a central structural element 46 may be of an electrically conductive material , such as tungsten , which can be controllably produced using electro - etching or electropolishing techniques , typically on the order of 100 angstroms or less in diameter . the element 46 is electrically insulated with a thin layer of insulator or dielectric material 48 over all the regions of the structural element with the exception of a small region near the extreme end 44 . one example of the dielectric material 48 may be material sold by union carbide corporation , new york , new york under the trademark , &# 34 ; parylene - c &# 34 ;. thereupon , the structural element 46 and dielectric layer 48 are coated with a thin electrically conducting layer 50 , such as nickel which is ion beam sputtered onto the tip 26 , and resulting in a thermocouple junction 52 adjacent the extreme end 44 . when an electrical current is driven through the thermocouple junction 52 as by an emf source 54 , after a short initial period of time , the extreme end 44 of the scanning tip 26 arrives at a steady state temperature . the magnitude of the temperature depends upon the amount of thermal loading of the tip temperature caused by the surrounding environment . if the scanning tip 26 is then brought close to the surface structure 22 , the temperature of the tip would also be loaded by the presence of the surface structure . thus , as seen in fig3 a curve 56 is a plot of tip temperature versus separation distance z from the sample surface structure 22 , assuming a relatively hot tip and a relatively cold surface structure . of course , the alternate situation can be envisioned in which the tip is relatively cold and the surface structure relatively hot . the curve 56 extends from a region 58 at which a steady state temperature is achieved when the tip is remote from the surface structure 22 down to a region 60 of minimum temperature when the tip is proximate to the surface structure . it will be recognized that the conductivity of the surface structure 22 is much greater than that of the air or surrounding medium in which probe 24 is located . thus , as the scanning tip 26 is brought into closer proximity with the surface structure , more heating flux leaves the tip because it is much more conductive that is , is a much more effective heat sink , than the surrounding air . the preceding discussion assumes that the steady state temperature is greater than that of the surface structure , but in fact the steady state temperature may just as likely be less than that of the surface structure . thus , the term &# 34 ; heat source &# 34 ; is also broadly intended to include a &# 34 ; heat sink &# 34 ; should such an arrangement be desired . it will be understood that the operation of the invention is not to be limited only to the customary situation in which the surrounding environment is gaseous , whether air or otherwise , and the surface structure is solid . indeed , the invention is applicable to other situations such as where the surrounding environment and the surface structure are dissimilar liquids , or where the surrounding environment is gaseous and the surface structure is liquid . however , it will be recognized that the scanning tip 26 is not only subject to the heat sinking ability of the surface structure 22 , but is also subject to environmental temperature changes . for example , steady state temperatures which fig3 indicates as occurring in the region 58 can increase if the environmental temperature increases , or conversely , decrease if the environmental temperature decreases . however , the apparatus 20 is so designed as to be unaffected by such environmental changes . specifically , the analyzing means 38 includes suitable electronic circuitry having the ability to differentiate finite values of the curve 56 to thereby generate a curve 62 ( fig4 ) representing the rate of change of the temperature at any given distance z from the surface structure 22 . in order to obtain an output having the characteristics of the curve 62 , the scanning tip 26 is vibrated or oscillated by a small amplitude in the order of hundreds of angstroms . to this end , the scanning tip 26 is energized by a cyclic emf source 68 which causes oscillations in the piezo drive 32 . this cyclic emf source is operated at a frequency ω m . thus , as seen in fig3 if the scanning tip 26 is oscillated over a range δz in an intermediate region 64 of the curve 56 , it results in a modulation of the temperature δt 1 . by same token , for the same amplitude of vibration , δz in the region 60 , temperature modulation δt 2 is achieved , and in a region 66 intermediate the regions 58 and 64 , for the same range of vibration , a temperature modulation δt 3 is achieved . thus , it will be seen from fig3 that δt 2 is much smaller than δt 1 , while δt 3 is much larger than δt 1 . thus , the rate of temperature variation increases with increasing distance of the scanning tip 26 from the surface structure 22 . furthermore , this gradient of temperature variation does not change appreciably with temperature changes in a surrounding environment . turn now to fig5 which depicts a slightly modified construction for the probe 24 . because of the miniature size of all of the components comprising the invention , substantial efforts must be made to eliminate potential sources of noise . a superior method of achieving this end result is to modulate the heating of the tip as well as the movement imparted to the tip and to assure that the frequencies employed in these instances are different . by varying the heat at the scanning tip 26 at the frequency ω h as can be achieved with a cyclic emf source 70 , and by varying the spacing between the tip and the surface structure 22 at the frequency ω m , components of the temperature fluctuation of the tip will exist either at the frequency ω m - ω h or at the frequency ω m + ω h and can be detected by a temperature sensor which may be of the form of the thermocouple junction 52 located at the extreme end 44 of the scanning tip 26 . as seen in fig2 and 5 , the scanning tip 26 is moved laterally above the surface structure 22 in the direction of an arrow 74 at a distance in the order of magnitude of about 10 angstroms to 1000 angstroms . while the scanning tip 26 should not strike against the surface structure 22 to thereby prevent damage either to itself or to the scanning structure , it also should not be removed to such a remote position away from the surface of the surface structure that temperature variations no longer exist . the diameter or width of the extreme end 44 of the scanning tip 26 may be generally in the range of 100 angstroms to 5000 angstroms . applying known fabrication techniques , it is anticipated that the diameter or width of the extreme end 44 might eventually be less than 100 angstroms . it is noteworthy that the scanning tip 26 does not have the drawback of the scanning tunneling microscope which has only a narrow focus and does not readily accommodate rapid , severe changes in topography . that is , the scanning tip 26 can readily detect rapid and severe changes in topography by reason of its ability to sense around an arc of approximately 270 °. it will be appreciated that the vertical piezo drive 32 must be particularly accurate because , as seen in fig4 temperature variation depends heavily upon the separation distance z from the surface structure 22 . the drive mechanism 27 should not only be adjustable over small distances in all dimensions , but set positions should also be definite and reproducible . the piezo drives 28 , 30 , and 32 are capable of such operation , although other suitable drive means can be employed . the exact position of the scanning tip 26 can be determined from the values set , that is , from the voltages applied to the piezo drives . the new apparatus 20 for the investigation of surface structures not only delivers data about individual measuring points but also gives information about a whole area of a sample surface within a short time period . it operates much like a scanning microscope . the sample surface is investigated in raster lines one after the other , and the whole image is composed of the scanning lines of the scanning pattern . during the scan , the drive means of a first lateral dimension is operating for a raster line , while the drive means of the transverse other lateral dimension is kept fixed . after a lateral shift of about a line width , the next line is scanned by the first drive means and so forth . while scanning with a tip 22 poised above a sample surface structure 22 , a certain danger exists of making inadvertent contact between the tip and sample because roughness of the surface may be on the order ot magnitude of the vertical distance of the tip above the sample . such involuntary contact should be avoided . the apparatus of the invention avoids such danger automatically . the scan operation is defined in the lateral dimensions . however , the tip &# 39 ; s vertical distance is variable . the measuring method itself , or the control method , automatically keeps a correct distance between the tip and the sample surface . by continuously measuring temperature variation at the thermocouple junction 52 , the separation distance z of the tip 26 can be determined at all times from the graph in fig4 . the operation can be conducted such that the temperature variation in the tip is kept constant by fine adjustment of the tip &# 39 ; s vertical distance above the sample to follow the surface contours as the lateral scan is made . the sensed temperature signal may be used to control the vertical distance of the apparatus if temperature variation is kept constant . the apparatus is controlled during scan in a lateral dimension according to an electrical variable which is proportional to the temperature variation . a temperature variation is measured and kept constant by fine adjustment of the vertical drive in the z dimension by means of a closed loop control system . the scanning pattern is preferably a line raster whereby the area is scanned in a first lateral dimension ( x ) in straight parallel lines , one after the other . the second lateral dimension ( y ) is the other scanning parameter . the vertical distance ( dimension z ) is controlled with a feedback system in accordance with the measured variable which is proportional to the temperature variation . since the position of a piezo drive is proportional to the piezo voltage , or to the respective drive current , the drive currents of the three piezo electrical drive means represent values equivalent to the position of the tip in each dimension . generally , the coordinates are cartesian coordinates with three orthogonal axes . however , curved scanning measured and kept constant by fine adjustment of lines is also permitted , if the lines are reproducible . data analysis is made as a three dimensional representation . both lateral dimensions can easily be shown in the plotter 40 or on the display screen 42 . a suitable representation must be chosen , however , for the third dimension . one possibility is to represent the measuring values as a set or family of curves z ( x ) as a function of parameter y . another possibility is to show the z values as brightness steps at point x , y . a corresponding graphical representation may comprise points with different areas of other symbols . when the representation occurs on a screen , the brightness of the cathode ray tube may be controlled according to the values of the third dimension . the tip passes across the surface of the sample at a vertical distance such that during scan the temperature variation at the thermoelectric junction 52 is controlled to a constant value . this means that during the scanning movement , the tip is following all unevenness and roughness of the sample surface at a constant distance therefrom . the drive current of the vertical piezo drive 32 thus is a true image , or replication , of the surface structure . the image , or replication , produced by the apparatus 20 is an extremely enlarged image of the sample surface . after completing the scanning of a raster line in a first lateral dimension ( x ), the tip 26 is shifted in the transverse second lateral dimension ( y ) by about the thickness of a raster line . subsequently , another raster line is scanned parallel to that first line . by repeated lateral scanning of parallel raster lines , the whole sample surface will be scanned , line by line . in fig6 both elements 22 and 26 are diagrammatically shown much enlarged . at the sample surface , the dashed line indicates the path of the shadow of tip 26 over the surface of the sample surface structure 22 . the dotted line indicates the path of the tip itself at a distance over the surface determined by the constant temperature variation . the axis system x , y , z indicates the coordinates of the dimensions . for example , scanning may occur in the x dimension . between repeated scans , the tip is shifted in the y dimension about the thickness of a raster line in each case . fine adjustment by the vertical drive means automatically controls the z dimension position of the tip so as to maintain a constant temperature variation . the results of the scan performed by the scanning tip 26 are displayed by plotting the drive current or piezo voltages as a set of curves representing three dimensions . these measured currents or voltages correspond to the position dimensions of the fine tip 26 in three coordinate directions . for example , fig7 shows the z direction piezo voltage vz as a function of the x direction piezo voltage vx for each of a family of different y direction piezo voltages vy . the family of curves of fig7 is then a true enlarged image , or replication , of the sample surface structure . the invention is operable in a wide range of surrounding atmospheres or media , although air or the inert gases are preferred . even using such preferred atmospheres , however , it will be appreciated that at high resolution ( that is , as the scanning tip 26 is moved closer and closer to the surface structure 22 being investigated ), the distance between the tip and the surface structure actually becomes less than the mean free path of atoms or molecules of the surrounding atmosphere . as a result , the thermal conductivity of the surrounding atmosphere becomes reduced . in order to prevent this occurrence , the pressure of the surrounding atmosphere is preferably increased . this serves to reduce the mean free path of the atoms or molecules of the media and thereby maintain the previous level of thermal conductivity . the illustrations presented in fig9 and 10 are representative of the results which can be achieved when the apparatus and techniques of the invention are employed to investigate a surface structure . fig8 by way of example , depicts a profile 76 which has been obtained when the scanning tip 26 has performed an investigation of a surface structure 78 along a single line scan . a scale 80 represents a measure of 1000 angstroms in the vertical dimension and a scale 82 represents a measure of one micron in the lateral dimension . in this instance , the scanning tip has a tip diameter of approximately 1000 angstroms and the surface structure is a silicon wafer on which a 1000 angstrom thick aluminum film has been deposited . the noise level indicated by the heaviness of the line depicting the profile 76 demonstrates vertical resolution achieved by the probe 24 . furthermore , spikes 84 and 86 occurring in the profile 76 portray actual topography such as burrs which may have occurred during the deposition process . these spikes illustrate the capability of the probe 24 to resolve very small structures . for example , the half width of left hand spike 84 ( the smaller of the two spikes ) represents the lateral resolution achieved , or approximately 1000 angstroms . fig9 by way of example , depicts a profile 88 which has been obtained when the scanning tip 26 has performed an investigation of a surface structure 90 , again along a single line scan , but at different heights above the surface structure . a scale 92 represents a measure of microns in the vertical dimension and a scale 94 represents a measure of 30 microns in the lateral dimension . again , the scanning tip 26 has a tip diameter of approximately 1000 angstroms . the surface structure 90 is a 7 micron photoresist insulating layer deposited on a silicon wafer . the profiles 88a - 88f represent successive scans at ever increasing heights above the surface structure 90 . it is apparent from a study of fig9 that the resolution in the lateral dimension is a function of the closeness of the tip 26 to the surface structure . resolution becomes increasingly good as the distance between the tip and the surface structure decreases and simultaneously the signal to noise ratio which represents vertical resolution increases dramatically . another embodiment of the invention is illustrated in fig1 which illustrates a modified scanning tip 96 . in this instance the scanning tip 96 , which is dimensionally similar to the scanning tip 26 , has a central structural element 98 which is of optical quality glass or plastic material with an outer layer 100 of metallic coating , for example , chromium . in a known fashion , a laser beam 102 is directed onto an extreme end of the scanning tip 96 . the laser beam impinges on the coating which serves to absorb power from the beam and supply heat into the central structural element 98 . as with the constructions illustrated in fig2 and 5 , the scanning tip 96 is also provided with a temperature sensor effective to measure the temperature of the scanning tip 96 and to communicate that temperature to the control system 36 . to this end , a second beam 104 is directed at the metallized surface at the extremity of the tip 98 . the beam 104 is then reflected off the metallized surface , as represented by an arrow 106 , and is phase modulated by the temperature variation in the tip . this phase modulation can be detected by standard interferometric techniques , preferably in a fiber optic interferometer . in all other respects , apparatus utilizing the modified scanning tip 96 for purposes of the invention would be as previously described . while the preferred embodiments of the invention have been disclosed in detail , it should be understood by those skilled in the art that various modifications may be made to the illustrated embodiments without departing from the scope as described in the specification and defined in the appended claims .