Franz J. Giessibl achieved atomic resolution imaging of the silicon (111)-(7×7) surface using atomic force microscopy (AFM) under ultrahigh vacuum (UHV) conditions. The challenge lies in the strong interaction forces between the AFM tip and reactive surfaces. Giessibl developed a force detection scheme using a modified cantilever beam and frequency modulation to sense the force gradient. The AFM image showed atomic resolution with 6 angstroms lateral and 0.1 angstrom vertical resolution. The AFM's ability to achieve atomic resolution is more challenging than the scanning tunneling microscope (STM) due to the complexity of tip-sample forces and the difficulty in measuring nanonewton-range forces. Initial AFM images in vacuum showed periodic NaCl(001) lattices but lacked singularities like defects. Contact mode AFM was used in ambient conditions but was problematic in UHV due to surface sticking. Noncontact mode AFM, using a frequency modulation method, allowed imaging without direct contact, reducing chemical bonding risks. Giessibl used a combined STM and AFM system (AutoProbe VP) in UHV to image the Si(111)-(7×7) surface. The AFM used a Piezolever (PL) with a high eigenfrequency and a conductive channel, enabling precise force detection. The PL's eigenfrequency was around 120 kHz, and the frequency shift was used to map the force gradient. The image showed 12 protrusions per unit cell, likely corresponding to dangling bonds in the adatom layer. The AFM image of the Si(111)-(7×7) surface showed a high signal-to-noise ratio and atomic-scale details. The image revealed a 7×7 unit cell structure with cornerholes and adatoms. The AFM's noncontact method avoided mechanical contact, reducing contamination and maintaining resolution. The image compared well with STM images, showing similar structures but with different depth measurements. The AFM's noncontact method offered advantages over contact AFM, including higher eigenfrequency, reduced 1/f noise, and sensitivity to force gradients rather than force magnitude. These benefits enabled high-resolution imaging at small interaction forces. The study demonstrated the feasibility of achieving atomic resolution on reactive surfaces using AFM, with potential for larger area imaging in the future. The results highlight the importance of understanding the signal variation with distance for scanning probe techniques, emphasizing the role of force gradients in achieving high-resolution imaging.Franz J. Giessibl achieved atomic resolution imaging of the silicon (111)-(7×7) surface using atomic force microscopy (AFM) under ultrahigh vacuum (UHV) conditions. The challenge lies in the strong interaction forces between the AFM tip and reactive surfaces. Giessibl developed a force detection scheme using a modified cantilever beam and frequency modulation to sense the force gradient. The AFM image showed atomic resolution with 6 angstroms lateral and 0.1 angstrom vertical resolution. The AFM's ability to achieve atomic resolution is more challenging than the scanning tunneling microscope (STM) due to the complexity of tip-sample forces and the difficulty in measuring nanonewton-range forces. Initial AFM images in vacuum showed periodic NaCl(001) lattices but lacked singularities like defects. Contact mode AFM was used in ambient conditions but was problematic in UHV due to surface sticking. Noncontact mode AFM, using a frequency modulation method, allowed imaging without direct contact, reducing chemical bonding risks. Giessibl used a combined STM and AFM system (AutoProbe VP) in UHV to image the Si(111)-(7×7) surface. The AFM used a Piezolever (PL) with a high eigenfrequency and a conductive channel, enabling precise force detection. The PL's eigenfrequency was around 120 kHz, and the frequency shift was used to map the force gradient. The image showed 12 protrusions per unit cell, likely corresponding to dangling bonds in the adatom layer. The AFM image of the Si(111)-(7×7) surface showed a high signal-to-noise ratio and atomic-scale details. The image revealed a 7×7 unit cell structure with cornerholes and adatoms. The AFM's noncontact method avoided mechanical contact, reducing contamination and maintaining resolution. The image compared well with STM images, showing similar structures but with different depth measurements. The AFM's noncontact method offered advantages over contact AFM, including higher eigenfrequency, reduced 1/f noise, and sensitivity to force gradients rather than force magnitude. These benefits enabled high-resolution imaging at small interaction forces. The study demonstrated the feasibility of achieving atomic resolution on reactive surfaces using AFM, with potential for larger area imaging in the future. The results highlight the importance of understanding the signal variation with distance for scanning probe techniques, emphasizing the role of force gradients in achieving high-resolution imaging.