A two-stage Ar-ion sputter deposition of Ag/Au on mica, followed by sample immersion into a dilute halide solution (chloride, bromide, and iodide), allows preparation of highly planar Ag(111) films covered with a halide monolayer, a useful model system for the silver halide surface. The monolayer structures and properties have been analyzed by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) methods. The XPS data indicate that an oxide monolayer on the as-grown but air-exposed Ag(111) film is substitutionally replaced in 1:1 atomic ratio by a halide monolayer that closely simulates the ionicity of the bulk silver halide. Some substantial change in the substrate work function caused by the ionic adlayer is also addressed in connection to the STM imaging mechanism. The results of our in-air STM imaging markedly differ from those recently reported for similar halogen adlayers on Ag(111). Atomically resolved images became increasingly more difficult to obtain in the order of decreasing stability in air from iodide to chloride, but the resolved atomic arrangements invariably suggest a slightly contracted root 3 x root/3 structure with an estimated interatomic spacing 4.6 +/- 0.4 Angstrom. Static and dynamic disorders in this structure, more likely to occur with decreasing size of halide anion, may also be included in the factors that influence the probability of successful imaging. Furthermore, atomically resolved images could be obtained on both positively and negatively biased samples with respect to the tip. The relevant imaging mechanism probably involves some significant variations in the local electric potential on Ag(111) covered with a halide monolayer. Such local potentials may be better sensed by a W tip with its smaller work function than that of Ag(111).