Hexagonally closed packed monolayers of colloids have found more and more applications, e.g. as lithographic masks. The monolayers are usually produced with the help of a self-organizing process where a suspension of colloids is applied to the desired substrate and left to dry. This method requires a good wettability and smoothness of the substrate, which severely limits the number of possible substrates. We present a new method for the application of colloid monolayers to almost any surface where these difficulties are circumvented. At first the monolayers are fabricated on glass substrates and afterwards floated off on a water surface. From there, they are transferred to the desired substrate. Examples where transferred monolayers were used as lithographic masks are shown on glass, indium tin oxide, and tungsten diselenide. The transfer of a colloid monolayer to a copper grid for transmission electron microscopy demonstrates the applicability of the technique to curved surfaces as well.

We hnvc invcqtigntcd the Iqland growth of Au on the van dcr Mials surfaces of WS, and WSe, by STM. We show hou the STM can he uwd to 1m;rgc af well ac to rnanipult~le nm-sized crystallites on these altornically smooth non-reactive substrares. The irlandq on thc van dcr Waals planes arc tr~angular in shape and are well aligned with the suhstrate lattlce. Statisttcal analyqir of our data yield subtle differenceb rn the growth of Au on WS, comparcd la WSc,. c? 1998 Elrcv~cr Sclencc B.\I All n_chts resenred. surface! of gQlc investigations of clusters and small islands nically smooth non-reactive svbslratcs have . _ ._. . _1 increasing attention over the past several years [I-51. STM allows For directly mapping physical properties on an atomic scillc, and rhercfore it is we11 suited to the investigation of sinyle clusters, grown or deposited on a surface. Quite often, however, these investigations arc rendered in~possible because the islandc are dispFstced by the tip [5-71. In this context, havc studied the growth of gold on the van der Waals surfaces of the layered semiconductors WSe, and WS,, which n r n v i d~ ideal chemically passive semiconductor s. Evaporation of submonolayer amounts J an to cleaved surfaces leads to the on of nm-sized gold islands. We find that, -sponding author. Fax: 1+49) 7531 R83127; e-mail. armin.rettenberser@~~ni-konstanz.de depending on thc rip configuration and tunneling parameters. the STM can be used to imase as well as to manipulate the islands on these weakly interacting substrates. The analysis of our data yields information about the _erowth on the van der Waals surfaccs as well as on crystal defects snch as cleavage steps. ExperimentalFor the investiptions to be described, we used p-type WSe2 and WS2 single crystals with typical doping densities of 10'-crn-l, which were produced by chemical vapor phase transport. Fresh surfaces were prepared by cleaving in UHV, which produces atomically flat areas of several pm2. Occasionally, defects such as monolayer steps can be ohservecl.After cleavage, Au was evaporated from a resistively heated tungsten boat with rates of 0039-6028'98'S19 O1) C 1998 Elsevier Science R V. All rights reservcil PFI: $0039-6028(97)00961-tE

We present a method for the controlled fabrication of stable nanostructures under ambient conditions. The surfaces under consideration, WSe 2 , are imaged by an atomic force microscope. By applying a voltage between the tip and the sample, we can control an etching process at the surface: different voltage thresholds for the creation and the growth of structures of one monolayer ͑Se-W-Se͒ depth are observed. Our measurements on p-doped WSe 2 strongly support an electrochemical corrosion reaction in a physisorbed water film. This method allows the in situ preparation and characterization of individual nanometer-sized structures on WSe 2 and other metal dichalcogenides.

An atomic force microscope (AFM) was utilized as a Kelvin probe to determine work functions of several metals and semiconductors quantitarively. Most of the experimental data show excellent agreement with published values measured by photoemission. Variations in work functions as low as 5 mV could be detectcd with a typical lateral resolution of 20 nm. This method allowed us to analyze and explain thc energetics of an electrochemical reaction on the surface of WSe2, which could be in situ induced and con&olled by an externally applied voltage between AFM tip and sample. Thus it could be exploited for etchng nanosfructwes.

Abstract. We used a quartz tuning fork vibrating at 30 kHz both as an acoustic near field microscope and at the same time as a microscopic Kelvin probe. One leg of the tuning fork carried a small gold electrode serving as a conducting vibrating tip. By using this instrument and the method described here it is possible to measure simultaneously both the surface topography of the sample surface and the contact potential between tip and sample. The topography is observed by operating the instrument as an acoustic near field microscope. The contact potential between the vibrating tip and the sample gives rise to a displacement current which is used here for the determination of the contact potential. In first applications of this method we demonstrate that the contact potential can be measured with a sensitivity of at least 100 mV and a local resolution of about 5 m. It seems possible to use the microscopic method described here also for investigating local potentials at low temperatures and even in high magnetic fields. For example, the microscopic study of the Hall voltages in the quantum Hall effect might be an interesting application.