The scanning force microscope is used to deposit charge carriers on insulating Si3N4 films and to monitor their recombination. The charge decay shows up as a discontinuous staircase, demonstrating singlecarrier resolution. The decay is found to be controlled by thermionic emission.PACS numbers: 73.25.+i, 61.16.Di, 73.40.Bf, 73.50.Gr The scanning force microscope (SFM) introduced by Binnig, Quate, and Gerber' is a remarkably useful instrument to map the surface topography of virtually any solid.Most noticeably, atomic resolution has been achieved on insulating crystals. Besides the repulsive contact force used in profilometry, attractive forces like the quantum-mechanical exchange, electrostatic, and magnetic dipolar forces were utilized to measure such quantities as metallic adhesion, electric surface potential variation, and magnetic domain structures.In two recent Letters, Stern et al. and Terris er al.have demonstrated that the SFM can be used to deposit and image charges on insulators, both by contact electrification (CE) as well as by corona discharge (CD).They speculated that single carriers could be observable.In this Letter the observation of single-charge recombination events is described. Ionized particles are deposited by a short CD (10 ms) onto silicon nitride (Si3N4) films prepared by plasma-enhanced chemical-vapor deposition (PECVD) onto degenerately doped (conducting) GaAs substrates. The detected charge signal following the CD was observed to decay within a few seconds in a staircase fashion, showing the charge quantization. The experiments described were performed in air at ambient conditions. The force is detected with a diA'erential interferometer described elsewhere. Figure 1 is a schematic of the tip apex, positioned at a distance d above an insulating film of thickness h. A voltage V applied to the tungsten tip (-) v" Insulator . :=. -, -'--==: Substrate~W~~~F IG. 1. Schematic explaining the detection of the excess charge q on an insulating film via the force Fl related to the image charge q;. results in the Coulomb force F=(V+&) G, where Gcontains the tip radius R, d, and h, as well as the relative dielectric constant s of the film. The term p is the contact potential between the tip and sample. Applying an ac voltage V= J2V", sin(cot) results in two measured oscillating force terms at m and 2', with the respective rms amplitudes F~=2V PG and F2 = V J2G from which G and p can be extracted. The tip-to-sample distance d is adjusted by a controller loop so that F2 and hence G remain constant. Since V and G are both constant, any contrast in F~is due to a varying contact potential p. A charge carrier q lying on the surface of the insulator induces image charges q; and q in the tip and the substrate, respectively (Fig. 1). Since charge conservation requires q;+q =q, the magnitude of q;/q is always less than unity, increasing when the tip-sample distance d is decreased with respect to the film thickness h.The value of F I is approximately given by F I =q; E" where E, is the rms electric field ...

Hall-effect and resistivity study of the heavy-fermion system Uru2si2 Schoenes, J.; Schönenberger, C.; Franse, J.J.M.; Menovsky, A.A.

Fast image reconstruction for fluorescence microscopy AIP Advances 2, 032174 (2012) Spectrally resolved fluorescence lifetime imaging microscope using tunable bandpass filters Rev. Sci. Instrum. 83, 093705 (2012) Holographic microrefractometer Appl. Phys. Lett. 101, 091102 (2012) Foucault imaging by using non-dedicated transmission electron microscope Appl. Phys. Lett. 101, 093101 (2012) Micro optical power meter for direct in situ measurement of light transmitted from microscopic systems and focused on micro-samples Rev. Sci. Instrum. 83, 083107 (2012) Additional information on Rev. Sci. Instrum.We present a polarizing optical interferometer especially developed for force microscopy. The deflections of the force-sensing cantilever are measured by means of the phase shift of two orthogonally polarized light beams, both reflected off the cantilever. This arrangement minimizes perturbations arising from fluctuations of the optical path length. Since the measured quantity is normalized versus the reflected intensity, the system is less sensitive to intensity fluctuations of the light source. The device is especially well suited to static force measurements. The total rms noise measured is :5 0.01 A in a frequency range from 1 Hz to 20 kHz.

Ultrasmall ( S 5 nm in lateral diameter) double-barrier tunnel junctions have been realized using a scanning tunnelling microscope, and an optimized metal particle-oxide-metic substrate system. Three electrical transport effects, all in good agreement with the semi-classical theory of single-electron tunnelling, have been found at room temperature: the Coulomb gap, the Coulomb staircase and zero-bias conductance oscillations as a function of tip-particle distance.

A procedure to pattern thin metal films on a nanometer scale with a scanning tunneling microscope ͑STM͒ operating in air is reported. A 30 nm film of hydrogenated amorphous silicon ͑a-Si:H͒ is deposited on a 10 nm film of TaIr. Applying a negative voltage between the STM tip and the a-Si:H film causes the local oxidation of a-Si:H. The oxide which is formed is used as a mask to wet etch the not-oxidized a-Si:H and subsequently, the remaining pattern is transferred into the metal film by Ar ion milling. Metal wires as narrow as 40 nm have been fabricated. Since a-Si:H can be deposited in very thin layers on almost any substrate, the presented procedure can be applied to structure all kind of thin films on a nanometer scale. © 1995 American Institute of Physics.During the previous 5 years, the scanning tunneling microscope ͑STM͒ has attracted interest as a tool for lithography on a nanometer scale. [1][2][3][4][5][6][7] In scanning tunneling microscopy tip-substrate interactions are very local, making it possible to modify the surface of a substrate to a very high lateral resolution ͑Ͻ20 nm͒. Several methods to fabricate metallic nanowires using this technique, have been demonstrated. Ehrichs et al. 2 and McCord et al. 3 have used an STM induced chemical vapor deposition ͑CVD͒ process in which a metalorganic gas is decomposed between the STM tip and the substrate, depositing metal on the substrate surface. A drawback of this technique is that there is only a limited choice of metals which can be deposited, due to the number of gas precursors which are available. Alternatively, the STM can be used to expose organic resist layers. For example, McCord et al. 3 have used poly͑methylmethacrylate͒ PMMA, Marrian et al. 4 have used SAL 601 and recently Stockman et al. 5 have used a Langmuir-Blodgett film. Since these layers do not always conduct sufficiently, the STM tip can penetrate the resist during lithography which can limit the tip lifetime due to mechanical interactions between tip and layer.In this letter, we present a method to pattern a thin film on a nanometer scale with an STM operating in air, using on a conducting resist layer. The method was inspired by the work of Dagata et al. 1 who demonstrated that a hydrogen terminated silicon ͑111͒ surface can be locally oxidized with the STM. The oxide layer which is formed can act as a mask for etching the silicon, as was demonstrated by Snow et al. 6A thin film could be patterned with this method if a silicon layer which is both stable against oxidation in air and sufficiently conducting could be deposited on the metal film. Hydrogenated amorphous silicon ͑a-Si:H͒ is a material which can fulfill both requirements. It is stable against oxidation in air because of its high hydrogen content ͑Ϸ10 at. %͒.8 Thin films of a-Si:H can be highly doped, to make them electrically conducting for STM operation. In addition, with plasma enhanced chemical vapor deposition ͑PECVD͒ a layer of a-Si:H can be deposited on almost any surface at low temperature, because of the high r...

In a scanning tunneling microscope experiment, the luminescence induced by the recombination of holes with electrons tunneling into cleaved (110) GaAs/AlGaAs heterostructures is used to image the interface region with nanometer resolution.

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