Heterojunctions of undoped solid C60 and n- or p-type-doped crystalline Si have been obtained. Current-voltage measurements show that both C60/n-Si and C60/p-Si contacts are rectifying but their directions of rectification are opposite. Thermal activation measurements at a fixed forward bias show an exponential dependence of current on the reciprocal of temperature, from which we determine the effective barrier height as 0.30 eV for C60/n-Si and 0.48 eV for C60/p-Si. Using energy-band models for heterojunctions we assign values to the positions of the conduction and valence bands of the solid C60 relative to those of crystalline Si and derive the electron affinity and band gap of solid C60 film as 3.92 eV and <1.72 eV, respectively.
The two-dimensional doping by charge "fer and/or diffusion of metal utoms into CM) has been studied by in situ elecmnic Uansport meaSurements during the deposition ofmetal-CM) ultrathin bilayers. The ~s u l t s show thal the transpon properties of these interfacial systems are significantly a l t d by such doping processes. Some useful information about the charge transfer f " metal to CM) and the electronic transport properties of the metal-doped-monolayer Cm can be obtained &er careful analysis.
Solid Cso film was @own on B p-gpe Si substnte and a rectifying Nb/Cnu/pSi Structure was prepared Capacitance-voltage (C-V) measurements showed thar for temperam above 260 K the C-V curve of the NbICodp-Si structu~ shiRed dong the voltage axis depending on biasing conditions. We analysed this effect to reveal the existence of mobile negative charges in b e CM, layer and determine the density of the mobile charges.Advances in preparation of abundant quantities of fullerene Cm [I] has stimulated a great deal of experimental work on solid CSO films [2][3][4][5][6][7][8][9][10][11][12]. Thermal s u b l i t i o n of purified C6o powder in ultra-high-vacuum conditions (UHv) has been a popular method for the CSO film growth. By use of this method we have grown solid C60 films on crystalline Si substrates and found that an Nb/c6o/p-Si structure exhibited rectifying properties due to a heterojunction formation at the interface of solid c 6 0 film and p-type Si substrate [12]. This enabled us to study the C a film properties by capacitance measurements of the Nb/C6o/p-Si structure under reversebias conditions. In this letter we report an important bias-temperature effect on the capacitance of the Nb/Cso/p-Si structure. Our results provide the first evidence for the existence of mobile negative charges in conventionally prepared c60 film.Crystalline Si(] 11) wafers of 40 Q cm resistivity were polished on the front for c 6 0 film deposition. A good ohmic contact to the back of the Si wafer was achieved by a thin AI film deposition followed by a 30 min annealing at 500°C in an N2 atmosphere. The Si wafers were dipped in an aqueous 5% HF solution immediately prior to being loaded into the uttv chamber, in order to strip off any surface oxide from the substrate. Source c 6 0 powder was prepared by the conventional AC arc method and purified by repeated liquid chromatography to achieve c60 purity of 99.9%. Evaporation of the C a powder was performed in a Balzers UMS-500 UHV system with a chamber pressure of lo-' Torr and an
By measuring tlle resistance bt sinr during the deposition of metal-& multilayer thin films on sapphire substrates at mom temperature, we find that the resistance decreases sharply when adding & on some metal layers. There are WO possible explanations: one is h e formation of a conduction layer of metal-(Sn-, Ba-, Ga-) doped Cfi: the otller is a Landing interfacial interaction bemeen the metal and Ca layers, which may result in a k i t e r mntinuous metal layer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.