Surface Transfer Doping Research Articles

Surface Passivation and Transfer Doping of Silicon Nanowires

Surface Passivation and Transfer Doping of Silicon Nanowires

The influence of ammonia on the electrical properties of detonation nanodiamond

Detonation nanodiamonds (DNDs) are an interesting class of materials for sensing applications, but little is currently understood about their electrical properties. Here, aggregated DNDs are explored with impedance spectroscopy and are found to offer near-to-ideal dielectric characteristics, which is intriguing given their nanostructure. When exposed to ammonia, two highly conductive pathways emerge through the material; these appear to be associated with grain boundary and grain interior processes, the latter potentially due to surface transfer doping. This process is reversible given modest temperature increases suggesting DNDs may offer a solid state electrical platform for ammonia sensing applications.

Lead selenide nanocrystals decorated with fullerenes by dithiocarbamate linkage and their photoelectric response

We report on the chemical linkage of fullerenes to lead selenide (PbSe) nanocrystals by exchanging oleic acid ligands on PbSe nanocrystals with C 60-bound dithiocarbamate ligands. To improve the solubility of C 60-PbSe nanocrystals, a small-molecular-weight dithiocarbamate was used as a co-ligand in the ligand exchange reaction. The as-synthesized C 60-PbSe nanoconjugates were characterized by 1H NMR, UV–vis and transmission electron microscopy (TEM). Photoelectrochemistry (PEC) of the C 60-PbSe nanoconjugate revealed a reversed polarity of the photocurrent compared to those of C 60 and PbSe nanoparticles separately, suggesting that C 60 may serve as p-dopants to PbSe nanocrystals through the surface transfer doping process.

Electronic States of Acceptor Molecules Adsorbed on Solids and Surface Transfer Doping

Recently, the p-type doping by the adsorption of acceptor molecules on surfaces has been investigated in order to control the electronic properties of substrates. Valence and core-level photoelectron spectroscopy, X-ray absorption spectroscopy, scanning tunneling microscopy etc. have been utilized to elucidate the electronic structures and adsorbed states. In this article, recent studies on the adsorption of F4TCNQ on various surfaces are reviewed.

Chemical Bonding of Fullerene and Fluorinated Fullerene on Bare and Hydrogenated Diamond

We investigate the interface between a C(60) fullerite film, C(60)F(36), and diamond (100) by using core-level photoemission spectroscopy, cyclic voltammetry (CV), and high-resolution electron energy loss spectroscopy (HREELS). We show that C(60) can be covalently bonded to reconstructed C(100)-2x1 and that the bonded interface is sufficiently robust to exhibit characteristic C(60) redox peaks in solution. The bare diamond surface can be passivated against oxidation and hydrogenation by covalently bound C(60). However, C(60)F(36) is not as stable as C(60) and desorbs below 300 degrees C (the latter species being stable up to 500 degrees C on the diamond surface). Neither C(60) fullerite nor C(60)F(36) form reactive interfaces on the hydrogenated surface-they both desorb below 300 degrees C. The surface transfer doping process of hydrogenated diamond by C(60)F(36) is the most evident one among all the adsorbate systems studied (with a coverage-dependent band bending induced by C(60)F(36)).

Controlled hydroxylation of diamond for covalent attachment of fullerene molecules

Diamond can adopt a p-type sheet conductivity by surface transfer doping. Fullerene and fluorinated fullerene derivatives have been shown in the past to take the role as efficient surface acceptors. In order to improve the thermal stability of the sheet conductivity so obtained, we have studied the covalent attachment of C 60F 48 to a hydrogen terminated and partially hydroxylated diamond (100) surface by photoelectron spectroscopy and in situ conductivity measurements. A careful control of the hydroxylation process turned out to be crucial in order to obtain a sufficient amount of OH groups on the surface and keep the concentration of ketone, ether, and carboxyl small.

Dissociative Gas Sensing at Metal Oxide Surfaces

The low- and high-temperature gas sensing behavior of hydrogenated diamond (HD) and metal oxide (MOx) materials is compared and contrasted. We present evidence that at room temperature and above both kinds of materials are coated with a thin surface electrolyte layer in which gas molecules can be adsorbed and in which adsorbed gases may undergo electrolytic dissociation. We show that both kinds of materials respond in a very similar way when exposed to acid and base vapors and that no gas response is observed otherwise. Heating beyond 200degC removes the surface electrolyte layer from both kinds of materials. Whereas at MOx surfaces, the established combustive gas sensing effect sets in, the surface conductivity and the gas sensitivity of HD samples is lost due to the disappearance of the surface transfer doping effect.

Surface Transfer p-Type Doping of Epitaxial Graphene

Epitaxial graphene thermally grown on 6H-SiC(0001) can be p-type doped via a novel surface transfer doping scheme by modifying the surface with the electron acceptor, tetrafluoro-tetracyanoquinodimethane (F4-TCNQ). Synchrotron-based high-resolution photoemission spectroscopy reveals that electron transfer from graphene to adsorbed F4-TCNQ is responsible for the p-type doping of graphene. This novel surface transfer doping scheme by surface modification with appropriate molecular acceptors represents a simple and effective method to nondestructively dope epitaxial graphene for future nanoelectronics applications.

Surface Transfer Doping of Diamond (100) by Tetrafluoro-tetracyanoquinodimethane

Surface transfer doping is demonstrated on hydrogenated diamond (100) by the electron acceptor, tetrafluoro-tetracyanoquinodimethane (F4-TCNQ). Synchrotron-based photoemission spectroscopy reveals that electrons are transferred from diamond to adsorbed F4-TCNQ, leaving a diamond surface p-type doped with a high areal density of holes of about 1.6 × 1013 cm-2.

Surface Transfer Doping of Semiconductors

The local conductivity of semiconductors can be changed by incorporating various atoms into the semiconductor material. New work shows that manipulation of the surface can produce the same effect.

Surface conductivity induced by fullerenes on diamond: Passivation and thermal stability

The surface conductivity of hydrogen terminated diamond under atmospheric conditions is a well known phenomenon. Inspired by the surface transfer doping model [F. Maier, M. Riedel, B. Mantel, J. Ristein, L. Ley, Phys. Rev. Lett. 85, (2000) 3472] we have recently investigated thin C 60 layers as an alternative to atmospheric adsorbates. We could indeed show that C 60 induces a sub-surface accumulation layer that results in a surface conductivity comparable to the air induced one [P. Strobel, M. Riedel, J. Ristein, L. Ley, Nature 430, (2004) 439]. In the present work we investigate fluorinated fullerenes, namely C 60F 18, C 60F 36, and C 60F 48, as transfer dopants. The surface conductivity induced by fluorinated fullerenes increases with higher fluorination and achieves for C 60F 48 a level that exceeds that observed under atmospheric conditions by up to a factor of three. Furthermore, we study the thermal stability of the fullerene layers on diamond and their stabilisation by passivation with different dielectric films (SiO, CaF 2, and Si 3N 4). In the case of fluorinated fullerenes we observe a significant improvement in thermal stability after passivation with dielectrics but the pristine conductivity level cannot be kept. A different kind of stabilisation is achieved for C 60. After the simultaneous exposure to oxygen, light, and temperature of about 150 °C the surface conductivity induced by C 60 is stable up to 350 °C in vacuum with an undiminished doping efficiency. We ascribe this effect to an oxygen mediated polymerisation of the C 60 layer.

Surface transfer doping of diamond by fullerene

Fifteen years after Landstrass and Ravi [1] [I.M. Landstrass, K.V. Ravi, App. Phys. Lett, 55 (1989) 975] reported a hydrogen induced surface conductivity of diamond, it has now been established that the phenomenon is based on a sub-surface hole accumulation layer. A quantitative model for the origin of this layer has been proposed by our group earlier and is based on the charge exchange between the diamond surface and solvated ions in a water layer that forms spontaneously on all surfaces in air. The process relies on the particularly low ionization energy of the hydrogenated diamond surface [2] [F. Maier, M. Riedel, B. Mantel, J. Ristein, and L. Ley, Phys. Rev. Lett. 85 (2000) 3472]. Here, we report on fullerenes (C 60) and fluorinated fullerenes (C 60F 48) as alternative adsorbate systems. They induce surface conductivity on a level comparable (C 60) or even higher (C 60F 48) than that observed under atmospheric conditions. Whereas in the case of C 60 efficient doping requires the formation of the van-der Waals solid on top of the surface of diamond, C 60F 48 acts as surface acceptor even as isolated molecule. In both cases, the doping efficiency can be modeled by considering the electrochemical equilibrium between the diamond and the adsorbate layer.

Electrochemical Surface Transfer Doping : The Mechanism Behind the Surface Conductivity of Hydrogen-Terminated Diamond

Intrinsic diamond with a bandgap of 5.4 eV exhibits a surface conductivity (SC) of the order of when terminated by hydrogen. This conductivity is carried by a hole-accumulation layer close to the surface with an areal carrier concentration of about and it has already been utilized for a unique kind of field effect transistor [H. Kawarada, Surf. Sci. Rep., 26, 205 (1996)]. Although the microscopic doping mechanism is still under debate. Based on the results of a variety of surface-sensitive experiments we propose a new surface-transfer doping mechanism by which electron transfer from the valence band to adsorbed, hydrated ionic species at the surface creates the holes for the surface conductivity. In order to draw a complete picture of the surface conductivity concepts from surface and semiconductor physics as well as electrochemistry have to be adopted. © 2004 The Electrochemical Society. All rights reserved.

Surface Transfer Doping of Diamond.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Surface transfer doping of diamond.

The electronic properties of many materials can be controlled by introducing appropriate impurities into the bulk crystal lattice in a process known as doping. In this way, diamond (a well-known insulator) can be transformed into a semiconductor, and recent progress in thin-film diamond synthesis has sparked interest in the potential applications of semiconducting diamond. However, the high dopant activation energies (in excess of 0.36 eV) and the limitation of donor incorporation to (111) growth facets only have hampered the development of diamond-based devices. Here we report a doping mechanism for diamond, using a method that does not require the introduction of foreign atoms into the diamond lattice. Instead, C60 molecules are evaporated onto the hydrogen-terminated diamond surface, where they induce a subsurface hole accumulation and a significant rise in two-dimensional conductivity. Our observations bear a resemblance to the so-called surface conductivity of diamond seen when hydrogenated diamond surfaces are exposed to air, and support an electrochemical model in which the reduction of hydrated protons in an aqueous surface layer gives rise to a hole accumulation layer. We expect that transfer doping by C60 will open a broad vista of possible semiconductor applications for diamond.

Surface conductivity of nitrogen-doped diamond

Synthetic type Ib diamond crystals with (001) surfaces that expose growth sectors of different nitrogen content have been used to study the phenomenon of p-type surface conductivity upon plasma hydrogenation and upon overgrowth with thin epitaxial CVD diamond layers. We found that an unbiased microwave-driven hydrogen plasma leads to surface conductivity only on well-defined regions on the substrates that correlate with growth sectors of low nitrogen content; whereas no conductive layer is found on top of growth sectors with higher nitrogen concentrations in the range of 200 ppm. After growing a homoepitaxial intrinsic diamond layer of only 20 nm on top of the nitrogen doped diamond, these differences are no longer observed and surface conductivity is established homogeneously over the whole sample. The same effect can be achieved by exposing the Ib substrates to a pure hydrogen plasma provided the sample is biased with an additional DC voltage of −250 V. Both results can be understood in the framework of the surface transfer doping model suggested earlier by Maier and colleagues when the compensation of nitrogen donors by surface acceptors and their passivation by hydrogen is taken into account. The quantitative discussion shows that the doping capability of the surface acceptors is exhausted at lateral concentrations of approximately 1×1013 cm−2, which also corresponds to the maximum hole concentration usually observed in hydrogen-induced p-type conductive layers.

Simple system for temperature control and cycling in the range 4–300°K: PM Angelo et al, Rev Sci Instrum, 38, 1967, 415–419

The properties of surface conductivity (SC) of impurity-non-doped CVD diamond (001) samples were studied by various methods of sheet-resistance (RS) measurement, Hall-effect measurement, XPS, UPS, SES, SR-PES, PEEM and 1D band simulation taking into account special emphases on deriving the information about the surface band diagram (SBD). The RS values in UHV conditions were determined after no-annealing or 200 ∼ 300 °C annealing in UHV. C 1 s XPS profiles were measured in detail in bulk-sensitive and surface-sensitive modes of photoelectron detection. The energy positions of valence band top (EV) relative to the Fermi level (EF) in UHV conditions after no-annealing or 200 ∼ 300 °C annealing in UHV were determined. One of the samples was subjected to SR-PES, PEEM measurements. The SBDs were simulated by a band simulator from the determined RS and EV − EF values for three samples based on the two models of surface conductivity, namely, so-called surface transfer doping (STD) model and downward band bending with shallow acceptor (DBB/SA) model. For the DBB/SA model, there appeared downward bends of SBDs toward the surface at a depth range of ∼ 1 nm. C 1 s XPS profiles were then simulated from the simulated SBDs. Comparison of simulated C 1 s XPS profiles to the experimental ones showed that DBB/SA model reproduces the C 1 s XPS profiles properly. PEEM observation of a sample can be explained by the SBD based on the DBB/SA model. Mechanism of SC of CVD diamonds is discussed on the basis of these findings. It is suggested that the STD model combined with SBD of DBB/SA model explains the surface conductivity change due to environmental changes in actual cases of CVD diamond SC with the presence of surface EF controlling defects.