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Thin films of barium titanate (BTO) are controllably grown to produce two different memory applications: ferroelectric Schottky diodes and resistive switching cells. The entire structure and fabrication of the two cells are identical, except for a slight adjustment to the calcination temperature for the BTO films. Films calcined at 800°C were ferroelectric and were used to create the ferroelectric Schottky diode. Conversely, films calcined at 700°C displayed resistive switching behavior and were used to create memristor cells. The ferroelectric Schottky diodes showed an ON/OFF ratio of over three orders of magnitude and the resistive switching cells showed an ON/OFF ratio of nearly two orders of magnitude, though both can likely be improved through electrode optimization. The identification of the critical process parameter shows that both memory cells can be fabricated on the same die with nearly identical processes, which would reduce process complexity for creating multiple advanced memories on a single die.

Layered transition metal dichalcogenide (TMD) materials, i.e. 1T-TiSe$_2$ and 2H-NbSe$_2$, harbor a second order charge density wave (CDW) transition where phonons play a key role for the periodic modulations of conduction electron densities and associated lattice distortions. We systematically study the transport and capacitance characteristics over a wide temperature range of Schottky barriers formed by intimately contacting freshly exfoliated flakes of 1T-TiSe$_2$ and 2H-NbSe$_2$ to \textit{n}-type GaAs semiconductor substrates. The extracted temperature-dependent parameters (zero-bias barrier height, ideality and built-in potential) reflect changes at the TMD/GaAs interface induced by CDW formation for both TMD materials. The measured built-in potential reveals chemical-potential shifts relating to CDW formation. With decreasing temperature a peak in the chemical-potential shifts during CDW evolution indicates a competition between electron energy re-distributions and a combination of lattice strain energies and Coulomb interactions. These modulations of chemical potential in CDW systems, such as 1T-TiSe$_2$ and 2H-NbSe$_2$ harboring second-order phase transitions, reflect a corresponding conversion from short to long-range order.

We report on the use of bromine intercalation of graphite to perform in situ tuning of the Schottky barrier height (SBH) formed at many-layer-graphene (MLG) semiconductor interfaces. The intercalation of Br into MLG simultaneously increases interlayer separation between the graphene planes, while at the same time giving rise to an increase (decrease) in the free hole carrier density (Fermi energy) because of the transfer of electrons from carbon to bromine. The associated increase in the graphite work function results in an increase of the SBH, as manifested by lower forward/reverse current densities and higher depletion capacitances. These results are quantitatively understood within the context of the Schottky–Mott model and thermionic emission theory. The presented results have important implications for sensing and high power applications as well as the integration of carbon into semiconductors and carbon/graphene electronics.

Layered electrodes based on graphene or transition metal dichalcogenides have enriched the development of nanoelectronics due to their uniqueness in flexibility, transparency, thermal stability, and electronic structure. Here, we report on resistive switching behavior observed in graphite/Nb:SrTiO 3 (Gr/NbSTO) junctions. Straightforward in situ bromine intercalation of graphite modulates the transport properties of Gr/NbSTO devices, an effect which cannot be achieved using traditional metal electrodes. At low temperatures, the strong electric field dependence of the dielectric constant of NbSTO also plays an important role in further enhancing the resistive switching performance. Our findings here suggest that to optimize the performance and to perform more complex functions, tunability of the Fermi level of the layered graphite electrode in combination with the nonlinear dielectric constant of the NbSTO substrate is critically important for interface-type resistive switching devices.

We have used the “two-step” growth technique, quench condensing followed by an anneal, to grow ultra-thin films of silver on glass substrates. As has been seen with semiconductor substrates this process produces a metastable homogeneous covering of silver. By measuring the in situ resistance of the film during growth we are able to see that the low temperature growth onto substrates held at 100 K produces a precursor phase that is insulating until the film has been annealed. The transformation of the precursor phase into the final, metallic silver film occurs at a characteristic temperature near 150 K where the sample reconstructs. This reconstruction is accompanied by a decrease in resistance of up to 10 orders of magnitude.

Spin-dependent phenomena in ZnO may lead to devices with new or enhanced functionality, such as polarized solid-state light sources and sensitive biological and chemical sensors. In this paper, we review the experimental results on transition metal doping of ZnO and show that the material can be made with a single phase at high levels of Co incorporation (~15 at.%) and exhibits the anomalous Hall effect. ZnO is expected to be one of the most promising materials for room-temperature polarized light emission; but to date, we have been unable to detect the optical spin polarization in ZnO. The short spin relaxation time observed likely results from the Rashba effect. Possible solutions involve either cubic phase ZnO or the use of additional stressor layers to create a larger spin splitting in order to get a polarized light emission from these structures or to look at alternative semiconductors and fresh device approaches

Recent efforts on doping ZnO films for charge and spin functionality are reviewed, focusing on chemical doping for charge and spin device formation. Discussion includes the behavior of phosphorus as an acceptor and magnetism in transition metal-doped ZnO. Evidence for p-type behavior in phosphorus-doped (Zn,Mg)O grown by pulsed laser deposition is presented. The magnetic properties of ZnO co-doped with Mn and Sn are also discussed.

Optical and Hall-effect measurements have been performed on single crystals of Pb₀.₇₇Sn₀.₂₃Se, a IV-VI mixed chalcogenide. The temperature dependent (10–300 K) reflectance was measured over 40–7000 cm⁻¹ (5–870 meV) with an extension to 15,500 cm⁻¹ (1.92 eV) at room temperature. The reflectance was fit to the Drude-Lorentz model using a single Drude component and several Lorentz oscillators. The optical properties at the measured temperatures were estimated via Kramers-Kronig analysis as well as by the Drude-Lorentz fit. The carriers were p-type with the carrier density determined by Hall measurements. A signature of valence intraband transition is found in the low-energy optical spectra. It is found that the valence-conduction band transition energy as well as the free carrier effective mass reach minimum values at 100 K, suggesting temperature-driven band inversion in the material. Thus, density function theory calculation for the electronic band structure also make similar predictions.

Recent results on achieving ferromagnetism in transition-metal-doped GaN, A1N and related materials are discussed. The field of semiconductor spintronics seeks to exploit the spin of charge carrier ...

Semiconducting oxides offer the potential for exploring and understanding spin-based functionality in a semiconducting host material. Theoretical predictions suggest that carrier-mediated ferromagnetism should be favored for p-type material. Cu2O is a p-type, direct wide bandgap oxide semiconductor that may hold interest in exploring spin behavior. In this paper, the properties of Mn-doped Cu2O are described. Activities focused on understanding Mn incorporation during thin-film synthesis, as well as magnetic characterization. The epitaxial films were grown by pulsed-laser deposition. X-ray diffraction was used to determine film crystallinity and to address the formation of secondary phases. SQUID magnetometry was employed to characterize the magnetic properties. Ferromagnetism is observed in selected Mn-doped Cu2O films, but appears to be associated with Mn3O4 secondary phases. In phase-pure Mn-doped Cu2O films, no evidence for ferromagnetism is observed.

Both ion implantation and epitaxial crystal growth provide convenient methods of introducing transition metals such as Mn,Cr,Fe,Ni and Co into GaN, GaP, SiC and ZnO for creating dilute magnetic semiconductors exhibiting room temperature ferromagnetism. In this paper we review progress in wide band gap ferromagnetic semiconductors and the role of defects and doping on the resulting magnetic properties.

Existing semiconductor electronic and photonic devices utilize the charge on electrons and holes in order to perform their specific functionality such as signal processing or light emission. The relatively new field of semiconductor spintronics seeks, in addition, to exploit the spin of charge carriers in new generations of transistors, lasers and integrated magnetic sensors. The ability to control of spin injection, transport and detection leads to the potential for new classes of ultra-low power, high speed memory, logic and photonic devices. The utility of such devices depends on the availability of materials with practical (>300 K) magnetic ordering temperatures. In this paper, we summarize recent progress in dilute magnetic semiconductors (DMS) such as (Ga, Mn)N, (Ga, Mn)P, (Zn, Mn)O and (Zn, Mn)SiGeN2 exhibiting room temperature ferromagnetism, the origins of the magnetism and its potential applications in novel devices such as spin-polarized light emitters and spin field effect transistors.

Recent advances in the theory and experimental realization of ferromagnetic semiconductors give hope that a new generation of microelectronic devices based on the spin degree of freedom of the electron can be developed. This review focuses primarily on promising candidate materials (such as GaN, GaP and ZnO) in which there is already a technology base and a fairly good understanding of the basic electrical and optical properties. The introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature. There are a number of other potential dopant ions that could be employed (such as Fe, Ni, Co, Cr) as suggested by theory [see, for example, Sato and Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000)]. Growth of these ferromagnetic materials by thin film techniques, such as molecular beam epitaxy or pulsed laser deposition, provides excellent control of the dopant concentration and the ability to grow single-phase layers. T...

Structural and magnetic characteristics of Ni-implanted GaP were measured for doses in the range 3/5/10 16 cm 2 . After subsequent annealing at 700 8C, transmission electron microscopy (TEM) showed residual lattice damage which was more significant in highly carbon-doped epi layers as compared to bulk GaP substrates. The magnetization measurements showed two different contributions, one present at 5/75 K and the other below � /225 K. No secondary phase formation was detected in either type of GaP. # 2002 Elsevier Science B.V. All rights reserved.

Wet etch processing techniques for InGaAs/InAl/As/InGaAs transistors are used to fabricate an N-channel HEMT (High Electron Mobility Transistor) with Fe contacts. These processing techniques can easily be extended for dilute magnetic semiconductor regrowth and for testing of various spin injection geometries.

We report on a low temperature study of Schottky barriers between Au, Cr or Al electrodes deposited directly onto moderately-doped Si or GaAs substrates with doping densities in the range cm−3 and find the unexpected result that for temperatures 150 K both the zero-voltage Schottky barrier height, and the reciprocal ideality factor, , have linear temperature dependences that extrapolate to zero at T = 0. Accordingly, the thermionic emission equation with these modified temperature-dependent parameters gives a good description of the current–voltage (I–V) characteristics at temperatures where thermionic field emission and field emission (direct tunneling) in addition to thermionic emission are known to be important. Our analysis utilizes a barrier inhomogeneity model to show that the temperature-independent product determined from forward bias characteristics defines a flat band voltage which is shown to be equivalent to the built-in voltage separately determined by extrapolation of capacitance versus voltage measurements made in the reverse bias region.

Ion implantation of Mn or Cr at concentrations of 1–5 at. % were performed in AlxGa1−xP (x=0.24,0.38) epilayers grown by gas source molecular beam epitaxy. Ferromagnetic-like ordering above 100 K for Cr and 300 K for Mn was observed in superconducting quantum interference device measurements. Structural characterization revealed no second phases that could influence the measured magnetic properties. As the AIP mole fraction in the AlxGa1−xP layers increased, the magnetic ordering temperatures were generally observed to increase, while the calculated magnetic moment decreased. Mn appears to be a more promising choice than Cr for high temperature ferromagnetism in AlGaP.

We demonstrate single layer graphene/n-Si Schottky junction solar cells that under AM1.5 illumination exhibit a power conversion efficiency (PCE) of 8.6%. This performance, achieved by doping the graphene with bis(trifluoromethanesulfonyl)amide, exceeds the native(undoped) device performance by a factor of 4.5 and the best previously reported PCE in similar devices by a factor of nearly 6. Current-voltage, capacitance-voltage and external quantum efficiency measurements show the enhancement to be due to the doping induced shift in the graphene chemical potential which increases the graphene carrier density (decreasing the cell series resistance) and increases the built-in potential., 14 pages, 5 figures

Thin-film multilayer structures with up to 20 repeat layers have been grown in a high-vacuum chamber by sequential deposition of aluminum (Al) and fullerene (${\mathrm{C}}_{60}$) onto room-temperature substrates. The periodicity of the layers is confirmed by x-ray-diffraction and in situ resistance measurements. The presence of underlying layers of ${\mathrm{C}}_{60}$ reduces the critical thickness at which Al becomes conducting from \ensuremath{\sim}35 to \ensuremath{\sim}20 \AA{}. In addition, there is a sudden increase in resistance that occurs when each Al layer is covered by a monolayer of ${\mathrm{C}}_{60}$. These observations, together with the measurement of a downward shift in frequency of a considerably broadened Raman-active ${\mathit{A}}_{\mathit{g}}$(2) pentagonal-pinch mode, imply that up to six electrons per ${\mathrm{C}}_{60}$ are transferred from the Al to the ${\mathrm{C}}_{60}$ layer. This demonstration of charge transfer across planar metal-${\mathrm{C}}_{60}$ interfaces suggests that multilayers may be a useful vehicle for forming fullerene interface compounds in two-dimensional structures.

We report on the p doping of graphene with the polymer TFSA ((CF(3)SO(2))(2)NH). Modification of graphene with TFSA decreases the graphene sheet resistance by 70%. Through such modification, we report sheet resistance values as low as 129 Ω, thus attaining values comparable to those of indium-tin oxide (ITO), while displaying superior environmental stability and preserving electrical properties over extended time scales. Electrical transport measurements reveal that, after doping, the carrier density of holes increases, consistent with the acceptor nature of TFSA, and the mobility decreases due to enhanced short-range scattering. The Drude formula predicts that competition between these two effects yields an overall increase in conductivity. We confirm changes in the carrier density and Fermi level of graphene through changes in the Raman G and 2D peak positions. Doped graphene samples display high transmittance in the visible and near-infrared spectrum, preserving graphene's optical properties without any significant reduction in transparency, and are therefore superior to ITO films in the near infrared. The presented results allow integration of doped graphene sheets into optoelectronics, solar cells, and thermoelectric solar cells as well as engineering of the electrical characteristics of various devices by tuning the Fermi level of graphene.

We demonstrate the formation of semimetal graphite/semiconductor Schottky barriers where the semiconductor is either silicon (Si), gallium arsenide (GaAs) or 4H-silicon carbide (4H-SiC). Near room temperature, the forward-bias diode characteristics are well described by thermionic emission, and the extracted barrier heights, which are confirmed by capacitance voltage measurements, roughly follow the Schottky-Mott relation. Since the outermost layer of the graphite electrode is a single graphene sheet, we expect that graphene/semiconductor barriers will manifest similar behavior., Comment: 5 pages, 3 figures, 1 table

The resolution of electrostatic force microscopy (EFM) is enhanced when multiwalled carbon nanotubes are used as extensions on conventional silicon cantilevers. Multiwalled nanotubes provide robust, high aspect ratio, conducting tips that minimize topographic dependence of gradients in the capacitance between the tip/cantilever and the substrate. Comparison of simultaneously acquired topographical and EFM images taken at the intersection of overlapping electrodes of electrically biased Al–Al2O3–Al tunnel junctions confirm the improved performance. This enhancement enables us to determine the surface contact potential differences between individual nanotubes within a bundle with resolutions of 5 mV and 10 nm.

The ultrafast non‐linear optical dynamics of C60 thin films were investigated at low excitation levels. The pump‐probe response observed at low power is found to differ significantly from the ultrafast non‐exponential behavior observed at higher intensity. It is determined that the ultrafast relaxation processes measured at higher fluence levels are affected by phototransformation of C60.

When high quality bismuth or graphite crystals are placed in a magnetic field directed along the c-axis (trigonal axis for bismuth) and the temperature is lowered, the resistance increases as it does in an insulator but then saturates. We show that the combination of unusual features specific to semimetals, i.e., low carrier density, small effective mass, high purity, and an equal number of electrons and holes (compensation), gives rise to a unique ordering and spacing of three characteristic energy scales, which not only is specific to semimetals but which concomitantly provides a wide window for the observation of apparent field induced metal-insulator behavior. Using magnetotransport and Hall measurements, the details of this unusual behavior are captured with a conventional multi-band model, thus confirming the occupation by semimetals of a unique niche between conventional metals and semiconductors., 4 pages, 4 figs, data and discussion on bismuth added, final published version

N‐channel field effect transistors with excellent device characteristics have been fabricated by utilizing C60 as the active element. Measurements on C60 thin films in ultrahigh vacuum show on‐off ratios as high as 106 and field effect mobilities up to 0.08 cm2/V s.

In recent years, significant interest has emerged in the synthesis of magnetically-doped semiconductors. For computing, these materials provide a venue to exploit spin for computation. Direct bandgap spin-doped semiconductors are potential sources for polarized optical emission. In addition, quantum-entangled spins have been proposed as mediators in photon-based quantum communication schemes. In this paper, we discuss the properties of spin-doped ZnO. Mn-doped ZnO demonstrates ferromagnetism at relatively high temperatures as evidenced in hysteretic behavior in the magnetic flux versus field behavior. Transition metal doping was explored via ion implantation. Investigations of group V doping for p-type conduction are also discussed.

Epitaxial growth of the ferromagnetic semiconductors GaMnP:C and GaMnN has been investigated by Gas Source Molecular Beam Epitaxy (GSMBE). GaMnP:C films grown with 9.4% Mn are found to be p-type with hysteretic behavior to room temperature. GaMnN films grown at 700 °C with 2.8% Mn show hysteresis at 300 K, while temperature-dependent magnetization measurements indicate that the magnetism may persist to much higher temperatures (> 325 K). Samples of AlGaMnN have also been prepared for the first time that show improved surface morphology compared to GaMnN but which show only paramagnetic behavior.

THE recent syntheses1,2 of macroscopic quantities of C60 have suggested possible applications in host–guest and organic chemistry, tribology, electrochemistry and semiconductor tech-nology. Here we report the preparation of alkali-metal-doped films of C60 and C70 which have electrical conductivities at room temperature that are comparable to those attained by n-type doped polyacetylene. The highest conductivities observed in the doped films are: 4Scm−1 (Cs/C60), 100 (Rb/C60), 500 (K/C60), 20 (Na/C60), 10 (Li/C60), 2 (K/C70). The doping process is reversed on exposure of the films to the atmosphere. At high doping levels, the films become more resistive. We attribute the conductivity induced in these films to the formation of energy bands from the π orbitals of C60 or C70, which become partially filled with carriers on doping. The smaller alkali metal ions should be able to fit into the interstices in the lattice without disrupting the network of contacts between the carbon spheroids. In the case of C60, this would allow the development of an isotropic band structure, and we therefore propose that these materials may constitute the first three-dimensional 'organic' conductors.

We present a technique for resolving multiple spatial components of the remanent polarization vectors in thin film ferroelectrics. Using complementary electrode configurations of surface and embedded interdigital microelectrode arrays, both the in-plane and out-of-plane polarizations were measured independently. As a result, we found that the ferroelectric polarization vector was 16% larger than what typical measurement geometries would report. The spatial sensitivity exhibited by the method presented here is crucial to identifying novel coupling mechanisms which lead to modified ferroelectric polarization vector components.

We investigate the electronic transport properties across the pentacene/graphene interface. Current transport across the pentacene/graphene interface is found to be strikingly different from transport across pentacene/HOPG and pentacene/Cu interfaces. At low voltages, diodes using graphene as a bottom electrode display Poole–Frenkel emission, while diodes with HOPG and Cu electrodes are dominated by thermionic emission. At high voltages conduction is dominated by Poole–Frenkel emission for all three junctions. We propose that current across these interfaces can be accurately modeled by a combination of thermionic and Poole–Frenkel emission. Results presented not only suggest that graphene provides low resistive contacts to pentacene where a flat-laying orientation of pentacene and transparent metal electrodes are desired but also provides further understanding of the physics at the organic semiconductor/graphene interface.

A technique is presented to selectively graphitize regions of SiC by ion implantation and pulsed laser annealing (PLA). Nanoscale features are patterned over large areas by multi-ion beam lithography and subsequently converted to few-layer graphene via PLA in air. Graphitization occurs only where ions have been implanted and without elevating the temperature of the surrounding substrate. Samples were characterized using Raman spectroscopy, ion scattering/channeling, SEM, and AFM, from which the degree of graphitization was determined to vary with implantation species, damage and dose, laser fluence, and pulsing. Contrasting growth regimes and graphitization mechanisms during PLA are discussed.

As developed by Senturia and co-workers [1], microdielectrometry is a technique for measuring complex permittivity utilizing microfabrication technology to incorporate both the interdigital sensing electrodes and associated circuitry on the same microchip. By covering a microdielectrometer chip with a thin layer of C60, it is possible to dynamically monitor the film's frequency response and dielectric properties as a function of doping with selected gases and other species.It is known that solid C60 has a substantial amount of interstitial volume. The presence of mobile ions in these spaces compromises the breakdown voltage and makes pure C60 unsuitable for applications requiring high-quality dielectric films. However, various immobile ions or neutral species (e.g. oxygen) can be made to fill the interstitial volume, changing the characteristics of the C60 films and, in some cases, improving the dielectric properties. In-situ microdielectric measurements of pristine and modified C60 films were performed for frequencies ranging from 0.005 Hz to 100 kHz. Based on the low-frequency behavior of the dielectric constant, a model is proposed for the mechanism of oxygen diffusion into the interstitial spaces of the fullerene material.

Rectification and thermal stability of diodes formed at graphene/GaN interfaces have been investigated using Raman Spectroscopy and temperature-dependent current-voltage measurements. The Schottky barriers formed between GaN and mechanically transferred graphene display rectification that is preserved up to 550 K with the diodes eventually becoming non-rectifying above 650 K. Upon cooling, the diodes show excellent recovery with improved rectification. We attribute these effects to the thermal stability of graphene, which acts like an impenetrable barrier to the diffusion of contaminants across the interface, and to changes in the interface band alignment associated with thermally induced dedoping of graphene.

Infrared-absorption studies of thin fullerene films as a function of temperature reveal a splitting of an absorption line at 245±3 K. Another absorption line narrows and its frequency shifts without splitting. These observations support earlier neutron- and x-ray-diffraction findings of an orientational phase transformation at 250 K in bulk samples. We provide an explanation based on an accepted crystal structure of C 60

The authors show that ionic liquids are well suited to specialized electric field gating applications in which large surface charge densities can be induced on the surfaces of low-carrier density thin-film metals. Using either coplanar or overlay gate configurations, they demonstrate field-induced resistance changes on the order of a factor of 104 for thin conducting InOx films. The areal capacitances and field effect mobilities noticeably exceed those that can be achieved using AlOx dielectrics. In addition, the charge state can be frozen in by reducing the temperature, thus providing an opportunity for electric field tuning of metal-insulator transitions in a variety of thin-film systems.

The discovery of epitaxially grown ferromagnetic, type III–V semiconductors (Ga,Mn)As (Tc=110 K) and (In,Mn)As (Tc=35 K) holds promise for developing semiconductor electronics that utilize the electron’s spin degree of freedom in addition to its charge. It has been theoretically predicted that some semiconducting systems could be ferromagnetic above room temperature, when optimally doped (p-GaN with 5% Mn). We report here on the use of ion implantation to incorporate magnetic ions into a variety of semiconducting substrates, thereby facilitating investigation of the nature of ferromagnetism in semiconducting systems that are difficult to grow with other methods. The magnetic ions, Mn, Fe, and Ni, were implanted into each of the epitaxially grown semiconductors GaN, GaP, and SiC to achieve volume concentrations between 1 and 5 at. %. The implanted samples were subsequently annealed at 700–1000 °C to recrystallize the samples and remove implant damage. The implanted samples were examined with both x-ray dif...

Trilayer structures, comprising a thin-film In/InO x superconductor separated from an Al gate electrode by an overgrown dielectric, have been studied to ascertain the feasibility of electric-field control of superconductivity for device applications, Modulation of the areal charge density of 50-A thick In/InO x films has been found to cause more than a 350Ω/ box$^b$ change in the sheet resistance near the midpoint of the resistive transition in one film and the creation of ~10Ω/ box$^b$ of resistance from the superconducting state of a second film. We report on efforts to increase this modulation by decreasing the electron density of unperturbed films, improving the charge storage capabilities of the thin-film gate dielectrics, and improving the carrier mobility which has been found to be sensitive to interface preparation. Device implications, based on these results, are also discussed.

The technique of Reactive Ion Beam Sputter Deposition has been used in the preparation of metal oxide thin-film composites which have a promising potential for superconducting device applications. We have investigated the correlation between film deposition parameters such as reactive gas (oxygen) partial pressure, substrate temperature, target composition etc., with the film microstructure and superconducting properties. The resulting granular and amorphous films are extremely stable with respect to repeated temperature cycling. We have demonstrated the use of these materials as base electrodes in Josephson tunnel junctions and as weak-link Josephson switches. The extremely smooth surface topography of the films also implies low flux-pinning thresholds which should be useful in fluxoid memory and logic devices.

Periodicities associated with columnar microstructure have been observed in the electron diffraction patterns obtained from a thin-film overlay structure. This structure consists of a copper/copper-oxide film containing a small regularly-spaced array of columns and covered by a polycrystalline gold film. Both the transmitted and diffracted beams within the gold film act as independent incident beams for the underlying copper film, the latter giving rise to the formation of sub-diffraction rings around strongly-diffracted spots of gold lines. These sub-rings, appearing only because of this double diffraction effect, were found to represent the spatially-periodic distribution of columns in the copper film.

ZnO is a very promising material for spintronics applications, with many groups reporting room-temperature ferromagnetism in films doped with transition metals during growth or by ion implantation. In films doped with Mn during pulsed laser deposition (PLD), we find an inverse correlation between magnetization and electron density as controlled by Sn-doping. The saturation magnetization and coercivity of the implanted single-phase films were both strong functions of the initial anneal temperature, suggesting that carrier concentration alone cannot account for the magnetic properties of ZnO:Mn and factors such as crystalline quality and residual defects play a role. Plausible mechanisms for ferromagnetism include the bound magnetic polaron model or exchange that is mediated by carriers in a spin-split impurity band derived from extended donor orbitals. The progress in ZnO nanowires is also reviewed. The large surface area of nanorods makes them attractive for gas and chemical sensing, and the ability to control their nucleation sites makes them candidates for microlasers or memory arrays. Single ZnO nanowire depletion-mode metal-oxide semiconductor field effect transistors exhibit good saturation behavior, threshold voltage of ∼−3 V, and a maximum transconductance of 0.3 mS/mm. Under ultraviolet (UV) illumination, the drain-source current increased by approximately a factor of 5 and the maximum transconductance was ∼5 mS/mm. The channel mobility is estimated to be ∼3 cm2/Vss, comparable to that for thin film ZnO enhancement mode metal-oxide semiconductor field effect transistors (MOSFETs), and the on/off ratio was ∼25 in the dark and ∼125 under UV illumination. The Pt Schottky diodes exhibit excellent ideality factors of 1.1 at 25°C, very low reverse currents, and a strong photoresponse, with only a minor component with long decay times thought to originate from surface states. In the temperature range from 25°C to 150°C, the resistivity of nanorods treated in H2 at 400°C prior to measurement showed an activation energy of 0.089 eV and was insensitive to ambient used. By contrast, the conductivity of nanorods not treated in H2 was sensitive to trace concentrations of gases in the measurement ambient even at room temperature, demonstrating their potential as gas sensors. Sensitive pH sensors using single ZnO nanowires have also been fabricated.

Existing semiconductor electronic and photonic devices utilize the charge on electrons and holes in order to perform their specific functionality such as signal processing or light emission. The relatively new field of semiconductor spintronics seeks, in addition, to exploit the spin of charge carriers in new generations of transistors, lasers and integrated magnetic sensors. The ability to control of spin injection, transport and detection leads to the potential for new classes of ultra-low power, high speed memory, logic and photonic devices. The utility of such devices depends on the availability of materials with practical (>300K) magnetic ordering temperatures. In this paper, we summarize recent progress in dilute magnetic semiconductors such as (Ga,Mn)N, (Ga,Mn)P and (Zn,Mn)O exhibiting room temperature ferromagnetism, the origins of the magnetism and its potential applications in novel devices such as spin-polarized light emitters and spin field effect transistors.