G. Nunes

Bio: G. Nunes is an academic researcher from DuPont. The author has contributed to research in topics: Scanning probe microscopy & Scanning tunneling microscope. The author has an hindex of 17, co-authored 44 publications receiving 1949 citations. Previous affiliations of G. Nunes include University of California & IBM.

Transparent ZnO thin-film transistor fabricated by rf magnetron sputtering

Abstract: We fabricated ZnO thin-film transistors by rf magnetron sputtering on Si substrates held near room temperature. The best devices had field-effect mobility of more than 2 cm2/V s and an on/off ratio>106. These ZnO films had resistivity ∼105 ohm cm, with high optical transparency (>80% for wavelength >400 nm), and compressive stress <0.5 GPa. The combination of transparency in the visible, excellent transistor characteristics, and low-temperature processing makes ZnO thin-film transistors attractive for flexible electronics on temperature sensitive substrates.

Picosecond resolution in scanning tunneling microscopy

Abstract: A method has been developed for performing fast time-resolved experiments with a scanning tunneling microscope. The method uses the intrinsic nonlinearity in the microscope's current versus voltage characteristics to resolve optically generated transient signals on picosecond time scales. The ability to combine the spatial resolution of tunneling microscopy with the time resolution of ultrafast optics yields a powerful tool for the investigation of dynamic phenomena on the atomic scale.

Organic Transistors Based on Di(phenylvinyl)anthracene: Performance and Stability**

Abstract: The electrical performance of organic thin-film transistors (TFTs) often degrades when the devices are exposed to air. This is generally ascribed to the generation of trap states, [1] possibly as a result of the oxidation of the organic semiconductor. [2] One strategy to improve the stability of p-channel organic TFTs is the synthesis of conjugated semiconductors with a relatively large ionization potential. [3–8] However, most of the TFTs based on organic semiconductors with large ionization potentials reported up till now have shown carrier mobilities that are smaller than that of pentacene. Here, we report on a new organic semiconductor, di(phenylvinyl)anthracene (DPVAnt), [9] that combines large carrier mobility (similar to that of pentacene) with increased ionization potential and improved stability as compared to pentacene. DPVAnt has been synthesized by a Suzuki coupling reaction between 2,6-dibromoanthracene and 4,4,5,5-tetramethyl2-[2-phenylvinyl]-[1,3,2]dioxaborolane [9] with a yield of 85%. Pentacene has been purchased from Fluka. Both semiconductors have been purified by temperature gradient sublimation in a stream of inert gas. Cyclic voltammetry indicates a highest occupied molecular orbital (HOMO) energy of –5.4 eV for DPVAnt, as compared to –5.0 eV for pentacene. From UV-vis absorption spectroscopy we have determined an optical bandgap of 2.6 eV for DPVAnt and 1.8 eV for pentacene. These results are consistent with the general observation that molecules characterized by a smaller conjugated p-system have more negative HOMO energies and larger bandgaps. Simple TFT test structures have been prepared on heavily doped silicon substrates (serving as the gate electrode) with a thermally grown SiO2 gate dielectric. The dielectric surface has been treated with octadecyltrichlorosilane (OTS), [10] and the organic semiconductor has been vacuum deposited onto the substrate. Gold source/drain contacts have been thermally evaporated throughashadowmask(Fig. 1a).Duringthedeposition of the semiconductor, the substrates are held at a temperature of 60°C for pentacene and 80°C for DPVAnt. The carrier mobilities extracted from the transfer characteristics measured in air are 1 cm 2 V –1 s –1 for pentacene and 1.3 cm 2 V –1 s –1 for DPVAnt (Fig. 1b). Both TFTs have an on/off current ratio of 10 7 and a subthreshold swing of 500 mV decade –1 . Perhaps the most striking differences between the two devices are the much more negative turn-on and threshold voltages of the DPVAnt transistor (Vturn-on =– 14 V,Vth = –16 V) as compared to the pentacene TFT (Vturn-on =– 2 V,Vth = –5 V). The exact reason for this difference is not known, but it may be related to the more negative HOMO energy of DPVAnt as compared to pentacene. As shown by the atomic force microscopy (AFM) images in Figure 1c and d, both semiconductors form well-ordered polycrystalline films, which is a prerequisite for obtaining large carriermobilities.

Metal compositions, thermal imaging donors and patterned multilayer compositions derived therefrom

Abstract: The invention provides metal compositions, including silver compositions, and thermal imaging donors prepared with the compositions. The donors are useful for thermal transfer patterning of a metal layers and optionally, a corresponding proximate portion of an additional transfer layer onto a thermal imaging receiver. The compositions are useful for dry fabrication of electronic devices. Also provided are patterned multilayer compositions comprising one or more base film(s), and one or more patterned metal layers, including EMI shields and touchpad sensors.

Ultrafast scanning tunneling microscopy with 1 nm resolution

Abstract: We present data demonstrating that junction-mixing scanning tunneling microscopy (JM–STM) can provide simultaneous picosecond time resolution and nanometer spatial resolution. Experiments were performed on an Au surface with a patterned Ti overlayer. Our measurements under ultrahigh vacuum conditions achieve a spatial resolution of 1 nm using the tunneling currents generated by 20 ps voltage transients. The observed contrast in a JM–STM signal is demonstrated to arise entirely from the difference in electronic structure between the Au and Ti surfaces. These results confirm that JM–STM signals originate in the tunnel junction and maintain the atomic-scale spatial resolution inherent in STM.

A comprehensive review of zno materials and devices

Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Abstract: Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances

Abstract: Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.