Many metal–insulator–metal systems show electrically induced resistive switching effects and have therefore been proposed as the basis for future non-volatile memories. They combine the advantages of Flash and DRAM (dynamic random access memories) while avoiding their drawbacks, and they might be highly scalable. Here we propose a coarse-grained classification into primarily thermal, electrical or ion-migration-induced switching mechanisms. The ion-migration effects are coupled to redox processes which cause the change in resistance. They are subdivided into cation-migration cells, based on the electrochemical growth and dissolution of metallic filaments, and anion-migration cells, typically realized with transition metal oxides as the insulator, in which electronically conducting paths of sub-oxides are formed and removed by local redox processes. From this insight, we take a brief look into molecular switching systems. Finally, we discuss chip architecture and scaling issues.

http://chialvo.org/Curso/UBACurso/DIA7/Papers/Aono_NatMat_07_Ionic%20Switching%20Memory.pdf

Nanoionics-based resistive switching memories

In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.

Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

Since the first reports in the late 1970s on transition metal complexes contain- ing pincer-type ligands—named after the particular coordination mode of these ligands—these systems have at- tracted increasing interest owing to the unusual properties of the metal centers imparted by the pincer ligand. Typical- ly, such a ligand comprises an anionic aryl ring which is ortho,ortho-disubsti- tuted with heteroatom substituents, for example, CH2NR2 ,C H 2PR2 or CH2SR, which generally coordinate to the met- al center, and therefore support the MC s bond. This commonly results in a terdentate and meridional coordina- tion mode consisting of two metalla- cycles which share the MC bond. Detailed studies of the formation and the properties of a large variety of pincers containing platinum group metal complexes have provided direct access to both a fundamental under- standing of a variety of reactions in organometallic chemistry and to a range of new applications of these complexes. The discovery of alkane dehydrogenation catalysts, the mecha- nistic elucidation of fundamental transformations (for example, CC bond activation), the construction of the first metallodendrimers for sustain- able homogeneous catalysis, and the engineering of crystalline switches for materials processing represent only a few of the many highlights which have emanated from these numerous inves- tigations. This review discusses the synthetic methodologies that are cur- rently available for the preparation of platinum group metal complexes con- taining pincer ligands and especially emphasizes different applications that have been realized in materials science such as the development and engineer- ing of sensors, switches, and catalysts.

Platinum Group Organometallics Based on “Pincer” Complexes: Sensors, Switches, and Catalysts

Several novel synthetic reactions of arenes and alkanes discovered and investigated in our laboratory are summarized here. These include olefin arylation, hydroarylation of alkynes, hydroxylation of arenes, carboxylation of arenes and alkanes, and aminomethylation and acetoxylation of alkanes. Most of these reactions are catalyzed by highly electrophilic transition metal cationic species generated in situ in an acid medium, involving electrophilic metalation of C−H bonds of arenes and alkanes which lead to the formation of aryl−metal and alkyl−metal σ-complexes.

Catalytic functionalization of arenes and alkanes via C-H bond activation.

Electrochromic (EC) materials are able to change their optical properties, reversibly and persistently, by the application of an electrical voltage. These materials can be integrated in multilayer devices capable of modulating the optical transmittance between widely separated extrema. We first review the recent literature on inorganic EC materials and point out that today's research is focused on tungsten oxide (colouring under charge insertion) and nickel oxide (colouring under charge extraction). The properties of thin films of these materials are then discussed in detail with foci on recent results from two comprehensive investigations in the authors' laboratory. A logical exposition is obtained by covering, in sequence, structural features, thin film deposition (by sputtering), electronic band structure, and ion diffusion. A novel conceptual model is given for structural characteristics of amorphous W oxide films, based on notions of defects in the ideal amorphous state. It is also shown that the conduction band density of states is obtainable from simple electrochemical chronopotentiometry. Ion intercalation causes the charge-compensating electrons to enter localized states, implying that the optical absorption underlying the electrochromism can be described as ensuing from transitions between occupied and empty localized conduction band states. A fully quantitative theory of such transitions is not available, but the optical absorption can be modeled more phenomenologically as due to a superposition of transitions between different charge states of the W ions (6+, 5+, and 4+). The Ni oxide films were found to have a porous structure comprised of small grains. The data are consistent with EC coloration being a surface phenomenon, most likely confined to the outer parts of the grains. Initial electrochemical cycling was found to transform hydrated Ni oxide into hydroxide and oxy-hydroxide phases on the grain surfaces. Electrochromism in thus stabilized films is consistent with reversible changes between Ni hydroxide and oxy-hydroxide, in accordance with the Bode reaction scheme. An extension of this model is put forward to account for changes of NiO to Ni2O3. It was demonstrated that electrochromism is associated solely with proton transfer. Data on chemical diffusion coefficients are interpreted for polycrystalline W oxide and Ni oxide in terms of the lattice gas model with interaction. The later part of this review is of a more technological and applications oriented character and is based on the fact that EC devices with large optical modulation can be accomplished essentially by connecting W-oxide-based and Ni-oxide-based films through a layer serving as a pure ion conductor. Specifically, we treat methods to enhance the bleached-state transmittance by mixing the Ni oxide with other oxides characterized by wide band gaps, and we also discuss pre-assembly charge insertion and extraction by facile gas treatments of the films, as well as practical device manufacturing and device testing. Here the emphasis is on novel flexible polyester-foil-based devices. The final part deals with applications with emphasis on architectural “smart” windows capable of achieving improved indoor comfort jointly with significant energy savings due to lowered demands for space cooling. Eyewear applications are touched upon as well.

/pdf/electrochromics-for-smart-windows-thin-films-of-tungsten-aw0rai8h60.pdf

Electrochromics for smart windows: thin films of tungsten oxide and nickel oxide, and devices based on these

Experiments on Si-rich SiGe layers show an exponential increase in Ge diffusion and an exponential decrease in B diffusion as a function of compressive strain, indicating a linear dependence of activation energy on strain. The effect arises from the structural relaxation of the lattice around the defect mediating diffusion (inward for a vacancy, outward for an interstitial). We infer the mechanisms of Ge and B diffusion in strain-free and compressively strained Si(Ge) at T1030 \ifmmode^\circ\else\textdegree\fi{}C, and draw some general conclusions on strain-modified diffusion in crystalline solids.

Diffusion in strained Si(Ge).

It is shown that thin layers of palladium coated magnesium lanthanide alloys reversibly go through an optical transition by variation of the hydrogen concentration, just as has recently been shown for pure lanthanides. With these layers optical switches can be constructed that exhibit three different optical states: a color-neutral transparent state at high hydrogen concentration, a nontransparent dark absorbing state at intermediate hydrogen pressures, and a highly reflective metallic state at low hydrogen pressures. The ratio in transmission between the transparent state and the reflecting state is more than 1000.

Optical switches based on magnesium lanthanide alloy hydrides

It is shown that backscatter Kikuchi diffraction in the scanning electron microscope can be used for the determination of elastic strain with μm resolution. From the shift of Kikuchi bands in backscatter Kikuchi diffraction patterns of epitaxial Si1−xGex layers on Si(100) the perpendicular elastic strain was determined to be 2.5% for x=0.34 and at 1.0% for x=0.16 with an accuracy of about 0.1%. The values found on a μm scale were in good agreement with high‐resolution x‐ray diffraction measurements averaging over mm distances.

Microscale elastic‐strain determination by backscatter Kikuchi diffraction in the scanning electron microscope

The unusual bridging-hydrogen complexes PtX(L-C,N)(LH-C,H) containing a zwitterionic Pt(II)[sup [minus]][center dot][center dot][center dot]H-N[sup +] moiety have been obtained in a reaction of cis-Pt(L-C,N)[sub 2] with R[sub 2]SnX[sub 2] (R = Me, Ph; X = Cl, Br) in a mixture of CH[sub 2]Cl[sub 2] and MeOH. The chelating amine ligand systems L used in this reaction are [1-C[sub 10]H[sub 6]NMe[sub 2]-8][sup [minus]], [C[sub 6]H[sub 4]CH[sub 2]NMe[sub 2]-2][sup [minus]], and [C[sub 6]H[sub 4]CH[sub 2]NEt[sub 2]-2][sup [minus]]. The complex PtCl(1-C[sub 10]H[sub 6]NMe[sub 2]-8-C,N)(1-C[sub 10]H[sub 6]NHMe[sub 2]-8-C,H) can also be obtained by reaction of cis-Pt(1-C[sub 10]H[sub 6]NMe[sub 2]-8-C,N)[sub 2] with dry HCl. The bridging proton of the zwitterionic Pt(II)[sup [minus]][center dot][center dot][center dot]H-N[sup +] moiety shows a characteristic [sup 1]H NMR resonance at ca. 11-16 ppm with a [sup 1]J([sup 195]Pt,[sup 1]H) of ca. 65-180 Hz; the latter decreases with increasing ligand flexibility. In the Pt[center dot][center dot][center dot]H-N moiety of the PtX(L-C,N)(LH-C,H) complexes, an increase of the Pt[center dot][center dot][center dot]H interaction is associated with a simultaneous decrease of the H-N interaction. When L is chiral [C[sub 6]H[sub 4]CH(Me)NMe[sub 2]-(R)-2][sup [minus]], cis-Pt(L-C,N)[sub 2] affords in a reaction with Me[sub 2]SnBr[sub 2] the nonbridging complex PtBr(C[sub 6]H[sub 4]CH(Me)NMe[sub 2]-(R)-2-C,N)(C[sub 6]H[sub 4]CH(Me)NHMe[sub 2]-(R)-2-C) as themore » major product. The X-ray crystal structures of both a bridging complex and a nonbridging complex are described. Especially the latter shows good evidence that the bridging interaction is largely electrostatic. Internal steric influences only affect the stability of the bridging moiety when they arise from groups on the benzylic carbon atom. 48 refs., 5 figs., 4 tabs.« less

A hydrogen atom in an organoplatinum-amine system : Part 1: Synthesis, spectroscopic and crystallographic characterization of novel zwitterionic complexes with a Pt(II)-...H-N+ unit

High-resolution X-ray diffraction is used to obtain the strain profile of a wide range of epitaxial semiconductor samples. The samples are divided into five categories: Strained layers on a substrate, (partly) relaxed layers on a substrate, strained-layer superlattice structures, multiple relaxed layers and relaxed superlattice structures and ionimplanted samples. For each category a measurement strategy and analysis method is given. Representative examples for each category are shown.

https://iopscience.iop.org/article/10.1088/0022-3727/26/4A/039/pdf

P. van der Sluis

Papers

Diffusion in strained Si(Ge).

Optical switches based on magnesium lanthanide alloy hydrides

Microscale elastic‐strain determination by backscatter Kikuchi diffraction in the scanning electron microscope

A hydrogen atom in an organoplatinum-amine system : Part 1: Synthesis, spectroscopic and crystallographic characterization of novel zwitterionic complexes with a Pt(II)-...H-N+ unit

Determination of strain in epitaxial semiconductor layers by high-resolution X-ray diffraction